Zeyang Dai

An Adaptive Cooperation Communication Strategy for Enhanced Opportunistic Spectrum Access in Cognitive Radios

To guarantee the continuity of secondary transmission (ST) in cognitive radio networks (CRNs), a beamforming-based cognitive cooperative communication protocol, referred to as BCC, is proposed in this paper. In BCC, a secondary user (SU) can increase the transmit power to reach its destination directly when the primary users (PUs) are absent. On the other hand, when new PUs come in, the SU will reduce its power and choose an intermediate relay to reach its destination to avoid the impact on the primary transmission (PT); in this case, the SU destination will leverage beamforming to receive data from both the SU and relay respectively. We analyze the performance of BCC and obtain the closed-form expressions of the ST outage probability. Simulation results are presented to validate the theoretical analysis and demonstrate that BCC achieves lower SU outage probability than the traditional cognitive radio scheme without using beamforming-based cooperation.

Cooperative transmissions for secondary spectrum access in cognitive radios

In cognitive radio networks CRNs, the primary users PUs and secondary users SUs will interfere with each other, which may severely degrade the performances of both primary and secondary transmissions. In this paper, we propose a two-phase cognitive transmission TCT protocol for secondary spectrum access in CRNs, aiming at improving the secondary transmission performance while guaranteeing the quality-of-service QoS of primary transmissions. In TCT protocol, SUs gain the opportunities to access the licensed spectrum through assisting primary transmissions using superposition coding SC, where SUs limit their transmit power to satisfy a given primary QoS requirement and also employ interference cancelation technique to mitigate the interference from PUs. Under the constraint of satisfying a required primary outage probability, we derive the closed-form expressions of secondary outage probabilities over Rayleigh fading channels for proposed TCT protocol. Numerical and simulation results reveal that, with a guaranteed primary outage probability, TCT achieves better secondary transmission performance than traditional case. Copyright

Selective-Reporting-Based Cooperative Spectrum Sensing Strategies for Cognitive Radio Networks

Cooperative spectrum sensing may cause a high sensing overhead to secondary users (SUs) and induce much interference to primary users (PUs) due to detection result reporting, although it can improve the detection probability. In this paper, we propose two novel selective-reporting-based cooperative spectrum sensing strategies, called random-selection reporting (RSR) and best-selection reporting (BSR), aimed at reducing the sensing overhead of SUs and limiting the induced interference to PUs. By considering the interference impact on decision reporting from PUs, we derive closed-form expressions of false-alarm probability and detection probability over Rayleigh fading channels for traditional, RSR, and BSR strategies, respectively. We also analyze the interference impact on PUs from cooperative SUs and then show that such interference can be limited by power control to satisfy a given quality-of-service (QoS) requirement of primary transmissions. Finally, numerical and simulation results reveal that the proposed strategies can remarkably reduce the sensing overhead without degrading the detection performance compared with the traditional case. Moreover, we show that both RSR and BSR can achieve minimized miss detection probability and sensing overhead by adjusting the sensing time allocation.

QoS-based device-to-device communication schemes in heterogeneous wireless networks

This study considers spectrum sharing problems in the heterogeneous wireless networks where different device-to-device (D2D) users coexist with the cellular users. The authors propose a novel scheme, called ‘spectrum partition-based D2D transmission’ (SPDT), to improve spectrum efficiency of the D2D and cellular networks. In SPDT, the D2D users assist the cellular transmissions to gain some spectrum released from the cellular system. Then, the obtained spectrum is divided into several frequency bands and each band is assigned to a different D2D pair for its data transmission. Under the quality-of-service (QoS) constraints of both the D2D and cellular users, the authors exploit the tradeoff in the power allocation of the D2D transmitters and show that the number of the allowed accessing D2D pairs can be maximised by optimising the D2D transmitters power for SPDT. For comparison the power optimisation problem is also investigated with the objective of maximising the number of allowed users accessing D2D pairs in the power control scheme, called ‘underlay D2D transmission’ (UDT). This is where the D2D users access the spectrum being used by the cellular users with power control while ensuring that the QoS of the cellular transmissions is satisfied. Finally, the simulation results show evident performance gains of the proposed SPDT scheme over the UDT scheme.

Improved energy detection with interference cancellation in heterogeneous cognitive wireless networks

Energy detection is the most popular method among spectrum sensing techniques due to its low implementation complexity. However, its performance will be severely degraded by the interference from other secondary users (SUs). In this paper, we first analyze the interference impact on the energy detection in a heterogeneous cognitive wireless network (HCWN). Then, we propose an interference cancellation based energy detection method, referred to as ICED, to combat the interference. Based on ICED, closed-form expressions of the false alarm probability and detection probability are derived for the local detection and the results are extended to the cooperative detection as well. Our analysis is validated by numerical and simulation results which show that the proposed ICED method can significantly improve the performance of energy detection when there exists an interference SU in the HCWN. We also observe that ICED can achieve higher detection probability than the energy detection without interference under certain conditions.

Efficient secondary access with intelligent spectrum sensing in cognitive radio networks

In cognitive radio networks, cooperative sensing can significantly improve the performance in detection of a primary user via secondary users SUs sharing their detection results. However, a large number of cooperative SUs may induce great sensing delay, which degrades the performance of secondary transmissions. In this paper, we jointly consider cooperative sensing and cognitive transmission in cognitive radio networks, aiming to achieve efficient secondary access with low sensing overhead under both the sensing time and reporting power limitations, where primary users are guaranteed to be sufficiently protected. We first propose an adaptive sensing scheme to lower the detection time while not degrading the detection probability. Then, based on the proposed adaptive sensing scheme, an efficient cognitive transmission protocol is well designed, which improves the throughput of secondary transmissions while ensuring the QoS of primary transmissions. We analyze the performance for the proposed secondary access framework in terms of misdetection probability, average detection time and normalized secondary throughput, respectively, and derive their closed-form expressions over Rayleigh fading channels with considering the reporting errors accordingly. We also study the problems of optimizing the number of cooperative SUs to minimize the misdetection probability and average detection time, and maximize the normalized secondary throughput for proposed framework. Simulation results reveal that the proposed framework outperforms the traditional case significantly. Copyright

Adaptive cooperative sensing with low overhead for cognitive radio networks

Although user cooperation improves sensing accuracy, a large number of secondary users (SUs) reporting decisions may cause significant overhead. In this paper, we propose a distributed scheme, called adaptive cooperative sensing (ACS), to reduce the sensing overhead while satisfying sensing accuracy requirements. In ACS, an anchor SU requires cooperative sensing only when it does not detect the presence of primary user (PU) by itself. When performing cooperative sensing, both selective reporting and sequential detection are employed. We derive the generalized-form expressions of false alarm and detection probabilities over Rayleigh fading channels with considering reporting errors for ACS. The sensing overheads are also analyzed. Then, we study overhead minimization problems and show that the sensing time allocation can be optimized to minimize the miss detection probability and sensing overhead, respectively. By simulations, the effectiveness and efficiency of ACS are validated.

A novel rateless codes design scheme based on two-stage encoding and forward equal probability

This paper proposes an ideal rateless codes model to comprehensively describe rateless codes and extends the definition of systematic linear block code to generalized systematic code. Under the proposed model, average delay, maximum disorder, and uniformity recovery entropy are introduced as performance indices to design efficient rateless codes. A novel coding scheme based on two-stage encoding and forward equal probability is proposed to optimize the proposed indices. In the first stage, the first k symbols are encoded, aiming to improve the performance of order recovery, uniformity recovery, and transmission efficiency as much as possible. In the second stage, the remaining infinite symbols are encoded, where the symbols with high degree are used to compensate the symbols loss in the first stage. Simulation results show that the proposed scheme can achieve generalized systematic rateless codes with high probability and also has less average delay and maximum disorder, better capacity achievability, and uniformity recovery performance than Luby trasform LT codes and rateless coded symbol sorting algorithm. Besides, the proposed scheme has the aforementioned advantages compared with expending window fountain codes except for uniformity recovery and maximum disorder performance when the erasure rate is higher than about 0.25. Copyright

Enhanced Cognitive Relaying for Providing Continuous Connections in Wireless Networks

Typically, when a target user moves from its own network, which is denoted Net1, into another one, which is denoted Net2, its services would be interrupted. In this case, the target user can be viewed as a secondary user (SU), whereas the user of Net2 is a primary user (PU). By taking the advantage of cognitive radios, we propose a two-phase cognitive relaying (TCR) protocol to provide continuous connections for Net1 while guaranteeing the quality-of-service (QoS) of Net2 in wireless networks. The interference cancelation and time optimization techniques are also employed in TCR to further improve the transmission performance of Net1. Under TCR, both the downlink and uplink transmissions of the target user are investigated. We derive the closed-form expressions of outage probabilities for traditional and proposed transmission protocols over Rayleigh fading channels, respectively. Simulation results demonstrate that, with a guaranteed QoS of Net2, TCR transmissions can not only ensure continuous connections for the target user but achieve lower outage probabilities than traditional cases as well. In addition, it is shown that the outage probabilities of TCR transmissions can be minimized by optimizing the transmission time allocation.

An intelligent cooperative sensing strategy with low overhead for cognitive radios

As is well known, cooperative sensing can remarkably improve the sensing accuracy by exploiting the spatial diversity of different secondary users. However, a large number of cooperative secondary users reporting their local decisions would induce great detection delay and traffic burden, which degrades the performance of secondary spectrum access. This paper proposes an intelligent cooperative sensing ICS strategy with selective reporting and sequential detection to enhance the sensing reliability as well as reduce the sensing overhead for cognitive radios. The tradeoff in the sensing time allocation is studied for ICS and then two novel fusion rules are developed to efficiently obtain the optimum sensing time allocation with different objectives. The performance of ICS is analyzed in terms of miss detection probability and average sensing time, where their closed-form expressions are derived over Rayleigh fading channels. Simulation results reveal that ICS achieves higher sensing reliability with less sensing overhead than the traditional strategy. It is also shown that the miss detection probability and average sensing time of ICS can be minimized by optimizing the sensing time allocation. Copyright