Chengshi Zhao

An Optimal Soft Fusion Scheme for Cooperative Spectrum Sensing in Cognitive Radio Network

This paper proposes an optimal soft fusion scheme for cooperative spectrum sensing in cognitive radio (CR) network. Multiple cooperative secondary users (SUs) simply serve as relay nodes in the network to provide space diversity for spectrum sensing. An optimal soft fusion scheme of the relayed sensing observations is derived in Neyman-Pearson framework, on the basis of maximizing the deflection coefficient of the global test statistic at the fusion center. However, the proposed fusion scheme requires instantaneous measurements of the received PU signal strengths in SUs with high accuracy, which are extremely difficult to obtain in an energy detection based spectrum sensing scenario. An iterative algorithm is therefore proposed to perform the estimation of the received PU signal strengths. Simulation results illustrate that the proposed optimal soft fusion scheme can significantly improve the spectrum sensing performance and the estimate algorithm can effectively approach the ideal performance of the proposed optimal fusion scheme.

User clusters based hierarchical cooperative spectrum sensing in cognitive radio networks

This paper investigates secondary user clusters based cooperative spectrum sensing. Secondary users in the cognitive radio network are grouped into multiple clusters and the cooperative spectrum sensing is performed on a hierarchical architecture of these user clusters, through two levels of user collaborations. The low level cooperation is carried out within each cluster while the high level one is accomplished inside the cluster of the clusterheads. We propose soft fusion and hard fusion according to the bandwidth constraints of the control channels and the spectrum sensing agility requirement. An optimal soft fusion scheme and a double-threshold strategy are proposed to improve the overall spectrum sensing performance in soft fusion and hard fusion, respectively. Analysis and simulations verify that the proposed hierarchical cooperative spectrum sensing schemes can significantly improve the spectrum sensing performance.

Mutual interference considered power allocation in OFDM-based cognitive networks: The single SU case

Efficient and conflict-free power allocation strategies in cognitive radio networks are being extensively studied in current research in order to meet the requirements of future wireless applications. In this paper, specifying the single secondary user (SU) with multiple primary user (PU) case, a novel power allocation scheme is developed for orthogonal frequency division multiplexing (OFDM) - based cognitive radio networks designed to maximize the capacity of the SU while limiting the interference to the PUs. First, the mutual interference between the SU and the PUs is comprehensively formulated as the restrictions on the SUs transmission power. Secondly, the power allocation problem is analyzed and formulated as a constrained optimization problem which is concluded to a peak-power constrained water-filling formulation. Finally, a novel low-complexity water-filling algorithm is proposed to solve the optimization problem and the optimal power allocation result is achieved. In a simplified scenario, numerical results are exhibited to confirm the efficiency of the proposed water-filling algorithm, and the influence of the mutual interference on the power allocation and the system capacity is further illustrated.

Mutual interference considered power allocation in OFDM-based cognitive networks: the multiple SUs case

Power allocation for secondary users (SUs) in cognitive networks is an important issue to ensure the SUs’ quality of service. When the mutual interference between the primary users (PUs) and the SUs is taken into consideration, it is wanted to achieve the conflict-free power allocation while synchronously maximizing the capacity of the secondary network. In this paper, the optimal power allocation problem is considered in orthogonal frequency division multiplexing cognitive networks. The single SU case is primarily formulated as a constrained optimization problem. On this basis, the multiple SUs case is then studied and simulated in detail. During the analysis, the mutual interference among the PUs and the SUs is comprehensively formulated as the restrictions on the SU’s transmission power and the optimization problems are finally resolved by iterative water-filling algorithms. Consequently, the proposed power allocation scheme restrains the interference to the primary network, as well as maximizing the capacity of the secondary network. Specifying the multiple-SUs case, simulation results are exhibited in a simplified scenario to confirm the efficiency of the proposed water-filling algorithm, and the influence of the mutual interference on the power allocation and the system capacity is further illustrated.

Miller-coded PPM UWB transreceiver for low-rate WBAN networks with non-coherent detection

Ultra Wide Band (UWB) is an appropriate candidate used into the physical layer of the Wireless Body Area Networks (WBAN). In this paper, a novel UWB transreceiver structure is presented, where a Miller encoder is adopted in the transmitter side and a non-coherent detection scheme is used in the receiver side. Since the Power Spectral Density (PSD) of the UWB signal plays a major role in the coexistence with conventional radio systems, a mathematical framework evaluating the PSD of the proposed pulse radio signal is presented, and it is proved that the proposed scheme smoothes the spectrum which is useful for the coexistence with other conventional radio systems. The transreceiver structure is discussed in detail with a non-coherent detection receiver. The receiving performance is investigated by the simulations, and it is proved that the system is reasonable and the requirement of the WBAN system can be completely satisfied by analyzing the link budget of the system. Analyses and simulations show that the proposed scheme has a higher power efficiency and it is easy to match the FCC radiation requirement mask compared with the conventional UWB systems; furthermore, the proposed scheme is easy to be realized. The proposed scheme is more suitable for WBAN systems than the conventional pulse-based UWB systems.

Comprehensive Capacity Ensured Distributed Binary Power Allocation in Dense Cognitive Networks

Considering the capacity gain of the secondary system and the capacity loss of the primary system caused by the newly accessing user, a distributed binary power allocation (admittance criterion) is proposed in dense cognitive networks including plentiful secondary nodes. The case that the secondary nodes can detect both transmitter and receiver of the primary system is analyzed first; considering that it is hard for the secondary system to detect the primary receiver without assuming the cooperation with primary system, the case that the secondary nodes only have the information about the primary transmitter is analyzed thereafter. In particular, we propose a simple estimation strategy to transform the problem of detecting primary receiver to the problem of detecting primary transmitter for the latter case. And a general power allocation scheme which is suitable for both of two cases is proposed afterward. By simulations, the restriction on the distance between secondary transmitter and primary receiver, and the restriction on the distance between secondary and primary transmitters are respectively achieved for the two cases. These two restrictions reflect that the capacities of both primary system and secondary system can be ensured to the predefined extents if these two restrictions on the distances are respectively satisfied in two cases.

Uniqueness of punctured binary sequence pairs

The uniqueness of punctured binary sequence pairs is proposed and proved. In particular, perfect punctured binary sequence pairs(PPBSP), almost perfect punctured binary sequence pairs(APPBSP), pseudorandom punctured binary sequence pairs(PRBPSP) and punctured binary sequence pairs with two-level autocorrelation(PBSPT) are proved as the specific cases of perfect punctured LCZ/ZCZ sequence pairs. As a result, the unique receiving is guaranteed theoretically when they are applied in engineering.

Energy change detection of appearance of the primary signal with unknown power

In this paper, a sequential change detection scheme is proposed to detect the emergence of a primary signal with unknown power. It can be shown that the proposed test can do better than the generalized likelihood ratio (GLR) test, under the same worst case average run length (ARL) of detection delay constraint. And performance of our test is evaluated using theoretical analysis and numerical simulations.

Distributed power allocation in dense cognitive networks: Primary receiver detectable case

In this paper, a binary power allocation scheme is proposed for dense cognitive networks with plentiful secondary nodes. During the power allocation, the capacity loss of the primary system is controlled to be lower than a predefined level; and the capacity of the secondary system is ensured to some extent. Most importantly, based on the theoretical derivations, the power allocation is proved to be executable distributedly by local decisions at each secondary node, which is especially suitable for cognitive networks. By the simulation, the restriction on the distance between the secondary sender and the primary receiver is achieved straightforwardly, which reflects that the capacity of both primary system and secondary system can be ensured to the predefined level if the distance between secondary senders and the primary receiver satisfies certain conditions.

Power allocation for single secondary user in OFDM-based cognitive networks with comprehensive interference considerations

Conflict-free power allocation for secondary user (SU) in cognitive networks is a challenging problem since the accessible spectrum of the SU is shared with the primary user (PU); the problem becomes to be especially difficult when it is wanted to achieve the maximum network capacity considering the mutual interference between PU and SU. In this paper, specifying the single SU case with multiple PUs, the power allocation for the subcarriers of the SU is modeled into a single user water-filling framework, where the mutual interference between the PUs and the SU is comprehensively formulated into the restrictions on the SUs transmission power. As a result, proposed modeling scheme restrains the interference to the PUs as well as maximizes the capacity of the SU. Simulation results illustrate the influence of the mutual interference on the power allocation and the network capacity.