| With the booming development of mobile communication and the sustainedincreasing of user requirements, high rate, large bandwidth, multiple-sevices, low costand low energy consumption has become a new trend of mobile communication system.as a representative of spatial diversity technical, multiple-input multiple-output (MIMO)technology can take full advantage of the space to resist multipath fading of radiochannels effectively, which has a great potential in improving the reliability andspectrum utilization of future wireless communication systems. However, due to thesize, the power dissipation limitation, hardware complexity of the mobile terminal andother factors, it is much more difficult to popularize the MIMO technique in wirelesscommunication system. Recently, cooperative diversity, which forms a virtual MIMOsystem by sharing their own single-antenna with other resources in a multi-userenvironment to obtain spatial diversity gain, providing a new idea for the practical useof multi-antenna technology. Based on the research of cooperative hybrid automaticrepeat request (HARQ) scheme design in the field of cooperative diversity and energyefficiency enhancement technology, we propose the schemes of a specific scene andgive the theoretical analysis and simulation. The main contribution of this dissertation issummarized as follows:1. In terms of retransmission scheme design: traditional retransmission schemescannot make the most of the characteristics of cooperative communication, which leadsto the low retransmission efficiency of cooperative communication. Thus, newcooperative communication retransmission schemes for a particular scene are raisedfrom two aspects of the combination of network coding and retransmission timingselecting:1). For the problem of low retransmission efficiency in traditional two-way DFrelay system and quadrature modulated cooperative diversity system, we proposenovel two-way relaying hybrid automatic retransmission request (NC-TR-HARQ)scheme and hybrid automatic repeat request (NC-QM-HARQ) scheme, respectively.The two schemes save nearly5%of the transmission time and increases thetransmission efficiency by using the method of the calculation of joint likelihood valueto combine the likelihood value of network coding information. The closed-formsolution of frame error rate (FER) and throughput are derived by analyzing first-orderMarkov process in units of data frame. Numerical results demonstrated that theproposed scheme outperforms the traditional two-way relaying system HARQ scheme by a throughput gain of approximate6%around the middle of the two users.2). For the problem of low utilization of channel in traditional cooperativetransmission scheme, two cooperation-hybrid automatic repeat request schemes areproposed, one is FFC-HARQ (Fixed-Length Frame Cooperation-HARQ) scheme andthe other is VFC-HARQ (Variable-Length Frame Cooperation-HARQ) scheme, whichadopts the HARQ strategy of the native frame structure and the variable frame structurerespectively. Then, the outage probabilities and throughput performances of the systemsrespectively adopting VFC-HARQ and FFC-HARQ schemes are investigated.Simulation results show that the proposed schemes can not only reduce the outageprobability but also improve the throughput for the FDC transmission system.2. In terms of energy efficiency enhancement scheme design: Based on theresearch of energy efficiency in cooperative system, the solution of how to transmit withhigh rate and low energy consumption is proposed for particular scene.1). This scheme measures the energy efficiency by using the ratio between energydissipation of two-way amplifier forward (AF) relaying and the energy dissipation ofstraight transmission, and analyzes the effect of channel estimation error. Under thecondition of satisfacting requirement of outage probability, the Lagrange optimizationKKT conditions is used to calculate the optimal power allocation factor for the purposeof minimizing energy loss. Then, relay priority region, which is the energy gain ofrelay-assisted bidirectional transmission over direct transmission, is identified. On thisbasis, a low-complexity transmission selection scheme which optimizes powerallocation and transmission mode selection policy is proposed to enhance the energyefficiency. The computer simulation, which verifies our analytical results, indicates thatthe two-way AF relaying transmission loses its superiority to direct transmission interms of energy efficiency when relative channel estimation error reaches0.03.2).By introducing incremental relaying to the quadrature modulated cooperativediversity system (QM), an incremental QM (IQM) cooperative diversity system isproposed. Then, the closed-form solution of FER is derived by analyzing first-orderMarkov process in units of data frame. At last, a quasi-optimized power allocationschemes (QOPA) with low complexity is presented. By minimizing FER, the optimalpower factors are obtained through iterative computation. The simulation result showsthat the IQM system outperforms the traditional QM system by a maximum signal noiseratio (SNR) benefit of4dB when the FER is in the range [10-4,10-2], moreover, anadditional3dB performance gain is obtained adapting the QOPA schemes.3).An energy efficiency enhancement scheme is presented for the incremental decode-and-forward relay with hybrid automatic repeat-request (IDF-HARQ) system.Firstly, the closed-form expression of the energy per good-frame (EPGF) of IDF-HARQsystem is acquired by using energy consumption model which includes the energyconsumption of baseband processing and the state transition model of Markov chain.Then, under the constrained conditions of total power, the objective function ofminimizing EPGF is transformed into a convex function with parameters to obtain theoptimal power allocation and choose the best way of modulation. Simulation resultsshed light on that the proposed scheme could improve the energy efficiency of theIDF-HARQ system effectively comparing with the traditional scheme which onlyconsidered the performance of throughout. |
PDF Full Text Request