==Quality of Service(QoS)==
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 transport block is divided into different processes and all the channels of like QoS are included in one process. The standard steps of multiplexing, encoding, and interleaving are followed by an important procedure of rate matching, wherein the data rate is varied in accordance with the Eb/I ratio(QoS parameter). 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.
[[Image:cdma25.jpg|thumb|600px|center|QoS Management in CDMA - Pathway]]
[[Image:cdma23.jpg|thumb|600 px|center|QoS Management in CDMA - Analysis restricted till 1999]]
The process of Implementation of rate Matching is done using Puncturing 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. 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 SEIMENS]]
===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>