Ratnajit Bhattacharjee

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.

Robust Time and Frequency Synchronization in OFDM based 802.11a WLAN systems

In this paper, robust and efficient time and frequency synchronization technique suitable for IEEE 802.11a wireless LAN system is proposed. The proposed method performs OFDM symbol boundary detection and frequency offset estimation using correlation techniques. The conjugate property of long preamble is used to reduce the computational complexity. In this proposed method, coarse time and fine frequency offset are estimated jointly and the frequency offset is estimated accurately before fine time estimation

Time and Angle of Arrival Statistics of Mobile-to-Mobile Communication Channel Employing Circular Scattering Model

Abstract of mobile-to-mobile communication channel have been studied through a geometrical single bounce scattering model and analytical expressions for angle of arrival and time of arrival probability density functions have been derived for such models. Analytical expressions have been verified through computer simulations. This paper aims to provide a better understanding of mobile-to-mobile channel behavior in terms of the parameters studied.

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.

MPSCTP: A Simple and Efficient Multipath Algorithm for SCTP

A simple multipath algorithm is proposed to augment Stream Control Transmission Protocol (SCTP) so that multiple available paths may be used concurrently. This requires an additional sequence number in the SCTP header for packets of each path and additional algorithms to handle the reordering that may naturally arise due to flow division over multiple paths. Performance of the proposed protocol has been studied using ns2 based simulation. The results indicate that our algorithm reduces the transmission delay and improves the throughput of the network.

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.

Time and Angle of Arrival Statistics of Mobile-to-mobile Communication Channel Employing Dual Annular Strip Model

Abstract In this paper, a generalized channel model for mobile-to-mobile communication based on the single bounce geometry-based channel modeling techniques has been proposed and analyzed. The model assumes the scatterers to be present in annular strips around the transmitting and the receiving mobile stations. Time of arrival and angle of arrival statistics, being two important channel parameters, have been derived and verified through computer simulations.

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.

An energy efficient hybrid MAC protocol for WSN containing mobile nodes

Design of energy efficient medium access control (MAC) protocol for wireless sensor network (WSN) containing mobile nodes is a challenging task. Majority of the MAC protocols for wireless sensor networks assume static sensor nodes, which results in poor performance of such protocols in a network containing mobile nodes. In this paper we propose a MAC protocol which is energy efficient as well as suitable for a WSN containing mobile nodes. The proposed protocol is based on both TDMA and CSMA. It adjusts the frame size to adapt to the changes in mobility and traffic conditions. The performance of the proposed protocol has been compared with LEACH-C protocol. It outperforms LEACH-C in terms of average energy consumption, packet delivery ratio and network life time.