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What is special sub frame in LTE?

As the single frequency block is shared in time domain between UL and DL thetransmission in TDD is not continuous. All UL transmission need to be on hold

while any downlink resource it is used and the other way around.Switching between transmission directions has a small hardware delay (for both

UE and ode!" and needs to be com#ensated. To control the switching betweenthe UL and DL a guard period GP is allocated which com#ensates for thema$imum #ro#agation delay of interfering com#onents.

Descri#tion of the switching mechanism%&n LTE TDD there is ma$imally one UL'DL and one DL'UL transition #er )ms#eriod (half frame"UL-> DL transition&s done for all intra'cell UEs by the #rocess of time alignment. The ode!

instructs each UE to use a s#ecific time offset so that all UEs signals are alignedwhen they arri*e at ode'!. So UL is synchronous *ery similar to +DD (intra cellcase only,"DL->UL transitionThe interference coming from other DL neighbors has to be a*oided

As shown in abo*e figure there are - frame configurations according todifferent DL/UL #artition.1. Downlink / U#link ratio can *ary from 0/1 (+rame configuration 2 3" to 4/0(+rame configuration 2 0" de#ending on the ser*ice requirements of the carrier2. +rame always starts with a downlink subframe used for ad*ertising theframe descri#tor 56+&67 and 5D667. UE hence learns the frame structure in

this subframe.3. 1rd frame is always used for u#link

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4. 8hen switching from downlink to u#link there is need for a s#ecial switchingsubframe. o s#ecial subframe is used when switching from u#link to downlink.

As s#ecial subframe is introduced at subframe0 and subframe 9. Each halfframeof 3.)ms carries one s#ecial subframe that is di*ided into 1 #arts as shown inbelow figure%Dw5TS :5 and U#5TS (U#link 5ilot Time slot". Subframe 3 and Dw5TS are

reser*ed for downlink; subframe0 and U#5TS are reser*ed for UL. <emainingfields are dynamically assigned between UL and DL.

This s#ecial subframe re#lace the subframe 0. The indi*idual time duration in=+D> symbols of the s#ecial subframe #arts are ad?ustable.

1. The :5 im#lements the DL'UL transition #oint and the :5 has to be largeenough to co*er the #ro#agation delay of DL interferers.&ts length determines the ma$imum su##ortable cell si@e.2. Dw5TS is considered as a normalB DL subframe and carries reference signalsand control information as well as data for those cases when sufficient duration

is configured. &t also carries 5SS.3. U#5TS is #rimarily intended for sounding reference signals (S<S"transmission from UE.>ainly used for <A67 transmission.

Special Subframe onfiguration

Total length of s#ecial subframe is 0ms but the length of the each field may *aryand there are C formats are a*ailable as shown in figure.

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UE always needs a guard #eriod in order to switch from recei*er to transmitter.The guard #eriod includes <TD (<ound Tri# Delay" as shown in figure.