Research On Cross-Layer Adaptive Transmission Schemes With Multiple Antennas Technology For Wireless Networks

Future wireless communication aims not only to provide larger system capacity and support higher data rates communication services, but also satisfy the quality of service (QoS) requirements of different services. However, with the continuous growth of diverse wireless service demands, radio resources such as frequency spectrum would be far from adequate and has become a bottleneck in restraining the development of wireless communication networks. Thus how to improve the spectral efficiency has become a hot research topic of the current wireless communications network. An attractive technique known as adaptive cross-layer mechanism based on multiple antennas has been identified as one of the most promising techniques to solve this problem. On one hand, adaptive cross-layer mechanism allows information sharing and information exchange among different layers and optimizes them under limited radio resources and harsh wireless channel conditions in order to achieve both higher system spectral efficiency and better QoS. On the other hand, multiple antennas technology can double spectral efficiency and guarantee the transmission reliability without increasing system bandwidth and antenna transmit power.In this dissertation, adaptive MIMO schemes at physical layer and adaptivecross-layer schemes based on single-user MIMO system and multi-user MIMO systemare intensively studied, respectively, in order to improve the spectral efficiency and thetransmission performance of wireless link. The research results could potentially workas the standardization reference for the next generation wireless communicationnetworks. The main novelty contributions of my work are as follows:1. We proposed two novel adaptive schemes for the physical layer adaptive MIMOsystem to make the system performance better. Firstly, based on the extensiveinvestigation of orthogonal matrix design of space-time coding, an adaptivehigh-rate orthogonal space-time coding scheme from the Grassmann manifold wasproposed. This scheme has no limitation on the number of transmitter and receiverantennas, and has a simple decoding algorithm. Secondly, driven by the idea of channel inversion, we proposed a sub-optimal adaptive power allocation algorithm combined with asymmetric adaptive modulation in double space-time transmit diversity (DSTTD) system. It can enhance the system performance significantly.2. Considering the correlated channel conditions of single-user MIMO system, under the constraint of QoS of packet loss probability and time delay at data link layer, we analyzed the effect that antenna fading correlation has on the spectral efficiency in AMC_OSTBC_T-ARQ system, combining of adaptive modulation and coding (AMC) and truncated automatic repeat request (T-ARQ) in the presence of orthogonal space-time block coding (OSTBC) transmit diversity by using the cross-layer information analysis. We deduced the closed-form expressions for the spectral efficiency, packet error rate, and outage probability of this AMC_OSTBC_T-ARQ system under correlated Nakagami-m channels. Results showed that correlation reduced spectral efficiency of the cross-layer system under Rayleigh channel more than that under Nakagami-2 channel.3. Considering the problem that the multiple transmit antenna deployment with multiple RF-chains may result in increasing complexity, size, and cost, we proposed that transmit antenna selection / orthogonal space-time block coding(TAS/OSTBC) scheme was extended to be in adaptive single-user cross-layer scheme that combines AMC with hybrid ARQ techniques. We derived the analytical closed-form expression for probability density function (PDF) of the receiver signal-to-noise ration (SNR) and the overall average spectral efficiency under adaptive cross-layer TAS/OSTBC transmission scheme with the arbitrary number of transmitter antennas.4. In order to resolve the problem between the spatial diversity and the multi-user diversity in multi-user MIMO system, we proposed an adaptive multi-user cross-layer scheduling strategy that incorporated the AM, TAS/OSTBC technologies of physical layer into the multi-user selection diversity. Based on the constraint of QoS of target bits error rate, we derived the closed-form analytical expressions for the overall spectral efficiency based on maximum SNR scheduling and maximum normalized SNR scheduling when users have non-identical channel conditions. Results showed that the adaptive multi-user cross-layer scheduling strategy based on TAS/OSTBC can dramatically enhance the spectral efficiency of the system and offset the multi-user diversity performance degradation caused by OSTBC.