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1
Compatibility of Digital Broadcasting and Mobile Services
Regional Seminar on Digital TV Broadcasting
Algiers, 4-5 December 2007
Presented byJan Doeven
Where’s mypicture gone?
or
2
Interference scenarios
Non-co-sited transmitters
Moving interferencesources
Cross border interference
Digital TV receiver
Selectivity
Channel interactions
Concerns about Digital DividendAnalogue TV transferred to
digital
Digital dividend
Band IV/V spectrum
If part of the
Digital Dividend is
allocated to mobile
communication services,
black screens could be
expected.
3
Non co-sited transmitters:The issue
Non co-sited transmitters are increasingly used because of:
Different network operators for the same type of service
Different network structures for different service types
The interference is mainly localized around the interfering transmitter site
Non co-sited transmitters: Coverage gaps
Field strength
Distance
Wanted field
strength
Interfering field
strength
Maximum acceptable difference between
wanted and unwanted signals
Service area
Interference area
Wanted DVB-T transmitter
Channel N
Where’s my picture gone?
Non co-sited transmitter
Channel N+x
5
Non co-sited transmitters: The solution
Careful planning using mitigation techniques:
Interference between non co-sited transmitters is an issue, but still is manageable through careful planning
Remedy Comment
Cross polarisationOnly effective in case of rooftop reception
Power adjustment Coverage of second transmitter may not be sufficientAntenna adjustment
Adequate frequency separation
Provided that GE06 Plan entry with at least 4 channels difference is available
Fill-in transmitter As SFN; relative expensive
6
Moving interference sources: The issue
Mobile communication systems:
The Downlink is technically similar to broadcasting and therefore can be controlled
The Uplink is initiated from moving terminals and therefore can not be controlled
Mobile hand-heldDVB-T receiver
Radiated energy :Hand-held to DVB
Moving interference sources:Portable –indoor and outdoor- reception
Each GE06 Plan entry has a specified reception mode
Portable reception
Portable or rooftop reception
Rooftop reception Portable
(indoor and outdoor)
possible in limited area because of
high required field strength
8
Moving interference sources: New convenient reception modes
Portable antennas
Indoor reception
USB stick receivers
Hand-held receivers
Mobile in-car receivers
Portable and mobile reception can be exposed to interference from mobile uplinks
at very short distances (few metres)
Where’s my picture gone?
Band partitioning, with:
Sufficient guard bands
Adequate maximum transmitting power
Sufficiently low out of band emissions
9
Moving interference sources: The solution
Guard band
Cross border interference:to the Mobile service!
Uplink reception at Base station is very sensitive
Sub-band use is not mandatory,
Neighbouring country may continue to use high power broadcasting transmitters in the same sub-band
Cross border coordination becomes very difficult
10
Cross border interference:The issue
Mobile hand-held tx
Radiated energy :Hand-held to Base station
Base station receiver
Channel N
DVB-TtransmitterChannel N
Interfering Radiated energy :DVB to Base station
Country A Country B
Where’s my picture gone?
Receiver selectivityOverloading and N+9 issues
Source: BBCChannel offset
Average values of 7 DVB-T receivers
64QAM 2/3
C/I (dB)
Receiver selectivity Performance
Out of band protection ratios below specifications under normal operating conditions
Specifications exceeded in case of overloading.
In order to improve compatibility out of band performance need to be improved.
Channels interactions:some band-plan examples
N+9
DVB-T channel where there could be N+9 interference on some receivers if overloaded
Guard band or duplex gap (between Downlink and Uplink)
16
CONCLUSIONS
Careful planning is needed to avoid interference between non co-sited transmitters;
DVB-T transmitters and mobile base stations.
Interference from mobile uplink transmissions could be an issue even with sub band operation;
Needs careful investigations.
Use of same channel by DVB-T and Mobile uplinks will in borders areas will give severe restrictions to mobile service.
Improved digital receiver performance with regard to interference is required;
In particular in case of overloading.