Kwan L. Yeung

Channel management in microcell/macrocell cellular radio systems

In this paper, we study spectrum management in a two-tier microcell/macrocell cellular system. Two issues are studied: micro-macro cell selection and frequency spectrum partitioning between microcells and macrocells. To keep the handoff rate in a two-tier cellular system at an acceptable level, low mobility users (with speed /spl upsi/ V/sub 0/) should undergo handoffs at macrocell boundaries. The mobile determines user mobility from microcell sojourn times and uses it for channel assignment at call origination and handoff. The probability of erroneous assignment of a mobile to a microcell or macrocell is shown to be significantly lower than previous approaches. We investigate the optimal velocity threshold, V/sub 0/, and propose that it may be dynamically adjusted according to traffic load. Finally, we propose a systematic way for finding an optimal partition of frequency spectrum between microcells and macrocells. This partitioning is based on the traffic load and velocity distribution of mobiles in the system.

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. >

Compact pattern based dynamic channel assignment for cellular mobile systems

A new compact pattern based dynamic channel assignment strategy called CP-based DCA is proposed. The strategy aims at dynamically keeping the cochannel cells of any channel to a compact pattern. A compact pattern of a channel is defined as the pattern with minimum average distance between cochannel cells. CP-based DCA consists of two phases: channel allocation and channel packing. Channel allocation is used to assign an optimal idle channel to a new call. Channel packing is responsible for the restoration of the compact patterns and is performed only when a compact channel is released. Simulation results indicate that the CP-based DCA always performs better than the borrowing with directional channel locking (BDCL) strategy. The latter being the strategy that gives the lowest blocking probability among the class of known strategies that do not require system-wide information. In the designed example, CP-based DCA is shown to have 5% more traffic-carrying capacity than that of the BDCL in case of uniform traffic and 9% more traffic-carrying capacity in case of non-uniform traffic, both at a blocking rate of 0.02. Besides, the number of channels reassigned per released call in CP-based DCA is at most one and is therefore another advantage over BDCL. >

Cell group decoupling analysis of a dynamic channel assignment strategy in linear microcellular radio systems

We develop a simple but very accurate analytical model for a channel borrowing based dynamic channel assignment strategy in linear microcellular systems. Our approach is to decouple a particular cell together with its neighbors, i.e., those cells under its interference range, from the rest of the system for finding the blocking probability of that cell. We call this the cell group decoupling analysis. This analysis is applicable to both homogeneous and heterogeneous traffic distributions. We show that the effect of this decoupling causes the blocking probability so obtained to be an upper bound. The bound is found to be very tight when compared with simulation results. Besides, this analysis gives accurate results to boundary cells as well as inner cells, and is therefore quite different from the other approaches which neglect boundary effects. >

The optimization of nominal channel allocation in cellular mobile systems

Channel management in cellular systems involves the initial allocation of a set of nominal channels to each cell and the assignment of channels to each incoming call. The design of heuristic algorithms for the allocation of nominal channels is stressed. The concept of compact pattern for cellular systems with irregular cell sizes is generalized. The K-optimal variations and backtracking strategies are studied for their effectiveness in homing towards optimality. In a 49-cell network example, it is found that the hybrid allocation with backtracking can increase the systems traffic-carrying capacity by 38% at 2% blocking when compared to the uniform channel allocation.<<ETX>>

Phantom cell analysis of dynamic channel assignment in cellular mobile systems

In this paper, we propose phantom cell analysis for dynamic channel assignment. This is an approximate analysis that can handle realistic planar systems with the three-cell channel-reuse pattern. To find the blocking probability of a particular cell, two phantom cells are used to represent its six neighboring cells. Then, by conditioning on the relative positions of the two phantom cells, the blocking probability of that particular cell can be found. We found that the phantom cell analysis is not only very accurate in predicting the blocking performance, but also very computationally efficient. Besides, it is applicable to any traffic and channel-reuse patterns.

Cell group decoupling analysis of a channel borrowing based dynamic channel assignment strategy in microcellular radio systems

Develops a simple but very accurate analytical model for a channel borrowing based dynamic channel assignment strategy in both one-dimensional (linear) and two-dimensional (planar) microcellular systems. The approach is to decouple a particular cell together with its neighbors, i.e., those cells under its interference range, from the rest of the system for finding the blocking probability of that cell. The authors call this the cell group decoupling analysis. This analysis is applicable to both homogeneous and heterogeneous traffic distributions. In linear microcellular systems, they show that the effect of this decoupling causes the blocking probability so obtained to be an upper bound. The bound is found to be very tight when compared with simulation results. In planar microcellular systems, the analytical model can no longer guarantee an upper bound on the blocking probabilities. But very close agreement with the simulation results is observed. Also, the analysis gives accurate results to boundary cells as well as inner cells, and is therefore quite different from the other approaches which neglect boundary effects.<<ETX>>

A new ATM switch design using wrapped around multiple (WAM) banyan network

A new ATM switch called wrapped around multiple (WAM) banyan network is proposed. A. WAM banyan switch is constructed using 2d/spl times/2d switch elements. It consists of K parallel banyan switch planes and a packet is allowed to switch/overflow from one switch plane to another when packet contention occurs. This degree of freedom is provided by connecting the d logically equivalent output links from a switch element to d logically equivalent switch elements in the next stage, one in each plane. To further enhance the performance of this switch design, packet broadcasting is used together with priority switching. It is found that under full loading, a WAM banyan switch with K=R=d=3 can have a packet loss probability P/sub loss//spl les/10/sup -6/ for a switch with size up to 4096/spl times/4096. Changing the loading from /spl lambda/=1.0 to 0.8 can give about one order of magnitude further improvement in P/sub loss/.

Performance analysis of borrowing with directional carrier locking strategy in cellular radio systems

Borrowing with directional carrier locking (BDCL) strategy is a carrier borrowing based DCA for FDMA/TDMA cellular systems. When a call arrives at a cell and finds all voice channels busy, a carrier which consists of multiple voice channels can be borrowed from its neighboring cells if such borrowing does not violate the cochannel interference constraint. Analytical models for the BDCL strategy are proposed. Those models are the extensions of previous studies in which single voice channel per carrier were considered. Two approaches are used: cell group decoupling analysis and phantom cell analysis. In cell group decoupling analysis, a cell is decoupled together with its neighbors from the rest of the network for finding its blocking probability. Phantom cell analysis is an approximate analysis that can handle realistic planar cellular systems with a three cell channel reuse pattern. To find the blocking probability of a cell, two phantom cells are used to represent its six neighboring cells. For low to medium traffic loads and small number of voice channels per carrier, we show that both analytical models provide accurate prediction of the system blocking probability.

Node placement optimization in ShuffleNets

The node placement problem in ShuffleNets is a combinatorial optimization problem. An efficient node placement algorithm called the gradient algorithm is proposed. A communication cost function between a node pair is defined and the gradient algorithm places the node pairs one by one based on the gradient of the cost function. Then two lower bounds on the traffic weighted mean internodal distance h are proposed. The performance of the gradient algorithm is compared to the lower bounds as well as some algorithms in the literature. Significant reduction of h is obtained with the use of the gradient algorithm, especially for highly skewed traffic distributions. For a ShuffleNet with N=64 nodes, the h found is only 22% above the lower bound for the uniform random traffic distribution, and 14.7% for a highly skewed traffic distribution with skew factor /spl gamma/=100.