Discontinuous Transmission - Technical Details

Technical Details

SP flag = 0 indicates SID frame SP flag = 1 indicates speech frame

Speech frame = 260 bit

Transmit side:

TX DTX handle performs speech encoding, comfort noise computation, voice activity detection TX Radio Subsystem (RSS): Performs SP flag monitoring and Channel coding

Hangover period: After the transition from VAD=1 to VAD=0 it take N+1 consecutive frames to make a new updated SID frame available the bursts are directly passed to RSS with SP=1 this period is defined as Hangover period.

Noise Background spikes can often be confused with the speech frame and hence in order to nullify this issue a check list for SID computation is Nelapsed >23, old SID is utilized with VAD=0.

Once after the end of speech SID is computed it is continuously passed to the RSS marked with SP=0 as long as VAD=0.

If a SID (SP=0) is chosen for transmission is stolen for FACCH signaling than the subsequent frame is scheduled for transmission.

Receive side:

BFI=0 Meaningful information bit BFI=1 Not Meaningful information bit

Interestingly a FACCH frame in not considered as a meaningful information and should be transmitted with BFI=1

Traffic frames aligned with SACCH multi frame have TAF(Time alignment flag) =1

RX DTX handler performs speech decoding and comfort noise computation. RX Radio subsystem: Performs Error Correction and Detection and SID frame detection

Whenever a good speech frame is detected the RX DTX handler shall pass directly to speech decoder Whenever a lost speech or lost SID frames are detected the substitution or mutation shall be applied. Whenever a valid SID frame result in comfort noise generation. In case of invalid SID frame after consecutive Speech frames the last valid SID frame will be applicable