【作者】 金彦龄；

【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】 多输入多输出(MIMO)技术充分开发空间资源,利用多个天线实现多发多收,在不增加频谱资源和天线发送功率的情况下,可以成倍地提高信道容量。正交频分复用(OFDM)技术是多载波窄带传输的一种,其子载波之间相互正交,可以高效地利用频谱资源。两者结合构成的MIMO-OFDM系统,技术上相互补充,可以充分利用时间、频率和空间三种分集技术,使无线系统对噪声、干扰、多径的容限大大增加。MIMO-OFDM在提高无线链路的传输速率和可靠性方面具有巨大潜力,这些优点使MIMO-OFDM系统成为第四代移动通信系统的热点技术。空时分组码思想是MIMO系统的一种实用的实现方式,作为一种新兴的技术,空时编码在近年来倍受人们的关注。准正交空时分组码(QO-STBC)是在正交空时分组码(OSTBC)的基础上发展起来,通过牺牲一定的正交性来获取全速率。为了将准正交空时分组码的编码矩阵重新正交化,可以引入CO-STBC/SFBC编码技术。本文对MIMO-OFDM系统中的自适应CO-STBC/SFBC编码技术进行了研究,主要工作如下:首先,本文研究了CO-STBC/SFBC编码技术,即对QO-STBC/SFBC编码进行信道正交化问题,利用接收端反馈回的信道信息对原来非正交的QO-STBC/SFBC编码的编码矩阵进行部分元素的旋转,使信道间相互正交,并且给出了设计CO-STBC/SFBC编码的原则。同时,在已有CO-STBC/SFBC编码矩阵基础上又提出了两种新的CO-STBC/SFBC编码矩阵形式。通过仿真结果可以证明CO-STBC/SFBC编码能在全编码速率的情况下明显改善QO-STBC/SFBC编码的性能。其次,研究了不同CO-STBC/SFBC编码方案的量化问题。在实际中CO-STBC/SFBC编码的反馈角度进行量化会引入误差,不同形式的CO-STBC/SFBC编码方案经过量化后引入的误差范围也不同。本文详细分析了量化过程,并给出了CO-STBC/SFBC编码引入的误差范围。通过仿真可知当系统的反馈比特数在3位以上时与未量化时的性能已经非常接近,在要实现相同的系统性能的前提下,CO-STBC/SFBC B所需的反馈比特位数总是比CO-STBC/SFBC A要多一位。再次,本文研究了基于天线选择技术的SFBC-OFDM系统,分别分析了TAS、RAS和TRAS的天线选择方案下系统的平均SNR、中断率、BER等性能指标,并将发射天线选择技术应用到CO-SFBC-OFDM系统中。仿真结果证明了通过使用发射天线选择技术可进一步提高CO-SFBC编码系统的性能。最后,在研究自适应调制SFBC-OFDM系统的基础上对自适应调制和天线选择这两种策略的性能进行了比较,并将自适应调制技术使用到CO-SFBC编码的系统中,对基于自适应编码调制技术的CO-SFBC-OFDM系统进行了仿真和分析。仿真结果可证明通过使用自适应调制技术可改善SFBC-OFDM系统及CO-SFBC-OFDM系统的性能,并且在系统中使用自适应调制技术能比使用天线选择技术带来更多的性能增益。更多还原

【Abstract】 The multi-input-multi-output（MIMO） technology utilizes multiple transmit and receive antennas to fully exploit the spatial resources,which can exponentially improve the channel capacity but do not need extra frequency resources or power of transmit antennas.The orthogonal frequency-division multiplexing（OFDM） is one of the multi-carrier narrow-band transmission technologies which features its orthogonal subcarriers.It can utilize the frequency resources effectively.Therefore,the MIMO-OFDM system integrating the advantages of the two technologies above can significantly increase the tolerance of wireless system toward the noise,disturbance and multipath by effectively using time diversity,frequency diversity and spatial diversity.The MIMO-OFDM technology has great potentials in improving the transmit speed and reliability of wireless link,thus has become a hot technology in the 4^th Generation communication.The space-time block coding（STBC） is a practical implementation of the MIMO system,and it has attracted much attention in recent years.The quasi-orthogonalized STBC（QO-STBC） is developed based on the orthogonalized STBC（OSTBC） which can acquire full speed at the cost of incomplete orthogonality.However,the non-orthogonal coding matrix of QO-STBC can be retrieved to orthogonal by applying channel-orthogonalized STBC（CO-STBC） or channel-orthogonalized space-frequency block coding（CO-SFBC）.In this paper,the adaptive CO-STBC/SFBCs in the MIMO-OFDM system are the main topics to be discussed.The general organization of this paper is as below.First,the CO-STBC/SFBC technologies is introduced,mainly focusing on the orthogonalization of channels in QO-STBC/SFBC.Such orthogonalization can be achieved by rotating some elements in the non-orthogonal coding matrix of QO-STBC/SFBC by utilizing the channel information fed back from the receive antennas.Some principles for designing QO-STBC/SFBC schemes are also provided. Beside of this,two novel forms of coding matrix for CO-STBC/SFBC are proposed based on the existing CO-STBC/SFBC coding matrices.Simulation results demonstrate that the CO-STBC/SFBC schemes can significantly improve the performance of QO-STBC/SFBC at full coding speed.Second,the quantization schemes of different CO-STBC/SFBC schemes are investigated.In the actual communication systems,the quantization for the feedback phase angles in the CO-STBC/SFBC schemes is always followed by the quantization errors,and the values of such errors differ from different CO-STBC/SFBC schemes applied.In this paper,the scopes of quantization errors in CO-STBC/SFBC are discussed in details.The theoretical analysis and the related simulations all demonstrate that the performances of the QO-STBC/SFBC systems with over 3 feedback bits are very close to that in the unquantized system.In order to reach the same performance,the number of feedback bits required in the proposed CO-STBC/SFBC Scheme B is always one more than that in the proposed CO-STBC/SFBC Scheme A.Next,the SFBC-OFDM system based on the antenna selection technology is investigated,and some performance indices including average signal-to-noise ratio （SNR）,outage probability and bit error rate（BER） are analyzed within different antenna selection schemes such as transmit antenna selection（TAS）,receive antenna selection（RAS） and transmit and receive antenna selection（TRAS）.This paper also makes further research on the implementation of TAS in the CO-SFBC-OFDM systems in order to seek better performance in the whole architecture.Simulation results demonstrate that the overall system performance can be further improved by utilizing TAS in the CO-SFBC-based systems.At the end of this paper,a comparison towards the performances between the SFBC-OFDM systems utilizing adaptive modulation and antenna selection is conducted.The adaptive modulation technology is then applied to the CO-SFBC systems,and the CO-SFBC-OFDM system based on the adaptive coding and modulation technology is simulated and analyzed.Simulation results demonstrate that the performances of both the SFBC-OFDM system and the CO-SFBC-OFDM system can be improved by utilizing adaptive modulation technologies,and such adaptive modulation technology can bring more gain improvement than the antenna selection technology.更多还原