Higher layers can request a UE to monitor cells on other frequencies (FDD, TDD), or other systems (GSM). This implies that the UE has to perform measurements, on the other frequencies/systems and thus higher layers command the UE to ENTER Compressed Mode. The UTRAN need to send to the UE all the parameters for the Compressed Mode.

Compression Methods:

When in Compressed Mode the information normally transmitted during a 10 ms frame is compressed in time sothat gaps of adequate length are created. To achieve this one of three mechanisms

• Puncturing: This method is NOT applicable to downlink.
• Spread Factor Reduction: Actually halving the Spread Factor. So with this method if SF is used in non-compressed frames then SF/2 is used in the compressed frames.
• Higher Layer Scheduling: Higher Layers set restrictions so that only a subset of allowed TFCs are used in Compressed Mode.

Compressed Mode Parameter:

TGSN (Transmission Gap Starting Slot Number): A transmission gap pattern begins in a radio frame, called firstradio frame of the transmission gap pattern, containing at least one transmission gap slot. TGSN is the slot numberof the first transmission gap slot within the first radio frame of the transmission gap pattern;

• TGL1 (Transmission Gap Length 1): Duration of the first transmission gap within the transmission gap pattern, expressed in number of slots;
• TGL2 (Transmission Gap Length 2): Duration of the second transmission gap within the transmission gap pattern, expressed in number of slots. If this parameter is not EXPLICITLY set by higher layers, then TGL2 =TGL1;
• TGD (Transmission Gap Start Distance): Duration between the starting slots of two consecutive transmission gaps within a transmission gap pattern, expressed in number of slots. The resulting position of the second transmission gap within its radio frame(s) shall comply with the limitations of TS 25.101 (Ref [2]). If this parameter is not set by higher layers, then there is only one transmission gap in the transmission gap pattern;
• TGPL1 (Transmission Gap Pattern Length): Duration of transmission gap pattern 1;
• TGPL2 (Transmission Gap Pattern Length): Duration of transmission gap pattern 2. If this parameter is not explicitly set by higher layers, then TGPL2 = TGPL1.

The following two parameters (integers) CONTROL the transmission gap pattern sequence start and repetition:

1. TGPRC (Transmission Gap Pattern Repetition Count): Number of transmission gap patterns within the transmission gap pattern sequence; From Figure 10 it seems TGPRC is even, therefore the number of slots in TG Sequence is: 0.5*TGPRC (TGPL1+TGPL2)
2. TGCFN (Transmission Gap Connection Frame Number): CFN of the first radio frame of the first pattern 1 within the transmission gap pattern sequence.

Higher layers can request a UE to monitor cells on other frequencies (FDD, TDD), or other systems (GSM). This implies that the UE has to perform measurements, on the other frequencies/systems and thus higher layers command the UE to enter Compressed Mode. The UTRAN need to send to the UE all the parameters for the Compressed Mode.

Compression Methods:

When in Compressed Mode the information normally transmitted during a 10 ms frame is compressed in time sothat gaps of adequate length are created. To achieve this one of three mechanisms

Compressed Mode Parameter:

TGSN (Transmission Gap Starting Slot Number): A transmission gap pattern begins in a radio frame, called firstradio frame of the transmission gap pattern, containing at least one transmission gap slot. TGSN is the slot numberof the first transmission gap slot within the first radio frame of the transmission gap pattern;

The following two parameters (integers) control the transmission gap pattern sequence start and repetition: