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The performance of an OFDM system can be improved by performing per-subcarrier antenna selection, which facilitates the exploitation of frequency and spatial diversity in the wireless channel. In this paper, we extend the concept of per-subcarrier antenna selection to a multiuser cognitive radio environment and present a practical subcarrier and antenna selection algorithm that exploits the multiuser,...
It has been well recognized that channel state information (CSI) feedback is important for dowlink transmissions of closed-loop wireless networks. In this paper, we investigate the CSI feedback rate control problem in the analytical setting of a game theoretic framework, where a multiple-antenna base station (BS) communicates with a number of co-channel mobile stations (MS) through a minimum mean...
A spectrum-sharing communication system where the secondary user is aware of the instantaneous channel state information (CSI) of the secondary link, but knows only the statistics and an estimated version of the secondary transmitter-primary receiver (ST-PR) link, is investigated. The optimum power profile and the ergodic capacity of the secondary link are derived for general fading channels (with...
A fundamental choice in femtocell deployments is the set of users which are allowed to access each femtocell. Closed access restricts the set to specifically registered users, while open access allows any mobile subscriber to use any femtocell. The main results of the paper are lemmas which provide expressions for the SINR distribution for various zones within a cell as a function of this MBS-femto...
In the paper, we consider the end-to-end routing and link scheduling problem for multi-hop wireless sensor networks. The efficient link scheduler under our consideration is intended to assign time slots to different users so as to minimize channel usage subject to constraints on data rate, delay bound, and delay bound violation probability. We also present a coupled robust multi-path routing structure...
Cognitive Radio (CR) networks are emerging as a viable candidate to resolve the conflict between increasing demand for spectrum and spectrum shortage. The essential purpose of a CR network is to improve the network spectrum efficiency, which, however, may not be achieved if a CR network is inappropriately configured. In decentralized overlaid networks, the throughput of the primary network will decrease...
In this paper, we investigate Sybil attacks on spectrum allocation in distributed dynamic spectrum access (DSA) networks. Using IEEE 802.11 devices as secondary nodes, we demonstrate the feasibility of mounting Sybil attacks in the cognitive radio testbed, in which the malicious node poses as multiple normal secondary nodes with different identities in order to steal more spectrum bands. We also show...
Recent studies have shown that network coding (NC) directly applied at the physical layer -physical layer network coding (PLNC)- is a promising technique for two-way relay channels (TWRC). Unfortunately, to date, most existing PLNC works have mainly addressed cases of time-invariant channels rather than more realistic multipath time-varying wireless channels. To make further progress in understanding...
In wireless networks, interference that is generated by undesired transmitters dominantly limits network performance. The correlation of node locations (in mobile or static networks) makes the interference temporally correlated. In this paper, we quantify the temporal correlation of the interference in mobile Poisson networks. More specifically, we obtain closed-form expressions for the interference...
The performance of spatial multiplexing systems with linear minimum-mean-squared-error receivers is investigated in ad hoc networks. We present new exact closed-form expressions for the outage probability and transmission capacity. These expressions reveal that from a transmission capacity perspective, single-stream transmission is preferable over multi-stream transmission.
We consider an opportunistic channel access problem over multiple primary bands. We exploit primary ACK/NAK packets overhearing to overlay secondary communications on top of permanently busy primary channels. Through the theory of multi-armed restless bandit processes (MARB), we prove optimality of the myopic policy with a simple structure that does not require channel state-transition probabilities...
In this paper, we consider $K$-user MIMO Y channels where users simultaneously exchange messages with each other via an intermediate relay. Degrees of freedom (DOF) of this channel are not known in general. The investigation of the feasibility conditions of signal space alignment for network coding is an initial step for addressing this open problem. We verify that when user has antennas ($i=1,...
Cognitive radio has attracted a lot of attention recently as an effective method of alleviating the spectrum scarcity problem in wireless communications. However, the constraints imposed on cognitive radio networks as secondary networks restrict their achievable throughput and highlight the importance of efficient spectrum sensing and power allocation. In this paper, we focus on maximizing the ergodic...
This paper addresses the problem of interference coordination in relay-aided cellular OFDMA systems, aiming at exploiting the benefits of RNs while minimizing the negative effects of interferences introduced. We first analyze the possible interference scenarios in multi-cell OFDMA systems. Based on the insights in our analysis, we propose an Integrated Interference Coordination Scheme (IICS) for cellular...
Block Diagonalization (BD) algorithm is a generalization of channel inversion scheme in multiuser multi-input multi-output (MIMO) broadcast channels. Although the BD algorithm is effective in removing interuser interference, it has a drawback that additional information should be delivered to the receiver. Recent work on BD with vector perturbation (VP) avoids the need for additional information and...
In this paper, we maximize the throughput of a cognitive radio (CR) network with respect to the frame length when quickest sensing is used. The amount of interference to the primary network, measured by the probability of collision with primary users (PUs), is constrained below a certain maximum. The corresponding problem when CRs use block sensing is also solved, assuming that collision with PUs...
In previous works, Vandermonde-subspace frequency division multiplexing (VFDM) has been shown to promote overlay networks by enabling a secondary transmitter to cancel its interference to a primary receiver, while simultaneously transmitting useful information to its own receiver at nonnegligible rates. Interference cancelation is achieved by exploiting the null-space of the channel from the secondary...
Femtocells have been considered by the wireless industry as a promising solution not only to improve indoor coverage, but also to unload traffic from already overburdened macrocells. In spite of potentially excessive interference caused by densely deployed femtocells, macrocells may have to share the same spectrum with femtocells, due to spectrum availability and network infrastructure considerations...
In this paper, we consider a large system analysis of regularized channel inversion (RCI) beamforming for MISO broadcast channels (BC) with transmit-side channel correlation. In the analysis, we assume that both the number of users and transmit antennas grow unbounded with a constant ratio. We also assume that the channel correlation model is separable. Under this channel condition, we are particularly...
Compared to real cellular systems where users are spatially distributed and interference levels vary by several orders of magnitude over a cell, in the Wyner model user locations are fixed and the interference intensity is characterized by a single fixed parameter. Although it is a fairly extreme simplification, the Wyner model has been extensively used to analyze cellular networks. Does it capture...
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