Transmission quality reporting

Details Transmission quality reporting Transmission quality reporting

1999-03-25

2002-11-05

Le, Thanh Cong (Department: 2684)

Telecommunications

Carrier wave repeater or relay system

Portable or mobile repeater

C455S067150, C455S069000, C455S423000, C455S522000

Reexamination Certificate

active

06477355

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to improvements in and relating to reporting transmission quality for use in radio resource management of a radio telecommunications system, for example a satellite mobile telecommunications system, and has particular application to a base station subsystem and also a user terminal for the telecommunications system.
BACKGROUND
Terrestrial mobile telecommunications systems are well known and a number of different systems have developed which operate according to different standards. These public land mobile networks (PLMNs) may operate according to analog or digital standards. In Europe, the Far East, excluding Japan and elsewhere, the Global System Mobile (GSM) network has become popular, whereas in USA, the Advanced Mobile Phone Service (AMPS) and the Digital American Mobile Phone System (DAMPS) are in use, and in Japan, the Personal Handiphone System (PHS) and the Personal Digital Communication (PDC) network are used. More recently, proposals have been made for a Universal Mobile Telecommunications System (UMTS). These networks are all cellular and land based with transmitter/receivers which communicate with mobile user terminals.
Considering for example the GSM system, individual cells of the mobile network are served by a series of geographically spaced, terrestrial base station subsystems (BSS) which each comprise a base transceiver stations (BTS) which are coupled through base station controllers (BSCs) to a mobile switching centre (MSC) which may provide a gateway out of the network to a conventional public switched telephone network (PSTN). The PLMN includes a home location register (HLR) which stores information about the subscribers to the system and their user terminals (UTs). When a UT is switched on, it registers with the HLR. If the user roams to a different GSM network, the user terminal registers with a visitor location register (VLR) of the visited network, which communicates with the HLR of the home network for routing and other purposes. DAMPS, PHS and PDC networks have a generally similar architecture.
The telephone call is routed to the subscriber's UT through the MSC, to the BSC and then to the selected BTS, which provides a full duplex channel to the UT. The channel comprises a downlink channel from the BTS to the UT and an uplink channel from the UT to the BTS. The channels include time division multiple access (TDMA) time slots on frequencies allocated on initiation of the call.
In a GSM system, the telephone call is directed over a dedicated traffic channel or TCH. Each TCH has an associated slow rate control channel or SACCH, which is interleaved with the TCH. These channels are described in more detail on pp 195-201 of “The GSM System for Mobile Communications” by M. Mouly and M-B. Pautet, 1992 Cell & Sys, ISBN: 2-9507190-0-7.
The SACCH communicates control information between the UT and the BSS. In particular, the SACCH is used for power control, so as to control the power of signals transmitted by the BTS to the UT, and to control the power of signals transmitted from the UT to the BTS, in order to conserve battery power in the UT.
On commencement of a call, initial UT power level settings are transmitted in the uplink SACCH to the BTS and the UT. The UT then periodically measures the quality of the received signals on the downlink, for example every 0.5 sec. and the measured values are transmitted back on the SACCH uplink to the BTS and then to the BSC. The BSC includes processing circuitry to update the power settings and appropriate instructions are then communicated from the BSC to the BTS and the UT using the downlink SACCH.
The quality measurements carried out at the UT consist of successive measurements of the bit error rate (BER) in signals received from the BTS through the downlink, the measurement values being an average of the BER over a measurement period e.g. 0.5 sec.
The BSC uses these measurement values and its own measurements of received UT uplink emissions to calculate a desired power transmission level for the BTS and the UT, the desired power level being computed as a function of the average BER. A margin m is added to accommodate fading and shadowing of the transmitted signal. The margin has a fixed value e.g. 2db.
A number of different mobile telecommunication systems have been proposed that use satellite communication links to the mobile user terminals. One network known as the IRIDIUM™ satellite cellular system is described in for example EP-A-0365885 and U.S. Pat. No. 5,394,561 (Motorola), which makes use of a constellation of so-called low earth orbit (LEO) satellites, that have an orbital radius of 780 km. Mobile user terminals such as telephone handsets are configured to establish a link to an overhead orbiting satellite, from which a call can be directed to another satellite in the constellation and then typically to a ground station which is connected to conventional land-based networks.
Alternative schemes which make use of so-called medium earth orbit (MEO) satellite constellations have been proposed with an orbital radius in the range of 10-20,000 km and reference is directed to Walker J. G. “Satellite Patterns for Continuous Multiple Whole Earth Coverage” Royal Aircraft Establishment, pp 119-122 (1977). These orbits are also known as intermediate earth orbits (IEOs). As examples, reference is directed to the ICO™ satellite cellular system described for example in GB-A-2 295 296, and to the ODYSSEY™ satellite cellular system described in EP-A-0 510 789. With both the ICO™ and the ODYSSEY™ systems, the satellite communication link does not permit communication between adjacent satellites and instead, a signal from a mobile user terminal such as a mobile handset is directed firstly to the satellite and then directed to a ground station or satellite access node (SAN), connected to conventional land-based telephone network. This has the advantage that many components of the system are compatible with known digital terrestrial cellular technology such as GSM.
In satellite communications networks, ground stations are located at different sites around the world in order to communicate with the orbiting satellites. In the ICO™ system and others, a visitor location register is associated with each of the satellite ground stations, which maintains a record of the individual user terminals that are making use of the particular ground station.
In a satellite telecommunication system, it would be advantageous to control the power level of the individual UTs and the power of the satellite transmission which conveys signals from the satellite to the UT. This would conserve battery power for the UT and also would conserve power in the satellite, which has a limited power supply from its solar panels and batteries. It has therefore been proposed to include a power control arrangement, which makes use of measured values of a quality metric for signals received at the UT so that the satellite and UT can be commanded to operate at an optimum power level.
SUMMARY OF THE INVENTION
The present invention involves measurement of a quality metric for radio signals received by a user terminal during a given measurement period. An average of the values of the quality metric is produced together with a deviation signal which is a function of deviation between the average and at least one value for the measurement period. This data is transmitted to a remote subsystem which produces a set value of a transmission characteristic for the radio signals transmitted to the user terminal as a function of the average of the quality metric and a margin which is selected as a function of the deviation signal.
Thus, the margin is set adaptively as a function of the deviation rather than being a fixed value as in the prior art. In this way, the margin can be reduced when the deviation is small thereby conserving power.
More particularly, the invention includes a user terminal for a radio telecommunications system, comprising: measuring circuitry operable to provide respective measured values of a quality

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