Communications Laboratory

1
Communications Laboratory

• DTTB Equalisation

Presentation by Neil Pickford
2
DTTB - Channel Estimation

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

3
Channel Estimation Equalisation
ATSC
Time
DVB-T
Time
4
Data Multiplex - 8-VSB
5
8-VSB Segment Sync Data
Symbol Duration 93 ns
6
Digital Modulation - 8-AM
7
6
5
4
3
2
1
0
Before Equaliser
After Equaliser
8-VSB - Coaxial Direct Feed through Tuner on
Channel 8 VHF
3 Bits/Symbol
7
8-VSB - Field Sync
Field Sync is Repeated Every 24 ms
8
8-VSB - Field Sync
7
6
5
4
3
2
1
0
Before Equaliser
After Equaliser
9
DVB-T Transmission Frame
2k mode - 3906 Hz - Kmax1704 8k mode - 977 Hz
- Kmax6816
Kmin0
Carrier Spacing Position
Kmax
Data
TPS - Pilot
Scattered Pilot
Continuous Pilot
Symbol Duration 256 us (2k) or 1024 us (8k)
10
DVB-T - Estimating the Channel
A
A
B
B3/4A1/4E
C
C1/2(AE)
D
D1/4A3/4E
E
E
A to E - 1.024 ms (2k) or 4.096 ms (8k)
For a varying transmission channel DVB-T
estimation is 23.5 times faster than ATSC
11
Estimation Rate Comparison

• ATSC Equaliser is updated every 24 ms (260 000
  symbols)
• DVB-T Equaliser is updated every symbol period
  (256 us). 1/12 of data carriers are pilots
• DVB-T Full Channel estimate is available every 4
  symbols (1.024 ms)
• For a varying transmission channel DVB-T
  estimation is at least 23.5 times faster than ATSC