Communications Laboratory DTTB Equalisation Presentation by Neil Pickford

Communications Laboratory DTTB Equalisation Presentation by: Neil Pickford 1

DTTB - Channel Estimation The Terrestrial transmission channel is continuously varying (position & time) n Variations occur in Amplitude, Phase & Frequency n To correct for this variation Information needs to be added to the transmission to quantify the channels response at any instant n Equalisers in the Digital receiver use this information to remove these transmission impairments n 2

Channel Estimation & Equalisation ATSC Time DVB-T Time 3

Data Multiplex - 8 -VSB 4

8 -VSB Segment Sync & Data Symbol Duration 93 ns 5

Digital Modulation - 8 -AM 7 Before Equaliser 6 5 4 3 2 1 0 After Equaliser 8 -VSB - Coaxial Direct Feed through Tuner on Channel 8 VHF 3 Bits/Symbol 6

8 -VSB - Field Sync is Repeated Every 24 ms 7

8 -VSB - Field Sync 7 Before Equaliser 8 6 5 4 3 2 1 0 After Equaliser

DVB-T Transmission Frame Kmin=0 9 2 k mode - 3906 Hz - Kmax=1704 Kmax Carrier Spacing & Position 8 k mode - 977 Hz - Kmax=6816 Data TPS - Pilot Scattered Pilot Continuous Pilot Symbol Duration 256 us (2 k) or 1024 us (8 k)

DVB-T - Estimating the Channel A B C D E A B=3/4 A+1/4 E C=1/2(A+E) D=1/4 A+3/4 E E A to E - 1. 024 ms (2 k) or 4. 096 ms (8 k) For a varying transmission channel DVB-T estimation is 23. 5 times faster than ATSC 10

Estimation Rate Comparison ATSC Equaliser is updated every 24 ms (~260 000 symbols) n DVB-T Equaliser is updated every symbol period (256 us). 1/12 of data carriers are pilots n DVB-T Full Channel estimate is available every 4 symbols (1. 024 ms) n For a varying transmission channel DVB-T estimation is at least 23. 5 times faster than ATSC n 11