WO2005109704A1

WO2005109704A1 - Method for operating a dab communication network

Info

Publication number: WO2005109704A1
Application number: PCT/NL2005/000339
Authority: WO
Inventors: Willem Toerink
Original assignee: Brasned Enterprise B.V.
Priority date: 2004-05-10
Filing date: 2005-05-03
Publication date: 2005-11-17
Also published as: NL1026149C1

Abstract

The invention relates to a method for operating a T-DAB communication network (T, terrestrial; DAB, Digital Audio Broadcast) for a service area, the service area being greater than the maximum DAB transmitter distance A. The T-DAB signals are transmitted to the service area by means of low output DAB transmitters mounted upon fixed terrestrial mounting devices (2), the mutual distance a between the DAB transmitters being less than half of the maximum DAB transmitter distance A (a ≤ 0,2A). Furthermore the invention relates to a method for obtaining information on a receiver by a user by means of a combined T-DAB band-III and T-DAB L-band transmitter network. Both transmitter networks are centrally operated by a central DAB server.

Description

TITLE Method for operating a DAB communication network.

The present invention relates to a method for operating a DAB communication network. Particularly this method is suitable to be used in a T-DAB or DAB-T transmitter network. Transmitter networks and communication technology for digital audio and video transfer or broadcasting by means of a digital format have been developed for replacing existing outdated analogue transmitting technology like e.g. FM (Frequency Modulation) radio signals and VHF/UHF television signals. For Europe the "Eureka 147 DAB" protocol was agreed for DAB based upon the ETSI EN 300 401 V1.3.3 standard.

Eureka DAB has been specially developed for improved, interference-free mobile signal reception of high quality sound and may be applied on frequencies between 30 MHz and 3 GHz. In order to guarantee a good mobile reception within moving objects like e.g. a moving car or train, time interleaving or guard interval together with a robust synchronisation and strong error protection is applied for correction of time dependant interferences, like severe multipath propagation and intersymbol interferences (also known as own network distortion). The DAB transmission signal has a bandwidth of 1.536 MHz comprising a large number of carrier waves, or carrier frequencies, dependent on the selected transmission mode (TM). For broadcasting frequencies below 375 MHz generally TM-I is applied, transmitting 1536 carrier waves, transmitting the digital information in low bit rates. This technology is known as OFDM (Orthogonal Frequency Division Multiplexing) having the advantage that frequency interference is strongly suppressed, because only a part of the carriers waves may show interference and distortion, while the greater part of the carrier waves are received interference- free.

The bits to be transferred are transmitted in a 'transmission frame of symbol' having a fixed order or sequence of symbols, divided amongst the individual carrier waves. Each DAB transmitting frequency having a bandwidth of 1.536 MHz (DAB-ensemble or DAB-block) may comprise a multiplex of audio and/or multimedia services, depending on the selected configuration. The gross bit-rate of a multiplex is approximately 2,3 Mbit/s, but as a result of redundancy, error protection and other overhead for improvement of receiving, a net data stream is available of about 1.5 Mbit/s. The 'transmission frame' may be flexible, and dependent on the need be subdivided in segments like data streams or audio broadcasters; e.g. subdivided in six 192 Kbits/s digital audio data streams or in ten 100 Kbits/s multimedia data streams or other combinations thereof This so-called TM-I technology for DAB-transmitters below 375 MHz is very suitable for a SFN (Single-Frequency Network, common frequency network or one frequency network). Particularly because in transition areas between different transmitters interference problems like intersymbol interference are also suppressed by the added robust redundancy and fault correction for obtaining a good mobile signal reception.

For higher transmitting frequencies like the L-band two more transmitting modes are defined; TM-I I en TM-IV. Particularly TM-I I en TM-IV are suitable for use in the so-called L-band transmitters having frequencies between 1.452 and 1.492 GHz. In this transmission mode the transmission signal is subdivided into 384 (mode I) or 768 (mode IV) carrier waves. The higher frequency of the carrier waves results in a maximum mutual L-band transmitter distance, or transmitter separation, of about 25 kilometres for TM- II and about 50 kilometres for TM-IV. For VHF-III (band-Ill) frequencies (174-230 MHz) the maximum transmitter distance is about 100 kilometres. As a result often band-Ill frequencies are used for nationwide DAB SFN broadcasting networks and L-band frequencies are used on a limited scale, usually only for regional SFN applications or for local one transmitter applications. Particularly the method according to the invention is directed towards transmitter networks configured by means of on earth positioned transmitters; the so-called terrestrial or T-DAB networks in contrast to e.g. cable broadcasting or satellite networks.

In a T-DAB transmitter network the transmitters are positioned at a regular mutual distance. Each transmitter is transmitting in a first option each having their own transmission frequency or in a second option all transmitters are broadcasting having the same frequency and so creating nationwide reception for this block, multiplex or allotment.

Up till now implemented T-DAB transmitter networks having a nationwide coverage are using band-Ill frequencies and TM-I. For that purpose high output transmitters are applied positioned on high transmitter mounting devices like masts or high towers. Disadvantage thereof is distortion of own networks and of networks in neighbouring countries. Because transmitter networks are usually built for a nation or a language area, they preferably should not extend beyond the border of a nation or beyond a language boundary. Because the course of the border of a nation is usually irregular it is difficult to fulfil at the same time both requirements of a good reception near the border and of a minimal distortion of other transmitting networks. High output transmitters have a great range and interfere with other transmitters in other service areas and also interfere with their own network. Furthermore high output transmitters have the disadvantage of producing high field intensity in the area around the transmitter location having a radius of a couple of kilometres. This high field intensity may cause interference within electrical devices.

Object of the invention is to provide for a method for operating a T-DAB- communication network (T, terrestrial; DAB, Digital Audio Broadcast) for a service area, the service area being greater than the maximum DAB transmitter distance A.

Above mentioned object is achieved according to the invention by a method comprising the following step: transmitting the DAB signals to the service area by means of low output DAB transmitters positioned on fixed terrestrial mounting devices , the mutual distance a between the DAB transmitters, A, being less than half of the maximum DAB transmitter distance a; in other words a ≤V /k.

Preferably the T-DAB network is a SFN (single frequency network) comprising transmitters broadcasting on a DAB-frequency on band-Ill (174-240 MHz), the mutual distance a between the DAB transmitters on band-Ill being equal or less than the maximum L-band transmitter distance (between 0,2A and 0,5A), between the DAB transmitters, so that preferably a ≤ 0,2A.

Preferably the mutual distance a between the DAB transmitters on band-Ill lies between 5 and 25 kilometres, more preferably the distance is about 10 kilometres. Particularly the low mounting devices have a maximum height of about 50 meter and the transmitter output of each DAB transmitter amounts less than 100 W. For transmitters having an output lower than 100 W a MER (Environment Effect Report) is not mandatory in the Netherlands currently, resulting in lower construction and project costs for initiating the signals. By using the same mounting devices for the L-band and the band-Ill transmitters the project cost will be reduced and also cost reductions may be obtained during construction of the necessary hardware. Preferably the low mounting devices comprise at least one DAB transmitter on band-Ill and at least one DAB transmitter on the L-band. Preferably the DAB transmitter on band-Ill and the DAB transmitter on the L-band are centrally operated from a central DAB server.

The invention also relates to a communication system.

The communication system according to the invention comprises at least one network consisting of SFN DAB band-Ill transmitters and at least one network consisting of T-DAB L-band transmitters, whereby the transmitters both are centrally operated from a central DAB server by means of a communication bus, a receiver configured for receiving T-DAB signals on band-Ill and for receiving T- DAB signals on the L-band.

The invention also relates to a method for obtaining information, like e.g. an Internet page, by a user by means of a receiver.

The method according to the invention comprises a central DAB server broadcasting a SFN T-DAB band-Ill transmitter signal covering a service area by means of a number of transmitters on mounting devices, data streams being transmitted in the frame of the DAB signal like an EPG (electronic programme guide), so that as a result the user may select additional information from the received data by sending a request signal to a bidirectional network like a mobile phone network like a GPRS of UMTS network, subsequently the central DAB server will receive the requested data or signal from service provider supplemented with geographical data about the position of the receiver, so that the requested information may be collected from Internet, whereafter by means of the geographical data of the receiver the central DAB server makes a connection with the T-DAB L-band transmitter in the service area of the receiver by means of the communication bus and adjusting the DAB frame thus creating band width for transferring the requested information from the central T-DAB transmitter to the receiver of the user by means of the communication bus and the T-DAB transmitter using an on-demand segment of the frame.

The invention will now be further explained by means of the drawing.

Fig.1 schematically shows a high output network consisting of high mounting devices and a low output network consisting of low mounting devices;

Fig.2 schematically shows the information and signal data streams according to the invention.

In Fig.1 schematically shows two different embodiments of a DAB transmitter network. As an example is shown a state of the art high output network consisting of VHF-lll band-Ill transmitters on high mounting devices, each transmitter transmitting with high field intensity. The high mounting devices 1 are mutually positioned at a great maximum distance. As a result field intensity strongly decreases with increasing distance from the high mounting device 1. In case of a band-Ill DAB network the transmitters have an output of e.g. 4 kW and the maximum mutual distance A between the transmitters 1 amounts 80 - 100 kilometres. Caused by interference of its own network the resultant field intensity 5 at a great distance from the network transmitters reaches distortion level. It is obvious that adjacent to the high mounting device 1 a very high field intensity 3 is radiated to the surrounding area, possibly causing interference e.g. in other electrical devices. While at the same time in between both high masts the field intensity reaches a distortion field intensity 5.

In Fig.1 is also shown the embodiment of a DAB transmitter network according to the invention. Instead of two high output transmitters upon high mounting devices a greater number of low mounting devices 2 is used, each provided with a low output transmitter generating a low field intensity 4. In this example the mutual distance a between the low mounting devices 2 is a factor 10 less than the mutual distance A between the high mounting devices 1. In Fig.1 is shown that by applying low mounting devices the field intensity is more homogeneous and furthermore no areas can be found having very high or low field intensity. Furthermore irregular national borders may be allowed for so that service areas of other transmitter networks in neighbouring countries will experience less distortion. By using low antenna mounting devices combined with low output transmitters, the transmitting antennas will transmit less far so that own network distortion is suppressed. By positioning the transmitting antennas in valleys on low antenna mounting devices instead of on mountains or hill tops using high mounting devices the distortion of the own network is suppressed. By using the infrastructure of existing mounting devices already used for mobile phone networks like GSM, GPRS, UMTS and C2000 the costs for constructing a nationwide DAB SFN network will even be lower then for a high mounting devices network. The above mentioned advantages will occur when a is chosen equal or smaller then ! A, so that a < Vz . Moreover advantageously these low mounting devices may also be used for L- band T-DAB low output transmitters. This results in the advantage that the costs of infrastructure, connecting up and operating cost may be shared by different networks. When band-Ill as well as L-band T-DAB transmitters are mounted together upon the same mounting devices, like a GSM mast, advantageously mutual synergy will be generated between both networks. In spite of the fact that the T-DAB band-Ill transmitter separation is now much smaller then the maximum distance A and consequently more transmitters have to be installed in order to provide a signal to a certain service area, the total project costs may not increase because of cost reduction obtained by applying this method of the invention; e.g. no obligation to make a MER (environmental effects report), integration of supporting devices, reduction installation costs and maintenance costs. Preferably mounting device separation distance a is equal or less than the maximum L-band distance, being about 0.2 A - 0,5A, so that e.g. the mutual distance between the antenna masts is equal or less than 20 kilometres. In Fig.2 is shown how synergy benefits may be obtained by a combined operation of band-Ill and L-band networks. In the scheme reference number 10 shows a receiver of a user. The receiver and the user may both be mobile, e.g. when both are inside a moving car or train. This receiver 10 is located within the transmission area of a low output T-DAB band-Ill transmitter 11 mounted upon a low mounting device. According to the invention a T-DAB L-band transmitter 12 is also mounted upon the low mounting device 2 and optionally also a mobile telephone transmitter and receiver 13 for GSM, but preferably GPRS and/or UMTS, bi-directional communication. By means of communication bus 15 both T-DAB transmitters 11 , 12 are receiving e.g. a SFN T-DAB signal 33 for the band-Ill transmitter having a nationwide coverage and a local signal 34 for the L-band transmitter 12. In Fig.2 is shown one band-Ill transmitter and one L-band transmitter; other configurations and combinations including more T-DAB transmitters will also fall within the scope of the invention. The communication bus 15 may be a satellite connection; a cable connection or a beam transmission being in contact with the central DAB server 16. This central DAB server 16 provides data to the entire band-Ill and L-band transmitter network within the service area e.g. in this example multiplex 37 for L- band transmitter 12 and SFN multiplex or allotment 38 for band-Ill transmitter 11. As a result of this combined configuration of transmitters and of central operation by means of the central DAB server 16 many interesting options become available for transmitting different types of information streams to the receiver 10 of the user. Firstly the receiver 10 may receive a T-DAB block or multiplex 20 comprising e.g. five digital audio channels including Programme Associated Data (PAD) 21 and Service Information (SI) 22. For clarification purposes both data streams are represented in Fig.2 by a separate arrow; actually however both data streams are included in the digital transmission frame or symbol within the Eureka-DAB protocol and are separated in the receiver 10 in the different data streams. According to the invention also a separate data stream 23 may be included in the transmission frame comprising e.g. an electronic programme guide (EPG). This data stream may provide for the coupling and synchronisation between the band- Ill and L-band transmitter network. By transmitting data about the L-band network within the EPG data stream 23 the L-band may be used for on-demand data streams 26 or for alerting data streams 27. As a result the central SFN network is relieved from the various local data streams, for that purpose bandwidth may be used on the L-band network, which may be subdivided and configured more flexible. L-band transmitter 12 e.g. may be a local broadcaster using a L-DAB block or multiplex 24 of e.g. three local stereo transmitters, each having a data stream of 128 Kbit/s. Furthermore local data are also transmitted like PAD 25. As a result space remains available within the frame for data streams like e.g. 26 and 27. Consequently the configuration of Fig.2 may be used for delivering on-demand information to the user by means of receiver 10. For example a basic set of Internet pages may be transmitted to receiver 10 within the EPG data stream 23. When the receiver is connected with a GPRS/UMTS service provider 14 by means of a mobile telephone transmitter/receiver system, it is possible by means of connection 32 to request for a specific information page by clicking or following a (http) link on one of the basic Internet pages. By means of connection 36 this request is transferred to (internet) service provider 14. Thereafter the request 39 together with the geographical data of the receiver 10, or the geographical data of the GPRS/UMTS receiver 13 or geographical data obtained by another method, is transmitted to the central DAB server 16. The central DAB server is connected with the Internet 28 and collects the requested page. Based upon the transmitted geographical data of receiver 10, now at least for one L-band T-DAB transmitter, the frame is reconfigured by adding an on-demand data stream 26 into the frame. Subsequently the requested Internet page is transmitted by means of this data stream to the receiver 10. By using this method a very high information transfer bandwidth may be offered for additional data traffic on each mounting device. Because little additional bandwidth is available within the SFN band-Ill blocks and moreover in the whole service area the same signal has to be broadcasted, this band-Ill network is not suitable for supplying on request additional data transfer to users. Using local L-band T-DAB transmitters per each mounting device allows for handling a great amount of requests for information, like an Internet page request, and for transmitting of the data to the user. In doing so the available DAB transmission bandwidth is being used very efficiently. Because T-DAB is very suitable for receiving data by moving receiver's, fast mobile Internet connection will be possible at low costs. Costs for receiving information may e.g. be invoiced by means of the GPRS/UMTS network and its service provider 14.

Claims

1. Method for operating a T-DAB-communication network (T, terrestrial; DAB, Digital Audio Broadcast) for a service area, the service area being greater than the maximum DAB transmitter distance (A), comprising the following step: transmitting the DAB signals to the service area by means of low output DAB transmitters positioned on fixed terrestrial mounting devices (2), the mutual distance (a) between the DAB transmitters being less than half of the maximum DAB transmitter distance; in other words a ≤ ¹/ A.

2. Method for operating a T-DAB communication network according to claim 1 , characterized, in that the network consists of a SFN (single frequency network) comprising transmitters broadcasting on a DAB-frequency on band-Ill (174-240 MHz), the mutual distance (a) between the DAB transmitters on band-Ill being equal or less than the maximum L-band transmitter distance (between 0,2A and 0,5A), between the DAB transmitters, so that preferably a < 0,2A.

3. Method for operating a T-DAB communication network for a service area according to anyone of the claims 1 or 2, characterized in that the mutual distance (a) between the DAB transmitters on band-Ill is between 5 and 25 kilometres, more preferably the distance is about 10 kilometres.

4. Method for operating a T-DAB communication network for a service area according to anyone of the claims 1 - 2, characterized in that the low mounting devices have a maximum height of about 50 meter and that the transmitter output of each DAB transmitter amounts less than 100 W.

5. Method for operating a T-DAB communication network for a service area according to anyone of the claims 2 - 4, characterized in that the low mounting devices comprise at least one DAB transmitter on band-Ill and at least one DAB transmitter on the L-band.

6. Method for operating a T-DAB communication network for a service area according to claim 5, characterized in that the DAB transmitter on band-Ill and the DAB transmitter on the L-band are centrally operated from a central DAB server.

7. Communication system comprising at least one network consisting of SFN DAB band-Ill transmitters (11) and at least one network consisting of T-DAB L- band transmitters (12), whereby the transmitters (11 ,12) both are centrally operated from a central DAB server (16) by means of a communication bus (15), a receiver (10) configured for receiving T-DAB signals on band-Ill (20, 21 , 22, 23) and for receiving T-DAB signals on the L-band (24, 25, 26, 27).

Method for obtaining information, like e.g. an Internet page, by a user by means of a receiver (10), a central DAB server (16) broadcasting a SFN T-DAB band-Ill transmitter signal (33) covering a service area by means of a number of transmitters (11 ) on mounting devices (2), data streams being transmitted in the frame of the DAB signal like an EPG (electronic programme guide) (23), so that as a result the user may select additional information from the received data by sending a request signal (32) to a bidirectional network like a mobile phone network (13) like a GPRS of UMTS network, subsequently the central DAB server (16) will receive the requested data or signal from service provider

(14) supplemented with geographical data about the position of the receiver, so that the requested information may be collected from Internet (28), whereafter by means of the geographical data of the receiver (10) the central DAB server makes a connection with the T-DAB L-band transmitter (12) in the service area of the receiver by means of the communication bus (15) and adjusting the DAB frame thus creating band width for transferring the requested information from the central T-DAB transmitter to the receiver (10) of the user by means of the communication bus and the T-DAB transmitter using an on-demand segment (26) of the frame.