Compressed mode places gaps in the downlink and uplink transmissions that allow a UE, while on a call, to perform measurements on neighboring cells of a different frequency than its current serving cell. The UE can perform measurements on neighboring GSM, W-CDMA or E-UTRAN cells.
The network specifies the transmission gap pattern sequences (TGPSs), which control when the transmission gaps occur and their duration. During radio frames that contain transmission gaps, the UE and network use a lower spreading factor to avoid losing any data due to the smaller transmit/receive window caused by the transmission gap.
The compressed mode feature allows you to specify up to 4 TGPSs, each with a different measurement purpose, if desired. Each TGPS consists of repetitions of one transmission gap pattern, which can include one or two transmission gaps.
Not sure what to say about techniques, sorry?