The impact of Rayleigh fading on packet loss in FEC-protected real-time packet-based transmission systems

This contribution deals with the transmission of video packets over a wireless link subject to slow Rayleigh fading. In order to provide protection against transmission errors and video packet erasures, we apply forward error correction (FEC) both on the physical layer and the packet layer, which involves the transmission of parity bits and parity packets that enable to recover a number of bit errors and packet erasures. We present an expression for the diversity gain provided, in terms of the fading coherence time, the allowable latency, and the allowable transmission overhead

Application layer ARQ for protecting video packets over an indoor MIMO-OFDM link with correlated block fading

The quality of experience (QoE) of IP-packetized streaming video is affected by both packet loss and packet delay variations. When the network delivering the video content contains a wireless link, occasional deep fades give rise to bursts of packet losses. In order to maintain a sufficient video QoE at the end user, video packets must be protected against losses by means of a suitable form of error control. In this contribution, we consider an indoor radio MIMO-OFDM transceiver operating over a Rayleigh block-fading channel with arbitrary correlation in the time and frequency dimensions, which makes use of an application layer Automatic Repeat reQuest (ARQ) protocol to provide additional protection of the video content against packet loss. We analyze the resulting residual packet loss performance, under a latency constraint imposed by the requirement of a small TV channel switching delay. This analysis makes direct use of the fading characterization (correlation functions in time and frequency dimensions) of the indoor environment, rather than relying on a Markov model that only approximately describes the packet loss process. Numerical results are obtained by Monte Carlo integration combined with an efficient importance sampling technique devised for the problem at hand. Assuming a 2.4 GHz wireless link, we point out how to select the system parameters (number of antennas, number of retransmissions) in order to achieve a residual packet loss performance yielding a satisfactory QoE for HDTV transmission

Comparison of error-control schemes for high-rate communication over short DSL loops affected by impulsive noise

We consider Discrete Multitone Transmission over short Digital Subscriber Lines using bandwidths applicable to G.fast, in the presence of impulsive noise. Various combinations of coding and retransmission schemes are compared in terms of bit error ratio performance and error-free information bitrate (goodput). Our study shows that, under an error performance constraint, retransmission schemes allow to achieve larger good-put with smaller latency as compared to the traditional combination of Reed-Solomon coding and Trellis Coded Modulation with a large interleaver in between

Protection of Video Packets over a Wireless Rayleigh Fading Link: FEC versus ARQ

Video content can be provided to an end user by transmitting video data as a sequence of internet protocol (IP) packets over the network. When the network contains a wireless link, packet erasures occur because of occasional deep fades. In order to maintain a sufficient video quality at the end user, video packets must be protected against erasures by means of a suitable form of error control. In this contribution, we investigate two types of error control: (1) forward error correction (FEC), which involves the transmission of parity packets that enables recovery of a limited number of erased video packets, and (2) the use of an automatic repeat request (ARQ) protocol, where the receiver requests the retransmission of video packets that have been erased. We point out that FEC and ARQ considerably reduce the probability of unrecoverable packet loss, because both error control techniques provide a diversity gain, as compared to the case where no protection against erasures is applied. We derive a simple analytical expression for the diversity gain resulting from FEC or ARQ, in terms of the channel coherence time, the allowable latency, and (for FEC) the allowable overhead or (for ARQ) the time interval between (re)transmissions of copies of a same packet. In the case of HDTV transmission over a 60 GHz indoor wireless link, ARQ happens to outperform FEC

Semi-analytical evaluation of concatenated RS/LDPC coding performance with finite block interleaving against impulsive noise

This contribution considers the word error rate (WER) performance of a concatenated coding scheme in the presence of impulsive noise (IN), which is modeled as gated white Gaussian noise, with on-and off-times governed by a 2-state Markov model. The scheme consists of a Reed-Solomon (RS) outer code and a low-density parity-check (LDPC) inner code, which are separated by a block interleaver with finite depth. The Monte Carlo (MC) simulation of the WER of such communication systems is time-consuming, especially when targeting low error rates and examining several interleaver settings. We present a semi-analytical evaluation of the WER, which relies on a simple semi-analytical statistical model for the number of byte errors in a segment of the information word after LDPC decoding. To compute the error performance of the concatenated code corresponding to different parameters of the RS code and the interleaver, we require only the WER and byte error rate (ByteER) of the inner subsystem, determined by the LDPC code and the considered constellation, in the presence of stationary white noise. We show that the semi-analytical WER of the concatenated system closely matches the WER resulting from MC simulations and use the proposed model to investigate the effect of the interleaver depth on the WER performance

Novel bitloading algorithms for coded G.fast DSL transmission with linear and nonlinear precoding

Precoding is a technique that counteracts the crosstalk in downlink digital subscriber line (DSL) transmission. While linear precoding is adequate in the VDSL2 technology because of the moderate crosstalk environment, this might no longer be the case in the G.fast technology, which uses higher frequencies and therefore is affected by higher crosstalk levels. In this contribution we compare linear and nonlinear precoding for G.fast transmission protected by trellis-coded modulation, and present two bitloading algorithms that are suited for both precoding schemes. We show that for a set of measured broadband channels, each representing a binder of eight twisted-pair cables, these bitloading algorithms have substantially different complexities but yield a similar information bitrate, which is about 10% higher for nonlinear precoding as compared to linear precoding