Event-Driven Optimal Feedback Control for Multiantenna Beamforming

Kaibin Huang,Lau, Vincent K N,Dongku Kim IEEE 2010 IEEE transactions on signal processing Vol.58 No.6

<P>Transmit beamforming is a simple multiantenna technique for increasing throughput and the transmission range of a wireless communication system. The required feedback of channel state information (CSI) can potentially result in excessive overhead especially for high mobility or many antennas. This work concerns efficient feedback for transmit beamforming and establishes a new approach of controlling feedback for maximizing throughput under a constraint on the average feedback rate. The feedback controller using a stationary policy turns CSI feedback on/off according to the system state that comprises the channel state and transmit beamformer. Assuming channel isotropy and Markovity, the controller's state reduces to two scalars. This allows the optimal control policy to be efficiently computed using dynamic programming. Consider the unquantized feedback channel free of error, where each feedback instant pays a fixed price. The corresponding optimal feedback control policy is proved to be of the threshold type. This result holds regardless of whether the controller's state space is discretized or continuous. Under the threshold-type policy, feedback is performed whenever a state variable indicating the accuracy of transmit CSI is below a threshold, which varies with channel power. The practical quantized feedback channel is also considered. The optimal policy for quantized feedback is proved to be also of the threshold type. The effect of CSI quantization is shown to be equivalent to an increment on the feedback price. Moreover, the increment is upper bounded by the expected logarithm of one minus the quantization error. Finally, simulation shows that feedback control increases throughput of the conventional periodic feedback by up to 0.5 bit/s/Hz without requiring additional bandwidth or antennas.</P>

Information and Power Transfers Using A Large-Scale Distributed Arrays

Kaibin Huang 대한전자공학회 2015 ITC-CSCC :International Technical Conference on Ci Vol.2015 No.6

Large Scale Energy Harvesting and Transfer Networks

Kaibin Huang 에스케이텔레콤 (주) 2015 Telecommunications Review Vol.25 No.4

Allowing wireless networks to harvest energy from renewable sources provides a solution for rapidly growing energy consumption by the networks. However, the temporal and spatial variations of the energy field can lead to fluctuations in power supplied to the network and thereby degrade the network performance. This has motivated recent research on modeling large scale energy harvesting networks and quantifying the effects of energy randomness on network performance. This paper reviews a series of recent works that apply stochastic geometry as the primary tool to model and analyze such networks and shows that this branch of mathematics provides a power and versatile tool for designing large scale energy harvesting networks. Furthermore, the paper presents the new concept of connecting the networks to the grid for supplying residual harvested energy to the grid and quantifies the expected amount.

Cooperative Precoding with Limited Feedback for MIMO Interference Channels

Kaibin Huang,Rui Zhang IEEE 2012 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.11 No.3

<P>Multi-antenna precoding effectively mitigates the interference in wireless networks. However, the resultant performance gains can be significantly compromised in practice if the precoder design fails to account for the inaccuracy in the channel state information (CSI) feedback. This paper addresses this issue by considering finite-rate CSI feedback from receivers to their interfering transmitters in the two-user multiple-input-multiple-output (MIMO) interference channel, called cooperative feedback, and proposing a systematic method for designing transceivers comprising linear precoders and equalizers. Specifically, each precoder/equalizer is decomposed into inner and outer components for nulling the cross-link interference and achieving array gain, respectively. The inner precoders/equalizers are further optimized to suppress the residual interference resulting from finite-rate cooperative feedback. Furthermore, the residual interference is regulated by additional scalar cooperative feedback signals that are designed to control transmission power using different criteria including fixed interference margin and maximum sum throughput. Finally, the required number of cooperative precoder feedback bits is derived for limiting the throughput loss due to precoder quantization.</P>

Feedback-Topology Designs for Interference Alignment in MIMO Interference Channels

Sungyoon Cho,Kaibin Huang,Dong Ku Kim,Lau, V. K. N.,Hyukjin Chae,Hanbyul Seo,Byoung-Hoon Kim IEEE 2012 IEEE transactions on signal processing Vol.60 No.12

<P>Interference alignment (IA) is a joint-transmission technique for the interference channel that achieves the maximum degrees-of-freedom and provides linear scaling of the capacity with the number of users for high signal-to-noise ratios (SNRs). Most prior work on IA is based on the impractical assumption that perfect and global channel-state information (CSI) is available at all transmitters. However, to implement IA, each receiver has to feed back CSI to all interferers, resulting in overwhelming feedback overhead. In particular, the sum feedback rate of each receiver scales quadratically with the number of users even if the feedback CSI is quantized. To substantially suppress feedback overhead, this paper focuses on designing efficient arrangements of feedback links, called feedback topologies, under the IA constraint. For the multiple-input multiple-output (MIMO) <I>K</I>-user interference channel, we propose the feedback topology that supports sequential CSI exchange (feedback and feedforward) between transmitters and receivers so as to achieve IA progressively. This feedback topology is shown to reduce the network feedback overhead from a quadratic function of <I>K</I> to a linear one. To reduce the delay in the sequential CSI exchange, an alternative feedback topology is designed for supporting two-hop feedback via a control station, which also achieves the linear feedback scaling with <I>K</I>. Next, given the proposed feedback topologies, the feedback-bit allocation algorithm is designed for allocating feedback bits by each receiver to different feedback links so as to regulate the residual interference caused by finite-rate feedback. Simulation results demonstrate that the proposed bit allocation leads to significant throughput gains especially in strong interference environments.</P>

Analysis of RF-DC Conversion Efficiency of Composite Multi-Antenna Rectifiers for Wireless Power Transfer

( Chao Deng ),( Kaibin Huang ),( Yik-chung Wu ),( Minghua Xia ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.10

This paper studies the radio frequency to direct current (RF-DC) conversion efficiency of rectennas applicable to wireless power transfer systems, where multiple receive antennas are arranged in serial, parallel or cascaded form. To begin with, a 2.45 GHz dual-diode rectifier is designed and its equivalent linear model is applied to analyze its output voltage and current. Then, using Advanced Design System (ADS), it is shown that the rectifying efficiency is as large as 66.2% in case the input power is 15.4 dBm. On the other hand, to boost the DC output, three composite rectennas are designed by inter-connecting two dual-diode rectifiers in serial, parallel and cascade forms; and their output voltage and current are investigated using their respective equivalent linear models. Simulation and experimental results demonstrate that all composite rectennas have almost the same RF-DC conversion efficiency as the dual-diode rectifier, yet the output of voltage or current can be significantly increased; in particular, the cascade rectenna obtains the highest rectifying efficiency.

Interference Alignment for Uplink Cellular Systems with Limited Feedback

Sungyoon Cho,Kaibin Huang,Dongku Kim,Hanbyul Seo IEEE 2012 IEEE COMMUNICATIONS LETTERS Vol.16 No.7

<P>Assuming perfect channel state information, the existing interference alignment (IA) algorithm proposed in [2] suppresses inter-cell interference (ICI) by aligning ICI to a randomly selected reference vector. However, IA in practice relies on limited feedback, resulting in residual ICI. In this letter, we propose the optimization of the reference vector for regulating the residual ICI. Specifically, it is shown that the reference vector that minimizes an upper bound on the residual ICI power is the eigenvector corresponding to the largest eigenvalue of the sum of the interference-channel matrices multiplied by their corresponding Hermitian matrices. Moreover, the performance gain of the proposed IA algorithm compared with the existing one in [2] is analyzed and demonstrated by simulation to be significant.</P>

Novel torsional spring with corrugated flexible units for series elastic actuators for cooperative robots

Yanlin Chen,Yanjiang Huang,Kaibin Chen,Yeping Wang,Yanbin Wu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.6

Reasonable robot joint stiffness is necessary to guarantee the safety and control accuracy of cooperative robots. In this study, a novel flat torsional spring with corrugated flexible units for a series elastic actuator (SEA) was developed to meet the requirements of cooperative robots. The torsional spring can absorb impact energy. The spring was optimized through the design of experiment method, and its theoretical stiffness was verified through numerical calculation and finite element analysis. Compared with other existing flat torsional springs in the simulation, the proposed torsional spring showed reasonable torsional stiffness and high radial and axial stiffness, which could guarantee safety and control accuracy. The proposed torsional spring was also evaluated through real experiments. Simulation and experimental results revealed that the proposed torsional spring has a linear torque versus angle characteristic.

Live Prefetching for Mobile Computation Offloading

Ko, Seung-Woo,Huang, Kaibin,Kim, Seong-Lyun,Chae, Hyukjin IEEE 2017 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.16 No.5

<P>Mobile computation offloading refers to techniques for offloading computation intensive tasks from mobile devices to the cloud so as to lengthen the formers' battery lives and enrich their features. The conventional designs fetch (transfer) user-specific data from mobiles to the cloud prior to computing, called offline prefetching. However, this approach can potentially result in excessive fetching of large volumes of data and cause heavy loads on radio-access networks. To solve this problem, the novel technique of live prefetching, which seamlessly integrates the task-level computation prediction and prefetching within the cloud-computing process of a large program with numerous tasks, is proposed in this paper. The technique avoids excessive fetching but retains the feature of leveraging prediction to reduce the program runtime and mobile transmission energy. By modeling the tasks in an offloaded program as a stochastic sequence, stochastic optimization is applied to design fetching policies to minimize mobile energy consumption under a deadline constraint. The policies enable real-time control of the prefetched-data sizes of candidates for future tasks. For slow fading, the optimal policy is derived and shown to have a threshold-based structure, selecting candidate tasks for prefetching and controlling their prefetched data based on their likelihoods. The result is extended to design close-to-optimal prefetching policies to fast fading channels. Compared with fetching without prediction, live prefetching is shown theoretically to always achieve reduction on mobile energy consumption.</P>

셀 섹터화가 적용된 하향링크 셀룰러 환경에서의 확률기하적 접근 방법

박지홍(Jihong Park),Kaibin Huang,김동구 한국통신학회 2011 한국통신학회 학술대회논문집 Vol.2011 No.2