Wireless Communications

Mobile users' data rate and quality of service are limited by the fact that, within the duration of any given call, they experience severe variations in signal attenuation, thereby necessitating the use of some type of diversity. In this two-part paper, we propose a new form of spatial diversity, in which diversity gains are achieved via the cooperation of mobile users. Part I describes the user cooperation strategy, while Part II (see ibid., p.1939-48) focuses on implementation issues and performance analysis. Results show that, even though the interuser channel is noisy, cooperation leads not only to an increase in capacity for both users but also to a more robust system, where users' achievable rates are less susceptible to channel variations.

http://dns2.asia.edu.tw/~ysho/YSHO-English/2000%20Engineering/PDF/IEE%20Tra%20Com51,%201927.pdf

User cooperation diversity. Part I. System description

Meyn & Tweedie is back! The bible on Markov chains in general state spaces has been brought up to date to reflect developments in the field since 1996 - many of them sparked by publication of the first edition. The pursuit of more efficient simulation algorithms for complex Markovian models, or algorithms for computation of optimal policies for controlled Markov models, has opened new directions for research on Markov chains. As a result, new applications have emerged across a wide range of topics including optimisation, statistics, and economics. New commentary and an epilogue by Sean Meyn summarise recent developments and references have been fully updated. This second edition reflects the same discipline and style that marked out the original and helped it to become a classic: proofs are rigorous and concise, the range of applications is broad and knowledgeable, and key ideas are accessible to practitioners with limited mathematical background.

Markov Chains and Stochastic Stability

In Distributed Algorithms, Nancy Lynch provides a blueprint for designing, implementing, and analyzing distributed algorithms. She directs her book at a wide audience, including students, programmers, system designers, and researchers.



Distributed Algorithms contains the most significant algorithms and impossibility results in the area, all in a simple automata-theoretic setting. The algorithms are proved correct, and their complexity is analyzed according to precisely defined complexity measures. The problems covered include resource allocation, communication, consensus among distributed processes, data consistency, deadlock detection, leader election, global snapshots, and many others.



The material is organized according to the system model-first by the timing model and then by the interprocess communication mechanism. The material on system models is isolated in separate chapters for easy reference.



The presentation is completely rigorous, yet is intuitive enough for immediate comprehension. This book familiarizes readers with important problems, algorithms, and impossibility results in the area: readers can then recognize the problems when they arise in practice, apply the algorithms to solve them, and use the impossibility results to determine whether problems are unsolvable. The book also provides readers with the basic mathematical tools for designing new algorithms and proving new impossibility results. In addition, it teaches readers how to reason carefully about distributed algorithms-to model them formally, devise precise specifications for their required behavior, prove their correctness, and evaluate their performance with realistic measures.


Table of Contents

1 Introduction 
2 Modelling I; Synchronous Network Model 
3 Leader Election in a Synchronous Ring 
4 Algorithms in General Synchronous Networks 
5 Distributed Consensus with Link Failures 
6 Distributed Consensus with Process Failures 
7 More Consensus Problems 
8 Modelling II: Asynchronous System Model 
9 Modelling III: Asynchronous Shared Memory Model 
10 Mutual Exclusion 
11 Resource Allocation 
12 Consensus 
13 Atomic Objects 
14 Modelling IV: Asynchronous Network Model 
15 Basic Asynchronous Network Algorithms 
16 Synchronizers 
17 Shared Memory versus Networks 
18 Logical Time 
19 Global Snapshots and Stable Properties 
20 Network Resource Allocation 
21 Asynchronous Networks with Process Failures 
22 Data Link Protocols 
23 Partially Synchronous System Models 
24 Mutual Exclusion with Partial Synchrony 
25 Consensus with Partial Synchrony

Distributed algorithms

Multiuser diversity is a form of diversity inherent in a wireless network, provided by independent time-varying channels across the different users. The diversity benefit is exploited by tracking the channel fluctuations of the users and scheduling transmissions to users when their instantaneous channel quality is near the peak. The diversity gain increases with the dynamic range of the fluctuations and is thus limited in environments with little scattering and/or slow fading. In such environments, we propose the use of multiple transmit antennas to induce large and fast channel fluctuations so that multiuser diversity can still be exploited. The scheme can be interpreted as opportunistic beamforming and we show that true beamforming gains can be achieved when there are sufficient users, even though very limited channel feedback is needed. Furthermore, in a cellular system, the scheme plays an additional role of opportunistic nulling of the interference created on users of adjacent cells. We discuss the design implications of implementing. this scheme in a complete wireless system.

https://web.stanford.edu/~dntse/papers/oppbf_it.pdf

Opportunistic beamforming using dumb antennas

This paper develops a general framework for analyzing a wide class of vehicle dispatching strategies for bulk arrival, bulk service queues. We provide a simple derivation of the queue length transform for the embedded Markov chain, and present a new computational procedure for finding the moments of the queue length distribution. Extensive computational tests demonstrate that the new procedure is significantly faster and more stable than the standard method, from the literature, that requires solving a set of simultaneous linear equations. We give formulas for the mean and variance of the length of the queue for the general case of compound Poisson arrivals, random batch capacities, general service times and a general control strategy.

The Bulk Service Queue with a General Control Strategy: Theoretical Analysis and a New Computational Procedure

An important question in stochastic modeling is whether or not a denumerable state Markov chain is ergodic. We extend a result of Kaplan giving a condition for the non-ergodicity of a chain based on its drifts. We also clarify the condition under which the mean drift in the stationary chain is zero.

Technical Note-Mean Drifts and the Non-Ergodicity of Markov Chains

This work considers the transmission of information from many independent sources to a common receiver over a channel impaired by multipath propagation. In cellular radio communications this is the case of the uplink. We start by examining the achievable rate region of the multiuser frequency-selective fading channel without knowledge of the channel on the transmission end. It has been shown that SSMA (Spread Spectrum Multiple Access) is theoretically capable of higher data rates than FDMA (Frequency Division MuZfiple Access) or slow frequency-hopping[l]. When the average received power for all the users is equal, which corresponds to a perfect slow power control, we show that the maximum spectral efficiency of SSMA exceeds that of FDMA or slow frequency-hopping by 5772 nats/s/Hz for many users and Rayleigh fading. Also, we formulate the optimal multiple-access scheme when all the channels are known to the transmitters. In turns out that only one user should transmit at any given frequency. Morecver, the input power spectra for the transmitters are water-filling formulae both in frequency and time. It is shown that the spectral efficiency for the optimal scheme is significantly higher than both those of SSMA and FDMA.

Multiple-accessing over frequency-selective fading channels

The effect of crosstalk introduced due to gain saturation in an optical amplifier when it is used for amplifying multiple channels in a wavelength division multiplexed (WDM) network employing ON-OFF keying with direct detection is studied. The system power penalty is quantified as a function of the amplifier input power, the number of channels, and the extinction ratio. >

Amplifier induced crosstalk in multichannel optical networks

A media-access protocol for high-speed packet-switched multichannel networks that are based on a broadcast topology, such as optical passive star networks using wavelength-division multiple access, is described. The protocol supports connection-oriented traffic with or without bandwidth reservation, as well as datagram traffic to integrate transport-layer functions with the media-access layer. It uses the bandwidth efficiently while keeping the processing requirements low by requiring stations to compute their transmission and reception schedules only at the start and end of each connection. Analysis results show that low blocking probabilities for connections and high network throughput can be achieved. >

Pierre A. Humblet

Papers

The Bulk Service Queue with a General Control Strategy: Theoretical Analysis and a New Computational Procedure

Technical Note-Mean Drifts and the Non-Ergodicity of Markov Chains

Multiple-accessing over frequency-selective fading channels

Amplifier induced crosstalk in multichannel optical networks

An efficient communication protocol for high-speed packet-switched multichannel networks