Showing papers by "Albert Kai-Sun Wong published in 2010"

Received Signal Strength-Based Wireless Localization via Semidefinite Programming: Noncooperative and Cooperative Schemes

Abstract: The received signal strength (RSS)-based approach to wireless localization offers the advantage of low cost and easy implementability. To circumvent the nonconvexity of the conventional maximum likelihood (ML) estimator, in this paper, we propose convex estimators specifically for the RSS-based localization problems. Both noncooperative and cooperative schemes are considered. We start with the noncooperative RSS-based localization problem and derive a nonconvex estimator that approximates the ML estimator but has no logarithm in the residual. Next, we apply the semidefinite relaxation technique to the derived nonconvex estimator and develop a convex estimator. To further improve the estimation performance, we append the ML estimator to the convex estimator with the result by the convex estimator as the initial point. We then extend these techniques to the cooperative localization problem. The corresponding Cramer-Rao lower bounds (CRLB) are derived as performance benchmarks. Our proposed convex estimators comply well with the RSS measurement model, and simulation results clearly demonstrate their superior performance for RSS-based wireless localization.

Hybrid TOA/AOA-Based Mobile Localization with and without Tracking in CDMA Cellular Networks

Abstract: This paper proposes a hybrid TOA/AOA (Time of Arrival/Angle of Arrival)-based localization algorithm for Code Division Multiple Access (CDMA) networks. The algorithm extends the Taylor Series Least Square (TS-LS) method originally developed for TOA-based systems to incorporate AOA measurements. In addition, tracking algorithms utilizing velocity and acceleration measurements are investigated. Simulation results illustrate that the proposed TOA/AOA TS-LS can provide better performance than conventional schemes in localization accuracy and in reduced likelihood of encountering non-convergence problem compared with TOA TS-LS. Tracking algorithms using the Extended and Unscented Kalman Filter (EKF and UKF) can track the objects relatively well, further decreasing the positioning error. UKF is found to provide closer tracking of the trajectory than EKF, for it truly captures the statistical mean and variance of the noises.

Energy Efficient Assisted GPS Measurement and Path Reconstruction for People Tracking

Abstract: In the use of a wearable GPS and cellular tracker for applications such as elderly tracking, device power consumption is an important consideration. To save power, assisted GPS (AGPS) location fixes should not be performed frequently. On the other hand, we also do not want to lose important information about the user's mobility patterns and routines. To solve this dilemma, in this paper, we present the design of a system that intelligently schedules on-line AGPS location fixes only when necessary based on information extracted from user's historical mobility data, and then reconstruct the user path based on these sparsely taken on-line location fixes. Experimental results show that our on-line algorithm can significantly reduce the number of AGPS fixes needed and the reconstruction method works well without a priori knowledge of a map and streets information.

Rate matching: a new approach to hidden terminal problem in ad hoc networks

Abstract: Prior works on the hidden terminal problem in wireless networks often assume that the SNR requirement and the transmission range in a network are fixed. In fact, they are rate dependent. Because of this assumption, many of the prior conclusions about the hidden terminal problem are not accurate. A new analysis of the hidden terminal problem is presented in the paper. The new insights provided by the analysis lead to a rate-matching scheme for tackling the hidden terminal problem in wireless networks. The new method is simple, yet efficient, and requires no protocol changes from the 802.11 standard. NS2-based simulations are given in the paper to demonstrate the advantages of the new scheme.

On Fairness Enhancement for CSMA/CA Wireless Networks

Abstract: Location dependency and its associated exposed receiver problem create the most severe unfairness scenario in CSMA/CA protocol. To address this issue, we develop an analytical model to study 1) the likelihood of the exposed receiver problem and how this likelihood varies with the carrier sensing and the transmission ranges; 2) the probabilities of successful RTS receptions and of successful RTS/CTS handshakes of the disadvantaged link under the typical exposed receiver scenario. Based on the analytical insights, we propose a receiver assistance feature as addition to the CSMA/CA protocol so that the receiver of a disadvantaged link can help the sender to contend for channel access. In terms of compatibility with the existing 802.11 protocol, the proposed feature requires only one bit of modification in the packet header. Simulation results show that the proposed feature not only significantly improves the fairness of the CSMA/CA protocol, but also increases the overall throughput, all accomplished without creating other side effects, such as aggravation of the hidden terminal problem.

Simultaneous Localization and Time Synchronization in Wireless Sensor Networks via Semidefinite Programming

Abstract: For Wireless Sensor Networks (WSNs), utilizing the same set of measurement data for simultaneous localization and time synchronization is potentially useful for achieving higher estimation accuracy, lower communication overhead and power consumption. However, localization and time synchronization are traditionally treated as two separate problems. In this paper, we propose to use Semidefinite Programming (SDP) to jointly solve the two problems at the same time. Two scenarios, Sensor Nodes (SNs) with sufficient and insufficient number of neighboring beacons, are considered. The Cramer-Rao Lower Bound (CRLB) is then derived. Simulation results are presented to contrast the performance of the proposed Simultaneous Localization and Time Synchronization-SDP (SLTS-SDP) and Generalized SLTS-SDP (GSLTS-SDP) algorithms with the conventional SDP method and the corresponding CRLBs.

Enhanced floor control protocol for PoC application in data packet voice communication

Abstract: Push-to-Talk over Cellular (PoC) is a one-to-one or one-to-many Push-To-Talk (PTT) service designed to work over the cellular network. In the PTT, a participant may speak as soon as he/she has obtained the permission through pushing a “talk” button. The typical telephone setup delay is avoided. In the traditional floor control protocol defined in the Open Mobile Alliance standard (FCP-OMA) for PoC, at any time only one participant is permitted to speak. The permitted speaker is totally “deaf” and the listeners are fully “dumb” until the speaker releases or is revoked the floor. In this article, we propose an enhanced floor control protocol (EFCP) for PoC application in a packet voice scenario where full-duplex communications can be supported. The proposed protocol is divided into two categories: EFCP-M and EFCP-NM depending on whether media mixing is needed or supported. Through a queuing model, we compare the performance of EFCP against FCP-OMA. Experimental results show that our scheme can significantly reduce the probability that floor requests are denied and the expected waiting time in queue.

Relay-assisted partial packet recovery with IDMA method in CDMA wireless network

Abstract: Automatic Repeat Request (ARQ) is an effective technique for reliable transmission of packets in wireless networks. In ARQ, however, only a few erroneous bits in a packet will cause the entire packet to be discarded at the receiver. In this case, it's wasteful to retransmit the correct bit in the received packet. The partial packet recovery only retransmits the unreliable decoded bits in order to increase the throughput of network. In addition, the cooperative transmission based on Interleave-division multiple-access (IDMA) can obtain diversity gains with multiple relays with different locations for multiple sources simultaneously. By exploring the diversity from the channel between relay and destination, we propose a relay-assisted partial packet recovery in CDMA wireless network to improve the performance of throughput. In the proposed scheme, asynchronous IDMA iterative chip-by-chip multiuser detection is utilized as a method of multiple partial recovery, which can be a complementarity in a current CDMA network. The confidence values' concept is applied to detect unreliable decoded bits. According to the result of unreliable decoded bits' position, we use a recursive algorithm based on cost evaluation to decide a feedback strategy. Then the feedback request with minimum cost can be obtained. The simulation results show that the performance of throughput can be significantly improved with our scheme, compared with traditional ARQ scheme. The upper bound with our scheme is provided in our simulation. Moreover, we show how relays' location affects the performance.

Fairness Enhancement for 802.11 MAC

Abstract: Location dependency and its associated exposed receiver problem create the most severe unfairness scenario of the CSMA/CA protocol. An analytical model is built up to study the success probabilities of RTS reception and RTS/CTS handshake of the typical disadvantaged link under the exposed receiver scenario. Derived from the analytical insights, we propose a receiver assistance feature (RcvAssist) for the CSMA/CA protocol which not only significantly enhances the fairness of disadvantaged links suffering from exposed receiver problem, but also increases the overall throughput without introducing other side effects, such as aggregating the hidden terminal problem.

Relay-Assisted Partial Packet Recovery with IDMA Method in CDMA Wireless Network

Abstract: Automatic Repeat Request (ARQ) is an effective technique for reliable transmission of packets in wireless networks. In ARQ, however, only a few erroneous bits in a packet will cause the entire packet to be discarded at the receiver. In this case, it's wasteful to retransmit the correct bit in the received packet. The partial packet recovery only retransmits the unreliable decoded bits in order to increase the throughput of network. In addition, the cooperative transmission based on Interleave-division multiple-access (IDMA) can obtain diversity gains with multiple relays with different locations for multiple sources simultaneously. By exploring the diversity from the channel between relay and destination, we propose a relay-assisted partial packet recovery in CDMA wireless network to improve the performance of throughput. In the proposed scheme, asynchronous IDMA iterative chip-by-chip multiuser detection is utilized as a method of multiple partial recovery, which can be a complementarity in a current CDMA network. The confidence values' concept is applied to detect unreliable decoded bits. According to the result of unreliable decoded bits' position, we use a recursive algorithm based on cost evaluation to decide a feedback strategy. Then the feedback request with minimum cost can be obtained. The simulation results show that the performance of throughput can be significantly improved with our scheme, compared with traditional ARQ scheme. The upper bound with our scheme is provided in our simulation. Moreover, we show how relays' location affects the performance.

Application-layer bandwidth allocation algorithm for service differentiation in hybrid content distribution network

Abstract: Hybrid content distribution network (HCDN) makes use of the highly complementary advantages of conventional CDN (content distribution network) and pure P2P (peer-to-peer). In HCDN, clients can concurrently retrieve content from both CDN and P2P networks. In this paper, service differentiation is formulated as a constraint optimization problem, in which two critical factors are taken into consideration: quality factor of a link and demand factor of a file. With the convex optimization theory, two bandwidth allocation algorithms, HBAA-P for source peer and HBAA-S for surrogate server, are proposed and proved for service differentiation in the hybrid architecture. Some experimental results are illustrated to make sense of the performance features of our approaches.