Capacity of M-ary CDMA cellular communication network

We know that the CDMA (code division multiple access) technique can provide efficient multiple access to a large number of users but has the disadvantage that it requires a high bandwidth. It is also known that CDMA as a multiple access method could be combined with any desired modulation technique. An interesting question is what would be the result of combining CDMA access with a high-efficiency modulation technique, e.g. 256-QAM (quadrature amplitude modulation). In this paper we consider whether the bandwidth efficiency of high-level QAM can be used to overcome the bandwidth inefficiency of CDMA. A mathematical model is built to compare cellular capacity obtained with and without MQAM-CDMA use. It is seen that in fact, MQAM-CDMA leads to reduced capacity as compared to FDMA. However, MQMA-CDMA capacity increased as compared to simple CDMA multiple access scheme. We also consider the effect of voice activity detection (VAD) and sectorisation. This work is the extension of R.R .Gezzi (1993)