1、 Rep. ITU-R BT.2139 1 REPORT ITU-R BT.2139 Diversity reception of digital terrestrial television broadcasting signals (2008) 1 Abstract Diversity reception of digital terrestrial television broadcast signals offers substantial improvement in coverage of television services. Planning parameters for m
2、obile reception can be found in Recommendation ITU-R BT.1368-7. The use of diversity receivers is increasing. The results of tests performed in Italy and Japan with mobile reception of digital terrestrial television can be found in this Report. Part 1 of this Report presents mobile diversity case re
3、ception field test regarding present DVB-T. It presents the results of a study carried out by RaiWay on the possibility to receive present digital terrestrial television (DTT) broadcasting (64-QAM, FEC 2/3) in vehicular mobility conditions. Herein is proposed a receiving system capable of properly m
4、anaging and possibly solving the typical problems concerning the reception of DTT broadcastings in vehicular environments and are outlined the results of a comparison between the performances achieved in several field tests by the proposed receiving system and a reference single antenna professional
5、 receiver. Part 2 of this Report presents mobile reception with four-branch space diversity for ISDB-T. Mobile reception of digital terrestrial broadcasting carrying a digital high definition television (HDTV) signal was successful with four-branch space diversity. The effect of 4-branch diversity r
6、eception in a moving vehicle for a 64-QAM-OFDM signal was experimentally investigated by using prototype hardware. Field-based experiments showed evidence of a drastic improvement in reception performance and a reduction in the required minimum field strength as compared to that obtained using singl
7、e dipole antenna. 2 Rep. ITU-R BT.2139 CONTENTS Page 1 Abstract. 1 Part 1 Digital terrestrial television: Mobile diversity case reception field test regarding present DVB-T . 3 1 Scope 3 2 Introduction 3 3 Carriers coherent sum diversity receiver system 3 4 Test development 4 4.1 Choice of the test
8、vehicle and of the best receiving antenna system 4 4.2 Analysis of available instruments (directly by RaiWay and with the cooperation of Rohde remarkably higher reception quality, both in terms of screen resolution and of available bit-rate, compared to the reception quality currently available or e
9、xpected by DVB-H broadcastings, allowing therefore to install high-quality display up to large-sized screen on board of vehicles (cars, vans, coaches, tramway cabs, trains, ); availability for the end user of a wide range of subscription-free contents. We assumed that this type of mobile DVB-T recep
10、tion can be achievable by the use of “diversity” receivers with carriers coherent sum (CCS) system. 2 Introduction Presently, broadcasted TV emissions in DVB-T standard allow Italian operators to cover the majority of the population resident in urban and rural areas. The network planning carried out
11、 by all DVB-T operators was targeted to guarantee the so-called “fixed antenna reception”, that is to say by means of a rooftop antenna. Also because of the Italian law constraints concerning electromagnetic pollution, said network planning considered the so-called “indoor reception” (without the us
12、e of external antennas) as a far secondary priority, and mobile reception was not included in the scope of work. In this market scenario the DVB-H standard was developed to the scope of allowing an adequate-quality mobile reception of a large number of programmes to be displayed on stand-alone porta
13、ble receivers approximately sized as mobile phones or PDA, capable of a battery life adequate to the enjoyment of the broadcasted services. The DVB-H Standard practically requires a QPSK or 16-QAM modulation. This limits the available bandwidth per single programme, and in order to broadcast several
14、 programmes in the same channel it is commonly accepted to limit the screen resolution of each programme according to the typical resolution performance of the screen generally available on handheld equipments (CIF or similar). Such a compromise can be considered as adequate for pedestrian mobile re
15、ception, but limits the achievable performance in the case of vehicular mobile reception (vehicles, bus in city or intercity service, trains.), where larger displays are typically implemented. It is here useful to point out that vehicular reception can take advantage of the on-board electrical power
16、 plugs, and therefore any concern about battery duration is superseded. 3 Carriers coherent sum diversity receiver system A diversity system commonly implies the employment of a receiving system whose main characteristic is the redundancy of some or all of the functional parts included in it. Each o
17、f the redounded part is in all capable to carry out its own task independently from the concerned “twin”, 4 Rep. ITU-R BT.2139 and from an overall point of view we can say the redundancy allows to choose dynamically, moment by moment, the part which is offering the best performances. In short, the c
18、oncept of diversity implies the concept of “choose of the best receiving condition”. The CCS diversity system represents a remarkable step ahead, and it can be adopted thanks to the COFDM modulation used in DVB-T standard. In the CCS case the RF system is completely redounded: Each of the two differ
19、ent antennas is connected to one receiver. Each receiver demodulates the carrier mask of the received signal. The two receivers are linked through a data bus by which receiver A “sends” to receiver B the carrier mask of the received signal. An appropriate circuit allows to re-synchronize (coherent)
20、the two carrier masks to add, carrier by carrier, the amplitude of each pair of matching carriers (sum in phase of carriers amplitude, sum in power of the noise). The idea of “choose” here is definitely replaced by the idea of “merge”: even in case of two received signals, each of them is not lockab
21、le by the receiver, it could happen (and it happens!) that a signal, whose carrier content is the sum of the carrier content on each of the received signals, can be perfectly locked and decoded. This receiving mode can be usefully adopted in mobile reception. Our field test testifies the correct ope
22、ration in vehicular mobility conditions of the CCS receiver under test. Given to the “consumer” nature of CCS receivers nowadays available in the market, it is not yet possible to carry out quantitative objective measurements on the reception quality in vehicular mobility conditions, because of cons
23、umer receivers supply no indication on the necessary data to determine the objective quality of reception. 4 Test development Our field test has been developed in four consequent steps: Step 1: Choice of the test vehicle and of the best receiving antenna system. Step 2: Analysis of the available ins
24、truments (directly by RaiWay and with the cooperation of Rohde it was strictly requested to select a receiver designed to mobile use. Some high-end measurement instruments, designed to laboratory (stationary) use, revealed themselves definitely not adequate to our purposes, because they lose any sig
25、nal locking as far as the vehicle speed exceeded 10-20 km/h. To ensure a conservative comparison, the choice of the reference single antenna receiver led us to a professional Rohde the remaining two inputs were connected to the decoded video out of the CCS receiver, in order to compare the performan
26、ce of the CCS receiver inner decoder Vs. the reference decoder (R it is an average speed journey (due to traffic congestion) but characterized by frequent obstacles in fast movement across the transmitter line of sight (the vehicles on adjacent tracks and on the opposite tracks) which cause rapid an
27、d continuous changes of near reflection conditions. Path 2: Monza Sesto Calende and back along the A4, the A8 and the A26 highways; it is a high speed journey (thus compliant with the 130 km/h Italian speed limit) with some passages in earth trench. Path 3: A circular route along an urban Milan city
28、 ring; medium average speed (70 km/h speed limit in some parts, 50 km/h in the rest), wide roads surrounded by 5/7 storey buildings, one tramway overhead power line in the centre of the track, intense but flowing traffic. Path 4: A route in the historical centre of Milan; crowded traffic, narrow roa
29、ds surrounded by high buildings (no direct beam, pure Ricean channel). 6 Rep. ITU-R BT.2139 For all of the four paths we set the receivers on channel 64, on which the so-called RAI “MUX A” is radiated from the sites of Valcava (mountain site at the borders between the province of Lecco and Bergamo)
30、and from the mountain site of Campo dei Fiori (Varese), operating in SFN with two other systems in Lombardy, with 64-QAM modulation and 2/3 FEC. The field tests were carried out during September and October 2006. 4.4 Analysis of the acquired data We have herein to testify that the performances shown
31、 in this field test by the single antenna receiver have no reference to the proper performances of the diversity receiver Rohde the performances shown in this field test refer only to the case of the same professional receiver in a mobile environment, but under the specific conditions in which just
32、one of the two inlets of the diversity receiver is connected to a receiving antenna. Said receiver is composed by two independent receivers and one logic of selection; therefore if connected to a single receiving antenna it performs just in the same way of a single antenna receiver of similar capabi
33、lities and quality. Rep. ITU-R BT.2139 7 The performance achieved in this field test by the TSM-DVB cannot therefore be used, in any way, even indirectly, in order to estimate the performances of the same receiver when used in its native mode of “diversity receiver”. Path 1: Monza Dalmine and return
34、 along the A4 highway. This path has been evaluated in two parts: outward and return. The outward path has been monitored between the toll stations of Agrate and Dalmine, in order to evaluate the systems in an exclusively highway background. The return path has been monitored between the toll statio
35、n of Dalmine and the RaiWay Control Centre in Monza, in order to include, beyond to the highway environment, a sample of ordinary, suburban and crowded roads. We have to point out how the single antenna system allows the receiving when the vehicle is still (traffic lights, crossings, queues) or move
36、s itself at a very low speed because of the crowded traffic. As soon as the traffic constraints cease, the single antenna system typically stops working. The CCS system achieve an optimal performance also in typical highway background (looks at the outward path). Path 2: Monza Sesto Calende and retu
37、rn along the A4, the A8 and the A26 highway (outward) and Milan North Ring, “Peduncolo”, and the Milan/Meda freeway (return). As above, the path has been evaluated in two parts, outward and return. The outward path has been monitored the RaiWay Control Centre in Monza and the highway toll station of
38、 Sesto Calende, in order to evaluate the systems in a highway background with heavy traffic (A4), and then with high speed (A8) with various passages in earth trench, mainly after the junction to Sesto Calende (A26). The return path has been monitored between the toll station of Sesto Calende and th
39、e RaiWay Control Centre in Monza, leaving the highway A8 at the New Milan Fair junction, going on along the Milan North Ring, the “Peduncolo” and the Milan/Meda freeway until Monza, in order to include, beyond to the highway feature, a sample of a freeway with high traffic and high speed. Like in th
40、e previous path, the single antenna system allows the receiving when the vehicle is still (crossings, queues) or moves itself at a very low speed because of the crowded traffic. As soon as the traffic constraints cease, the single antenna system typically stops working. Along fast highway paths (A8/
41、A26) the single antenna system has not been capable to lock any signal for 24 (outward) and 22 (return) minutes. The video interruptions suffered from the CCS system are concentrated close to Sesto Calende, where the highway A26 often runs in earth trenches and where is the fixed antenna reception b
42、orderline. In any case the CCS system confirms an outstanding performance in both paths. Path 3: Circular route along an urban Milan city ring, the so-called “third ring”. This path allows us to evaluate the performance of the systems in a city background: medium average speed (70 km/h speed limit i
43、n some parts, 50 km/h in the rest), wide roads surrounded by 5/7 storey buildings, one tramway overhead power line in the centre of the track, intense but flowing traffic. Once again, we have found that the single antenna system allows the receiving when the vehicle is still (traffic lights, crossin
44、gs, queues) or moves itself at a very low speed because of the crowded traffic. As soon as the traffic constraints cease, the single antenna system typically stops working. It is useful to consider that the reference single antenna receiver is a professional product specifically designed for mobilit
45、y use. Further to the overall time of successful receiving, equal to 51% of the total time of the path, the total number of registered breakdowns (114, that is to say one breakdown per every 53 s on average) from a practical point of view prevents any possible audience. Also in this path the CCS sys
46、tem achieves a high-level performance, with 99% total time successful receiving and just 10 breakdowns. Path 4: Circular path in the historical centre of Milan; crowded traffic, narrow roads surrounded by high buildings (no direct beam, pure Ricean channel) in the narrowest and more winding streets
47、open to private cars in the historical centre of Milan. This type of path has been intentionally chosen in order to test the performance of the systems in really extreme conditions: roads just a little wider than the vehicle itself, and surrounded by high historical buildings with four or five floor
48、s, and overhead power lines for the public lighting system. For sure a very challenging test. Beyond the usual indications about the operation of the single antenna system, it is worth pointing out that 8 Rep. ITU-R BT.2139 inside the more critical part of the path, the single antenna system remaine
49、d continuously unlocked in two major circumstances: the former lasting 22 min and the latter 12 min. The performance of the CCS system is not at all negative (91% total time successful receiving), but suffers for the critical receiving conditions: practically all of the 34 breakdowns, thus of limited duration (all of them lasting a few seconds, with the exception of two, respectively lasting 4 31“ and 1 15“) took place inside of the more critical part of the path. Considering the mountain location of the transmitting sites (Valcava and Campo dei Fiori), we believe that the CCS s
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