Abstract not found

In this paper, we investigate the behavior of block errors which arise in data transmission on fading channels. Our approach takes into account the details of the specific coding/modulation scheme and tracks the fading process symbol by symbol. It is shown that a Markov approximation for the block error process (possibly degenerating into an iid process for sufficiently fast fading) is a good model for a broad range of parameters. Also, it is observed that the relationship between the marginal error rate and the transition probability is largely insensitive to parameters such as block length, degree of forward error correction and modulation format, and depends essentially on an appropriately normalized version of the Doppler frequency. This relationship can therefore be computed in the simple case of a threshold model and then used more generally as an accurate approximation. This observation leads to a unified approach for the channel modeling, and to a simplified performance analysi...

system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission of the author.

Abstract — Hidden Markov models (HMM’s) are a powerful tool for modeling stochastic random processes. They are general enough to model with high accuracy a large variety of processes and are relatively simple allowing us to compute analytically many important parameters of the process which are very difficult to calculate for other models (such as complex Gaussian processes). Another advantage of using HMM’s is the existence of powerful algorithms for fitting them to experimental data and approximating other processes. In this paper, we demonstrate that communication channel fading can be accurately modeled by HMM’s, and we find closed-form solutions for the probability distribution of fade duration and the number of level crossings. Index Terms — Fading channels, hidden Markov models, parameter estimation.

In local wireless communications, retransmission techniques to recover from channel errors are a feasible solution, which in some instances may be more efficient than forward error correction. In this paper, we compare the performance of BCH block codes and pure ARQ when a continuous stream of bits is to be transmitted across a bursterror channel. The presence of a delay constraint is considered, which causes degraded BCH error-correction performance (due to non-ideal interleaving) and block dropping in ARQ (due to retransmission delay). In most cases, for practical values of the parameters, better performance is achieved by ARQ schemes. I. INTRODUCTION Packet-switching communications schemes will likely be the basis for the next generation of wireless systems. This will increase the degree of flexibility in managing the traffic, and will open up new opportunities. In particular, communications techniques which have been developed in the circuit-switching environment do not necessari...

Bluetooth is an emerging technology for constructing adhoc wireless Personal Area Networks (WPANs). In this paper we analyze an innovative scheduling algorithm for asynchronous data traffic specifically tailored to the Bluetooth characteristic. This algorithm, named Efficient Double-Cycle (EDC), dynamically adapts the polling frequency to the traffic conditions. By considering a scenario where a Bluetooth master is used as wireless access point to the Internet, we show that our EDC scheduler significantly enhances the system performance with regard to a Round Robin (RR) scheduler.

In this paper we identify important characteristics of a fading/shadowing fading channel and present the work of measurement-based channel modeling for packet-level network queueing analysis. Our integration of wireless channel modeling and data queueing analysis at the packetlevel provides a unique approach to study the effect of various channel dynamics on high layer network performance, which otherwise cannot be captured through the traditional bit-level physical-layer channel modeling. In our study, the channel statistics are decomposed into three frequency regions (i.e., low, mid and high); the statistics in each frequency region is found to have significantly different impact on the queueing performance. While the high-frequency statistics can be largely ignored in channel modeling due to its negligible impact on queueing performance, the low-frequency statistics plays the most important role in channel modeling because of its substantial impact on queueing performance....

Since high error rates are inevitable in the wireless environment, energy efficient error control is an important issue for mobile computing systems. When error-correction mechanisms are implemented on general-purpose processors the power consumption that is required to perform the errorcorrection mechanism can be significant. To illustrate this we have studied two different error correction mechanisms with different characteristics and capabilities, i.e. EVENODD and Reed-Solomon.

In this paper, the outage concept is discussed. Classic definitions, only based on the marginal statistics, are found not to be adequate for a proper characterization of the effect of channel impairments at the application level. A more flexible definition, which incorporates time parameters and appears suitable for the characterization of the performance of packet communications systems, is proposed. An analytical framework for the computation of various performance metrics is also presented. A Markov description is assumed for the channel, which allows closed-form solutions and can effectively model many situations of interest. Outage events are defined as being triggered by b consecutive channel errors, and being ended by g consecutive successes. A numerical example of application is given, and extensions of the analysis to more general definitions are discussed. Keywords---Outage, Minimum duration outage, Bursty errors, Correlated channel, Error statistics, Error events. I. INTR...

We consider the energy efficiency of error control mechanisms for wireless communication. Since high error rates are inevitable to the wireless environment, energy efficient error control is an important issue for mobile computing systems. Although good designed retransmission schemes can be optimal with respect to energy efficiency, they can introduce problems to fulfill the required QoS of an application. Since the channel conditions and the requirements vary dynamically, we concentrate on adaptive implementations of error correction mechanisms. Error correction mechanisms traditionally optimize the performance and provide an optimal solution to withstand all possible errors. In the context of energy consumption we have studied the energy efficiency of three different error correction mechanisms and have implemented these in software. We show that the energy efficiency trade-off between error correction and communication can have a great impact on the energy efficiency of a system. It will be shown that from energy efficiency perspective it is not always profitable to minimize the number of bits transmitted over the air. A general strategy will be provided that can be used to determine an energy efficient error correction scheme of a minimal system consisting of a general-purpose processor and a wireless interface. As an example we have investigated a system with a WaveLAN card as wireless interface.