IEEE Communications Letters

We consider a two-hop relay link in which orthogonal frequency division multiplexing (OFDM) is used on both hops. Under a joint sum-power constraint, our aim is to allocate power over subcarriers on the two hops such that the instantaneous rate of the relay link is maximized. Ordered subcarrier pairing (OSP) has been proposed in the literature to further improve the relay link rate; however, the o... View full abstract»

This letter addresses the issues on performance degradation caused by channel estimation error of quasiorthogonal space-time block (QO-STBC) coded OFDM systems employing array processing decoder. The least square (LS) channel estimator is employed to obtain the required channel state information (CSI). Taking mean square error (MSE) as a performance metric, we evaluate the performance of the LS es... View full abstract»

This paper presents a generalized eigen-combining algorithm for an adaptive array system that provides a diversity gain in angular spread, and a maximum signal-to-interference ratio (SIR) in the presence of strong interference. The proposed technique generates the maximum ratio of signal components distributed in the spatial channel subspace using channel bases that span the signal subspace and nu... View full abstract»

In this letter we develop an average-value analysis of the TCP performance in 802.11 WLANs. Our model characterizes the equilibrium conditions of the network, and this method yields a simple, yet precise, estimate of the throughput obtained by persistent TCP flows. Via simulations we study the accuracy of the model predictions. View full abstract»

This work presents a new MAC protocol for WSNs that combines an unscheduled channel access, based on lowpower listening, with an opportunistic scheduled wake up after transmissions mechanism. The proposed MAC provides a good tradeoff between energy consumption, complexity and performance in terms of throughput and delay. It achieves the benefits of scheduled MAC protocols without the cost of maint... View full abstract»

A three-phase transmission scheme for the linear four-node half-duplex wireless relay network is proposed. In each of its two cooperative phases, the setting is equivalent to the broadcast channel with cognitive receiver, whose capacity region is determined. Based on that result, the three-phase scheme is shown to be capacity achieving. Its performance is compared with two suboptimal schemes. View full abstract»

The performance of a two hop amplify-and-forward relay system, where the source-relay and the relay-destination channels experience Rayleigh and Rician fading respectively, is investigated. We derive exact and lower bound expressions for the outage probability and average bit error probability, where the bounds become tight at high signal-to-noise ratios (SNR). Our results are verified through com... View full abstract»

In this work, a grouped linear constellation precoded orthogonal frequency-division multiplexing (GLCP OFDM) system, with the transceiver in-phase/quadrature (I/Q) imbalance operating over frequency-selective fading channels are studied. A new subcarrier grouping scheme in such a system is proposed. Through analysis and simulations, we demonstrate that with the proposed scheme, low-complexity solu... View full abstract»

In this letter, two common protocols in cooperative communications, namely one-way and two-way amplify-andforward (AF) half-duplex relaying, are investigated and compared in terms of rate. It is generally accepted that two-way AF half-duplex relaying is always better than its one-way counterpart in terms of rate. However, we found that depending on the definition of the total power constraint and ... View full abstract»

A novel scheme for spatially multiplexing two BPSK signals using a 3-element ESPAR (electronically steerable parasitic array radiator) antenna was reported in. In this paper we first optimize the set of loads controlling the parasitic elements within the transmission mode by maximizing the outage capacity. We also propose different reception techniques for spatially demultiplexing real and complex... View full abstract»

In a typical macrocell network, the mobile users are synchronized to the macrocell base station (mBS), where users further away to the mBS transmit their signals earlier. In such a network, the signals of the macrocell users arrive at a femtocell base station (fBS) asynchronously, which may yield interference problems such as inter-carrier-interference in orthogonal frequency domain multiple acces... View full abstract»

Two novel receivers for transmitted-reference ultrawide bandwidth wireless systems are proposed. The new receivers are derived by using iterative algorithms to implement the channel template estimators employed in previous receivers. While the new receiver structures are simple, simulation results confirm their superiority over previous receivers. The performances of the new receivers can be furth... View full abstract»

Some authors seem to believe that the average number of sons in a Wireless Sensor Network (WSN) data aggregation tree can be kept constant, even when the distances from the sink increase. But this assumption is impossible to stand in a dense and uniformly deployed network, as the number of nodes in a given level would grow exponentially, while the perimeter just grows linearly. In this letter, it ... View full abstract»

Analysis of the persistency and birth/death of multipath components of the channel impulse response is essential for performance evaluation of indoor geolocation algorithms using indirect paths for ranging. The use of indirect paths via multipath diversity is particularly important for situations where the direct path gets blocked. In this letter, we propose a statistical model for the spatial beh... View full abstract»

In this paper we investigate the problem of optimal unitary precoding for multiuser multiple-input multiple-output (MIMO) wireless communication systems. In the case that there exist two users, we derive a closed-form solution for the unitary precoder that maximizes the sum rate. To provide additional insight, the optimal precoder is also characterized in several asymptotic regimes. Monte Carlo si... View full abstract»

For geometrically based single bounce circular model (GBSBCM), a new grid-search based technique is proposed to solve the constraint, nonlinear, underdetermined equations for wireless location in non-lineof-sight (NLOS) environments. Under the assumption of relatively small measurement errors of angle of arrival (AOA) and time of arrival (TOA), more accurate location results than those of existing... View full abstract»

Parallel decodable turbo codes (PDTCs) are suitable for concurrent decoding and hence have low latency. Memory collision issue is an important problem met during parallel processing. In this article, we propose a collision free interleaver for parallel processing operations. The performance of PDTCs is analyzed with the proposed random interleaver preventing the memory collision problem. Distance ... View full abstract»

In this letter, burst erasure correction of low density parity check codes based on a hybrid approach is presented. The proposed method preserves as much as possible the original low density representation and augments it by specific check sums judiciously selected. View full abstract»

In this letter, lossy distributed source coding using graphs is considered. This corresponds to the source coding part of the graph-based framework for transmission of analog correlated sources over the multiple-access channel (MAC). Consequently, it is shown that a pair of analog correlated sources can be reliably represented into a bipartite graph by allowing certain amount of distortion. An ach... View full abstract»

We consider a wireless communication environment in which a large number of local area cells are deployed within the coverage of wide area cells. In this environment, a scanning operation to detect a suitable local area cell for handoff can degrade the performance of a mobile station, because repeated scanning trials are likely to cause disruption of service and require considerable consumption of... View full abstract»

The concept of soft state (i.e., the state that will expire unless been refreshed) has been widely used in the design of network signaling protocols. The approaches of refreshing state in multi-hop networks can be classified to end-to-end (E2E) and hop-by-hop (HbH) refreshes. In this article we propose an effective Markov chain based analytical model for both E2E and HbH refresh approaches. Simula... View full abstract»

This letter focuses on power allocation schemes for a basic multicast cell with wireless regenerative network coding (RNC). In RNC, mixed signals received from the two sources are jointly decoded by the relay where decoded symbols are superposed in either the complex field (RCNC) or Galois field (RGNC) before being retransmitted. We deduce the optimal statistical channels state information (CSI) b... View full abstract»

In this paper, we describe an attack against one of the most efficient authentication protocols for low-cost RFID tags recently proposed by Song and Mitchell. A weak attacker, i.e. an attacker that has no access to the internal data of a tag, is able to impersonate a legitimate reader/server, and to desynchronize a tag. The attack is very efficient and has minimal computational complexity. Finally... View full abstract»

This letter proposes an IP-based finely-distributed routing scheme based on two-phase routing (TPR) over shortest paths for the hose model. It is called the fine-TPR (F-TPR) scheme. Compared to the original TPR, F-TPR distributes traffic from a source node to intermediate nodes more finely, where the distribution ratio is determined for each source-destination pair. To determine an optimum set of ... View full abstract»