Himanshu Katiyar

Performance of two-hop regenerative relay network under correlated nakagami-m fading at multi-antenna relay

Performance of cooperative relaying employing infrastructure based fixed relays having multiple antennas has been investigated. Here, both relay and destination perform maximal ratio combining combining of the signals. Closed form expressions for outage probability and bit error rate have been derived for Nakagami-m fading channels, with integer values of m. The effect of fading correlation among relay antennas and relay positioning on the system performance have also been studied.

Cooperative Communication: A Review

Abstract The next generation wireless systems are supposed to handle high data rate as well as large coverage area. It should consume less power and utilize bandwidth efficiently. At the same time, the mobile terminals must be simple, cheap, and smaller in size. In wireless environment, the quality of received signal level degraded due to path-loss and shadowing from various obstacles in propagation path. In addition to this, signal quality suffers from fading due to constructive and destructive interference of multi-path components which makes it difficult for the receiver to extract the message correctly. Effect of fading can be suppressed by diversity technique in which replicas of signal is provided to the receiver. Receiver can make a decision on behalf of these replicas; hence, reliability of reception can be improved. Diversity can be achieved with the help of multi-antenna system where multiple antennas are installed at transmitter/receiver. However, implementing multiple antennas at wireless terminal is not practical due to size, cost, and weight constraints. Recently, cooperation among nodes has been the subject of great interest among the research community because it creates spatial diversity in wireless network, even if individual nodes do not use antenna arrays for transmis sion and reception. Here, achieved diversity gains can be translated into robustness against fading for same transmit power or substantially reduced transmitted power for same level of performance. In this paper, we discussed the state of art of cooperative communication.

Outage Performance of Multi-Antenna Relay Cooperation in the Absence of Direct Link

Cooperation among relays can achieve spatial diversity, which improves the link quality in a wireless network. In this letter, we investigate the performance of an infrastructure based multi-antenna relay network in the absence of a direct link. A closed form expression of outage probability has been derived, when the cooperating relays and destination coherently combine the received signals. The effect of number of relay antennas and relay placement on the system performance have also been studied.

User Cooperation in TDMA Wireless System

Abstract Reliability of radio link is limited, owing to path loss, shadowing and multi-path fading. This necessitates the use of a certain type of diversity. In recent years, cooperative diversity has gained considerable attention. Here, wireless nodes cooperate in such a way that they share their antennas and other resources, to create a virtual array through distributed transmission and signal processing. This increases coverage and reduces transmitted power, thereby bringing down co-channel interference, which results in increased system capacity. This paper gives an overview of the state of art of various cooperation schemes and issues related to their implementation.

Performance of regenerative relay network operating in uplink of multi-antenna base station under rayleigh fading channel

Communication through intermediate relay node, splits the channel between source and destination into two possibly shorter links, which improves link quality as well as combat with harsh multi-path fading. Close form expressions of average received SNR, outage probability and average bit error rate (BER) have been derived, for the case when communication between source and multi-antenna destination (base station) is supported by single antenna regenerative relay in asymmetric Rayleigh fading channel. Comparative performance of such system with conventional SIMO (single input multiple output) system, in various path-loss condition and different number of antenna elements on destination, have also been studied. Numerical results shows that, transmission through relay is superior than SIMO in higher path-loss condition.

Average Error Rate of Multi-Antenna Decode and Forward Cooperative Relay Network

Cooperative relaying is emerging as a powerful mean of exploiting broadcast nature of the channel to provide diversity gain and improve link performance for single-antenna wireless terminals. In this paper, we investigate the average error performance of cooperative relay network employing infrastructure based fixed relays having multiple antennas. A closed form expression of average error rate for such system has been derived when the relay performs selection combining and destination performs MRC combining of signals. The effect of relay placement on the system performance has also been studied.

Adaptive power allocation for repetition based cooperative relay in Nakagami-m fading channel

Reliability of radio link is limited due to path loss, shadowing and multi-path fading, thereby necessitating the use of some type of diversity. Cooperative relaying has gained considerable attention in recent years. Relays cooperates in such a way that they share their antennas and other resources to create a virtual array through distributed transmission and signal processing. Energy issue for such limited energy wireless relays is important, which spurred a great deal of recent research. In this paper we optimize the capacity of limited energy wireless relay network. This limited energy can be allocated adaptively to any node of relay network, according to the instantaneous channel state information. Through simulation the capacity for such a model is calculated and optimized over the power allocation scheme. This optimization is a convex problem. A general approach for solving such problem has also been outlined.

Power Allocation Strategies for Non-regenerative Relay Network in Nakagami-m Fading Channel

Abstract Cooperative relaying is a promising approach to enlarge coverage area and enhance system capacity. Capacity of such a system depends on the SNR of the received signal. Therefore, allocation of available power between source and relay, to achieve maximum SNR, is an important issue. A power allocation scheme depends not only on channel state information (CSI) but also on the degree of knowledge of this CSI. This paper investigates different power allocation strategies in presence of full CSI, without CSI, and statistical CSI through simulation studies. Knowledge of full CSI can be utilized to obtain optimal performance at the cost of system complexity. Use of statistical feedback reduces complexity and its performance is found to be close to optimal one. Its performance is close to optimum one for the placement of relay node near destination or with decrease in fading severity. However, in the absence of CSI, placement of relay at middle is the best solution, for similar channel conditions.

BER performance of regenerative multi-antenna cooperative relay network in Rayleigh fading channel

BER performance of cooperative relay network, employing infrastructure based fixed relays having multiple antennas has been investigated. Closed form expression for average BER has been derived, when destination is assumed to perform selection combining of the signals, received from direct path and through relay path. BER expressions are derived for both the cases of selection and maximum ratio combining at the relay terminal. The effect of relay placement on the system performance has also been studied under different path loss conditions.

Outage performance of dual-hop opportunistic relaying compared to a single-hop SIMO under Rayleigh fading

Cooperative relaying technique has shown potential in enhancing coverage area and reliability of transmission by forming virtual arrays. Opportunistic relaying tries to utilize best available channel between source and destination. Outage performance of relay based system can be improved through proper allocation of power and positioning of relay node. Analytical expression for outage probability for the opportunistic relaying scheme under consideration has been derived and its performance has been compared with an equivalent SIMO system performing selection combining. Results shows that opportunistic relaying outperform single-hop SIMO in high path-loss condition and performance of relay based system can further be improved by proper power allocation and relay positioning. The work presented in this paper is expected to be useful for the deployment of relay based system in various channel conditions.