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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...
Limited feedback precoding is part of the LTE standard. Despite standardization, important fundamental questions, especially relating to the performance due to the use of codebooks and receiver processing techniques, remain to be explored. In order to understand these questions, we consider a single user in a single cell employing single or multi-stream transmission using a variety of codebooks and...
An asymptotic technique is developed to find the Signal-to-Interference-plus-Noise-Ratio (SINR) and spectral efficiency of a link with N receiver antennas in wireless networks with non-homogeneous distributions of nodes. It is found that with appropriate normalization, the SINR and spectral efficiency converge with probability 1 to asymptotic limits as N increases. This technique is applied to networks...
We present a link capacity estimation model and a hybrid routing scheme for wireless mesh networks which aims at improving throughput. The multi-source interference between links and frame capture behaviors of nodes are analyzed. Our model provides estimated values which can indicate the relative quality of wireless links. And we present a routing metric which combines multiple factors based on the...
In this paper we propose a general model to estimate the maximum allowed transmit power of a secondary node based on the measured signal from the primary transmitter that is willing to share its downlink spectrum. The transmit power should satisfy primary constraints related to the minimum required Signal to Interference and Noise Ratio (SINR) of its users. The model can be used by secondary nodes...
In this paper, we propose a multiple-state other-cell interference (OCI) model, which takes into account the interference variability and uncertainty created by scheduling and other fast resource allocation adaptivity. This situation is modeled by a set of states, each described by a spatial covariance matrix and a probability. In order to illustrate the usefulness of such a model, we study two receive...
We consider prefiltering for a single-carrier transmission over frequency-selective channels, where reduced-state trellis-based equalization is employed at the receiver, such as delayed decision-feedback sequence estimation (DDFSE) or reduced-state sequence estimation (RSSE). While previously proposed prefiltering schemes are based on the optimum filters of decision-feedback equalization (DFE), the...
Impulse radio ultra-wide bandwidth wireless is a fast emerging technology where its applications underlay coexisting narrowband services over a huge bandwidth. Therefore, the coexistence problem between ultra-wide bandwidth and narrowband systems warrants investigation. A time-hopping sequence design is proposed for impulse radio ultra-wide bandwidth systems to suppress the mutual interference between...
Optimum capacity scaling in the downlink of a single-cell multiple-input-multiple-output communication system can be achieved by a communication strategy called opportunistic beamforming in which information carrying beams are randomly formed and users are opportunistically scheduled based on their partial channel state information. Even though opportunistic beamforming reduces the amount of feedback...
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...
We study optimal transmission strategies in interfering wireless networks, under Quality of Service constraints. A buffered, dynamic network with multiple sources is considered, and sources use a retransmission strategy in order to improve packet delivery probability. The optimization problem is formulated as a Markov Decision Process, where constraints and objective functions are ratios of time-averaged...
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...
A three-dimensional (3D) multi-cell multi-user system model along with spatial array processing are presented and studied in this paper. Most of the radio propagation in the literature has been studied and modeled in a two dimensional plane. The 3D propagation channel modeling has drawn attentions recently. This is due to the fact that, in some scenarios, the assumption of small elevation domain angular...
In this paper, we formulate a joint optimization problem for resource allocation and scheduling in full-duplex orthogonal frequency division multiple access (OFDMA) relaying systems with amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols. Our problem formulation takes into account heterogeneous data rate requirements for delay sensitive users. Besides, a theoretically optimal...
This paper studies the \emph{robust weighted-sum rate} optimization problem in the presence of channel uncertainty over a $K$-user Gaussian Interference Channel (GIFC), where multiple antennas are present at all transmitters and receivers. Motivated by recent results on \emph{interference alignment} that show the optimality of linear precoders and simple receivers in achieving the maximum degrees-of-freedom...
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...
Nanotechnology is providing the engineering community with a new set of tools to design and manufacture integrated devices just a few hundred nanometers in total size. Communication among these nano-devices will boost the range of applications of nanotechnology in several fields, ranging from biomedical research to military technology or environmental science. Within the different alternatives for...
Opportunistic spectrum access creates the opening of under-utilized portions of the licensed spectrum for reuse, provided that the transmissions of secondary radios do not cause harmful interference to primary users. Therefore, it is important to characterize the effect of cognitive network interference due to such secondary spectrum reuse. In this paper, we show how a new statistical model for aggregate...
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...
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