Kin Mun Lye

A fast handoff scheme for wireless networks

In this paper, we propose a fast and efficient handoff scheme to handle the movements of mobile nodes among small wireless cells at the fringes of the Internet. Our scheme adopts a hierarchical mobility management architecture to restrict the handoff processing overheads within the vicinity of the mobile node, and uses multicast as the packet forwarding mechanism to deliver packets to multiple base stations within the vicinity of the mobile node to achieve fast handoff performance. Our scheme is based on the Internet Protocol (IP) and is compatible with Mobile IP and its route optimization option. We also present simulation results for our simulation using the Network Simulator (ns2). The simulations show that our handoff scheme is fast enough to meet the requirements of an interactive voice communication session. The first packet from the new base station arrives at the mobile node within 10 ms after the mobile node initiates a handoff. Hence our scheme is suitable for roaming mobile nodes which may encounter numerous handoffs while they are in the midst of an interactive voice communication session such as Internet telephony.

Error rates for narrow-band digital FM with discriminator detection in mobile radio systems

Error rates for a narrowband digital FM system with discriminator detection in a land mobile radio channel characterized by fading and Doppler frequency shift are obtained using a new analytical method. The fading rate is assumed to be much slower than the bit rate so that signal distortion through a narrow bandpass filter can be analyzed via a quasistatic approach. An experiment was conducted using a Rayleigh fading simulator, and the error rate measurements are shown to agree well with the calculated results, except at high SNR (signal-to-noise ratio) where an irreducible error rate was observed. >

Performance of CSMA/CD networks connected by bridges

The performance of two bridged carrier-sense multiple access with collision detection (CSMA/CD) local area networks is investigated by using a finite-state slotted model of the networks. From solving the main equations governing the behavior of the networks, the effects of various design parameters on the network performance are studied. It is shown that the proper use of a bridge can lead to substantial improvement in the throughput and delay performance.<<ETX>>

CSMA/CD-based protocol with dynamic segmentation

Abstract A medium access protocol for a shared, multiaccess bus network is proposed. The principles of this access method, called Segnet, are described. A simulation model for studying the performance of this protocol has been developed, and the results of the simulation show that Segnet performs significantly better than CSMA/CD when the offered load to the network is high.

Performance of segnet—a simulation study

Abstract This paper describes the performance evaluation of Segnet, a CSMA/CD-based protocol with dynamic network segmentation. Segnet is shown to be suitable for network environments where the traffic pattern is highly localized into groups of stations clustered together. Some further improvements in performance are also shown to accompany the incorporation of store-and-forward buffers in Segnet stations. This is because degradations in performance caused by the segmenting of the network are minimized by temporary storage of packets which would otherwise have to be abandoned.

Research note: Performance of PRMA in a mobile radio channel

The performance of the packet reservation multiple access (PRMA) protocol in a real mobile radio channel that suffers from propagation impairments including multipath fading, shadowing and distant-dependent path loss, is studied by simulation. Significant performance degradations, measured by the number of simultaneous conversations supportable in a cell subject to a packet dropping probability of 1%, are observed. Additionally, receiver capture is also found to be ineffective in increasing this supportable number of simultaneous conversations. A modified PRMA protocol is then introduced, and shown to be capable of improving performance through minimizing premature loss of reservations and avoiding additional collisions that arise due to the channel errors.

Packet reservation multiple access over erroneous channels

A reservation-ALOHA protocol in microcellular structure, packet reservation multiple access (PRMA) suits well the characteristics of future microcellular telecommunication systems. However, in erroneous channels, the performance of PRMA degrades because terminals can lose their reservations before talkspurts end. This can lead to increased delay and packet dropping in the middle of the talkspurts, which are highly perceptible. A variation of the PRMA protocol, called modified-PRMA (MPRMA), is proposed for improved performance in erroneous channels. Its performance is investigated mathematically and validated by simulations. Performance improvement is observed for both error-free and erroneous channels. MPRMA supports 36 speech terminals with less than 1% packets dropped when packet header error rate is 0.01. In comparison, PRMA supports only 32 terminals under similar conditions.

Performance analysis of an adaptive token bus protocol

The authors study the performance of an adaptive token-passing bus protocol where only active stations participate in the token passing, and therefore make up the logical ring. A station is active over an interval of time if during that interval data are generated at the station to be sent over the network. The size of the logical ring thus varies randomly according to the traffic intensity of the system. Existing analytical results for token-passing systems assume a fixed number of stations, which will take part in the token passing regardless of whether a station is active or not. An approximate analytical model is provided for a token-passing system where the effective size of the ring changes dynamically according to the network traffic.<<ETX>>

Performance of a dynamically segmentable ring network

Abstract The performance of a dynamically segmentable ring network (R-Segnet) based on the CSMA/CD local area network protocol is studied in this paper. Two routing algorithms for the bidirectional rign are considered. The first transmits a packet in either direction with equal probability while the secons always sends a packet via the shortest path to its destination. Throughput and delay performance comparisons are made against CSMA/CD and against a linear version of this segmentable network (Segnet). These comparisons are conducted for both clustered and nonclustered traffic patterns within the network. The results show that in all cases R-Segnet performs significantly better than conventional CSMA/CD. In the random-destination random-routing case, the performance of R-Segnet is almost similar to that of linear Segnet. When shortest-path routing is used, R-Segnet is shown to be clearly superior. The performance gains are also shown to be shared equitably by all stations in R-Segnet.

Analysis of a CSMA/CD-based protocol with dynamic segmentation

Abstract An approximate performance analysis of CSMA/CD-based protocol capable of dynamic network segmentation is presented. This protocol, Segnet, was previuosly studied using simulation and shown to perform better than CSMA/CD. In this paper, analytical results on the throughput and mean packet transfer delay of a slotted, non-persistent Segnet are obtained. These are shown to agree well with the simulation results.