Fractional frequency reuse (FFR) is an effective technique to mitigate co-channel interference in orthogonal frequency division multiple access (OFDMA)-based broadband cellular systems.In this paper,we present a generalized model for FFR under which all existing FFR schemes can be considered as its special cases.Additionally,quality factor has been proposed to indicate the quality of the subband.An interesting conclusion can be drawn that,as the power ratio in FFR is adjusted continuously,the corresponding quality factor varies smoothly.Subsequently,simulation is conducted based on worldwide interoperability for microwave access (WiMAX),and the result agrees well with our theoretical analysis.Finally,an effective range for power ratio is presented,which is very instructive to practical system design.
This article puts forward a new solution to the bound of the outage probability and transmission capacity of Ad-hoc networks.For the proofs of the upper and lower bounds are too complex,a much easier way is introduced to get the same results,and by using Taylor series,the asymptotic bound is derived.By comparing with the simulation results,we found that the asymptotic bound is sufficient accurate when the network parameters are selected properly,and is tighter than the upper and lower bounds.
This article puts forward a partial channel state information(CSI) feedback scheme for fractional frequency reuse(FFR)-based orthogonal frequency division multiple access(OFDMA) systems.Efficient CSI feedback strategy plays an important role in opportunistic scheduling because base station(BS) can employ adaptive modulation and coding(AMC) technique to adaptively change transmission rates according to CSI feedback,and therefore the spectrum efficiency can be improved significantly.On the other hand,FFR is a simple but effective technique to improve the throughput of users at cell edge.To exploit opportunistic scheduling in FFR-based OFDMA systems,both users and spectrum are divided into multiple groups in this article,and specific feedback pattern is designed for each user group on each spectrum sub-band.Simulations results prove that the proposed algorithm can reduce the feedback load significantly,while maintain nearly the same performance as the system with full feedback.
The Internet of Things (IoT) is called the world's third wave of the information industry.As the core technology of IoT,Cognitive Radio Sensor Networks (CRSN) technology can improve spectrum utilization efficiency and lay a solid foundation for large-scale application of IoT.Reliable spectrum sensing is a crucial task of the CR.For energy detection,threshold will determine the probability of detection (Pd) and the probability of false alarm Pf at the same time.While the threshold increases,Pd and Pf will both decrease.In this paper we focus on the maximum of the difference of Pd and Pf,and try to find out how to determine the threshold with this precondition.Simulation results show that the proposed method can effectively approach the ideal optimal result.
In this paper,a cluster-based virtual multiple-input multiple-output(MIMO)transmission architecture is proposed for energy-constrained wireless sensor networks.In the proposed architecture,instead of using cluster members as cooperative nodes,multiple cluster heads cooperate to form virtual antenna array so that MIMO transmission can be implemented.According to the MIMO techniques used in this architecture,two different schemes,vertical Bell Laboratories layered space-time(V-BLAST)based cluster heads cooperative transmission(VCHCT)and space time block code(STBC)based cluster heads cooperative transmission(SCHCT),are developed.Based on the communication energy consumption model,the overall energy consumption model for both VCHCT and SCHCT are derived.Detailed comparison between these two schemes and the original low-energy adaptive clustering hierarchy(LEACH)is performed to investigate the performance of these two schemes.Simulation results not only verify the theoretical analysis but also show that the two schemes have their specific application scenarios.When the sink is far from the sensor area,SCHCT scheme is much more energy efficient than LEACH and VCHCT scheme even if it consumes additional inter-cluster communication energy.When the distance to sink is near the sensor area,VCHCT is preferable.
