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The main challenge for Cognitive Radio Networks (CRNs) is avoiding interference with PUs caused by unlicensed access, especially in any disaster where the Cognitive Radio (CR) nodes may lose the connection to the data base entity. To cope with this challenge, each CR node depends on its observations, such as Signal to Noise Ratio (SNR) and Signal Strength (SS), to define the free channel. However,...
In this paper, we study allocation of power and modulation order (rate) to secondary users in a competitive cognitive radio network (CRN). In a competitive CRN, multiple secondary users share a single channel and multiple channels are simultaneously used by a single secondary user (SU) to satisfy their rate requirements [1]. In such an environment, we compute optimal power and modulation order choices...
We consider a multi-channel cognitive radio network (CRN) where multiple secondary users share a single channel and multiple channels are simultaneously used by a single secondary user (SU) to satisfy its rate requirement. For such an environment, we develop a user-based distributed approach based on a game theoretic formulation. The overall objective is to determine the optimal power and rate (modulation...
Performance optimization of practical communication networks should be performed by considering some practical constraints such as limitation of maximum transmitted power, discrete bit allocation to carriers and users, and quality of service (QoS) requirements for different users. In this paper, we provide the optimum resource allocation solution for an OFDMA downlink in which subcarriers are loaded...
In this paper, we investigate spectrum sharing and multiple access problems for the high-rate ultra-wideband (UWB) systems. Based on the use of the linear precoded orthogonal frequency division multiplexing (LP-OFDM) proposed as an evolution of the well known multi-band OFDM (MB-OFDM) solution supported by the WiMedia Alliance for future high-rate UWB systems, the objective of this paper is to study...
For multiple half-duplex amplify-and-forward (AF) relays in cellular communications, a statistical power allocation (control) method is designed to minimize network power under the relay-transmit-power and the signal-to-interference-plus-noise ratio constraints. Computer simulation corroborates that the designed relay processing yields significant performance enhancement and network power reduction...
We consider a multichannel cognitive radio network where multiple secondary users (SUs) share a single channel and where multiple channels are simultaneously used by a single SU to satisfy their rate requirements. We attempt to evaluate the optimal power and rate distribution choices that each SU has to make to maintain their quality of service (QoS). Our measures for QoS include bit error rate (BER)...
In this paper, we investigate the optimization problem of resource allocation in downlink of multiuser MISO-OFDM system. Multiple users with different BER and minimum transmission rate requirements are considered. We propose a novel heuristic allocation algorithm (HAA) of radio resource, which minimizes the total transmit power of the base station while meeting individual users'QoS requirements. The...
In this paper, an energy efficient adaptive modulation scheme is proposed for a wireless cognitive radio ad hoc network, where each node is equipped with cognitive radio and the network is an OFDMA system operating on time slots. In each slot, the users with new traffic demand will sense the spectrum and locate the available subcarrier set. Then they choose subcarriers with favorable channel condition...
This paper investigates effects of pilot assisted channel estimation on dynamic resource allocation in a multiuser orthogonal frequency division multiplexing (OFDM) system. The channel estimation is done in each OFDM symbol through least-squared error (LSE) or minimum mean-squared error (MMSE) algorithm. The performance of each of these algorithms is evaluated through computer simulations. The maximal...
This paper explores the attributes, layering models and objective functions in cross layer designs for mobile ad hoc wireless networks by taking all the statistical characteristics and constraints from the physical (PHY) layer, media access control (MAC) layer and network (NET) layer into consideration. This paper reviews the entire network optimization across all the PHY/MAC/NET layers. At the PHY...
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