MIMO Ad Hoc Networks-Mutual Information and Channel Capacity

With the rapid growth of wireless communication infrastructure over the recent few years, new challenges has been posed on the system and analysis on wireless ad hoc networks. Ad hoc network functionalities and securities using the single path as well as multi paths routing are analyzed by many researchers [1,2,3] But, one of the most important events in wireless communication is the advent of MIMO technologies which uses multiple antennas to coherently resolve more information than possible using a single antenna [4,5]. In fact, both the Wi-Fi (IEEE 802.11n) standard and the WiMAX (IEEE 802.16e) standard incorporated MIMO transmitter and receiver by adding a 40MHz channels to the physical layer (PHY) and frame aggregation to the MAC layer[6]. The key advantage of MIMO wireless communication system lies in their ability to significantly increase the wireless channel capacity as well the data rates without requiring additional bandwidth. The MIMO channel model development originates from the fundamental of information theory [7, 8, 9]. In this paper we presented a MIMO Ad Hoc network channel model where with the received signal, interference and noise is added. Here the interference and noise is assumed to be Gaussian and optimal distribution of the transmitted signal is also symmetric complex Gaussian. The ergodic mutual information between the channel input and output is computed in terms of two conditional entropies of the channel and this is maximized over a set of transmitted signal to compute the channel capacity. Finally some simulated results are shown for the channel capacities with different set of input transmitting and output receiving antennas and SNR. And we get maximum spectral efficiency for a certain set of antennas. The simulated result shows that the there is no need to increase the number of antennas after certain limit, that means number of antenna becomes constant for maximize spectral efficiency.