In orthogonal frequency division multiplexing （OFDM） systems, spectrum notch can be generated to mitigate interference to other narrow-band services by turning off corresponding subcarriers. However, the inter-carrier interference may limit considerably the produced notch depth. Another problem in OFDM is the high peak-to-average power ratio （PAPR）. In this paper, a technique combining subcarriers precoding with tone reservation is proposed to deepen spectrum notch and simultaneously reduce peak-to-average power ratio. Simulation results show that this presented joint algorithm can produce satisfied results to solve these problems at the expense of a moderate loss in bit error rate （BER） performance.
ZHAO Cheng-lin LIU De-qiang SUN Xue-bin JIANG Ting
This paper proposes a novel energy efficient unequal clustering algorithm for large scale wireless sensor network （WSN） which aims to balance the node power consumption and prolong the network lifetime as long as possible. Our approach focuses on energy efficient unequal clustering scheme and inter-cluster routing protocol. On the one hand, considering each node＇s local information such as energy level, distance to base station and local density, we use fuzzy logic system to determine one node＇s chance of becoming cluster head and hand, adaptive max-min ant colony optimization is used to estimate the corresponding competence radius. On the other construct energy-aware inter-cluster routing between cluster heads and base station （BS）, which balances the energy consumption of cluster heads and alleviates the hot spots problem that occurs in multi-hop WSN routing protocol to a large extent. The confirmation experiment results have indicated the proposed clustering algorithm has more superior performance than other methods such as low energy adaptive clustering hierarchy （LEACH） and energy efficient unequal clustering （EEUC）.
Orthogonal frequency division multiplexing （OFDM） is considered to be one of the promising schemes for cognitive radios （CR） systems, due to its flexibility in spectrum shaping. However, the traditional way of spectrum-notching failed to suppress out-of-band leakage enough, resulting in interference with licensed users （LUs）. A novel spectrum shaping scheme is proposed in this article, where a precoder with interference suppression sequence （ISS） is for the first time introduced for shaping the spectrum of OFDM signals in OFDM-based CR systems. The precoder matrix together with ISS matrix is obtained by minimizing the power of out-of-band interference, which results in the sufficient interference suppression of OFDM signal to LUs Analysis and simulation results show that the proposed scheme can significantly suppress the interference power to LUs at a little cost of precoding efficiency. Meanwhile, the peak-to-average-power-ratio （PAPR） is invariable and the bit-error-rate （BER） performance over Rayleigh fading channel is improved.
The integration of cognitive radio and Ultra wideband (UWB) networks has attracted lots of research interests. Cognitive UWB networks not only provide very high data rates but also guarantee the uninterrupted communication of primary system operated in the same frequency band. In this work, the problem of the capacity analyses of cognitive UWB networks is investigated. Different from the conventional cognitive spectrum sharing model which can only utilize the idle spectrum hole, the cognitive UWB system can operate adaptively based on spectrum sensing results. Taking into account several factors such as the transmission power constraint of UWB, the interference constraint of the receivers in primary systems, the secondary UWB network capacity problem is modeled as a convex optimization problem over the transmission power. The optimal power allocation strategy and algorithm are derived based on this optimization problem. Two cases (Perfect Spectrum Sensing and Imperfect Spectrum Sensing) are studied in the paper. Numerical simulation results show that the proposed adaptive power allocationscheme improves the ergodic and outage capacity under both transmission power and interference constraints compared with constant transmission power scheme.
This paper addresses the problem of joint optimization of subchannel selection and spectrum sensing time for multiband cognitive radio networks under the sensing capability constrains. In particular, we construct a multiband spectrum sensing framework, and derive the probabilities of detection and false alarm taking the different subchannel gain into account. Furthermore, we formulate the multi- band sensing as a two-parameter optimization prob- lem under the sensing capability constrains and guaranteeing the QoS of the secondary user. Moreover, we develop a semi-analytical optimization scheme to achieve the optimal solution.
In this paper,the impact of the interference from multiple ultra wideband（UWB） transmitters to a 3rd-generation（3G） terminal is evaluated under UWB emission power limit regulations of federal communications commission（FCC）,european telecommunications standards institute（ETSI） and Japan respectively.A three-dimensional interference model is presented where a discrete spatial distribution of UWB transmitters is considered.It is assumed that a mobile terminal and a large number of UWB devices exist in one room simultaneously.A parameter which characterizes the link budget degradation at the victim receiver is defined to measure the UWB interference to 3G systems.The maximum acceptable density of UWB transmitters and the minimum acceptable distance between UWB transmitters and the 3G terminal are analyzed under different link budget degradations.The simulation results demonstrate that the performance of time division-synchronous code division multiple access（TD-SCDMA） is the best,the one of code division multiple access 2000（CDMA2000） is the worst and the one of wideband code division multiple access（WCDMA） lies between them in presence of UWB interference.
SUN Xue-binGAO Ming-liangZHOU ZhengZHAO Cheng-linLIU Wei
