Current Issue : July - September Volume : 2016 Issue Number : 3 Articles : 4 Articles
In order to increase performance of a system while saving power consumption, multiple hop MIMO relay systems\n(MHMRSs) have been considered. There are many researches on the physical (PHY) layer, medium access control\n(MAC) layer, and MAC-PHY cross-layer to avoid a co-channel interference, such as the matched/orthogonal weight\nalgorithm, TDMA-based smart antenna and so on. The matched/orthogonal algorithm is available for bi-directional\ncommunications; however, it requests at least three antenna elements at every relay. Consequently, it is unavailable\nfor small wireless devices that are being demanded. In this paper, we propose an algorithm to cancel the co-channel\ninterference of bi-directional communication MHMRSs by signal processing at receivers using precoding at\ntransmitters. The proposal algorithm can perform with only two antenna elements while maintaining character of\nMIMO. The proposal algorithm is compared to the TDMA-based smart antenna algorithm which also can perform\nwith two antenna elements, in both perfect and imperfect channel state information (CSI) schemes. Numerical\ncalculation results indicate that a channel capacity of proposal algorithm is much higher than that of TDMA-based\nsmart antenna algorithm in the perfect CSI scheme due to complete cancellation of co-channel interference and\nviability of bi-directional communications of proposal algorithm. In the imperfect CSI scheme, the channel capacity of\nthe TDMA-based smart antenna algorithm is more robust when channel estimation errors increase; however, the\nchannel capacity of proposal algorithm is still higher when the channel estimation error is large....
Link adaptation (LA) process is a core feature for the downlink of 3GPP long-term evolution (LTE) and LTE-advanced\n(LTE-A). Through a channel quality indicator (CQI), the receiver suggests to the base station (BS) an appropriate\nmodulation and coding scheme (MCS) according to the current channel conditions. In order to overcome any\nnon-ideality in this process, the outer loop link adaptation (OLLA) algorithm is used to adaptively modify the mapping\nfrom signal-to-noise ratio (SNR) to CQI. OLLA basically modifies the measured SNR by an offset, according to whether\ndata packets are received correctly or not, in order to adjust the average block error rate (aBLER) to a target. Although\nthe OLLA technique has been extensively used, there exists a lack of analysis in the literature about its dynamics and\nconvergence conditions. In this paper, a deep analysis of this algorithm has been carried out in order to cover this gap.\nFrom this analysis, we propose a new approach to the OLLA, the enhanced OLLA (eOLLA), which is able to adaptively\nmodify its step size as well as to update its offset according to the reception conditions even if no data packets have\nbeen received. Thus, for LTE- and LTE-A-realistic scenarios, simulation results show that the proposed eOLLA\noutperforms the traditional OLLA, achieving a performance gain of up to a 15 % in terms of throughput....
Due to its low cost and popularity, the IEEE 802.11 WLAN (wireless local area network) is considered as one of the\nmost promising wireless technologies for IoT (Internet of Things). 802.11 WLAN also provides a PSM (power saving\nmechanism), by which the devices that have no data to transmit are enabled to turn into doze mode where much less\npower is consumed. However, the 802.11 PSM is known to be inefficient because of its contention-based mechanism,\ni.e., it suffers from the performance degradation due to hidden terminals, especially in a network with a large number\nof devices. In this paper, in order to improve the performance of the 802.11 PSM, we propose a BC (backoff counter)\nreservation scheme that is combined with a neighbor polling solution. By building analytic models and performing\nextensive simulations, we show that our proposed scheme provides a much improved performance...
This paper presents the mathematical model for symbol error probability of triangular quadrature amplitude modulation\nin a single-input multi-output environment. The symbol error probability performance is evaluated over fading channels\nnamely Rayleigh, Nakagami-m, Nakagami-n, and Nakagami-q. The maximal-ratio combining technique is considered as\nspatial diversity algorithm and unified moment-generating-function-based approach is applied to derive the results. The\nmultiple channels considered are independent but not necessarily identically distributed. The results presented are valid\nfor slow and frequency non-selective fading channels only. The symbol error probability expressions obtained contain\nsingle integrals with finite limits and integrand composed of elementary functions which help us evaluate our analytical\nexpressions numerically. We also compare these expressions with the error performances obtained through computer\nsimulation, which show excellent agreement. In addition, an example has been simulated to validate our derived\nmathematical expressions....
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