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

The authors consider the performance of an optical communication system where an unmodulated reference signal is transmitted along with the information-carrying signal to alleviate the effect of phase noise. When the power of the two signals and the receiver bandwidths are optimized, the resulting performance is significantly better than that of traditional amplitude and frequency modulation schemes. This makes reference transmission with a joint optimization of signal and receiver parameters a promising scheme for coherent optical communications. >

/pdf/reference-transmission-and-receiver-optimization-for-2epcuyalgt.pdf

Reference transmission and receiver optimization for coherent optical communication systems

Intersymbol interference (ISI) in direct detection optical systems can limit channel spacing in frequency division multiplexing systems, and data rates, and transmission distances in long-haul transmission. It is desirable to reduce or cancel ISI in these situations, We investigate zero-forcing electrical filters to cancel ISI, and obtain tight performance bounds for minimum noise variance zero-forcing filters. We apply the results to Mach-Zehnder and Fabry-Perot filters, and to fibers with second order dispersion. We compare the performance of zero-forcing filters to that of rectangular impulse response filters and find that zero-forcing filters are advantageous in severe ISI situations with multilevel signalling.

/pdf/zero-forcing-electrical-filters-for-direct-detection-optical-2ywvdjv2p2.pdf

Zero-forcing electrical filters for direct detection optical systems

A novel tunable optical filter with a tuning speed of 2 microsecond(s) , a tuning range of approximately 60 nm at 1.55 micrometers , and a resolution of 0.5 angstrom (6.3 GHz) has been proposed and demonstrated for application in wavelength division multiaccess computer network. The principle of operation is by positioning an optical beam emitting from an optical fiber that carries all wavelengths onto two crossed wedge etalons. Depending on the location of the optical beam incident on the etalon assembly, only a certain wavelength that matches the thickness of the etalons at that location is transmitted. The optical beam positioning is achieved by two single-axis acousto-optical deflectors. The number of channels supported by the filter is estimated to be approximately 600.

Tunable optical filter for wavelength-division multiaccess computer network

The authors study the performance of the unslotted ALOHA multiple access protocol in a high speed bidirectional bus network. For point-to-point communications, its maximum throughput is known to be independent of the ratio of end-to-end propagation delay to packet transmission time. For broadcast communications, it is shown that, if the offered load density is uniform along the bus, the maximum throughput achievable by a station depends on its location along the bus. To achieve a uniform throughput density, the offered load density has to vary along the bus. The optimal profile for the offered load density is derived. In any case, the maximum throughput degrades with the ratio of end-to-end propagation delay to packet transmission time. >

/pdf/unslotted-aloha-in-high-speed-bidirectional-bus-networks-4p49zqbiyq.pdf

Unslotted ALOHA in high speed bidirectional bus networks

A new access protocol that handles isochronous traffic in a much better way than previous protocols for wavelength division multiplexing (WDM) star networks is presented. This protocol allows the stations to reserve part of the bandwidth for their isochronous traffic while the rest is used for asynchronous traffic. In addition, this technique requires only one transmitter and one receiver per station and is free from the constraint of a control channel. >

Pierre A. Humblet

Papers

Reference transmission and receiver optimization for coherent optical communication systems

Zero-forcing electrical filters for direct detection optical systems

Tunable optical filter for wavelength-division multiaccess computer network

Unslotted ALOHA in high speed bidirectional bus networks

A method for isochronous traffic in a WDM star network