[STDS-802-16] AW: [STDS-802-16] TTG may be too small for the scaleable OFDMA
Dear Weidong Yang,
you are right.
This has been detected and modified in
IEEE P802.16-2004/Cor1-D1, 2005-02-11
11.4.1 DCD channel encodings
TTG in two byte length in PS size for SCa,OFDM,OFDMA
Kind Regards
Juergen Otterbach, Alcatel
> -----Ursprüngliche Nachricht-----
> Von: weidong yang [mailto:weidong_yang@NAVINI.COM]
> Gesendet am: Freitag, 4. März 2005 17:31
> An: STDS-802-16@listserv.ieee.org
> Betreff: [STDS-802-16] TTG may be too small for the scaleable OFDMA
>
> Dear all,
>
> On P.11 of 802.16-2004, TTG is defined:
>
> "3.63 transmit/receive transition gap (TTG): A gap between
> the downlink burst and the subsequent uplink
> burst in a time division duplex (TDD) transceiver. This gap
> allows time for the base station (BS) to switch
> from transmit to receive mode and SSs to switch from receive
> to transmit mode. During this gap, the BS and
> SS are not transmitting modulated data but simply allowing
> the BS transmitter carrier to ramp down, the
> transmit/receive (Tx/Rx) antenna switch to actuate, and the
> BS receiver section to activate. Not applicable
> for FDD systems."
>
> On P.500 of 802.16-2004, the insertion of TTG and RTG between
> downlink subframe and
> uplink subframe is shown.
>
> On P.659 of 802.16-2004, 8 bits are assigned for specifying
> TTG and RTG duration in PSs respectively.
>
> On P.643, PS is defined as 4/Fs, and Fs is defined in P.495
> as the sampling frequency of the OFDMA mode.
>
> For a 5 MHz OFDMA system, Fs is calculated as specified in P. 495:
> Fs=floor(8/7*5e6/8e3)*8e3=5712000.
>
> So the biggest TTG one can specify will be 2^8*4/Fs= 179.2717 µs.
>
> For 10 MHz and 20 MHz systems, TTG is limited to 89.2857 µs
> and 44.6272 µs respectively.
>
> The maximum TTG one can specify for 5, 10 and 20 MHz systems
> seems to be too small.
> For example, on P. 771 of 802.16-2004, for the 1.25 MHz
> bandwidth TDD OFDMA profile,
> TTG is required to be larger than 200 µs.
>
>
> One possible solution is to fix the unit used for specifying
> TTG and RTG.
> e.g. for all OFDMA systems, the unit can be fixed at 2.8 µs
> (which is the current unit (4/Fs) for the 1.25 MHz system).
>