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Lab Report 98/01 By Neil Pickford |
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Draft - January, 1998
Selection Committee Updated Draft - April 1998
Final Release - June 1998
Report compiled by Neil Pickford
1. Introduction
1.1 Background
2. Equipment Operation
2.1 DMV COFDM Equipment
2.2 Zenith/Harris 8-VSB Equipment
2.3 Transmission Equipment
3. Tests and Measurements
3.1 Test Rig
3.2 DTTB into PAL Interference
3.3 PAL into DTTB Interference
3.4 CW into DTTB interference
3.5 C/N Threshold
3.6 Minimum Signal level
3.7 Spot Measurements
3.8 Echo Performance
7. Annex
7.1 DVB Comments
7.2 ATSC Comments
This report presents the results of laboratory testing at the Communications Laboratory of both the DVB - COFDM and ATSC - 8-VSB digital television modulation technologies. The systems have been evaluated under Australian 7 MHz channel conditions, primarily on VHF channel 8. These modulation systems have been evaluated as data pipes and no quality or performance measurements of the proposed video systems have been made.
Using bit error rates system parameters such as Carrier to Noise, Signal levels, Interference protection ratios, Doppler and Static Echo performance have been measured. Subjective assessment of DTTB into PAL interference protection levels has also been performed on a small sample of domestic television receivers. The systems have also been tested through real transmission equipment.
Areas such as UHF performance, Cable operation and Field testing were outside the scope of this investigation.
The laboratory tests have shown some performance differences between the systems however the laboratory tests by themselves do not provide sufficient basis to choose between the DTTB modulation technologies.
The data contained within this report will be one of many inputs to the recommendation of which digital television modulation Australia should adopt in the future.
1. Introduction
Digital media is rapidly replacing analog communications technology and recent research has allowed the concept of digital television broadcasting to be implemented. Such systems are already operating on satellite and cable systems around the world, however, the more difficult area of terrestrial transmission has only recently become possible. Presently there are 3 digital terrestrial television modulation systems being developed around the world. All of these systems are being developed overseas with the primary focus being on satisfying each regions specific problems. Accordingly any testing of these systems focuses on the system requirements within the developers' region. The broadcasting infrastructure in Australia is different to any of the countries that are developing these systems. The broadcast industry in Australia has an interest in evaluating the performance of these modulation technologies under typical Australian conditions. This report describes the results of laboratory testing of the European COFDM and American 8-VSB transmission systems, in the context of the 7 MHz Australian broadcasting infrastructure. Measurements were performed on a DMV System 3000 DVB-T pre-production receiver and a ATSC 8-VSB prototype receiver. In November 1996 the FACTS engineering specialists' group arranged a demonstration of over the air digital television in conjunction with the ITU-R Study Group 11 meeting in Sydney and the FACTS annual general meeting. This demonstration used the just developed DMV System 3000 DVB-T 7 MHz COFDM equipment. As part of this demonstration NEC Australia and Comsys loaned transmitters to the group to assist with the demonstration. It was decided at the completion of the demonstration that further testing of the COFDM 7 MHz system should proceed under Australian conditions. The DMV representatives returned the receivers to the UK and the rest of the equipment shipped to the Communications Laboratory in Canberra where the Laboratory test rig described in this report was developed. During this period, initial tests of COFDM into PAL protection ratios were undertaken. In late February 1997 the VHF receiver arrived back from the UK with upgraded 7 MHz system software and testing of the COFDM system commenced. Initially there were a number of operational system bugs which once corrected required the re-testing of the COFDM into PAL protection ratios. The objective was to conduct an extensive range of laboratory tests on the 7 MHz COFDM system in a 7 MHz environment and then take the receiver into the field and measure the real field performance of the COFDM system. In April 1997 the idea of testing the competing ATSC 8-VSB system was proposed and after many e-mails, faxes and conference calls the Zenith "Blue Racks" arrived on the 19th of June 1997. With 2 representatives from both Zenith and Harris present, testing commenced on the 8-VSB system and continued for around a month. Wherever possible, the same measurements that had been conducted on the COFDM equipment were also performed, in a similar manner, with the 8-VSB equipment. The 8-VSB equipment left the Communications Laboratory on 15th of August to return to the USA. Some retesting of the COFDM equipment occurred after the 8-VSB equipment left to verify the effects of test system changes and improvements that occurred during the course of the 8-VSB system testing. The COFDM equipment was shipped from the Communications Laboratory to Sydney during the 1st week in September 1997. The DTTB equipment then entered the next test phase with field trials and on air demonstrations of both the 8-VSB and COFDM systems in Sydney.
Section 2
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