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Compared to OFDM systems with cyclic prefix, filterbank multicarrier with offset quadrature amplitude modulation (FBMC/ OQAM) system is considered as an alternative technology for next generation wireless communication systems. However, FBMC systems suffer from intrinsic imaginary interference caused by the real-field orthogonality destruction when passing through complex-valued fading channels. By analyzing the transmultiplexer's response of FBMC/OQAM systems, in this paper, a simple conjugated transmission scheme is proposed for FBMC/OQAM systems. Following the specific conjugation design, the intrinsic imaginary interference including the intrinsic inter-symbol and the inter-carrier interference can be eliminated at the receiver side through linear signal processing operation. Meanwhile, the proposed conjugated transmission scheme is able to obtain extra linear combination diversity gains for improving the systematic performance of FBMC/OQAM. Simulation results show that the proposed scheme is more efficient than conventional methods, especially in practical application scenarios with large Doppler spread caused by high-speed movement.

Toward the era of mobile internet and Internet of Things (IoT), numerous sensors and devices are being introduced and interconnected. To support such amount of data traffic, traditional wireless communication technologies are facing challenges both in terms of increasingly shortage of spectrum resource and massive multiple access. In this paper, cognitive code division multiple access (Cognitive-CDMA) is proposed by combining the concept of cognitive radio with dynamic noncontinuous spectrum bands and code division multiple access. In order to suppress multiple access interference resulting from the non-orthogonality of partial available spectrum bins, carrier frequency offset, and spectrum sensing mismatch, an enhanced receiver design using frequency-domain oversampling (FDO) with linear minimum mean square error (MMSE) is considered in this paper for Cognitive-CDMA systems. By spectrum sensing to mitigate spectral interference in the transceiver and by utilizing FDO in the receiver to project received signal to a higher dimension, the proposed Cognitive-CDMA is able to support robust and massive multiple access for IoT applications. The simulation results show that the cognitive-CDMA with FDO-MMSE receiver outperforms that with conventional per-user MMSE receiver in the presence of multipath fading channels, carrier frequency offset, and spectrum sensing mismatch.

Localizing noncooperative transmitter (Tx) and receiver (Rx) that belong to another system is important in many scenarios, e.g., interference management in cognitive radio systems and user behavior learning in ad hoc wireless networks. However, obtaining the locations of these nodes in particular in frequency-division duplex systems is challenging, since the localization network usually does not know the spectrum that the Rx uses for backward transmission. In this paper, we propose to use the full-duplex relay technique to localize a noncooperative Rx, which does not require the knowledge of the Rx’s backward transmission spectrum. In the proposed method, localization sensors alternatively act as a full-duplex amplify-and-forward relay to trigger the power control of the Tx–Rx link. Then, by detecting the power adjustment of the Tx, each localization sensor can estimate the time difference of arrival between the direct and relay signals. Finally, the Rx location can be calculated from triangulation. Simulation results show that the proposed method can effectively localize the Rx, which validates its potential for receiver-aware applications and services.

In this paper, we propose a cooperative method to estimate the cross-channel gain (CCG) between the cognitive transmitter (CT) and primary receiver (PR) for underlay spectrum sharing. This method belongs to spectrum sensing technique. In particular, we introduce multiple cognitive receivers to assist the CT to estimate the CCG. Here, we design and compare three estimators for the CT based on the CT's collected measurements. Compared with conventional non-cooperative CCG estimation method, the proposed method can improve the root mean square error by 3 dB and the successful estimation probability by 37% under a typical scenario.

This paper is focused on training sequence design for efficient channel estimation in multiple-input multiple-output filterbank multicarrier (MIMO-FBMC) communications using offset quadrature amplitude modulation (OQAM). MIMO-FBMC is a promising technique to achieve high spectrum efficiency as well as strong robustness against dispersive channels due to its feature of time-frequency localization. A salient drawback of FBMC/OQAM signals is that only real-field orthogonality can be kept, leading to the intrinsic imaginary interference being a barrier for high-performance channel estimations. Also, conventional channel estimations in the MIMO-FBMC systems mostly suffer from high training overhead especially for large number of transmit antennas. Motivated by these problems, in this paper, we propose a new class of training sequences, which are formed by concatenation of two identical zero-correlation zone sequences whose auto-correlation and cross correlation are zero within a time-shift window around the in-phase position. Since only real-valued symbols can be transmitted in MIMO-FBMC systems, we propose “complex training sequence decomposition (CTSD)” to facilitate the reconstruction of the complex-field orthogonality of MIMO-FBMC signals. Our simulations validate that the proposed CTSD is an efficient channel estimation approach for practical preamble-based MIMO-FBMC systems. NRF (Natl Research Foundation, S’pore) Published version

As an alternative to OFDM systems with Cyclic Prefix (CP), filter bank multicarrier (FBMC) transmission technique leads to an enhanced physical layer conventional communication network and it is an enabling technology for the new concepts and, particularly, cognitive radio. Due to the feature of good time-frequency localization, there is no need for FBMC systems adding any guard interval, definitely leading to higher spectral efficiency compared with CP-OFDM. FBMC has the potential to fulfill the requirements of the new concepts, but a major research effort is necessary for full exploitation and optimization in all aspects of the radio context. In this paper, a testbench based on National Instrument universal software radio peripheral has been developed for FBMC systems. Meanwhile, systematic performances, including synchronization, channel estimation and bit error rate are evaluated.

Transform domain communication system (TDCS) has been proposed to support multiuser communications through spectrum bin nulling and frequency domain spreading for overlay cognitive radio networks. In TDCS systems, specific pseudorandom spreading sequences are assigned to different users for the purpose of multiple access. However, due to the non-zero cross-correlations between any pair of TDCS signals, multiuser interference always exists and becomes a main factor of bit error rate performance degradation. To improve multiple access capability, in this paper, a novel spread phase coding scheme is introduced for multiuser TDCS systems. It is proved that the key point is the design of sequence with impulse-like correlation. In addition, a new algorithm to design unimodular sequence is proposed. Following this way, we can obtain a class of almost perfect sequences through spreading, whose autocorrelation and cross-correlations are much better than that of traditional sequences. Simulation results demonstrate that multiuser TDCS systems employing our proposed sequences can achieve a significant BER performance improvement.

Towards the era of mobile Internet and the Internet of Things (IoT), numerous sensors and devices are being introduced and interconnected. To support such an amount of data traffic, traditional wireless communication technologies are facing challenges both in terms of the increasing shortage of spectrum resources and massive multiple access. The transform-domain communication system (TDCS) is considered as an alternative multiple access system, where 5G and mobile IoT are mainly focused. However, previous studies about TDCS are under the assumption that the transceiver has the global spectrum information, without the consideration of spectrum sensing mismatch (SSM). In this paper, we present the deterministic analysis of TDCS systems under arbitrary given spectrum sensing scenarios, especially the influence of the SSM pattern to the signal to noise ratio (SNR) performance. Simulation results show that arbitrary SSM pattern can lead to inferior bit error rate (BER) performance.

A real-time network level platform (DySNet) for dynamic spectrum sharing network is presented. A dynamic spectrum sharing network takes the opportunistic use of dynamic changing spectrum. It also dynamic changes its working spectrum to avoid interference to primary users. To support research on the network level of cognitive radio, The DySNet has capability of sensing the spectrum, it also support transmitting and receiving signals to form a complete radio node in a wireless network. It has flexibility and scalability to meet different requirements of researches. A center based network, a distributed network and a hybrid network has been implemented on DySNet.

This paper presents an iterative random interleaver design (IRID) scheme for reducing the high peak-to-average power ratio (PAPR) of orthogonal frequency-division multiplexing (OFDM) systems. The main idea is based on utilizing a processing of iteratively interleaving with only one fixed pattern for saving the memory size of conventional transmitter and receiver. Numerical simulation results show that the proposed IRID scheme is with identical PAPR reduction performance with the conventional scheme by introducing only one fixed interleaving pattern.