Research On Diversity Code And Detection Technology For Wireless Cooperative Communications Systems

The next generation mobile communication network system has higherrequirements on communication speed, communication reliability. Wirelesscooperative communication technology posses the characteristics of multi-antennasystem and meets these performance requirements by exploiting the multipathpropagation. Therefore, ones have received extensive attention. The basic idea ofcooperative communication technology is to assist communication between the sourceand the sink through the virtual antenna array comprised multiple single antenna userterminals. Through diversity coding wireless cooperative communication can improvethe channel capacity, obtain the diversity gain, and share the link resources. Based ontheses advantage, the research focus on the wireless cooperative diversity codingtechnology, and discusses the substantive issues of wireless cooperative diversitycoding technology in orthogonal forwarding protocol, non-orthogonal forwardingprotocol, and two channel relay forwarding protocol. Finally, some novel diversitycoding method and signal detection method are proposed. Also the correspondingperformances are analyzed. To be specific, the main results of this research are asfollows:1．In order to solve the deficiency from distributed space time coding (DSTC) anddistributed space frequency coding (DSFC) applied to the high-speed mobile broadbandcommunication system, this dissertation firstly proposed the high-speed mobilebroadband cooperative communication system model and the corresponding relay nodeschannel model. A new distribution space time frequency coding (DSTFC) issubsequently proposed, which can obtain the potential cooperative diversity, timediversity and frequency diversity gain without communication rate loss. Finally, theswitching strategy of DSFC and DSTFC is proposed, so as to solve the problem thatDSFC has poor BER performance at high SNR but DSFTC at low SNR.2．The novel space frequency coding based on multiple relay cooperation anddifferential unitary modulation is proposed, so as to solve the problems that channelestimation is difficult over fast fading, multi-carrier, and frequency selective channel.Theoretical analysis and simulation results show that the proposed method can obtainthe maximum cooperation diversity gains and frequency diversity gains. According tothe principle of maximum receive signal combination SNR, the mean SNR analytical formula of combining signal is deduced in order to optimize the BER performance ofthe proposed coding method. Moreover, the influence of relay numbers, relay positionand combine factor on the SNR value is analyzed. Since the optimization solution of therelay number and relay location fall on the boundary of the interval, which caused thatparameter optimization is insignificant. Therefore, the most used relay number and relaylocation is firstly determined. Subsequently the theoretical optimal solution of powerallocation factor and the maximum ratio combination factor ratio is given. Thesimulation results demonstrate the validity of the theoretical optimized solution and theadvantages of multiple parameters joint optimization.3. The novel differential network encoding with complex field symbolmultiplication is presented to solve these problems that the relay has more highdifferential detection complexity and more cumbersome coding process at decodingforward mode. Based on the differential network encoding idea, the relay detectionmethodⅠis presented in the dissertation to obtain the differential block encoding fromtwo terminals. And the relay detection method Ⅱ is presented to obtain differentialnetwork encoding without detecting the two-way grouping messages. Compared withthe existing relay detecting method, two proposed relay detect methods could decreasethe detection complexity, and the process complexity significantly. Meanwhile, a novelrandom differential space-time network coding method is also proposed in thisdissertation, which can obtain high-order diversity gain, and the cooperative diversityorder equals the active relay number.4. Based on AF-CDC-OFDM technology, a novel differential network encodingmethod with multi-relay cooperation is proposed over the multi-carrier and frequencyselective two-way relay channel. The two-way terminals can obtain the maximumcooperation diversity gains and frequency diversity gains through the distributed relaycyclic delay coding and power amplification processing. But two terminals need toeliminate the self-interference component from received signal before detecting thetransmit signals. Therefore, the correlation statistical self-interference eliminationmethod is proposed. The simulation results demonstrated that the proposed differentialnetwork encoding method and interference eliminates method is valid.5. High-order diversity gain can be obtained by applying the opportunities relaystrategies to the non-orthogonal forward protocol. In this dissertation we derive theclosed-form expression of ergodic capacity of non-orthogonal selectiveamplify-and-forward protocol and non-orthogonal selective decode-and-forward protocol over Rayleigh fading channel. Subsequently, the ergodic capacity of these twoprotocols under the different candidate relays number is obtained by numericalsimulation. The simulation results show that the ergodic capacity of these two protocolsimproves along with the increase of the candidate relay number. Moreover, thenon-orthogonal selective amplify-and-forward protocol has the larger ergodic capacityat the low SNR, while non-orthogonal selective decode-and-forward protocol has largerergodic capacity at the high SNR.6. The signal joint likelihood detecting method has higher time complexity andmore poor BER performance in non-orthogonal forwarding protocol. Therefore, a novelinterference cancellation rapid detection method is presented in this dissertation. Inproposed detection scheme, the strong signal frame can obtain second-order diversitygain with the maximum ratio combining technology and can be firstly detected. Afterthe interference component of the weak signal frame eliminated by subtracting thedetection value from the received signal weak signal frame is detected. Theoreticalanalysis shows that the proposed method can reduce the time overhead effectively.Moreover, the simulation results also verify that the BER performance of proposedmethod improves significantly and the simulation value of proposed detect method isconsistent with its theoretical value at high SNR.