In this paper we review the most peculiar and interesting information-theoretic and communications features of fading channels. We first describe the statistical models of fading channels which are frequently used in the analysis and design of communication systems. Next, we focus on the information theory of fading channels, by emphasizing capacity as the most important performance measure. Both single-user and multiuser transmission are examined. Further, we describe how the structure of fading channels impacts code design, and finally overview equalization of fading multipath channels.

Abstract The Finite-State Markov Channel (FSMC) is a discrete-time varying channel whose variation is determined by a finite-state Markov process. These channels have memory due to the Markov channel variation. We obtain the FSMC capacity as a function of the conditional channel state probability. We also show that for i.i.d. channel inputs, this conditional probability converges weakly, and the channel's mutual information is then a closed-form continuous function of the input distribution. We next consider coding for FSMCs. In general, the complexity of maximum-likelihood decoding grows exponentially with the channel memory length. Therefore, in practice, interleaving and memoryless channel codes are used. This technique results in some performance loss relative to the inherent capacity of channels with memory. We propose a maximum-likelihood decisionfeedback decoder with complexity that is independent of the channel memory. We calculate the capacity and cutoff rate of our technique, and show that it preserves the capacity of certain FSMCs. We also compare the performance of the decision-feedback decoder with that of interleaving and memoryless channel coding on a fading channel with 4PSK modulation.

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We consider the design of power-adaptive systems for minimizing the average bit-error-rate over flat fading channels. Channel state information, obtained through estimation at the receiver, is sent to the transmitter over a feedback channel, where it is used to optimally adapt the transmit power. We consider finite-state optimal policies to reflect the limitations of the feedback channel. We develop an iterative algorithm that determines the optimal finite-state power control policy given the probability density function of the fading. Next, we present a discretized formulation of the problem and obtain a suboptimal solution via standard dynamic programming techniques. The discretization of the problem enables us to obtain a suboptimal policy for arbitrary fading channels for which the analytic expression of the fading probability density function is not available. Simulation results are used to draw conclusions regarding the effects of limited feedback channel capacity, delay and numb...

Abstract—In this paper, an analytical model for studying the performance behaviors of wireless application protocol (WAP) over wireless links is proposed. A Rayleigh fading channel model is used to characterize the behaviors of wireless channel. Mathematical expressions that represent the performance of WAP as a function of the protocol and the channel parameters are derived. Computer simulation results are presented to validate the analytical results. It is shown that WAP performs better in a bursty error environment than in a random error environment. The goodput of WAP can be improved by increasing the WAP packet group size, but the significance of the improvement depends on the underlying channel condition. Index Terms—Markov channel model, performance analysis, Rayleigh fading channel, wireless application protocol. 1

Recent initiatives to add mobility to the Internet and packet data services in third-generation (3G) cellular systems are being considered as candidate solutions for the delivery of IP data to mobile users. Transport Control Protocol (TCP) will continue to be the most widely used transport protocol for a certain duration in 3G cellular Internet networks. Initially designed for high-speed wireline networks where random packet loss can be negligible, TCP can yield a significant throughput deterioration when applied to lossy links without modification since the primary cause of packet loss may not be network congestion. Two new types of loss can dominate TCP's performance: one is dropped packets because of route disconnection from frequent handoffs

Interest in ad hoc networks has been significantly increased over the past few years. The IEEE 802.11 standard is the most mature technology for Wireless Local Area Networks (WLANs) and thus widely adopted as a Medium Access Control (MAC) mechanism in ad hoc networks. However, the research on the performance of ad hoc networks under Rayleigh fading channel is still at its early age. Some work have indicated that the network performance could be badly affected by Rayleigh fading channel [1]. In addition, the behavior of IEEE 802.11 standard equipped mobile nodes in a Rayleigh fading environment requires further thorough studies. In this paper, we identify the causes for the network performance degradation under Rayleigh fading channel. We then employ the predictability of Rayleigh fading channel to propose a new cross-layer design approach which improves the network throughput, decreases the unnecessary packet transmission, thus saving power and bandwidth resource, and reduces the packet loss due to network contention under IEEE 802.11 MAC. In addition, we also propose a Markovian model to study the dynamics of Rayleigh channel and then extend the existing Markov models for IEEE 802.11 to analyze the theoretical network throughput, packet processing rate, packet loss probability and delay under under Rayleigh channel in details. The simulation of the new cross-layer-design approach is carried out and shows an increase in network throughput, decrease in unnecessary packet retransmission and reduction in packet loss due to network contention. We also present our analytical results and confirm them by simulation.

Diverse methods that have been proposed to model Rayleigh fading channels will be explored in this tutorial. Preliminary concepts related to wireless communications channel modeling are identified before introducing the models. The first model presented is the finite state Markov channel model which is based on the side information given by the received signal to noise ratio. The Markovian validity of the model is described along with the adequate conditions under which such validity holds. The relationships between the model and modulation schemes, error control protocols and channel coding are also described. Additionally hidden Markov models proposed to model Rayleigh fading channels are also studied along with their validity assumptions. 1.