空时分组码在自适应调制编码系统中的性能分析

0引言 移动通信频谱资源的有限性决定了未来移动通信必须采用频谱利用率高的抗衰落技术来提高系统的性能,从而支持高速率数据和多媒体业务的传输。在无线衰落信道中,利用多天线阵列的空时分组编码技术把编码、调制和空间分集结合起来,能很好地提高频谱利用率。     

MIMO OFDM系统中基于物理层与链路层的跨层优化设计

该文讨论了基于空时编码发射分集正交频分复用(OFDM)系统的跨层传输技术.该技术结合了传统物理层自适应调制和链路层自动请求重发,利用链路层的误包率和信道估计参数计算自适应调制门限,在系统给定时延和误包率约束的基础上最大程度地提高了频谱利用率.仿真结果表明,该算法相比传统物理层自适应传输,在频谱利用率性能上有1.5dB以上的增益.但随着最大重传次数的增加频谱利用率的提高越来越小,这就使得实际系统能以较小的时延代价换取足够的频谱利用率增益.     

网格编码调制结合低密度校验码的应用方案设计及性能分析

提出一种利用网格编码调制将低密度校验码与高阶数字调制相结合的应用方法，其中在网格编码调制中采用递归系统卷积码进行编码用以实现基于对数似然比的软译码方法，构造了低密度校验码和网格编码调制相结合的编译码系统。仿真结果表明，该方案将低密度校验码的高编码增益与多元调制的高频谱利用率有效结合在一起，是一种功率和频谱高效的编码调制方式，比传统的网格编码方式有更好的性能。     

空时编码及其在第3代移动通信中的应用

近年来,为了提高无线频谱的利用率,一些学者提出了一种结合分集发送、调制和编码的空时码.文中分别介绍了空时格栅编码和空时分组编码的编译码方法,并介绍了目前空时分组编码在第3代移动通信中的应用.     

MIMO OFDM系统中基于自适应编码调制的跨层设计方案

本文讨论了MIMOOFDM系统中一种基于自适应编码调制的的跨层传输技术。该技术结合传统物理层自适应编码调制和数据链路层自动请求重发,利用信道估计参数和数据链路层的误包率计算自适应编码调制门限,在系统给定时延和误包率约束的基础上最大程度地提高频谱利用率。仿真结果表明,编码系统具有很强的差错控制作用,相比传统物理层自适应编码调制系统和未编码系统都提高了频率利用率;当频率利用率为1时,相比于未编码系统,编码带来的增益为4dB。同时这种强差错控制作用也使得改变系统最大重传次数对切换门限的影响变小,因此跨层自适应编码调制相比传统物理层自适应带来的频谱效率的提高变小,这就使得实际系统能以较小的时延代价换取足够的频谱利用率增益。     

MIMO—OFDM系统下基于频谱利用率的自适应发射方案选择

本文提出并分析了一种MIMO-OFDM系统下,考虑相关空间信道的自适应发射方案选择算法.采用比特交织卷积编码,在以下三种发射模式间进行选择:空间复用、空间分集和复用/分集的混合模式.我们通过对MIMO-OFDM系统中采用迫零(ZF)接收机在高信噪比条件下的错误概率的简化分析,得出空间相关的多天线系统下的自适应选择算法,在给定的误码率条件下可获得使频谱利用率最大化的编码速率、调制模式和发射模式,并反馈到发射端,有效改善了系统的性能.     

无线通信系统中的低码率空时网格码

空时网格编码能在频带利用率、分集增益、调制方式与编码网络图复杂度之间达到最佳的折衷。本文给出了几种低码率空时网格码的好码。理论分析和系统仿真表明,在相同的频带利用率下,该空时网格码可具有比空时块码级联卷积码具有更好的误码率性能,更适合于对频带利用率要求不高的功率受限无线通信系统。     

基于平均频谱效率的自适应编码调制优化设计

自适应编码调制(ACM)技术能够很好地改善无线信道的频谱利用率.文中提出了一种基于平均频谱效率的自适应调制编码系统的优化方案,运用该方案,ACM系统需要数量很少的优化编码,使吞吐量接近于AWGN信道容量.     

Turbo码综合性能分析与Turbo编码调制

对 Ｔｕｒｂｏ码的 ＲＳＣ分量码、交织器、调制方式、信道以及迭代译码算法进行了综合研究与性能分析，并给出了一种基于逐比特ＭＡＰ算法的Ｔｕｒｂｏ编码与多元调制相结合的编码调制方式。仿真结果表明，该方案将Ｔｕｒｂｏ码的高编码增益与多元调制的高频谱利用率有效地结合在一起，是一种功率和频谱高效的编码调制方式，比传统的ＴＣＭ方式有更好的性能。     

MC-CDMA系统中自适应调制算法的性能分析

自适应调制能提高系统的频谱利用率和改善系统的误码率性能。该文提出了一种将自适应调制算法与MC-CDMA技术相结合的方案。采用这种方案的自适应MC-CDMA系统在获得频率分集增益和有效频谱利用率的同时,还能获得很好的误码率性能。文章分析了提出的自适应MC-CDMA系统的性能,并通过仿真结果说明了合并方式和信道环境都将影响自适应调制算法在MC-CDMA中应用的有效性。     

Design of efficient coding and modulation for a Rayleigh fading channel

The design of a coding/modulation structure for digital communications over a Rayleigh fading channel, the structure of the corresponding decoder, and the error rate performance of the resulting system are considered. Emphasis is on the use of constant weight codes for constructing equal energy waveforms for transmission over the channel. The performance gains that are achieved by the integrated coding/modulation approach relative to conventional methods for obtaining diversity are illustrated via some examples. Of special interest is the use of a concatenated coding technique for forming codes of large distance and hence high diversity. A new decoding algorithm is applied to enable efficient decoding of the concatenated code. An example is included that shows a performance increase of several dB resulting from concatenation.     

Combined turbo coding and unitary space-time modulation

Space-time coding is well understood for high data rate communications over wireless channels with perfect channel state information. On the other hand, channel coding for multiple transmit antennas when channel state information is unknown has only received limited attention. A new signaling scheme, named unitary space-time modulation, has been proposed for the latter case. In this paper, we consider the use of turbo coding together with unitary space-time modulation. We demonstrate that turbo coded space-time modulation systems are well suited to wireless communication systems when there is no channel state information, in the sense that the turbo coding improves the bit error rate (BER) performance of the system considerably. In particular, we observe that the turbo-coded system provides 10-15 dB coding gain at a BER of 10/sup -5/ compared to the unitary space-time modulation for various transmit and receive antenna diversity cases.     

两路接收分集Turbo乘积编码PSAM系统的研究

提出具有两路接收分集Turbo乘积编码引导符号辅助调制(TPC-PSAM）的16QAM系统的实现方法。该系统将Turbo乘积编码和分集接收用于改善16QAM系统在平坦衰落信道中的性能。通过对衰落信道中的数值仿真，结果表明具有接收分集的TPC-PSAM系统比TPC-PSAM系统明显的改善，同时可以减小接收机在不同衰落信道中的性能差异。     

基于准正交空时分组编码的空间激光通信

准正交空时分组编码(QOSTBC)是一种正交空时编码的变换编码结构,将时间分集和空间分集相结合,具有高效的分集利用率和编码效率。QOSTBC是解决大气湍流对光通信影响的有效手段之一。在研究了大气信道特性的基础上,提出一种基于QOSTBC结构和空间分集光通信系统的信道模型;介绍了QOSTBC原理,分析了系统的信道容量和误码率(BER);利用蒙特卡罗仿真比较了采用空时分集编码与未使用分集编码系统的容量及BER的情况。结果表明,使用QOSTBC系统的信道容量随发射天线数增加而递增,误码性能得到有效改善。QOSTBC与Alamouti编码系统相比系统信噪比节省约9dB,说明该系统具有编码所提供的良好信道容量和误码性能,能够有效地抑制大气湍流对光通信所产生的光强起伏影响。     

Information theoretic considerations for coded modulation overfading channels

We compute the random coding error exponent for coded modulation transmitted over a flat, memoryless, Rayleigh fading channel. In addition, estimates of code lengths required to achieve a certain error probability are determined and compared to those required for the additive white Gaussian noise channel. Finally, the effect of receiver antenna diversity is also considered as a method to compensate for fading and is shown to have a significant, positive impact on the error exponent. The results we obtain represent an information theoretic view that complements the existing literature on the performance of coded modulation over fading channels with receiver diversity     

下一代地面数字电视广播系统关键技术

较全面地介绍了下一代中国地面数字电视广播系统的关键技术,其中包括改进的帧结构、发射分集、先进的信道编码和调制、多业务支持、广播回传信道和时频域定位等。仿真结果表明这些技术的应用使系统性能良好。     

Adaptive coded modulation for fading channels

We apply coset codes to adaptive modulation in fading channels. Adaptive modulation is a powerful technique to improve the energy efficiency and increase the data rate over a fading channel. Coset codes are a natural choice to use with adaptive modulation since the channel coding and modulation designs are separable. Therefore, trellis and lattice codes designed for additive white Gaussian noise (AWGN) channels can be superimposed on adaptive modulation for fading channels, with the same approximate coding gains. We first describe the methodology for combining coset codes with a general class of adaptive modulation techniques. We then apply this methodology to a spectrally efficient adaptive M-ary quadrature amplitude modulation (MQAM) to obtain trellis-coded adaptive MQAM. We present analytical and simulation results for this design which show an effective coding gain of 3 dB relative to uncoded adaptive MQAM for a simple four-state trellis code, and an effective 3.6-dB coding gain for an eight-state trellis code. More complex trellis codes are shown to achieve higher gains. We also compare the performance of trellis-coded adaptive MQAM to that of coded modulation with built-in time diversity and fixed-rate modulation. The adaptive method exhibits a power savings of up to 20 dB     

Impact of diversity reception on fading channels with codedmodulation. I. Coherent detection

We address the problem of designing and analyzing the performance of a coded modulation scheme for the fading channel when space diversity is used. Under fairly general conditions, a channel affected by fading can be turned into an additive white Gaussian noise (AWGN) channel by increasing the number of diversity branches. Consequently, it can be expected (and is indeed verified by our analyses and simulations) that a coded modulation scheme designed to be optimal for the AWGN channel also will perform asymptotically well on a fading channel with diversity. This paper presents bounds on the bit-error probability of a system with coded modulation and diversity for space- and time-correlated Rician flat fading. Specifically, we derive a new method which allows evaluation of the pairwise error probability extremely easily, as well as accurately and computationally fast. The accuracy achieved improves considerably on the widely used, but rather loose Chernoff bound. Starting from this analysis, we study the asymptotic behavior of the fading channel with diversity as the number of diversity branches increases, and we address the effects of diversity on coded modulation performance and design criteria, including the effect on interleaver depth (which affects the total delay of the system)     

Variable rate adaptive modulation for DS-CDMA

An adaptive coding scheme is introduced for a discrete sequence code-division multiple-access system. The system uses noncoherent M-ary orthogonal modulation with RAKE receiver and power control. Both a fast fading channel and a combined fast fading, shadowing and power control channel are considered. Analytical bounds and simulations are done to evaluate the performance of the system. It is found that there is significant improvement in the average throughput and the bit-error-rate performance in the adaptive coding scheme. The amount of improvement drops with the increase of diversity branches used. More importantly, it is found that adaptive coding scheme is relatively robust to shadowing, while fix-rate codes are ineffective in the shadowing environment. Finally, adaptive coding scheme is found to be robust to mobile speed, feedback delay, and finite interleaving depth     

A novel repetition space-time coding scheme for mobile FSO systems

In this paper,we present an innovative method of double balanced differential configuration,in which two adjacent single photon avalanche diodes(SPADs)from the same wafer are configured as the first balanced structure,and the output signal from the first balanced stage is subtracted by the attenuated gate driving signal as the second balanced stage.The compact device is cooled down to 236 K to be characterized.At a gate repetition rate of 400 MHz and a1 550 nm laser repetition rate of 10 MHz,the maximum photon detection efficiency of 13.5%can be achieved.The dark count rate is about 10-4 ns-1 at photon detection efficiency of 10%.The afterpulsing probability decreases with time exponentially.It is shown that this configuration is effective to discriminate the ultra-weak avalanche signal in high speed gating rates.