Changes

'''Effect of Power Control''': Power control is capable of compensating the fading fluctuation. Received power from all MS are controlled to be equal. Near　Near-Far problem is mitigated by the power control.

CDMA is being accepted as a third generation (3G) system and a specific feature of 3G systems is that they offer a radio interface adapted for all kinds of services and combination of services (such as data, voice, video etc). The big challenge is multiplexing these services which do not have the same demands in terms of quality of service(QoS) which can be represented as BER(bit error rate), processing delay, frame error rate etc. Different QoS will require different channel encoding and interleaving strategies. The demand of BER can be satisfied when the coding bits have at least a code dependent ratio Eb/I(ratio of bit energy to interference). There are several influences that might change system performance(BER) and hence Eb/I ratio, of which the most effective is variation of Bit Rate by a step of '''Rate Matching'''. The standard framework for the management of QoS in CDMA systems is shown below. The following framework highlights the various steps involved in providing variable QoS. The received data from the transport block is divided classified into different processes and based on their QoS. Data is split onto various transport channels to which a CRC code is attached for error correction. Further, all the these transport channels of like QoS are included in multiplexed on one process. The standard steps of multiplexingline by concatenation, encodinginterleaved, segmented and interleaving are followed by an important procedure of then rate matched. The rate matching, wherein step is performed using the data rate matching ratio and puncturing ratio which is varied in accordance with received from the Eb/I ratiosending entity (QoS parameteran exchange of handshaking signals occurs). Apart from this pathway, there are other pathways which focus on the power control aspect and a relation ship to rate matching can be backtracked through this approach.<br>[[Image:cdma25.jpg|thumb|600px|center|QoS Management in CDMA - PathwayStandard Framework]]

The process of Implementation of rate Matching matching step in above figure is done using Puncturing essentially implemented by repetition or Repetition. If the number of bits are more than the calculated rate of transmission then the bits of transmission block are punctured otherwise they are repeated till the calculated size is reached. Siemens puncturing, SEIMENS has proposed an algorithm to ETSI, to obtain a non-integer punture/repetition ratio referenced SM/G2/UMTS-L1/Tdoc428/98 and it is given as follows. This algorithm is used as a standard approach for Rate Matching. [[Image:cdma21.jpg|thumb|700px|center|Rate matching algorithm by SiemensSEIMENS]]===Rate Matching and QoS===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). 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>The following framework highlights the various steps involved in providing variable QoS. The received data from the transport block is classified into different processes based on their QoS. Data is split onto various transport channels to which a CRC code is attached for error correction. Further, all these transport channels are multiplexed on one line by concatenation, interleaved, segmented and then 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).

The above algorithm avoids puncturing consecutive bits when operating in the puncturing mode. In the repetition mode, the repetition bits follow the bits which they repeat. [[Interleaving]] is an essential step in a communication systems. In the current scenario of repetition,when interleaving is executed after rate matching it would space the repeated bits apart. While Puncturing, if the interleaver precedes the rate matching it may puncture consecutive bits of the channel encoder which were dispersed by interleaving. Hence it is always preffered to have the rate matching step as close as possible to the Channel Encoder ===Power Control, Rate Matching and QoS using Code Hoppingand QoS pathway===

From the above analysis, we observe that when the bit rate mobile is inversely proportional to sent the spreading factor optimal power at which will inversely effect it should transmit. It can back track and calculate the power index and spreading factor and hence the optimal powerData ate is changed accordingly. Therefore, This step can be considered to be an equivalent to the Bit Rate and Optimal power go hand in hand, and have the same effect on Eb/I and QoSMatching Pathway explained above. The method and algorithm to schedule optimal power is detailed in the IEEE paper 765366 [[Media:IEEEGurbuz.pdf|Dynamic Resource Scheduling for Variable QoS Traffic in W-CDMA - Ozgur Gurbuz, Henry Owen]].