Spectral efficiency for MIMO orthogonal MC DS-CDMA system over Nakagami-m fading channels

Multiple Input Multiple Output (MIMO) systems have appeared as one of the promising approaches for increasing the capacity and lowering symbol or bit error probability of the wireless communication systems without increasing the bandwidth or the transmission power of the system. In this paper, we investigate the average channel capacity for MIMO orthogonal multicarrier direct Sequence Code Division Multiple Access (OMC DS-CDMA) system in Nakagami-m fading environment. We also consider the influence of the normalized space between two adjacent subcarriers of the system in average channel capacity analysis. Gaussian approximation method is employed to model multiuser interference (MUI) which mostly degrades the system performance. Hence, probability density function (PDF) of the instantaneous signal to interference noise ratio (SINR) is derived using Characteristic Function (CF) based method. Therefore, the exact closed form expression for the average channel capacity is derived by taking the expectation of Shannon channel capacity over the PDF of SINR. The results reveal that the average channel capacity of the MIMO OMC DS-CDMA system outperforms that of the conventional OMC DS-CDMA system. Similarly, we observe that MIMO MC DS-CDMA system has better spectral efficiency. Thus, we confirm the numerical results using Monte Carlo simulation technique.