An Efficient Implementation of NC-OFDM Transceivers for Cognitive Radios

Abstract

In this paper, we present an efficient implementation of a non-contiguous orthogonal frequency division multiplexing (NC-OFDM) transceiver for cognitive radio systems. NC-OFDM is designed to transmit information in the presence of incumbent users, deactivating subcarriers located in the vicinity of these users to avoid interference. Given that the core component of an NC-OFDM transceiver is the fast Fourier transform (FFT), and that several of the subcarriers are deactivated, it is possible to reduce the execution time by "pruning" the FFT. We propose an algorithm that efficiently and quickly prunes the FFT for NC-OFDM transceivers. Results show that the proposed algorithm substantially outperforms other FFT pruning algorithms when a medium to large number of subcarriers have been deactivated.

An OFDM throughput analysis for cognitive radio application in contiguous or noncontiguous TV white spaces

“…The OFDM subcarriers corresponding to the spectrum occupied by local broadcasters, which are determined by sensing measurements, are deactivated or turned "off". This kind of transceiver implementation is called NC-OFDM [12][13][14]. The data carriers are transmitted on channels not used by the local broadcasters.…”

“…Two or more contiguous TVWSs can be merged into a single broad channel to obtain a larger bandwidth by using channel bonding techniques. Noncontiguous TVWSs can be combined by using NC-OFDM, which is capable of deactivating subcarriers across its transmission bandwidth that could potentially interfere with the transmission of other users [12]. The OFDM subcarriers corresponding to the spectrum occupied by local broadcasters, which are determined by sensing measurements, are deactivated or turned "off".…”

“…A TVWS device must effectively deal with the fragmented nature of the TVWS spectrum, with the possibility of each fragment being of different width. Aggregating contiguous [8][9][10][11] and noncontiguous [12][13][14] channels may result in improved throughput. Consequently, a TVWS device must be able to support dynamic channel width adaptation.…”

Peak to Average Power Ratio Reduction in NC–OFDM Systems

“…CR also requires an adaptable multicarrier modulation technique to be used at its physical layer. Non contiguous orthogonal frequency division multiplexing (NC-OFDM) [2] can be the very suitable modulation technique for DSA networks as it provides the agile use of spectrum when it is occupied by both primary and secondary users. It achieves high data rates by deactivating some sub-carriers that can interfere with the primary sub-carriers.…”

An Efficient Non-Uniform Multi-Tone System Based On Ramanujan Sums

“…complexity are less than the other non-uniform schemes [10], including non-contiguous OFDM(NC-OFDM) [11,12] and Warped Discrete Fourier Transform(WDFT) based nonuniform multi-carrier system [13,14].…”