Research On Cross-layer Dsign With Antenna Selection In Distributed Antenna OFDM System

Distributed antenna system, as a hot topic in the field of wireless communications, has comparable advantages in reducing transmit power, increasing spectral efficiency, and covering blind spots et al. Multi-carrier OFDM(Orthogonal Frequency Division Multiplexing), for its ability to overcome multipath fading, can be better combined with distributed antenna system in order to unearth the system space time frequency resources. Using the relevant information between layers, Cross-layer design(CLD) can optimize wireless network protocol to meet different requirements of various transactions. Therefore, in this thesis, by combining adaptive modulation(AM) at physical layer and automatic repeat request(ARQ) at the data link layer, the performance of CLD in distributed antenna OFDM system is well investigated. With the performance of the system based on imperfect channel information, the CLD scheme can improve the spectral efficiency(SE) greatly and provide a theoretical basis for the further application. The main contents in this thesis are summarized as follows:1. The CLD scheme in distributed antenna system is investigated. By combining AM,ARQ, and antenna selection, the cross-layer design scheme based on improved thresholds and approximate thresholds is proposed. On the basis of the performance analysis, the closed-form expressions for the SE and average packet error rate(PER) are derived, respectively. Simulation results show that the theoretical analysis is in good agreement with the corresponding simulation, and the approximate thresholds are basically the same as the improved thresholds and both of them can effectively enhance the system performance. Moreover, approximate thresholds calculate easy and the corresponding expressions of performance evaluation become much simpler.2. The CLD scheme and corresponding performance in distributed antenna OFDM system is investigated. In view of the difficulty to obtain the perfect channel information, CLD scheme based on imperfect CSI is presented. The use of multiple estimates from different subchannels of OFDM is then proposed to avoid the performance loss of existing scheme with single estimate, and the resultant SE and PER are effectively improved. Based on this, the closed-form expression of average SE and PER of the system are respectively derived, which will provide the effective method for the performance evaluation in theory.3. The CLD scheme based on the position statistical information for distributed antenna OFDM system is studied. Considering the position of MS is distributed randomly, CLD schemes based on uniform distribution and non-uniform distribution are given. Using numerical calculation methods, closed-form expressions of average SE and PER are derived. This shceme with more general characteristics than fixed model shceme can better reflect the actual performance of Cross-layer system. Simulation results confirm the validity of the proposed computation formulae.