Extended Subcarrier Weighting for Sidelobe Suppression in OFDM Based Cognitive Radio

Abstract

Subcarrier weighting (SW) is a recognized technique for sidelobe suppression in OFDM systems. In this paper SW is discussed in the context of cognitive radios where some portion of the spectrum is shared with primary users so it is required to notch that portion. A major disadvantage with SW scheme is bit error rate (BER) degradation due to unequal power distribution among different subcarriers therefore the primary objective of the paper is to enhance the performance of SW without additional degradation in BER performance. To this extent we propose an Elliptical-SW scheme by expanding the locus of weights to elliptical region. Simulation results show that the proposed scheme can produce deeper notch as compared to Conventional-SW for same BER performance. In second part we present a Partial-SW scheme by applying SW to lesser number of subcarriers. It can enhance BER performance significantly with negligible loss in sidelobe suppression capacity. Another scheme namely Guarded-SW is also proposed in this paper to provide further means to obtain very deep notches without any additional degradation in BER however it has to scarify some throughput. Finally an effective way of implementing SW in MIMO systems is presented by jointly optimizing weights over selected number of antennas.

Orthogonal spectral precoder for minimizing adjacent channel leakage ratio in OFDM based cognitive radio

“…In Subcarrier weighting scheme, sidelobe suppression is achieved by multiplying each symbol by optimum real weights, but it results in bit error rate (BER) performance degradation. An improved Extended‐SW is presented in where, constraints on weights are expanded to elliptical domain thereby improving sidelobe suppression and BER. Paper presented a new technique namely antiphase tones across multiple transmitting antennas which can utilize PUs band for data transmission while creating spectral notch at PUs receiver.…”