Just-in-Time (JIT) Techniques Assignment Example | Topics and Well Written Essays - 1000 words

In the nick of time (JIT) Techniques - Assignment Example In this way by pondering the issue the difficult it very well may be seen lastly when the issue in the long run turns out to be clear prompts kaizen. On the off chance that one makes it a standard to manage absconds simply after they happen and therefore the quantity of its staffs will in general fall. Subsequently, things that are running easily ought not be dependent upon any control. On the off chance that you subscribe to simply finding and fixing issues, you'll have the option to do viable control (inside an association) with less personnel†. This idea is very much applied in Toyota. Since everybody at Toyota is included similarly at the business improvement plan. The individuals at Toyota took part in the gatherings which are held consistently and talk about the advance and furthermore think about the new activities. Hence, everybody at Toyota is required to contribute and all the thoughts are similarly tuned in to by the administration of Toyota. Not at all like other as sociation there are no proposal encloses Toyota as individuals are not hesitant to discuss the new thoughts and plans (Hope and Player, 2012, p. 211). The accomplishment of Toyota a car organization has had the option to made progress with the methods of lean which is observed by the greater part of the association (Blanchard, 2007, p. 97). As indicated by the overseeing executive of Toyota, the long rule of Toyota creation System (TPS) will keep on working with the arrangement of Just In time and won't change later on and its creation can address all the forthcoming difficulty. In the nick of time rotates around the idea of creating of just what is required and hence moving just what is required. Rather than the arrangement of push framework, it spoke to just to the draw framework where the laborers get and get what is required. Instruments, for example, the Kanban (the data card); and on the showcase board, just as poka burden the blunder anticipation, was created so as to execute the force system (Toyota, 2012). The Toyota Production System had the capacity to satisfy the interest of the clients effectively and instantly by method of connecting the creation to commercial center. JIT depends on the way toward gathering the succession just when they are required and required (Toyota (A), n.d). In the nick of time offers a ceaseless, smooth and an enhanced work process with estimated and cautious work cycles and with the on request development of products, materials limit and decrease the expense of the time squandered. The individuals from the group can focus on every one of their errand with no translation which at long last prompts better quality; convey at the given time and obviously genuine feelings of serenity for the clients of Toyota. Potential Benefits †and Drawbacks †of Such JIT Techniques Are Limited to Large Manufacturing Businesses or Whether They Have Wider Applications for Other Organizations Benefits and Drawbacks Just in time has pr ofited a considerable lot of the association from multiple points of view and a portion of the advantages incorporates, for example, with the assistance of in the nick of time the set up time can be diminished which permits the association to kill the time expected to set the stock; the progression of stock increments from the stockroom to the selves; workers with multi aptitudes are utilized at a powerful and productive way. Representatives with multi aptitudes permits the organizations to move the laborers to the necessary office easily and certain; the connection between the providers and the

Social Worker Within The Welsh Context Social Work Essay Essay Example

Social Worker Within The Welsh Context Social Work Essay Paper Social work is a calling built up to progress and get the prosperity of families, children, adults and the environing networks. Social work in Wales is managed under the guidance and resolution law of the Care board for Wales. This guidance is represented by a codification of example which every single Social specialist are to follow too much. Anybody taking to use the rubric social laborer is required to be enlisted with the consideration committee for Wales, or some other chamber for different states inside the UK. The Care committee for Wales territories that the plan of the codification is to set out the conduct that is anticipated from cultural consideration laborers and to educate administration clients and the masses about the models of conduct they can envision . ( WAG, 2012:5 ) These rules permit every cultural laborer to hold an away from of their capacity and what is anticipated from them. The reason for this task is to talk the capacity and undertaking of the Social labor er, solidly demoing a trepidation of moral issues, and hostile to harsh example inside Welsh setting. We will compose a custom exposition test on Social Worker Within The Welsh Context Social Work Essay explicitly for you for just $16.38 $13.9/page Request now We will compose a custom article test on Social Worker Within The Welsh Context Social Work Essay explicitly for you FOR ONLY $16.38 $13.9/page Recruit Writer We will compose a custom article test on Social Worker Within The Welsh Context Social Work Essay explicitly for you FOR ONLY $16.38 $13.9/page Recruit Writer The capacity of the Social laborer is oftentimes shaped by the requests of the single assistance client or family unit. Social laborers play a prima work in providing wellbeing and assurance to adults and children. Anyway the capacity will on occasion must be adjusted so as to the full run into the single assistance clients requests. A few capacities did by the Social laborer could perchance incorporate being an advisor, advocator, social specialist, chief of consideration, a person of cultural control and having the option to work effectually as part of a mulit-disciplinary crew. Every one of these capacities will require a figure of various achievements, Such similar to a useful communicator, holding the capacity to perceive and see decent variety, and do adequate risk examinations. The cultural laborer requests to have the option to regard the administration client independent of their reason for asking a cultural specialist. Corresponding with these the Social specialist will req uire to hold esteems and regard for ethnicity, sexual orientation, class, human progress, confidence, age, sex or capacity. In making these cultural specialists have a figure of Acts and Laws in which they should comply, for example, All Wales Framework for the Assessment of Children sought after and so on . The Laws are mandates which empower the cultural specialist to ship out their capacity and endeavors in a positive way leting for approval, adjustment, and against harsh example and to attempt undertakings of oppression. The arrangements and rule law give approval to design. Close by the capacity of the cultural specialist is the endeavor of the cultural laborer. The capacity of the cultural laborer may require a wide collection, in footings of the extent of endeavors requiring to be done. A portion of these endeavors could incorporate back uping the guardians/s to create and increase child rearing achievements, back uping the administration client to go monetarily subordinate w ith the end goal for them to chop down the potential dangers of falling into poverty, and advancing and back uping the administration client back to work and business. This is just to call a couple of numerous endeavors completed inside the capacity of a cultural laborer. Social specialists are to design hostile to harsh example while working with administration clients, this is planned to empower them to choose any employments and defeat hindrances being looked by the administration client. Dominelli. ( 2002 ) states that Anti-severe example tries to smother enslavement inside expert example each piece great as add to its demolition inside the more extensive society ( :83 ) Dominelli ( 2002 ) so proceeds to suggest that being clear about their principles, esteem base and moral direction will help single practicians in the dynamic technique where and how they will coordinate their work ( :84 ) In keeping up with clear standards and moral issues and taking into history the codification of moralss as set by BASW which expresses that, ( 2012 ) Respect for human sense of pride, and for single and social decent variety Value for each person, their convictions, closures, affinities and requests . One of the guidelines that is of import in regarding a help c lients requests and rights is that cultural specialists inside Wales actualize the use of the Welsh Language Act 1993 this is one delineation of where Torahs among England and Wales are noticeably unique in cultural work. In co-occuring with this Act, the Welsh Language is proposed to hold equivalent position. While recognizing moral issues, it became obvious that an assistance client has an option to make up ones psyche what etymological correspondence their cultural laborer utilizes, thus, as expressed by Davies ( 1994 ) Principles for hostile to abusive example in Cymrus: 1. A help client has the privilege to take which etymological correspondence to use with a specialist ; 2. Language is in excess of an office of conveying: it is a fundamental bit of a singular s uniqueness ; 3. People groups can give themselves all the more effectively and easily in their semantic correspondence of pick ; 4. Great example offices offering clients existent etymological correspondence pick ; 5. A complete and decision administration in Wales implies a bilingual assistance . ( :60 ) Denying this administration can be perceived as a way of stifling a man. This task has examined and explored a portion of the nations of cultural work, for example, the capacity and undertaking of the cultural laborer. It became apparent that the capacity of the cultural specialist and the nation wherein they example will gracefully the lineation of the endeavors they will be required to ship out. There is an extraordinary significance of qualities, and the interest to follow the strategies and mandates is unmistakably fundamental in all nations and example of cultural work. The task has so proceeded to put the distinction in mandates and strategies inside Wales and England, and the significance of against severe example, Likewise perceiving the privileges of the administration client, and the interest to regard these rights. At long last the task went onto demonstrate a dread of the interest to be aware of moral example.

Design of a global network using wimax - Free Essay Example

Introduction Previous Work Previous work that is closely related to this project involves experience with similar software simulation tool to the one that is used for the completion of the practical part of the project. OPNET simulator was used for the set up of a small network and its division into subnets. The project was completed as a lab assignment in the City University laboratories. It was divided into two main lab sessions each of them explained as follows. The aim of first lab session was to demonstrate the need for implementation of switches in the design of the local area networks. Two 16-station LANs were designed, using a hub for the first one; two hubs and a switch for the second one. The main task of the second laboratory was to demonstrate the basics of designing a network, taking into consideration the users, services location of hosts. Using OPNET software, the concepts of networking were easily implemented and tested against the criteria set for satisfactory performance of the network model. The visual representation of the obtained results was used for a detailed analysis of the complexity of the network and its services provided to the users. 1 Technical Overview of the WiMAX Standard 1.1 Spectrum of the Standard The IEEE 802.16 standard is initially designed to provide a flexible, cost-effective, standards-based last-mile broadband connectivity to fill in the broadband coverage gaps that are not currently served by the wired solutions such as DSL. The advanced versions of the standard are aiming to create new forms of broadband services both with high speed and mobility. The IEEE 802.16 standard envisages the use of a wide range of frequencies from 2 to 66 GHz. However, the WiMAX Forum has focused on the use of 2 to 10GHz as the operating frequencies. A graphical representation of the WiMAX spectrum bands is listed below. It includes a comparison with other wireless standards; as well as indication of the regions using the listed bands. WiMAX is a technology that supports the delivery of last-mile wireless broadband access as an alternative to cable and DSL. WiMAX provides fixed, nomadic, portable and ultimately mobile wireless broadband connectivity without the need for line-of-sight with a base station. The design of a WiMAX network is based on the following major principles: Spectrum: to be deployed in both licensed and unlicensed spectra. Topology: supports different RAN topologies. Interworking: autonomous RAN architecture that enables faultless incorporation and interworking with Wi-Fi, 3GPP and 3GPP2 networks and existing IP core networks (e.g. DSL, cable, 3G) using IP-based interfaces. IP connectivity: supports a mix of IPv4 and IPv6 network interconnects. Mobility management: opportunity to expand the fixed access to mobility and broadband multimedia services delivery. WiMAX has defined two MAC classification profiles -the ATM and the IP. They have also defined two primary PHY system profiles: 25 MHz-wide channel (in the US) in the 10-66 GHz range. 28 MHz-wide channel (in Europe) in the 10-66 GHz range. IEEE 802.16 standard is designed to develop as a set of air interfaces standards for WMAN based on a universal MAC protocol but using the physical layer specifications, which one dependent on the range of use and the related regulations. The IEEE 802.16 working group designed a flexible MAC layer and associated physical layer for 10-66 GHz. It is more important to recognize certain factors that make some frequencies more suitable for use in WiMAX systems, both fixed and mobile [1new]. 1.1.1 Path Loss The first important factor is the operating frequency and path loss, which may arise from three basic factors: Free space path loss (FSL) It is defined by using the following formula (Equation 1): FSL=10log(4DFC)2 (1) D=distance from transmitter; F=frequency; C=speed of light. The path losses increase with the square of the frequency. For example, the path loss at 2 GHz frequency band is about 12 dB higher than the band at 0.5 GHz. This effect may be compensated with the antenna size. The increase in FSL with the square of the frequency requires the cell sizes at higher frequencies to be smaller in order to maintain link margins. High frequencies such as 5.8 GHz and above are best suited for line of sight environment. In NLOS conditions, a link at 5.8 GHz would support NLOS customer premises equipment at distances less than a kilometre. Loss due to NLOS operations In urban environments, WiMAX systems operate in a NLOS manner, there is a loss in received signals which depends on the reflected signal strengths. Frequencies above 10 GHz are treated separately. In general, lower frequencies such as 800-2000 MHz have better performance for NLOS than the higher bands. Due to the reception of waves reflected from many objects, the signal strength in most NLOS conditions varies sharply. Ground propagation models are required for path loss analysis and as a result additional margin needs to be given for the loss expected. Hence, multiple antenna techniques with spatial diversity are used to improve the margins in NLOS conditions. Loss caused by in-building penetration This kind of loss depends largely on the type of wall and whether the indoor location has windows. They are not very frequency dependent, at least in the zone of consideration of 2 GHz to 4 GHz. In buildings, losses can vary from 2 dB for a room with windows; to 6 dB for a brick wall. An increase up to 10-12 dB can be expected if the indoor areas were built using metal materials. 1.1.2 Doppler Shift and Coherence Time The second important factor is the Doppler Shift. It is an essential consideration for systems meant for mobile use. In the case of mobile WiMAX systems, which are meant to cater to vehicular speeds of up to 120 km/h, the effects of the Doppler shift are only relevant to the higher frequencies. It is given by the following formula (Equation 2): Ds=(VFC)cos (2) Ds=Doppler shift; V=velocity of user; F=frequency; C=speed of light and =angle between the incoming signal and direction of motion. Frequency shifts need to be less than 10% of the subcarrier spacing in order to maintain correct timing between different mobile stations, which may be operating with a base station. Table 1 represents the relationships between Doppler shift with operating frequency and speed. Frequency (MHz) Doppler shift (Hz) Coherence time (ms) Symbol duration (ms) 800 88.9 11.3 0.2 1600 177.8 5.6 0.2 2400 266.7 3.8 0.2 3400 377.8 2.6 0.2 5800 644.4 1.6 0.2 10000 1111.1 0.9 0.2 Table 1. Coherence time in ms is relevant to time synchronisation of mobile stations with the base station (times are in milliseconds) WiMAX is a multicarrier transmission system based on OFDM. The uplinks in WiMAX (both FDD and TDD systems) operate in a TDMA mode. Each subscriber station is assigned its own time slot and the transmission must take place within the slot. Other devices have the right to transmit in the other slots as allotted in the frame of WiMAX. In other words, the coherence of timing between different devices is important, which must operate in synchronisation. The coherence time is defined as 1Ds and it is inversely proportional to the Doppler shift. An indicator of how the motion is affecting the connection between symbols from different devices, a comparison of coherence time and the symbol time in OFDM. Hence, rather than considering a shift in the centre frequency, which is more likely for single-carrier systems, it is more suitable to consider the same shift in time in the subcarriers. Reducing subcarrier spacing would have adversely affected the Doppler spread, whereas increasing the subcarrier spacing would have reduced the delay spread and consequently intersymbol interference and the data rate. 1.2 Architecture In addition to the standard spectrum analysis and factors that are important for the appropriate selection of correct frequencies, the next part of the report presents the ideas of WiMAX network architecture and specifications. 1.2.1 Backhaul Solutions In telecommunications, thebackhaulportion of the network comprises the intermediate links between thecore networks, orbackbone, of the network and the small sub networks at the edge of the entire hierarchical network. Based on principle explained above, one of the architecture models is based on fixed IEEE 802.16 equipment. Independent of the used version, the technology can be employed in a fixed infrastructure as shown in Fig. 2. In this setting, the deployment of point-to-point connections can span tens of kilometres. WiMAX backhauling is defined by the infrastructure between the WiMAX ASN-GW and the base stations. [2 new] The control of the wireless network towards the client devices, as well as the transport traffic to the operator CSN is aggregated by the base stations. Fig. 3 is another example of how the system may be structured. A critical achievement factor in the deployment of the WiMAX systems is the numerous options the service provider can choose from. As the variety of options for the service providers were mentioned, there is time to focus on a topic much more related to the economic point of a network system. In particular, how the network will be develop in terms of cost and charges and they are agreed upon. A list of the important factors is presented as follows: Fixed costof providing a network infrastructure. Non-fixed cost of connection to the network- typically paid by the user in the form of connection cost. Cost of increasingthe networks capacity. Users who want to reschedule their transmission during peak times should not be charged for the growth of the networks capacity. Incremental cost of sending an extra packet. This cost should be very small or equal to zero without congestion, in view of the fact that the bandwidth of a broadband network is in general a shared resource. Social costdefined as the extra delay which occurs to other users by the transmission of data. Figure 4 shows the cost flow of a WiMAX network. WiMAXpoint to multipoint WiMAXmesh Clients WiMAX MS/RS or WiMAX mesh BS Clients WiMAX MS/RS or WiMAX mesh BS + Wi-Fi router WiMAXcell layout Cell dimensioning Number of WiMAX mesh BS in a cluster Wi-FiCell layout Number of AP in a single WiMAX cell Wi-Fi technology options Dual interface boards (WiMAX/Wi-Fi) Average subscribers per square mile Data traffic assumptions for Wi-Fi users and WiMAX SS/RS (utility/demand function) High QoS VoIP connections for Wi-Fi users and WiMAX SS Average number of data connections per square mile / month Backhaul capacity planning WiMAX BS to ISP WiMAX mesh to WiMAX main BS Wi-Fi routers to WiMAX BS Radio capacity planning Channel size Modulation type Frequency reuse FCC limitations Economic considerations CAPEX: WiMAX BS, Wi-Fi routers, spectrum costs, site preparation, site installation, backbone network equipment OPEX: Operation-administration-management costs, site Leases, equipment maintenance, customer acquisition Network revenue pricing model Time unit fees for Internet subscribers and VoIP subscribers (flat rate pricing) On-demand Service (user-based pricing) Charges: access, usage, congestion and QoS Fig. 4 Cost flow diagram for WiMAX networks 1.2.2 Mobile WiMAX Network Solution The second architecture model that is discussed is that of the mobile WiMAX. It is of great interest and use for the simulation project as it explains the principles behind the simulation that has been set. A WiMAX network consists of an ASN in the lowest level and network itself is in fact, quite intuitive. [1 new] An ASN is comprised of a number of BS connected to an access network, where the ASN is connected to the external networks using ASN-GW. The functions of the ASN are represented in Fig. 5 and include a number of BS, access networks, and access gateways. The functions are discussed in details as follows: Establishing of a connection with the MS, including PHY and MAC layer connectivity. Providing handover and roaming services for the MS within the ASN The user should be provided AAA facilities in conjunction with its home network; the ASN is capable of providing proxy AAA services Relay facilities between the ASN and the external networks should also be present Two functional entities are defined in ASN shown in Fig. 6: The base stationconnects to the MS using the WiMAX PHY air interface. The functions of the BS are to maintain the air interface with the MS, providing the DHCP proxy and to maintain its status idle or active. Fig. 6 is an illustration of a typical WiMAX BS. The uplink and downlink traffic scheduling as well as the QoS enforcement are provided by the BS, as the air interface is managed by the BS. The access service network gateway is the second functional entity. The ASN-GW is the point where traffic from all BS is aggregated for interface to external networks. Usually, the ASN-GW is physically a router. Functions such as QoS management, AAA functionalities are also part of the aggregation point responsibilities. ASN-GW may also have control functions over the BS. The alternative architecture embeds those control functions in the BS. Fig. 7 represents the typical ASN functions. If a comparison between WiMAX network architecture and a cellular network model such as GSM was to be done, similarities can easily be identified. The ASN-GW of the WiMAX network serves the functions that are provided by the SGSN; the access network is recognised as BSC in the GSM model, and the air interface is respectively the BST. Further reading and understanding of the GSM model architecture is recommended for the comparison between the two models. Generally, the WiMAX networks are defined to be much more open in building networks and they have greater level of functionalities in its network entities. Three distinct entities comprise a WiMAX network and its application environment: Network access provider entity that operates one or more ASNs. Typically, it is a WiMAX operator that operates ASN in one or more areas. Network service provider provides connectivity and services to NAPs. NSP needs only to connect to other NSPs and expect all services to be delivered through these connections; NSPs provide connectivity to NAPs via CSN. They are also responsible for providing mobility between their own nodes as well as nodes from other NSPs. Application service providers provide services such as HTTP, video streaming, file download, e-mail, etc. Fig. 8 introduces one more entity of the WiMAX network architecture the connectivity service network. The diagram shows that CSNs have AAA servers which are policy functions for QoS. They provide connectivity to external networks such as managed IP networks or the public internet. Policy functions for each device, user and service on the network as well as the security and authentication frameworks are provided by the AAA servers. Authentication at multiple levels is a key feature of the WiMAX network architecture. Additional key features of the mobile WiMAX network architecture include: Both the core and the radio access networks should be based on IP; protocols based on IEEE802.16 and IETF Open interfaces should be defined by fully-defined reference points Support of fixed network, nomadic, or mobile usage with full migration path to mobility A modular network architecture, which can grow based on usage requirements Integration into different types of IP and non-IP networks (for example: ATM, TDM, and others) Network core architecture is not based on support of any particular service, such as voice, data, or video; as a multi-service core network it supports QoS for each service and each connection QoS is based on both policy functions and enforcement The network architecture is relatively flat, which enables a WiMAX service to start with a single ASN; NWG has defined different ASN profiles for this purpose Inter-networking is supported with 3GPP, 3GPP2, Wi-Fi, or wired networks using IETF protocols. 2 WiMAX Layers After the spectrum and network analysis discussions, it is important to look deeper into WiMAX fundamentals. The following chapter has the aim to introduce the two main layers defined in the WiMAX standard, and to explain the related to them topics such as adaptive modulation, QoS, etc. As the WiMAX belongs to the IEEE 802 group, then the bridging or layer-2 concepts should be mentioned. [2] The addressing is based on MAC addresses and the base station is perceived as a bridge. In order to implement all layer 2 functionalities, the device used should be a bridge-not a router. For the identification for nodes addressing is used; as long as the node is recognized by the network, the address is replaced by use of circuits with circuit identifier. The WiMAX physical layer is based on orthogonal frequency division multiplexing. [2new] OFDM is a transmission scheme that enables high-speed data, video, and multimedia communications. It is used by numerous broadband systems DSL, Wi-Fi, DVB-H, MediaFLO and WiMAX. OFDM is an efficient scheme used for high data rate transmission in a non-line-of-sight or multipath radio environment. The MAC layer is based on connection-oriented principle and it is very similar to the ATM transport protocol, which connection uses a context that describes the mapping between the incoming flows and the underlying QoS. A station registers itself to the base station, negotiates the physical layer characteristics and then can communicate bidirectionally. A service flow defines the negotiated QoS for all matching packets (service-specific sub layer). The QoS can be changed dynamically and it supports extremely well data bursts. Everything is negotiated separately for uplink and downlink. 2.1 Physical Layer Details 2.1.1 OFDM Basics OFDM is a multicarrier modulation scheme that is based on the idea of dividing a given high-bit-rate data stream into several parallel lower bit-rate streams. Each of those streams is then modulated on separate carriers, the so called subcarriers or tones. Multicarrier modulation schemes eliminate or minimize ISI by making the symbol time large enough so that the channel induced delays are an insignificant proportion of the symbol duration. For that reason, in high-data-rate systems, in which the symbol duration is relatively small and it is inversely proportional to the data rate, splitting the data stream into many parallel streams increases the symbol duration of each stream. By doing so, the delay spread is only a small fraction of the symbol duration. OFDM is a spectrally efficient version of multicarrier modulation, in which the subscribers are selected in such way that they are orthogonal to one another over the symbol duration. In that way, it avoids the necessity to have no overlapping subcarrier channels to eliminate ISI. The first subcarrier has to have a frequency such that it has an integer number of cycles in a symbol period. The spacing between adjacent subcarriers (subscriber bandwidth Bsc) has to be defined by the following Equation 3: Bsc=BL (3) Where B is the nominal bandwidth, it is also equal to the data rate. L is the number of subcarriers. This relation ensures that all tones are orthogonal to one another over the symbol period. It can be shown that the OFDM signal is equivalent to the inverse discrete Fourier transform of the data sequence block taken L at a time. Therefore, it is very straightforward to implement OFDM transmitters and receivers in discrete time using IFFT and FFT, respectively. In order to completely eliminate the ISI, OFDM introduces guard intervals between the symbols. For the successful elimination, the guard interval should be larger than the expected multipath delay spread. On the other hand, the introduction of the guard interval implies power wastage and decrease in bandwidth efficiency. The amount of power waste depends on the proportion between the OFDM symbol duration and the guard time. Thus, the larger the symbol period, the smaller the power loss and bandwidth efficiency. Large symbol periods also mean more subcarriers. The size of the FFT in an OFDM design should be chosen carefully as a balance between protection against multipath, Doppler shift, and design cost/complexity. For a given bandwidth, selecting a large FFT size would reduce the subcarrier spacing and increase the symbol time. This is the reason why it makes it easier to protect against multipath delay spread. In contrary, the reduced subcarrier spacing makes the system more vulnerable to intercarrier interference owing to Doppler spread in mobile applications. Careful balancing is required to compete the influence of delay and Doppler spread. 2.1.2 Advantages and Disadvantages of OFDM There are several advantages of OFDM over other solutions for high-speed transmission. Reduced computational complexity: OFDM can be easily implemented using FFT/IFFT, where the processing requirements grow only slightly faster than linearly with data rate or bandwidth. The computational complexity of OFDM can be represented the following Equation 4. O(BlogBTm) (4) Where B is the bandwidth and Tm is the delay spread. This complexity is much lower than that of standard equalizer-based system, which complexity is shown by Equation 5: O(B2Tm) (5) Graceful degradation of performance under excess delay: the performance of an OFDM system degrades gracefully as the delay spread exceeds the value designed for. Greater coding and low constellation sizes can be used to provide fallback rates that are significantly more robust against delay spread. In other words, OFDM is well suited for adaptive modulation and coding, which allows the system to make the best of the available channel conditions. This is in contrast with the abrupt degradation owing to error propagation that single-carrier systems experience as the delay spread exceeds the value for which the equalizer is designed. Exploitation of frequency diversity : OFDM facilitates coding and interleaving across subcarriers in the frequency domain, which can provide robustness against burst errors caused by portions of the transmitted spectrum undergoing deep fades. WiMAX defines subcarrier permutations that allow systems to exploit this. Use as a multi-access scheme : OFDM can be used as multi-access scheme, where different tones are partitioned among multiple users. This scheme is also known as OFDMA and is exploited in mobile WiMAX. The ability to provide fine granularity in channel allocation is also offered by the OFDMA. In relatively slow time-varying channels, it is possible to significantly enhance the capacity by adapting the data rate per subscriber according to the SNR of that particular subcarrier. Robust against narrowband interference Suitable for coherent demodulation : it is relatively easy to do pilot-based channel estimation in OFDM system, which renders them suitable for coherent demodulation schemes that are more power efficient. Apart from the advantages that were already described, there are two main disadvantages: There is a problem associated with OFDM signals having a high peak-to-average ratio that causes nonlinearities and clipping distortion. This can lead to power inefficiencies that need to be countered. The second disadvantage is related to OFDM signals which are very susceptible to phase noise and frequency dispersion, and the design must mitigate these imperfections. This also makes it critical to have accurate frequency synchronization. 2.1.3 OFDMA: Sub channelization Sub channels are formed by the division of available subcarriers into groups. [3new] Fixed WiMAX based on the OFDM-PHY allows a limited form of sub channelization in the uplink only. There are 16 defined sub channels, where 1,2,4,8 or all sets can be assigned to a subscriber station in the uplink. Uplink sub channelization in fixed WiMAX allows SSs to transmit using only a fraction (as low as 1/16) of the bandwidth allocated to it by the BS. The scheme used allows link budget improvements and can be used to improve range performance and/or improve battery life of SSs. A typical 1/16 sub channelization factor provides a 12 dB link budget enhancement. In contrast, mobile WiMAX uses OFDMA-PHY and it allows sub channelization in both the uplink and downlink. Sub channels effectively form the minimum frequency resource-unit, which is allocated by the BS. Therefore, different users may be allocated different sub channels as this is multiple-access mechanism. It is also known as orthogonal frequency division multiple access, which gives mobile WiMAX PHY its name. Sub channels may be formed using wither contiguous subcarriers or subcarriers pseudo-randomly distributed across the frequency spectrum. More frequency diversity is achieved by using distributed sub carriers, which is particularly useful for mobile applications. WiMAX defines several sub channelization schemes based on distributed carriers for both the uplink and downlink. One of them is partial usage of subcarriers, which is mandatory for all mobile WiMAX implementations. The second sub channelization scheme is based on contiguous subcarriers and is also known as adaptive modulation and coding. Although the frequency diversity is lost, band AMC allows system designers to exploit multiuser diversity, allocating sub channels to users based on their frequency response. Multiuser diversity can provide significant gains in overall system capacity, if the system strives to provide each user with a sub channel that maximizes its received SINR. Generally, the contiguous sub channels are more suited for fixed and low-mobility applications. Fig. 9 shows a typical sub carrier structure. FIGURE 9 + explanation 2.1.4 Frame Structure Mobile WiMAX used to support Time Division Duplex only but recently full and half-duplex Frequency Division Duplex support has been added. [4 new] It is mainly because of local restrictions in some areas. A major disadvantage of the TDD is that it needs to be synchronised over the whole system. On the other hand, there are several reasons why TDD usage is preferred. One of them is that the ratio of DL/UL data rates can be adjusted freely. It is in contrast with the FDD where the ratio is always constant and in most cases symmetric. Channel reciprocity is assured by using TDD, which gives better support of link adaptation, MIMO and other closed loop advanced antenna technologies. Whereas FDD requires a pair channel, but TDD can share one for both DL/UL traffic. Additionally, from economical point of view, FDD transceivers are more complex and therefore more expensive to manufacture. For the simulation project that has been set up, FDD mode was used and for this purpose the next part of this chapter explains the FDD frame structure in relation to relaying. For information purposes TDD frame structure is also discussed. 2.1.4.1 Frame Format for FDD The FDD mode does not provide guard times and parallel transmissions in DL and UL. [5new] The BS always sets up the master frame, in other words, it generates the timing schedule for the next period. The process begins with synchronisation pilots, a broadcast channel and a random/contention access channel; a few regular frames follow, but this very much depends on the technology used. Some of the frames are reserved for the second hop(s) by the BS, which are later used in the responsibility of the relay(s). A term called stealth relaying is used when the BS does not even distinguish between relays and ordinary SSs. It is preferable to use centrally and relay-aware BS controlled resource allocation for further systems. Interleaved multihop frames are incorporated by modern multihop systems, where frames for the first and second hops alternate in time and they are all controlled by the BS. The smallest granularity resource unit is a chunk, 100 chunks form a basic frame. Symbols, on the other hand, are used for signalling and synchronization, but they are out of focus here. They are shown in grey in Fig. 10(a) and the only impact here is the overhead-resources not available for data throughput. DL and UL transmissions happen simultaneously in the same frame raster. There are 3 ways of integrating relaying (the frames used for the second hop or beyond: Time Domain Relaying: resources for hop1 and hop2 are separated in time (sequentially) Frequency Domain Relaying: recourses for hop1 and hop2 are separated in frequency (neighbour band) OFDMA Domain Relaying: recourses for hop1 and hop2 are separated in frequency (sub channels) As OFDMA was already introduces as topic earlier, it is important to describe what its advantages are over OFDM relaying. First one is that the resources can be subdivided in a finer granularity than it is possible using OFDM only. Fig. 10(b) shows that first-hop transmissions are always treated the same way. They only occupy the required resources for their traffic and there is not waste due to completely assigned but incompletely filled frames. In the UL several SSs share the full bandwidth and each of them transmits on a subset of sub channels, with a guard band between them. The BS or RN coordinates the orthogonal interference-free use of these sub channels by the SSs. OFDMA subdivision in the DL is also available, where the BS and RN send on distinct sub channels, but using sufficient guard band. Even if the side band power is below the signal level, this can cause serious interference trouble at the SS when receiving the useful signal from a far dist ant BS and the interference from the RN nearby. In this case, interference mitigation strategies in the BS are helpful. This also leads to proper association decisions for intra-cell handover. The handover concept is introduced later in the report and the fundamental principles are discussed in details. 2.1.4.2 TDD Frame Structure Mobile WiMAX TDD mode allows the DL and UL transmissions to share the same transmission medium. [6new] Fig. 11 shows the typical structure of TDD frame. Transmission and reception cannot occur simultaneously, due to the prohibitively complex filtering, which is essential for the separation of UL and DL. Something more, in order to avoid interference between the signals transmitted from the BS and other SSs, time gaps such as the transmit/receive transition gap or receive/transmit transition gap are needed. The TTG allows sufficient time for the BS to switch from transmit to receive mode. RTG provides time for the BS to switch from receiving to transmitting. Parameters that form the size of the time gaps are: cell radius, the transceiver turnaround time and other implementation constraints. 2.1.5 Adaptive Modulation and Coding in WiMAX It is inevitable to mention the modulation and coding techniques that are employed by the WiMAX standard. Their principles are important as later in the report; those modulations are used for the simulation purposes and are base on the discussion how the SSs can be connected to the BSs and what effect the modulation and coding have on the connectivity. WiMAX supports a variety of modulation and coding schemes. [3 new]This allows the scheme to change on a burst-by-burst basis per link, depending on channel conditions. The SS can provide feedback on the DL channel quality to the BS by using channel quality feedback indicator. For the UL, the BS can easily estimate the channel quality, based on the received signal quality. The BS scheduler can take into account the channel quality for each users UL and DL and assign a modulation and coding technique that maximizes the throughput for the available SNR. Adaptive modulation and coding increases the overall system capacity, as it allows real-time trade-off between throughput and robustness on each link. Table 2 lists various modulation and coding scheme used by WiMAX. In the DL, QPSK, 16 QAM, and 64 QAM are mandatory for both fixed and mobile WiMAX. 64 QAM is optional in the UL. FEC coding using conventional codes is mandatory as well. Conventional codes are combined with an outer Reed-Solomon code in the downlink for OFDM-PHY. Turbo codes and low-density parity check codes are optionally supported at a variety of code rates as well. There are 52 combinations of modulation and coding techniques that are defined in WiMAX as burst profiles. Downlink Uplink Modulation BPSK, QPSK, 16 QAM, 64 QAM; BPSK optional for OFDMA-PHY BPSK, QPSK, 16 QAM; 64 QAM optional Coding Mandatory: convolution codes at rate , 2/3, , 5/6 Mandatory: convolution codes at rate , 2/3, , 5/6 Optional: convolution turbo codes at rate , 2/3, , 5/6; repetition codes at rate ,1/3, 1/6, LDPC, RS-Codes for OFDM-PHY Optional: convolution turbo codes at rate 1/2., 2/3, , 5/6; repetition codes at rate , 1/3, 1/6, LDPC Table 2. Modulation and Coding supported by WiMAX. 2.2 MAC Layer Details The second important layer of the WiMAX standard is the MAC medium access control. In general, the 802.16 MAC is designed to support multipoint-to-multipoint architecture, where a centrally located BS handles multiple independent sectors simultaneously. [7 new] On the downlink, data to SSs are multiplexed in TDM fashion. On the contrary, the uplink is shared between SSs in TDMA fashion. IEEE standard 802.16 defines 2 general service-specific convergence sub-layers for mapping services to and from 802.16 MAC connections. The first one is the ATM convergence sub-layer, which is defined for ATM services. The second one is the packet convergence layer, defined for mapping packet services such as IPv4, IPv6, Ethernet, and virtual local area network. There are 3 primary tasks of the sub-layer: To classify service data units to the correct MAC connection Preserve or enable QoS Enable bandwidth allocation Depending on the type of service, the mapping takes a range of forms. Additionally to the basic convergence sub-layer tasks, the layers can also perform more complicated functions payload header suppression and reconstruction to enhance air link efficiency. As it was already mentioned, the 802.16 MAC is connection-oriented and all services, including inherently connectionless services, are mapped to a connection. Thus, it provides a mechanism for requesting bandwidth, associating QoS and traffic parameters, transporting and routing data to the appropriate convergence sub-layer; as well as all other actions associated with the contractual terms of service. Connections are referenced with 16-bit connection identifiers and may require continuously granted bandwidth or bandwidth on demand. Every SS has a standard 48-bit MAC address, which serves mainly as an equipment identifier. The primary addresses used during operation are the CIDs. Three management connections are assigned to the SS when entered the network. These connections reflect the three different management connections in each direction: Basic connection- used for the transfer of short, time-critical MAC and radio link control massages. Primary management connection- used to transfer short longer, more delay-tolerated messages (e.g. those used for authentication and connection setup). Secondary management connection- used for the transfer of standards-based management messages, such as DHCP, TFTP, and SNMP. Apart from the management connections, transport connections for the contracted services are also allocated to the SSs. Transport connections are unidirectional and facilitate different DL and UL QoS and traffic parameters; they are typically assigned to services in pairs. Additional connections for other purposes may also be reserved by MAC: Contention-based initial access Broadcast transmissions in the DL, as well as for signalling broadcast connection-based polling of SS bandwidth needs Multicast, rather than broadcast, connection-based polling. SSs may be instructed to join multicast polling groups associated with these multicast polling connections. 2.2.1 MAC PDU Construction and Transmission As it was already discussed, the MAC sub-layer is independent of the higher-layer protocol and performs such operations as scheduling, [3 new] ARQ, bandwidth allocations, modulation and code rate selection. The SDUs arriving from the higher-layer to the sub-layer are assembled to create the MAC PDU, which is the basic payload unit handled by the MAC and PHY layers. Multiple SDUs can be carried on a single MAC PDU, or a single SDU can be fragmented to be carried over multiple MAC PDUs; this is entirely based on the size of the payload. When an SDU is fragmented, the position of each fragment within the SDU is labelled by a sequence number. The usage of the sequence number is to ease assembling of the SDU from its fragments in the correct order at the receiver MAC layer. Multiple MAC PDUs destined to the same receiver can be concatenated and carried over a single transmission opportunity or data region. This is purely done to use the PHY resources more efficiently. This is shown in Fig. 12. For non-ARQ-enabled connections, each fragment of the SDU is transmitted in sequence. For ARQ-enabled connections, the SDU is first divided into fixed length ARQ blocks. Each ARQ block has its own block sequence number. ARQ BLOCK-SIZE parameter is used by the BS for each CID to specify the length of the block. The length of the SDU should be integral multiple of the ARQ BLOCK-SIZE, if it is not the last ARQ block is padded. Once the SDU is portioned into ARQ blocks, the partitioning remains until all the ARQ blocks have been received and acknowledged by the receiver. After the partitioning, the SDU is assembled into MAC PDUs in a normal fashion as it is shown in Fig. 12. For ARQ-enabled connections, the fragmentation and packing sub head er contains the BSN of the first ARQ block following the sub header. The ARQ feedback from the receiver comes in the form of ACK indicating successful reception of the ARQ blocks. The feedback is sent either as a stand-alone MAC PDU or piggybacked on the payload of a regular MAC PDU. ARQ feedback can be two types: Selective:indicates that the ARQ block has been received without errors Cumulative:indicates that all blocks with sequence number less than or equal to the BSN have been received without error. Each MAC PDU consists of a header followed by a payload and cyclic redundancy check. The CRC is based on IEEE 802.3 and is calculated on the entire MAC PDU; the header and the payload. Two types of PDUs (Fig. 13) are introduced, and each of them has different header structure: Generic PDU- used to carry data and MAC-layer signalling massages. It starts with a generic header, which structure is shown on Fig.13, and then followed by a payload and a CRC. The different information elements in the header of a generic MAC PDU are shown in Table 3. Bandwidth PDU- used by the SS to inform the BS that more bandwidth is needed in the UL, due to pending data transmission. This type of PDU consists of bandwidth-request header, and there is no payload or CRC. The header information elements are shown in Table 4. Field Length (bits) Description HT 1 Header type (set to 0 for such header) EC 1 Encryption control (0= payload not encrypted; 1= payload encrypted) Type 6 Type ESF 1 Extended sub header field (1 = ES present; 0 = ES not present) CI 1 CRC indicator (1 = CRC included; 0 = CRC not included) EKS 2 Encryption key sequence (index of the traffic encryption key and the initialization vector used to encrypt the payload) Rsv 1 Reserved LEN 11 Length of MAC PDU in bytes, including the header CID 16 Connection identifier on which the payload is to be sent HCS 8 Header check sequence Table 3, Generic MAC header fields Field Length (bits) Description HT 1 Header type (set to 1 for such header) EC 1 Encryption control (set to 0 for such header) Type 3 Type BR 19 bandwidth request (the number of bytes for uplink bandwidth request by the SS for the given CID) CID 16 Connection identifier HCS 8 Header check sequence Table 4. Bandwidth request MAC header fields Once a MAC PDU is constructed, it is handed over to the scheduler, which schedules the MAC PDU over the PHY resources available. The scheduler checks the service flow ID and the CID of the MAC PDU, which allows it to gauge its QoS requirements. Based on the QoS requirements of the MAC PDUs belonging to different CIDs and service flow Ids, the scheduler determines the optimum PHY resource allocation for all the MAC PDUs, on a frame-by-frame basis. 2.2.2 DL and UL MAP WiMAX MAC supports both TDD and FDD modes. [7 new] In FDD, both continuous and burst downlinks are supported. Continuous downlinks allow for certain robustness improvement techniques for example interleaving. Burst downlinks allow the use of more complex robustness and capacity enhancement techniques, e.g. subscriber level adaptive burst profiling and advanced antenna systems. The MAC builds the DL sub frame, starting with a frame control section. The frame control section contains the DL-MAP and UL-MAP messages. They indicate PHY transitions on the downlink; bandwidth allocations and burst profiles on the uplink. The DL-MAP is applicable to the current frame and is always at least 2 FEC blocks long. In both TDD and FDD modes, the UL-MAP provides allocations starting no later than the next downlink frame. If the processing times and the round trip delays are observed, then the UL-MAP may allocate starting in the current frame. The minimum time between receipt and applicability of the UL-Map for an FDD system is shown in Fig. 14 2.2.3 Authentication, Registration and Security Another important factor of the MAC protocol is that it manages procedures such as authentication, registration and security. Each of the SS holds two certificates: factory installed X.509 digital certificate and certificate of manufacturer. Those certificates are sent from the SS to the BS in the Authorization Request and Authentication Information messages. The certificates establish a link between the 48 bit MAC address of the SS and its public RSA key. The network is able to identify the SS using the certificates, and afterwards it can check the authorization of the SS. If the SS is authorized to join the network, BS will respond with an Authorization Reply containing an Authorization Key. The Authorization Key is encrypted with the SSs public key and used to secure further transactions. When the authorization is successful, the SS will be registered with the network. This will establish the secondary management connection of the SS and determine capabilities related to connection setup and MAC operation. The version of IP used on the secondary management connection is also determined during registration. WiMAXs privacy protocol is based on the Privacy Key Management protocol. It is based on the DOCSIS BPI+ specification, but has been modified to fit seamlessly into the MAC protocol. It accommodates stronger cryptographic methods, such as the Advanced Encryption Standard. PKM is build around the concept of security associations. SA is a set of cryptographic methods and the associated keying material. It contains the information about which algorithms to apply, which key to use, and so on. Every SS establishes at least one SA during initialization. Apart from the basic and primary management connections, all other connections are mapped to an SA either at connection setup time or dynamically during operation. For the traffic encryption, the PKM uses the Data Encryption Standard, running in the cipher block chaining more with 56-bit keys. The CBC initialization vector depends on the frame counter and differs from the frame to frame. To reduce the number of computationally intensive public key operations during normal operation, the transmission encryption keys are exchanged using 3DES with a key exchange key derived from the authorization key. The PKM protocol messages are authenticated using the Hashed Message Authentication Code protocol with SHA-1. Message authentication in essential MAC functions, such as the connection setup, is provided by the PKM protocol. 2.2.4 Services and Parameters The last part of the MAC layer is the services and their parameters. It is an essential part of the standard implementation and this part of the chapter lists all QoS that are provided by the WiMAX family. Scheduler is the one that controls the scheduling services for the standard and handles the mechanisms supported by the MAC to transport data. [9 new] Each connection is associated with a single data service. Data services are associated with a set of QoS parameters that define their behaviour. Two data parameters are used for the management of the parameters: dynamics service addition and dynamic service change. Five different services are supported: unsolicited grant services, real-time polling services, extended real-time polling services non-real-time polling services, and best effort. Table 5 lists the application and specification for each of those services. [10 new] QoS Category Applications QoS Specifications UGS VoIP Maximum sustained rate Maximum latency tolerance Jitter tolerance rtPS Streaming audio and video Minimum reserved rate Maximum sustained rate Maximum latency Traffic priority ertPS Voice with activity detection (VoIP) Minimum reserved rate Maximum sustained rate Maximum latency tolerance Jitter tolerance Traffic priority nrtPS File transfer protocol Minimum reserved rate Maximum sustained rate Traffic priority BE Data transfer, web browsing, etc. Maximum sustained rate Traffic priority Table 5. Mobile WiMAX applications and QoS UGS- supports real-time data streams. Each stream is of fixed-size data packets issued at periodic time intervals. It is particularly useful for applications such as VoIP without silence suspension. Mandatory service flow parameters are: maximum sustained rate, maximum latency tolerance, jitter tolerance and request/transmission policy. If the policy is present, the minimum reserved traffic rate parameter will be the same value as the maximum sustained traffic rate parameter. rtPS- supports real-time data streams, each of which is issued at periodic intervals. It is useful for MPEG videos and consists of variable-size data packets. Compulsory parameters are: minimum reserved rate, maximum sustained rate, maximum latency, traffic priority, and again request/traffic policy. ertPS- it is a combination of USG and rtPS. [4new] ertPS is designed to support VoIP with activity detection, which means that when there is a silence period in the communication, the bandwidth can be saved by downsizing the packets length. The maximum sustained traffic rate, which defines the default size of the allocations, may be changed with ertPS. nrtPS- used for delay-tolerant data streams, which consist of variable data packets. Minimum data rate is required as it used the FTP. Flow parameters are: minimum reserved rate, maximum sustained rate, traffic priority, and request/transmission policy. BE is used to support data streams for which no minimum service level is required and therefore may be handled on a space-available basis. Associated parameters are: maximum sustained rate, traffic priority, and request/transmission policy. 3 Handovers The aim of the next chapter is to introduce the term handovers and to explain their importance for the WiMAX standard features. Handovers are very vital part of a wireless technology.[11new] When an SS moves between different BSs, the connection should also move and in order to do so a seamless handover should be performed. By the term seamlessness, it defines the necessity to maintain current session, QoS and service level agreements during and after the handover. In other words, the seamless handover should not be noticeable by the user; however, this very much depends on the kind of services the user is requiring. With real-time applications, such as videoconferencing or streaming media, s slight decrease of the connection may be observed. In contrast, while a user is browsing a website or transfers files, they will most probably not notice any change in their connection. There are two crucial factors related to the handover procedure: the latency and the packet loss. They have to be as small as possible to make the handover seamless. Several reasons why and when a handover should be initiated are listed below: SS current position and velocity high velocity may lead to different handover decisions Link quality in case a BS is overloaded, the network can decide to relocate some of the SSs Conserving battery power for battery saving purposes, an SS may chose to switch to a closer station and be energy efficient Context and requirements if an SS requires different type of service, it may be necessary to change BS. Handovers have a significant effect on the performance of channel allocation algorithms. At high traffic loads, the majority of forced call terminations are as a result of the lack of channels available for handover rather than to interference. This is a major problem in microcellular systems, where the rate of handovers is considerably higher than that in normal cellular systems. There are a number of solutions to reduce the performance penalty caused by handovers. One of them is to reserve some channels solely for handovers, generally referred to as cut-off priority or guard channel schemes. However, this solution reduces the maximum amount of carried traffic or system capacity and hence yields increased new call blocking. Algorithms that give higher priority to requests for handovers than to new calls are called Handover prioritization schemes. Guard channel schemes are therefore a type of handover prioritization arrangement. Another type of handover prioritization is constituted by handover queuing schemes. Normally, when an allocation request for handoff is rejected, the call is forcibly terminated. By allowing handover allocation requests to be queued temporarily, the forced termination probability can be reduced. The simplest handover queuing schemes use a First-In First-Out (FIFO) queuing regime. A non-pre-emptive priority handover queuing scheme in which handover requests in the queue that are the most urgent ones are served first. A further alternative to help reduce the probability of handover failure is to allow allocation requests for new calls to be queued. New call allocation requests can be queued more readily than handovers because they are less sensitive to delay. Handover queuing reduces the forced termination probability owing to handover failures but increase the new call blocking probability. New call queuing reduces the new call blocking probability and also increases the carried teletraffic. This is because the new calls are not immediately blocked but queued, and in most cases they receive an allocation later. Handovers have a significant effect on the performance of channel allocation algorithms. At high traffic loads, the majority of forced call terminations are as a result of the lack of channels available for handover rather than to interference. This is a major problem in microcellular systems, where the rate of handovers is considerably higher than that in normal cellular systems. There are a number of solutions to reduce the performance penalty caused by handovers. One of them is to reserve some channels solely for handovers, generally referred to as cut-off priority or guard channel schemes. However, this solution reduces the maximum amount of carried traffic or system capacity and hence yields increased new call blocking. Algorithms that give higher priority to requests for handovers than to new calls are called Handover prioritization schemes. Guard channel schemes are therefore a type of handover prioritization arrangement. Another type of handover prioritization is constituted by handover queuing schemes. Normally, when an allocation request for handoff is rejected, the call is forcibly terminated. By allowing handover allocation requests to be queued temporarily, the forced termination probability can be reduced. The simplest handover queuing schemes use a First-In First-Out (FIFO) queuing regime. A non-pre-emptive priority handover queuing scheme in which handover requests in the queue that are the most urgent ones are served first. A further alternative to help reduce the probability of handover failure is to allow allocation requests for new calls to be queued. New call allocation requests can be queued more readily than handovers because they are less sensitive to delay. Handover queuing reduces the forced termination probability owing to handover failures but increase the new call blocking probability. New call queuing reduces the new call blocking probability and also increases the carried teletraffic. This is because the new calls are not immediately blocked but queued, and in most cases they receive an allocation later. There are two main types of handovers: horizontal (handovers within the same technology) and vertical (handovers between different network access technologies). Horizontal handovers- are Layer-2 handovers and are also referred to as micro-mobility. In this case only the BS is changed and the IP-information is kept the unchanged. This kind of handover causes small latency and low packet loss Vertical handovers- Layer-3 handovers and are also referred as macro-mobility. It changes the IP-connection point, and as a result the IP information is changed as well. As a result, significant latency and packet loss are observed. 3.1 Handover Types WiMAX specification supports three types of handovers: Hard Handover, Fast Base Station Switching, and Macro Diversity Handover.[4new] HHO is compulsory, whereas the other two are optional. The WiMAX forum has been working on the enhancement of the HHO techniques to achieve handovers in less than 50 milliseconds. 3.1.1 Hard Handover HHO is a procedure that changes the serving BS using a break-before-make approach. Effectively, this means that the connection to the old BS is broken before the new BS is connected to the SS. Using this approach, excess signalling traffic is avoided during the handover procedure, however, the time before the connection is again in normal operation may be longer. While the SS is connected to a BS, it listens to the link-layer messages for another BS, which periodically broadcasts neighbour advertisement messages. The advertising messages are used for network identification and recognition of the services that are provided. Facts about the signal quality from a neighbouring BS are included in the messages. In case a better BS is not found, the SS stores the information that has been received for future handovers. Fig. 15 illustrates a typical scenario of HHO, when a moving user reaches the point where the signal level is of better quality with another BS. A further decision criterion has to be set up to avoid constant handover back and forth between BSs. 3.1.2 Macro Diversity Handover When MDHO is supported by MS and by BS, the Diversity Set (or in some cases it is called Active Set) is maintained by SS and BS. Diversity set is a list of the BSs, which are involved in the handover procedure. Diversity set is defined for each of SSs in network. SS communicates with all BSs in the diversity set (Fig. 16). For downlink in MDHO, two or more BSs transmit data to SS such that diversity combining can be performed at the SS. For uplink in MDHO, MS transmission is received by multiple BSs where selection diversity of the received information is performed. The BS, which can receive communication among SSs and other BSs, but the level of signal strength is not sufficient is noted as Neighbour BS. While the SS is moving towards the neighbouring BS, at some moment the signal from the neighbouring BS becomes strong enough and the BS can be included in the active set. The factor that is used to measure the inclusion/exclusion of the BS is the long term CINR. There are two ways that the SS uses to monitor DL control information and broadcast messages: It listens only to the anchor BS for burst allocation information of other BSs in the active set Listens to all BSs in the active set. By listening to all active set BSs, a DL/UL-MAP message from any BS may include information for other BSs. The MDHO is started when the SS decides to receive/transmit from multiple BSs at the same time. For DL traffic, two or more BSs transmit the data to the SS, which performs diversity combining. For the UL traffic, the traffic generated by the SS is received by all BSs in the active set and selection diversity is then performed. Interestingly, the MDHO requires all BSs to communicate on synchronised basis, because of the frames sent by the BSs at a certain time frame have to be received by the SS within the specific prefix interval. The BSs frame structure have to be synchronised and the frequency assignments to have the same values. Furthermore, the same set of CIDs and MAC/PHY PDUs sent to the SS have to be generated by the BSs. The encryption information and network entry exchanged information have to be shared between the SS and the BSs as well. 3.1.3 Fast Base Station Switching In FBSS, the SS and BS diversity set is maintained similar as in MDHO. SS continuously monitors the base stations in the diversity set and defines an Anchor BS. Anchor BS is only one base station of the diversity set that MS communicates with for all uplink and downlink traffic including management messages (Fig. 17). This is the BS where SS is registered, synchronized, performs ranging and there is monitored downlink channel for control information. The anchor BS can be changed from frame to frame depending on BS selection method, which means each frame can be sent via different BS in diversity set. Generally, the requirements for the FBSS are the same as the ones of MDHO without the demand for the same CIDs and MAC/PHY PDUs.

Examples Of Format A Resume - 794 Words

1 Format your resume. It is unquestionable that formatting plays a vital role in an effective resume, as the first thing will jump into a possible employer’s sight is how well-organized your resume is. In most cases, your resume will not get a thorough reading at the first time no matter how well written it is. Therefore, it is a good idea to make your resume attractive and readable by formatting. There are some useful tips for you to format your resume. First, keep your resume short and simple. Most people do not need more than two pages unless you have extensive related skills and experience. Second, invite employers’ attention by using wide margins and a logical format. A logical format contributes to the effect of the overall design†¦show more content†¦It not only focuses on what you can do but also provides â€Å"when and where† information; however, it is the most difficult to write and organize. 3 Make your content shine. The description of your education and work experience is the core of your resume, which is also the section that employers will mainly focus on. Hence, making your content interesting and descriptive will enable your resume to stand out from competitors. Here are some ways that can help your resume gets noticed. First, use the active voice and expressive verbs to describe the specific things that you have done. These can highlight your abilities and skills, and spice up your resume to make it stand out. For example, if you were an administrative assistant, you might want to use words such as â€Å"scheduled† and â€Å"coordinated†. You can use them by writing â€Å"Scheduled and coordinated appointments.† Another good way to make your content shine is to put more emphasis on your achievements and accomplishments. By emphasizing the results you have delivered with specific facts and highlighting the ways you have added value in the past, you will be able to demonstrate your competence in solving problems with convincing evidence. The last effective way is to choose descriptive titles for your previous job positions. For instance, instead of saying you were a secretary, say you were an administrative assistant. In addition, think about how well the title can describe the job. For example,Show MoreRelatedExamples Of Format A Resume780 Words   |  4 Pages1 Format your resume. It is vital to make the right first impression to your prospective employers because the first thing that will jump into their sight is how well-organized your resume is. In most cases, your resume will not get a thorough reading at the first time no matter how well written. Therefore, it is a good idea to make your resume attractive and readable by formatting. There are some useful tips for you to format your resume. 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Essay about Talking Back to Civilization - 1475 Words

Talking Back to Civilization Talking Back to Civilization , edited by Frederick E. Hoxie, is a compilation of excerpts from speeches, articles, and texts written by various American Indian authors and scholars from the 1890s to the 1920s. As a whole, the pieces provide a rough testimony of the American Indian during a period when conflict over land and resources, cultural stereotypes, and national policies caused tensions between Native American Indians and Euro-American reformers. This paper will attempt to sum up the plight of the American Indian during this period in American history. American Indians shaped their critique of modern America through their exposure to and experience with â€Å"civilized,†Ã¢â‚¬ ¦show more content†¦An advocate for Indian education, Henry Roe Cloud wrote, â€Å"Is the Indian a ward of the government or a citizen? What are his rights and duties? . . . [He] must be trained to grapple with these economic, educational, political, religious and social problems† (59, 60). Cloud challenged the American educational system by rhetorically questioning the meaning of Indian citizenship and campaigning for more Indian societal responsibilities. In the Society of American Indians (SAI) Quarterly Journal , progressivist Carlos Montezuma wrote, â€Å"Reservations are prisons where our people are kept to live and die, where equal possibilities, equal education and equal responsibilities are unknown† (93). In Indian schools, children were not even allowed to speak their native language for fear that they might retu rn to their savage ways. Essentially, American Indians only wanted equal rights and equal citizenship; they wanted Euro-Americans to stop treating them like lower-level beings. But Euro-Americans continued their quest to mother the â€Å"savage† race by assimilating and converting Indians. Understandably, American Indians soon began to distrust and resent their white oppressors. Simon Pokagon put it nicely in his speech The Red Mans Greeting : We nursed and fed them, fed the ravens that were soon to pluck out our eyes and the eyes of our children; . . . weShow MoreRelatedNative Americans And American History1396 Words   |  6 Pagespeople, but a history of the land and the extensive traditions that shadowed it, like footprints in the sand. However, when the Europeans staggered over with indifference towards the natives and their unusual customs, a conflict erupted that dates back hundreds of years and continues into the present. As the United States grew further more intolerant of the natives, the daring judgment to either assimilate into the American society, or face extinction of the Indian race and culture was presentedRead MoreCharacteristics Of Civilization938 Words   |  4 PagesCivilization to me is what makes up our lives. 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Energy crisis Essay Example For Students

Energy crisis Essay Late in the autumn of 1973, energy (or the lack of it) grabbed headlines like never before. It was not until the war between the Arab countries and Israel that the United States noticed a sharp decrease in our oil supplies. This was due to the fact that we the U.S. were supplying aids and weapons to Israel. Arab, who produced the majority of the worlds oil, decided to punish us by cutting off our oil shipments. In November of the same year, President Nixon appeared on live television to inform the United States public about the crisis. He informed the people they were going to have the most crucial energy shortage since World War II. In order to conserve energy there were a few emergency polies being enforced. These new rules were said to help everyone get through the shortage, but they ended up having the opposite effect. A few of the policies included lowering highway speed limits to 55 miles per hour in hopes of saving gasoline. Also, factories worked shorter shifts and air travel time was cut by about 10 percent. During this time, children were effected a lot. Nixon ordered that clocks were not to be turned back an hour late as they usually were in October. Instead, the U.S. was to stay on summers daylight savings time in order to conserve energy. Therefore, kids had to go to school when it was still dark. Some children carried with them flashlights. Christmas was a very sad time in 1973. People were unable to use Christmas lights or any other electronic decorations in order to save energy. The President announced that because of the crisis, the lights of the national Christmas tree would not be turned on. Increase of prices made it hard for families to buy things and pay bills. Demand for oil created hardships for gas station owners as well. There were long lines of cars snaking for miles, and impatient drivers starting fights and sometimes shooting one another. Nixon proposed that the best solution to future trouble would be to completely eliminate the use of foreign oil. He suggested that Americans find other sources of energy along with finding new oil reserves in the United States. The President asked for more concentration on the use of coal and the development of other power sources such as solar or nuclear energy. Obviously Nixons solution did not help as the demand for oil became greater. With the increase in technology and factories, alternative forms of energy showed to be more expensive than originally thought. Although the U.S. now has a wide variety of energy sources, it is still a good idea to conserve our energy. History does repeat, and we never know when a sudden shortage may occur. Bibliography:

Similarities and Differences in the Criminal Subculture free essay sample

The Similarities and Differences in the Criminal Subculture and the police A police officers job is to protect and serve. An officer is to offer assistance to those in need and to enforce the laws established by the law makers. A police officers job is not the monotonous 8-5 job that most have.. It is ever changing, 24-7. It is not a normal environment. Think about it, a police officer runs into a gun fight.. .. Normal folks run away from it!A criminal is the exact opposite of a police officer. They often do not have jobs and those that do are normally using their job to commit their crimes! They are interesting in protecting and serving themselves and those in their group but thats where it stops. A criminal is normally self-absorbed and is obviously not enforcing laws but rather breaking them. However, a criminals job is rarely monotonous and is certainly not normal. We will write a custom essay sample on Similarities and Differences in the Criminal Subculture or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page As for the gun fights that cops run to, the criminals are the ones having it in the first place!So you see, while the goals and objectives of a police officer and a criminal are polar opposite, they also have many similarities. They are both a subculture of the population as a whole. A subculture is a subdivision of a culture defined by occupation, ethnicity, class, or residence. A subculture forms a functioning group, unified by shared values, beliefs, and attitudes. The police subculture and the criminal subculture are both based on shared expectations about human behavior (Lyman, 1999). It is interesting to research how these subcultures develop. The police subculture develops from a work environment.Officers see multiple problems and are placed in situations where they must grapple with he serious problems in life. These include the problems of injustice, pain, suffering, and death. This environment begins shaping an officers interpretation of events. What they would normally view as heart wrenching over the years becomes just another day/ (Lyman, 1999). Police officers have an incredible amount Of authority. Police officers are a symbol Of authority that must often be assertive in establishing authority with citizenry. This can lead to conflict, hostility, and perhaps overreaction and police brutality.Officers are expected to remain detached, neutral, and unemotional even hen challenged and in situations of conflict. There is a high sense of morality in the law enforcement subculture. Morality helps police overcome dilemmas. These dilemmas include the dilemma of contradiction between the goal of preventing crime and the polices inability to do so, the dilemma of using discretion to handle situations that do not always strictly follow established procedure and the dilemma officers face when they must invariably act against at least one persons interest, including the possibility of injuring or killing someone.Morality is helpful in encouraging police to serve he public under difficult conditions, but may also lead to negative impact if police use morality to engage in categorizing people (Hickman, Vaquero, and Greene, 2004). Police officers are also constantly faced with danger. Officers become what a normal person might see as paranoid because they are so attentive to signs of potential violence because they work in dangerous situations. The colonization process starts from the beginning and teaches recruits to be cautious and suspicious.Orientation toward watching and questioning can also contribute to tension and conflict in contacts with the public. Police officers are constantly on edge watching for unexpected dangers, on duty and off duty (Layman, 1999). Based on all of the factors and even though the public is generally supportive of the police, the police often perceive the public to be hostile. For this reason, officers tend to socialize primarily with other officers. An officers contact with the public is frequently during moments of conflict, crisis, and emotion.Because police officers are identified by their jobs, members of the public frequently treat them as police, even when off-duty. This increases the need for bonding and socializing between officers, officers families, and families of other officers. Officers are often unable to step back from jobs and separate their professional and personal lives (Hickman et al, 2004). Because this separation is so difficult, officers often manifest a perceived sense of factorization. This is where someone feels like a victim, whether real or imagined, is also the first step on the Continuum of Compromise.As a sense of perceived factorization intensifies, officers become more distrusting and resentful of anyone who controls their job role (Lyman, 1999). Sometimes the perceived sense of customization leads to the second step on the slippery slope which is Acts of Omission. This occurs when officers rationalize and justify not doing things they are responsible for doing. Acts of Omission can include selective non- productivity, such as ignoring traffic violations or certain criminal violations.It can also include Not seeing or avoiding on-sight activity, superficial investigations, omitting paperwork, lack of follow up, doing enough to just get by and other activities which officers can easily omit (Lyman, 1999). Once officers routinely omit job responsibilities, the journey to the next Step is not difficult one to make, Acts of Commission. At this stage, instead of just omitting duties and responsibilities, officers commit administrative violations. Breaking small rules is no big deal. Unsuspecting officers can unwittingly travel to the next and final stage of the continuum, Act of Commission- Criminal. A gun not turned into evidence and kept by the officer can become Its just a dopers. Whats the big deal? The initially honest, dedicated, above reproach officer is now asking, Where did it all go wrong? How did this happen as they face realities of personal and professional devastation and rimming prosecution. Officers who reach the final stage did not wake up one day and take a quantum leap from being honest hard working officers to criminal defendants (Lyman, 1999).According to Lawrence (201 0), The code of silence prevails among many police officers. Policemen often face a difficult decision every day on their beat: loyalty to their community versus loyalty to their fellow officers. Because of this code of silence, some officers may choose loyalty to their fellow officers rather than protecting and serving the community. Lawrence (2010) suggests that this can be attributed to the allowing: First of all, police officers are an identifiable group with uniforms, badges and guns. Secondly, this group shares a common way of life.They share similar dangers, setbacks, and rewards that outsiders rarely see outside of the movies. Thirdly, these dangers foster an us against them mentality not just against criminals but politicians, bureaucrats and concerned citizens who are perceived as impediments to enforcing the law. Police officers have a hard job. They truly are servants who see things most could never even fathom. It is a subculture filled with adrenaline rushes where failure is not an option. It is one where the officer must out smart and out fight the bad guy.To do otherwise could and has often lead to the demise of the officer or to those he is trying to protect. It is no wonder they develop a subculture and while this subculture is not necessarily wrong and may even be healthy, It can also spiral across the line and become a different kind of subculture. There are multiple theories on the criminal/delinquent subculture. One that has similarities with the police subculture is Walter Millers theory. Miller explained crime in terms of a distinctive lower-class subculture.He believed hat Americans in the lower-class social bracket had developed a subculture which had its own values and traditions separate from those in a higher social bracket. These values and way of life were passed on from generation to generation. The values inherent in the lower-class culture actively encouraged lower-class men to commit crime. This subculture had a range of interests and characteristics, sometimes referred to as focal concerns, of its own which included an appreciation of toughness, smartness and excitement (Jacobs, 1994).Miller explained toughness as an expression of masculinity, rejecting immunity and weakness. The toughness manifestation can lead to violence in order to maintain a reputation for toughness. Toughness can be seen in the police subculture as well (Jacobs, 1994). Another focal concern that Miller explained was smartness. Smartness is the quality that emphasizes the ability to outsmart or con another person (Jacobs, 1994). As previously discussed, officers must outsmart the criminal, even if they must use trickery, which is allowed by the courts.Police officers are not normally lab. Years but they must have the smartness of not only a lawyer, but also a social worker, actor, judge, psychologist, etc. Another focal concern that Miller explained was excitement. In this focal concern, the person is searching for emotional stimulus and excitement. Excitement is found in gambling, sexual adventures and alcohol. All these activities can be obtained during a night out on the town (Jacobs, 1994). The desire to be tough and smart and to seek excitement, carries risk. The result can be physical harm and disruption to ones life.Miller explained that with specific regard to adolescents in lower- class subculture, such activities and focal concerns are particularly exaggerated because the generally belong to a peer group which demands conformity to group norms. In addition, adolescents are especially concerned about status which is achieved via peer group norms. In other words, status here will derive from being tough and smart in the eyes of peers (Jacobs, 1994). Miller believed that delinquency was essentially about the acting out of the focal concerns Of lower-class subculture (toughness, smartness etc. Its roots lay in the colonization into a subculture with a distinctive tradition, many centuries old with an integrity of its own. Such a subculture has a life of TTS own. The reason for its existence is due to a need for a pool of low-skilled laborers. These kinds of workers had to be able to tolerate routine, repetitive work as well as periods of unemployment. Lower-class subculture, with its emphasis on excitement and risk-taking activities, allowed these workers to endure the monotony of their work. The activities of the delinquent subculture relieved them from the boredom of their working lives (Jacobs, 1994).While Miller focused on a social approach to explaining delinquent subcultures, Gresham Sykes and David Matzo wanted to build upon Arthur Sutherland Differential Association theory which stated that an individual learns criminal behavior through (a) techniques of committing crimes and (b) motives, drives, rationalizations, and attitudes which go against law-abiding actions Jacob, 1994). Naturalization is a technique which allows the person to rationalize or justify a criminal act. Sykes and Matzo defined five techniques of naturalization.They are denial of responsibility, denial of injury, denial of victim, condemnation of the condemners, and the appeal to higher loyalties (Jacobs, 1994). Denial of responsibility is a technique used hen the deviant act was caused by an outside force. This technique goes beyond looking at the criminal act as an accident. The individual feels that they are drawn into the situation, ultimately becoming helpless. These juveniles feel that their abusive families, bad neighborhoods and delinquent peers predispose them to criminal acts (Jacobs, 1994). Denial of injury occurs when the criminal act causes no harm to the victim. Criminal acts are deemed deviant in terms of whether or not someone got hurt. Using this technique, the delinquent views stealing as merely borrowing. The use of this quench is reaffirmed in the minds of these juveniles when society does not look at certain acts, such as skipping school or performing practical jokes, as criminal, but merely accepts them as harmless acts (lacily, 1994). Denial of victim is used when the crime is viewed as a punishment or revenge towards a deserving person.This technique may be used by those who attack homosexuals or minority groups. They deserve it. Jacob, 1994) The technique called the condemnation of the condemners places a negative image on those who are opposed to the criminal behavior. The juvenile ends p displacing his deviant behavior on those they are victimizing and also viewing the condemners as hypocrites, such as corrupt police and judges (Jacobs, 1994). The appeal to higher loyalties technique is used when the person feels they must break the laws of the overall community to benefit their small group or family.This technique comes into play when a juvenile gets into trouble because vitrifying to help or protecting a friend or family member (Jacobs, 1994). So how does the police subculture and the criminal subculture because one in the same? Are there focal concerns truly similar as Miller suggested? Or are there similarities emerge due to the five techniques of naturalization? While both arguments are compelling, a recent article in the Arkansas Democrat Gazette summarized this potential similarity in the two grou ps very well so I will end with this article.YOURE SPECIAL. Youre special because you have a badge. You can ticket mayors. You can stop a governor on the highway. Havent you seen the movies? Cops are special. Youre special because you can give an athlete a break. A hell of a break. Youre special because you can even chew him out while youre doing it. Youve got a career ahead of you What I should do is bend you over here and whap your butt. Youre special because you can tell a prominent athlete you should whap his butt.Youre special because you can tell a kid youre taking his gun and letting his coach decide what to do with it. Not a judge and jury. Youre special enough that you dont need a judge and jury. You are judge and jury. Its confirmed. Youre special. Then the whole matter becomes public. Then youre no longer so special. Youre not even on the force any longer. What happened? When did you stop being special? Answer: not soon enough. Because if you hadnt been allowed to think you were special, you would have stuck to the rules and regulations and still have that badge.Those of us who let you develop that illusion did you no favors. There are a couple of lessons here-?at least. Certainly for Arkansas State University athletes, or any athletes at any college. Certainly for the Arkansas State Police, or any lawmen at any agency. Heres hoping other athletes and other law officers have learned by these sad examples in last weeks news. And that the rest Of us have learned something, too-?about humility and equal treatment under the law and not to assume were so special, either.