Low Complexity Zero-Forcing Beamforming for Distributed Massive MIMO Systems in Large Public Venues

Li, Haoming,Leung, Victor C.M. The Korea Institute of Information and Commucation 2013 Journal of communications and networks Vol.15 No.4

Distributed massive MIMO systems, which have high bandwidth efficiency and can accommodate a tremendous amount of traffic using algorithms such as zero-forcing beam forming (ZFBF), may be deployed in large public venues with the antennas mounted under-floor. In this case the channel gain matrix H can be modeled as a multi-banded matrix, in which off-diagonal entries decay both exponentially due to heavy human penetration loss and polynomially due to free space propagation loss. To enable practical implementation of such systems, we present a multi-banded matrix inversion algorithm that substantially reduces the complexity of ZFBF by keeping the most significant entries in H and the precoding matrix W. We introduce a parameter p to control the sparsity of H and W and thus achieve the tradeoff between the computational complexity and the system throughput. The proposed algorithm includes dense and sparse precoding versions, providing quadratic and linear complexity, respectively, relative to the number of antennas. We present analysis and numerical evaluations to show that the signal-to-interference ratio (SIR) increases linearly with p in dense precoding. In sparse precoding, we demonstrate the necessity of using directional antennas by both analysis and simulations. When the directional antenna gain increases, the resulting SIR increment in sparse precoding increases linearly with p, while the SIR of dense precoding is much less sensitive to changes in p.

Receiver-oriented load-balancing and reliable routing in wireless sensor networks

Chen, Min,Leung, Victor C. M.,Mao, Shiwen,Kwon, Taekyoung John Wiley Sons, Ltd. 2009 WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Vol.9 No.3

<P>Routing protocols in wireless sensor networks (WSNs) typically employ a transmitter-oriented approach in which the next hop node is selected based on neighbor or network information. This approach incurs a large overhead when the accurate neighbor information is needed for efficient and reliable routing. In this paper, a novel receiver-oriented load-balancing and reliable routing (RLRR) protocol is proposed. In RLRR, an intermediate node solicits next hop candidates, each of which is to respond with its own backoff time dubbed a temporal gradient (TG). In this way, the next hop is selected without any central coordination on a packet-by-packet basis. Thus, each node needs not maintain any neighbor information. The remaining energy level used to determine the TG is always accurate and up-to-date. Furthermore, neighbor nodes whose hop count is less than the soliciting node participate in the next-hop selection process with loop-free operation guarantee. Comprehensive simulations are carried out to show that RLRR achieves relatively longer network lifetime and higher reliability than other existing schemes. Copyright © 2007 John Wiley & Sons, Ltd.</P>

Wireless Three-Pad ECG System: Challenges, Design, and Evaluations

Huasong Cao,Haoming Li,Victor C.M. Leung 한국통신학회 2011 Journal of communications and networks Vol.13 No.2

Electrocardiography (ECG) is a widely accepted approach for monitoring of cardiac activity and clinical diagnosis of heart diseases. Since cardiologists have been well-trained to accept 12-lead ECG information, a huge number of ECG systems are using such number of electrodes and placement configuration to facilitate fast interpretation. Our goal is to design a wireless ECG system which renders conventional 12-lead ECG information.We propose the three-pad ECG system (W3ECG). W3ECG furthers the pad design idea of the single-pad approach. Signals obtained from these three pads, plus their placement information, make it possible to synthesize conventional 12-lead ECG signals.We provide one example of pad placement and evaluate its performance by examining ECG data of four patients available from online database. Feasibility test of our selected pad placement positions show comparable results with respect to the EASI lead system. Experimental results also exhibit high correlations between synthesized and directly observed 12-lead signals (9 out of 12 cross-correlation coefficients higher than 0.75).

Coverage-Guaranteed and Energy-Efficient Participant Selection Strategy in Mobile Crowdsensing

Ko, Haneul,Pack, Sangheon,Leung, Victor C. M. IEEE 2019 IEEE Internet of things journal Vol.6 No.2

<P>In mobile crowdsensing (MCS), a participant selection strategy should be carefully designed to guarantee sufficient coverage and avoid unnecessary energy consumption. In this paper, we propose a coverage-guaranteed and energy-efficient participant selection (CG-EEPS) strategy, in which the MCS server determines participants based on the data usage profile and mobility level of mobile devices. In addition, CG-EEPS adopts a piggyback approach of sensory data for energy-efficient transmissions. To attain the optimal performance in CG-EEPS, a constraint Markov decision process (CMDP) problem is formulated and its optimal policy is obtained by a linear programming. To address the curse of dimensionality in CMDP, a greedy heuristic is proposed and evaluated. Trace-driven evaluation results demonstrate that CG-EEPS can achieve sufficient coverage rate only with 20% of participants compared to random selection schemes.</P>

Dynamic Bandwidth Allocation of NOMA and OMA for 5G

Man Hee Lee(이만희),Leung C. M. Victor,Soo Young Shin(신수용) 한국통신학회 2017 韓國通信學會論文誌 Vol.42 No.12

Joint opportunistic user scheduling and power allocation: throughput optimisation and fair resource sharing

Ge, Xin,Jin, Hu,C. M. Leung, Victor Institution of Electrical Engineers 2018 IET communications Vol.12 No.5

<P>Despite extensive studies on optimal power allocation, how to design an efficient joint user scheduling and power allocation scheme for uplink multiuser networks remains largely unexplored. This study investigates joint opportunistic user scheduling and power allocation in uplink multiuser networks to maximise user throughput subject to the power and resource sharing constraints. By exploiting the cumulative distribution function-based scheduling method, the authors first characterise the optimal power allocation subject to both long-term and short-term power constraints. Instead of calculating the transmit power in an iterative and central manner, users can independently decide their instantaneous transmit power in the proposed scheme, which facilitates the algorithm implementation for each user in uplink networks. The closed-form throughput of the proposed scheme is also derived, which can provide an efficient way to estimate and evaluate user performance. Numerical results reveal that compared with several benchmark schemes, the proposed scheme improves throughput performance significantly.</P>

Mobility-Aware Vehicle-to-Grid Control Algorithm in Microgrids

Ko, Haneul,Pack, Sangheon,Leung, Victor C. M. IEEE 2018 IEEE transactions on intelligent transportation sy Vol.19 No.7

<P>In a vehicle-to-grid (V2G) system, electric vehicles (EVs) can be efficiently used as power consumers and suppliers to achieve microgrid (MG) autonomy. Since EVs can act as energy transporters among different regions (i.e., MGs), it is an important issue to decide where and when EVs are charged or discharged to achieve the optimal performance in a V2G system. In this paper, we propose a mobility-aware V2G control algorithm (MACA) that considers the mobility of EVs, states of charge of EVs, and the estimated/actual demands of MGs and then determines charging and discharging schedules for EVs. To optimize the performance of MACA, the Markov decision process problem is formulated and the optimal policy on charging and discharging is obtained by a value iteration algorithm. Since the mobility of EVs and the estimated/actual demand profiles of MGs may not be easily obtained, a reinforcement learning approach is also introduced. Evaluation results demonstrate that MACA with the optimal and learning-based policies can effectively achieve MG autonomy and provide higher satisfaction on the charging.</P>

Quantum Packet for the Next Generation Network/ISDN3

Lam, Ray Y. W.,Chan, Henry C. B.,Chen, Hui,Dillon, Tharam S.,Li, Victor O. K.,Leung, Victor C. M. The Korea Institute of Information and Commucation 2008 Journal of communications and networks Vol.10 No.3

This paper proposes a novel method for transporting various types of user traffic effectively over the next generation network called integrated services digital network 3 (ISDN3) (or quantum network) using quantum packets. Basically, a quantum packet comprises one or more 53-byte quanta as generated by a "quantumization" process. While connection-oriented traffic is supported by fixed-size quantum packets each with one quantum to emulate circuit switching, connectionless traffic (e.g., IP packets and active packets) is carried by variable-size quantum packets with multiple quanta to support store-and-forward switching/routing. Our aim is to provide frame-like or datagram-like services while enabling cell-based multiplexing. The quantum packet method also establishes a flexible and extensible framework that caters for future packetization needs while maintaining backward compatibility with ATM. In this paper, we discuss the design of the quantum packet method, including its format, the "quantumization" process, and support for different types of user traffic. We also present an analytical model to evaluate the consumption of network resources (or network costs) when quantum packets are employed to transfer loss-sensitive data using three different approaches: cut-through, store-and-forward and ideal. Close form mathematical expressions are obtained for some situations. In particular, in terms of network cost, we discover two interesting equivalence phenomena for the cut-through and store-and-forward approaches under certain conditions and assumptions. Furthermore, analytical and simulation results are presented to study the system behavior. Our analysis provides valuable insights into the. design of the ISDN3/quantum network.

Fundamental Limits of CDF-Based Scheduling: Throughput, Fairness, and Feedback Overhead

Hu Jin,Bang Chul Jung,Leung, Victor C. M. IEEE 2015 IEEE/ACM transactions on networking Vol.23 No.3

<P>In this paper, we investigate fundamental performance limits of cumulative distribution function (CDF)-based scheduling (CS) in downlink cellular networks. CS is known as an efficient scheduling method that can assign different time fractions for users or, equivalently, satisfy different channel access ratio (CAR) requirements of users while exploiting multiuser diversity. We first mathematically analyze the throughput characteristics of CS in arbitrary fading statistics and data rate functions. It is shown that the throughput gain of CS increases as the CAR of a user decreases or the number of users in a cell increases. For Nakagami-m fading channels, we obtain the average throughput in closed form and investigate the effects of the average signal-to-noise ratio, the shape parameter m, and the CAR on the throughput performance. In addition, we propose a threshold-based opportunistic feedback technique in order to reduce feedback overhead while satisfying the CAR requirements of users. We prove that the average feedback overhead of the proposed technique is upper-bounded by -lnp, where p is the probability that no user satisfies the threshold condition in a cell. Finally, we adopt a novel fairness criterion, called qualitative fairness, which considers not only the quantity of the allocated resources to users, but also the quality of the resources. It is observed that CS provides a better qualitative fairness than other scheduling algorithms designed for controlling CARs of users.</P>

Quantum Packet for the Next Generation Network/ISDN3

Ray Y. W. Lam,Henry C. B,Hui Chen,Tharam S. Dillon,Victor O. K. Li,Victor C. M. Leung 한국통신학회 2008 Journal of communications and networks Vol.10 No.3

This paper proposes a novel method for transporting various types of user traffic effectively over the next generation network called integrated services digital network 3 (ISDN3) (or quantum network) using quantum packets. Basically, a quantum packet comprises one or more 53-byte quanta as generated by a “quantumization” process. While connection-oriented traffic is supported by fixed-size quantum packets each with one quantum to emulate circuit switching, connectionless traffic (e.g., IP packets and active packets) is carried by variable-size quantum packets with multiple quanta to support store-and-forward switching/routing. Our aimis to provide frame-like or datagram-like services while enabling cellbased multiplexing. The quantum packet method also establishes a flexible and extensible framework that caters for future packetization needs whilemaintaining backward compatibility with ATM. In this paper, we discuss the design of the quantum packet method, including its format, the “quantumization” process, and support for different types of user traffic. We also present an analytical model to evaluate the consumption of network resources (or network costs) when quantum packets are employed to transfer losssensitive data using three different approaches: cut-through, storeand- forward and ideal. Close form mathematical expressions are obtained for some situations. In particular, in terms of network cost, we discover two interesting equivalence phenomena for the cut-through and store-and-forward approaches under certain conditions and assumptions. Furthermore, analytical and simulation results are presented to study the system behavior. Our analysis provides valuable insights into the design of the ISDN3/quantum network.