Distributed coherent MIMO system with advanced CDMA channel estimation

Multiple-input multiple-output (MIMO) technique exploits advanced signal processing and multiple antennas to increase wireless transmission data rates as well as suppressing interference and improving received signal-to-noise ratio (SNR). The technique is widely used in many mobile communication systems. In the aerospace communication environment, data rate and SNR are important factors when considering communication quality. However, due to the limitation of onboard communication units for the systems like aircraft and satellite, multiple antennas may not always be available at a single communication unit. In this paper, we propose a phase coherent distributed MIMO communications system design for existing airborne networks. The main idea is to utilize multiple distributed communication elements within the range, each is equipped with single antenna and coherently transmits the same information to achieve MIMO performance. The phases of the signals from different transmitters are adjusted properly in order to make sure the signals combine constructively at each receiver. This is possible when signals combined are in identical phase, otherwise they may cancel each other. To tackle this problem, we design a novel phase adjustment algorithm to optimize the performance when there are single or multiple transmitter and receivers in the networks. In addition, in order to employ the new algorithm, the channel state information needs to be known since it essentially causes the phase distortion as signal travels through the air. We propose a code division multiple access (CDMA) estimation scheme which achieves more efficient and accurate channel condition estimation. We also provide a simplified channel estimation method that only measures the phase changes of the radio frequency (RF) channel by their geolocations. This method is limited to the conditions where the line of sight (LoS) dominates and the multipath is negligible which is true for most aircraft communications and satellite communications (SATCOM) environment. The extensive simulation and numerical results show that the proposed distributed coherent MIMO system significantly improve the received SNR when the number of cooperative transmitters increases, which enhance the communication quality and data rate of the system.