Wireless Networks

Wireless networks have become increasingly pervasive in everyday life, offering greater convenience, flexibility, and lower infrastructural costs than wired networks. An outstanding challenge in wireless communications is to maximize the usage of the limited RF spectrum in the presence of propagation impairments such as fading and shadowing. In wireless networks, the mobility of the users introduces additional challenges in maintaining connectivity in the wireless medium. The broadcast nature of the wireless channel and the mobility of users make secure communications a compelling problem for wireless networks. In ad hoc networks, the challenges are even greater as the mobile stations themselves serve as relay points for data traffic in the absence of base stations. Our recent research in wireless network architectures and protocols has focused on three main areas: handoff algorithms for cellular networks, mobility modeling and management, and wireless network security.

Handoff Algorithms for Cellular Networks

Cellular networks are equipped with base stations that partition the serving area into so-called cells associated with the base stations that allow for spectrum reuse and provide the interface to wired networks. As the mobile station moves in the network it is assigned to one or more base stations. The assignment set is determined dynamically based on pilot signal strength measurements from base stations in the proximity of the mobile and the handoff algorithm that is employed. A change in the assignment set is referred to as a handoff. We distinguish two types of handoff: hard handoff and soft handoff. Hard handoff algorithms are employed in current cellular networking standards such as GSM and GPRS. In a hard handoff algorithm, the assignment set contains at most one base station. When a handoff occurs, the mobile station leaves the cell associated with one base station and enters the cell associated with another base station. In soft handoff algorithms, the assignment set may contain more than one base station. Soft handoff employs diversity in order to make handoff transitions smoother. Soft handoff is employed in networks based on CDMA (Code Division Multiple Access), e.g., the IS-95 standard as well as third-generation standards such as WCDMA and cdma2000.

Our recent research has focused on developing analytical models for evaluating the performance of handoff algorithms. In particular, we have developed a discrete-time approach to evaluating handoff performance for both hard and soft handoff algorithms [LeuMark06, LeuMark03, LeuMark02a]. Our approach leads to exact numerical procedures for calculating handoff and assignment probabilities for a mobile station moving in a cellular network. Our analytical work has led us to develop new handoff algorithms [LeuMark03, LeuMark02b] that have improved performance in microcellular environments in which the mobile speed is relatively high.

References:

[LeuMark06] A.E. Leu and B.L. Mark, "A Discrete-time Level-Crossing Analysis of Soft Handoff Performance in Cellular Networks," IEEE Trans. on Information Theory , July 2006 (to appear).

[LeuMark04] A.E. Leu and B.L. Mark, "A Discrete-time Approach to Analyze Hard Handoff Performance in Cellular Networks," IEEE Trans. on Wireless Communications, vol. 3, no. 5, pp. 1721-1733, Sept. 2004.

[ZaidiMark04s] Z.R. Zaidi and B.L. Mark, "A Mobility-aware Handoff Trigger Scheme for Seamless Connectivity in Cellular Networks," in Proc. IEEE Fall Vehicular Technology Conf. (VTC), Los Angeles, CA, vol. 5, pp. 3471-3475, Sept. 2004.

[LeuMark04] A.E. Leu and B.L. Mark, "Analysis of Handoff Interference along Arbitrary Trajectories in Cellular Networks," in Proc. IEEE Wireless Comm. and Networking Conf. (WCNC'2004), Atlanta, Georgia, vol. 2, pp. 1969-1974, Mar. 2004.

[LeuMark03] A.E. Leu and B.L. Mark, "An Efficient Timer-based Hard Handoff Algorithm for Cellular Networks," in Proc. IEEE Wireless Comm. and Networking Conf. (WCNC'2003), New Orleans, Mar. 2003.

[LeuMark02b] A.E. Leu and B.L. Mark, "Modeling and Analysis of Fast Handoff Algorithms for Microcellular Networks," in Proc. IEEE/ACM MASCOTS '2002, pp. 321-328, Fort Worth, Texas, Oct. 2002.

[LeuMark02a] A.E. Leu and B.L. Mark, "Discrete-time Analysis of Soft Handoff Algorithms for CDMA Cellular Networks," in Proc. IEEE Int. Conf. on Comm. '2002 (ICC'02), Vol. 5, pp. 3222-3226, New York City, April/May 2002.

Mobility Modeling and Management

Mobility is a distinguishing feature of wireless networks that makes service provisioning a challenging task. Our research is concerned with modeling mobility for the purpose of evaluating network performance, and also for application to mobility tracking and mobility management. Mobility information can be used to provide more efficient access to network resources. We have developed integrated models of mobility and traffic based on hidden semi-Markov models that can be used to improve wireless Internet access [Yu02, Yu00, Kob00]. We have also developed efficient and accurate network-based mobility tracking procedures based on a dynamic system model of mobility [MarkZaidi02]. The mobility tracking model has be extended to ad hoc networks [ZaidiMark03].

References:

[MSSR06] B.L. Mark, V. Suri, S. Singh, and Y. Roh, "Link Mobility Tracking for MANETs," in Proc. Int. Conference on Computer Communications (ICCCN), Arlington, VA, Oct. 2006 (to appear).

[ZaidiMark04d] Z.R. Zaidi and B.L. Mark, "Distributed Mobility Tracking for Ad Hoc Networks Based on an Autoregressive Model," in Lecture Notes in Computer Science (LCNS), volume 3326 [Proc. 6th International Workshop on Distributed Computing (IWDC), Indian Statistical Institute, Kolkata, India], pp. 447 - 458, December 2004.

[ZaidiMark04n] Z.R. Zaidi and B.L. Mark, "Mobility Estimation for Wireless Networks based on an Autoregressive Model," in Proc. IEEE Globecom, Dallas, TX, pp. 3405-3409, November 2004.

[ZMT04] Z.R. Zaidi, B.L. Mark, and R.K. Thomas, "A Two-Tier Representation of Node Mobility in Ad Hoc Networks," in Proc. 1st IEEE Int. Conference on Sensor and Ad Hoc Communications and Networks (SECON), Santa Clara, CA, pp. 153-161, Oct. 2004.

[ZaidiMark03] Z.R. Zaidi and B.L. Mark, "A Mobility Tracking Model for Wireless Ad Hoc Networks," in Proc. IEEE Wireless Comm. and Networking Conf. (WCNC'2003), New Orleans, Mar. 2003.

[Yu02] S.-Z. Yu, B.L. Mark, and H. Kobayashi, "Dynamic Web Pages for Location-Based Services," in Proc. Int. Conf. on Wireless and Optical Communications (WOC 2002), pp. 457-463, Banff, Canada, July 2002.

[MarkZaidi02] B.L. Mark and Z.R. Zaidi, "Robust Mobility Tracking for Wireless Cellular Networks," in Proc. IEEE Int. Conf. on Comm. '2002 (ICC'02), Vol. 1, pp. 445-449, New York City, April/May 2002.

[Yu00] S.-Z. Yu, B.L. Mark, and H. Kobayashi, "Mobility Tracking and Traffic Characterization for Efficient Wireless Internet Access," in Multiaccess, Mobility and Teletraffic for Wireless Communications, Vol. 5, Eds. G. Stuber and B. Jabbari, pp. 279-290, Kluwer Academic Publishers, Boston, 2000.

[Kob00] H. Kobayashi, S.-Z. Yu, and B.L. Mark, "An Integrated Mobility and Traffic Model for Resource Allocation in Wireless Networks," in Proc. 3rd ACM Int. Workshop on Wireless Mobile Multimedia, Boston, pp. 39-47, August 2000.

Dynamic Spectrum Sharing

References:

[LMM06] A.E. Leu, M. McHenry, and B.L. Mark, "Modeling and Analysis of Listen-Before-Talk Spectrum Access Schemes," Int. Journal of Network Management, vol. 16, pp. 131-147, 2006.

Last updated on July 11, 2006.