Sudharsan Srinivasan

In this paper, we investigate the effects of RF transceiver’s imperfections on the multi-antenna interference rejection combing (IRC) based black-space cognitive radio (BS-CR) operation. In particular, we explore the effects of power amplifier (PA) nonlinearities and carrier frequency offset (CFO) on the blind IRC technique. The BS-CR operation mode supports effective reuse of the primary user (PU) spectrum, especially for relatively short-distance CR communication. We assume that both the PU system and the BS-CR use orthogonal frequency division multiplexing (OFDM) waveforms with common numerology. In this case the PU interference on the BS-CR signal is strictly flat-fading at subcarrier level, and it can be suppressed using subcarrier-wise IRC processing. Spatial sample covariance matrix-based IRC adaptation is applied during silent gaps in CR operation. We propose an analytical framework for modeling CFO effects, together with experimental study of CFO and PA nonlinearity effects. The performance of the IRC scheme is tested considering terrestrial digital TV broadcasting (DVB-T) as the primary service. The validity of the offered expressions for CFO effects are justified through comparisons with respective results from computer simulations. The effect of CFO between the primary and secondary systems is found to be critical for BS-CR operation, while the effect of CR transmitter’s nonlinearity is no worse than in basic OFDM schemes, and the PU transmitter’s nonlinearity has minor effect on BS-CR operation.

In this paper, we investigate multi-antenna interference rejection combing (IRC) based black-space cognitive radio (BS-CR) operation in time-varying channels. The idea of BS-CR is to transmit secondary user (SU) signal in the same frequency band with the primary user (PU) such that SU’s power spectral density is clearly below that of the PU, and no significant interference is inflicted on the PU receivers. We explore the effects of interpolation and mobility on the novel blind IRC technique which allows such operation mode for effective reuse of the PU spectrum for relatively short-distance CR communication. We assume that both the PU system and the BS-CR use orthogonal frequency division multiplexing (OFDM) waveforms with common numerology. In this case the PU interference on the BS-CR signal is strictly flat-fading at subcarrier level. Sample covariance matrix-based IRC adaptation is applied during silent gaps in CR operation. We propose an interpolation-based scheme for tracking ...

In this paper, we investigate multi-antenna interference rejection combing (IRC)-based black-space cognitive radio (BS-CR) operation in time-varying channels. The idea of BS-CR is to transmit secondary user (SU) signal in the same frequency band with the primary user (PU) such that SU’s power spectral density is clearly below that of the PU, and no significant interference is inflicted on the PU receivers. We explore the effects of interpolation and mobility on the novel blind IRC technique which allows such operation mode for effective reuse of the PU spectrum for relatively short-distance CR communication. We assume that both the PU system and the BS-CR use orthogonal frequency division multiplexing (OFDM) waveforms with common numerology. In this case, the PU interference on the BS-CR signal is strictly flat-fading at subcarrier level. Sample covariance matrix-based IRC adaptation is applied during silent gaps in CR operation. We evaluate the effect of the gap length on the link ...

ABSTRACT Multicarrier waveforms have been commonly proposed as strong candidates for cognitive radio (CR) due to their high spectrum efficiency, flexibility in resource allocation and commonality of signal processing for spectrum sensing and spectrum utilization. OFDM based 802.11 Wireless Local Area Network (WLAN) technologies are good candidates as CR waveforms. However, the OFDM based systems have significant limitations as CR due to their limited spectral containment, which degrades the performance in determining the free spaces and in coordinating the spectrum usage. Therefore, methods for suppressing the spectral sidelobes of OFDM are considered in this study. In particular, a combination of edge windowing and cancellation carrier techniques is applied for sidelobe suppression. In this study, such an enhanced OFDM scheme is compared with traditional OFDM and filter bank based schemes in spectrum sensing and spectrum allocation, considering also the spectral leakage effects appearing in practical WLAN devices due to power amplifier nonlinearity.

Wireless Local Area Networks (WLAN) such as the OFDM based 802.11g system is designed to operate in 2.4 GHz ISM band. IEEE 802.11 devices are used at the same frequency band with various other applications, which causes interference between different users and leads to significant performance degradation. Hence, Cognitive Radio (CR) technology has been considered for coordinating the spectrum usage in a better way in this band. Spectrum sensing is one of the most important functions in a CR. In this study, filter bank based wideband spectrum sensing techniques are applied for detecting WLAN signals and spectral holes. Also filter bank based multicarrier techniques, together with a water-filling based subcarrier loading algorithm, are considered for effective exploitation of the detected holes. Clear benefit is demonstrated for using spectrally well-contained subband processing instead of basic FFT approaches.

ABSTRACT OFDM based 802.11g Wireless Local Area Networks (WLAN) operate in the 2.4 GHz ISM band. Various other wireless systems use the same band which causes interference and leads to significant performance degradation. Hence, Cognitive Radio's (CR) could better determine free spectrum and coordinate the spectrum usage in this band. Apart from this, to reduce the interference due to spectral leakage, Filter Bank Multicarrier (FBMC) type of system is considered as an alternative to FFT based systems. In this study, FFT and filter bank based spectrum sensing methods are compared by applying them for detecting spectral holes between WLAN and FBMC channels, considering also the spectral leakage effects appearing practical WLANs. Also the performance of alternative multicarrier techniques regarding the efficiency of spectrum utilization is studied.