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We derive an optimum power and rate adaptation for maximizing the spectral efficiency based on an imperfect channel estimate and subject to average power and instantaneous bit error rate (BER) constraints for multilevel quadrature amplitude modulation (MQAM) over Rayleigh flat-fading channels. The optimal solution is derived for continuous- and(More)
Due to the half-duplex transmission nature of cooperative protocols, almost all cooperative diversity systems suffer from low spectral efficiency. In general, adaptive modulation can offer a good tradeoff between spectral efficiency and bit-error-probability (BEP) performance of wireless communication systems. In this paper, we propose two adaptive(More)
The importance of localization task has drawn much attention to location estimation and object tracking systems in wireless sensor networks. Many methods have been proposed to improve the location accuracy in which received signal strength (RSS) values of sensor nodes are used as an indicator of the distance between sensor node and the source node. Some of(More)
The optimization of pilot symbol parameters can improve the spectral efficiency of adaptive modulation for orthogonal frequency division multiplexing (OFDM) systems, since pilot symbols impose an overhead on the system consuming power and bandwidth. An optimal pilot symbol assisted adaptive modulation (PSAAM) scheme for OFDM systems is proposed that(More)
In this paper, the problem of mode switching in multiple-input-multiple-output (MIMO) broadcast channels utilizing the Per-User Unitary Rate Control (PU2RC) transmission scheme is considered. Since there is no mathematical expression for the achievable rate of the PU2RC systems, it is proposed to approximate them using proper bounds. It is shown that(More)
In this paper, we consider the fast and slow multipath fading scenarios in which the coherence time of the channel between primary transmitter and secondary receiver is compared to the sensing time. We formulate the detection problem under fast fading, then we show that there are situations in which the detection performance under the fast fading scheme(More)
In this paper, we consider one secondary user sensing the radio spectrum, and find its optimal sensing parameters to maximize its throughput in a periodic sensing framework, while keeping its interference to primary network below a certain level. To this end, we propose a new interference measure which takes into account not only the probability of(More)
Error propagation from the relay to the destination is a major drawback of digital relaying protocols that substantially diminishes the cooperative diversity gain of the system. Appropriately designed selection relaying schemes can effectively mitigate this phenomenon and improve the diversity order, especially when the source-relay channel state(More)
We derive optimum power and rate adaptation for maximizing the spectral efficiency based on imperfect channel estimate and subject to average power and instantaneous bit error rate (BER) constraints for multilevel quadrature amplitude modulation (MQAM). The channel estimation method considered is linear minimum mean square error (MMSE) estimation using(More)