Sung Sik Nam

Threshold-based parallel multiuser scheduling

In this paper, we propose two new threshold based parallel multiuser scheduling schemes, namely (i) an on-off based scheduling (OOBS) scheme and (ii) a switched based scheduling (SBS) scheme. The objective is to reduce the complexity of implementation without a considerable performance loss in comparison with conventional selection based scheduling. While the OOBS scheme schedules all the users with an SNR above a fixed preselected signal to noise ratio (SNR) threshold, the SBS scheme schedules only the Ks users with an acceptable SNR if there are enough acceptable users. Otherwise, the scheduler selects the best Ks users. We analyze statistical characteristics and performances of these proposed schemes. Numerical results show that the proposed schemes can offer some decrease in the average feedback load without an important degradation in average bit error rate and average spectral efficiency.

Multi-Human Detection Algorithm Based on an Impulse Radio Ultra-Wideband Radar System

In this paper, we propose a multi-human detection algorithm based on impulse radio ultra-wideband radar system. With our proposed algorithm, the multi-human detection can be performed by repeatedly performing clustering and detecting processes. More specifically, the system detects an effective peak of the first single cluster which is composed of peaks adjacent to each other and then repeat this process until effective peaks of clusters caused by multiple people are successfully detected sequentially. As our performance metrics, we take into account the performance analysis in terms of the error probability based on the results of the statistical analysis. More specifically, we first cross-verify that the empirical result theoretically follows the Log-normal distribution by comparing the theoretical and empirical results obtained through laboratory experiments. Then, we statistically analyze the received signals under the Log-normal distribution assumption. After that, this statistical result is adopted to the performance analysis of the error probability in terms of the total error probability. Note that the performance of our proposed algorithm is affected by the threshold value. Based on it, the optimal threshold is analyzed and we provide the sample guidelines for optimally adjusting the threshold value under given various environment factors. Finally, some selected experimental results are presented to show the validity of our proposed algorithm by comparing the performance between the proposed algorithm and the conventional algorithm.

Diversity Combining with Up-Link Power Control

We introduce in this paper a new adaptive power-controlled diversity combining scheme that reduces the average transmitted power of the mobile units while meeting a certain minimum required quality of service. The key idea is (i) to collect and combine all the available diversity paths at the base station and then (ii) to request the mobile unit to increase or decrease its transmitted power just to track the required target signal-to-noise ratio (SNR). Four power control variants accounting for practical implementation constraints including discrete power levels and transmitter gain saturation are proposed and studied. Some selected numerical results, show that the proposed scheme offers considerable savings in the transmitted power levels over a wide SNR range but amplifier saturation leads to a violation of the target BER requirement in the low average SNR range. Additional numerical examples, show that the power control variants that take into account practical implementation constraints conserve the main features of the ideal continuous power algorithm

Joint Statistics of Partial Sums of Ordered Exponential Variates and Performance of GSC RAKE Receivers over Rayleigh Fading Channel

Spread spectrum receivers with generalized selection combining (GSC) RAKE reception were proposed and have been studied as alternatives to the classical two fundamental schemes: maximal ratio combining and selection combining because the number of diversity paths increases with the transmission bandwidth. Previous work on performance analyses of GSC RAKE receivers based on the signal to noise ratio focused on the development of methodologies to derive exact closed-form expressions for various performance measures. However, some open problems related to the performance evaluation of GSC RAKE receivers still remain to be solved such as the exact performance analysis of the capture probability and an exact assessment of the impact of self-interference on GSC RAKE receivers. The major difficulty in these problems is to derive some joint statistics of ordered exponential variates. With this motivation in mind, we capitalize in this paper on some new order statistics results to derive exact closed-form expressions for the capture probability and outage probability of GSC RAKE receivers subject to self-interference over independent and identically distributed Rayleigh fading channels, and compare it to that of partial RAKE receivers.

A rapid multi-device wireless power transfer scheme using an intermediate energy storage

We introduce a new time-division multiplex wireless power transfer (TDM-WPT) scheme for charging multiple devices with a single transmitter. More specifically, our proposed scheme adopts the intermediate energy storage (IES) circuit which enables storing the received energy from the source temporarily and then supplying it to the load. Thus, by adopting the IES, the receiver can charge the battery with the stored energy in the IES even while the receiver is not performing the direct charging process (from the transmitter). This allows charging multiple receivers simultaneously in a virtual manner, and it eventually leads to the reduction of overall charging time. For the theoretical verification, we analyse the performance of our proposed scheme based on the identical environment and in some selected results. We show that with our proposed scheme the required total charging time can be reduced compared to the conventional TDM-WPT. We also consider practical load (battery charger) requirements which change continuously. We present the simple guidelines for some key design parameters such as the optimal capacity of the IES and the proper number of receivers. Note that we additionally present the sample IES circuit and the related circuit simulation to show the detailed operation and the feasibility of the proposed scheme.

An MGF-Based Unified Framework to Determine the Joint Statistics of Partial Sums of Ordered i.n.d. Random Variables

Order statistics find applications in various areas of communications and signal processing. In this paper, we introduce an unified analytical framework to determine the joint statistics of partial sums of ordered random variables (RVs). With the proposed approach, we can systematically derive the joint statistics of any partial sums of ordered statistics, in terms of the moment generating function (MGF) and the probability density function (PDF). Our MGF-based approach applies not only when all the K ordered RVs are involved but also when only the Ks (Ks <; K) best RVs are considered. In addition, we present the closed-form expressions for the exponential RV special case. These results apply to the performance analysis of various wireless communication systems over fading channels.

Threshold-based Parallel Multiuser Scheduling

In this paper, we propose two new threshold based parallel multiuser scheduling schemes, namely (i) an on-off based scheduling (OOBS) scheme and (ii) a switched based scheduling (SBS) scheme. The objective is to reduce the complexity of implementation without a considerable performance loss in comparison with conventional selection based scheduling. While the OOBS scheme schedules all the users with an SNR above a fixed preselected signal to noise ratio (SNR) threshold, the SBS scheme schedules only the Ks users with an acceptable SNR if there are enough acceptable users. Otherwise, the scheduler selects the best Ks users. We analyze statistical characteristics and performances of these proposed schemes. Numerical results show that the proposed schemes can offer some decrease in the average feedback load without an important degradation in average bit error rate and average spectral efficiency.

Exact capture probability analysis of GSC receivers over i.n.d. Rayleigh fading channels

A closed-form expression of the capture probability of generalized selection combining (GSC) RAKE receivers was introduced in [1]. The idea behind this new performance metric is to quantify how the remaining set of uncombined paths affects the overall performance both in terms of loss in power and increase in interference levels. In this previous work, the assumption was made that the fading is both independent and identically distributed from path to path. However, the average strength of each path is different in reality. In order to derive a closed-form expression of the capture probability over independent and non-identically distributed (i.n.d.) fading channels, we need to derive the joint statistics of ordered non-identical exponential variates. With this motivation in mind, we first provide in this paper some new order statistics results in terms of both moment generating function (MGF) and probability density function (PDF) expressions under an i.n.d. assumption and then derive a new exact closed-form expression for the capture probability GSC RAKE receivers in this more realistic scenario.

Adaptive Threshold Based Relay Selection for Minimum Feedback and Channel Usage

To enable relay selection in multiple relay network, using an average channel gain is not enough to achieve acceptable performance, but using an instantaneous gain causes undue system overhead due to feedback. In this paper, we propose adaptive threshold based relay selection scheme for minimum feedback to avoid system overhead, where a relay reports if its relay-destination (R-D) instantaneous channel gain is above threshold. A source selects the best relay among those which has the highest source-relay (S-R) instantaneous channel gain, and adjusts adaptive threshold according to an operating signal-to-noise ratio. Exact and upper bound on the symbol error rate are derived for M-PSK signaling, and it is shown that the proposed scheme yields acceptable performance in operating range, though full diversity order is not achieved. The theoretical results presented here are validated through simulation.

Performance evaluation of threshold-based power allocation algorithms for down-link switched-based parallel scheduling

In this paper, we propose threshold-based power allocation algorithms for a recently proposed down-link switched based parallel scheduling (SBS) scheme and we present their performance results via computer simulations. As its name indicates it, the system re-allocates the extracted excess signal to noise ratio (SNR) from some acceptable users to unacceptable users among the scheduled users. After the power allocation process, the unacceptable users can reach acceptable SNRs and as such the number of effective acceptable users with an acceptable SNR threshold among the scheduled users is increased without any additional down-link transmit power. Some selected numerical results, show that the proposed power allocation algorithms offer a certain improvement in average spectral efficiency (ASE) and an increase in the average number of effective acceptable users. Although the average bit error rate (BER) performance degrades especially when the average SNR is close to the SNR threshold, this average BER performance still meets the average BER requirement.