Optimization of Hybrid ARQ for IP Packet Transmission

This paper presents, optimizes, and analyzes the performance of a novel hybridSelective Repeat/Multi Copy(SR/MC) Automatic Repeat Request (ARQ) scheme for transmitting fragmentedInternetProtocol (IP) packets. The ARQ scheme works in the SR mode until the last IPpacket fragment istransmitted. If a fragment is negatively acknowledged after the last fragmentis transmitted, then the system goes into theMC mode. In the MC mode, multiple copies of the erroneous fragment aretransmitted. After the IPfragments are received without error, the system returns to the SR mode.The optimization of the ARQ is done in terms of two parameters: fragment sizeand the optimum number of packetsto be transmitted in the MC mode, M. Optimum values for both parameters arecalculated for Bit ErrorRate (BER), throughput, IP packet size, and delay. The fragment size is alsocalculated for actual datathroughput for a given IP packet size, both with and without Forward ErrorCorrection (FEC). Then,the performance of the proposed scheme is evaluated in terms of BER andIP packet size with theoptimum M and fragment size. Performance results are obtained with and withoutBose ChaudhuriHocquenghem (BCH) error correction codes under Additive White Gaussian Noise(AWGN) as wellas Flat Rayleigh Fading channels. The ARQ scheme gives optimum performance forM equal to 10fragments and fragment size of 75 bytes. Under the AWGN channel, a throughputof 0.9 is achieved for any IPpacket size and at higher BER conditions compared to the Selective Repeat +Stutter Scheme 2 (SR + ST 2).An 8 dB improvement is achieved under the flat Rayleigh fading channel usingBCH(63, 51, 2) for a throughputof 0.9.     

Performance of hybrid ARQ for IP packet transmission on fadingchannel

This paper proposes and analyzes the performance of a hybrid selective repeat (SR)/multicopy (MC) automatic repeat request (ARQ) scheme to transmit fragmented Internet protocol (IP) packets. The ARQ scheme works in the SR mode until the last IP packet fragment is transmitted. If a fragment is negatively acknowledged after the last fragment is transmitted, then the system goes in the MC mode. In the MC mode, multiple copies of the erroneous fragment are transmitted. After all IP fragments are received without error, the system goes back to the SR mode. The performance of the proposed scheme is evaluated in terms of the bit error rate (BER), IP packet size, and fragmentation size with and without Bose Chaudhuri Hocquenghem (BCH) error correction codes. Both the results are obtained under additive white Gaussian noise (AWGN) as well as flat Rayleigh fading channels. The proposed scheme gives a throughput of 0.9, even at high BER conditions, for any IP packet size under an AWGN channel while, an 8-dB improvement is achieved, when using BCH(63, 51, 2) for throughput of 0.9, over selective repeat+stutter scheme 2 (SR+ST 2) under a flat Rayleigh fading channel     

Transmit power optimization for video transmission over slowly-varying Rayleigh-fading channels in CDMA systems

An optimum transmit power management scheme is proposed for wireless video service in code-division multiple-access systems. The scheme minimizes the transmit power subject to the constraint on the distortion resulted from the loss of each packet and the error propagation effect caused by the motion compensation. It implicitly controls the target bit-error rate (BER) of the video packet according to the importance of the packet. The more important the packet is, the more securely it is transmitted over noisy channel. Furthermore, the scheme adjusts the target BER as if the water filling concept is applied to the problem of minimizing the transmit power. The simulation results show that the proposed scheme considerably outperforms the conventional schemes.     

小波包跳频通信系统的性能分析

介绍了将小波包调制（WPM）技术与跳频技术相结合的高效通信方式,即小波包跳频（WPM-FH）通信系统。利用特征函数法分析和推导了系统在高斯信道、瑞利衰落信道下的误码性能,给出了用户数,跳频点数及子信道数与系统性能之间的关系。理论分析和实验仿真表明,该系统不仅保持了小波包调制技术的优点,提高了频谱利用率,且具有较好的抗多径衰落和抗干扰能力,较好地改善了通信系统性能。同时,为了进一步改善多径衰落对系统性能的影响,在接收端加入了自适应均衡技术,实验结果表明系统性能得到了一定的提高。      

An adaptive coding scheme with code combining for mobile radiosystems

The authors propose and study an adaptive error-control coding scheme for binary digital FM (BFM) mobile radio transmission. The scheme employs code combining through packet retransmissions. The number of transmissions of a packet is in proportion to the channel fading/noise levels, which is in contrast to time diversity techniques where a fixed number of repetitions of a data packet is performed even in the absence of channel errors. Furthermore, the receiver uses received signal envelopes as channel state information, which significantly improves the throughput and bit error rate (BER) performance. Performance of the proposed scheme is analyzed for frequency-flat Rayleigh fading channels with additive white Gaussian noise (AWGN), co-channel interference and random FM noise     

基于降低ISI和ICI的小波分组调制结构的研究

从降低误码率和系统复杂度的角度,探讨了基于降低ISI和ICI的小波分组调制结构的优化方法。首先考虑小波分组调制结构本身对调制信号性能的影响,粗选出具有较小ISI和ICI的结构,然后考虑无线信道对调制信号的影响,利用最小均方误差方法,进一步优选出与信道相匹配的树结构,从而实现小波分组调制结构优化的目的。仿真结果表明,所选择的小波分组树结构更加简单,降低了系统的复杂度,同时提高了小波分组调制系统的抗干扰性能。     

Cross-layer Adaptive Transmission: Optimal Strategies in Fading Channels

We consider cross-layer adaptive transmission for a single-user system with stochastic data traffic and a time- varying wireless channel. The objective is to vary the transmit power and rate according to the buffer and channel conditions so that the system throughput, defined as the long-term average rate of successful data transmission, is maximized, subject to an average transmit power constraint. When adaptation is subject to a fixed bit error rate (BER) requirement, maximizing the system throughput is equivalent to minimizing packet loss due to buffer overflow. When the BER requirement is relaxed, maximizing the system throughput is equivalent to minimizing total packet loss due to buffer overflow and transmission errors. In both cases, we obtain optimal transmission policies through dynamic programming. We identify an interesting structural property of these optimal policies, i.e., for certain correlated fading channel models, the optimal transmit power and rate can increase when the channel gain decreases toward outage. This is in sharp contrast to the water-filling structure of policies that maximize the rate of transmission over fading channels. Numerical results are provided to support the theoretical development.     

BER Analysis of M-QAM with Packet Combining Over Space-Time Block Coded MIMO Fading Channels

We analyze the bit error rate (BER) performance of M-ary quadrature amplitude modulation (M-QAM) when using space-time block coding (STBC) along with packet combining triggered by automatic repeat request (ARQ) retransmission over multiple-input multiple-output (MIMO) fading channels. Specifically, adopting a log-likelihood ratio (LLR) based approach and considering the 16-QAM case of study, we provide an exact formulation for the aggregate LLR distribution in the case the STBC codeword can be transmitted twice, and derive the resulting BER. For higher number of retransmissions, an approximation of the error function is used to derive the LLR distributions and the system's ensuing BER. Considering different values of combined transmissions and M-QAM with possible constellation rearrangement (CoRe), validation of the proposed BER analytical model through simulations and assessment of the advantages of packet combining are provided for transmissions over additive white Gaussian noise (AWGN) channel and orthogonalized MIMO Rayleigh fading channels with different STBC mappings.     

40 Gbit/s packet bit error ratio and loss real-time measurement for ultrahigh-speed packet switched network

A novel packet bit error rate (BER) and loss measurement method and system is proposed. A proposed 40 Gbit/s packet BER and loss measurement system is expressed in detail. A 40 Gbit/s BER and loss measurement with various conditions is demonstrated experimentally. In real time, only the payload part of a packet and burst stream with fluctuated guard time is evaluated. The BER and packet loss of a randomly received packet sequence due to routing and buffering can be also evaluated by the measurement system. A 10 Gbit/s packet BER and loss measurement with optical label switching, buffering, and preamble-free optical packet 3R are demonstrated experimentally.     

Retransmission diversity schemes for multicarrier modulations

In this work, we present some simple techniques for enhancing the diversity provided by retransmissions in OFDM and DMT modulations. The primary techniques of interest are symbol interleaving and mapping diversity for retransmissions. Symbol interleaving involves retransmitting packet symbols through different subcarriers of the same channel, while mapping diversity involves adapting the bit-to-symbol mapping for each retransmission. An analysis of the ability of interleaving to produce lower bit error rates is provided. Also, a discussion of optimally adapting the mappings and their application to OFDM and DMT is presented. Simulation results validate the efficiency of these methods in reducing BER and increasing throughputs.     

Determination of buried channel parameters from IV and CV measurements

A simple, direct method is described for the extraction of the minimum carrier potential vs charge packet size in a buried channel CCD. Also obtainable from this technique is a direct measurement of the location of the top of the charge packet with respect to the silicon surface. Close correlation is found between the results obtained from this technique and the predictions of the step junction depletion layer approximation.     

基于复小波包的MC-CDMA系统及上行链路性能分析

文章在分析多载波扩频码分多址的基础上，利用优化生成的复小波包及变换，研究了一种基于复小波包的多载波CDMA系统在多径瑞利衰落环境下的上行链路性能。仿真结果表明该系统要优于通常的MC-CDMA系统和基于实小波包变换的MC-CDMA系统，具有良好的抗衰落能力。并采用多天线分集接收技术进一步完善系统性能，从而增强了系统抗多径干扰和多址干扰的能力，且得到了更低的误码率。     

T-DMB外码的误码防御策略研究

为了在较差的接收环境下提高T-DMB视频的质量,通过分析不同位置字段差错带来的可能影响,提出了一种在T-DMB视频流RS(204,188)外部编码的基础上,对T-DMB已进行外部编码的视频码流进行非均等错误防御(UEP)的方法.通过在"空闲子信道"上,对视频流中含有Ⅰ帧的TS包进行2次复传,在码率增加小于8 Kbit/s的情况下,可在10-2信道误码率下较好地降低Ⅰ帧差错率.     

Symbol mapping diversity design for multiple packet transmissions

In this paper, we present a simple, but effective method of enhancing and exploiting diversity from multiple packet transmissions in systems that employ nonbinary linear modulations such as phase-shift keying (PSK) and quadrature amplitude modulation (QAM). This diversity improvement results from redesigning the symbol mapping for each packet transmission. By developing a general framework for evaluating the upper bound of the bit error rate (BER) with multiple transmissions, a criterion to obtain optimal symbol mappings is attained. The optimal adaptation scheme reduces to solutions of the well known quadratic assignment problem (QAP). Symbol mapping adaptation only requires a small increase in receiver complexity but provides very substantial BER gains when applied to additive white Gaussian noise (AWGN) and flat-fading channels.     

A reduced complexity channel estimation for OFDM systems withtransmit diversity in mobile wireless channels

A reduced complexity channel estimation for OFDM systems with transmit diversity is proposed by exploiting the correlation of the adjacent subchannel responses. The sizes of the matrix inverse and the FFTs required in the channel estimation at every OFDM data symbol are reduced by half of the existing method for OFDM systems with nonconstant modulus subcarrier symbols or constant modulus subcarrier symbols with some guard tones. The complexity reduction of half FFTs size and some matrix multiplications is still achieved for constant modulus subcarrier symbols with no guard tones. The price for the complexity reduction is a slight BER degradation and for the channels with small relative delay spreads, the BER performance of the reduced complexity method becomes quite comparable to the existing method. An alternative approach for the number of significant taps required in the channel estimation is described which achieves a comparable performance to the case with the known suitable number of significant taps. A simple modification which reduces the lost leakage of the nonsample-spaced channel paths is also proposed. This modification achieves a substantial performance improvement over the existing method without any added complexity     

Evaluation of bit error rate for packet combining with constellation rearrangement

In this paper, we propose a method for evaluation of the bit error rate (BER) for packet combining based on constellation rearrangement (CoRe). Such mapping diversity scheme, adopted in the high speed downlink packet access (HSDPA), uses Gray‐mapped constellations and is based on suboptimal accumulation of the reliability metrics generated in each of the transmissions. We present an exact model for the logarithmic likelihood ratios (LLR) obtained by means of the so‐called max‐log approximation, and we show that their conditional probability density functions (pdf) are piecewise Gaussian. We then present the derivation of the uncoded BER and illustrate it with simulation results that confirm our formulation. Finally, we propose simplifications which significantly reduce the complexity of the evaluation method and provide results with a very good accuracy; an extension to transmissions over faded channel is also presented. Copyright © 2007 John Wiley & Sons, Ltd.     

On the general BER expression of one- and two-dimensional amplitude modulations

Quadrature amplitude modulation (QAM) is an attractive technique to achieve high rate transmission without increasing the bandwidth. A great deal of attention has been devoted to the study of bit error rate (BER) performance of QAM, and approximate expressions for the bit error probability of QAM have been developed in many places in the literature. However, the exact and general BER expression of QAM with an arbitrary constellation size has not been derived yet. We provide an exact and general closed-form expression of the BER for one-dimensional and two-dimensional amplitude modulations, i.e., PAM and QAM, under an additive white Gaussian noise (AWGN) channel when Gray code bit mapping is employed. The provided BER expressions offer a convenient way to evaluate the performance of PAM and QAM systems for various cases of practical interest. Moreover, simple approximations can be found from our expressions, which are the same as the well-known approximations, if only the dominant terms are considered.     

自适应比特分配算法在高速遥测系统中的应用

提出了一种简单、快速的正交频分复用(OFDM)系统的自适应调制算法。该算法在子信道分配已经完成的前提下,通过信道参数的估计,动态地分配子信道上的比特和功率,使得发送的每个符号的总比特数最大,从而提高信道的利用率及数据传输速率,满足了高速遥测系统所要求的传输速率及误码率。仿真结果表明,与等比特分配算法相比,本自适应比特分配算法相对简单,降低了系统的传输功率,其误码率性能明显好于等比特分配算法。     

Hybrid DS/SFH-SSMA with predetection diversity and coding overindoor radio multipath Rician-fading channels

The authors investigate the bit-error-rate (BER) performance of hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access (DS/SFH-SSMA) systems operating over a multipath Rician-fading channel (which models indoor radio propagation in factories). They consider both phase-shift-keying (PSK) modulation with coherent demodulation and differential phase-shift-keying (DPSK) modulation with noncoherent demodulation. Predetection multipath diversity (maximal ratio combining for coherent reception and equal gain combining for noncoherent reception) and simple interleaved channel coding are employed for improving the BER performance. The BER of both coherent and noncoherent hybrid systems is obtained using a Gaussian interference approximation     

Nonselective Fading Channel Estimation with Nonuniformly Spaced Pilot Symbols

Recently, there has been great demand for multimedia and data communications in mobile communication systems. In order to enhance voice quality and increase packet data throughput rate for the existing mobile systems and the next generation mobile systems, a number of new standards are being developed. 8-PSK/QPSK modulation has been adopted by most of these standards as one of the modulation schemes, and nonuniformly spaced pilot symbols are employed in slot structures to have successful demodulation. In this paper, an accurate and computationally efficient method is presented for estimating nondispersive channel fading with non-uniformly spaced pilot symbols. By employing a least-squares method with time-variant complex-valued coefficient polynomials, it is proven that nonselective channel fading of each slot can be estimated by the product of a constant matrix and the fading at pilot symbol locations of the slot. The constant matrix is further optimized by least-squares off-line training method provided by this paper. Using the estimated fading process, the fading on the data symbols can be removed by using the estimated amplitude and phase of the fading as the reference, greatly improving the BER. Closed form results for the BER of coherent 8-PSK are included in this paper as well. Simulation results indicate that our method provides BER performance very close to the analytic BER result.