We present an interference alignment (IA) technique that allows multiple opportunistic transmitters (secondary users) to use the same frequency band of a pre-existing primary link without generating any interference. The primary and secondary transmit-receive pairs are equipped with multiple antennas. We exploit the fact that under power constraints on the primary transmitter, the rate of the

Spectrum sensing is one of the most challenging tasks required of a cognitive radio receiver. In this paper, we consider the first stage of spectrum sensing, where it is required to perform the sensing as fast as possible and with an acceptable performance under different channel conditions. The target signal to be sensed is a Long Term Evolution (LTE) signal. We first propose sensing the whole

Inspired by our earlier work on Automatic Repeat reQuest (ARQ) secrecy, we propose a simple, yet efficient, security overlay protocol to existing 802.11 networks. Our work targets networks secured by theWired Equivalent Privacy (WEP) protocol because of its widespread use and vulnerability to a multitude of security threats. By exploiting the existing ARQ protocol in the 802.11 standard, our

An authentication counterpart of Wyner's study of the wiretap channel is developed in this work. More specifically, message authentication over noisy channels is studied while impersonation and substitution attacks are investigated for both single- and multiple-message scenarios. For each scenario, information-theoretic lower and upper bounds on the opponent's success, or cheating, probability are

In many hybrid wireless sensor networks (HWSNs) applications, sensor nodes are deployed in hostile environments where trusted and un-trusted nodes co-exist. In such hybrid networks, it becomes important to allow trusted nodes to share information, especially, location information and, at the same time, prevent un-trusted nodes from gaining access to this information. We focus on anchor-based

Clustering is a standard approach for achieving efficient and scalable performance in wireless sensor networks. Traditionally, clustering algorithms aim at generating a number of disjoint clusters that satisfy some criteria. In this paper, we formulate a novel clustering problem that aims at generating overlapping multihop clusters. Overlapping clusters are useful in many sensor network

In this paper we propose a novel technique for hybrid automatic repeat request (HARQ) systems where turbo codes are used as the forward error correction (FEC) techniques. This technique uses the histogram of the soft values generated by the turbo decoder to control the size and the contents of the retransmissions needed when the packet can not be decoded correctly. These soft values represent the

This paper proposes using adaptive puncturing for rate-adaptive OFDMA systems utilizing turbo codes. The scheme is based on adaptively puncturing a Single Code Word (SCW) and hence adaptively changing the rate within the codeword. We compare the SCW against the Multiple Code-Words (MCWs) scheme where different rates are obtained by separate encoding, puncturing, and interleaving on a per-tile

In this paper, the delay limited secrecy capacity of the flat fading channel is investigated under two different assumptions on the available transmitter channel state information (CSI). The first scenario assumes perfect prior knowledge of both the main and eavesdropper channel gains. Here, upper and lower bounds on the secure delay limited capacity are derived and shown to be tight in the high

A scheme is proposed for adaptively changing the code rate of coded OFDMA systems via changing the puncturing rate within a single codeword (SCW). In the proposed structure, the data is encoded with the lowest available code rate then it is divided among different resource blocks (tiles) where it is punctured adaptively based on some measure of the channel quality for each tile. The proposed