This paper evaluates the achievable transmission capacity of the secondary system in cognitive radio networks, defined by the spatial density of successful transmissions while guaranteeing the target outage probabilities of the secondary and the primary systems. By using stochastic geometry, the effects of the spatial densities and the transmission powers on the achievable transmission capacity is presented. Subsequently, the optimal spatial density of the secondary system and the optimal transmission power ratio of the primary system to the secondary system are derived. Furthermore, the maximum achievable transmission capacity is defined using the derived optimal values. From the theoretical results, it is shown that the optimal transmission power ratio is affected by not the density of the primary system, but the system parameters including the target outage probability. In addition, the achievable transmission capacity of the secondary system decreases as the spatial density of the primary system increases at the decreasing rate determined by the system parameters of the primary system.

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Acute and severe cases of Henoch-Schönlein purpura (HSP) nephritis have been treated with plasmapheresis (PA) in both adults and children. It has been used either alone or with steroids, antiplatelets or cytoxic drugs. Generally, renal function has been shown to improve when PA is utilized. The role of PA in recurrent HSP after renal transplantation is unclear and has not been well described in the literature. We report a 29-year-old female with HSP who developed end-stage renal disease and subsequently underwent a renal transplantation with eventual loss of the allograft 5 years later due to recurrent HSP nephritis. Retransplantion was performed and the patient developed active HSP nephritis in her second allograft within a week after transplantation. In an effort to preserve her allograft, four cycles of PA were performed. Her proteinuria resolved and renal biopsies afterwards demonstrated marked reduction in mesangial IgA deposition. We conclude that PA may be useful in recurrent HSP nephritis, especially when used early. The risk of additional immunosuppression caused by PA needs to be considered. More studies need to be done to evaluate the efficacy of PA in this setting as well as to define the optimal treatment regimen.

In this paper, we propose a new grouping-maximum likelihood detector (GMLD) for single carrier-frequency division multiple access (SC-FDMA) systems. The proposed detector performs local maximum likelihood (ML) detection by grouping the received symbol block based on orthogonal projection to reduce the complexity of ML detector. As a result, the proposed detector offers lower complexity than the ML detector, while its performance approaches that of the ML detector. In addition, the efficient group size to guarantee the lowest complexity and the BER performance close to the ML is also presented.