12 Radio Resource Management Procedures

03.523GPPLower layers of the GSM Cordless Telephony System (CTS) radio interfaceStage 2TS

12.1 Radio Resources management states

RR Idle state: for the CTS-FP, the state where it has been initialised (see GSM 03.56); for the CTS-MS, the state where it is attached to a CTS-FP (see GSM 03.56).

RR Active state: the state where the CTS-MS and the CTS-FP have successfully established a dedicated RR connection.

12.2 General procedures

12.2.1 Initial synchronization of a CTS-MS and CTS-FP

Some procedures, e.g. the enrolment of a CTS-MS, shall require the synchronization of a CTS-FP and CTS-MS, whereas no parameters have yet been exchanged between the CTS-FP and CTS-MS, such as the used CTSBCH frequency. A special procedure shall be implemented in the CTS-FP by which the CTS-MS synchronization, i.e. decoding of the CTSBCH, is eased. This procedure shall include ways for the CTS-MS to detect the CTS beacon frequency more rapidly.

At the end of this procedure, the CTS-FP and CTS-MS are synchronised and can establish a dedicated RR connection if requested by the upper layers.

12.2.2 Frequency management

The following figure 3 gives an overview of the frequency management in the CTS-FP and CTS-MS.

The purpose of the frequency management is to avoid that a CTS-FP and a CTS-MS use the same frequencies as the surrounding PLMN and cause a too high interference level to it, to other CTS-FP and to the corresponding MS (GSM or CTS).

Figure 3: frequency management overview

– The GFL is allocated to a certain CTS-FP.

– The AFA table contains the frequencies of the GFL ranked and ordered by the AFA algorithm (see subclause 12.2.2.2); it is managed by the CTS-FP only.

– The TFH list is a reduced AFA table: the AFA / TFH interworking procedure (see subclause 12.2.2.3) has excluded some of the frequencies of the AFA table depending on an acceptance threshold and other parameters; the TFH list shall be known by both CTS-FP and CTS-MS, as it is the list of frequencies on which hopping is performed.

The whole management of the frequencies in the CTS system can be sub-divided into the following procedures.

12.2.2.1 Interference measurements exchange

The AFA algorithm shall periodically specify which interference measurements are to be performed on the Lower Layer in both CTS-FP and CTS-MS, then the interference measurements shall be reported from the Lower Layer of the CTS‑FP and CTS-MS to the AFA algorithm.

The protocol to request and report the interference measurements shall use a dedicated RR connection (see subclause 12.3.3).

12.2.2.2 Adaptive Frequency Allocation (AFA) algorithm

The AFA algorithm shall perform a ranking with regard to interference measurements (see subclause 11.6), among the frequencies of the GFL, taking into account system parameters.

The reaction time of the AFA algorithm shall decrease in case high interference is measured on the used frequencies, e.g. to adapt to strong changes in the interference environment caused by frequency replanning on the cellular network. It shall, however, be resistant against interference fluctuations caused by short time traffic variations, e.g. day and night traffic.

12.2.2.3 AFA / TFH interworking

A set of frequencies from the AFA table shall be selected by the CTS-FP to be used by the Total Frequency Hopping (TFH) algorithm: this subset is the TFH list. The selection mechanisms shall use parameters, such as an acceptance criteria. All frequencies fulfilling the acceptance criteria shall be part of the TFH list.

12.2.2.4 CTSBCH frequency selection

Any frequency from the TFH list shall be selected as the CTSBCH frequency, i.e. the frequency on which the CTSBCH is transmitted. The CTSBCH frequency can be either the frequency showing the lowest interference level with respect to reported interference measurements, either a random frequency chosen in the TFH list.

12.2.3 CTSBCH-SB information

The CTSBCH-SB shall be periodically transmitted by the CTS-FP on the CTS radio interface (see subclause 11.1). The information described in subclause 10.1.4, shall be sent by the CTS-FP at every CTSBCH-SB transmission.

12.2.4 Control of CTS-FP service range

The control of the CTS-FP service range can be performed using MS timing offset measurements (as defined in subclause 11.7). Considering the present MS requirements for synchronisation (see GSM 05.10 clause 6), the CTS-FP service range can be only controlled with an accuracy of 750 m.

Methods for increasing this accuracy are needed in order to see if the CTS-FP service range can be restricted to 375 m. They are specified in GSM 05.10.

12.2.5 CTS-FP selection

When attempting to attach to a CTS-FP (see GSM 03.56), the CTS-MS shall periodically attempt to detect the CTSBCH-FB (see subclause 11.3) on the CTSBCH frequency. The CTSBCH frequency shall be stored in the CTS-MS for each CTS-FP it is enrolled with.

12.3 RR Idle state procedures

12.3.1 CTSBCH monitoring

In the RR Idle state, the CTS-MS RR layer shall periodically request the CTS-MS Lower Layer to decode the CTSBCH-SB (see subclause 11.4).

The periodicity of the CTSBCH monitoring shall ensure that synchronisation to the CTS-FP can be maintained and that the response time to information given in the CTSPCH is acceptable.

12.3.2 Alive check

The CTS-FP shall periodically verify the presence of its attached CTS-MS.  This shall be performed in four steps:

– the CTSPCH indicator flag of the CTSBCH shall indicate the need to decode the next following CTSPCH;

– the CTS-FP shall transmit on the CTSPCH an alive check message: this message shall contain a CTSMSI, which is used by the CTS-FP to address one particular CTS-MS;

– the addressed CTS-MS shall transmit an access request message on one of the six CTSARCH which are mapped onto the physical channel as specified in subclause 10.2.2. The choice of the CTSARCH to be used shall be randomly performed;

– the alive check message shall be maintained on the CTSPCH until the access request message is received from the CTS-MS; however if after a timer has expired, no message is received from the CTS-MS, an alive check failure message shall be sent to the MM upper layer.

12.3.3 Establishment of a dedicated RR connection

12.3.3.1 Timeslot assignment for dedicated connection

The timeslot assignment for a dedicated channel shall be based on interference measurements performed by the CTS-FP in the uplink direction on any timeslot of the frequencies of the TFH list. The least interfered timeslot shall be used to establish a dedicated connection.

12.3.3.2 CTS-MS initiated RR connection establishment

When the CTS-MS is willing to establish a dedicated RR connection with a CTS-FP, it shall access the CTS-FP using one of the two following procedures. The choice is dependent on the type of request for dedicated RR connection as triggered by the upper layers: e.g. attachment, CTS-MS initiated call set-up, etc.

12.3.3.2.1 Non-hopping access procedure

An access request message shall be sent by the CTS-MS on the CTSARCH. The CTS-MS shall send two bursts on the CTSARCH: these two bursts shall be sent on two successive frames and shall contain the same access request message. The first sent burst can be used by the CTS-FP to assess the path loss between the CTS-MS and itself, in order to effectively decode the second burst. The choice of the two CTSARCH to be used among the eight CTSARCH which are mapped onto the physical channel as stated in subclause 10.2.2, shall be randomly performed, with the requirement of the first burst being sent in a TDMA frame with even FN.

On receipt of the access request message, the CTS-FP shall transmit a message on the CTSAGCH which is mapped onto the physical channel as stated in subclause 10.3.2.

This message shall contain the dedicated channel description.

Upon receipt of this message, the CTS-MS shall switch to the assigned channel, set the channel mode to "Signalling only", activate the assigned channel in non-hopping mode and establish the main signalling link. The dedicated RR connection is then considered as established: the CTS-FP shall transmit to the CTS-MS the required information to perform hopping, i.e. the hopping parameters to be used by the Total Frequency Hopping algorithm (see subclause 10.8.2) and the TFH list. Upper layers shall then be informed, in order to perform the required procedure.

12.3.3.2.2 Hopping access procedure

An access request message shall be sent by the CTS-MS on the CTSARCH. The CTS-MS shall send two bursts on the CTSARCH: these two bursts shall be sent on two successive frames and shall contain the same access request message. The first sent burst can be used by the CTS-FP to assess the path loss between the CTS-MS and itself, in order to effectively decode the second burst The choice of the two CTSARCH to be used among the six CTSARCH which are mapped onto the physical channel as stated in subclause 10.2.2, shall be randomly performed, with the requirement of the first burst being sent in a TDMA frame with even FN.

On receipt of the access request message, the CTS-FP shall transmit a message on the CTSAGCH which is mapped onto the physical channel as stated in subclause 10.3.2. This message shall contain the dedicated channel description.

Upon receipt of this message, the CTS-MS shall switch to the assigned channel, set the channel mode to "Signalling only", activate the assigned channel in hopping mode and establish the main signalling link. The dedicated RR connection is then considered as established: upper layers shall be informed, in order to perform the required procedure.

12.3.3.3 CTS-FP initiated RR connection establishment

When the CTS-FP is willing to establish a dedicated RR connection with a CTS-MS, it shall perform the paging procedure.

The CTSPCH indicator flag of the CTSBCH shall indicate the need for the CTS-MS to decode the next following CTSPCH. Then the CTS-FP shall transmit on the CTSPCH a paging message: this message shall contain a CTSMSI, which is used by the CTS-FP to address one particular CTS-MS.

On receipt of this paging message, the CTS-MS shall perform the hopping access procedure, similar to subclause 12.3.3.2.2.

The paging message shall be maintained on the CTSPCH until the access request message is received from the CTS‑MS; however if after a timer has expired, no message is received from the CTS-MS, an paging failure message shall be sent to the MM upper layer.

The dedicated RR connection is then considered as established: upper layers shall be informed, in order to perform the required procedure.

12.3.4 CTSBCH failure detection

If the CTSBCH-SB can not be decoded by the CTS-MS performing CTSBCH monitoring, the CTS-MS shall attempts to monitor the CTSBCH again on the next 52-multiframe. If it cannot monitor the CTSBCH for a defined number of consecutive attempts, a CTSBCH failure message shall be sent to the upper layers.

12.4 RR Active state procedures

In the RR Active state, a dedicated RR connection has been successfully established between a CTS-MS and a CTS-FP.

12.4.1 Radio link failure detection

The radio link failure detection in the CTS-FP and the CTS-MS shall ensure that dedicated RR connection with unacceptable quality, which cannot be improved either by RF power control (see subclause 12.4.2) or intracell handover (see subclause 12.4.3) shall be released by the CTS-FP or the CTS-MS. A radio link failure message shall be sent to the upper layers.

12.4.2 RF power control

In the RR Active state, RF power control shall be employed to minimise the transmit power required by the CTS-MS or the CTS-FP whilst maintaining the quality of the radio link. Both the CTS-MS and CTS-FP shall apply power control in the uplink and downlink.

The output power control level to be used by the CTS-MS shall be determined in the CTS-FP and shall be communicated to the CTS-MS on the SACCH.

The requirements for the power control algorithm are specified in GSM 05.08.

12.4.3 Intracell handover

Intracell handover (change of active timeslot) shall be carried out in the case of unacceptable connection quality when in RR Active state. The handover shall be triggered by the CTS-FP.

If an intracell handover is triggered, the CTS-FP shall re-assign another randomly chosen timeslot for the dedicated connection.

12.4.4 Channel release

When triggered by the upper layers or if a radio link failure is detected (see subclause 12.4.1), the dedicated RR connection shall be released by the CTS-MS and CTS-FP.

Annex A (informative):
GSM backwards compatibility issues

This annex is intended to study the impacts on a GSM-MS behaviour in a PLMN due to the deployment of CTS-FPs in the PLMN coverage area.

This study is split in 3 scenarios:

– Scenario 1: CTS is not operated by PLMN operator, or CTS and GSM are operated in separate bands. It means that PLMN and CTS-GFL have no common frequency in the whole overlapping coverage area;

– Scenario 2: CTS and GSM are operated in shared band with optimal GFL definition in the considered area. It means that at every given location PLMN and CTS-GFL have no common frequency;

– Scenario 3: CTS and GSM are operated in shared band with sub-optimal GFL definition for some considered area. It means that at some given locations PLMN and CTS-GFL (then possibly FPs) have common frequencies.

NOTE: PLMN refers either to the home PLMN when the GSM-MS is under its coverage, or the roaming PLMN otherwise.