Planning of Single Frequency Networks

For full format paper (including table, picture, graphic etc) Please open at   Planning of Single Frequency Networks


Subjects
• General aspects
• Network gain
• Internal network
interference
• Practical cases
• References
Single Frequency
Network
“A network of
synchronised
transmitting stations
radiating identical
signals in the same RF
channel”


Pros and Cons of SFNs
• Spectrum efficient due to
power distribution
• Network gain due to
simultaneous reception of
multiple useful signals
• No need to retune when
travelling through area
(mobile reception)
• No option for local
windows in programming
• Reduced bitrate due to
long guard interval
• Relay transmitters more
complicated
• More complicated
frequency planning
General
aspects
Pro Con
• MFNs and SFNs are based in principle on the same
network topology (main transmitters with auxiliary gap
fillers if necessary)


Application of SFNs
• SFNs can be used in small and large areas
– Extent of area is limited by internal network
interference
• SFNs can be used with all reception modes
– Most applications are in relation to indoor and
mobile reception
• SFNs can be used in a mixed configuration
with MFNs, e.g.
– Main transmitters in MFN and additional fill-in
transmitters in SFN mode
– Main transmitter supplemented by lower power
transmitters in towns to improve indoor reception


Network gain
• Network gain consists of two components
– Statistical gain due to higher change to receive a
signal. Location variation of the field strength is the
dominating factor
– Additive gain due to the increase in field strength
because of the incidence of two or more signal at
the receiving antenna
• Network gain varies:
– From point to point depending on the relative field
strength values
– Location variation for which the coverage is
calculated


Example 1
0.01 0.1 1 5 10 20 30 40 50 60 70 80 90 95 99 99.9 99.99
40
45
50
55
60
65
70
75
80
cumulative distribution function / %


Example 2
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40
Distance (km)
Field strength (dBuV/m)
37.5 m
37.5 m
network
statistical
Network gain as function of
distance between two equal
transmitters


Amsterdam
coverage
Practical case 1
1 transmitter
10 kW
2 transmitters
5 kW
Splitting of
one
transmitter
into two
with same
total power
to improve
coverage


Aspects regarding internal network
interference (1)
• Length of guard interval
• Delay between signals
– Transmitter separation distance
– Artificial delays
– Delays in distribution links
• Nuissance field of interfering signal
– Propagation path
– ERP
– C/N (system variant)
Internal network
interference
8
17
34
67
D/Tu μsec km
1/32 28
1/16 56
1/8 112
1/4 224
Example
T-DAB
246 μsec


Solving internal network
interference
• In most cases in frequency planning the
following measures are possible:
– Increase guard interval (one of the 4 options)
– Adding artificial delay at one of tx
– Reducing power
– Add fill-in transmitter
– Remove tx from SFN (that is: use different
frequency)
• Some times it is possible:
– Chose alternative site (with delay inside
guard interval)
– Use obstructions in propagation path
Internal network
interference
In general
internal
network
interference
is not a
major
problem
with DAB


SFN CH 34 1% time
Internal network
interference
Practical case 2
Internal network
interference


SFN CH 34 1% time
Artificial delay
5 μsec
Artificial delay
15 μsec
Practical case 2
Additional fillin
station
Other
SFN


SFN CH 34 Useful signals: 50% time
All interferers: 1% time