Dynamic channel allocation in mobile cellulat networks

Abstract

DDCA (Distributed Dynamic Channel Allocation) is a fundamental problem in mobile cellular networks and other networks with similar structure. Geographical area is divided into a hexagonal cells. Bandwidth is common for all cells and is divided into channels. Every phone call uses one channel. Cells have different usage of channels – every cell could need different quantity of channels. Allocation algorithm should allocate channels (resources) to cells, to get the most efficient usage of available bandwidth. The idea of proposed algorithm is based on mutual exclusion solution, extended to multiple channel case. The proposed improvements of GRME algorithm are: deadlock avoiding mechanism, and broken cells serving.
Author: Grzegorz CHMAJ

1. INTRODUCTION

Geographical structure of mobile cellular networks (or other wireless networks) is made with hexagonal cells[1]. Each cell has its own base-transceiver station (BTS) located in the centre of cell, which is servicing mobile telephones. BTS stations are connected to BSC (Base Station Controller), BSCs are connected each other using wired network (usually, fiber cables are used). Each mobile network has an assigned bandwidth. Each BTS can manage this resource. Available bandwidth is divided into channels. Each channel is able to support one communication session at one time. Given channel can be used simultaneously in many cells, but there cannot be interference (simultaneous usage will be successful when distance between cells is greater than minimum reuse distance). When a cell receives a call, it attempts to serve the call by assigning a channel to a call. If no channel is available, the call is blocked. If user with a phone is moving to the other cell and there is no available channels, the call is dropped.

The problem of channel allocation is to allocate channels to various cells, with the most efficient usage of available bandwidth. The usage traffic can be different for each cell. The key idea is to move channels between cells, allocating more channels to cell with heavier traffic. The simplest method is a static allocation – the traffic for each cell is known and the set of channels is permanently assigned for each cell. This is not effective, when conditions of use are changing. When traffic does not correspond to the initial traffic patterns, there could occur a situation, where there won’t be enough channels in cell A, but there will be many unused channels in an adjacent cell B.

Other possibility to solve the problem is a centralized allocation [3] – cellular network has one central management system, which distributes channels to cells. This strategy can be quite effective[3], but that kind of structures have high centralization overhead and are sensible for failure.

More effective way is dynamic channel allocation. This problem can be solved as a special case of mutual exclusion problem [2]. Algorithms proposed here are trying to solve dynamic channel allocation problem and also try to avoid the deadlocks. The key of DDCA algorithms is efficiency of channel allocation and its speed. Described algorithm handles dealing with multiple channels, deadlocks and channel selection strategies. Also, methods of avoiding deadlocks and broken cells serving are proposed here by author.

This paper is organized as follows: section 2 defines nomenclature and describes problem, section 3 presents algorithm, in section 4 the proposed improvements are described.