Ilan Kessler

Mobile users: to update or not to update?

Tracking strategies for mobile users in wireless networks are studied. In order to save the cost of using the wireless links mobile users should not update their location whenever they cross boundaries of adjacent cells. This paper focuses on three natural strategies in which the mobile users make the decisions when and where to update: the time-based strategy, the number of movements-based strategy, and the distance-based strategy. We consider both memoryless movement patterns and movements with Markovian memory along a topology of cells arranged as a ring. We analyze the performance of each one of the three strategies under such movements, and show the performance differences between the strategies.

Tracking mobile users in wireless communications networks

Tracking strategies for mobile wireless networks are studied, assuming a cellular architecture where base stations interconnected by a wired network communicate with mobile units via wireless links. The cost of utilizing the wireless links for the actual tracking of mobile users is investigated. A tracking strategy in which a subset of all base stations is selected and designated as reporting centers is proposed. Mobile users transmit update messages only upon entering cells of reporting centers, while every search for a mobile user is restricted to the vicinity of the reporting center to which the user last reported. It is shown that for an arbitrary topology of the cellular network (represented by the interference graph), finding an optimal set of reporting centers is an NP-complete problem. Optimal and near-optimal solutions for important special cases of the interference graph are given.<<ETX>>

Topology-based tracking strategies for personal communication networks

This paper explores tracking strategies for mobile users in personal communication networks which are based on thetopology of the cells. We introduce the notion oftopology-based strategies in a very general form. In particular, the known paging areas, overlapping paging areas, reporting centers, and distance-based strategies are covered by this notion. We then compare two topology-based strategies with the time-based strategy on the line and mesh cell topology.

Splitting algorithms in noisy channels with memory

Multi-access networks are considered in which the shared channel is noisy. The authors assume a slotted-time collision-type channel, Poisson infinite-user model, and binary feedback. Due to the noise in the shared channel, the received signal may be detected as a collision even though no message or a single message is transmitted. This kind of imperfect feedback is referred to as error. A common assumption in all previous studies of multi-access algorithms in channels with errors is that the channel is memoryless. The authors consider the problem of splitting algorithms when the channel has memory. They introduce a two-state, first-order Markovian model for the channel and analyze the operation of the tree collision-resolution algorithm in this channel. They obtain a stability result, i.e., the necessary conditions on the channel parameters for stability of the algorithm. Assuming that the stability conditions hold, they calculate the throughput of the algorithm. Assuming that the stability conditions hold, they calculate the throughput of the algorithm. Extensions to more general channel moders are discussed. >

On the cost of fairness in ring networks

The impact of fairness on the throughput of ring networks with spatial reuse is investigated. A model for a slotted ring with spatial reuse that employs a simple fairness mechanism is presented. An exact expression for the expected time taken to evacuate this ring when each node initially contains one packet is derived. The expected evacuation time is used to obtain an exact expression for the throughput of the ring. It is shown that as the number of nodes on the ring increases, the penalty for fairness in terms of throughput becomes negligible. >

Analysis of a Statistical Multiplexer with Generalized Periodic Sources

We provide solution techniques for the analysis of multiplexers with periodic arrival streams, which accurately account for the effects of active and idle periods and of gradual arrival. In the models considered in this paper, it is assumed that each source alternates (periodically) between active and idle periods of fixed durations. Incoming packets are transmitted on the network link and excess information is stored in the multiplexing buffer when the aggregate input rate exceeds the capacity of the link. We are interested in the probability distribution of the buffer content for a given network link speed as a function of the number of sources and their characteristics, i.e., rate and duration of idle and active periods. We derive this distribution from two models: discrete time and continuous time systems. Discrete time systems operate in a slotted fashion, with a slot defining the base unit for data generation and transmission. In particular, in each slot the link is capable of transmitting one data unit and conversely an active source generates one data unit in that time. The continuous time model of the paper falls in the category of fluid models. Compared to previous works we allow a more general model for the periodic packet arrival process of each source. In discrete time, this means that the active period of a source can now extend over several consecutive slots instead of a single slot as in previous models. In continuous time, packet arrivals are not required to be instantaneous, but rather the data generation process can now take place over the entire duration of the active period. In both cases, these generalizations allow us to account for the progressive arrival of source data as a function of both the source speed and the amount of data it generates in an active period.

Tracking strategies in wireless networks

Summary form only given. Tracking strategies for mobile users in wireless networks are studied. In order to save the cost of using the wireless links mobile users should not update their location whenever they cross boundaries of adjacent cells. This paper focuses on three natural strategies in which the mobile users make the decisions when and where to update: the time-based strategy, the number of movements-based strategy, and the distance-based strategy. We consider both memoryless movement patterns and movements with Markovian memory along a topology of cells arranged as a ring. We analyze the performance of each one of the three strategies under such movements, and show the performance differences between the strategies.Tracking strategies for mobile users in wireless networks are studied. In order to save the cost of using the wireless links mobile users should not update their location whenever they cross boundaries of adjacent cells. This paper focuses on three natural strategies in which the mobile users make the decisions when and where to update: the time-based strategy, the number of movements-based strategy, and the distance-based strategy. We consider both memoryless movement patterns and movements with Markovian memory along a topology of cells arranged as a ring. We analyze the performance of each one of the three strategies under such movements, and show the performance differences between the strategies.<<ETX>>

Mixing collision resolution algorithms exploiting information of successful messages

Algorithms for accessing a slotted-time collision-type broadcast are considered under a Poisson infinite-user model, where each user observes the channel and determines for each slot whether idle or success or collision has occurred. The highest throughput previously achieved for this model is 0.4878. A new scheme is introduced which does not exceed the limitations of the system model, yet achieves a throughput of 0.4892. Extra information is added to the message that can be used only when the message is received successfully. One form of extra information is described, and a new algorithm that exploits it is proposed. >

Growing binary trees in a random environment

A class of binary trees that grow in a random environment, where the state of the environment can change at every vertex of the trees, is studied. The trees considered are single-type and two-type binary trees that grow in a two-state Markovian environment. For each kind of tree, the conditions on the environment process for extinction of the tree are determined, and the problem of calculating the expected number of vertices of the tree is addressed. Different ways of growing the trees are compared. >