DAB+ Basics DAB+ Family of Digital Transmitters and DAB+ Coverage
T-DAB Receiver testing
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Transcript of T-DAB Receiver testing
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T-DAB Receiver testingT-DAB Receiver testing
Richard Drinkwater Radiocommunications Agency
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IntroductionIntroduction
Complaints received from DAB listeners about poor reception
Is this due to poor service coverage or poorly performing receivers?
Receiver tests performed to establish the sensitivity of a selection of current domestic receivers
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TechnologyTechnology
DAB technology– Benefits
• More rugged transmission format• Much less spectrum usage – capable of
carrying 6 quality audio stereo programmes in 1.5MHz against 2.2MHz per programme for complete mainland UK FM coverage
– Drawbacks• More complicated (= expensive) receivers for
the listeners
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UK Spectrum Occupancy FM v DABUK Spectrum Occupancy FM v DAB
BBC Radio 2 BBC Radio 3
88.0
90.2
92.4
MHz
2.2MHz 2.2MHz
BBC national radio
1.5MHz
Local radio
1.5MHz
Digital One (National6 stereo programmes + data
1.5MHz
221.
310
222.
810
MHz
223.
186
224.
686
224.
898
226.
398
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BS 50248:2001 test criteriaBS 50248:2001 test criteria
BS EN 50248:2001, “Characteristics of DAB receivers”– Minimum power of -81dB(mW) for a BER
of 10-4 at the convolutional decoder output of the receiver (VHF and L-band)
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MethodologyMethodology
Objective tests were not possible without connections to internal circuitry
Subjective tests were performed which established the minimum field-strength at which audio impairments (more than 1 click in 5 seconds) were heard
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Test set-upTest set-up
GTEM! cell
DABreceiver
X
V volts
Measuring voltage V and height X enables a known field strength (V/m) to be established at the receiver under test
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GTEM! cellGTEM! cell
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Results on channel 12D Results on channel 12D (229.075 MHz)…(229.075 MHz)…
UEPprotectio
n
Bit ratekb/s
Sampling
ratekb/s
DABRx #1
DABRx #2
DABRx #3
DABRx #4
3 48 24 44.74 31.15 44.80 41.74
3 64 24 43.74 30.15 39.80 41.74
3 96 48 45.74 31.15 46.80 40.74
3 112 48 45.74 32.15 48.80 41.74
3 128 48 44.74 31.15 44.80 42.74
3 160 48 45.74 31.15 46.80 41.74
3 192 48 45.74 33.15 44.80 42.74
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……graphicallygraphically
Audio break-up Field Strength
20.0
25.0
30.0
35.0
40.0
45.0
50.0
55.0
60.0
48 64 80 96 112 128 144 160 176 192
Audio bit rate
dB
µV/m
DAB # 1 DAB # 2
DAB # 3 DAB # 4
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which means…which means…
For a field strength of 45dBµV/m, the receiver input power at 222MHz would be-77dBm if the receiver had a 50Ω input impedance, and a dipole antenna
Tested receivers did not, and the standard is written in antenna port power terms, so it is impossible to equate the tests with the standard
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Receivers testedReceivers tested
DAB #1– Miniature personal receiver using earphone
lead as antenna DAB #2
– Portable receiver with rod antenna DAB #3
– Portable stereo unit with rod antenna DAB #4
– Miniature personal receiver using rod antenna
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Service planning criteriaService planning criteria
National DAB services– Edge of service area is considered to be when
field strength is 58dB(µV/m) at 10m above ground level for 99% locations, 99% of the time
Field strength at 1.5m agl is very approximately 10dB lower than at 10m agl in open terrain
In a single frequency network, other transmitters within about 70km (246us) add to the signal available to the receiver
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Portable equipmentPortable equipment
Inefficient antennasLow antenna heightBody shieldingBuilding shielding and reflections
– Shielding attenuates the signal– Local reflections tend to add to the
signal received
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Analysis of test methodAnalysis of test method
Strengths– Straightforward, repeatable method
using GTEM! cellWeaknesses
– Subjective assessment – No multipath reception distortion– Incomparable with BS test method
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Some thoughtsSome thoughts
Assuming a field strength at the edge of the service area of approximately 48dBµV/m at 1.5m agl, it would appear that the tested receivers would work in free space conditions. Due to shielding effects there is probably inadequate margin in sensitivity (in 3 out of the 4 tested receivers) for satisfactory reception under everyday usage conditions.
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Possible solutionsPossible solutions
Very low power fill in transmitters– Relatively inexpensive solution
• No international clearance required
Improve receiver antenna performance– Particularly the match to input circuitry
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ContactsContacts
[email protected] [email protected]
RTCGRadiocommunications AgencyWhyteleafe HillWhyteleafeSurreyCR3 0YY +44 (0)20 8655 8300