Population adaptation for genetic algorithm-based cognitive radios

Abstract — Genetic algorithms are best suited for optimization problems involving large search spaces. The problem space encountered when optimizing the transmission parameters of an agile or cognitive radio for a given wireless environment and set of performance objectives can become prohibitively large due to the high number of parameters and their many possible values. Recent research has demonstrated that genetic algorithms are a viable implementation technique for cognitive radio engines. However, the time required for the genetic algorithms to come to a solution substantionally increases as the system complexity grows. In this paper, we present a population adaptation technique for genetic algorithms that takes advantage of the information from previous cognition cycles in order to reduce the time required to reach an optimal decision. Our simulation results demonstrate that the amount of information from the previous cognition cycle can be determined from the environmental variation factor (EVF), which represents the amount of change in the environment parameters since the previous cognition cycle. I

WILEY WIRELESS COMMUNICATIONS AND MOBILE COMPUTING 1 DSP Implementation of a Bit Loading Algorithm for Adaptive Wireless Multicarrier Transceivers

In this paper, we present a proof-of-concept, fixed-point, DSP hardware implementation of an adaptive bit loading algorithm that is designed for wireless multicarrier transceivers. Adaptive bit loading is used to enhance the performance of multicarrier transceivers by tailoring the subcarrier signal constellations to the channel conditions, which can vary across the subcarriers. Since most bit loading algorithms possess a high computational cost and are unable to cope with rapid variations of wireless channels, they are seldom used in present wireless standards. To prove that adaptive bit loading is feasible for wireless transceivers, our work focuses on the implementation of a known bit loading algorithm that can quickly search for the final bit allocation in an iterative manner. The goal of this algorithm is to yield the largest-possible throughput while satisfying a mean BER constraint. The performance of the hardware implementation operating in time-varying channel conditions is studied in terms of the overall throughput. Furthermore, the robustness of the hardware implementation is evaluated, relative to sudden changes in the channel that interrupts the run of the algorithm. Real-time operations and fixed-point representation issues are included in the discussion. Additionally, we propose a modifie

SUBCARRIER POWER ADJUSTMENT TECHNIQUE FOR PEAK-TO-AVERAGE POWER RATIO REDUCTION OF OFDM SYSTEMS

Abstract — In this paper, we propose a novel peakto-average power ratio (PAPR) reduction algorithm for OFDM systems that employs a two-step approach for adjusting the subcarrier power levels. The first step redistributes the power level across all subcarriers, which slightly reduces the error robustness of the system, while the second step ensures the subcarrier power distribution obeys a subband power constraint. The resulting power levels satisfy spectrum regulatory requirements across the transmission spectrum while simultaneously reducing the PAPR and maintaining a degree of error robustness. Since no overhead information is required, the proposed algorithm does not incur a throughput penalty. Simulation results for a 256-subcarrier OFDM system employing QPSK symbols and the proposed algorithm show a PAPR reduction of 1.5 dB for a complementary cumulative distribution of 0.1%. I

Tap Loading of Subcarrier Equalizers for Wireless Multicarrier Transceivers

Abstract—We present a novel algorithm for defining the lengths of subcarrier equalizers employed by wireless multicarrier transmission systems operating in frequency-selective fading channels. The equalizer lengths across the subcarriers are incrementally varied in a “greedy ” fashion until the global cost function is below some prescribed threshold. By varying the equalizer lengths, the overall complexity of the equalization is constrained while the system meets a minimum error performance. Moreover, we investigate four strategies for terminating the proposed algorithm when an adequate number of equalizer taps have been allocated in this process. The results show that a system that employs variable-length equalizers defined by the proposed algorithm can achieve an improvement in error robustness of as much as an order of magnitude, relative to a system that employs constantlength equalizers with the same overall complexity. Index Terms—Adaptive allocation, equalization, loading algorithms, multicarrier modulation. I

Submitted to DySPAN’07 Feasibility of Dynamic Spectrum Access in Underutilized Television Bands

Abstract — This paper presents the preliminary results from a feasibility study regarding the operation of secondary spectrum users within unused television spectrum. Television spectrum is known within the wireless communications community as being underutilized, making it a prime candidate for dynamic spectrum access. Nevertheless, the quality of this spectrum for enabling secondary transmissions has never been assessed. Two unique scenarios are examined:(i) the possibility of unlicensed devices interfering with digital TV reception, and (ii) the possibility of secondary users experiencing interference when operating within close proximity to television towers. With respect to the former, we investigate the critical operating parameters for developing the technical rules for device operation in bands adjacent to a digital television transmission. Regarding the latter, we examine, via measurement campaign, how non-ideal transmission properties of television broadcasts, including intermodulation and saturation effects, can potentially impair the performance of secondary transmissions. Index Terms—Digital TV, spectrum measurements, spectrum white space I

Adaptive dynamic radio open-source intelligent team (ADROIT): Cognitively-controlled collaboration among SDR nodes

Abstract — The ADROIT project is building an open-source software-defined data radio, intended to be controlled by cognitive applications. The goal is to create a system that enables teams of radios, where each radio both has its own cognitive controls and the ability to collaborate with other radios, to create cognitive radio teams. The desire to create cognitive radio teams, and the goal of having an open-source system, requires a rich and carefully architected system that provides great flexibility (enabling cognitive applications to change the radio’s behavior) and also has a clear structure (both so that others may add or enhance the software, and also so that the system can be clearly modeled for cognitive applications). What follows is a summary of the ADROIT system and the key architectural features intended to enable cognitive radio teams. 1 I