Tak-Shing Peter Yum

Comparisons of channel-assignment strategies in cellular mobile telephone systems

Two novel channel-assignment strategies are proposed: the locally optimized dynamic assignment (LODA) strategy and the borrowing with directional channel-locking (BDCL) strategy. Their performance is compared with the fixed-assignment (FA) strategy (currently used on certain systems) and the borrowing with channel ordering (BCO) strategy (the strategy that has given the lowest blocking probability in previous research). Computer simulations on a 49-cell network for both uniform and nonuniform traffic showed that the average call-blocking probability of the BDCL strategy is always the lowest. The LODA performance is comparable with that of BCO under nonuniform traffic conditions but is inferior under uniform traffic conditions. >

Analysis of Cognitive Radio Spectrum Access with Optimal Channel Reservation

A Markov chain analysis for spectrum access in licensed bands for cognitive radios is presented and forced termination probability, blocking probability and traffic throughput are derived. In addition, a channel reservation scheme for cognitive radio spectrum handoff is proposed. This scheme allows the tradeoff between forced termination and blocking according to QoS requirements. Numerical results show that the proposed scheme can greatly reduce forced termination probability at a slight increase in blocking probability

Analysis of least congested path routing in WDM lightwave networks

Analyzes an adaptive routing rule in a WDM lightwave network. Each switching node in the network may have a number of wavelength converters which can be used to resolve wavelength conflicts in multi-hop paths. The authors found that without any wavelength converters, the wavelength conflict possesses an inherent blocking to alternate route traffic and that the use of wavelength converter to resolve wavelength conflicts does not give any significant reduction of blocking probability.<<ETX>>

Optimal routing and data aggregation for maximizing lifetime of wireless sensor networks

An optimal routing and data aggregation scheme for wireless sensor networks is proposed in this paper. The objective is to maximize the network lifetime by jointly optimizing data aggregation and routing. We adopt a model to integrate data aggregation with the underlying routing scheme and present a smoothing approximation function for the optimization problem. The necessary and sufficient conditions for achieving the optimality are derived and a distributed gradient algorithm is designed accordingly. We show that the proposed scheme can significantly reduce the data traffic and improve the network lifetime. The distributed algorithm can converge to the optimal value efficiently under all network configurations.

The nonuniform compact pattern allocation algorithm cellular mobile systems

An algorithm for allocating nominal channels according to traffic distribution is designed. The algorithm attempts to minimize the average blocking probability as nominal channels are allocated one at a time. Simulation results show that the systems traffic-carrying capacity can be increased by about 10% by the use of this algorithm, and that the gain is additional to the improvement obtained from the channel-borrowing strategies. If the effect of shadow blocking is considered in the assignment of channels, only a very small increase in the traffic capacity is observed. >

Delay distributions of slotted ALOHA and CSMA

We derive the closed-form delay distributions of slotted ALOHA and nonpersistent carrier sense multiple access (CSMA) protocols under steady state. Three retransmission policies are analyzed. We find that under a binary exponential backoff retransmission policy, finite average delay and finite delay variance can be guaranteed for G<2S and G<4S/3, respectively, where G is the channel traffic and S is the channel throughput. As an example, in slotted ALOHA, S<(ln2)/2 and S<3(ln4-ln3)/4 are the operating ranges for finite first and second delay moments. In addition, the blocking probability and delay performance as a function of r/sub max/ (maximum number of retransmissions allowed) is also derived.

Blocking and handoff performance analysis of directed retry in cellular mobile systems

A new analytical model for finding the call blocking probability of a cellular mobile system with directed retry is developed. It can give very accurate results for systems with both uniform and nonuniform traffic distributions. With that, we are able to formulate a second analytical model for obtaining the probability of additional handoffs due to directed retry. Numerical results show that the probability of additional handoff due to directed retry is more sensitive to the percentage of cell overlap than to the mean path length travelled by a mobile unit. In our example of a cellular system with a typical 30% cell overlap the probability of additional handoff is about 0.02. The use of directed retry, therefore, is expected to cause only a minimum amount of additional load in handoff processing and has only a minimal effect on the probability of handoff failure. >

Hausdorff Clustering and Minimum Energy Routing for Wireless Sensor Networks

The authors present a new method for data gathering that maximizes lifetime for wireless sensor networks. It involves three parts. First, nodes organize themselves into several static clusters by the Hausdorff clustering algorithm based on node locations, communication efficiency, and network connectivity. Second, clusters are formed only once, and the role of the cluster head is optimally scheduled among the cluster members. We formulate the maximum lifetime cluster-head scheduling as an integer-programming problem and propose a greedy algorithm for its solution. Third, after cluster heads are selected, they form a backbone network to periodically collect, aggregate, and forward data to the base station using minimum energy (cost) routing. This method can significantly lengthen the network lifetime when compared with other known methods.

Design algorithms for multihop packet radio networks with multiple directional antennas stations

A protocol called the simple tone sense (STS) protocol is designed for multihop packet radio networks (PRNs) with multiple directional antennas stations. The protocol can minimize transmission interference by using a group of tones to identify the active neighbors. A variation of the STS protocol called the variable power tone sense (VPTS) protocol is also designed to further reduce interference. Algorithms for assigning tones and for determining the orientation and broadcasting angles of the directional antennas are designed. Design examples are given. Simulation result shows that the STS protocol gives better throughput-delay performance than the busy-tone multiple access protocol, especially when the traffic is heavy. The VPTS protocol gives still better throughput-delay performance than the STS protocol. >

Hot-spot traffic relief in cellular systems

By analyzing mathematical models, it is shown that combining channel borrowing with a coordinated sectoring or overlying scheme provides effective ways to handle hot-spots in the system. Blocking probabilities with these arrangements are derived, and the dynamic sharing with bias (DSB) rule is suggested for increasing the trunking efficiency. A simple handoff model is formulated and analyzed for comparing the probabilities of additional handoffs due to sectoring and overlaying of cells. With the nominal allocation of 60 channels per cell and a donor cell having a load of 30 Erlangs, numerical results show that at a blocking requirement of 1%, the traffic load in the hot-spot cell can be increased from 47 to 63 Erlangs with the use of the channel borrowing with the cell sectoring scheme: while with the use of the DSB rule, the load can be increased further to 71 Erlangs. A slightly higher load can be carried in the hot-spot cell with the use of cell overlaying arrangement. >