The Effects of Narrowband and Wideband Public Safety Mobile Systems Operation (in television channels 63/68) on DTV and NTSC Broadcasting in Television Channels 60‑69 (746 MHz‑806 MHz)
CRC Report Number CRC-RP-2003-001
Douglas W. Prendergast, P.Eng,
Benoit Ledoux, ing., Sébastien Laflèche,
Dr. Yiyan Wu, Dr. Xianbin Wang,
Bernard Caron, P.Eng.
Ottawa, 30 April 2003
Table of Contents
- Executive Summary
Points of view or opinions expressed in this document are those of the authors and do not necessarily represent the official position of Industry Canada. This information is provided with the express understanding that proprietary and patent rights will be protected
As part of the development of spectrum policy proposals to designate a modest portion of spectrum for mobile services such as Public Safety (PS) in television broadcasting channels 63 and 68, Industry Canada required an assessment of the interference potential between Broadcasting and Mobile services. The goal of this study is to assess the impact of PS communications on the performance of both analog and digital television broadcasting in TV channels adjacent to 63/68 specifically in order to allow the co-existence of broadcasting and public safety services. While Industry Canada has indicated that only television channels 63/68 will be designated for public safety use in the near term, we have also provided the co-channel results of our assessment that may be relevant in the longer term i.e. when the transition from analog to digital television broadcasting has been completed.
The results of the assessment would allow Industry Canada to establish the appropriate interference protection criteria in order to enable the two services to share adjacent spectrum and co-exist on an interference-free basis. This assessment could also assist the Department in determining the means and conditions under which public safety services could use a modest amount of spectrum in these channels without negatively impacting the roll out of digital television in Canada.
To study the impact of PS interference into analog National Television Standards Committee (NTSC) and Digital Television (DTV) channels adjacent to channels 63/68, Industry Canada's contracted the Communications Research Center (CRC). Also, CRC carried out testing on sharing the spectrum between the two services on a co-channel basis.
The technical parameters used by the CRC study relating to transmitter power, emission limits, spectrum efficiency, channel bandwidth and the number of required PS channels, were obtained from Canadian Sources and from FCC documentation.
From the parameters obtained, a test plan was developed to evaluate the effects of interference from single and multi-channel PS channel transmitters on the performance of NTSC and DTV broadcasting.
The single channel tests were done to determine the effects of the interference created by a single channel (narrowband and wideband) PS transmitter in channels 63/68 into adjacent channel DTV or NTSC transmission. The Multi channel tests were done to determine the effects of a typical combination of some narrowband and wideband PS transmissions in channel 63/68 into adjacent DTV or NTSC channels. The multi channel tests were also done to determine the need for a guard band between the PS and the TV channels.
As no PS equipment was available, CRC used an Arbitrary Function Generator (AFG) to create the test signals. These PS test signals were used to determine the Desired to Undesired (D/U) ratios for the DTV and NTSC TV signals against PS interference at the Threshold Of Visibility (TOV) for DTV and at a level defined by the ITU-R3 (grade 3 — video or audio slightly annoying) for NTSC.
The purpose of the single channel tests is to determine the effect of the interference created by a single narrowband or wideband PS channel transmitting into DTV or NTSC services on a co-channel or adjacent channel basis. The single channel test results show the following:
Co-channel PS single channel Interference into DTV
- Under co-channel conditions, a D/U of at least 15 dB is required in general for DTV threshold performance over most of the channel bandwidth. However, placing PS channels in the vicinity of the DTV pilot and modulation carrier frequency (around PS channel 480) will require about 5 dB more protection.
- About 6 to 10 dB less protection is required if the PS channels are placed within the DTV receiver's notch filter bandwidth1.
Adjacent channel PS single channel Interference into DTV
For Adjacent Channel Interference, the results show that a modest amount of upper and lower guard2 band would provide enough protection at the grade B equivalent contour of a DTV station if the transmitters were co located3.
- For the upper adjacent PS channel about 200 kHz of guard band taken inside PS channels 63/68 would provide a D/U better than -20 dB in the DTV.
- For the lower adjacent channel, about twice as much guard band may be required.
Co-channel PS single channel Interference into NTSC
Single channel results for NTSC show the requirement for a D/U of about 50 dB for good NTSC performance. A few dB of additional protection will be needed around the NTSC visual, chroma and audio carriers.
Adjacent channel PS single channel Interference into NTSC
For Adjacent Channel Interference, the results show that around 200 kHz of upper and lower guard band would allow for a D/U better than 0 dB into the NTSC channel. This would provide enough protection at the grade B equivalent contour of a NTSC station if the transmitters were co-located3.
The purpose of the multi channel test is to determine the effects of a typical combination of narrowband and wideband PS channels transmitting into DTV or NTSC services on a co-channel or adjacent channel basis into DTV and NTSC.
Co-channel PS multi channel Interference into DTV and Adjacent channel PS multi channel Interference into DTV.
- The D/U requirement is similar to a DTV co-channel interferer when 22 to 244 PS channels are used i.e. PS can be treated as an equivalent DTV signal.
Co-channel PS multi channel Interference into NTSC
- The D/U requirement is similar to a DTV co-channel interferer when 22 to 24 PS channels are used i.e. PS can be treated as an equivalent DTV signal.
Adjacent channel PS multi channel Interference into NTSC
- For lower adjacent channel, the D/U requirement is similar to a DTV co-channel interferer when 22 to 24 PS channels are used i.e. PS can be treated as an equivalent DTV signal.
- For the upper adjacent channel, in some cases, PS was up to 5 dB worse than an equivalent DTV signal. This is because, in this case, the PS signal is close to the NTSC video carrier, and the NTSC signal sensitivity to the interference is frequency dependent.
In the case of interference to NTSC, it should be mentioned that the NTSC threshold is rather softly defined. The threshold was defined as an ITU Grade 3 picture (slightly annoying). Even a value of 5 dB below the adjacent channel threshold will not cause a signal drop out, but only a loss of around 0.5 ITU grade. Therefore, in the case of multi channel systems, for planning purposes, the PS multi carrier system may be treated as a DTV system since, within the margin of experimental error, the DTV Canadian planning parameters are either met or exceeded by the multi channel PS results.
1 It is noteworthy that not all DTV receivers have notch filters implemented, as this is not mandatory in the specifications. Also, it is expected that this filter will not be implemented anymore once the NTSC system is turned down.
2 This guard band is assumed to be removed from the PS channel bandwidth (inside channels 63 and 68), so that adjacent TV channels are not affected.
3 Co located means a PS transmitter at the same location of the TV transmitter or with in a radius of up to 8 km from the TV transmitter.
4 These are the maximum numbers of narrowband and wideband channels combinations allowed under practical implementation scenario for any one combiner. For a lessor number of channels, a correction factor will have to be applied to the current results.
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