Last updated: December 2, 2008
This section is only applicable to the EGPRS lab application.
The ability of an EGPRS network to adapt the link to the existing radio environment by changing the modulation and coding scheme (MCS) is a fundamental EGPRS capability. There are nine modulation coding schemes used by an EGPRS system, each using different data and channel coding rates with either GMSK or 8PSK modulations. During an established communication, the modulation coding schemes can only be changed within families defined in the 3GPP standard.
When you enable MCS Switching, the following transitions are supported:
The data rate for MCS6 (padding) is 13.6kbit/s. See Modulation Coding Scheme/Puncturing Scheme (MCS/PS) for the data rates of other MCSs.
Link adaptation to MCS below MCS5 requires the original RLC data block to be resegmented between two radio blocks. When you enable downlink resegmentation in the test set, all the downlink transitions defined in the 3GPP standard become available:
Resegmentation is only supported on the downlink.
The data rate is 13.6kbit/s for MCS3 (padding) and 27.2kbit/s for MCS6 (padding). See Modulation Coding Scheme/Puncturing Scheme (MCS/PS) for the data rates of other MCSs.
You can test the mobile station's ability to decode data and header information when the test set switches the modulation and coding scheme used for retransmission of downlink blocks. The test set is triggered to switch the modulation coding scheme based on a user specified number of retransmissions. Once a block has been Not Acknowledged (NACK) by the mobile station and retransmitted the number of times you specify, the test set switches to a modulation coding scheme with a greater probability of being received correctly. The user can force this condition by defining some downlink blocks to be corrupted intentionally by the test set. See Downlink Corruption for more information.
You may observe some interesting behavior regarding the MCS on Uplink TBFs. For example, the uplink TBF may start using a different MCS than the one you've specified for the test set to communicate to the MS via RLC MAC Control messages.For the first transmission of RLC data blocks, when the commanded MCS is MCS-7, MCS-5 is used, and for MCS-9, MCS-6 is used. (Refer to 3GPP TS 04.60 Section 8.1.1 for more information.)You can observe this MS behavior using the Wireless Protocol Advisor.
Additionally, you may observe an MCS different than the one commanded being used for the Uplink TBF during additional transmissions as well. This is allowed and typically occurs when the transmission only requires as many radio blocks as are available using an alternate MCS. For example, if the commanded MCS is MCS-9 which sends 2 RLC data blocks, and the mobile station only needs to send one RLC data block, it may choose to send it using MCS-6, which sends only one data block and is also more robust. These exceptions are also specified in 3GPP TS 04.60 Section 8.1.1.
| Parameter | GPIB Command |
|---|---|
| Allow MCS Switching | CALL:(PDTCH|PDTChannel):MCSCheme:SWITch[:STATe] |
| Retransmissions before MCS Switch | CALL:(PDTCH|PDTChannel):MCSCheme:SWITch:RETRansmit |
The operating mode must be Active Cell and the serving cell must be EGPRS. However, parameters associated with MCS Switching can be changed in other operating modes, but do not effect the test set's operation until the operating mode is changed to Active Cell.
MCS Switching is only applicable when the connection type is set to Auto.
Tips for analyzing protocol logs of Incremental Redundancy and Retransmission MCS Switching