Browse Prior Art Database

SATELLITE SYSTEM BEAM MANAGEMENT IN CONTINUOUS TIME MODE

IP.com Disclosure Number: IPCOM000008585D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jun-25
Document File: 3 page(s) / 136K

Publishing Venue

Motorola

Related People

Kenneth M. Peterson: AUTHOR [+3]

Abstract

In satellite cellular communication systems, the radio frequency (RF) beams need to be managed to ensure proper balance between system performance, system capacity and system power consumptions. The system performance includes statistical distrib- utions of calls blocked and calls dropped. The signal carrier to noise ratio is also an important factor in the system performance evaluation. The system capacity is the number of calls the system can sup- port under varying environment conditions. Since satellite available power is limited, the system needs to properly arrange the beam activation schedules so that satellite power can be effectively utilized to provide maximum system capacity.

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MO7OROLA Technical Developments

SATELLITE SYSTEM BEAM MANAGEMENT

IN CONTINUOUS TIME MODE

by Kenneth M. Peterson, Yih G. Jan, Victor H. Cutler

I. PROBLEM STATEMENT

  In satellite cellular communication systems, the radio frequency (RF) beams need to be managed to ensure proper balance between system performance, system capacity and system power consumptions. The system performance includes statistical distrib- utions of calls blocked and calls dropped. The signal carrier to noise ratio is also an important factor in the system performance evaluation. The system capacity is the number of calls the system can sup- port under varying environment conditions. Since satellite available power is limited, the system needs to properly arrange the beam activation schedules so that satellite power can be effectively utilized to provide maximum system capacity.

  The beam activation schedules are generally designed in a 'static state' or 'snapshot' fashion, i.e. the beam activation states at one time instant are not correlated with any other time instant. This static or snapshot process will result in the loss of some system capacity since some callers which are ser- viced by the system at one time instant are possibly dropped off in the next few time instants due to short beam life time effects. This condition occurs when beams are activated at a certain time instant but are turned off after only a short on period of time. This means that for existing calls to continue, they must be handed off to neighboring beams from the present serving beams. The handoff procedures are prone to dropping calls.

  The IRIDIUM" System also has what are known as 'seam planes,' i.e., the satellites in one plane are moving in the opposite direction to the satellites in an adjacent plane. If the beam activation schedules along seam planes are not processed properly, when users which are served by one of the seam plane beams are handed off to another neigh- boring seam plane beam at one time instant, they may sometimes be handed off back to the original

seam plane beams after a short period of time. That is users may experience a 'zigzag' or 'ping-pang' handoff phenomena. This situation will result in a high probability of dropped calls in the seam planes. The system capacity will consequently be adversely effected along the seam planes. In addition, system performance will not be evenly distributed among planes of the constellation of satellites.

  Furthermore in the design of beam activation schedules, advantage is usually taken of the periodic nature of the constellation. This permits the beam activation schedules utilized in one time to be applied to another period of time by properly manipulating and indexing the satellite locations in these two different time periods. However this mode of operation will create some discontinuity of b...