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== Cellular Communication communication==A cellular mobile communications system uses a large number of low-power wireless transmitters to create cells — the basic geographic service area of a wireless communications system. Variable power levels allow cells to be sized according to the subscriber density and demand within a particular region. As mobile users travel from cell to cell, their conversations are handed off between cells to maintain seamless service. Channels (frequencies) used in one cell can be reused in another cell some distance away. Cells can be added to accommodate growth, creating new cells in unserved areas or overlaying cells in existing areas. [http://www.IEC.org Source[CDMA Basics]]
== Cellular System Architecture =Need for Rate Matching===Cellular systems are increasing In a system using Multiple Access CDMA technology, the greater the Eb/I ratio the greater is the QoS. Transport channels having different QoS requirement do not have the same need in demand as more users are added to their systemsterms of Eb/I ratio. The amount If all the channels are allocated a fixed Eb/I ratio which corresponds with the maximum required by a transport channel then other channels will have "too" good a Quality of frequency spectrum available for mobile cellular use was limitedService, needlessly causing '''interference and efficient use of resource blocking'''. There are several influences that might change system performance(BER) and hence Eb/I ratio,in accordance with the required frequencies was needed QoS of which the most effective is variation of Bit Rate by a step of '''Rate Matching'''. The standard framework for mobile cellular coveragethe management of QoS in CDMA systems is shown below. In modern cellular telephony, rural and urban regions are divided The following framework highlights the various steps involved in providing variable QoS. The received data from the transport block is classified into areas according to specific provisioning guidelinesdifferent processes based on their QoS. Provisioning for each region Data is planned according split onto various transport channels to an engineering plan that includes cellswhich a CRC code is attached for error correction. Further, clustersall these transport channels are multiplexed on one line by concatenation, frequency reuseinterleaved, segmented and handoversthen rate matched.The rate matching step is performed using the rate matching ratio and puncturing ratio which is received from the sending entity (an exchange of handshaking signals occurs).<br>[[Image:cdma_2_7.jpg|thumb|700px|center|QoS Management in CDMA - Standard Framework]]
==== Cell Splitting =QoS Management Algorithms=== As a service area becomes full Quality of users, this approach is used to split a single area into smaller ones. In this way, urban centers Service can be split into as many areas as necessary managed according to provide acceptable service levels in heavy-the varying type of traffic regionsi.e. data, while largervoice, less expensive cells can be used to cover remote rural regionsvideo in the following four ways.# Rate Matching Algorithm# Code Hopping Algorithm# Dynamic Resource Scheduling(DRS) Algorithm# Optimal Power Control Algorithm[[Image:cdma_22.jpg|thumb|600 px|center|QoS Management in CDMA - Analysis restricted till 1999]]
===Rate Matching Algorithm= Handoff ==The patent [http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=EP1385290&F=0 EP1385290] titled "Method for balancing Eb/I ratio in a service multiplexing CDMA system and a telecommunication system using this method" targets this concept of Rate matching and introduces an algorithm for calculating effective data output bits by a process of repetition or puncturing of the input bits governed by a '''rate matching ratio''' and '''puncturing ratio''' received from the sending entity (can be a BS or MS). As the number of services increases the number of potential combinations will also increase. There arises a need for simple arithmetic procedures to calculate the transport sizes which is done using the following three rules.# The first rule concerns Channel encoding wherin the transport block is converted into the coded block by a possible relation of the form Y=X/(coding rate)+Ntail# The second rule concerns segmentation of the coded block into the size of the segment produced by segmentation per multiplexing frame# The third rule is about obtaining the size of the oputput block Y from the Input block X according to a rate matching step explained below.<br>The Parameters Ei(Energy per bit),Pi(Max puncture Rate) and Xi(Input data rate) are the characteristic constants of a transport channel both at the Mobile Station(MS) and the Base Station(BS). Initially Ei,Pi and Xi are determined at the Base Station and a maximum possible payload is calculated. This is known as the intermediate size and and a vector of expected is transmitted to the Mobile Station(MS) along with the parameters Ei and Pi. Using the values of Pi,Ei and Xi the mobile will also calculate its output frame size Yi. Then final step is matching this value of Yi with the received vector of Intermediate values Yi and decide the final frame size. The bits are repeated or punctured according to the required Final Frame Size.<br>
==Evolution of Cellular Systems=<span style=[[Image"color:cdma1.jpg|500 px|center]]#C41E3A">Like this report?</span>== Multiple Access Methods =<p align="center"> '''This is only a sample report with brief analysis''' <br>There are predominantly three types of multiple access methods.'''Dolcera can provide a comprehensive report customized to your needs'''</p>{|border="2" cellspacing="0" cellpadding= Frequency Division Multiple Access "4" align="center" "|style="background:lightgrey" align =In this system, each user is allotted a different set of frequencies to operate upon"center" colspan = "3"|'''[mailto:info@dolcera. The uplink(mobile to base station) frequency is different com <span style="color:#0047AB">Buy the customized report from downlink frequency(base station to mobile)Dolcera</span>]''' |-| align = "center"| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services Patent Analytics Services]|align = "center"| [http://www.dolcera.com/website_prod/services/business-research-services Market Research Services]|align = "center"| [Imagehttp:cdma6//www.jpgdolcera.com/website_prod/tools/patent-dashboard Purchase Patent Dashboard]|thumb-|700pxalign = "center"|[http://www.dolcera.com/website_prod/services/ip-patent-analytics-services/patent-search/patent-landscapes Patent Landscape Services]|align = "center"|[http://www.aidolcera.ucom/website_prod/research-hyogoprocesses Dolcera Processes]|align = "center"| [http://www.acdolcera.jpcom/~thaiwebsite_prod/industries Industry Focus]|-proj|align = "center"| [http:/presen/20051222www.dolcera.com/website_prod/services/ip-Ishikawapatent-analytics-services/patent-search/patent-landscapes Patent Search Services]|align = "center"| [http://www.ppt FDMA]dolcera.com/website_prod/services/ip-patent-analytics-services/alerts-and-updates Patent Alerting Services]|align = "center"| [http://www.dolcera.com/website_prod/tools Dolcera Tools]|-|}<br>=== Time Division Multiple Access Code Hopping Algorithm===In this systemAccording to one of the methods of dynamic power control (Code Hopping) used in W-CDMA technology, the Rate Information (RI) field in the uplink control channel in W-CDMA frame can be used to notify the base station about the variable bit rates (VBR) it wants to send, then the base station assigns a new spreading factor for each user data rate and hence the optimal power calculation is allocated a different time slotdone according to the spreading factor as follows. Forward link frequency and reverse link frequency <br> Spreading factor(Gi) is defined as the sameratio of bandwidth of the system to the data rate of the radio frame. Mathematically,<br>'''Gi = W / Ri''',where W=system bandwidth which is a constant for a system and Ri= data rate of radio frame.<br>A synchronous switch power index (gi) is responsible calculated from this Spreading Factor(Gi) using the following expression<br>'''gi= (vi / (vi+Gi))''', where vi is minimum QoS for the time switchingith session which is a constant.<br> [[Image:cdma10This power index will ascertain the optimal power to be alloted to each service channel(each data rate for different services).<br> '''Pi = (gi*No*W )/ (Hi*(1-(Sgj)'''<br>where No is AWGN(Additive White Guassian Noise)a constant,<br> Hi is path loss which is dependent on the distance and is a constant for a path,<br> and Sgj is sum of the power index of all the sessions which is constant for all sessions of the radio frame.jpg|thumb|600px|center|TDMA]]
==Code Division Multiple Access=Dynamic Resource Scheduling(DRS) Algorithm===The CDMA technology can be implemented Mobile Station(MS) performs Matching of Traffic Descriptors such as Peak Cell Rate(PRC),Sustainable Cell Rate(SCR) and obtains the connection parameters like average cell rate, SIR, Delay from them. These parameters are sent to the Base Station(BS) where they are queued in two ways* Direct Sequence a FIFO. The BS determines a spreading factor which allocates the Orthogonal Varible Spread Sprectrum - DSSS CDMA* Frequency Hopping - FH CDMAcode(OVSF) using '''Direct Sequence Spread Sprectrum - DSSS CDMA:Gi = W / Ri''' In this method the direct sequence(input data) ,where W=system bandwidth which is spread over a limited bandwidth is multiplied with constant for a code or spreading sequence (a pseudorandom sequence) which will spread the input system and Ri= data over the entire bandwidth rate of the communication channelradio frame. <br> The base station calculates a value of power density is also reduced index '''gi= (vi / (vi+Gi))'''and hence Power levels using '''Pi = (gi*No*W )/ (Hi*(1-(Sgj))''', where S stands for sumof, and transmits them to the MS. This information is spread over conveyed to the frequency spectrum MS using TPC(Transmission Power Control) bits and hence is known as spread spectrum a closed loop power control method. The modulation part of DSSS is as shown below<br>[[Image:cdma13explained in section 5.jpg]]The modulated signal 6 above is transmitted over performed to obtain the channel and all users can receive it but only the user final value of power at which knows the correct code can only decode the messagetransmission should be done. This The method and algorithm to schedule optimal power using Dynamic Resource Scheduling is depicted detailed in the figure below.<br>IEEE paper 765366 [[ImageMedia:cdma14IEEEGurbuz.jpgpdf|Dynamic Resource Scheduling for Variable QoS Traffic in W-CDMA - Ozgur Gurbuz, Henry Owen]]===Features of CDMA=======Frequency Reuse==== Number of radio channel frequencies are limited. The concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area. Cells are assigned a group of channels that is completely different from neighboring cells. The coverage area of cells is called the footprint. This footprint is limited by a boundary so that the same group of channels can be used in different cells that are far enough away from each other so that their frequencies do not interfere.
===Optimal Power Control Algorithm=Soft Handoff==== Handoff means Switching The Base Station receives a cellular phone transmission Pilot Signal from one cell to another as a mobile user moves into a new cellular areathe Mobile station and calculates BER based on Distance,Transmission rate and No of Users in the Cell. It Ptk is so called because the radio link with transmitted signal power which is expressed by the previous sectorpower control function g (srt , k ) is not broken before , a link is established with a new sector; this type function of handoff the distance from the mobile tobase station,'''Ptk= g(rt,k)Po''' where Po is described as "make before break"the maximum transmission power. In CDMA due The optimum power functions are transmitted to this soft handoff there is no interruption of call even at the border of cell site Mobile station which means more number of customers can be accommodated automatically increasing calculates the capacity of optimal power and starts transmitting at that value. Thus meeting the cell siterequired QoS parameters.The method and algorithm for optimal power control is detailed in the IEEE paper 503476 [[Media:IEEEYao.pdf|Optimal power control law for Multi-media - Multi-rate CDMA systems- Shee Yao and Evaggelos Geraniotis]].
====Multipath Fading==== In a mobile environment a mobile station will receive one direct signal from the base station and multiple signals which are reflected from obstructions like building and towers. Each signal would have travelled a different length and would be displaced Research Activity (Non Patent) in time. Due to this when they are combined at the mobile it will cause interference resulting in poor signal quality. This is called as fading. This problem is handled in a very good way in CDMA. Here the phase of the multiple signals is modified such the only positive interferencePeriod (addition1991-2003) takes place the overall signal strength increases. A receiver that implements the above principle is known as a RAKE receiver as shown in the figure below<br>==[[ImageNOTE:cdma15.jpg]]====Near Far Problem==== The problem analysis presented below is described by taking an example consider a receiver and two transmitters (one close with respect to the receiver; the other far away). If both transmitters transmit simultaneously and at equal powers, then due to the inverse square law the receiver will receive more power from the nearer transmitter. This makes the farther transmitter voice more difficult to understand. Since one transmission's signal is the other's noise the signalIEEE Papers published between 1991-to-noise ratio (SNR) for 2003 which focus on the farther transmitter is much lower. If the nearer transmitter transmits a signal that is orders aspect of magnitude higher than the farther transmitter then the SNR for the farther transmitter may be below detectability and the farther transmitter may just as well not transmit. This effectively jams the communication channel. In CDMA systems this is commonly solved by dynamic output power adjustment Quality of the transmitters. That is the closer transmitters use less power so that the SNR for all transmitters at the receiver is roughly the same. This sometimes can have a noticeable impact on battery life, which can be dramatically different depending on distance from the base station.<br>[[Image:cdma16.jpg]]====Power Control:==== As the propagation losses between BS Service and MS's are different according to individual communication distancesits Management using various paramters like Rate matching, the received levels at the base station are different from each other when all mobile stations transmit their signals at the same power. Moreover, the received level fluctuates quickly due to fading. In order to maintain the strength of received signal level at BS, power control technique must be employed in CDMA systems.<br>.[[Image:cdma17.jpg]]<br>Power control can be implemented in two ways : open loop power control and closed loop power control<br>[[Image:cdma18, Variable Spreading Factor etc.jpg]]
==Conclusion==
Substantial amount of research has been done in the field of QoS in CDMA communication system in the year 1998-99 and this has led to the invention of multitude of methodologies ranging from power control to Rate matching and so on Dynamic Resource scheduling, all with the sole aim of improving QoS. ==<span style="color:#C41E3A">Like this report?</span>==<p align="center"> '''This is only a sample report with brief analysis''' <br>'''Dolcera can provide a comprehensive report customized to your needs'''</p>{|border="2" cellspacing="0" cellpadding="4" align="center" "|style="background:lightgrey" align = "center" colspan = "3"|'''[mailto:info@dolcera.com <span style="color:#0047AB">Buy the customized report from Dolcera</span>]''' |-| align = "center"| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services Patent Analytics Services]|align = "center"| [http://www.dolcera.com/website_prod/services/business-research-services Market Research Services]|align = "center"| [http://www.dolcera.com/website_prod/tools/patent-dashboard Purchase Patent Dashboard]|-|align = "center"| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services/patent-search/patent-landscapes Patent Landscape Services]|align = "center"| [http://www.dolcera.com/website_prod/research-processes Dolcera Processes]|align = "center"| [http://www.dolcera.com/website_prod/industries Industry Focus]|-|align = "center"| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services/patent-search/patent-landscapes Patent Search Services]|align = "center"| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services/alerts-and-updates Patent Alerting Services]|align = "center"| [http://www.dolcera.com/website_prod/tools Dolcera Tools]|-|}<br>==Contact Dolcera== {| style="border:1px solid #AAA; background:#E9E9E9" align="center"|-! style="background:lightgrey" | Samir Raiyani|-| '''Email''': [mailto:info@dolcera.com info@dolcera.com]|-| '''Phone''': +1-650-269-7952|}