Browse Prior Art Database

STATIC CHANNEL ALLOCATION ALGORITHM

IP.com Disclosure Number: IPCOM000008298D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2002-Jun-04
Document File: 3 page(s) / 208K

Publishing Venue

Motorola

Related People

Victor H. Cutler: AUTHOR [+3]

Abstract

All mobile telephony services require that a channel be established between the mobile subscriber and a system base station. It is necessary to reuse these channels as often as possible to maximize the number of users that the system can serve but the channels must be spatially separated from like channels to avoid interference. In terres- trial mobile telephony, such as standard cellular phone service, this channel assignment process is well defined because the base stations are at fixed locations. The advent of satellite based mobile telephony adds a new dimension to this problem. The problem of maintaining adequate channel sepa- ration becomes very difficult in systems that employ polar or near polar orbits to provide global coverage. The use of polar orbits requires that at some point the globe is being covered by adjacent satellites that are traveling in opposite directions, this area is normally referred to as the "seam." In light of this, and other constraints, this paper discusses a simple algorithm to allocate channels to subscribers in a satellite based system.

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Technical Developments

STATIC CHANNEL ALLOCATION ALGORITHM

by Vktor H. Cutler, Yih 0. Jan and Arthur E. Arrington, Jr.

  All mobile telephony services require that a channel be established between the mobile subscriber and a system base station. It is necessary to reuse these channels as often as possible to maximize the number of users that the system can serve but the channels must be spatially separated from like channels to avoid interference. In terres- trial mobile telephony, such as standard cellular phone service, this channel assignment process is well defined because the base stations are at fixed locations. The advent of satellite based mobile telephony adds a new dimension to this problem. The problem of maintaining adequate channel sepa- ration becomes very difficult in systems that employ polar or near polar orbits to provide global coverage. The use of polar orbits requires that at some point the globe is being covered by adjacent satellites that are traveling in opposite directions, this area is normally referred to as the "seam." In light of this, and other constraints, this paper discusses a simple algorithm to allocate channels to subscribers in a satellite based system.

  The IRIDIUM system employs both Frequency Division Multiplexing (FDMA) and Time Division Multiplexing (TDMA). This means that a channel has a specific frequency as well as a specific time slot. This additional "degree of freedom" allows more channels to be placed in the allocated spectrum. Both FDMA and TDMA constraints are discussed in the channel allocation algorithum described in this paper.

  As discussed above, the main goal of a channel allocation process is to allocate as many reuse units (a grouping of one or more channels) as possible while, at the same time, separating reuse units with the same frequency, so that the system interference performance will meet requirements. Furthermore, it is necessary to allocate reuse units so that the effect of Doppler frequency shift, due to space vehicle movement, and the effect of time slide/time

shift, due to propagation path delays among neighboring space vehicles, will be reduced to a minimum. These requirements formed the basis for the static table design that will be discussed in the following sections.

II.1 Maximum Distance Separation Among Reuse Units With The Same Subbands

  It is a well-known design principle in terrestrial cellular telecommunication networks that if the antenna beams coverage area can be modeled as hexagons, then the same frequency channels (reuse units) are located by applying the formula:

N=i'+jl+i*j

where

N: the number of discrete channel sets available in the spectrum being assigned;
i: a shift parameter for a first direction
j: a shift parameter for a second direction; and

i>=j

  Using this formula, the locations of the same frequency subbands are determined by moving i beams in a direction away from the first location, then rotating clockwise (or counterclockwise) 60" and m...