Fast Flat Fading Channels Research Articles

Cubic interpolation based channel estimator for rectangular M-QAM

This paper propose a Pilot Symbol Assisted Modulation (PSAM) channel estimation and compensation technique for rectangular M-QAM based on Cubic interpolation in order to determine the channel state information (CSI) over flat Rayleigh fading channels. The proposed Cubic channel estimator technique is based on sliding window approach and pilot symbol estimates adjustment in order to reduce its computational time complexity. The Cubic estimator is combined with the Koetter and Vardy (KV) Reed-Solomon (RS) decoder to test its performance. The simulation results show that the Cubic interpolation gives the same performance as the Linear, and Sinc interpolators over slow flat Rayleigh fading channel; however, it achieves significant performance improvement of +1.0dB in symbol error rate (SER) over fast flat Rayleigh fading channel.

Game Theoretic Distributed Power Control Algorithms for Uplink Wireless Data in Flat Fading Channels

<p>In this paper we present a game-theoretic power control algorithms for wireless data in CDMA cellular systems under two realistic channels: (a1) Fast flat fading channel and (a2) Slow flat fading channel. The fading coefficients under both (a1) and (a2) are studied for three appropriate small scale channel models that are used in the CDMA cellular systems: Rayleigh channel, Rician channel and Nakagami channel. This work is inspired by the results presented by [1] under nonfading channels. In other words, we study the impact of the realistic channel models on the findings in [1] through the followings: we evaluate the average utility function, the average number of bits received correctly at the receiver per one Joule expended, for each channel model. Then, using the average utility function we study the existence, uniqueness of Nash equilibrium (NE) if it exists, and the social desirability of NE in the Pareto sense. Results show that in a non-cooperative game (NPG) the best policy for all users in the cell is to target a fixed signal-to-interference and noise ratio (SINR) similar to what was shown in [1] for non-fading channel. The difference however is that the target SINR in fading channels is much higher than that in a non-fading channel. Also, for spreading gain less than or equal to 100, both NPG and non-cooperative power control game with pricing (NPGP) perform poorly, where all the terminals except the nearest one were not able to attain their corresponding minimum SINR even if sending at the maximum powers in their strategy spaces.</p>

Game-Theoretic Approach for Primary-Secondary User Power Control Under Fast Flat Fading Channels

Power control is an important concern in cognitive radio networks in which secondary users compete to access spectrum allocated to primary users. However, most existing studies have ignored the impact of primary users and only considered the interactions between secondary users. Hence in this study a realistic primary-secondary game-theoretic scheme is proposed in which primary users are rewarded for sharing their spectrum. The proposed model is analyzed for Rician and Rayleigh fast flat fading channels. In addition, closed-form expressions are also derived for the average utility functions and the existence of a unique Nash equilibrium is also shown. Finally, detailed simulation results are presented to verify the realistic performance of the scheme under those new channel conditions.

BER analysis of space–time diversity in CDMA systems over frequency-selective fading channels

The performance of direct-sequence code division multiple access (DS-CDMA) using space-time spreading system, over frequency-selective fading channels, is investigated. The underlying transmit diversity scheme, previously introduced in the literature, is based on two transmit and one receive antenna. It was shown that when employed in flat fast-fading channels, the received signal quality can be improved by utilising the spatial and temporal diversities at the receiver side. We study the problem of multiuser interference in asynchronous CDMA systems that employ transmit/receive diversity using space-time spreading. To overcome the effects of interference, a decorrelator detector is used at the base station. Considering binary phase-shift keying transmission, we analyse the system performance in terms of its probability of bit error. In particular, we derive the probability of error over frequency-selective Rayleigh fading channels for both fast and slow-fading channels. For the fast-fading channel, both simulations and analytical results show that the full system diversity is achieved. On the other hand, when considering a slow-fading channel, we show that the scheme reduces to conventional space-time spreading schemes where the diversity order is half of that of fast-fading.

Finite-state Markov modeling of fading channels - a survey of principles and applications

This article's goal is to provide an in-depth understanding of the principles of FSMC modeling of fading channels with its applications in wireless communication systems. While the emphasis is on frequency nonselective or flat-fading channels, this understanding will be useful for future generalizations of FSMC models for frequency-selective fading channels. The target audience of this article include both theory- and practice-oriented researchers who would like to design accurate channel models for evaluating the performance of wireless communication systems in the physical or media access control layers, or those who would like to develop more efficient and reliable transceivers that take advantage of the inherent memory in fading channels. Both FSMC models and flat-fading channels will be formally introduced. FSMC models are particulary suitable to represent and estimate the relatively fast flat-fading channel gain in each subcarrier.

Delayed two-streams division, a diversity technique to improve signal transmission in relatively fast flat fading channels

We consider in this paper a combination of data symbols that serves to provide time diversity and to reduce flat fading effect at receiver, when no other source of diversity is available. This technique, called delayed two-streams division (D2SD), is particularly interesting in relatively fast fading channels. By D2SD, the stream of the data symbols is divided into two substreams, the symbols of which are mixed pairwise together, and transmitted through the channel by a sufficiently long time delay between each pair. At receiver, a simple detector based on maximum likelihood criterion is used to “equalize” the symbol combination made at transmitter. The presented results show that with the negligible complexity added to the system, and while implying no loss in the spectral efficiency nor any increase in the transmit power, D2SD permits to obtain a considerable improvement in the receiver performance. Selection of the design parameters of D2SD is discussed for different cases of fading statistics, based on the bit error probability criterion.

Soft decision-directed map estimate of fast rayleigh flat fading channels

An iterative receiver with soft-decision feedback is derived by using the expectation-maximization algorithm for maximum a posteriori estimate of fast Rayleigh flat fading channels. Simulation results indicate that in a fast fading environment, the derived receiver can perform better than an iterative receiver with hard-decision feedback.

Differential space–time modulation for DS‐CDMA systems

AbstractDifferential space–time modulation (DSTM) schemes were recently proposed to fully exploit the transmit and receive antenna diversities without the need for channel state information. DSTM is attractive in fast flat fading channels since accurate channel estimation is difficult to achieve. In this paper, we propose a new modulation scheme to improve the performance of DS‐CDMA systems in fast time‐dispersive fading channels. This scheme is referred to as the differential space–time modulation for DS‐CDMA (DST‐CDMA) systems. The new modulation and demodulation schemes are especially studied for the fast fading down‐link transmission in DS‐CDMA systems employing multiple transmit antennas and one receive antenna. We present three demodulation schemes, referred to as the differential space–time Rake (DSTR) receiver, differential space–time deterministic (DSTD) receiver, and differential space–time deterministic de‐prefix (DSTDD) receiver, respectively. The DSTD receiver exploits the known information of the spreading sequences and their delayed paths deterministically besides the Rake‐type combination; consequently, it can outperform the DSTR receiver, which employs the Rake‐type combination only, especially for moderate‐to‐high SNR. The DSTDD receiver avoids the effect of intersymbol interference and hence can offer better performance than the DSTD receiver. Copyright © 2001 John Wiley & Sons, Ltd.

Waveforms for fast fading channels

A technique is presented to design a binary digital transmission system for frequency flat fast fading channels. The author shows that it is possible to design good transmission systems for fast fading channels, with the aid of the Karhunen-Loeve expansion of the fading process, the optimum receiver is noncoherent, very simple, and no error floor exists due to fast fading. A simpler suboptimum detector can be considered which gives comparable results. Using a simple example, the author showed that the higher the fading rate, the lower the error probability (implicit time diversity), although this involves a higher receiver complexity and transmitted signal bandwidth.

Incremental frequency, amplitude and phase tracker (IFAPT) for coherent demodulation over fast flat fading channels

The incremental frequency amplitude and phase tracker (IFAPT) is a recursive algorithm that estimates the parameters of piecewise-linear approximation to assumed continuous narrow-band signals. The parameters are amplitude, phase, and their respective slopes. The simple, recursive nature of IFAPT enables its direct interaction with recursive algorithms, such as the Viterbi and the BCJR in the APP SISO module, used for iteratively decoding concatenated codes. An augmented APP (A/sup 2/P/sup 2/)-module, containing IFAPT and BCJR algorithms, is here applied to iterative decoding serial concatenated convolutional codes under Rayleigh fading conditions with diversity reception. The bit-error rate under Rayleigh fading with dual diversity reception at E/sub bT//N/sub 0/=6 dB and f/sub d/T/sub s/=10/sup -2/ is 10/sup -4/, where E/sub bT/ is the total mean energy per bit in both diversity branches, f/sub d/ is the Doppler frequency, and T/sub s/ the symbol time.

Symbol timing tracking for continuous phase modulation over fast flat-fading channels

The symbol timing tracking problem for a class of continuous phase modulation (CPM) schemes transmitted over unfaded and fast flat-fading channels is studied. The specific family of CPM considered is that of M-ary continuous-phase modulation with a modulation index of h=1/M. A particular symbol synchronizer structure that constructs a tone at the symbol frequency by passing the received signal through an Mth power law nonlinearity and multiband filter followed by a squared-envelope nonlinearity and narrowband filter is proposed. The operation and parameters of this symbol synchronizer are discussed as well as the performance of the synchronizer. Simulation results giving the root-mean-square timing jitter of this system for several binary, quaternary and 8-ary instances of modulation using rectangular, raised-cosine, truncated Nyquist III, and truncated tamed FM pulse shapes are presented to illustrate the synchronizer performance. >