【作者】 于天月；

【导师】 仇润鹤；

【作者基本信息】 东华大学 ， 通信与信息系统， 2010， 硕士

【摘要】 混合ARQ技术(HARQ)结合了前向纠错(FEC)和反馈重发(ARQ)两者的优点,充分利用了重传和纠错机制,对数据包传输的可靠性以及系统吞吐量、频谱效率的提高都起着不可或缺的作用。因此,HARQ技术被列入了IEEE802.16系列标准的关键技术。特别是IEEE802.16e对此技术提出了非常明确的要求,在IMT-Advanced中沿用了IEEE802.16e的要求,并加入了新的元素。本文在对IMT-Advanced兼容的基础上,搭建起HARQ系统结构,并在此之上提出使系统吞吐量、误包率进一步提升的改进方案,分别从编码方式、天线数量、重传次数等方面入手,提出了两种新的HARQ重传机制,并对其进行了评估,证明了其性能的可靠性。本文首先分析了混合自动请求重传系统的基本原理,阐述了目前国内外在HARQ方面的研究现状,介绍了HARQ的三种基本结构及其各自的优缺点,并且分析了MIMO系统对HARQ机制的影响,着重分析了不同的线性空时编码在MIMO系统中的应用。然后本文对HARQ系统进行了理论分析,研究了混合自动重传发送模式中的传输功率、调制比特数、编码速率及最大重传次数。同时对现有的天线选择算法进行进一步的探讨,重点研究了系统的最大信道容量和最小误码率。根据STBC在MIMO系统中增益特性,利用空时分组码的正交性来降低系统的计算复杂度,提出了基于改进的发射天线选择算法,并将其应用于MIMO-HARQ系统中。通过MATLAB仿真证明,改进的算法可以得到更多的天线增益及系统容量。接下来提出了HARQ重传机制的最佳最大重传次数。如果采用无限次重传的HARQ,在信道过差的情况下有可能造成因重传次数太多而引起的吞吐量显著下降,更严重者会造成系统死锁。为了保证数据的传输质量,又要防止由于慢衰落条件下的信道长时间恶劣导致的某个用户的数据包一味地重发而浪费信道资源,通过MATLAB仿真验证将最大重传次数M设为3或4次为最佳。最后本文利用前面所获得的理论基础,充分挖掘MIMO-HARQ系统的特性,根据不同的空时编码特性提出基于BLAST、LDC和STBC结合的HARQ机制,这种机制可以获得空时码的分集增益,而在信道条件好和信噪比高时,由于没有重传的发生而可以获得BLAST的复用增益,所以该机制可以得到空间分集与空时复用特性的良好折中。MATLAB仿真验证了该机制既能够提高MIMO-HARQ系统传输速率,也能够提高MIMO-HARQ系统的抗干扰性能。更多还原

【Abstract】 Hybrid automatic repeat request(HARQ) technique,which is a combination of forward error control and automatic repeat request,is the main support technique for the high speed data transmission in 3GPP standard.It is indispensable for improving of data correctness,throughput,spectral efficiency,and quality of service.HARQ technology is one of the key technologies in IEEE 802.16 protocols.It is specified in details in IEEE802.16e.IMT-Advanced follow the instructions in IEEE802.16e,and add up new elements in it.Basing on the compatibility to IMT-Advanced,this thesis constructs a HARQ system.When the channel condition is bad,each packet is transmitted repeatedly, which lead to low reliability of the channel transmission.But the automatic repeat request could guarantee the correction of the packet,so it has high reliability.An improvement method of system throughput and packet error rate is put forward.Two new types HARQ scheme based on space-time codes are proposed and evaluated in this paper,and the main innovations and contributions are as follows:Firstly,the theorem of HARQ system is analyzed,and the research depth and diredction is expounded.Base on the regulations that are described in IMT-Advanced standard,three different types of HARQ system and their corresponding algorithms are compared.And different time-space codes in multiple-input multiple-output (MIMO) system are analyzed.Secondly,the HARQ system is analyzed in theory.The relation among maximum retransmission times,power in every transmission,modulation bits,coding rate in HARQ transmission mode and the system throughput is studied.A novel method to reduce packet error rate(PER) of MIMO-HARQ systems based on Space-Time Block Code(STBC) is proposed.The transmit antennas are selected based on the feedback from the receiver.The modulated symbols are encoded by STBC and obtained space time code blocks suitable for the number of selected antennas.The total PER is given by defining the decoding function and the best value of the maximum number of HARQ retransmissions is discussed.Theory and simulation results illustrate that this new HARQ scheme with antenna selection method has lower PER and the result is also satisfying.Finally,a new type HARQ scheme based on different space-time codes is proposed and evaluated.The new scheme is divided into three major steps which are V-BLAST processing and LDC processing also STBC processing.The orthogonal STBC can obtain all of the diversity gain of the MIMO system,the V-BLAST code can obtain all of the multiplexing gain of the MIMO system,and the LDC is the tradeoff between STBC and V-BLAST code.The traditional method simply retransfer signal,but the proposed method transfer the next line of data matrix and joint-decode them,so that can benefit from spatial diversity.At good condition of channel,the proposed method gets spatial multiplexing for retransfer hardly occur.The proposed method has the advantage of V-BLAST and LDC also STBC.It is a HARQ scheme that can improve transmit rate and improve resistance of interference at same time. Theory and simulation show the proposed method have higher throughput in most SNR regions and the gains are considerable.更多还原