Wai-Choong Wong

Teletraffic performance of highway microcells with overlay macrocell

The teletraffic performance of a highway microcellular digital mobile radio system having an oversailing macrocell that spans many microcells is presented. The microcellular cluster is composed of concatenated segments of the highway where each segment is a microcell, typically 500-2000 m in length, with the base stations located at lamp-post elevations. A narrowband time-division-multiple-access arrangement supporting ten channels per carrier and one carrier per base station is used. The teletraffic analysis assumes there are n-up and n-down lanes, and that the vehicular speeds conform to a truncated Gaussian distribution whose mean speed is 100 or 50 km/h when the vehicular traffic is free-flowing or in traffic-congested conditions, respectively. >

A robust dead-reckoning pedestrian tracking system with low cost sensors

The emergence of personal mobile device with low cost sensors, such as accelerometer and digital compass, has made dead-reckoning (DR) an attractive choice for indoor pedestrian tracking. In this paper, we propose a robust DR pedestrian tracking system on top of such commercially accessible sensor sets capable of DR. The proposed method exploits the fact that, multiple DR systems, carried by the same pedestrian, have stable relative displacements with respect to the center of motion, and therefore to each other. We first formulate the robust tracking task as a generalized maximum a posteriori sensor fusion problem, and then we narrow it to a simple computation procedure with certain assumptions. A prototype is implemented and evaluated with a benchmark system that collects ground truth efficiently and accurately. In a practical indoor testbed, the proposed scheme has exhibited robust tracking performance, with reduction in average tracking error up to 73.7%, compared to traditional DR tracking methods.

Ordered dynamic channel assignment scheme with reassignment in highway microcells

An ordered dynamic channel assignment with reassignment (ODCAR) scheme is proposed, and its performance is studied in a highway microcellular radio environment. Channels are assigned in an ordered basis in conjunction with a minimax algorithm under cochannel interference constraints, to provide high capacity and to alleviate worst case channel congestion in each microcell. Simulation results show significant performance improvements in terms of channel utilization and probability of call failure, at the expense of an increase in complexity and call switching requirements. >

Indoor localization with channel impulse response based fingerprint and nonparametric regression

In this paper, we propose a fingerprint-based localization scheme that exploits the location dependency of the channel impulse response (CIR). We approximate the CIR by applying inverse Fourier transform to the receivers channel estimation. The amplitudes of the approximated CIR (ACIR) vector are further transformed into the logarithmic scale to ensure that elements in the ACIR vector contribute fairly to the location estimation, which is accomplished through nonparametric kernel regression. As shown in our simulations, when both the number of access points and density of training locations are the same, our proposed scheme displays significant advantages in localization accuracy, compared to other fingerprint-based methods found in the literature. Moreover, absolute localization accuracy of the proposed scheme is shown to be resilient to the real time environmental changes caused by human bodies with random positions and orientations.

Energy Efficient Multiple Target Tracking in Wireless Sensor Networks

Energy awareness is a crucial component in the design of wireless sensor networks at all layers. This paper looks into efficient energy utilization of a target-tracking sensor network by predicting a targets trajectory through experience. While this is not new, the chief novelty comes in conserving energy through both dynamic spatial and temporal management of sensors while assuming minimal locality information. We adapted our target trajectory model from the Gauss-Markov mobility model, formulated the tracking problem as a hierarchical Markov decision process (HMDP), and solved it through neurodynamic programming. Our HMDP for target-tracking (HMTT) algorithm conserves energy by reducing the rate of sensing (temporal management) but maintains an acceptable tracking accuracy through trajectory prediction (spatial management) of multiple targets. We derived some theoretical bounds on accuracy and energy utilization of HMTT. Simulation results demonstrated the effectiveness of HMTT in energy conservation and tracking accuracy against two other predictive tracking algorithms, with accuracy of up to 47% higher and energy savings of up to 200%

Packet reservation multiple access in a metropolitan microcellular radio environment

The author examines the performance of a packet reservation multiple access (PRMA) protocol in a metropolitan microcellular radio environment using computer simulations. Call characteristics, mobility, and channel conditions have an impact on PRMA performance which is measured in terms of the average packet dropping rate per call. In order to maintain a reasonable level of service quality for calls in progress, teletraffic loading can be controlled by introducing a call setup queue and limiting the number of active subscribers. Call mobility is found to have a minor impact on PRMA performance. PRMA is also fairly robust against adverse channel conditions with a drop in performance of about 15% when the channel packet loss rate is less than 0.01. Performance comparisons to other protocols are also carried out. >

System aspects of cellular radio

The greatest single factor in enhancing spectral efficiency of a network is the mass deployment of microcells. By this simple technique we can repeatedly and efficiently reuse the precious spectrum. The number of users a network can support is fundamentally dependent on the common air interface (CAI) over which users communicate. User capacity is dependent on many factors, but the cardinal ones are the amount of spectrum the regulators allocate, the size of the radio coverage area from a base station (BS), and the amount of interference a particular radio link can tolerate. In this article we are primarily concerned with the system aspects associated with the CAI. We focus on the critical importance of BS siting. Starting with existing large cells, we deliberate on the problems that might arise in siting BSs in three dimensional microcells, in order to consider suitable multiple access methods for future cellular environments. >

Integrated data and speech transmission using packet reservation multiple access

The authors propose an integrated packet reservation multiple access (IPRMA) protocol for transmitting both speech and data information. While speech users are allowed to contend for reservation slots on a frame-by-frame basis, data users may reserve multiple slots across a frame to increase throughput. The protocol includes a priority mechanism which ensures that speech users have greater access to idle slots since speech packets have a more demanding delay constraint. The proposed scheme is shown to provide equitable access to channel resources for both types of users, yielding improvements in overall system performance while significantly increasing data throughput compared to a system without data packet reservation.<<ETX>>

A proposal of butterfly-graph based stream authentication over lossy networks

In this paper, we propose a butterfly-graph based stream authentication scheme for lossy networks where the streaming packets could be lost in both random and burst ways. Due to the nice properties of butterfly graph, the proposed scheme is quite robust and efficient. Theoretical analysis and simulation results show that the proposed scheme outperforms existing schemes in terms of overhead and authentication probability while maintaining the same levels of sender/receiver delay and robustness.

MAC Protocol Design and Performance Analysis for Random Access Cognitive Radio Networks

In this paper, we consider the medium access control (MAC) protocol design for random access cognitive radio network (CRN). Based on asynchronous spectrum sensing technique and RTS/CTS mechanism, a new MAC protocol, namely, cognitive-radio-based carrier sense medium access with collision avoidance (CR-CSMA/CA) is proposed to coordinate the channel access of secondary network as well as protect the operation of primary network, which applies to both single and multiple channel models. Using the G/G/1 queuing model with consideration of unsaturated and saturated network condition, we develop a framework to analyze the proposed MAC protocol and also derive closed-form expressions of specific performance metrics such as normalized throughput, average packet service time, etc. Performance evaluations illustrate and validate that the performance of CR-CSMA/CA varies with the offered traffic load of secondary network and the spectrum utilization rate of primary network, respectively, and also show that CR-CSMA/CA outperforms other relevant MAC protocols.