Changes
/* Quality of Service(QoS) */
[[Image:cdma19.jpg]]
== Quality of Service(QoS) ==CDMA is being accepted as a third-generation system and a specific feature of 3G system is that it offers a radio interface adapted for all kinds of services and combination of services(data, voice, video, image etc.). The big issue is of multiplexing of these services which have 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 atleast 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'''. <br><br>
===Rate Matching and QoS===
The patent '''EP 1385290 titled "Method for balancing Eb/I ratio in a service multiplexing CDMA system and a telecommunication system using this method"''' targets at this concept of Rate matching and introduces an algorithm of 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 BS or MS). 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 is occuring).[[Media:Patent.pdf]][[Image:cdma20.jpg]]
===Power Control, Rate Matching and QoS===
'''Gi = W / Ri''',where W=system bandwidth which is a constant for a system and Ri= data rate of radio frame.<br>
A power index (gi) is calculated from this Spreading Factor(Gi) using the following expression<br>
'''gi= (gi vi / (givi+Gi))''', where gi vi is minimum QoS for the ith session which is a constant.<br>
This power index will ascertain the optimal power to be alloted to each service channel.<br>
'''Pi = (gi*No*W )/ (Hi*(1-(Sgj)'''<br>
The method and algorithm to schedule optimal power is detailed in the IEEE paper '''Dynamic Resource Scheduling for Variable QoS Traffic in W-CDMA Ozgur Gurbuz, Henry Owen'''.
Thus we conclude that by adjusting the optimal power we are actually trying to implement a rate matching step.
[[Media:ieee1IEEE1.pdf]]
===Power control and QoS===
==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 with the sole aim of improving QoS.
Anonymous user