【作者】 敖珺；

【导师】 廖桂生；

【作者基本信息】 西安电子科技大学 ， 信号与信息处理， 2009， 博士

【摘要】 未来的无线通信系统的目标是实现无所不在的、高速、可靠的移动多媒体传输。由多发射和多接收天线组成的多输入多输出(MIMO,Multiple-InputMultiple-Output)技术正是在不牺牲发射功率和信号带宽的条件下,达到这一目标的有效技术之一。MIMO技术在无线通信链路两端均使用多个天线,可以充分利用无线传播中的多径传输,使频谱利用率和链路可靠性得到极大的提高。与MIMO技术紧密相关的就是空时编码。在现有的空时编码方案中,空时格形码(STTC,Space-Time Trellis Coding)和空时分组码(STBC,Space-Time Block Coding)已被第三代移动通信标准采纳。然而,要实现STTC和STBC在实际工程中的应用,仍有许多问题有待解决,例如降低STTC的译码复杂度、改善STTC发射分集增益、以及如何在STBC中有效的引入编码增益等。针对以上问题,本文结合网格编码调制(TCM,Trellis codingmodulation)技术,研究了在衰落信道下高增益的空时编码的方法。具体工作概括如下:1.研究了超正交空时网格码(SOSTTC,Super-Orthogonal Space-Time Trellis Code)和超准正交空时网格码(SQOSTBC,Super-Quasi-Orthogonal Space-Time TrellisCode)的网格图特性,提出了一种基于合并网格传输路径的超正交空时网格编码方法。新方法研究了2×2正交空时分组码和4×4准正交空时分组码之间的结构关系,并利用二重TCM(2-TCM)编码器构造出可用于四发射天线条件下的满速率、SOSTTC;并将2×2正交空时分组码矩阵结合星座图旋转的方法,使得新方法在获得高的编码增益同时,获得满分集增益。试验结果表明,在相同的仿真条件下,新方法获得的编码增益比现有的基于四发射天线的超准正交空时分组编码方法提高2dB以上。2.研究表明,将TCM技术与STBC结合起来可以进一步提高多天线系统的性能。本文研究了空时编码系统在编码增益,分集增益和传输能量效率的限定下最大化传输速率的问题,提出了一种在保留TCM编码方法校验位冗余的同时,还可获得满速率的级联空时分组TCM编码方法。新方法通过引入具有不同功率分集因子的正交发射码字矩阵,并给出新的最大似然(ML,MaximumLikelihood)译码算法,从而使得新方法在获得满速率的同时还可以获得满分集增益。MATLAB仿真结果表明,在相同的编码状态数下,新方法在编码增益上比现有的满速率SOSTTC提高1dB左右。3.研究表明在多天线系统中,可以利用级联结构来逼近信道容量。本文根据交织的STBC串行级联TCM编码设计标准,提出了一种STBC级联不对称网格编码调制(A-TCM,Asymmetic Trellis coding modulation)的优化设计方案,并推导出在空时分组码级联不对称8PSK调制的TCM情况下最优的星座图旋转角度。仿真和分析结果表明,在相同的频谱效益和译码复杂度的情况下,相比传统空时分组码串行级联TCM的方法,这种串行级联不对称星座图A-TCM方案可进一步提高了系统性能。4.理论和实践研究表明,当网格编码方法中存在并行路径时,相对于一般的TCM技术,采用多重网格编码调制(MTCM,Multi-Trellis coding modulation)技术可获得很好的分集增益。本文提出了基于Frobenius范数的空时多网格编码(ST-MTCM)方法。在新方法中,通过确定ST-MTCM方法的网格图中每个网格分支上传输的最优T×N码字矩阵结构,并采用Ungerboeck的星座扩展和集合分割思想,从而在获得满分集增益的同时,也得到了最优的编码增益。仿真结果表明,相对于传统的空时多网格编码方案,这种新的方法可以获得很好的性能改善;并且,网格分支传输矩阵正交性的确定,极大简化了好码的搜寻过程,无需要针对不同的信道衰落条件设计不同的编码方案。5.研究了TCM以及多重网格编码调制(MTCM,Multi-Trellis coding modulation)技术的原理,提出了一种新的串行级联正交空时M-TCM方法,并给出了不同的信道衰落条件下的码字设计方法。分析和仿真结果表明,在准静态Rayleigh衰落信道下,以及具有相同的编码状态数和译码复杂度的情况下,新编码方法相对于现有的串行级联空时编码方法,在编码增益上与仅相差0.4dB,却可以提高50%左右的传输速度,并且无需对系统的状态数进行限定,即在保证满分集增益的同时又允许网格图中存在并行路径。更多还原

【Abstract】 The future broadband wireless communication systems are expected to provide ubiquitous, high-reliability, and high-data-rate mobile multimedia transmission. MIMO (Multiple-Input Multiple-Output) technique utilizing multiple antennas to realize multiple transmissions and multiple receiving can exploit space resource adequately and can improve channel capacity without any loss in bandwidth and transmitting power. So it can meet the need of high data transmission in future wireless communications.Recently, the space time codes desinged for the multiple antennas system have inspired many attentions. As a kind of new technique, space-time trellis coding and space-time block coding attracts many investigators and has also adopted by 3GPP standard. However, there are still many technical problems to be solved for the STTC and STBC realization in practical engineering applications, such as STTC designs that can improving transmit diversity gain, both in terms of reducing decoding complexity, and the introduction of coding gain to STBC. In view of the above discussions, this dissertation focuses on several issues of the space-time coding and the corresponding Trellis coding modulation. The main contributions included in this dissertation can be summarized as follow:1. By studying the super-orthogonal space-time coding designs for 2 transmit antennas and super-quasi orthogonal space-time coding designs for 4 transmit antennas, a novel super-orthogonal space-time coding designs for four transmit antennas is proposed. By exploiting the inherent structure association between OSTBC and QOSTBC, the proposed schemes can obtain the full-rate and good performance while keeping the coding complexity as super-orthogonal space-time coding schemes for 2 transmit antennas. Simulations results demonstrate that the proposed schemes can gain the about 2dB performance gain with significant reduction in computational load over the super-quasi orthogonal space-time coding schemes.2. The maximization of data rate under the constraint of diversity gain, coding gain and total transmit power is a considerable issue in concatenated orthogonal space-time coding system. Based on the concatenated orthogonal space-time coding design criterion, this paper proposed a novel full-rate concatenated orthogonal space-time block codes with multiple trellis coded modulation approach. By introducing the power diversity factor, a new combining algorithm for maximum likelihood decoding is derived. Simulation are performed over the fast and the slow Rayleigh fading channels to demonstrate the 1dB coding gain of the proposed concatenated orthogonal space-time block codes with multiple trellis coded modulation schemes over the super orthogonal space-time coding schemes..3. The field of concatenated space-time block coding (inner) with trellis coded modulation (outer) has recently attracted interest as a means of jointly considering the error correction coding gain and diversity gain possible without bandwidth expansion and power expansion over fading channels.In this paper, a concatenated space-time block coding (STBC)with asymmetric MPSK TCM scheme, based on the design criteria for constructing optimal concatenated space-time block coding with TCM. is presented by introducing the new optimal signal point assignment. Analysis and simulation results demonstrate that these concatenated STBC with asymmetric MPSK TCM have better coding gain than traditional concatenated STBC with TCM under the same spectral efficiency, decoding complexity.4. In this paper, the design of space-time codes employing multiple trellis-coded modulation (ST-MTCM) is proposed based on Frobenius norm. In the new ST-MTCM approach, by properly labeling each trellis branch for ST-MTCM with an T×N orthogonal codematrix and then employing Ungerboeck’s set partitioning scheme, maximum transmit diversity gain and improved coding gain can be achieved. It is also shown that the scheme does not require different space-time code design criteria for fast fading channels and quasi-static channels. Furthermore, transmitted branch matrix orthogonality is exploited to ease systematic code search procedure. The performance of the proposed codes is demonstrated by simulation results.5. By studying the Trellis Coding Modulation (TCM) and Multi-Trellis Coding Modulation (MTCM), an improved concatenated orthogonal space-time multiple trellis coded modulation approach for different Rayleigh fading channel models is proposed in this paper based on the concatenated orthogonal space-time coding design criterion. Simulation and analysis results show that the coding gain loss of the modified concatenated orthogonal space-time coding approach is only 0.4dB compared with that a previously proposed concatenated orthogonal space-time coding approach but the data rate is 50 percent greater; the modified concatenated orthogonal space-time multiple trellis coded modulation approach producing 2.6dB coding gain over concatenated super orthogonal space-time coding approach.更多还原