Vinay Thumar

Distributed Power Allocation for Secondary Users in a Cognitive Radio Scenario

The major contribution of this paper is distributed power allocation for a multi-user multi-channel Cognitive Radio (CR) network which deploys overlay spectrum sharing by the Primary Users (PUs) and Secondary Users (SUs), and Frequency Division Multiplexing Access (FDMA) for the SUs. The transmit power of each SU is constrained by an individual node power budget, the interference threshold on the PU band, as well as the interference caused to the neighboring SUs. Motivated by the non-convex structure of the problem and the need to execute the power allocation distributedly, the problem is cast within a game theoretic frame-work. Pay-off functions for the SUs are formulated to suit the system model, and the Nash Equilibrium for the game is analyzed. Simulation results are provided to validate the mathematical concepts and to evaluate the performance of the proposed distributed power control algorithm in comparison with other relevant schemes.

A cross-layer framework for symbiotic relaying in cognitive radio networks

The prime focus of this work is in developing a Symbiotic Cooperative Relaying (SCR) architecture for the Commons model of Dynamic Spectrum Access. The incumbent Primary User (PU) of the spectrum, with a weak transmission link, seeks cooperation from the cognitive Secondary User (SU) nodes in its vicinity, and in return rewards them with a suitable incentive. The incentive may be offered in terms of time (Cognitive Relaying with Time Incentive), frequency bands (Cognitive Relaying with Frequency Incentive), or both (Cognitive Relaying with Time and Frequency Incentive). Cross-layer optimization problems are formulated, which maximize the transmission opportunities for the SUs in the multi-hop multichannel relay network, and offer a guaranteed throughput to the PU. To make the SCR scheme practically realizable, a MAC scheduling protocol is proposed within a unified framework for both the PU and SUs. Furthermore, cross-layer formulations are also proposed for multiple SUs to efficiently access the Time or Frequency Incentive for their own communication. Simulation results are furnished for each of the proposed SCR schemes to demonstrate their effectiveness from the perspective of both the PU and SUs.

Power allocation in Cognitive Radio: Single and multiple secondary users

Cognitive Radio (CR) improves spectral efficiency by allowing unlicensed (secondary) users to concurrently operate with licensed (primary) users. The side-lobe interference from an OFDM-based secondary user (SU) causes unwanted interference to the primary user (PU) of the spectrum. While interference mitigation to the PU spectral band has received a lot of attention in recent literature, the novelty of our work is in considering sub-bands of the PU, and ensuring that the interference to each of them is below a specified threshold. The approach is realistic and more effective in protecting the PU from the SU interference. We formulate an optimization problem for power allocation for a single SU to maximize its throughput, within a power budget, and an interference constraint on each PU sub-band. After extensively analyzing the solution form, we propose an iterative algorithm to meet the aforementioned objective. A power allocation algorithm is also proposed for a multiple SU scenario, which involves assigning sub-carriers to each user, besides the power and PU interference constraint, to maximize the sum throughput. Simulation results are provided, for both single and multi-user cases, which indicate that the proposed algorithms outperform those which have been previously presented in literature.

Cognitive Relaying with Time Incentive: Protocol design for Multiple Primary Users

The prime focus of this work is in developing a protocol for a symbiotic architecture called Cognitive Relaying with Time Incentive for Multiple Primary Users (CRTI-M). The rationale of CRTI-M is that the Primary Users (PUs) of a Cognitive Radio (CR) network, with weak transmission links, seek cooperation from the cognitive Secondary User (SU) nodes in their vicinity, and in return reward them with an incentive time for their own communication. Each PU has its own distinct bandwidth of operation; however, when relaying through the SU network it can use the bandwidth of the other PUs as well to enhance its throughput. A cross-layer optimization problem is formulated to that effect in a multi-hop multi-channel SU network. The time incentive that should be awarded to the SUs by each PU is analyzed by means of a utility-based decision-making process, and its efficient utilization is proposed. To make the CRTI-M scheme practically realizable, a MAC scheduling protocol is devised within a unified framework of the PUs and SUs. Simulation results are furnished to demonstrate the proof of concept.

Power allocation, bit loading and sub-carrier bandwidth sizing for OFDM-based cognitive radio

The function of the Radio Resource Management module of a Cognitive Radio (CR) system is to evaluate the available resources and assign them to meet the Quality of Service (QoS) objectives of the Secondary User (SU), within some constraints on factors which limit the performance of the Primary User (PU). While interference mitigation to the PU spectral band from the SUs transmission has received a lot of attention in recent literature; the novelty of our work is in considering a more realistic and effective approach of dividing the PU into sub-bands, and ensuring that the interference to each of them is below a specified threshold. With this objective, and within a power budget, we execute the tasks of power allocation, bit loading and sizing the sub-carrier bandwidth for an orthogonal frequency division multiplexing (OFDM)-based SU. After extensively analyzing the solution form of the optimization problems posed for the resource allocation, we suggest iterative algorithms to meet the aforementioned objectives. The algorithm for sub-carrier bandwidth sizing is novel, and not previously presented in literature. A multiple SU scenario is also considered, which entails assigning sub-carriers to the users, besides the resource allocation. Simulation results are provided, for both single and multi-user cases, which indicate the effectiveness of the proposed algorithms in a CR environment.

Optimum Bit Loading for Cognitive Relaying

Cognitive relaying is a recent communication paradigm that increases network coverage and improves spectral efficiency by allowing unlicensed (secondary) users to concurrently operate with licensed (primary) users. The major contribution of this paper is in proposing a bit allocation algorithm to be used in a cognitive relay network. The dynamic spectrum access in an OFDM-based cognitive relay network may lead to unwanted interference to the primary user. Assuming knowledge of the instantaneous channel gains for all links in the network and the primary user band, the proposed algorithm meets the twofold challenge of achieving optimum secondary system throughput while ensuring minimum interference to the primary. In its first pass, the proposed algorithm achieves optimum number of bits per subcarrier. However, in the process of achieving integer granularity for practical constellation sizing, the interference constraint may be violated. A second pass of the algorithm tackles this condition by executing a interference-based greedy bit removal. Simulation results are provided, which are indicative of the fact that the proposed algorithm exhibits enhanced performance for both primary and secondary users in the cognitive radio network.

Judicious power loading for a cognitive relay scenario

This paper introduces a power loading strategy for relays to be used in a cognitive scenario. A cognitive relay node allows unlicensed (secondary) users to concurrently operate with licensed (primary) users, thereby improving spectral efficiency. The dynamic spectrum access in an OFDM-based cognitive relay network may lead to unwanted interference to the primary user from the side lobes of the secondary users. Two judicious algorithms are formulated by means of which the cognitive relay meets the twofold challenge of achieving optimum system throughput while ensuring minimum interference to the primary. The simulation results demonstrate that the suggested algorithms exhibit enhanced channel capacity for the secondary users as compared to traditional power allocation methods.

Adaptive power allocation for secondary users in Cognitive Radio networks

In a Cognitive Radio spectrum sharing scenario, the side-lobe interference from an OFDM-based secondary user (SU) causes unwanted interference to the primary user (PU) of the spectrum. The objective of this work is to allocate power in the SU sub-carriers such that it maximizes its throughput, within a power budget, while ensuring that the interference to the PU is within a specified threshold. We assume a more realistic and effective solution by mitigating the interference to each of the sub-bands of the PU. Assuming knowledge of the instantaneous channel gains on the SU to SU link, as well as those of the SU to PU link, an iterative algorithm is proposed to achieve the aforementioned objective. Simulation results are provided, which indicate that the proposed algorithm outperforms those which have been previously presented in literature.

Cognitive Relaying with Time Incentive: Multiple Primary Users

This work is directed towards a symbiotic architecture called Cognitive Relaying with Time Incentive (CRTI) for multiple Primary Users (PUs) in a Cognitive Radio network. The rationale of CRTI is that the PU with a weak transmission link seeks cooperation from the cognitive Secondary User (SU) nodes in its vicinity, and in return rewards them with an incentive time for their own communication. Since each PU has its own distinct bandwidth of operation, it is crucial to decide the most favorable use of the spectrum when relaying through the SU network. We propose two schemes-Band-Restricted Relaying and All-Band Relaying to achieve this objective. Cross-layer optimization problems are formulated for the relaying schemes which create the time incentive, as well as for the SUs to efficiently access this incentive. The proposed schemes are compared, and simulation results are furnished to demonstrate their differences and individual merits from the PU and SUs perspective.

Cognitive Relaying with Frequency Incentive

The prime focus of this work is in describing a symbiotic architecture for a Cognitive Radio network, called Cognitive Relaying with Frequency Incentive. The incumbent Primary User (PU) of the spectrum, with a weak transmission link, seeks cooperation from the cognitive Secondary User (SU) nodes in its vicinity, and in return rewards them with incentive frequency bands for their own communication. We propose two schemes (Band-Set Minimization and Edge-by-Band Minimization) to achieve this objective. Cross-layer optimization problems are formulated to create the frequency incentive while ensuring a guaranteed throughput for the PU, as well as for the SUs to efficiently access this incentive. The proposed schemes are extensively compared, and simulation results are furnished to demonstrate their differences and individual merits from the perspective of both the PU and SUs.