02-06-2012, 12:39 PM
COOPERATIVE COMMUNICATION IN WIRELESS NETWORKS
COOPERATIVE COMMUNICATION IN WIRELESS NETWORKS.doc (Size: 1.78 MB / Downloads: 50)
Abstract:
This paper presents a tutorial overview of a class of techniques known as cooperative communication that allows single antenna mobiles to reap some of the benefits of MIMO systems. The basic idea is that single antenna mobiles in a multi user scenario can share their antennas such that it creates a virtual MIMO systems. Transmit diversity requires more than one antenna of the transmitter. It is more advantageous on a cellular base station and it may not be practical for other scenario.
INTRODUCTION
In cooperative wireless communication, we are concerned with a wireless network, of cellular or ad-hoc variety, where the wireless agents, which we call users, may increase their effective quality of service (measured at the physical layer by bit-error rates, block-error rates, or outage probability), via cooperation. In a cooperative communication system, unlike the relay channel model [1], each wireless user is assumed to both transmit data as well as act as a cooperative agent for another user (see Figure 2).
PERFORMANCE
The hybrid version of detect-and-forward is superior to the simple version, therefore it is used in this comparative study. In these experiments, BPSK modulation is used with coherent detection at the receiver. For both the hybrid decode-and-forward and amplify-and-forward, the users initially transmit a rate 1/2 code word. This code word is subsequently repeated by the partner, resulting in an overall rate of 1/4 (rate 1/2 code, repeated).
MULTIPLE ACCESS AND OTHER PRACTICAL ISSUES
Cooperative communication, as described previously, assumes that the base station can separately receive the original transmissions and the relayed transmissions. This is accomplished by transmitting the two parts orthogonally so that they can be separated. The most straight forward method is separation in time, i.e., the user's data and relayed data are transmitted in non-overlapping time intervals. In the example of Sendonaris et al. orthogonality is achieved through both time separation and orthogonal spreading codes. In principle, it is also possible to achieve separation in frequency.
. EXTENSIONS AND CONTINUING WORK
While several key results for cooperative communication have already been obtained, there are many more issues that remain to be addressed. An important question is how partners are assigned and managed in multi-user networks. In other words, how is it determined which users cooperate with each other, and how often are partners reassigned.
CONCLUSIONS
This tutorial paper describes wireless cooperative communication, a technique that allows single antenna mobiles to share their antennas and thus enjoy some of the benefits of multiple-antenna systems.