WO1996002118A1 - Cordless telecommunications handover - Google Patents

Cordless telecommunications handover Download PDF

Info

Publication number
WO1996002118A1
WO1996002118A1 PCT/GB1995/001519 GB9501519W WO9602118A1 WO 1996002118 A1 WO1996002118 A1 WO 1996002118A1 GB 9501519 W GB9501519 W GB 9501519W WO 9602118 A1 WO9602118 A1 WO 9602118A1
Authority
WO
WIPO (PCT)
Prior art keywords
base
station
pabx
handset
cordless
Prior art date
Application number
PCT/GB1995/001519
Other languages
French (fr)
Inventor
Peter Frank Rowlatt
Rick Dingle
Original Assignee
Gpt Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Gpt Limited filed Critical Gpt Limited
Priority to AU28001/95A priority Critical patent/AU2800195A/en
Publication of WO1996002118A1 publication Critical patent/WO1996002118A1/en

Links

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/24Reselection being triggered by specific parameters
    • H04W36/26Reselection being triggered by specific parameters by agreed or negotiated communication parameters
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W84/00Network topologies
    • H04W84/02Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/10Small scale networks; Flat hierarchical networks
    • H04W84/16WPBX [Wireless Private Branch Exchange]

Definitions

  • the present invention relates to a cordless telecommunications system in particular
  • cordless telephone apparatus comprising a cordless handset and base-station conforming
  • ETSI European Telecommunications Standards Institute
  • a network of base-stations which communicate, by means of a radio link, with the cordless handset.
  • the base-station usually the one geographically closest, will communicate with the cordless handset.
  • the strength of the radio link with a given base-station will depend upon the location of the cordless handset which being mobile may change during a call. It is therefore desirable during a call to switch, or handover the call between base- stations to ensure the radio link with the handset is of an acceptably high standard. It is an object of the present invention to provide a method for handover between a cordless handset and a burst synchronized base-station conforming to I-ETS 300 131 Rl in which neither a change
  • the present invention provides in a cordless telecommunications system a method of transferring a call carried by a first radio link between a first base-station and a cordless handset, to one carried by a second radio link between a new base-station which is one of a plurality of frame synchronised base-stations and the cordless handset, the base-
  • the PABX upon receipt of the first message initiating monitoring of the quality of radio transmissions from the cordless handset by the base-stations, (i ⁇ ) upon a new base-station detecting a radio link whose quality exceeds a predetermined value sending a second message to the PABX, and (iv) the PABX connecting the call from the handset to the new base-station in parallel with the first base-station, and transferring transmission between the first and second radio links.
  • cordless telecommunications system operates according to I-ETSI 300
  • the transfer of transmission between the first and second radio links includes the first base-station transmitting a PAR_REQ to the cordless handset, in response the cordless handset transmitting a PAR_RES, the first base-station ceasing transmission and the new base-station transmitting after a pre-selected delay.
  • FIG. 2 is a flow chart of the handover method in accordance with the present
  • FIG. 1 shows a schematic representation of a cordless telecommunications system, which comprises a telecommunications network 1 which is typically a Public Switched
  • PSTN Public Switched Telephone Network
  • Integrated Services Digital Network PSTN
  • ISDN may be more common.
  • the telecommunications network 1 is connected to Private
  • Each PABX 2 is connected to the
  • telecommunications network 1 by a network link, which will typically include some or all
  • the cordless telephone apparatus comprises a plurality of base-stations 4 and a cordless handset 6.
  • the cordless handset will typically be a telephone handset for speech communication but can also comprise a facsimile machine or other data communicating device.
  • the handset 6 communicates with the base-station 4 over a radio link 7.
  • the base-stations 4 are arranged to provide overlapping radio zones ensuring that a radio link 7 will always be available regardless of the geographic location of the cordless handset 6. In this way a user of the handset 6 has access to any other cordless handset, or conventional telephone 2, connected to the telecommunications network 1.
  • Figure 1 shows a single handset 6 communicating with a given base- station 4, a plurality of handsets could be simultaneously communicating with a single base-
  • Figure 2 is a flow chart for the handover operation between a first
  • the first base-station which has an established call with the handset continuously monitors the quality of the radio link.
  • the first base-station detects a trend of deteriorating quality in the radio link it requests Handover of the PABX to which it is connected. It does this by sending a first message, or Handover Request, to the PABX
  • the PABX in response to the Handover Request sends a message, referred to as
  • the Listen to Handset also serves to monitor the quality of radio transmissions from the handset.
  • the Listen to Handset also serves to monitor the quality of radio transmissions from the handset.
  • the base-stations in the neighbouring zones are frame synchronised they are able to detect and decode transmissions from the handset on the specified radio channel
  • This new base-station then sends a Handset Found message to the PABX if the quality of the transmission link exceeds a pre ⁇
  • the Handset Found message contains the PID of the handset.
  • the PABX sends a message to the first base-station to continue listening and connects the speech, or data, path to the new base-station in parallel with the first base-
  • the PABX sends a Handover Grant message to the first base-station which
  • first base-station ceases transmitting to the handset and sends a Base-Station Idle message

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

In a cordless telecommunications system a call carried by a first radio link between a first base-station and a cordless handset may be transferred to one carried by a second radio link between a new base-station which is one of a plurality of frame synchronised base-stations and the cordless handset, the base-stations being connected to a Private Automatic Branch Exchange PABX, by carrying out the steps of: (i) the first base-station monitoring the quality of the first radio link, and upon deterioration of the link-sending a first message to the PABX, (ii) the PABX upon receipt of the first message initiating monitoring of the quality of radio transmissions from the cordless handset by the base-stations, (iii) a new base-station detecting a radio link from the handset whose quality exceeds a predetermined value sending a second message to the PABX, and (iv) the PABX connecting the call from the handset to the new base-station in parallel with the first base-station, and then transferring transmission between the first and second radio links.

Description

CORDLESS TELECOMMUNICATIONS HANDOVER
The present invention relates to a cordless telecommunications system in particular
to cordless telephone apparatus comprising a cordless handset and base-station conforming
to the European Telecommunications Standards Institute (ETSI) I-ETS 300 131 Rl. This standard, which is incorporated herein by reference, is for radio equipment and systems and provides a common air interface specification to be used for the interworking between cordless telephone apparatus in the frequency band 864.1 MHz to 868.1 MHz, including public access services.
In a cordless telecommunications system a network of base-stations are provided which communicate, by means of a radio link, with the cordless handset. For a given call the base-station, usually the one geographically closest, will communicate with the cordless handset. The strength of the radio link with a given base-station will depend upon the location of the cordless handset which being mobile may change during a call. It is therefore desirable during a call to switch, or handover the call between base- stations to ensure the radio link with the handset is of an acceptably high standard. It is an object of the present invention to provide a method for handover between a cordless handset and a burst synchronized base-station conforming to I-ETS 300 131 Rl in which neither a change
of radio channel nor burst structure is necessary.
Accordingly the present invention provides in a cordless telecommunications system a method of transferring a call carried by a first radio link between a first base-station and a cordless handset, to one carried by a second radio link between a new base-station which is one of a plurality of frame synchronised base-stations and the cordless handset, the base-
stations being connected to a Private Automatic Branch Exchange PABX, comprising the
steps of;
(i) the first base-station monitoring the quality of the first radio link, and upon
deterioration of the link sending a first message to the PABX,
(ii) the PABX upon receipt of the first message initiating monitoring of the quality of radio transmissions from the cordless handset by the base-stations, (iϋ) upon a new base-station detecting a radio link whose quality exceeds a predetermined value sending a second message to the PABX, and (iv) the PABX connecting the call from the handset to the new base-station in parallel with the first base-station, and transferring transmission between the first and second radio links.
Preferably the cordless telecommunications system operates according to I-ETSI 300
131 Rl and the transfer of transmission between the first and second radio links includes the first base-station transmitting a PAR_REQ to the cordless handset, in response the cordless handset transmitting a PAR_RES, the first base-station ceasing transmission and the new base-station transmitting after a pre-selected delay.
A method of performing the invention will now be described by way of example
only with reference to the accompanying drawings in which :- Figure 1 is a schematic representation of a cordless telecommunications system and
Figure 2 is a flow chart of the handover method in accordance with the present
invention.
Figure 1 shows a schematic representation of a cordless telecommunications system, which comprises a telecommunications network 1 which is typically a Public Switched
Telephone Network (PSTN), although in the future an Integrated Services Digital Network
(ISDN) may be more common. The telecommunications network 1 is connected to Private
Automatic Branch Exchanges (PABX's) 2 which themselves control a plurality of CT2
base-stations 4 (CT2 - Cordless telephones of the second generation conforming to I-ETS
300 131 Rl) of a cordless telephone apparatus. Each PABX 2 is connected to the
telecommunications network 1 by a network link, which will typically include some or all
of a wired link, an optical fibre link or a long distance radio link.
As shown in Figure 1 the cordless telephone apparatus, to which the present invention relates, comprises a plurality of base-stations 4 and a cordless handset 6. The cordless handset will typically be a telephone handset for speech communication but can also comprise a facsimile machine or other data communicating device. The handset 6 communicates with the base-station 4 over a radio link 7. The base-stations 4 are arranged to provide overlapping radio zones ensuring that a radio link 7 will always be available regardless of the geographic location of the cordless handset 6. In this way a user of the handset 6 has access to any other cordless handset, or conventional telephone 2, connected to the telecommunications network 1.
Although Figure 1 shows a single handset 6 communicating with a given base- station 4, a plurality of handsets could be simultaneously communicating with a single base-
station using different radio channels . As the user of the handset moves away from the base- station the strength of the radio link within the zone covered by the base-station will weaken. There will come a point where the radio link would be stronger with the base- station in a neighbouring zone. At this point it is desirable to transfer, or Handover, the radio link to the new base-station serving this zone to maintain transmission quality.
A method of Handover in accordance with the invention will be described with
reference to Figure 2. Figure 2 is a flow chart for the handover operation between a first
base-station and a new base-station in a neighbouring zone.
The first base-station which has an established call with the handset continuously monitors the quality of the radio link. When the first base-station detects a trend of deteriorating quality in the radio link it requests Handover of the PABX to which it is connected. It does this by sending a first message, or Handover Request, to the PABX
which message includes the Portable Identification Code (PID) or serial number of the
handset, the radio channel currently in operation and the multiplex (MUX1.2 or MUX1.4).
All of the terms are defined in I-ETS 300 131 Rl.
The PABX in response to the Handover Request sends a message, referred to as
a Listen to Handset, to base-stations in neighbouring zones initiating the base-stations to
monitor the quality of radio transmissions from the handset. The Listen to Handset also
includes the same information as the Handover Request that in PID, radio channel and
multiplex. Since the base-stations in the neighbouring zones are frame synchronised they are able to detect and decode transmissions from the handset on the specified radio channel
in the appropriate multiplex. If the PID contained in the ID_OK matches the PID in the
Listen to Handset the base-station continues monitoring the quality of transmissions from
the handset for a short period, typically five seconds. This new base-station then sends a Handset Found message to the PABX if the quality of the transmission link exceeds a pre¬
selected threshold. The Handset Found message contains the PID of the handset.
In response the PABX sends a message to the first base-station to continue listening and connects the speech, or data, path to the new base-station in parallel with the first base-
station. The PABX sends a Handover Grant message to the first base-station which
transmits a PAR_REQ to the handset. Upon receiving a PAR_RES from the handset the
first base-station ceases transmitting to the handset and sends a Base-Station Idle message,
contain the PID to the PABX. The new base-station which is still monitoring transmissions
from the handset upon detecting the PAR_RES pauses a pre-selected period,
approximately 5mS, before transmitting data from the speech path to the handset thereby completing the handover sequence to the new base-station.

Claims

CLAΓMS
1. In a cordless telecommunications system a method of transferring a call carried by
a first radio link between a first base-station and a cordless handset, to one carried by a
second radio link between a new base-station which is one of a plurality of frame
synchronised base-stations and the cordless handset, the base-stations being connected to a Private Automatic Branch Exchange PABX, comprising the steps of; (i) the first base-station monitoring the quality of the first radio link, and upon deterioration of the link sending a first message to the PABX, (ii) the PABX upon receipt of the first message initiating monitoring of the quality of radio transmissions from the cordless handset by the base-stations,
(iii) a new base-station detecting a radio link whose quality exceeds a predetermined value sending a second message to the PABX, and
(iv) the PABX connecting the call from the handset to the new base-station in parallel with the first base-station, and transferring transmission between the first and second radio links.
2. A method according to Claim 1 in which the cordless telecommunications system operates according to I-ETSI 300 131 Rl and in which the transfer of transmission between the first and second radio links includes the first base-station transmitting a PAR_REQ to the cordless handset, in response the cordless handset transmitting a
PAR_RES, the first base-station ceasing transmission and the new base-station transmitting
after a pre-selected delay.
PCT/GB1995/001519 1994-07-07 1995-06-28 Cordless telecommunications handover WO1996002118A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU28001/95A AU2800195A (en) 1994-07-07 1995-06-28 Cordless telecommunications handover

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9413731A GB9413731D0 (en) 1994-07-07 1994-07-07 CT2 handover
GB9413731.2 1994-07-07

Publications (1)

Publication Number Publication Date
WO1996002118A1 true WO1996002118A1 (en) 1996-01-25

Family

ID=10757987

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1995/001519 WO1996002118A1 (en) 1994-07-07 1995-06-28 Cordless telecommunications handover

Country Status (4)

Country Link
AU (1) AU2800195A (en)
GB (1) GB9413731D0 (en)
WO (1) WO1996002118A1 (en)
ZA (1) ZA955372B (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6917807B1 (en) 1999-03-10 2005-07-12 Nokia Corporation Cell selection method

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1990009073A1 (en) * 1989-01-27 1990-08-09 British Telecommunications Public Limited Company Telecommunications system
WO1994005109A1 (en) * 1992-08-25 1994-03-03 Motorola, Inc. Method and apparatus for performing a hand-off in a wireless communication system
WO1994019913A1 (en) * 1993-02-26 1994-09-01 At & T Wireless Communications Products Ltd. Improvements relating to handover in a digital cordless telephone system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1990009073A1 (en) * 1989-01-27 1990-08-09 British Telecommunications Public Limited Company Telecommunications system
WO1994005109A1 (en) * 1992-08-25 1994-03-03 Motorola, Inc. Method and apparatus for performing a hand-off in a wireless communication system
WO1994019913A1 (en) * 1993-02-26 1994-09-01 At & T Wireless Communications Products Ltd. Improvements relating to handover in a digital cordless telephone system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6917807B1 (en) 1999-03-10 2005-07-12 Nokia Corporation Cell selection method

Also Published As

Publication number Publication date
GB9413731D0 (en) 1994-08-24
AU2800195A (en) 1996-02-09
ZA955372B (en) 1996-02-13

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