Frequency-domain equalisation for optical transmission systems

The first optical single-carrier (SC) transmission system to employ frequency-domain equalisation (FDE) is proposed; 25 Gbit/s SC with FDE is demonstrated in severe chromatic dispersion conditions. The results show that SC with FDE is very tolerant of the chromatic dispersion.     

Error recovery for ATM transmission over wireless channels

The authors present a technique for efficient recovery from transmission errors to be used when transmitting ATM-like data packets in a wireless channel affected by bursty errors (jamming). Issues related to packet format error protection code structure and retransmission protocol are discussed and simulation results are shown that prove the effectiveness of the proposed approach     

Rate-adaptive transmission over correlated fading channels

In this paper, we investigate link adaptation and incremental redundancy (IR) retransmission schemes over correlated wireless channels. While computer simulations have been used to study the performance of these techniques, a numerically tractable analytical approach is more desirable to analyze generic protocols, and to reveal insights into the performance tradeoffs. An error-recursion approach is developed in this paper to mathematically analyze the throughput, delay, and energy efficiency of rate-adaptation techniques over fading channels with arbitrary correlations between retransmissions. Using Reed-Solomon codes as an example, we quantitatively predict the performance tradeoff of throughput and latency for IR schemes and the performance dependency on the channel correlation. Numerical results also show that reactive rate-adaptation schemes with IR retransmission outperform proactive rate-adaptive schemes, even with perfect channel side information, in terms of throughput and energy efficiency.     

Rate control for robust video transmission over burst-errorwireless channels

We study the problem of rate control for transmission of video over burst-error wireless channels, i.e., channels such that errors tend to occur in clusters during fading periods. In particular we consider a scenario consisting of packet based transmission with automatic repeat request (ARQ) error control and a back channel. We start by showing how the delay constraints in real time video transmission can be translated into rate constraints at the encoder, where the applicable rate constraints at a given time depend on future channel rates. With the acknowledgments received through the back channel we have an estimate of the current channel state. This information, combined with an a priori model of the channel, allows us to statistically model the future channel rates. Thus the rate constraints at the encoder can be expressed in terms of the expected channel behavior. We can then formalize a rate distortion optimization problem, namely, that of assigning quantizers to each of the video blocks stored in the encoder buffer such that the quality of the received video is maximized. This requires that the rate constraints be included in the optimization, since violating a rate constraint is equivalent to violating a delay constraint and thus results in losing a video block. We formalize two possible approaches. The first one seeks to minimize the distortion for the expected rate constraints given the channel model and current observation. The second approach seeks to allocate bits so as to minimize the expected distortion for the given model. We use both dynamic programming and Lagrangian optimization approaches to solve these problems. Our simulation results demonstrate that both the video distortion at the decoder and packet loss rate can be significantly reduced when incorporating the channel information provided by the feedback channel and the a priori model into the rate control algorithm     

Pulse templates for transmission over an ensemble of channels

A method is given for finding the envelope of a family of pulses whose shapes are determined by a finite number of parameters. In addition, it is assumed that the parameters are analytically constrained collectively. In the second part of the paper, a family of pulse shapes is determined that can be efficiently transmitted through a channel that is selected at random from an ensemble of channels. The pulse envelope theory of the first part of the paper is then applied using this family of pulses to determine the envelope of mean-square channel outputs of the family of pulses that provide relatively low loss through an ensemble of channels     

Guard sequence optimization for block transmission over linearfrequency-selective channels

We show that the optimum length-ν guard sequence for block transmission over a linear Gaussian-noise dispersive channel with memory ν is a linear combination of the N information symbols of the block. A closed-form expression for the optimum guard sequence is derived subject to a total average energy constraint on the information and guard symbols. The achievable channel block throughput with the optimum guard sequence is compared with that achievable with two common guard sequence types, namely zero stuffing and cyclic prefix     

Blind CM equalisation for STBC over multipath fading

This Letter focuses on the development of a blind adaptive receiver for space-time block coding (STBC) over multipath fading. The constant modulus (CM) criterion is utilised on the received signals, whereby an orthogonality constraint of the transmitted STBC signals prevents the multiple extractions of the same source. Simulation results demonstrate the performance of the proposed algorithm in a fading channel.     

Adaptive non-linear equalisation of digital communications channels

Non-linear distortion introduced by communications channels increases the probability of error. In this paper, an adaptive non-linear canceller is presented which attempts to remove non-linear interference from the output of a feedforward or decision feedback equaliser, improving the error rate. It may be implemented using a memory look-up table architecture, making it suitable for high speed real time operation.     

Digital data transmission over nonlinear satellite channels

The M-ary PSK system over nonlinear satellite channels, in the presence of an arbitrary number of interferers and additive Gaussian noise on the uplink and downlink paths, is investigated. The effect of intersymbol interference due to the transmitter filter is also included. The bit error probabilities are obtained using the Gauss quadrature formula and a two-dimensional moment technique     

Packet data transmission over mobile radio channels

Since in mobile radio Rayleigh fading poses the main threat to accurate data transmission, a mathematical model of the dynamics of Rayleigh fading is used to explore the optimum duration of data packets. The performance criterion is the rate of information transfer through the mobile radio channel. In addition to packet size, the information rate depends on: the speed of the mobile terminal, the channel bit rate, the size of the packet header, and the fade margin of the modulation and coding techniques. In particular, attention is focused on line rates of 16 kb/s and 256 kb/s (which are representative of the rates proposed for digital mobile radio systems in North America and Europe, respectively). At 16 kb/s, the optimum packet size is approximately 17 B (8.5-ms duration). At 256 kb/s, maximum throughput occurs when the packet contains about 48 B (1.5-ms duration). The precise optimum depends on vehicle speed, header size, and fade margin. The optimum packets are considerably shorter than the 125-B packets customarily used in terrestrial and satellite systems     

Pilot-aided chip-interleaved DS-CDMA transmission over time-varying channels

Time-varying multipath fading associated with the wireless link limits the capacity of a wireless system. In order to adapt to this adverse radio environment efficiently, we investigate the use of a pilot-aided fade-resistant transmission scheme for the uplink of a chip-interleaved code-division multiple-access (CDMA) system. We analyze the tradeoff between the number of diversity branches and the channel estimation error. We derive the optimum ratio of pilot signal energy to information signal energy. Our numerical study indicates that the proposed system is capable of outperforming the conventional CDMA system depending on the transmitter energy and channel condition.     

Identification plus transmission over channels with perfectfeedback

We determine the region of all identification and transmission rate-pairs achievable over a discrete memoryless channel (DMC) with perfect and instantaneous feedback, for both randomized and deterministic encoding. As a by-product, we also have a new proof of Kemperman's (1973) strong converse to Shannon's coding theorem for DMC's with feedback     

Video image transmission over mobile satellite channels

This paper addresses the transmission of low bit-rate video image sequences through mobile satellite channels to provide portable communications services to remote areas. The particularly challenging aspects of this transmission channel include (1) rapid fading and log-normal shadowing, (2) low signal-to-noise ratio (SNR) due to the noise-limited channel, (3) the satellite's geostationary orbit which incurs a large 250 ms roundtrip propagation delay, (4) limited existing bandwidth near 2 GHz; the video service is to overlay existing Mobile Satellite (MSAT) voice service using a minimum number of 6 kHz (analog bandwidth) channels, and (5) the use of travelling-wave-tube amplifiers which preclude the bandwidth-efficient quadrature amplitude modulation (QAM) proposed for terrestrial high-definition TV (HDTV) broadcast. In the proposed concatenated system, the inner codec is compatible with both voice as well as future-oriented error-resilient, scalable video compression schemes. The key issues are the joint design of on-line channel estimation, soft-decision decoding, trellis-coded modulation (TCM), interleaving depths, and error correcting codes. We have shown through end-to-end bit-level simulation, that highly reliable transmission of 24 and 64 kbps video (H.263) can be realized at 15 and 40.5 kBd, respectively, with low delay, power and modest overall system complexity.     

Analysis of video transmission over lossy channels

A theoretical analysis of the overall mean squared error (MSE) in hybrid video coding is presented for the case of error prone transmission. Our model covers the complete transmission system including the rate-distortion performance of the video encoder, forward error correction, interleaving, and the effect of error concealment and interframe error propagation at the video decoder. The channel model used is a 2-state Markov model describing burst errors on the symbol level. Reed-Solomon codes are used for forward error correction. Extensive simulation results using an H.263 video codec are provided for verification. Using the model, the optimal tradeoff between INTRA and INTER coding as well as the optimal channel code rate can be determined for given channel parameters by minimizing the expected MSE at the decoder. The main focus of this paper is to show the accuracy of the derived analytical model and its applicability to the analysis and optimization of an entire video transmission system     

Cooperative diversity performance for OFDM transmission over partially jammed channels

Cooperative diversity is a transmission technique, where multiple terminals share their resources to form a virtual antenna array that realizes spatial diversity gain in a distributed fashion. In this paper, we focus on a performance evaluation for orthogonal frequency division multiplexing (OFDM) transmission in cooperative networks under partial-band jamming (PBJ) environments. We present a bit error rate (BER) analysis for a cooperative diversity system with amplifying-and-forward (AF) relays over partially jammed Rayleigh fading channels. In addition, a simple jamming mitigation technique, called relay-based sub-band shifting method, is proposed. Through this approach, each sub-band of the amplified OFDM symbol at the relay can be changed by the predefined shifting rule of each relay, and the jamming effects at the destination are partially removed. Simulation results show that the proposed method improves significantly the BER performance at a low signal-to-jamming ratio.     

一种抗误码能力强的无线信道图像传输方案

本文提出一种新的综合源编码和信道编码的无线信道图像传输方案，对子波变换后各个子带采用基于统计特性的变系数定长（VCFL）编码，数据经过Reed-Solomon编码后选择不同码率的码率兼容删除卷积码（RCPC）编码以提供不同程度的差错保护（UEP），最后数据经交织后传输。在给定传输的总比特数的情况下，通过优化算法使总体失真最小。模拟结果表明新方案在无线衰落信道上表现出良好的性能。     

A novel receiver architecture for single-carrier transmission over time-varying channels

In this paper, we present a single-carrier transceiver for rapidly time-varying channels, where the equalization step is implemented in the frequency domain. When the channel abides with both fast fading and severe inter-block interference, our equalizer relies on a band approximation of the frequency-domain channel matrix to maintain low complexity. We will show that the band approximation error can be associated in the time domain to a critically-sampled complex exponential basis expansion modeling error. Based on this property, we propose a novel receiver architecture that extends the original data model by inserting zeros at the receiver. The resulting effective channel can be characterized by an oversampled complex exponential basis expansion model, which has a considerably reduced modeling error compared to the critically-sampled one. In other words, the band assumption that is essential to the equalizer will be made more accurate and thus the equalization performance can be improved.     

Hierarchical constellation for multi-resolution data transmission over block fading channels

We propose a new technique for multi-resolution video/image data transmission over block fading channels. The proposed scheme uses an adaptive scheduling protocol employing a retransmission strategy in conjunction with a hierarchical signal constellation (known also as nonuniform, asymmetric, multi-resolution constellation) to give different transmission priorities to different resolution levels. Transmission priorities are given in terms of average packet loss rate as well as average throughput. Basically, according to the transmission scheduling and channel state (acknowledgment signal) of the previous transmission, it dynamically selects packets from different resolution levels to transmit for the current transmission. The bits from the selected packets are assigned to different hierarchies of a hierarchical 4/16-quadrature amplitude modulation to transmit them with different error protections. The selection of packets for transmission and the assignment of these selected packets to different hierarchies of the hierarchical constellation are referred to as the scheduling protocol in our proposed scheme. We model this protocol by a finite state first order Markov chain and obtain the packet loss rate and the packet transmission rate over Nakagami-m block fading channel in closed-form. Some selected numerical results show that the proposed scheme can control the relative packet loss rate and the packet transmission rate of different resolution levels by varying the priority parameter (or equivalently, the asymmetry) of the hierarchical constellation and the maximum number of allowed retransmissions.     

Error protection for progressive image transmission over memorylessand fading channels

Product channel codes are proposed to protect progressively compressed and packetized images for noisy channels. Within packets, the product code uses the concatenation of a rate-compatible punctured convolutional code and an error detecting parity check code. Across packets, Reed-Solomon codes are used. Benefits include flexible choice of delay, adaptability of error protection level (i.e., unequal error protection), and scalable decoding complexity. The system outperforms the best known image coders for memoryless channels and performs well on fading channels     

Adaptive equalisation for DECT systems operating in low time-dispersive channels

DECT (digital European cordless telecommunication) is the current standard for cordless indoor communication in Europe. In this work the authors present a scheme to increase the coverage area of DECT links in multipath propagation by the application of channel equalisation. The equaliser is a decision feedback equaliser using a recursive least squares algorithm for adaptation. As a training sequence for the equaliser, the standardised packet synchronising word of the DECT TDMA slots is used.<>