On channel estimation and capacity for amplify and forward relay networks

Abstract-Relay networks have received considerable attention recently, especially when limited size and power resources impose constraints on the number of antennas within a wireless sensor network. In this paper, we design and analyze a training based linear mean square error (LMMSE) channel estimator for time division multiplex amplify-and-forward (AF) relay networks. For the purpose of performance comparison we consider three distinct cases; In the first scenario, each relay estimates its backward and forward channels, in the second scenario each relay knows its backward and forward channels perfectly and finally in the third scenario relays have no knowledge of channels. Finally, we find a lower bound for the capacity considering the effect of training and estimation error. I. INTRODUCTION Next generation wireless networks are demanding high data rate services to accommodate requests from various applications. In order to provide reliable communications, one needs to compensate for the effects of signal fading due to multipath propagation and strong shadowing. One way to address these issues is to transmit the signal through one or more relays In this paper, we extend current work by considering a training based LMMSE estimator for K relays in an AF configuration assuming a time division multiplex system such that the channel from relays to destination and vice versa are reciprocal. We derive a lower bound for the capacity of this relay network considering the effect of channel estimation error as part of noise at the destination. To contrast the results, we consider three cases; In the first scenario, each relay estimates its backward and forward channels, in the second scenario each relay knows its backward and forward channels perfectly, and finally in the third scenario relays do not know their backward and backward channels

Performance Characteristics Evaluation for Cooperative Communication

Wireless channels suffer severely from the effect of multi-path and fading. To mitigate these effects of fading and, cooperative diversity protocols are used. In cooperative diversity, two or more users share their antennas to create a virtual MIMO system. Hence in cooperative communication several single antenna relays assist the transmission between a source and a destination. In this work, cooperative communication protocols such as amplify and forward and decode and forward are simulated for relaying. The received signals at the destination are combined using various diversity combination protocols such as Maximal Ratio Combining (MRC) and Fixed Ratio Combining (FRC). For the performance study of cooperative communication protocol in wireless network, the symbol error rate (SER), outage probability and channel capacity are simulated for single relay and multiple relay in a flat fading Rayleigh channel.. In addition to this, for a 3 node cooperative communication containing a source , a relay and a destination the impact of relay location is studied for 3 different location of relay i.e. relay placed closer to the source, closer to the destination and at the midway between the source and the destination. When the relay is located in the middle of source and destination, it gives the best system performance. When the relay is located closer to the source, the quality of source-relay link is good, and the relay can decode the received information. On the other hand, when the relay node is located close to the destination, the system performance degrades. Through simulation results, it is shown the positive role that the relay plays, as it improves significantly the performance of the system and leads to lower SER and lower outage probability