Configuring the Traffic Channel (TCH) Parameters

Configuring the Traffic Channel (TCH) Parameters

Last updated: May 13, 2009

This section is not applicable to GPRS and EGPRS.

The traffic channel parameters are configured using the following call processing subsystem commands.

For complete GPIB command syntax, see CALL:TCHannel .

The TCH Parameters can be accessed on the front panel by pressing TCH Parameters ( F8 ) on the Call Parms menu, see How Do I Change Call Parameters? .

TCH Parameters

Parameter

GPIB Command

Traffic Channel Band

CALL:TCHannel:BAND

Traffic Channel (ARFCN)

CALL:TCHannel[:ARFCn][:SELected]

Timeslot

CALL:TCHannel:TSLot

Mobile Loopback

CALL:TCHannel:LOOPback

Speech

CALL:TCHannel:DOWNlink:SPEech

Channel Mode

CALL:TCHannel:CMODe[:VALue]

Speech Channel

CALL:TCHannel:CMODe:HRSPeech:SCHannel

Downlink Burst Current Absolute Power Level

CALL:TCHannel:POWer[:AMPLitude]?

Downlink Burst Power Reduction Selection CALL:TCHannel:PREDuction:BURSt
Downlink Power Reduction Level (dB) CALL:TCHannel:PREDuction:LEVel([1]|2)

Unused Downlink Burst Current Absolute Power Level

CALL:TCHannel:POWer[:AMPLitude]:UNUSed?

Unused Downlink Burst Power Reduction Selection CALL:TCHannel:PREDuction:UNUSed

Adjacent Downlink Burst Current Absolute Power Level

CALL:TCHannel:POWer[:AMPLitude]:ADJacent?

Adjacent Downlink Burst Power Reduction Selection

CALL:TCHannel:PREDuction:ADJacent

Operating Considerations

Any changes to the TCH parameters result in new channel assignments when the mobile station is assigned to a TCH. No new channel assignments are sent to the mobile station when it is assigned to the SDCCH and changes are made to TCH parameters.

When configuring the base station emulator you must configure the broadcast channel (see CALL:BCHannel ) and the traffic channel (TCH). There are a number of parameters for the BCH and the TCH that can be configured; however, the test set's default parameters should allow a properly functioning mobile station to successfully camp on the cell and make a call under most circumstances.

When the Operating Mode is Active Cell and a call is connected, changes to the traffic channel number (ARFCN) or traffic channel timeslot, including a change to the value of the parameter's current setting, causes signaling on the downlink FACCH to initiate a channel reassignment, see How the Test Set Performs a Dualband Handover . This configures the TCH to use the new parameter. If a call is not connected, changes to the parameter are stored for when the next call is established.

When the operating mode is GSM BCH+TCH (see CALL:OPERating:MODE ), changes to the traffic channel number (ARFCN) or traffic channel timeslot will reconfigure the downlink TCH accordingly, but there will be no signaling initiated. The change will be immediate. If a TCH is not being generated, changes to the parameter are stored for when the next call is established.

Mobile Loopback

The loopback type must be set before starting a Fast Bit Error or a Bit Error measurement. A downlink TCH with PRBS data is generated at a known level, and the mobile receives it, loops it back to its transmitter, and returns the PRBS data to the test set. A comparison is then made in the test set between data sent and the data received, and the BER is calculated.

Currently, The test set provides the following loopback types:

  • Loopback type A - BER with Frame Erasure (FE) or Residual BER
    When the mobile loopback is set to type A, the comparison is made between the required class of bits within the 260 bits of speech data presented to the channel coder of the test set and the 260 bits of speech data received by the channel decoder of the test set. The mobile will indicate in the speech frame if the downlink frame was received and was found to have CRC errors which would cause the speech frame to be erased. The mobile indicates this on the uplink by setting all bits in the uplink speech frame to 0.
  • Loopback type B - BER without Frame Erasure (FE) or Non Residual BER
    When the mobile loopback is set to type B, the comparison is made between the required class of bits within the 260 bits of speech data presented to the channel coder of the test set and the 260 bits of speech data received by the channel decoder of the test set. The mobile does not provide any indication of whether or not the downlink speech frame was erased.
  • Loopback type C - Fast BER
    When the mobile loopback is set to type C, the comparison is made between the 114 bits of interleaved data presented to layer 1 in the test set and the 114 bits of interleaved data received by layer 1 in the test set. Note, this loopback type can only be used in the Fast BER measurement.
  • Loopback type D - BER with Frame Erasure and Unreliable Frame Rate Signaling
    The functionality of mobile loopback type D is for the most part identical to that of mobile loopback type A with one exception: loopback type D will include Unreliable Frames Rate (UFR) signaling in addition to the Frame Error Rate (FER). Hence the FER display during mobile loopback type D measurement is actually FER plus UFR.

The GPIB command to set the this parameter is: CALL:TCHannel:LOOPback .

Max Frames Allowed for Assignment Parameter

The Max Frames Allowed for Assignment parameter is used to specify the maximum number of TDMA frames the MS is allowed to take for a channel assignment. This is only applicable to changes in TCH Band, TCH ARFCN or TCH Timeslot. Changes to any other TCH parameter will not cause an error to be generated if the number of frames taken to perform the change exceeds the setting of the Channel Assignment TDMA Frames Allowed parameter. GSM 05.10 specifies a maximum of 26 frames allowed for assignment parameter, (GSM 11.10 extends the allowed period to approximately 28 frames for a channel assignment and approximately 31 frames for a handover), although specific MS implementations may take less. The test set allows you to set the Max Frames Allowed for Assignment parameter with the range of 15 to 999. If the mobile station does not complete the assignment within the user-specified time, the test set will generate a special RR sublayer error "Channel assignment exceeded specified number of frames", see +256 GSM protocol failure; No response to disconnect (Timer T305 expiry) . This is a non-fatal error, and does not cause the call to drop. If the channel assignment seriously fails, and timer T3107 expires, The test set only reports the "channel assignment fail" error and ignore the "Channel assignment exceeded specified number of frames" error. Note that the "Channel assignment exceeded specified number of frames" error is not generated if MS DTX State is "On". (See CALL:MS:DTX[:STATe] ) This is because when a mobile phone is in DTX mode, it is not required to transmit on the new channel, at least not until a SACCH, FACCH, or SID frame is ready and therefore the MS may actually have changed channel in the correct time, but had nothing to transmit.

This parameter is only accessible using the GPIB interface. The GPIB command to set this parameter is CALL:COUNt:TDMA:FRAMes? .

Speech

The downlink speech source controls what kind of speech data is transmitted on the downlink TCH. A TCH with speech data is generated when the call control status is connected (see Call Processing State Synchronization ) or when in GSM BCH+TCH operating mode.

When an FBER measurement is activated, PRBS15 data is transmitted on the downlink TCH, overriding the user setting of the downlink speech source. Any changes to the downlink speech source will be accepted and saved but not applied until the FBER measurement becomes inactive.

The command to set the Downlink Speech Source is CALL:TCHannel:DOWNlink:SPEech . The settings available for the downlink speech are as follows:

  • None
  • Echo

    Retransmits the uplink speech frames back on the downlink with a settable delay of 0 and 1 seconds. The speech echo loopback delay setting can be changed in any operating mode. The speech echo loopback delay can be set regardless of the speech source, however it is only applicable when the speech source is set to Echo .

    The command to set the speech echo loopback delay is CALL:TCHannel:DOWNlink:SPEech:LOOPback:DELay .

  • PRBS15

    The 260 speech frame bits (prior to channel coding) are generated using a pseudo random bit sequence.

  • PRBS 9

    The 114 speech frame bits (without channel coding and interleaving) are generated using a pseudo random bit sequence. PRBS9 is available when the operating mode is set to any operating mode except for GSM BCH, GPRS BCH, EGPRS BCH, Cell Off and CW.

  • SIN300

    The sequence of 260 speech bit frames represent a sine wave at 300 Hz.

  • SIN1000

    The sequence of 260 speech bit frames represent a sine wave at 1000 Hz.

  • SIN3000

    The sequence of 260 speech bit frames represent a sine wave at 3000 Hz.

  • Multi-Tone

    Control of the audio generator is given to the Multi-Tone Audio Instrument.

  • SID (Silence Descriptors)

    Silence Descriptors configure the test set to simulate a base station operating in Discontinuous Transmission (DTX) mode. The parameter is only applicable to the lab applications.

  • CUSTom

    You may set the values that make up the custom payload pattern that is repeated in each speech frame or use the default pseudo random bit sequence (PRBS) custom data pattern. The same custom payload pattern is used for GSM, GPRS and EGPRS connections.

    If you specify a custom payload pattern that is longer than the length of the speech frame, only the portion of the pattern that fits in the speech frame will be used so the end data will not be used. If the custom payload pattern is shorter that the length of the speech frame, the custom payload pattern is repeated as many times as necessary to fill the speech frame.

    There is no access through the front panel to configure the custom payload pattern. The GPIB command to configure the Custom pattern is CALL:TCHannel:CUSTom:DATA . The query for this command returns only the defined custom payload pattern rather than the repeated or truncated pattern used to fit to the size of the speech frame.

Related Topics


Configuring the Broadcast Channel (BCH)

Configuring Mobile Station Operating Parameters

Receiver Control

Traffic Band Parameter

CALL:TCHannel

Fast Bit Error Measurement Description

How Do I Change the Payload Pattern Sent to the Mobile Station?

How Do I Configure the Speech Source?

Frequency Bands

Mobile Calculated BER Test