Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2000-02-10
2003-03-04
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S067150, C455S436000
Reexamination Certificate
active
06529738
ABSTRACT:
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for monitoring radio signal strengths for a plurality of channels in a wireless communication system. In particular, but not exclusively, the present invention relates to such monitoring in a DECT-compliant communications system.
DECT is an abbreviation for Digital Enhanced Cordless Telecommunications to which the European Telecommunication Standard ETS 300 175 relates. Whilst the present invention has particular relevance to DECT-compliant communication systems, and is described hereinafter in relation to such systems, the skilled reader will recognize, however, that the method and apparatus described herein are more generally applicable and compliance with DECT standards should not be assumed unless explicitly stated.
A typical DECT compliant communications system includes at least one Portable Part (PP) which communicates over a wireless link with a radio fixed part (RFP) of a DECT Fixed Part (FP). The fixed part will be connected to other fixed equipment such as a PABX or a PSTN. The FP often includes more than one RFP, with each RFP serving to provide radio coverage of a particular area. The use of multiple RFPs allows large areas of radio coverage and a PP may move from one area covered by one RFP to an area served by another RFP with the same communication facilities being available. DECT PP's commonly take the form of mobile handsets and depending on the implementation of the system, a large number of portable parts may be supported.
Communication between a fixed part and a portable part is provided by so-called ‘bearers’ which are established on one or more DECT physical channels (channel). Each channel is created by transmitting in one particular slot on one particular radio frequency (RF) channel in successive time division multiple access (TDMA) frames.
According to the DECT standards, when a portable part is activated it is the responsibility of the PP to perform an operation to detect the presence of any nearby RFP's that are in range. This is made possible in a DECT-compliant system because each RFP broadcasts continuously on at least one bearer. Every bearer of a RFP broadcast carries Q-channel information (system information) and N-channel information (identity information). This information is used by the PP to determine if the RFP is one it has access rights to. If the RFP is not involved in supporting a traffic connection with a PP then the N-channel and Q-channel information is broadcast on a so called dummy bearer. If the RFP is involved in supporting one or more traffic connection with one or more PP, the Q-channel and N-channel information is present on each traffic bearer. A RFP supporting at least one traffic connection may drop the dummy bearer, although the broadcast of the N & Q-channel information on the dummy bearer must be restored should all traffic connections with that RFP cease . It is stated for clarity that the N-channel and the Q-channel are logical channels, not DECT physical channels.
Another task of the PP is to identify the RFP transmissions that are received at the PP with the highest detected radio signal strength. The RFP producing these transmissions is also identified and is designated as the strongest RFP. The strongest RFP will normally be the RFP that is closest to the PP and wherever possible communications between the PP and FP will be via the strongest RFP. Useful communication between the PP and the FP may only take place via the chosen RFP if the portable part has access rights to the FP associated RFP.
One procedure for selecting the strongest RFP is for the PP to monitor DECT system channels and build up a list of the channels that have the highest detected radio strength. The channels are included in the list in order of detected radio signal strength, with the channel having the highest detected radio signal strength appearing first.
Once the list has been produced the PP attempts to set up a synchronisation bearer on the channel listed as having the highest radio signal strength. This bearer set up operation is necessary to determine if the detected radio signal strength results from transmissions of a RFP of interest; that is an RFP of a required FP for which access rights will be granted to the PP. Indeed this step is also necessary because the source of the detected radio signals may originate from transmissions of an incompatible system or merely be due to noise. If it can be established from the N-channel and Q-channel information that the transmissions are associated with the required FP, further procedures are conducted allowing the PP to synchronise and lock with the FP and be in a state ready to set up and release traffic bearers in the interest of exchanging traffic (for example voice calls).
If the transmissions are not associated with the required FP the synchronisation bearer is released (if the set up attempt was successful) and the PP attempts to set up a synchronisation bearer on the channel listed as having the next highest detected radio signal strength. Again the PP carries out the steps necessary to determine if this channel carries transmissions from the required FP. This process is repeated until the PP finds a transmission that allows it to synchronise and lock with the required FP. This procedure, however, is not ideal as limits on list size may result in the list not including any entries that are associated with the required FP, as will be described in more detail in relation to
FIG. 1
below.
An alternative procedure for selecting the strongest RFP is where the RFP attempts to set up a synchronisation bearer on each DECT channel in turn irrespective of the detected radio signal strength on the channel. This is repeated for each channel until the PP detects transmissions originating from an RFP of an FP it has access rights to. Once such transmissions have been found, the PP must continue searching each DECT channel until it locates a channel carrying transmissions of the same FP but with the highest detected radio signal strength. Such transmissions will generally originate from the closest RFP of the FP of interest and the PP may then conduct further procedures to synchronise and lock with the RFP and be in a state ready to set up and release bearers in the interest of exchanging traffic (for example voice calls).
There are also disadvantages to employing this alternative procedure, including the amount of time required for the PP to reach the state where it is ready to set up and receive traffic bearers, because an attempt to set up the synchronisation bearer would need to be made on every possible DECT channel to guarantee that the required FP and strongest RFP have been identified.
The portable part is also required to keep an ordered list of the DECT channels that have the least activity in terms of the radio signal strength. These so called quietest channels are the ones that will be chosen for supporting traffic bearers when the PP sets up a connection with the FP.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for maintaining a record of radio signal strength for a plurality of channels in a wireless communication system, which may be used to facilitate the reliable identification of communication system components without the use of large amounts of memory.
In accordance with one aspect of the present invention there is provided apparatus for maintaining a record of radio signal strength for a plurality of channels in a wireless communication system, the apparatus having:
measuring means for detecting the radio signal strength on each channel; and
storage means for storing information relating to the detected signal strengths,
wherein the information is stored in the storage means in the form of a value for each channel, each value being representative of the respective detected signal strength on a channel, and the storage means includes an array, with the values being stored in positions in the array such that
Connolly Bronagh E.
Forde Brian J.
Halajian Dicran
Koninklijke Philips Electronics , N.V.
Nguyen Thuan T.
LandOfFree
Wireless communication channel management does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wireless communication channel management, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wireless communication channel management will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3038119