Mobile Digital TV Technology for the Terminal

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Mobile Digital TV Technology for the Terminal

• Dave Evans, Sri Andari Husen, Hans Brekelmans,
  Peter Massey
• Philips Research Laboratories

Philips first with a mobile phone
demonstration. 3GSM, February 2005
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Technology for the Terminal

• Technical challenge
• RF Tuner
• Antenna
• TV coexistence in the phone
• Channel decoding dealing with Doppler
• What next?
• Conclusion

3
Technical Challenge

• Reception in all situations
• Good picture quality
• Limited impact on phone battery life
• Global usage
• Mobile TV is now addressing the issues that are
  familiar in the design of mobile terminals
• Size
• Performance
• Reception on the move
• Low power
• Multi-standard

4
TV in the phone Generalised architecture
Display
Baseband controller interface

• Additional elements for broadcast TV reception

Software
Philips supplies complete system solutions for
the mobile terminal
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RF Tuner

• Major challenge was power consumption
• Starting point 500mW
• Now gt100mW (gt5 with DVB-H time slicing)
• Low/zero IF design
• Minimal off-chip components
• 470 to 860 MHz operation
• Separate on chip LNA for 1452 to 1675 MHz
  operation
• On-going work to improve performance

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Mobile DTV Antenna

• Two issues
• Close proximity between mobile DTV and GSM
  antennas
• Common ground plane
• Coupling between them disturbs the GSM antenna
  and affects its performance
• Co-design of the GSM and Mobile DTV antennas is
  essential
• Signal coupling from GSM to mobile DTV antenna is
  high
• Need to incorporate GSM signal blocking
• Ideally continuous operation from 470 to above
  700 MHz
• Limited to 700 MHz to assist GSM coexistence

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Interaction between GSM DVB-H
Strong coupling, poor isolation
DVB-H port
GSM feed
GSM
DVB-H
Reflection phase matters!
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Interaction between GSM DVB-H
open circuit at DVB-H monopole
DVB-H port
GSM feed
short circuit at DVB-H monopole
GSM S11

• GSM seriously effected by impedance of DVB-H
  circuit. Co-design is necessary.

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Antenna RF Tuner
Feed tab
Integrated GSM filter

• Compact PIFA
• 470 to 700 MHz continuous operation
• Antenna includes a GSM trap

Antenna RF tuner
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TV Coexistence in the Phone

• Interference from GSM900 transmissions due to
  very close co-location
• DTV receiver blocking
• 58 dB isolation between GSM TX and mobile DTV
  receiver is required
• Potential solutions
• Isolation between antennas limited to between 6
  to 10 dB
• Can be improved by use of GSM trap within mobile
  DTV antenna, 20 dB
• Managing GSM transmission at the terminal
  limited scope
• Managing DVB-H transmissions not possible
• Power cancellation not very promising
• Receiver filter, good solution but requires
  frequency separation restricts channel usage.
  TV channel 50 (700 MHz) OK, extending this to
  54/55 desired
• Coexistence best achieved by filter before TV RX
  antenna with GSM trap
• Out-of-band noise high pass filter at GSM TX
  output

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Broadband matching filtering, PIFA to LNA
NF lt4dB, 480 to 720 MHz G gt17dB, 470 to 710
MHz 50dB attenuation above 877MHz
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Channel Decoding

• Key issue for mobile TV
• Reception at high vehicle speed
• Problem
• Impact of Doppler effects on OFDM
• Channel changes during symbol period
• Inter carrier interference (ICI)
• 150 kph equates to typically 100 Hz Doppler
• 8k DVB-T mode has 1.1 kHz subcarrier spacing
• Solution
• Channel estimation and Doppler compensation
• ICI cancellation

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Mobile multipath channel

• The faster the vehicle, the more severe the ICI,
  the poorer the reception.
• Challenge DVB-T/H 8K mode (fs 1.12 kHz)
  reliable high throughput reception under high
  Doppler frequency (?10 fs) with low complexity.

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Channel Estimation

• The received signal in frequency domain is
  approximated as follows
• where
• H is the complex channel transfer function
  vector for all the subcarriers
• H is the the temporal derivative of H
  (proportional to vehicle speed)
• ? is the fixed Inter-Carrier Interference
  spreading matrix
• a is the transmitted data vector
• n is a complex circular white Gaussian noise
  vector

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Channel Estimation
OFDM symbol

• Estimation of H rather than time interpolation,
  frequency interpolation
• Estimation of H calculated from H estimation of
  past and future symbols

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Inter-carrier Interference

• ICI level is not constant but varies over
  frequency
• ICI level per sub-carrier can be estimated from
  H
• Soft demapper takes into account ICI level per
  sub-carrier, rather than average ICI power

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Basic Channel Decoding Scheme
Log likelihood ratio per bit
Soft demapper
Data Estimation
To de-interleaver Viterbi decoder
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Overall Scheme
Log likelihood ratio per bit
Data Estimation

• To de-interleaver Viterbi decoder

(Using regenerated ICI)
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Performance after Viterbi decoder when H is known
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Final points on channel decoding

• Channel model
• MBRAI specification defines the use of COST 207
  TU6 profile
• Modeling of the Doppler spectrum is not defined
• System performance is very sensitive to model
  parameters
• No conformance tests are defined in for the
  complete channel model
• Caution needs when comparing performance

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What next?

• On-going work to improve performance
• Further reductions in power consumption
• Move to a CMOS architecture
• Single chip solution that includes channel
  decoder
• Emerging RF filter technologies including MEMS
• Antenna diversity, extra dBs are very useful
  gain of a few dBs?
• Technology will evolve to meet that in the
  terminal, convergence!
• Multi-standard solutions
• Needed now to support multi-standard multi-band
  cellular requirements
• Also required for WLAN/BT, mobile DTV and GPS
• Reconfigurable, highly digitised radios
• Coexistence in the phone
• Exploitation of multiple radios to assist mobile
  DTV reception - diversity

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Conclusion

• Keys issues and challenges are understood
• Solutions are available now
• On-going process of performance improvement
• Continuing to maintain the leading position of
  Philips

Complete systems solution shown at IFA, Berlin,
September 2005
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