Viswanath Ganapathy

Power allocation schemes for cognitive radios

Coexistence of one or more cognitive radios with a primary radio where the cognitive radios transmit in a spectrum allocated to the primary radio has been investigated in this paper. We consider two distinct scenarios: one in which the cognitive radios give higher priority to one of the cognitive radios and a second in which all the cognitive radios compete to get maximum possible data rates for themselves. In first scenario, the cognitive radio with higher priority gets a choice to decide how much of available resources it wants to use, and rest of the cognitive radios scavenge the left-over resources. We propose power allocation strategies to be used by the radios under both scenarios. We show that proposed power allocation strategy to be used in the first and cooperative scenario leads to overall system capacity improvement. We also prove convergence of power allocation algorithm proposed for the second and greedy scenario. In both cases the cognitive radios ensure that sum of interference caused by them in the spectrum remains below interference threshold.

Performance of multi user detector based receivers for UWB body area networks

Recent developments in ultra wideband (UWB) technology have opened a way to create wireless networks for personal health care monitoring. This personal area wireless network with a set of wireless nodes mounted on body is popularly known as body area network (BAN). A typical BAN has a set of thirty to fifty wireless sensors with a low transmit power constraint. Also, the wireless channel seen in by a wireless node is unique when mounted on the human body. It has been shown that UWB supports reliable connectivity at low transmit power for body mounted wireless nodes. Further, the UWB also supports co-existence with other wireless networks and supports higher data rate. Given that large number of nodes are placed in close proximity the BAN operates in a multi-user interference limited environment. Therefore, we discuss the performance of multi-user based detectors for body area networks and compare the performance with conventional receiver architectures. We use the recently proposed channel model for the standard IEEE 802.15.4a. Our simulations show superior performance of MUD based receivers over RAKE based receivers for a body area channel.

Secure group communication in wireless sensor networks

In this paper we address the issues of forming secure multicast group within wireless sensor networks. We describe a protocol that establishes a secure multicast group, and distributes a group key by mutually authenticating a group of devices over an open insecure wireless channel. We choose a conference keying mechanism and extend it with symmetric authentication protocols and a key hierarchy on which group key could be distributed efficiently. We address two problems in this work. Firstly, the formation of secure groups in sensor network with a low communication complexity, secondly, provides an efficient solution to maintain such multicast group.

Simple Multiuser Detectors for DS-UWB Systems

UWB is an emerging technology inviting major advances in wireless communication, networking, radar and positioning systems. In this paper, we present novel algorithms for the multiuser detection based on minimum mean square error (MMSE) for a DS-UWB multiuser communication system. The algorithms exploit the inherent multipath diversity and also mitigate the effects of both inter symbol interference(ISI) and multiuser interference (MUI). Simulation results show that the given algorithms perform better than the other known detectors in literature. We also provide closed form expression for the BER results of the above scheme

Multiuser detection based receivers for diversity enhancing UWB systems

Ultra-wideband (UWB) transmissions have well-documented advantages for low-power, peer-to-peer, and multiple-access communications. In this paper, we present novel linear receiver algorithms for multiuser detection (MUD) based on minimum mean square error (MMSE) for diversity enhancing UWB multiuser communication systems. The algorithms exploit inherent multipath diversity and mitigate the effects of both inter symbol interference (ISI) and multiuser interference (MUI). Further more, the receiver algorithms also optimally exploit diversity. We also propose a coded transmission scheme for the MIMO-UWB system for exploiting transmit diversity. We provide performance evaluation of the detectors through detailed analysis and simulations for synchronous and asynchronous users. An analytical framework for obtaining closed form expression for the bit error rate (BER) of the above schemes is also discussed.