Research On Linear Dispersion Codes In Cooperative Communication Networks

Space diversity, which is based on MIMO systems, is widely studied for its significant advantage in performance. However, multi-antenna can hardly be implemented to real systems due to the physical constraints of mobile unit such as size and power cost. A new space diversity technique named cooperative communication was then proposed. Cooperative communication system enables users to share their antennas, which means that the antennas of other users in one communication network are adopted as relays to create a virtual MIMO system and thus attains higher data rate and reliability by avoiding detrimental effects of fading.As an effective way to improve performance of MIMO systems, space-time coding technique is generally used. By considering the similarity of cooperative and MIMO systems, this coding technique was also introduced into cooperative systems to achieve better performance. Linear dispersion code, as one of the space-time codes, improves system reliability greatly by creating several sub-streams which are linear combinations of the original data streams.This thesis studies the cooperative-LDC communication system. The definition of LDC is introduced in MIMO system together with the model of MIMO-LDC. The model of cooperative-LDC system, based on which the pairwise error probability is analyzed and the best power allocation scheme is derived, is then built. The design methods of LDC are also studied by using that of Space-Time Block Codes for reference. We also construct an explicit algebraic family of such linear codes that full diversity is guaranteed by using cyclotomic field theory and yields basis matrices which are unitary. Different design methods for LDC are compared in the last section and simulation results show that such algebraic codes outperform all the rest and full diversity is also demonstrated.