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/* Quality of Service(QoS) */
==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).
===Need for Rate Matching===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 terms of Eb/I ratio. 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 Service, needlessly causing interference and resource blocking. There are several influences that might change system performance(BER) and hence Eb/I ratio,in accordance with the required QoS 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 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).<br>
[[Image:cdma_2_7.jpg|thumb|700px|center|QoS Management in CDMA - Standard Framework]]
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