Cooperative Communications: A New Trend in the Wireless World

Abstract—This Wireless channel while offering independence of movement also introduces un-reliability in the messages received at the destination. Various strategies have been introduced so far to mitigate the effects of the channel on the message received. In this paper, we give an introductory overview of cooperative communications, a new trend in this field of wireless Communications where the transmitting users help each other to overcome the Effects of wireless channel on the message received at the destination. We compare the new idea of cooperative communications with traditional direct or noncooperative communications. In particular, we discuss the achievable rates and simulate the system to get the probability of outage performance of cooperative communications and compare it with direct or noncooperative communications

Proceedings of a IIASA Conference on Computer Communications Networks

This publication contains the papers presented at the Conference on Computer Networks organized by the Computer Science Project of IIASA in October 1974. This area is one of the main concerns of the Computer Science Project, but also has a broader significance for the Institute. IIASA deals with various problems of industrialization and its consequences, and inevitably depends on permanent working contacts with a number of national institutions. The interdisciplinary and international character of the Institute is essential to success in finding solutions to these problems. Applied research today depends heavily on the use of large amounts of data and data processing. We believe that connecting computers installed in various national institutions will contribute significantly to the achievements of the main goals, allowing for the exchange of data and programs, and in this way facilitating the understanding of problems, resulting in faster solutions. This Conference was the first of a series of conferences and workshops to be held on this topic. In addition to the exchange of ideas and the discussion of problems arising in networking, it was intended also to identify people and institutions that were interested in establishing links contributing to the achievement of the goals of the Institute. In addition to the presentation of papers and formal discussions, discussions on the periphery of the conference were probably of equal importance. The papers presented do not reflect the spirit of cooperation which was very characteristic of the conference. However, we feel that the publication of these papers will be useful to the scientific community and give a picture of recent developments in this area. Mr. J. Sexton and Miss U. Sichra are staff members of the Computer Science Project who devoted a great deal of their time and efforts to the editing of the papers. Mrs. H. MacKinnon was especially helpful in the technical editing and polishing of a number of the papers presented

Code-division multiplexing

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 395-404).(cont.) counterpart. Among intra-cell orthogonal schemes, we show that the most efficient broadcast signal is a linear superposition of many binary orthogonal waveforms. The information set is also binary. Each orthogonal waveform is generated by modulating a periodic stream of finite-length chip pulses with a receiver-specific signature code that is derived from a special class of binary antipodal, superimposed recursive orthogonal code sequences. With the imposition of practical pulse shapes for carrier modulation, we show that multi-carrier format using cosine functions has higher bandwidth efficiency than the single-carrier format, even in an ideal Gaussian channel model. Each pulse is shaped via a prototype baseband filter such that when the demodulated signal is detected through a baseband matched filter, the resulting output samples satisfy the Generalized Nyquist criterion. Specifically, we propose finite-length, time overlapping orthogonal pulse shapes that are g-Nyquist. They are derived from extended and modulated lapped transforms by proving the equivalence between Perfect Reconstruction and Generalized Nyquist criteria. Using binary data modulation format, we measure and analyze the accuracy of various Gaussian approximation methods for spread-spectrum modulated (SSM) signalling ...We study forward link performance of a multi-user cellular wireless network. In our proposed cellular broadcast model, the receiver population is partitioned into smaller mutually exclusive subsets called cells. In each cell an autonomous transmitter with average transmit power constraint communicates to all receivers in its cell by broadcasting. The broadcast signal is a multiplex of independent information from many remotely located sources. Each receiver extracts its desired information from the composite signal, which consists of a distorted version of the desired signal, interference from neighboring cells and additive white Gaussian noise. Waveform distortion is caused by time and frequency selective linear time-variant channel that exists between every transmitter-receiver pair. Under such system and design constraints, and a fixed bandwidth for the entire network, we show that the most efficient resource allocation policy for each transmitter based on information theoretic measures such as channel capacity, simultaneously achievable rate regions and sum-rate is superposition coding with successive interference cancellation. The optimal policy dominates over its sub-optimal alternatives at the boundaries of the capacity region. By taking into account practical constraints such as finite constellation sets, frequency translation via carrier modulation, pulse shaping and real-time signal processing and decoding of finite-length waveforms and fairness in rate distribution, we argue that sub-optimal orthogonal policies are preferred. For intra-cell multiplexing, all orthogonal schemes based on frequency, time and code division are equivalent. For inter-cell multiplexing, non-orthogonal code-division has a larger capacity than its orthogonalby Ceilidh Hoffmann.Ph.D