第三代移动通信中AMR语音编码的差错隐藏技术

介绍了第三代移动通信中AMR（自适应多码率）语音编码的帧格式，进一步描述了错误检测的基本方法，详细说明了语音编码对丢帧采用的差错隐藏技术。     

AMR-WB编码算法研究和复杂度分析

随着通用DSP性能的不断提升,通过软件实现AMR—WB等各种计算密集型媒体应用成为可能。首先研究了AMR-WB语音编码中采用的基本原理;然后采用YHFT-DSP/700模拟器详细分析了各种编码模式下各模块的计算复杂度,并给出每个模块所需的输入输出缓冲和访存带宽大小,为AMR—WB在通用DSP上的优化提供了指导。     

AMR系统中Viterbi译码的仿真与实现

本文根据AMR技术在GSM系统中物理层信道卷积编码规范,提出了一种可控制信道差错,降低工程实现难度的译码MATLAB仿真方案。结果表明,通过该仿真方案适合AMR语音业务信道卷积码的译码。     

无线广播系统的多级传输方案

为了充分利用信道的传输能力并满足不同用户和不同接收设备的要求,提出了一种多级传输的方案.该方案使用多级编码和多分辨率调制技术把广播数据分成多个优先级,为不同优先级的数据提供不同的差错保护.解码时采用多级译码的方法,使得用户可以根据自身的信道质量或者接收设备的能力,获得不同的数据传输率.仿真结果表明,该方案在AWGN和多径信道下都具有很好的性能.     

用于地面数字电视系统的多级编码调制技术

在地面数字电视广播系统中,为了满足不同信道条件和不同接收设备的用户需要,提出了一种多级编码调制的方案.把广播数据分成多个优先级,使用多级编码调制和集分割映射技术,为不同优先级的数据提供不同的差错保护.解码时采用多阶段译码的方法,使得用户可以根据自身信道的质量或者接收设备的能力,获得相应的数据传输率.仿真结果表明,该方案在AWGN和多径信道下都具有较好的性能.     

一种基于清浊音分类和参数冗余的语音差错隐藏算法

为避免信道误码条件下低速率编码语音质量的严重恶化,提出了一种针对MELP语音编码的差错隐藏算法.在利用一阶马尔可夫模型描述帧间参数转移概率的基础上,算法构造了帧内增益与分带清浊音判决参数之间的转移概率;在语音合成时,提出了基于最大似然(ML)的清浊音分类模式保护;并对清音帧和浊音帧采用不同的参数重构方案.将算法与近年来针对MELP的两种差错隐藏算法进行了比较,测试结果表明在10-2量级的随机误码的条件下,算法具有更好的差错隐藏性能.     

基于数据分割和可逆变长编码的数字视频传输差错复原技术

差错复原技术已成为易发生差错信道下视频编码的重要组成部分。本文实现了一个基于数据分割和可逆变长编码的具有差错复原性能的 H.2 63编解码器。通过利用数据分割、可逆变长编码、差错掩盖等技术 ,并利用第三代移动通信系统的信道差错模型对该编解码器的差错复原能力进行了实验。实验结果表明 ,在无线移动信道的恶劣环境下 ,在综合利用多种差错复原技术后 ,重建图像的主客观质量得到了明显的改善。     

语音编码技术进展

语音编码技术进展樊昌信一、语音编码的目的和应用语音编码是将模拟语音信号数字化的手段。语音信号数字化后，可以作为数字数据来传输、存储或处理，因而具有一般数字信号的优点。在实际应用中，这些优点是很重要的。１．数字语音信号在经过信道传输时，信道引入的噪声和...     

AMR语音编码算法研究及复杂度剖析

作为 3GPPWCDMA的语音编码 (SpeechCoding)候选方案 ,自适应多速率 (AMR)语音编码是一种多模式集成的ACELP类语音编码方案。本文根据该编码方案的标准 ,分析了其方案实现中的关键算法 :高性能码本设计、高效码本搜索算法、多级矢量量化技术、预处理算法的简化等。最后 ,设计了定点ANSI -C程序对AMR语音编码算法各部分的复杂度进行了测算     

宽带自适应多速率声码器

介绍了3GPP组织最新推出的宽带自适应多速率声码器AMR－WB，编解码原理以及速率控制机制等。较窄带语音编解码器，在语音的自然度效果及抗噪声能力等方面有较大改善。     

Progressive image transmission over space-time coded OFDM-based MIMO systems with adaptive modulation

This paper considers a progressive image transmission system over wireless channels by combining joint source-channel coding (JSCC), space-time coding, and orthogonal frequency division multiplexing (OFDM). The BER performance of the space-time coded OFDM-based MIMO system based on a newly built broadband MIMO fading model is first evaluated by assuming perfect channel state information at the receiver for coherent detection. Then, for a given average SNR (hence, BER), a fast local search algorithm is applied to optimize the unequal error protection design in JSCC, subjected to fixed total transmitted energy for various constellation sizes. This design allows the measurement of the expected reconstructed image quality. With this end-to-end system performance evaluation, an adaptive modulation scheme is proposed to pick the constellation size that offers the best reconstructed image quality for each average SNR. Simulation results of practical image transmissions confirm the effectiveness of our proposed adaptive modulation scheme.     

Progressive image transmission over differentially space‐time coded OFDM systems

In this paper, we consider progressive image transmission over differentially space‐time coded orthogonal frequency‐division multiplexing (OFDM) systems and treat the problem as one of optimal joint source‐channel coding (JSCC) in the form of unequal error protection (UEP), as necessitated by embedded source coding (e.g., SPIHT and JPEG 2000). We adopt a product channel code structure that is proven to provide powerful error protection and employ low‐complexity decision‐feedback decoding for differentially space‐time coded OFDM without assuming channel state information. For a given SNR, the BER performance of the differentially space‐time coded OFDM system is treated as the channel condition in the JSCC/UEP design via a fast product code optimization algorithm so that the end‐to‐end quality of reconstructed images is optimized in the average minimum MSE sense. Extensive image transmission experiments show that SNR/BER improvements can be translated into quality gains in reconstructed images. Moreover, compared to another non‐coherent detection algorithm, i.e., the iterative receiver based on expectation‐maximization algorithm for the space‐time coded OFDM systems, differentially space‐time coded OFDM systems suffer some quality loss in reconstructed images. With the efficiency and simplicity of decision‐feedback differential decoding, differentially space‐time coded OFDM is thus a feasible modulation scheme for applications such as wireless image over mobile devices (e.g., cell phones). Copyright © 2006 John Wiley & Sons, Ltd.     

A Combined Interleaving Technique for Trellis Coded MPSK Systems in Rayleigh Fading Channels

Freedom of mobility is the latesttrend in the evolution of digital communicationsystems. In these systems bandwidth and powerconstraints limit the mobility of the users. TCM(trellis coded modulation) is a combined coding andmodulation scheme which increases the productivity ofa digital communication system without increasing thetransmitted power or the required bandwidth. A mobilecommunication channel is affected from noise andfading because of the multipath propagation. On aRayleigh fading channel, coding should be used withtechniques which uncorrelate the received energy ofeach consecutive coded symbol. Interleaving is one ofthese techniques and used to make burst errors intorandom errors which can be corrected by errorcorrecting codes. In this paper, the trellis codingsystem which combines a regular convolutional encoder,bit interleaver, coordinate interleaver, and anappropriate decoder is considered. The analytical biterror probability upper bounds are derived for the8-PSK TCM system whose diversity is increased by usinga regular 2/3 rate convolutional code followed bythree bit interleavers and a 8-PSK signal mapperfollowed by two coordinate interleavers. Theanalytical and simulation results show that toincrease the diversity of the trellis coded M-PSKsystems in Rayleigh fading channels is the primary keyfor reliable transmission of high quality voice anddigital data.     

A highly efficient,low delay architecture for transporting H.264 video over wireless channel

Transporting hybrid coded video over wireless channel is very challenging. On the one hand, wireless link is much more error prone than wired network due to time varying channel conditions such as fading and multipath interference. On the other hand, hybrid coded video is very vulnerable to error propagation when transmitted over error prone channels. Numerous researches have been conducted to enhance error robustness for wireless video transmission. Among them, many schemes use retransmission to reduce packet loss rate and improve reconstructed video quality. However, retransmission is delay constrained due to the low delay nature of real-time video. Packet loss is inevitable even when retransmission is employed. In the proposed architecture, a novel error recovery scheme is introduced which switches adaptively between ACK and NACK modes according to channel conditions. Video proxy server at the base station is designed to make the retransmission and feedback based error recovery method more effective. State-of-the-art H.264 is used as video encoder since it provides not only high coding efficiency but also multi-frame which plays a key role in the framework. Simulation results demonstrate the effectiveness of this architecture.     

Turbo码在无线图像传输系统中的应用

通过Matlab仿真,信源编码采用矢量量化法,对静止图像通过无线瑞利(Rayleigh)衰落信道传输时,不采用信道编码和采用Turbo码作为信道编码两种情况进行了研究。依据失真度的主观评价,对两种情况下重构的图像进行了比较和分析。结果表明,Turbo码具有很强的抗衰落和抗多径效应能力,它不仅有效地提高了无线图像传输的可靠性,而且大大节省了系统发射功率。     

OFDM-based turbo-coded hierarchical and non-hierarchicalterrestrial mobile digital video broadcasting

The feasibility of terrestrial digital video broadcast (DVB) to mobile receivers is studied and turbo coded performance enhancements are proposed. Initially, the MPEG-2 codec is subjected to a rigorous bit error sensitivity investigation, in order to assist in designing various error protection schemes for wireless DVB transmission. The turbo codec is shown to provide signal-to-noise ratio (SNR) performance advantages in excess of 5-6 dB over conventional convolutional coding both in terms of bit error rate and video quality. Our experiments suggested that-despite our expectations-multi-class data partitioning did not result in error resilience improvements, since a high proportion of relatively sensitive video bits had to be relegated to the lower integrity subchannel, when invoking a powerful low-rate channel codec in the high-integrity protection class. Nonetheless, DVB transmission to mobile receivers is feasible, when using turbo-coded OFDM transceivers at realistic power-budget requirements under the investigated highly dispersive fading channel conditions. It is interesting to note furthermore that the 5-6 dB SNR improvement due to turbo coding allows us to invoke for example the double-throughput 16-level quadrature amplitude modulation (16-QAM) mode instead of the standard convolutional-coded 4-QAM mode. This facilitates doubling the bit rate and hence improving the video quality     

Cooperative Coding for OFDM Systems

In this paper, we study Orthogonal Frequency Division Multiplexing (OFDM) systems with cooperative coding over frequency selective Rayleigh fading channels. We derive the pairwise error probability (PEP) for the block-fading OFDM channel model. We use the derived PEP to get an upper bound on the frame error probability for the coded cooperative OFDM system. This bound is then utilized in the study of the diversity and coding gains achievable through cooperative coding in OFDM systems for various inter-user channel qualities. We consider the design of cooperative convolutional codes based on the principle of overlays and provide simulation results for different cooperation scenarios. We observe significant gains over conventional non-cooperative OFDM systems. Finally, based on some simple approximations, we provide guidelines for the choice of partners in coded cooperative OFDM systems.     

A New Union Bound on the Error Probability of Binary Coded OFDM Systems in Wireless Environments

Orthogonal Frequency Division Multiplexing (OFDM) systems are commonly used to mitigate frequency-selective multipath fading and provide high-speed data transmission. In this paper, we derive new union bounds on the error probability of a coded OFDM system in wireless environments. In particular, we consider convolutionally coded OFDM systems employing single and multiple transmit antennas over correlated block fading (CBF) channels with perfect channel state information (CSI). Results show that the new union bound is tight to simulation results. In addition, the bound accurately captures the effect of the correlation between sub-carriers channels. It is shown that as the channel becomes more frequency-selective, the performance get better due to the increased frequency diversity. Moreover, the bound also captures the effect of multi-antenna as space diversity. The proposed bounds can be applied for coded OFDM systems employing different coding schemes over different channel models.     

Capacity allocation for integrated voice/data transmission at apacket switched TOM

The integrated transmission of voice and data at a time-division multiplexer (TDM) is discussed and analyzed. The system operates in a frame format and the channel capacity is governed by the frame size. The allocation of channel capacity for the transmission of voice and data is performed by a controller. Digital speech interpolation (DSI) and embedded coding techniques are used to enhance the transmission efficiency and to facilitate the implementation of multiplexing. Using a dynamic programming approach, a capacity allocation policy which jointly optimizes the voice/data performance is introduced. Numerical results indicate that the aggregate throughput of the system can be improved with a slight degradation in voice quality     

An error protected 16 kbit/s voice transmission for land mobileradio channel

Robust speech coding and an efficient error correction coding is indispensable for toll-quality voice transmission in mobile radio because of degradation due to multipath fading. A decision procedure for the bit-selective forward-error-correction (BS-FEC) scheme is proposed as a promising solution to this problem, and backward-type prediction speech coding is shown to be more robust against transmission errors than forward-type prediction. Combinations of BS-FEC (channel coding) and backward-type prediction speech coding are designed, and improvements in the SNRs of transmitted voice signals are examined. Simulation results show that BS-FEC can provide good speech quality even at a bit error rate (BER) of 10^-2 in Rayleigh fading environments, at the cost of a slight degradation in the SNR (signal-to-noise ratio) at low BERs