In order to achieve more efficient overall spectrum utilization, it is possible to employ cognitive beamforming for secondary spectrum access. An important issue in such spatial spectrum sharing techniques is protecting the primary user from interference which arises due to estimation errors when the secondary users try to locate the available transmit opportunities. In this paper, we investigate the issue of primary user protection when the secondary user allocates too many spatial streams for the secondary transmission. We provide analysis for the interference power statistics and take advantage of the moment matching method in order to obtain an expression for the interference power that is tractable for practical analysis. In addition, we propose a protection constraint which limits the resulting interference and protects the primary user in terms of interference outage probability. We also show the achievable transmit power for the secondary user which can satisfy the protection constraint.
The simple decoding method we have proposed for short-range multiple-input multiple-output (SR-MIMO) transmission is a promising means for reducing power consumption. The method performs MIMO detection with analog devices, thus reducing the number of quantization bits required in the analog-to-digital converter (ADC) of the receiver and the amount of signal processing calculation for MIMO detection. However, when the method is applied to a wall transmissive wireless repeater on a multilayered wall, the transmission performance degrades due to multipath generated by the multilayered structure. In this letter, we evaluate the method’s performance using data for a millimeter wave propagation channel that we measured from wall samples and the measured S-parameters of the method’s analog circuit. As a result, we quantify the influence of multipath generated by a wall’s multilayered structure on transmission performance.
Recently, the wireless power transmission (WPT) system is expected to employ as a means to transmit power to capsular endoscope diagnosing the digestive organs. In order to increase transmission efficiency, in this study, we proposed a transmitting spiral antenna which can transmit adequate power to the capsular endoscope with being independent of its position and direction. In this paper, we discussed the power transmission efficiency and SAR on human body by means of FDTD method and experimentation.
In this paper, we propose a novel sparse particle filter applied for indoor pedestrian localization. Unlike the traditional particle filters that usually contain thousands of particles, this algorithm uses one or several particle sequences in location tracking. The particle is split to cover all the possible tracks when matching ambiguity occurs. This algorithm can significantly reduce the computation burden as well as energy consumption. Field experiments are conducted using mobile phones and the results show that the proposed method can perform localization with much higher efficiency, high reliability, and merely slight loss of accuracy.
The proliferation of mobile devices boosts mass multimedia content delivery in wireless environments. Wireless content delivery network systems strongly require a lightweight caching strategy because of the processing capability constraints. In this paper, we introduce a one-touch caching scheme that exploits a temporal locality property as the minimum intelligence by making cache servers blindly cache the most recently requested content. Simulation results show that our strategy with little overhead has a comparable performance to conventional schemes such as LRU (least recently used), LFU (least frequently used) and other variants with heavy computational overheads.