Haoming Li

Efficient HetNet implementation using broadband wireless access with fiber-connected massively distributed antennas architecture

We introduce a novel HetNet architecture employing fiber-connected distributed antenna systems, named broadband wireless access with fiber-connected massively distributed antennas (BWA-FMDA), which facilitates coordination of resource allocation and interference management. Among various opportunities realized by the proposed approach, our focus in this article is on CoMP for UMTS LTE femto- and picocells, to which we refer as femto-CoMP. Through extensive simulation results we demonstrate the superior performance gain of a femto-CoMP HetNet over independent femto- and picocell operation in traditional HetNet scenarios. We analyze both link- and system-level feasible throughput as well as scheduling delay for round-robin and proportional fair schedulers.

Green last mile: how fiber-connected massively distributed antenna systems can save energy

We introduce a novel last-mile architecture that integrates the advantages of a distributed antenna system with centralized processing capability, connected through an optical fiber medium. The proposed broadband wireless access with fiber-connected massively distributed antenna system (BWA-FMDA) is capable of enhancing spectral efficiency of the network through coordinated multipoint transmissions at the femtocell scale. Furthermore, by shortening the lastmile communication link and lowering the power consumption, BWA-FMDA represents a viable green wireless access solution. Through our detailed and extensive simulation results, we demonstrate the potentially superior performance of BWA-FMDA in comparison with micro base station and femtocell deployments.

Wireless three-pad ECG system: Challenges, design, and evaluations

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 pro pose 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).

An Energy Efficient Implementation of C-RAN in HetNet

This paper introduces the Cloud-based Radio Access Network (C-RAN) architecture into heterogeneous network (HetNet), in which distributed antennas are connected to a cloud-based baseband processing unit through optical fibers. Among various opportunities realized by this architecture, our focus in this paper is on the spectral efficiency (SE) advantages achieved by cooperative transmission and its associated power consumption that may affect the energy efficiency (EE) of the system. A simple but efficient pre-coding scheme is proposed to reduce the computation complexity of cooperative transmission, thus lowering the associated power consumption, and a detailed power model is then developed to benchmark the various sources of energy consumption in C-RAN. Through detailed simulation, an early performance evaluation of the potentially energy efficient C-RAN implementation was demonstrated.

Multi-User Medium Access Control in Wireless Local Area Network

We propose a multi-user medium access control (MAC) protocol to simultaneously support multi-packet transmission (MPT) and multi-packet reception (MPR) in wireless local area networks. By assuming perfect physical layer functions, we evaluate the maximum number of active stations that can be supported under different traffic arrival rates. Our analysis show that when the number of transmitting antennas is K=2, simultaneous MPT and MPR supports 40~50% more stations than previous multi-user MAC that uses only MPT. The gain increases to 60% when short packets (40 bytes) are used. When K=4, the advantage of MPT+MPR over MPT-only enlarges to 130%. We also investigated the impacts of imperfect physical layer functions and the effects of enabling or disabling RTS/CTS in uplink.

A Unified Scheduling Framework Based on Virtual Timers for Selfish-Policy Shared Spectrum

The issue of efficiency and fairness in resource allocation will continue to be of significant importance in scheduler designs for future wireless systems. Of particular importance is the development of distributed techniques for achieving desired efficiency and fairness tradeoffs. We will focus on the the design of selfishly efficient and as well as different fair policies through the use of a virtual timer. This virtual timer unifies various previously considered fairness methods including Round-Robin, Max-Min and Proportional fairness, which are rigorously investigated. The performance of the presented techniques are compared using extensive simulations.

Cognitive wireless local area network over fibers: Architecture, research issues and testbed implementation

We introduce a novel architecture incorporating broadband radio over optical fiber and cognitive radio technologies into a unified network platform named Cognitive Wireless Local Area Network over Fibers (CWLANoF). We first elaborate on the system architecture and more specifically on various topologies to integrate optical fibers and wireless devices in CWLANoF. The mixture of centralized processing capability as well as distributed sets of antennas in this system leads to a rich set of research issues that are presented in this article. Finally, we present a testbed architecture built on a software defined radio platform, along with its implementation and test plans.

Demonstration of a novel wireless three-pad ECG system for generating conventional 12-lead signals

Wireless monitoring of a patients electrocardiogram (ECG) is a typical application in mobile healthcare area. Inspired by application of linear transformations to ECG signals obtained in a vectorcardiographic system, we propose the wireless three-pad ECG system (W3ECG). Signals obtained from these three pads, plus their placement information, make it possible to synthesize conventional 12-lead ECG signals. W3ECGs system-level design, pad placements and evaluations are presented in a separate paper. This paper details W3ECGs pad design, software implementation, and experimental studies.

Collision Avoidance and Mitigation in Cognitive Wireless Local Area Network over Fibre

Cognitive wireless local area network (WLAN) over fiber (CWLANoF), which employs remote antenna units (RAUs) connected to a central cognitive access point, can provide a cost-effective and efficient architecture for devices to equally share the industrial, scientific, and medical band by taking advantage of cognitive radio capabilities. Based on the CWLANoF architecture, we propose two methods to reduce collisions among WLAN stations, with multiple independent channels operating at each RAU, and transmission and reception diversity through cooperation of adjacent RAUs. We evaluate the proposed methods through Monte-Carlo simulations. Compared with a conventional WLAN Extended Service Set with two access points, the proposed methods achieve 10% gain on Transmission Control Protocol (TCP) throughput and 10~25% reduction on packet error rate of constant-bit-rate traffic streams for spatially uniform traffic. When the traffic is spatially non-uniform with hotspots arising at certain locations, the TCP throughput gain increases by up to 26%. The results show the potential of CWLANoF in coping with dynamic traffic that often occurs in the indoor wireless access.

Design and evaluation of a novel wireless three-pad ECG system for generating conventional 12-lead signals

Electrocardiography (ECG) is a widely accepted approach for monitoring of cardiac activity and clinical diagnosis of heart diseases. In order to make ECG systems portable, easy to setup, comfortable to patients and tolerant of artifacts, wireless single-pad ECG systems have been developed. To tackle the problems raised by wireless single-pad ECG systems, we propose an upgraded version, the wireless three-pad ECG system (W3ECG). W3ECG furthers the pad design idea of the single-pad approach. We add two more pads to the W3ECG to gain spatial variety of heart activity. 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).