| Modern wireless communication is marching towards technologies with high reliability, high efficiency, and high throughput. Network coding emerges as big break through in the field of communication network, because it is able to highly enhance the throughput and transmitting capacity of networks. Its core idea is that transmitting node could encode the message dream, not just forward the information. Due to the fact that network coding can be applied at the physical layer to turn the broadcast property into a capacity-boosting advantage in wireless networks, wireless communication network is the first field, which network coding is applied in. After adopting network coding, relay systems can potentially achieve 100% and 50% throughput increases compared with traditional transmission and straightforward network. However, systems with network coding can inevitably face to threats from fading channel, overlapping signals and so on. Fortuanately, MIMO and STBC technologies can solve the problems well, which bring bright to the application of network coding.The investment in this thesis based on the wireless relay system with two source nodes and one relay node. The thesis mainly focuses on wireless system and STBC, network coding in single-antenna relay system, and concatenated system of network coding and STBC. The main work in the thesis is1) The thesis introduces the model of various fading channels, the diversity technology and the theory of MIMO system. Furthermore, this thesis analyzes the theory and performance of Space-time block codes, especially Alamouti scheme. And the thesis simulates the performances of STBC in MIMO systems with different numbers of transmitting and receiving antennas.2) The thesis introduces the theory of network codes. Network coding in wireless relay systems has two types:3-step scheme and 2-step scheme. This thesis analyzes the achievable code rate in 3-step scheme and 2-step scheme with amplify-and-forward, decode-and forward, detect-and forward scheme.3) Bit error rate(BER) performance of network coding in single-antenna relay systems is analyzed in this thesis. The thesis exhibits simulation result with different parameters:power allocation, relay position. Especially here proposed a optimized network coding method of two-slot scheme with QPSK modulation. Because the traditional straight XOR coding method is not the best network coding scheme under some certain channel conditions. A better mapping approach is proposed here.4) In order to improve the BER performance of network coding in wireless relay network, a concatenated system of network coding and STBC is proposed here. MIMO relay sytems with amplify-and-forward, detect-and-forward scheme is analyzed and simulated first. Then this thesis designs the transmitting and receiving scheme in the concatenated system. At last the results by simulation show that the BER performance in the relay systems can improve a lot with STBC. |
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