IEEE802．16d系统中自适应调制编码技术的应用研究

针对IEEE802．16d物理层标准,文章提出了适用于IEEE802．16d系统的自适应调制编码方案,包括调制编码方式、MCS切换门限的设置方法、信道信噪比SNR估计方法,并对采用分组Turbo码作为前向纠错码的自适应调制编码技术在AWGN信道上的性能进行了Matlab仿真,结果表明：自适应调制编码技术在保证一定误码率的前提下能够有效地提高系统的吞吐量。     

Trellis-coded complementary code keying for high-rate wireless LANsystems

In high-rate wireless LAN, complementary code keying (CCK) is adopted in the IEEE 802.11b standard to support data rates up to 11 Mbps, much higher than the 2-Mbps data rate in the previous wireless LAN standard. Due to less-than-ideal characteristics of the CCK codewords, the CCK performs quite poorly in large-delay-spread multipath channels. In this paper, a new modulation scheme that combines the trellis coding with the CCK modulation is proposed. This scheme is shown, through simulation, to achieve much better error rate performance in medium-to-large channel delay spread environments     

100 Mb/s data transmission on UTP and STP cabling for demandpriority networks

There have been considerable advances towards higher speed (100 Mb/s) workgroup LANs which support the existing UTP and STP structured cabling utilized by 10 BASE-T and token ring LANs. The paper describes the transmission techniques used by an IEEE 802.12 demand priority network with UTP and STP structured cabling. The UTP transmission scheme supports categories 3-5 UTP (i.e. voice-grade and data-grade) using a 5B6B block coded binary signalling scheme on four pairs. This binary signalling scheme is shown to provide better immunity against crosstalk and external (impulse) noise than multilevel signalling schemes. The STP scheme combines the strengths of the 5B6B block code with signalling technology similar to existing SDDI links     

A Concatenated Coding Scheme for Error Control

In this paper, a concatenated coding scheme for error control in data communications is presented and analyzed. In this scheme, the inner code is used for both error correction and detection; however, the outer code is used only for error detection. A retransmission is requested if either the inner code decoder fails to make a successful decoding or the outer code decoder detects the presence of errors after the inner code decoding. Probability of undetected error (or decoding error) of the proposed scheme is derived. An efficient method for computing this probability is presented. Throughput efficiency of the proposed error control scheme incorporated with a selective-repeat ARQ retransmission strategy is also analyzed. Three specific examples are presented. One of the examples is proposed for error control in the NASA Telecommand System.     

Reliability and Throughput Analysis of a Concatenated Coding Scheme

In this paper, the performance of a concatenated coding scheme for error control in ARQ systems is analyzed for both randomerror and burst-error channels. In particular, the probability of undetected error and the system throughput are calculated. In this scheme, the inner code is used for both error correction and error detection, and the outer code is used for error detection only. Interleaving/deinterleaving of the outer code is assumed. A retransmission is requested if either the inner code or the outer code detects the Presence of errors. Various coding examples are considered. The results show that concatenated coding can provide extremely high system reliability (i.e., low probability of undetected error) and high system throughput.     

The ERPC: an efficient error-resilient technique for encodingpositional information or sparse data

In many source and data compression schemes, information relating to positions of high-energy samples or areas of importance often needs to be relayed to the decoder. The error resilient positional code (ERPC) is an efficient fixed-rate coding scheme for encoding such positional information, or, equivalently, sparse binary data patterns. It has also been designed with good channel error robustness properties, such that the decoded data quality degrades gracefully with worsening channel conditions, without the possibility of catastrophic breakdown or loss of sync. In this work, the coding efficiency of the ERPC is compared to a few other standard schemes. It is found to be efficient and its error extension in terms of the expected number of samples corrupted per bit error is reported and shown to be low and noncatastrophic. The ERPC is applied to an image coding example based on subband coding and vector quantization. It results in an efficient adaptive codec capable of operating in harsh channel conditions, without the aid of error correction or detection techniques     

The Demand Priority MAC protocol

A new technology needs to offer more than just 100 Mb/s. To succeed in the LAN marketplace, a new LAN technology must be very cost competitive with the established LANs, such as Ethernet and Token Ring, while also providing backwards compatibility with existing network software. We describe a new 100-Mb/s LAN technology that has these characteristics This technology is being defined as an open standard within the IEEE Project 802.12 Demand Priority group. Two important objectives were established for this LAN technology: first, it should be able to use the unshielded twisted pair (UTP) wiring found in a large number of installations and, in particular, to use the same wiring as defined for use in 1OBase-T. This objective was later extended to encompass support for the shielded twisted pair (STP) used for IEEE 802.5. This will enable the majority of current LAN users to benefit from their enormous investment in cable plant. The second objective was that the network should support new applications, such as video conferencing and remote training, while also providing backwards compatibility with the massive installed software base. Both objectives have been met. The Demand Priority MAC protocol currently being standardized in IEEE 802.12, offers substantial benefits over the CSMA/CD protocol of IEEE 802.3. By preserving both the current wiring infrastructure and investment in software, and by using the very simple Demand Priority MAC protocol, 100 Mb/s LANs could soon be as low-cost as 10Base-T is today     

Training overhead for decoding random linear network codes in wireless networks

We consider multicast communications from a single source to multiple destinations through a wireless network with unreliable links. Random linear network coding achieves the min-cut flow capacity; however, additional overhead is needed for end-to-end error protection and to communicate the network coding matrix to each destination. We present a joint coding and training scheme in which training bits are appended to each source packet, and the channel code is applied across both the training and data. This scheme allows each destination to decode jointly the network coding matrix along with the data without knowledge of the network topology. It also balances the reliability of communicating the network coding matrices with the reliability of data detection. The throughput for this scheme, accounting for overhead, is characterized as a function of the packet size, channel properties (error and erasure statistics), number of independent messages, and field size. We also compare the performance with that obtained by individual channel coding of training and data. Numerical results are presented for a grid network that illustrate the reduction in throughput due to overhead.     

一种数据包合并跨层优化编码方案

在传统分层系统中,信息数据包首先在数据链路层进行数据包级的检错码编码,然后一个数据包对应一个信息分组在物理层进行符号级的纠错码编码,最后送入信道中传输。为提高系统的传输效率,提出了一种基于数据包合并的物理层与数据链路层编码的跨层优化方案,即数据链路层的多个数据包合并对应物理层的一个信息分组,然后进行纠错编码后再传输。通过理论推导得出了使系统传输效率最大的最优合并数据包个数和数据包长度表达式。通过仿真验证了理论推导的正确性,并与传统方案进行了比较,结果表明,该方案能有效提高系统的传输效率。     

CCK modulation: beyond Wi-Fi

The full-rate IEEE 802.11b standard for wireless local area networks, also known as Wi-Fi, employs 256-ary complementary code keying (CCK). For applications that do not require adherence to the standard, it may be desirable to use forward error correction coding with CCK, but the bit-tosymbol mappings used in IEEE 802.11b degrade the performance of most standard binary codes. We show that a standard binary convolutional code performs much better with alternative bit mappings, and we demonstrate that chip scrambling gives additional improvement.     

5G通信中的极化码在高阶调制下的应用

极化码作为信道编码领域的一类新型编码方案,已经被确定为5G移动通信系统中增强移动宽带(Enhanced Mobile Broadband,eMBB)场景下控制信道的编码方案。为了提高5G通信中的频带利用率和信息传输速率,提出将极化码与高阶调制技术相结合,针对16QAM和256QAM两种调制方式,建立和仿真了基于极化码的高阶调制通信系统。在加性高斯白噪声(Additive White Gaussian Noise,AWGN)信道模型下采用逐次消除(Successive Cancellation,SC)译码算法对不同参数的极化码进行仿真比较。仿真结果表明,在现有5G标准控制信道的16QAM模型下,码长N=1024,码率R=1/3,信噪比Eb/N0=6 dB时,极化码误码率可以达到10^-5。未来极化码的应用将推广到数据信道,在256QAM调制方式下,也体现出较好的纠错性能;在16QAM调制方式下,将极化码与同等速率的LDPC码及卷积码相比较,性能增益也有良好的体现。     

Performance of transmitted reference pulse cluster ultra‐wideband systems with forward error correction

Recently, an improved transmitted reference (TR) signaling scheme, referred to as transmitted reference pulse cluster (TRPC), was proposed for low‐rate ultra‐wideband (UWB) communications. Compared with conventional TR, TRPC has a more compact and uniform spacing for the reference and data pulses and therefore addresses the implementation problems posed by the long delay line requirement, as well as provides better bit error rate (BER) performance. In this paper, a TRPC‐UWB system, which includes practical forward error correction (FEC) coding such as that specified in the IEEE 802.15.4a standard, as well as more powerful convolutional codes, is developed. A performance analysis, which highlights the importance of selecting appropriate FEC codes, is presented. Results show that with a suitable FEC code, the TRPC‐UWB system is a promising candidate for low‐rate wireless personal area networks. Copyright © 2012 John Wiley & Sons, Ltd.     

Nonbinary error detection codes for data retransmission and biterror rate monitoring

The author discusses the use of (n, n-1) polynomial codes for data retransmission and bit error rate (BER) monitoring in nonbinary data transmission systems. For a particular type of polynomial code, called a simple polynomial code, a simple error detection scheme which exploits the Gray coding commonly employed in nonbinary data transmission systems can be devised. Even though its algebraic structure is the same as that of general (n, n -1) polynomial code, the simple polynomial code's performance, when using this detection algorithm, is either equal to or better than that of the corresponding general polynomial code, for data retransmission and BER monitoring. The improvement in the BER monitoring performance of the simple code relative to that of the corresponding general code increases as the data alphabet size becomes larger     

Energy Efficient Coded Communication for IEEE 802.15.4 Compliant Wireless Sensor Networks

The multipath nature of the wireless environment does not provide reliable links for robust communication in wireless senor networks (WSNs). These unreliable links increase the error level to a greater extent and therefore, reduces battery life. Hence, there arises a need for developing energy efficient forward error correction code that avoids more energy consuming Automatic Repeat request (ARQ) scheme used in WSNs to improve link reliability. In this paper, we consider a simple block error correction codes such as cyclic and Bose Chaudhuri Hocquenghem (BCH) codes to be used in IEEE 802.15.4 RF transceiver based sensor nodes. The simulations are performed to measure network parameters such as bit error rate, and energy spent per bit under Rayleigh fading channel environment. It is found that BCH code with code rate of 0.8 provides coding gain of 1.6 dB when compared with cyclic and ARQ schemes and proves to be an energy efficient code among the codes considered.     

IEEE802.16e标准LDPC译码器设计与实现

LDPC码自在上个世纪90年代被重新发现以来,以其接近香农极限的差错控制性能,以及译码复杂度低、吞吐率高的优点引起了人们的关注,成为继Turbo码之后信道编码界的又一研究热点。利用FPGA设计并实现了一种基于IEEE802.16e标准的LDPC码译码器。该译码器采用偏移最小和（Offset Min-Sum）算法,其偏移因子β取值为0.125,具有接近置信传播（Belief Propagation）算法浮点的性能。译码器在结构上采用了部分并行结构,可以灵活支持标准中定义的所有码率和码长的LDPC码的译码。此外,该译码器还支持对连续输入的数据块进行处理,并具有动态停止迭代功能。硬件综合结果表明,该译码器工作频率为150MHz时,固定15次迭代,最低可达到95Mb/s的译码吞吐率,完全满足802.16e标准的要求。     

Channel coding for narrow-band Rayleigh fading with robustnessagainst changes in Doppler spread

For digital transmission over frequency-nonselective fading channels, data security can be obtained by error correction coding, but the coding scheme has to be adapted to the channel properties. For many vehicular applications, the range of possible vehicle speeds is large and in the UHF band the resulting Doppler frequency may not be small relative to the symbol rate-suggesting a differential detection scheme. Therefore, the channel coding should be robust against changes in Doppler spread. A combination of a convolutional code (soft-decision decoding) and a Reed-Solomon (RS) code is considered, and the performance in a narrow-band Rayleigh-fading channel with differential quaternary phase shift keying (DQPSK) modulation without interleaving is evaluated as a function of signal-to-noise ratio (SNR) and Doppler spread by computer simulations. This transmission scheme is proved to have good performance over a large variety of vehicle speeds     

Performance of multidimensional multicode DS-CDMA using codediversity and error detection

High rate transmission can be realized using multiple orthogonal codes (MOC), as proposed in the third-generation wide-band code-division multiple-access (W-CDMA) standard. However, the linear sum of MOC channels is no longer constant amplitude, and a highly linear, power-inefficient amplifier may be required for transmission. Recently, a nonlinear block coding technique called precoding is introduced to maintain a constant amplitude signal after superposition of MOC channels. This is achieved by adding redundancy. In this paper, we first describe a multidimensional signaling scheme that recovers some information rate loss by precoding. Second, we propose a self-interference (SI) cancellation scheme resulting from a code diversity between the in-phase and quadrature subchannels among MOC channels. In a typical wireless channel with multipath fading, this type of SI can be detrimental especially when the number of parallel MOC channels is large. Third, we show that the error detection capability of precoding can be combined with code diversity, resulting in a diversity gain. In addition, we show that the diversity gain can be achieved using antenna diversity to assure the degree of freedom in code diversity, and even with the large number of MOC channels, the error performance can be maintained reliably while outperforming the variable spreading factor scheme in W-CDMA     

空时编码在单天线UWB通信系统中的应用

超宽带(UWB)适用于基带多用户通信、战场无线通信和高数据率多媒体业务等通信系统,其数据传输速率高、功耗低、多径分辨能力强。但超宽带脉冲信号时域支撑区极窄,信道为密集多径,将空时编码技术引入超宽带通信系统,能够提升无线通信系统的信道容量与抗误比特率性能。在对UWB空时分组编码系统模型性能理论分析的基础上,对空时分组码在单天线UWB系统应用方案与UWB空时分层码方案进进行了简要介绍,利用Matlab对IEEEUWB信道模型进行仿真,提出了空时编码在UWB通讯技术中应用后提升短距高速率无线通信的性能的结论 。     

LDPC码在IEEE802.16e标准中的编译码分析

为了能够在保证译码性能的同时进一步降低译码的复杂度,该标准还在译码的过程中引入由M Fossorier等人提出的BP-Based算法,并分析了这两类算法的实际译码性能。实验仿真结果表明,BP-Based算法与LLR-BP算法相比,在不同码长及不同码率条件下可以更好地实现译码算法度和译码性能的有效均衡,因而更加适合作为硬件译码器的优化算法而应用到实际的通信系统中。     

A Bandwidth Efficient Turbo Coding Scheme for VDSL Systems

The current forward error correction (FEC) scheme for very high bit-rate digital subscriber line (VDSL) systems in the ANSI standard employs a 16-state four-dimensional (4D) Wei code as the inner code and the Reed-Solomon (RS) code as the outer code. The major drawback of this scheme is that further improvement cannot be achieved without a substantial increase in the complexity and power penalty. Also, a VDSL system employing the 4D Wei-RS scheme operates far below the channel capacity. In 1993, powerful turbo codes were introduced whose performance closely approaches the Shannon limit. In this paper, we propose a bandwidth and power efficient turbo coding scheme for VDSL modems in order to obtain high data rates, extended loop reach and increased transmission robustness. We also propose a pipelined decoding scheme to reduce the latency at the receiver end. The objective of the proposed scheme is to provide a higher coding gain than that given by the 4D Wei-RS scheme, resulting in an improved performance of the VDSL modems in terms of bit rate, loop length and transmitting power. The scheme is investigated for various values of transmitting power, signaling frequencies and numbers of crosstalkers for a targeted bit error rate of 10⁻⁵ and is implemented in a system with a quadrature amplitude modulation in which a mixed set partitioning mapping is employed to reduce the decoding complexity. The effects of code complexity, interleaver length, the number of decoding iterations and the level of modulation on the performance of VDSL modems are explored. Simulation results are presented and compared to those of the 4D Wei-RS scheme. The results show that the choice of turbo codes not only provides a significant coding gain over the standard FEC scheme but also efficiently maximizes the loop length and bit rate at a very low transmitting power in the presence of dominant far-end crosstalk and intersymbol interference. In order to compare the hardware complexity, we synthesize the proposed and 4D Wei-RS schemes using SYNOPSYS with the target technology of Xilinx 4020e-3. The Xilinx field programmable gate array statistics of the proposed scheme is compared with that of the 4D Wei-RS scheme.