Ruolin Zhou

Novel overlay/underlay cognitive radio waveforms using SD-SMSE framework to enhance spectrum efficiency-part II: analysis in fading channels

Interest in Cognitive Radio (CR) remains strong as the communications community strives to solve the spectrum congestion problem. In conventional CR implementations, interference to primary users is minimized using either overlay waveforms that exploit unused (white) spectrum holes or underlay waveforms that spread their power spectrum density over an ultra-wide bandwidth. In Part I, we proposed a novel hybrid overlay/underlay waveform that realizes benefits of both waveforms and demonstrated its performance in an AWGN channel. This was done by extending the original Spectrally Modulated Spectrally Encoded (SMSE) framework to enable soft decision CR implementations that exploit both unused (white) and underused (gray) spectral areas. In Part II, we analyze and evaluate performance of the proposed hybrid overlay/underlay waveform in frequency selective fading channels. A simulated performance analysis of overlay, underlay and hybrid overlay/ underlay waveforms in frequency selective fading channels is presented and benefits discussed.

A novel hybrid overlay/underlay Cognitive Radio waveform in frequency selective fading channels

Cognitive Radio (CR) has attracted strong interest recently to solve the spectrum congestion problem. In conventional cognitive radio, either overlay waveform is used to exploit unused (white) spectrum holes to avoid interference to primary users, or underlay waveform is employed to spread over a ultrawide bandwidth with extremely low power spectrum density to minimize interference to primary users. In our previous work, we proposed a novel hybrid overlay/underlay waveform to combine the benefits of both overlay and underlay waveform, creating a soft decision cognitive radio to exploit both the unused (white) spectral regions and the underused (gray) spectral areas. Extending the spectrally modulated spectrally encoded (SMSE) framework, we provide the framework for the proposed soft decision cognitive radio. We also evaluate the performance of the hybrid overlay/underlay waveform in frequency selective fading channels. A simulated performance analysis of overlay, underlay and hybrid overlay/underlay waveforms in frequency selective fading channels is presented and benefits discussed.

A Software Defined Radio Based Adaptive Interference Avoidance TDCS Cognitive Radio

In this paper, we implement and demonstrate an adaptive interference avoidance TDCS (Transform-domain Communication System) based cognitive radio via software defined radio implementation. By dynamically notching the occupied bands prior to applying IDFT, the designed cognitive radio communicates without interference to primary users and from primary users, as well as provides coexistence between primary users and secondary users. The designed system applies GNU software radio as the platform, and USRP (Universal Software Radio Peripheral) as the hardware solution. This cognitive radio is capable of detecting primary users in real time and adaptively adjusting its transmission parameters to avoid interference to primary users. Additionally, we have demonstrated that when the primary user transmission changes, the cognitive radio dynamically adjusts its transmission accordingly. We have demonstrated seamless real time video transmission between two cognitive radio nodes, while avoiding interference from primary users and interference to primary users operating in the same spectrum.

Total Intercarrier Interference Cancellation for OFDM Mobile Communication Systems

For orthogonal frequency division multiplexing (OFDM) communication systems, the orthogonality among subcarriers is lost in mobile radio channels due to the frequency offsets caused by mobility. As a direct result, intercarrier interference (ICI) is observed on each and every subcarrier, leading to significant performance degradation. Many ICI cancellation methods such as windowing and frequency domain coding have been proposed in the literature to cancel ICI and improve the BER performance of OFDM in mobile channel. However, the performance improvement achieved by all the existing ICI cancellation methods is far from enough: the BER performance after ICI cancellation is still much worse than the BER performance of original OFDM without ICI. Moreover, popular ICI cancellation methods like ICI self-cancellation reduce ICI at the price of lowering the transmission rate and reducing the bandwidth efficiency. Other frequency-domain coding methods do not reduce the data rate, but produce less reduction in ICI as well. In this paper, we propose a novel ICI cancellation scheme which can eliminate the ICI entirely and offer a OFDM mobile system with the same BER performance of a OFDM system without ICI. More importantly, the proposed ICI cancellation scheme, namely Total ICI Cancellation, does not lower the transmission rate or reduce the bandwidth efficiency. Specifically, the Total ICI Cancellation scheme takes advantage of the orthogonality of the ICI matrix and offers perfect ICI cancellation and significant BER improvement at linearly growing cost. Simulation results in AWGN channel and multi-path fading channel confirm the superb performance of the proposed Total ICI Cancellation scheme in the presence of frequency offset or time variations in the channel, outperforming all the existing ICI cancellation methods.

Intercarrier Interference Immune Single Carrier OFDM via Magnitude Shift Keying Modulation

SC-OFDM (single carrier orthogonal frequency division multiplexing) has demonstrated excellent performance in multipath fading channels with very low peak to average power ratio (PAPR). Similar to other multi-carrier transmission technologies such as MC-CDMA and OFDM, SC-OFDM also suffers significant performance degradation to inter-carrier interference (ICI) when there is a frequency offset between the transmitter and receiver or in a high mobility environment. In this paper, we analyze the effect of ICI on SC-OFDM system and propose a novel modulation scheme called Magnitude Shift Keying (MSK) for SC-OFDM system. The MSK modulation provides SC-OFDM system immunity to ICI and significantly outperforms SC-OFDM system and OFDM system with Phase Shift Keying (PSK) modulations in severe ICI environment. Simulation results over AWGN channel and multi-path fading channels with different ICI confirm the effectiveness of the proposed system.

Software Defined Radio Implementation of SMSE Based Overlay Cognitive Radio

In this paper, we demonstrate an adaptive interference avoidance overlay cognitive radio implementation via software defined radio. Using spectrally modulated spectrally encoded (SMSE) framework, we implement a multi-carrier based overlay cognitive radio waveform via USRP (Universal Software Radio Peripheral) software defined radio boards and GNU radio software platform. This cognitive radio is capable of detecting primary users in real time and adaptively adjusting its transmission parameters to avoid interference to primary users. More importantly, this cognitive radio can take advantage of multiple spectrum holes by employing non-contiguous multicarrier transmission technologies. Additionally, we demonstrate that when the primary user transmission changes, the cognitive radio dynamically adjusts its transmission accordingly. We also demonstrate seamless real time video transmission between two cognitive radio nodes, while avoiding interference from primary users and interference to primary users operating in the same spectrum.

Total Inter-Carrier Interference Cancellation for MC-CDMA System in Mobile Environment

Multi-carrier code division multiple access (MC-CDMA)has been considered as a strong candidate for next generation wireless communication system due to its excellent performance in multi-path fading channel and simple receiver structure. However, like all the multi-carrier transmission technologies such as OFDM, the inter-carrier interference (ICI) produced by the frequency offset between the transmitter and receiver local oscillators or by Doppler shift due to high mobility causes significant BER (bit error rate) performance degradation in MC-CDMA system. Many ICI cancellation methods such as windowing and frequency domain coding have been proposed in the literature to cancel ICI and improve the BER performance for multi-carrier transmission technologies. However, existing ICI cancellation methods do not cancel ICI entirely and the BER performance after ICI cancellation is still much worse than the BER performance of original system without ICI. Moreover, popular ICI cancellation methods like ICI self-cancellation reduce ICI at the price of lowering the transmission rate and reducing the bandwidth efficiency. Other frequency-domain coding methods do not reduce the data rate, but produce less reduction in ICI as well. In this paper, we propose a novel ICI cancellation scheme that can eliminate the ICI entirely and offer a MC-CDMA mobile system with the same BER performance of a MC-CDMA system without ICI. More importantly, the proposed ICI cancellation scheme (namely Total ICI Cancellation) does not lower the transmission rate or reduce the bandwidth efficiency. Specifically, by exploiting frequency offset quantization, the proposed scheme takes advantage of the orthogonality of the ICI matrix and offers perfect ICI cancellation and significant BER improvement at linearly growing cost. Simulation results in AWGN channel and multi-path fading channel confirm the excellent performance of the proposed Total ICI Cancellation scheme in the presence of frequency offset or time variations in the channel, outperforming existing ICI cancellation methods.

A software-defined radio based cognitive radio demonstration over FM band

In this paper, we present a software defined radio (SDR) based cognitive radio implementation and demonstration. Using GNU Radio and USRP SDR boards, we implement and demonstrate a cognitive radio that detects spectrum holes in the FM band and exploits the available spectrum holes to transmit digital and analog data without interfering the existing FM transmission. Moreover, we demonstrate that when a primary users transmission starts over the original spectrum holes, the cognitive radio automatically adapts its transmission to avoid interference to the newly coming primary user. Additionally, we have implemented and demonstrated a frequency hopping over multiple spectrum holes to support multiple secondary users with minimum interference to each other.

Software defined radio based frequency domain chaotic cognitive radio

Chaotic communication system has attracted strong interests in high security communication due to robustness in multi-path fading environments, resistance to jamming, and low probability of interception. Recently, cognitive radio has emerged as a strong candidate to solve the spectrum congestion problem by operating over under utilized spectrum bands. Hence, it is highly desired to combine the security advantages of chaos communication with cognitive radio to create a chaotic cognitive radio communication system. However, traditional chaotic communication system is based on time-domain chaotic signal generator where the signal occupies one wide contiguous frequency band, making it inappropriate for cognitive radio applications. To apply the chaotic sequence onto cognitive radio to take advantage of multiple spectrum bands, we generate the chaotic signal in frequency domain. By applying a spectrum mask onto the chaotic signal in frequency-domain, a frequency domain non-contiguous chaotic waveform is created. In this paper, we use universal software radio peripheral and GNU radio software to implement and demonstrate a frequency domain chaotic cognitive radio. This demonstration has several unique features: (1) supporting real-time video transmission; (2) taking advantage of multiple non-contiguous spectrum bands; (3) dynamic cognitive radio waveform adaptation according to the primary user transmissions; (4) maintaining the security features of chaotic communication.

Software Defined Radio Implementation of SMSE Based Overlay Cognitive Radio in High Mobility Environment

A spectrally modulated spectrally encoded (SMSE) based overlay cognitive radio has been implemented and demonstrated in [1] via GNU software define radio (SDR). However, like most of the current cognitive radio implementations and demonstrations, this work does not consider the mobility between cognitive radio nodes. In a high mobility environment, the frequency offset introduced by Doppler shift leads to loss of the orthogonality among subcarriers. As a direct result, severe inter-carrier interference (ICI) and performance degradation is observed. In our previous work, we have proposed a new ICI cancellation method (namely Total ICI Cancellation) for OFDM [2] and MC-CDMA [3] mobile communication systems, which eliminates the ICI without lowering the transmission rate nor reducing the bandwidth efficiency. In this paper, we apply the total ICI cancellation algorithm onto the SMSE base overlay cognitive radio to demonstrate a high performance cognitive radio in high mobility environment. Specifically, we demonstrate an SMSE based overlay cognitive radio that is capable of detecting primary users in real time and adaptively adjusting its transmission parameters to avoid interference to (and from) primary users. When the primary user transmission changes, the cognitive radio dynamically adjusts its transmission accordingly. Additionally, this cognitive radio maintains seamless real time video transmission between the cognitive radio pair even when large frequency offset is introduced by mobility between CR transmitter and receiver.