Rain attenuation and intercell interference are two crucial factors in the performance of broadband wireless access networks such as local multipoint distribution systems (LMDS) operating at frequencies above 20 GHz. Power control can enhance the performance of downlink CDMA‐based LMDS systems by reducing intercell interference under clear sky conditions; however, it may damage system performance under rainy conditions. To ensure robust operation under both clear sky and rainy conditions, we propose a novel power‐control scheme which applies an adaptive neuro‐fuzzy inference system (ANFIS) for downlink CDMA‐based LMDS systems. In the proposed system, the rain rate and the number of users are two inputs of the fuzzy inference system, and output is defined as channel quality, which is applied in the power control scheme to adjust the power control region. Moreover, ITU‐R P.530 is employed to estimate the rain attenuation. The influence of the rain rate and the number of users on the distance‐based power control (DBPC) scheme is included in the simulation model as the training database. Simulation results indicate that the proposed scheme improves the throughput of the DBPC scheme.
In this paper, a systematic approach and their corresponding metrics for concurrent anti-jamming (AJ) and low probability of detection (LPD) performance evaluations of a secure communications system are investigated. In general, it is necessary to deal simultaneously with adversary threats of both active jamming and passive detection for a secure communications system concern. For independent or concurrent AJ and LPD performance evaluations, a single varying paired and multiple paired fixed collocated jammers/interceptors scenario is explored with real sinc type (sin(x)/x) antenna patterns being considered for the communicators. The error probability with both AJ and LPD being considered simultaneously can be derived as system-and geometry-dependent factors and categorized as system metrics related to jammers, interceptors, and communicators themselves only. Whenever multiple collocated jammers/interceptors are considered, we can observe interesting "smoothed" effects for bit energy to jamming density ratio (E b /J o ), when one of these varying jammers/interceptors is approaching or receding. In addition, by means of these system metrics, it is intuitive and straightforward to enhance system performance for the victim or to deteriorate system performance for the adversary, respectively. Moreover, the proposed approach and metrics have also paved one practical way for the developments of the latest emphasized cognitive radio (CR) communications systems, if all the collocated jammers/interceptors on the proposed scenario are replaced with "cooperative" communicators.
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