Accurate upper bound of SINR-based call admission threshold in CDMA systems with imperfect power control

Since the capacity of CDMA networks is interference-limited, it is vital to have a call admission control (CAC) mechanism to preserve the signal quality in terms of the signal-to-interference-and-noise ratio (SINR). SINR-based CAC schemes compare the SINR of the incoming call with a threshold value (SINRth). The call is accepted if the SINR is greater than SINRth, otherwise it is rejected. The choice of the SINRth value is restricted by two opposing factors: the signal quality and the network utilization. Setting SINRth at high value is desirable to increase the signal quality. However, a high SINRth value increases the blocking probability (P-b) and reduces the network utilization. An upper bound of SINRth (SINRth-ub) in CDMA systems with imperfect power control has been determined in [1]. However, the accuracy of that upper bound is questionable since the possibility of power control (PC) infeasibility has not been taken into consideration. Also, the analysis in [1] used the normal distribution to model SINR instead of the widely-accepted Lognormal distribution. Moreover, the noise and the inter-cell interference were ignored in [1]. In this letter, we derive a more accurate upper bound by taking the possibility of PC infeasibility into consideration and by using the Lognormal distribution of SINR for imperfect PC. In addition, our analysis takes the noise and the inter-cell interference into account.