Brage Ellingsæter

Digital Broadcasting: Increasing the Available White Space Spectrum Using TV Receiver Information

This paper discusses the increase in available white space spectrum using TV receiver information. TV receivers can increase the amount of available spectrum for cognitive radio devices in the TV bands by as much as 120 MHz.

Frequency allocation game in satisfaction form

In this paper, we analyse frequency allocation in wireless networks through a game in satisfaction form. Satisfaction form games are games without any optimisation aspects where a player is either satisfied or not. We show that such a formulation is especially suited for frequency allocation with quality-of-service constraints. We investigate different equilibrium concepts and show that there exists a mixed-strategy distribution where all players are satisfied with a probability not less than a certain threshold. In the case where there exists a pure-strategy action profile that can achieve satisfaction for all players, we present a learning algorithm that guarantees convergence to this action profile in finite time. In the case that no such pure-strategy action profile exists, we show that the satisfaction form formulation possesses an action profile yielding higher utility for unsatisfied players compared with a normal form game. Lastly we show extensive simulation results that highlight the differences between a frequency allocation game in satisfaction form compared with other game formulations. Copyright

Adaptive M-QAM signaling for dynamic spectrum access

In this paper we consider an OFDM multiuser system with K orthogonal subcarriers. We assume each user uses M-QAM modulation in each subcarrier. The modulation must be adaptive to cope with propagation changes and to meet the bit error rate requirement of the user. We maximize the sum of information bits per user selfishly, and compare the performance with other power allocation algorithms. Surprisingly, measuring rate by constellation size instead of Shannons capacity yields a power allocation algorithm that differ widely from previously known power allocation algorithms, such as the iterative water filling algorithm (IWFA). This is because we only accept bit error rates better than 10−3 and the rate achieved with modulation can only be discrete values, whereas other algorithms based on Shannons capacity can achieve any rate.

Single-tone spectrum allocation under SINR requirements

In this paper we investigate the problem of allocating spectrum among radio nodes under SINR requirements. This problem is of special interest in dynamic spectrum access networks where topology and spectral resources differ with time and location. The problem is to determine the number of radio nodes that can transmit simultaneously while still achieving their SINR requirements and then decide which channels these nodes should transmit on. Previous work have shown how this can be done for a large spectrum pool where nodes allocate multiple channels from that pool which renders a linear programming approach feasible when the pool is large enough. In this paper we extend their work by considering arbitrary individual pool sizes and allow nodes to only transmit on one channel. Due to the accumulative nature of interference this problem is a non-convex integer problem which is NP-hard. However, we introduce a constraint transformation that transforms the problem to a binary quadratic constraint problem. Although this problem is still NP-hard, well known heuristic algorithms for solving this problem are known in the literature. We implement a heuristic algorithm which yields both good solutions and can be implemented in a distributed manner. Simulation results show that this approach provides solutions within an average gap of 10% of solutions obtained by a genetic algorithm for the original non-convex integer problem.

Frequency Coordination in Wireless Ad-Hoc Networks

This paper considers coordination of users in wireless ad-hoc networks. We define coordination as a scheme that tries to achieve the rate region given by Shannons capacity by allowing users to exchange information and agree upon future actions, while still treating interference as noise. This differs from cooperative schemes which try to increase the achievable rate region by introducing and exploiting structure in the interference. The advantage of coordination compared to cooperation is that coordination does not require strict user synchronization and global knowledge of system parameters. Using orthogonalization as the means of coordination, we find conditions for when users should coordinate. Through simulations we investigate the performance of coordination compared to selfish and selfless autonomous power algorithms. Results show that in some scenarios coordination yield high gain, however since our coordination scheme only guarantees to outperform selfish algorithms; full orthogonalization can outperform our coordination scheme in some scenarios.

Power Allocation in Cognitive Radio Based on Minimum Interference Generation

This paper considers a wireless multiuser system with N users that can transmit over K orthogonal frequency bands. In this system, interference from other users is treated as noise. In this system we assume each user has a target rate and the goal is to allow as many users as possible to achieve their target rate. We propose a new power allocation algorithm that minimizes both number of frequency bands to be used and necessary power at any user to achieve a target rate. We show that this approach reduces the overall interference power in the system, and thus increases the number of users achieving a desired target rate compared to other power allocation algorithms. This is supported by simulation results, which also shows that in a dense network, sum capacity of the system is increased compared to regular water filling.

SCFP: sectored circle forwarding protocol: a system enabling dynamic spectrum access

Collaboration between radio devices before claiming a frequency usage is important to maximize spectral efficiency. Not only will the collaboration help the devices to get their required resources, it will also result in better performance for the whole network. In this paper, we propose a system to enable collaboration between cognitive radio devices in a Dynamic Spectrum Access (DSA) network. We present an efficient algorithm to forward a message to all devices within a given area, the Sectored Circle Forwarding Protocol (SCFP). SCFP makes it possible to collaborate between radio devices that may interfere with each other by efficiently identifying these devices. In an area containing N devices, SCFP only needs to send N-1 messages to identify all the devices in the area. A new overlay network implementation, Geographic Optimized Overlay Network (GOON), is also introduced in this paper to support SCFP and make the system as efficient as possible.