A study on the CAC schemes for wireless communication systems

Abstract

Direct Sequence Code Division Multiple Access(DS-CDMA) system is a highly interference limited system. Therefore, there should be considerations in tradeoffs between the number of users and the resource utilization. The more users accepted, the more interference created. From this reason, call admission control(CAC) which controls the number of users, holds an essential part in DS-CDMA system[20]. Congestion control such as power control restrains the interference so that the capacity may be maximized. Therefore, CAC scheme based on the power control uses this simple but important feature even though it may give rise to high signaling costs and may suffer from the slow speed in the accept/reject decision[15]. In this thesis, a distributed power control with active link protection is studied. CAC scheme based on DPC/ALP maintains the QoS of the ongoing users above their required QoS. And other various CAC schemes such as screening CAC and handoff prioritized CAC will be introduced. DPC/ALP CAC scheme accepts a new user at the moment it arrives in a controlled manner where the SIR of the ongoing users are adequately protected by the numbers of power updating iterations. Thus, a new user will not be erroneously accepted so that the outage may not occur[7][15]. The existing DPC/ALP CAC schemes did not consider the other cell interference and their updating interval was too slow to compensate fast fading. Therefore, this thesis proposes an efficient DPC/ALP CAC scheme which is considering the other cell interference and the fast updating interval. And this thesis measures its performance by evaluating blocking probability. Analysis and simulations are provided under the perfect power control and simulation parameters are based on WCDMA specifications. The performances of the proposed scheme are measured by taking the radio propagation, the traffic variation and the number of iterations etc. Throughout this thesis, only uplink will be taken into consideration. The ...