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Femtocells are expected as the surest way to increase the system capacity with higher-quality links and more spatial reuse in future networks. In spite of their great potential, the system capacity is highly susceptible to network density because a large portion of users are exposed to inter-cell interference (ICI). In this work, we proposed a dynamic interference avoidance scheme in densely deployed...
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...
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 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...
We derive a linear transmit precoding scheme based on interference alignment at the transmitters and zero-forcing at the receivers, for the MIMO X channel based on the Generalized Singular Value Decomposition (GSVD) that is able to attain the outer bound on the degrees of freedom (DoF) region [2] for any antenna configuration, except when all terminals have one antenna. Additionally, the proposed...
Deployment of multiple femtocells in a confined area may cause serious interference problem to each other. To mitigate the inter-femtocell interference, we consider combined use of coordinated user scheduling with transmit beamforming in femtocell networks. Femto base stations collaboratively schedule users to minimize the interference in an average sense and employ a beamforming technique to maximize...
This paper proposes an adaptive fractional frequency reuse (FFR) resource allocation scheme for downlink transmission of OFDMA cellular networks. Resource allocation is localized in the sense that in each region system resources are assigned based on local traffic demand. Furthermore, the allocated resources in each region adapt to changes in the environment (i.e. channel gains and number/mobility...
This paper considers the MISO broadcast channel with different spatial correlations of the user vector channels. The base station implements regularized zero-forcing (RZF) precoding based on an imperfect channel estimation. We derive a deterministic equivalent of the signal-to-interference plus noise ratio (SINR) by applying novel results from the field of large dimensional random matrices. Based...
We consider simultaneous operation of primary and secondary point-to-multipoint networks in the same frequency band when interference in treated as noise. The variations in channel and interference gains are characterized by path loss and multipath fading. Scaling laws for the primary and secondary sum-rates are derived when the scaling is in terms of the number of primary users. In order to maintain...
One of the most challenging issues in cognitive radio networks is to dynamically access the radio frequency spectrum in an uninterrupted manner. To achieve this, omniscient allocation of spectrum bands among cognitive radio users is crucial. Most of the existing spectrum allocation methods select a band from a pool according to the service requirements of a single user, neglecting the demand of multiple...
A novel carrier sensing method with self-cancelation of the inter-carrier emission inevitably existent in OFDMA-based coexisting systems is proposed. Different from the conventional energy-based carrier detector, which directly compares the carrier energy with some predefined thresholds without considering such inter-carrier emissions, our proposed method can remove them before making decision, thus...
We consider a multipoint-to-multipoint cognitive network wherein the communications from L sources to their designated destinations are carried out through the use of K relays in a dual-hop amplify-and-forward cooperative scheme. Aiming to maximize the worst signal-to-interference-plus-noise ratio of the L destinations, we develop a technique that jointly optimizes the sources' transmit powers and...
Coordinated multi-point (CoMP) has been selected as a key technology feature of LTE-Advanced, as it enables the exploitation of inter-cell interference in order to significantly increase spectral efficiency, especially at the cell-edge. While first field trials on CoMP schemes have delivered the proof-of-concept and shown that a moderate extent of theoretically predicated CoMP gains can indeed be...
This paper deals with the handover measurement in cellular networks. The work is dedicated to network modeling and performance evaluation. The exposition concentrates on temporal evolution of the scanning process with key events: (i) a suitable handover target found, (ii) call drop or service failure, and (iii) scan withdrawal. By observations on the stochastic properties of best signal quality and...
In this paper, we present a framework for analysis of self organized distributed coalition formation process for spectrum sharing in interference channel for large scale ad hoc networks. In this approach we define coalition clusters within the network where mutual interdependency between different clusters is characterized by the concept of spatial network correlation. Then by using stochastic models...
The capacity of a network in which a multiple access channel (MAC) generates interference to a single-user channel is studied. An achievable rate region based on superposition coding and joint decoding is established for the discrete case. If the interference is strong, the capacity region is obtained for both the discrete memoryless channel and Gaussian channel. A boundary point of the capacity region...
In this paper, an efficient rate allocation scheme to maximize the throughput in uplink multi-rate time-hopping ultra-wideband (TH-UWB) communications is proposed. This is a challenging task due to the lack of a suitable closed form expression of the multiuser interference in a multi-rate context. Moreover, an exhaustive search for the optimal solution would be too prohibitive due to the high complexity...
Downlink coverage issues for macrocellular users (UEs) in a macrocellular network with Closed Subscriber Group (CSG) femtocellular overlay have so far been investigated almost exclusively via simulation. However, consideration of specific scenarios via simulation may not provide general insights applicable to long-term planning for femto-macro deployments. In this paper, we employ general models for...
We consider a cognitive radio network where primary users (PUs) and secondary users (SUs) coexist and share the same spectrum. Secondary users access the spectrum randomly and limit the outage probability experienced by the primaries by controlling their transmission probability and by obeying a primary exclusion region (PER), within which all SUs have to be inactive. We propose a vertical cooperative...
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