TTG vs RTG-What is TTG and RTG Gaps in WIMAX,LTE
This page on TTG vs RTG gaps covers TTG gap and RTG gap specifications used in WiMAX and LTE systems. TTG stands for Transmission Time Gap and RTG stands for Receivers Time Gap.
It is used as transmit/receive transition gap. This is shown in figure after downlink subframe(of frame:N) and before uplink subframe of same frame "N".
This parameter is specified for both base station and subscriber station in wimax system.
During this time period or gap base station and subscriber station will not transmit any data or information.
For example, if we consider this specification for base station then it is the time required for Base station to switch from transmit mode to the receiver mode. The TTG gap will ascertain that there will not be any loss of data while switching.
• It allows enough time for Base Station RF carrier to ramp down before settling.
• It allows antenna switch enough time to switch from transmit to receive mode.
• It allows Base Station RF and baseband modules to get ready for reception of wimax bursts transmitted from subscriber stations.
For Subscriber station this gap is the time required to switch from receive mode to the transmit mode.
The value of the TTG gap is specified in the standard in units of Physical Slots.
1 PS = 4 /Fs
Where Fs is the sampling frequency which depends on Bandwidth and sampling factor.
Refer Wimax Terminology➤ for more information.
It is used as receive/transmit transition gap. This is shown in figure after uplink subframe(of frame: N) and before next downlink subframe (i.e. Frame: N+1) in the wimax frame structure.
During this time period equivalent to RTG gap, both BS and SS do not transmit any data. This gap allows Base Station (BS) to switch from receive mode to transmit mode. It allows Subscriber Station (SS) to switch from transmit mode to receive mode.
The RTG gap will ascertain that there will not be any loss of data while switching.
• It allows enough time for Base Station RF carrier to ramp up before settling.
• It allows antenna switch enough time to actuate.
• It allows Subscriber station's RF and baseband modules to get ready for reception of wimax bursts transmitted from base station.
For WiMAX OFDM specification, TTG/RTG should be >5 µS and <=100 µS. So typical choice is to use TTG and RTG of value about 80 µS (i.e. 1 OFDM symbol) . This works fine for Bandwidth of 3.5MHz and Fs of 4MHz.
The specification of TTG/RTG Gap vary for OFDMA specification. Pls. check respective wimax standard specifications for the same.
LTE, TDD frame structure uses Downlink Pilot Time Slot(DwPTS), Guard Period(GP) and Uplink Pilot Time Slot(UpPTS) in special frame similar to the gaps available in wimax.
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