1. Field of the Invention
This invention relates to an improved message access arrangement for a radio telecommunications system such as Universal Mobile Telecommunications System (UMTS) and relates especially to the selection of preamble signatures.
2. Description of the Related Art
During the set up of a call from a mobile telephone to the UMTS system, a mobile needs to select a preamble signature from the available signatures; subsequently, while waiting for an acquisition indication, the mobile may reselect a signature. It may occur that the mobile selects a signature associated with a stalled state, or that collisions occur, and call connection is delayed.
In WO98/18280 Ericsson, there is disclosure of a mobile telecommunication system in which each mobile requesting access can transmit one of a number of different preamble bit or signal patterns, referred to as “signatures”, stored in an internal memory location. The mobile selects one of the stored signatures randomly. However, the arrangement does not address the issue of avoiding stalled states or collisions.
It is an object of the invention to improve the efficiency of signature selection by a mobile.
According to the invention a mobile telephone for the universal radio mobile telecommunication system comprises a processor, a transmitter/receiver, and an antenna, characterised in that the processor is arranged, when the mobile is in an active mode to monitor the Acquisition Indication Channel (AICH) of the UMTS; to store for the duration of the active mode the usage by other mobiles of each available preamble signature; and to select when required a signature the recorded usage of which is unlikely to cause collisions.
In the accompanying drawings, the prior art is illustrated in
The invention will be described with reference to
In
When a mobile such as 12 wishes to make a call, it utilises the Random Access Channel (RACH) of the UMTS which is mapped to the Physical Random Access Channel (PRACH). Transmission in this transport channel is based on the well known slotted Aloha approach, that is, a mobile can start a transmission of the PRACH at any one of a number of well defined time offsets, denoted access slots AS and illustrated in
The data part 46 carries Layer 2/Layer 3 messages requesting radio resources or a user packet. The spreading factor of the data part is limited to SFε{256, 128, 64, 32} corresponding to channel bit rates of 16, 32, 64 and 128 Kbps respectively. The control part 48 carries pilot bits 50 and rate information 52, using a spreading factor of 256. The rate information indicates a spreading factor of the channelisation code which is used on the data part.
For RACH transmission, the technique of preamble power ramping is used, and the procedure used by a random request has the following actions:
It is clear that the MS 12 selects a preamble signature in action 3, and often reselects a preamble signature in action 9. Each selection may suffer from collisions or the selection of a preamble signature used by a stalled state.
Referring now to
The processor of the MS stores a set of preamble signatures available to the MS. If a signature is in use by a stalled state it is indicated as not available. Of the available signatures, the store records the usage count of each signature. The signatures are divided into relatively high and relatively low usage counts. The MS randomly selects one of the relatively low usage count signatures which is not indicated as unavailable due to use by a stalled state at step 6 or step 9.
Step 6 corresponds to action 3 above. Before selecting a preamble signature, the MS 12 checks its store and randomly selects from a set of preamble signatures which have a low usage count and are not used by any stalled state. The usage count of each preamble signature is refreshed by triggering, eg when the available preamble signatures change on the broadcast channel. It then performs the rest of action 3 and proceeds to action 4 etc. Simultaneously, in step 7, the MS 12 continues to read the AICH and in step 8 records any further acquisition indicators for other mobiles.
Step 9 corresponds to action 9 above. Before reselecting a preamble signature, the MS 12 checks its store and selects randomly a signature from a set of preamble signatures with the lowest usage count and which are not being used by any stalled state. The reselection step may be repeated. In step 10, the MS 12 sends its message, and in step 11 it is deactivated as the call terminates.
By application of the invention, the knowledge of the usage status for each available preamble signature allows a reduction in the number of unsuccessful preamble detections by the BTS 18, and reduces the unsuccessful decoding of messages by the BTS. Over all, the usage efficiency of the RACH is improved.
Number | Date | Country | Kind |
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9906198 | Mar 1999 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/GB99/04179 | 12/10/1999 | WO | 00 | 9/7/2001 |
Publishing Document | Publishing Date | Country | Kind |
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WO00/56096 | 9/21/2000 | WO | A |
Number | Name | Date | Kind |
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5754541 | Glisic et al. | May 1998 | A |
6381229 | Narvinger et al. | Apr 2002 | B1 |
6483826 | Akerberg | Nov 2002 | B1 |
6519240 | Dillinger et al. | Feb 2003 | B1 |
6621803 | Halton et al. | Sep 2003 | B2 |
6643275 | Gustafsson et al. | Nov 2003 | B1 |
Number | Date | Country |
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0 933 955 | Nov 1998 | EP |
WO 9818280 | Apr 1998 | WO |
WO 9853631 | Nov 1998 | WO |