Simulation Research On Relay-Selective Cooperative Technology Based On MIMO-OFDM System

Signal fading due to multi-path propagation is one of the major impairments to meet the demands of next generation wireless networks for high data rate services. To mitigate the fading effects, time, frequency, and spatial diversity techniques or their hybrid can be used. Among different types of diversity techniques, spatial diversity is of special interest as is does not incur system losses in terms of delay and bandwidth efficiency.Recently, cooperative diversity in wireless network has received great interest and is regarded as a promising technique to mitigate multi-path fading, which results in a fluctuation in the amplitude of the received signal. The cooperative communications is a new communication paradigm which generates independent paths between the user and the base station by introducing a relay channel. The basic idea behind cooperation is that several users in a network pool their resources in order to form a virtual antenna array which creates spatial diversity. Since the relay node is usually several wavelengths distant from the source, the relay channel is guaranteed to fade independently from the direct channel. This cooperative spatial diversity mitigates the limitation of communication equipment bulk and power consumption of users, who can not be equipped with multiple antennas.Although, MIMO system can create spatial diversity, it has no ability to mitigate the effect of frequency-selective-fading. Another, OFDM system can drastically simplify the equalization problem by turning the frequency-selective channel into a flat channel. Therefore, this thesis established a system of MIMO-OFDM by using advantage of MIMO and OFDM. Cooperative relay system of based on MIMO-OFDM is established, after relays added in.This thesis researching on these three kinds of algorithms of selecting relay--algorithms of instantaneous SNR-based relay selection, relative Error-Probability-Minimizing relay selection and Geographic-Based Approach to relay selection, is to how to find out the best relay of all to get the most cooperative gain. The principle of algorithms of instantaneous SNR-based relay selection is to figure out P(εsri|γsri)and BER-threshold PeiSNR-th, and to make a comparison between P(εsri|γsri)andPeiSNR-th, so the relay who has minimum of P(εsri|γsri) is the best relay. The best relay from the algorithms of relative Error-Probability-Minimizing relay selection is worked out the minimal BER of cooperative system PeiDF or PeiAF, which is the best Relay. For the Geographic-Based Approach to relay selection, we can find out the best relay with its geography information, which is simple and easily presentated. At last, some simulations having been done are to finish analysis and comparisons on these algorithms above all.Finally, according to analysis and comparisons on these algorithms above all, this thesis comes up with the category of improved algorithms based on threshold-Hybrid Selection Combine algorithm (HSC), whose theorem is that multiple DFs with the best AF forwards signal from source to destination, which will increase system spatial diversity, and decrease BER of cooperative system. In terms of simulations and comparisons, the improved algorithms based on threshold can have a higher performance on cooperative simulation system based on MIMO-OFDM system.