WO2007023156A1

WO2007023156A1 - Method for transmitting signals in a radio communications system

Info

Publication number: WO2007023156A1
Application number: PCT/EP2006/065541
Authority: WO
Inventors: Jürgen Hofmann; Eswar Vutukuri
Original assignee: Nokia Siemens Networks Gmbh & Co. Kg
Priority date: 2005-08-24
Filing date: 2006-08-22
Publication date: 2007-03-01

Abstract

According to the invention, a method for transmitting signals in a radio communication system is proposed wherein at least one traffic channel (TCH) and at least one control channel (SACCH) associated with the at least one traffic channel (TCH) are assigned for transmission of signals between a base station (BS) and a mobile station (MS), and wherein the mobile station (MS) reports in at least one frame of the associated control channel (SACCH) measurements made during a measurement period consisting of at least one frame of the associated control channel (SACCH) . The method is characterised in that the mobile station (MS) signals to the base station (BS) an indication of the length of the measurement period used by the mobile station (MS) .

Description

Method for transmitting signals in a radio communications system

The present invention relates to a method for the transmission of signals in a radio communications system, in particular for application in a mobile radio communications system based on the GSM standard.

Current Adaptive Multi Rate (AMR) speech codecs specified for GSM/GERAN mobile radio communications systems as well as for UMTS provide superior performance over previous standard speech codecs like Full Rate Speech (FR) defined in GSM Phase 1 or Enhanced Full Rate Speech (EFR) defined in GSM Phase 2. In particular, the new AMR codecs provide a series of modes which enable better speech quality at higher bit rates as well as adequate speech comprehensibility at lower bit rates. Typically, higher bit rate modes are used in good radio chan- nel conditions, whereas lower bit rate modes are applied in poorer radio channel conditions.

Nevertheless, it has been shown in field trials for GSM/EDGE networks that the performance of lower bit rate AMR codec modes used for Traffic Channel (TCH) exceed that of the associated signalling or control channels, namely that of the so called Fast Associated Control Channel (FACCH) and Slow Associated Control Channel (SACCH) . The SACCH channel is used for transmitting link quality information and neighbour cell measurements in uplink direction (UL) to the base station

(BS), as well as for the transmission of radio link control commands and neighbour cell information in downlink direction (DL) to the mobile station (MS) . Such an exemplary situation is shown in the block diagram of FIG 1, wherein a base station (BS) connected via a base station controller (BSC) to a mobile switching centre (MSC) of the radio communications system is in radio connection in downlink (DL) and uplink (UL) with a mobile station (MS) situated in a cell (C) of the base station.

In addition, link level simulations show a performance gap in the order of 5 dB between the traffic channel and correspond- ing signalling channel. As a consequence, the signalling channel quality may degrade before the corresponding traffic channel is affected, resulting in a user still experiencing good speech quality while the network suddenly releases the call due to not received signalling messages. The so called radio link failure algorithm, which terminates a call due to a decrease in link quality, is executed at the receiver side of each link, i.e. in the base station (BS) as well as in the mobile station (MS) . This algorithm acts on the basis of a determined SACCH frame error rate, as it is specified in the technical specification 3GPP TS 45.008, V6.13.0 (2005-07),

Technical Specification Group GSM/EDGE, Radio Access Network, Radio subsystem link control (Release 6) .

One possible solution to this problem may be to restrict the usage of AMR full rate mode operation to areas with sufficient signalling channel quality. An alternative approach might be to increase the so called Radio Link Timeout in order to avoid call releases, which of course would lead to mobile stations being attached for too long to their serving base station due to failed measurement reports, thereby causing additional interference in the cell. In the framework of the standardisation, it was agreed for the FACCH channel to implement a so called repeated FACCH solution. A similar solution, named serial SACCH repetition was proposed at the 3GPP TSG GERAN Meeting #25 in Montreal, 20-24 June 2005. According to the document Tdoc GP-051544, Agenda Item 7.1.5.15 (accessible via http : //www.3gpp . org/ftp/tsg_geran/TSG_GERAN/GERAN_25_Montreal /Docs/), also SACCH blocks are repeated in uplink as well as in downlink direction.

In general, speech and control frames are transmitted in TDMA frames. A mobile station is required to perform neighbour cell measurements during a given SACCH multiframe period - which is 480ms - and to report the measured values of the re- ceived signal levels from various neighbouring base stations to the serving network in a following uplink SACCH multi- frame. In case the transmission on the uplink SACCH is repeated, measurements by the mobile station in SACCH multi- frames may be reported to the network only every two SACCH multiframes. This of course leads to a disparity between the measurement period - which is 480 ms - and the measurement reporting period - which becomes 960 ms because of the repetition .

It is thus an object of the present invention to provide a method which enables a flexible yet robust detection of signalling channel information compared with traffic channel signals. This object is resolved by the inventive features of independent claims 1 and 6.

According to the invention, a method is provided wherein a mobile station indicates to the base station a change in the measurement period on which a signalled measurement report is based.

One possible implementation of the present invention consists in using a currently unused bit in the Measurement Results field of the Measurement Results Information Element disclosed in chapter 10.5.2.20 of the technical specification 3GPP TS 45.008, V6.13.0 (2005-07). This message on the uplink SACCH may be used by the mobile station to indicate whether the neighbour cell reports sent on the uplink SACCH comprise of measurements made during a normal measurement period or during an extended measurement period.

According to an alternative implementation of the present in- vention, one currently unused bit in the Layer 1 (i.e. physical layer) header of the uplink SACCH may also be used for this purpose.

Alternatively, a new message type may be specifically defined which at least indicates to the network whether measurements contained in the message are made during an extended measurement period or during a normal measurement period.

In any case, with such knowledge, the network is enabled to use appropriate averaging strategies, which in turn improve e.g. the handover performance.

FIG 2 shows examples of switchings between normal SACCH measuring N and reporting periods, and extended measuring E and reporting periods. In principle, the use of the so called serial SACCH repetition is commanded CMD by the base station. Nevertheless, the mobile station may also decide to change between the normal N and extended E measurement period, for example in case it detects a new neighbouring cell. In such a situation, the mobile station would change from the extended measurement period to the normal measurement period so that in a second SACCH multiframe, in which according to the se- rial SACCH repetition approach a repetition of the measurement report would be transmitted, measurements of the newly discovered cell are reported to the base station. This of course reduces significantly the time needed for a handover to such new cell.

Even in situations where measurements are averaged over the extended period of two SACCH multiframes, the mobile station is enabled to switch in the second SACCH multiframe to the reporting of measurements of a newly discovered cell, by sig- nailing the change to the serving base station.

In the following, possible adaptations of the current technical specifications are shown which reflect the features according to the invention. Additions to the given specifica- tions are underlined in the text passages, figures and tables. These amendments are to be read and understood in the context of the given and related specifications.

Changes to technical specification 3GPP TS 44.018 V6.13.0 (2005-07) :

3.4.1.2 Measurement Report and Enhanced Measurement Report When in dedicated mode or group transmit mode, the mobile station regularly sends MEASUREMENT REPORT or ENHANCED MEASUREMENT REPORT or ENHANCED MEASUREMENT REPORT 2 messages to the network. These messages contain measurement results about reception characteristics from the current cell and from neighbour cells. The BA (list) which is the initial ba- sis for the measurements is derived from information received on the BCCH in System Information 2 and optionally 2bis and/or 2ter messages and on the SACCH in System Information 5 and optionally 5bis and/or 5ter messages. MEASUREMENT INFORMATION and SI2quater messages may add information for the GSM Neighbour Cell List and provide 3G Neighbour Cell list. The Mobile Station shall use ENHANCED MEASUREMENT REPORT or ENHANCED MEASUREMENT REPORT 2 messages instead of MEASUREMENT REPORT messages if that is indicated by the pa- rameter REPORT_TYPE and if at least one BSIC is allocated to each BA (list) frequency. For report with the MEASUREMENT REPORT message, reporting is performed on two separate lists: the BA (list) and the 3G Neighbour Cell List (for a multi-RAT MS) . For report with the ENHANCED MEASUREMENT REPORT or the ENHANCED MEASUREMENT REPORT 2 message, reporting is performed on the Neighbour Cell List (defined in sub- clause 3.4.1.2.1.3) .

In addition, the MS with ECSD options implemented shall use fast in band procedure for downlink quality reporting if the use of such procedure has been ordered by the BSC.

When the information is received in more than one message the mobile station shall only combine information relating to the BA (list) from messages received on the same channel and indicating the same value of the BCCH allocation sequence number (BA_IND) without any message indicating a different value of BA IND received in between. After intracell change of channel (i.e. via ASSIGNMENT COMMAND, DTM ASSIGNMENT COMMAND, or HANDOVER COMMAND message) where the frequency band is not changed (GSM and E-GSM are considered to belong to the same frequency band), the MS may use the BA (list) received on SACCH in system information 5 and optionally 5bis and/or 5ter messages in the previous channel configuration during the time it has not yet received a new list in the new channel. In case the BCCH allocation sequence number (BA IND) received in the new channel indicates the same value as the one al- ready being used by the mobile station, the mobile station is not required to re-build the BA (list) in the new channel. If neighbour cell information for the serving cell is not available, the mobile station shall indicate this in the MEASUREMENT REPORT message. These measurement results are ob- tained as specified in 3GPP TS 45.008.

These messages are sent on the slow ACCH, in unacknowledged mode .

If no other message is scheduled on the SACCH at the instant when a layer 2 frame is due to be sent, then the mobile station shall send a MEASUREMENT REPORT message, an ENHANCED MEASUREMENT REPORT or ENHANCED MEASUREMENT REPORT 2 or an EXTENDED MEASUREMENT REPORT message (see sub-clause 3.4.1.3) in that frame. The interval between two successive layer 2 frames containing messages for measurement reporting shall not exceed one layer 2 frame.

3.4.1.2.1 Parameters for Measurements and Reporting Parameters from the Measurement Information, SI2quater or

PSI3quater messages allow an MS to build lists which are used for Measurement reporting, Enhanced Measurement reporting, ENHANCED MEASUREMENT REPORT 2 and for CCN mode settings. A full set/all instances of MEASUREMENT INFORMATION (respec- tively: SI2quater) messages is defined by a number of different instances indicated by the parameter MI_COUNT (respectively SI2quater_COUNT) . Two different instances of MEASUREMENT INFORMATION (respectively: SI2quater) messages are two MEASUREMENT INFORMATION (respectively: SI2quater) messages with different MI_INDEX (respectively: SI2quater INDEX) parameter values.

In the SI2quater message, the parameters with identical names in the GPRS specific structures (i.e. structures with the prefix GPRS) and in the non-GPRS specific structures (i.e. structures without the prefix GPRS) can have different values. For Measurement reporting, Enhanced Measurement report- ing and ENHANCED MEASUREMENT REPORT 2 the MS shall ignore the parameters in the GPRS specific structures unless otherwise specified (e.g. sub-clause 3.4.1.2.1.2 and sub-clause 3.4.1.2.1.4). If the SI2quater message is not broadcast or all instances are not yet received or non-GPRS specific pa- rameters in the SI2quater message are omitted, the MS in idle mode or dedicated mode or group transmit mode shall assume the default values defined in 3GPP TS 45.008. ...

3.4.1.2.1.3 Deriving the Neighbour Cell list from the GSM Neighbour Cell list and the 3G Neighbour Cell list

For report with the ENHANCED MEASUREMENT REPORT or ENHANCED MEASUREMENT REPORT 2 message, the Neighbour Cell list is the concatenation of the GSM Neighbour Cell list and the 3G Neighbour Cell list (if any) .

Table 9.1.54.1: Measurement Information information element details .

9.1.55a ENHANCED MEASUREMENT REPORT 2

This message containing measurement results is sent on the

SACCH by the mobile to the network.

This message may contain reports on GSM and/or 3G Radio Ac- cess Technologies. Measurements are defined in

3GPP TS 45.008.

Message type: ENHANCED MEASUREMENT REPORT 2

Significance: dual

Direction: mobile station to network The ENHANCED MEASUREMENT REPORT 2 message has the same format as ENHANCED MEASUREMENT REPORT described in sub clause 9.1.55. See figure 9.1.55.1. However it is used when the measurement results carried in this message are the ones made at the terminal during an extended measurement period of two SACCH multiframes (see 3GPP TS 45.008).

NOTE: This is necessary for example during the serial SACCH repetition in the UL.

Table 10.4.2: Message types for Radio Resource management messages using the RR short protocol discriminator

10.5.2.20 Measurement Results The purpose of the Measurement Results information element is to provide the results of the measurements made by the mobile station on the serving cell and the neighbour cells.

The Measurement Results information element is coded as shown in figure 10.5.2.20.1 and table 10.5.2.20.1. The Measurement Results is a type 3 information element with

17 octets length.

Figure 10.5.2.20.1: Measurement Results information element

Table 10.5.2.20.1: Measurement Results information element details

Changes to technical specification 3GPP TS 45.008 V6.13.0 (2005-06) :

8.1.3 Statistical parameters

For each channel, the measured parameters (RXLEV) shall be the average of the received signal level measurement samples in dBm taken on that channel within the reporting period of length one SACCH multiframe defined in 8.4. In averaging, measurements made during previous reporting periods shall always be discarded when using normal SACCH on the uplink. When using serial SACCH repetition on the uplink, the measurement samples shall be averaged over two SACCH multiframes.

8.4.1 Measurement reporting for the MS

In A/Gb mode, for a TCH and in Iu mode, for a DBPSCH, the reporting period of length 104 TDMA frames (480 ms) is defined in terms of TDMA frame numbers (FN) as follows:

Timeslot number (TN) TDMA frame number (FN) modulo 104 Full Half rate, Half rate, Reporting peSACCH Message

Rate subch .0 subch .1 riod block

0 0 and 1 0 to 103 12, 38, 64, 90

1 0 and 1 13 to 12 25, 51, 77, 103

2 2 and 3 26 to 25 38, 64, 90, 12

3 2 and 3 39 to 38 51, 77, 103, 25

4 4 and 5 52 to 51 64, 90, 12, 38

5 4 and 5 65 to 64 77, 103, 25, 51

6 6 and 7 78 to 77 90, 12, 38, 64

7 6 and 7 91 to 90 103 , 25, 51, 77

For a multislot configuration, the reporting period and SACCH Message block for each timeslot is defined as for TCH/F or PDTCH/F or DBPSCH/F for TN = 0.

The following table shows the reporting period of length 208 TDMA frames (960 ms) which is used when serial SACCH repeti- tion is in use on the uplink:

In A/Gb mode, when on a TCH, or in Iu mode, when on a DBPSCH, the MS shall assess during the reporting period and transmit to the BSS in the next SACCH message block the following:

RXLEV for the BCCH carrier of the 6 cells with the highest RXLEV among those with known and allowed NCC part of BSIC. For a multi band MS the number of cells, for each frequency band supported, which shall be included is specified in sub clause 8.4.3. For a cell of other radio access technology, see subclasses 8.1.5 and 8.4.7. NOTE 1: Since there are 104 TDMA frames in each SACCH multiframe (and measurement in 4 frames is optional) , the number of samples on each BCCH carrier will depend on the number of carriers defined in the BCCH Allocation (BA) and may be different. The following table gives examples of this

These figures are increased if the MS is able to make measurements on more than one BCCH carrier during each TDMA frame. The above number of samples will be doubled if serial SACCH repetition is in use on the uplink.

Claims

Patent claims

1. Method for transmitting signals in a radio communication system, wherein at least one traffic channel (TCH) and at least one control channel (SACCH) associated with the at least one traffic channel (TCH) are assigned for transmission of signals between a base station (BS) and a mobile station (MS) , and wherein the mobile station (MS) reports in at least one frame of the associated control channel (SACCH) measure- ments made during a measurement period consisting of at least one frame of the associated control channel (SACCH) characterised in that the mobile station (MS) transmits to the base station (BS) an indication of the length of the measurement period used by the mobile station (MS) .

2. Method according to claim 1, wherein the indication transmitted by the mobile station (MS) to the base station (MS) indicates a change in the length of the measurement period.

3. Method according to claim 1 or 2, wherein the measurements made by the mobile station (MS) comprise of measurements of received signal strength or signal quality parameters from at least one neighbouring base station.

4. Method according to one of the preceding claims, wherein the measurement report is repeatedly transmitted to the base station (BS) by the mobile station (MS) .

5. Method according to one of the preceding claims, wherein the mobile station (MS) adapts the measurement period to the measurement reporting period commanded by the base station (BS) .

6. Mobile station (MS) of a radio communication system, comprising at least means for transmitting signals to a base station (BS) of the radio communication system in at least one traffic channel (TCH) and at least one control channel (SACCH) associated with the at least one traffic channel (TCH) , for transmitting measurement reports to the base station (BS) in at least one frame of the associated control channel (SACCH) , wherein the measurement report is derived from measurements effected during a measurement period consisting of at least one frame of the associated control channel (SACCH), and for signalling to the base station (BS) an indication of the length of the measurement period used by the mobile station (MS) .