WO2002019754A1 - Procede utilise dans un systeme de radiocommunication pour retransmettre un message de signalisation de commande au moyen d'un deuxieme programme de modulation lorsqu'une premiere transmission a echoue - Google Patents

Procede utilise dans un systeme de radiocommunication pour retransmettre un message de signalisation de commande au moyen d'un deuxieme programme de modulation lorsqu'une premiere transmission a echoue Download PDF

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Publication number
WO2002019754A1
WO2002019754A1 PCT/SE2001/001755 SE0101755W WO0219754A1 WO 2002019754 A1 WO2002019754 A1 WO 2002019754A1 SE 0101755 W SE0101755 W SE 0101755W WO 0219754 A1 WO0219754 A1 WO 0219754A1
Authority
WO
WIPO (PCT)
Prior art keywords
control channel
modulation scheme
message
communication system
mobile station
Prior art date
Application number
PCT/SE2001/001755
Other languages
English (en)
Inventor
Arne Kristian Berglund
David BLADSJÖ
Stefan Eriksson
Joakim Sorelius
Original Assignee
Telefonaktiebolaget L M Ericsson (Publ)
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 Telefonaktiebolaget L M Ericsson (Publ) filed Critical Telefonaktiebolaget L M Ericsson (Publ)
Priority to AU2001280398A priority Critical patent/AU2001280398A1/en
Publication of WO2002019754A1 publication Critical patent/WO2002019754A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
    • H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
    • H04L1/1809—Selective-repeat protocols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/08—Reselecting an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/02—Terminal devices
    • H04W88/06—Terminal devices adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals

Definitions

  • the present invention relates to a method in a communication system and the communication system in accordance with the preambles of the independent claims.
  • Figure 1 in the present application illustrates the basic configuration of a cellular mobile telecommunication system.
  • a system comprises a number of cells, each cell comprising a base station for radio communication with a number of mobile stations, of which only one is shown in the figure.
  • the mobile station communicates with the hase station of the cell in which it is presently moving. As the mobile moves from cell to cell, communication with the mobile station is handed over from the base station of one cell to the base station of another cell. This is called handover procedure.
  • the old base station informs the mobile station to switch communication to another channel of the new base station. A handover command or message does this.
  • One object of the present invention is to protect the handover command in such a way that the chances of correctly receiving it by the mobile station are significantly increased.
  • a Fast Associated Control Channel is a logical signaling channel for the transmission of control and supervision messages between the base station and the mobile station during an ongoing call.
  • the FACCH by definition replaces or steals the speech or user data frames on the traffic channel whenever system considerations deem it appropriate to do so.
  • the FACCH is a blank and burst channel.
  • GPRS General packet radio service
  • ETSI European Telecommunications Standards Institute
  • TIA Telecommunications Industry Association
  • PLMN public land mobile network
  • IP Internet protocol-base
  • GPRS offers air-interface transfer rates up to 115 kbit/s subject to mobile terminal capabilities and carrier interference. Even higher transfer rates are provided by the use of so called EDGE technology, i.e. Enhanced Data Rates for Global Evolution. EDGE technology can increase end user data rates up to 384 kbit/s, and potentially higher in high quality radio environments. Moreover, GPRS allows several users to share the same air-interface resources and enables operators to charge customers for wireless services based on the amount of transferred data instead of on connection time.
  • the present invention is in particular applicable in GSM /EDGE Radio Access Network (GERAN).
  • GERAN GSM /EDGE Radio Access Network
  • FACCH Fast Associated Control Channel
  • this control channel is designed so that it is transmitted instead of speech frames. Because the speech has very high delay requirements, there is no meaning in transmitting the blanked speech frames at a later time.
  • Different modulation methods for the FACCH for the 8-PSK speech bearer may be used: e.g. 8-PSK modulated FACCH and GMSK modulated FACCH.
  • 8-PSK modulated FACCH blanks a minimum number of speech frames as it can be interleaved in the same way as speech data.
  • 8-PSK modulation is its limited robustness in bad channel conditions.
  • GMSK modulated FACCH is more robust to the propagation channel than 8-PSK modulated FACCH and can be transmitted at a higher power, which is well- known in the art, but results in the blanking of more speech frames due to the different interleaving pattern.
  • US-5,909,469 discloses a link adaptation method and system for communication links using modulation schemes that have different symbol rates.
  • the system supports at least two modulation schemes that do not have the same symbol rate.
  • the system measures the performance of the communication. This measurement may be performed by determining a number of parameters, including received signal strength at the mobile station, bit error rate at the mobile station, the multipath propagation property of the uplink RF channel, for example, time dispersion, or a combination thereof.
  • a higher (less robust) modulation scheme is maintained if the performance of the communication is acceptable, i.e. above some predetermined threshold.
  • the object of the present invention is to achieve a system where an optimal performance of the system is achieved, i.e. to achieve a robust logical control channel so that a minimum of speech frames are blanked.
  • the used control channel is a FACCH.
  • the invention is applicable on any control channel transmitting signaling messages during ongoing calls, e.g. handover information, in a communication system.
  • the network first transmits the FACCH message using the 8-PSK modulation, thus blanking a minimal number of speech frames. If this transmission fails, i.e. if the mobile station does not properly receive the FACCH message (detected by the network, e.g. that no acknowledgement is transmitted to the base station or if no handover is performed), the FACCH is retransmitted using the GMSK modulation. Then more speech frames are blanked, but it can be expected that the channel quality is so low that the speech is close to unintelligible anyway.
  • the system according to the preferred embodiment of the invention combines the minimal speech quality impact that comes from using the 8-PSK modulation, with the robustness of the GMSK modulation.
  • Figure 1 illustrates the basic configuration of a cellular mobile telecommunication system
  • Figure 2 illustrates an exemplary communication system in which the present invention may be implemented.
  • Figures 3a and 3b illustrate interleaving patterns when the FACCH message is transmitted with 8-PSK modulation and GMSK modulation, respectively.
  • FIG. 2 illustrates an exemplary communication system 2 in which the present invention may be implemented.
  • the system 2 depicted in figure 2 conforms to the GSM specifications and supports GPRS and Enhanced GPRS (EGPRS) (e.g. GERAN) technology.
  • the mobile telecommunications system 2 includes a circuit-switched network 4, a packet-switched network 6, and a radio network 8 that is shared by the circuit-switched an packet-switched networks 4 and 6.
  • the circuit-switched network 4 is primarily used for voice applications
  • the packet-switched network 6 is primarily used for data applications.
  • the circuit-switched network 4 can also support data communications, and the packet-switched network 6 can also support voice communications .
  • the circuit- switched network 4 includes a number of mobile services switching center/ visitor location registers (MSC/VLRs) 12. For purposes of simplifying the illustration, however, only on MSC/VLR 12 is shown. Each MSC/VLR 12 serves a particular geographic region and is used for controlling communications in the served region and for routing communications to other MSC/VLRs 12. The VLR portion of the MSC/VLR 12 stores subscriber information relating to mobile stations 10 that are currently located in the served region.
  • the circuit- switched network 4 further includes at least one gateway mobile services switching center
  • GMSC circuit- switched network
  • PSTN public switched telephone network
  • the packet-switched network 6 includes a number of serving GPRS support nodes (SGSN) 18, which are used for routing and controlling packet data communications, and a backbone IP network 20.
  • SGSN serving GPRS support nodes
  • GGSN gateway GPRS support node 22 interconnects the packet-switched network 6 with an external IP network 24 or other external data networks.
  • the radio network 8 includes a plurality of cells. Each cell in the mobile telecommunications system 2 is served by a base station 26 that communicates with mobile stations 10 in the cell via an air interface 28.
  • the radio network 8 comprises a plurality of base stations 26 and a base station controller (BSC) 27, alternatively referred to as a Radio Network Controller (RNC), controlling said plurality of base stations 26.
  • BSC base station controller
  • RNC Radio Network Controller
  • signals are routed from the MSC/VLR 12, to the base station controller 27 via an interface 34, to the base station 26 for the cell in which the target mobile station 10 is currently located, and over the air interface 28 to the mobile station 10.
  • signals are routed from the SGSN 18, to the base station controller 27 via an interface 35, to the base station 26 for the cell in which the target mobile station 10 is currently located, and over the air interface 28 to the mobile station 10.
  • Each mobile station 10 is associated with a home location register (HLR) 30.
  • the HLR 30 stores subscriber data for the mobile station 10 that is used in connection with circuit-switch communications and can be accessed by the MSC/VLRs 12 to retrieve subscriber data relating to circuit- switched services.
  • Each mobile station 10 is also associated with a GPRS register 32.
  • the GPRS register 32 stores subscriber data for the mobile station 10 that is used in connection with packet-switched communications and can be accessed by the
  • SGSNs 18 to retrieve subscriber data relating to packet-switched services.
  • a mobile station When a mobile station is moving around in a network, it eventually leaves the coverage area of one cell and enters another one. If there is no call in progress, the mobile station will tell the network if it has left one location area and in that case update the registration about its location area in the network. If there is a call going on, the network decides when it is time to change cells and to which new cell (to perform a handover) . The network takes the decision mainly based on the measurement reports from the mobile station. The performance of the handover procedure on the air interface will be described, e.g. how messages and timers are involved in the air interface for a handover. After the network has decided that a handover will be performed it sends a
  • Handover Command message on the downlink FACCH contains information on which new cell the mobile shall access and which frequency and time slot to use for the new Traffic Channel (TCH). It also specifies whether a synchronized handover (including type) shall be performed by the mobile station. In the case of frequency hopping, a list of hopping frequencies to be used is also added.
  • the number of bits necessary for the message will today not exceed 184 in GSM, but more bits are needed for a frequency hopping DCS 1800 system.
  • For GSM one message frame is needed while two frames are needed for DCS 1800 if frequency hopping is used. If necessary even more than two frames may be used.
  • the maximum number of frames that a message can contain is limited to 13 for FACCH.
  • a synchronized handover can be made in three different ways although the messages transmitted after the Handover Command are the same. The difference lies in the way the time alignment is calculated from the information in the Handover Command message.
  • the mobile station After reception of a Handover Command message the mobile station suspends the acknowledge mode, tunes to the new channel, transmits four Handover Access bursts and then initiates an establishment of acknowledge mode. After establishment, the mobile station transmits the Handover Complete message to finish the handover.
  • the mobile After reception of a Handover Command and suspension of acknowledge mode, the mobile sends Handover Access bursts in consecutive FACCH time slots.
  • the Handover Access bursts are transmitted until a reception of a Physical Information message from the network, or until a timer expires.
  • the timer is set when the first Handover Access burst is transmitted.
  • the network must correctly receive two of three Handover Access bursts to continue and transmit a Physical Information message.
  • the physical information message contains the calculated time alignment from the reception of the access bursts and is transmitted in an unnumbered information frame, thus the mobile station does not need to acknowledge this message. Therefore the network sets a timer when transmitting the Physical Information message.
  • the network retransmits the Physical Information message frame.
  • the first time the Physical Information message is transmitted it is transmitted in two consecutive frames.
  • a constant set to a default value limits the number of retransmissions.
  • the Handover Complete message is transmitted from the mobile station.
  • the Handover Complete message tells the network that the handover has been successful. After receiving a Handover Complete message the system erases the allocation of the old channel, thus the old channel hereafter is free to be used by another user.
  • the present invention is applicable during the above- described handover procedure whenever the network detects that the mobile station has failed to properly receive the various signaling messages transmitted from the base station. In practice, this may basically be detected in three different ways:
  • the mobile station continues to transmit speech frames on the old channel
  • the mobile station sends the Handover Failure message
  • the present invention is primarily implemented in the radio network 8 that comprises a plurality of base stations 26 and a base station controller (BSC) 27 controlling said plurality of base stations 26.
  • BSC base station controller
  • a communication system transmits a control signaling message, including e.g. handover information, during an ongoing call connection between a mobile station and a base station on a logical control channel using a first control channel modulation scheme.
  • the logical control channel is used during an ongoing call, e.g. when the quality of the radio communication, e.g. data or voice communication, is low. This is determined in accordance with well established techniques and is therefore not further described herein.
  • the method comprises the step of re-transmitting the control channel message using a second control channel modulation scheme, if the control channel message using the first control channel modulation scheme is not received or understood by the mobile station.
  • the re-transmission of the control channel message is triggered by a failed handover, i.e. the control channel message indicates that a handover should be performed but no handover is performed. This may be detected as described above.
  • control channel modulation scheme may thus be changed for re-transmission if no acknowledgement message is transmitted from the mobile station to the base station coni-timing proper receipt of the control channel message.
  • control channel is a Fast Associated Control Channel (FACCH).
  • FACCH Fast Associated Control Channel
  • the first control channel modulation scheme is an 8-PSK modulation and the second control channel modulation scheme is a GMSK modulation.
  • the invention is equally applicable when using any known control channel modulation schemes, such as: GMSK, 4-PSK, 8-PSK, 16 QAM and 64 QAM.
  • the first control channel modulation scheme may involve a lower number of blanked speech frames than the second control channel modulation scheme.
  • 8-PSK modulated control message in the embodiment using 8-PSK and GMSK as the first and second control channel modulation scheme, uses the same interleaving pattern as the 8-PSK modulated voice bearer. Therefore, the control message will fit exactly into the interleaving sequence without having to transmit empty frames as will be explained below.
  • Fig 3a illustrates the interleaving pattern when the FACCH message (F) is transmitted with 8-PSK modulation.
  • F FACCH message
  • TDMA Time Division Multiple Access
  • frame burst contains bits which are interleaved from two speech frames, e.g., the bursts in TDMA frames 1 and 2 contain bits from both speech frames 0 and 1, TDMA frames 3 and 4 contain bits from both speech frames 1 and 2 and so forth.
  • the FACCH frames F can replace speech frames 3 and 4 in TDMA frames 5 - 10 since the same modulation enables that FACCH and speech can share TDMA frames.
  • Fig 3b illustrates the interleaving pattern when the FACCH message (F) is transmitted with GMSK modulation.
  • the modulation changes from 8-PSK to GMSK in TDMA frame 7 and goes back again to 8-PSK in TDMA frame 11.
  • the modulation change can not occur in the middle of a speech frame but must wait until speech frame 2 in this case is transmitted, i.e. after TDMA frame 6.
  • the FACCH is then transmitted during TDMA frames 7 - 10, but three speech frames 3, 4 and 5 are blanked instead of only two speech frames 3 and 4 as in fig 3a.
  • the method comprises the step of re-transmitting the control channel message using a third control channel modulation scheme, if the control channel message using the second control channel modulation scheme is not received or understood by the mobile station. This step is triggered in the same way as when changing from the first to the second modulation scheme.

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

Abstract

La présente invention concerne un procédé utilisé dans un système de communication dans lequel un canal de contrôle logique achemine un message de canal de contrôle, y compris des informations de transfert, entre une station mobile (10) et une station de base (26) faisant partie dudit système, au moyen d'un premier programme de modulation du canal de contrôle. Le procédé comprend une étape de retransmission du message de canal de contrôle au moyen d'un deuxième programme de modulation de canal de contrôle si le message de canal de contrôle envoyé au moyen du premier programme de modulation du canal de contrôle n'est pas reçu ou compris par la station mobile. Une forme de réalisation préférée du canal de contrôle selon l'invention est un canal de signalisation rapide (FACCH).
PCT/SE2001/001755 2000-08-28 2001-08-15 Procede utilise dans un systeme de radiocommunication pour retransmettre un message de signalisation de commande au moyen d'un deuxieme programme de modulation lorsqu'une premiere transmission a echoue WO2002019754A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001280398A AU2001280398A1 (en) 2000-08-28 2001-08-15 A method in a radio communication system for re-transmitting a control signalingmessage using a second modulation scheme when a first transmission failed

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0003042-9 2000-08-28
SE0003042A SE0003042D0 (sv) 2000-08-28 2000-08-28 Communication system

Publications (1)

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WO2002019754A1 true WO2002019754A1 (fr) 2002-03-07

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PCT/SE2001/001755 WO2002019754A1 (fr) 2000-08-28 2001-08-15 Procede utilise dans un systeme de radiocommunication pour retransmettre un message de signalisation de commande au moyen d'un deuxieme programme de modulation lorsqu'une premiere transmission a echoue

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AU (1) AU2001280398A1 (fr)
SE (1) SE0003042D0 (fr)
WO (1) WO2002019754A1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5535215A (en) * 1995-05-01 1996-07-09 Motorola, Inc. Method and apparatus for providing control channels and message channels in a radio communication system
US5757813A (en) * 1995-10-18 1998-05-26 Telefonaktiebolaget Lm Ericsson Method for achieving optimal channel coding in a communication system
WO1999012303A1 (fr) * 1997-08-29 1999-03-11 Telefonaktiebolaget Lm Ericsson (Publ) Procede et systeme pour demande de repetition automatique (arq) par blocs avec codage et/ou modulation a correction aval des erreurs (fec)
US5909469A (en) * 1997-08-29 1999-06-01 Telefonaktoebolaget Lm Ericsson Link adaptation method for links using modulation schemes that have different symbol rates

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5535215A (en) * 1995-05-01 1996-07-09 Motorola, Inc. Method and apparatus for providing control channels and message channels in a radio communication system
US5757813A (en) * 1995-10-18 1998-05-26 Telefonaktiebolaget Lm Ericsson Method for achieving optimal channel coding in a communication system
WO1999012303A1 (fr) * 1997-08-29 1999-03-11 Telefonaktiebolaget Lm Ericsson (Publ) Procede et systeme pour demande de repetition automatique (arq) par blocs avec codage et/ou modulation a correction aval des erreurs (fec)
US5909469A (en) * 1997-08-29 1999-06-01 Telefonaktoebolaget Lm Ericsson Link adaptation method for links using modulation schemes that have different symbol rates

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AU2001280398A1 (en) 2002-03-13
SE0003042D0 (sv) 2000-08-28

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