Mobile Digital TV Technology for the TerminalDave Evans, Sri Andari Husen, Hans Brekelmans, Peter MasseyPhilips 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

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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

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TV in the phone – Generalised architecture

Additional elements for broadcast TV reception

TV tuner

Channel decoder

Media processor

Display

Cellular transceiver

Baseband controller+ interface

Coexistence

+ 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 >100mW (>5% 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

Reflection phase matters!

GSM DVB-H TV filter must bereflective at GSM

GSMfeed

DVB-Hport

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Interaction between GSM & DVB-H

open circuit at DVB-H monopole

short circuit at DVB-H monopole

GSM S11

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

GSMfeed

DVB-Hport

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Antenna + RF Tuner

• Compact PIFA

• 470 to 700 MHz continuous operation

• Antenna includes a GSM trap

Antenna & RF tuner

Feed tabIntegrated GSM filter

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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 <4dB, 480 to 720 MHz G >17dB, 470 to 710 MHz50dB 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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• 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.

Mobile multipath channel

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Channel EstimationThe 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)

• Ξ is the fixed Inter-Carrier Interference spreading matrix

• a is the transmitted data vector

• n is a complex circular white Gaussian noise vector

Wanted received signalInter-Carrier Interference

Noise

naHaHy }'{diag}{diag

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Channel Estimation

• Estimation of H: rather than time interpolation, frequency interpolation

• Estimation of H’: calculated from H estimation of past and future symbols

OFDM symbol

frequency

time

pilots empty carriersdata

carriers

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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

y

H

a

channel estimation

Soft demapper

'H

Data Estimati

on

Log likelihood ratio per bit

To de-interleaver & Viterbi decoder

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Overall Scheme

y

H

a

channel estimation

Soft QAM demapper

'H

Data Estimati

on To de-interleaver & Viterbi decoder

ICI cancellatio

n

'y

(Using regenerated ICI)

Log likelihood ratio per bit

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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