WO2010009927A2

WO2010009927A2 - Method of broadcasting and receiving time-sliced data

Info

Publication number: WO2010009927A2
Application number: PCT/EP2009/056411
Authority: WO
Inventors: Andrew Augustine Wajs; Benjamin Lian
Original assignee: Irdeto Access B.V.
Priority date: 2008-07-24
Filing date: 2009-05-27
Publication date: 2010-01-28
Also published as: WO2010009927A3; CN102150386A; CN102150386B

Abstract

The invention relates to a method of wirelessly transmitting (e.g. broadcasting) time-sliced service content data and service related data in a transmission system configured for transmitting service content data over a plurality of radio channels is proposed. The service content data are transmitted as bursts over a plurality of radio channels. The service related data are transmitted by distributing said service related data as bursts over the plurality of radio channels, method of broadcasting and receiving time-sliced data. Accordingly, bandwidth may be saved.

Description

Method of broadcasting and receiving time-sliced data

Television on mobile telephones and mobile television on dedicated user terminals is expected to become widespread technology in the near future. As with most wireless communication systems, the available bandwidth in the wireless network and the power consumption of mobile terminals are key factors for successful commercial exploitation.

A broadcasting standard used for mobile television is known as DVB-H (Digital Video Broadcast Handheld) or DVB-SH (Digital Video Broadcast-Satellite service to Handheld) . DVB-H and DVB-SH provide mandatory time-slicing in order to reduce the average power consumption of the receiving terminal. As set out in ETSI EN 301 192 Vl .4.1 (2004-6), incorporated herein by reference in its entirety, time-slicing comprises sending data in bursts using a significantly higher instantaneous bit rate com- pared to the bit rate required if the data were to be transmitted continuously. The data received in the burst is stored in a buffer of the terminal. Between the bursts, the receiver of the mobile terminal can be switched off and the received data can be played from the buffer. In this way, multi- pie services may share a particular radio channel using different time slots and a terminal may receive one specific service from the radio channel during specific time slots assigned for service content data of this service and switched off during other time slots, thereby saving a significant amount of power. Other systems, such as the China Multimedia Mobile Broadcasting (CMMB) system, described in GY/T220.1-2006 and GY/T220.2-2006, are also configured for using time-slicing.

Some broadcasts systems are configured for broadcasting service content data of different services over different radio channels.

Generally, bandwidth restrictions are understood to play a key role in commercializing mobile television. In particular, when service content data is to be secured to provide conditional access, service related data, such as entitlement management messages (EMM' s), should be provided to the termi- nals. An EMM, as generally known in the art, comprises private conditional access information which specifies the authorization levels or the services for specific decoders. EMM' s may be addressed to single decoders or to groups of decoders. Such service related data claims considerable bandwidth that would otherwise be available for broadcasting service content data. Other examples of service related data include metadata, such as electronic service guide data.

It is an object of the invention to reduce bandwidth requirements in wireless networks for broadcasting service related time-sliced data.

To that end, a method of wirelessly transmitting (e.g. broadcasting) time-sliced service content data and service related data in a transmission system configured for transmitting service content data over a plurality of radio channels is disclosed. The service content data are transmitted as bursts over a plurality of radio channels. The service related data are transmitted by distributing said service related data as bursts over the plurality of radio channels. Also, a method for wirelessly receiving time-sliced service content data and service related data in a user terminal comprising a single receiver, from a (broadcast) transmission system configured for transmitting said service content data over a plurality of radio channels is disclosed. During a first time slot, the receiver is tuned for receiving the service content data over a first radio channel of the plurality of radio channels. In a second time slot, preceding or following the first time slot, the service related data is received over a second radio channel of the plurality of radio channels. The first radio channel and second radio channels are different channels .

Furthermore, a broadcasting system and a terminal configured for executing the steps of the respective methods are proposed. Moreover, a data structure configured for providing information to the user terminal from the broadcasting system is proposed. The data structure may be broadcast using the plural- ity of radio channels used for broadcasting the service content data and/or service related data.

For time sliced broadcasting of services over multiple radio channels, the receiver at the user terminal may have suf- ficient time left for other operations. The applicant has realized that this idle time may be used for tuning to a different radio channel carrying service related data. This different radio channel for the service related data also carries service content data in other time slots. Consequently, the same service related data is not necessarily broadcasted over each of the radio channels of the broadcast system, i.e. at least one channel does not contain a particular service related data burst at a particular moment in time such that bandwidth can be saved,

In the prior art, the total load of service related data is copied to and transmitted over all of the available radio channels, as illustrated in FIG. 2, i.e. each channel has its own copy of the service related data. In contrast thereto, the applicant has found that by distributing the service related data over the available radio channels via multiplexing, band- width can be saved for one or more of the channels. Various embodiments can be considered, some of which will be discussed with reference to FIGS. 3A-3C.

The distribution of the service related data may be obtained by a deterministic algorithm that e.g. controls the distribution such that the service related data are distributed evenly over the available channels. Instead of such a predictable algorithm, statistical distribution algorithms may be used, possibly in combination with signalling to the user terminals.

The distributed service related data may be viewed as a virtual service related channel. The virtual channel comprises the distribution of a sequence of service related data blocks carried by the multiple channels. The user terminal may "tune" to the virtual channel by channel hopping between the multiple channels . The service related data may include at least one of entitlement management message (EMM) and metadata, such as electronic service guide information. It should be noted that for a particular user terminal, it is not harmful for reliable operation to miss particular EMM data, since EMM data are typically valid for a long term (e.g. a month) . Transmission of EMM' s can be optimized using the method according to the invention. It should be appreciated that the invention relates to the in-band transmission of service related data, wherein the user terminal only requires a single receiver. For the out-of- band transmission of service related data, e.g. EMM's, the user terminal needs a dedicated receiver. The user terminals are informed about the radio channels (e.g. frequency of the channel and/or time slots/frames carrying the service related data bursts) carrying the service related data by a data structure broadcast over the wireless network. The data structure may e.g. be a network information table (NIT) broadcast over the wireless network. The NIT (or some other equivalent mechanism) signals e.g. information on the location of EMM bursts to the user terminals. Other information that may be present in the NIT relates to the time slicing of the service content data. In case of EMM's, the data structure (or a part thereof) may be obtained from a conditional access system. The data structure is put on a radio channel (e.g. at particular frames of such a radio channel) known to the user terminal. The user terminal may then be tuned to this radio channel to obtain the information on the radio channels and the frames carrying the EMM's. Subsequently, the user terminal can be controlled to switch to the radio channel (s) carrying the EMM's during available time slots.

The distribution, as opposed to the prior art copying, of the service-related data bursts over at least two radio chan- nels, can be implemented in several embodiments, some of which are illustrated in FIGS. 3A-3C.

A particularly advantageous embodiment with regard to bandwidth savings is defined in claim 2, wherein the number of radio channels over which the service related data bursts are transmitted is less than the number of radio channels over which the service content data are transmitted. In particular, the number of radio channels over which the service related data bursts are played is a subset of the radio channels for playing out the service content data.

The service related data may e.g. be transmitted on one of the radio channels in the plurality of radio channels. This is particularly feasible when the service content data bursts to be received by the user terminal do not coincide with the service related data bursts. The user terminal may be controlled such that priority is given to receiving the service content data when the bursts coincide. It should be appreciated that EMM' s are typically used to provide longer term entitlements and that entitlement control messages (ECM' s) may still be processed by the user terminal to obtain content descrambling keys -

The embodiment of claim 3 reduces the chance that a service content data burst coincides with a burst of auxiliary data .

The embodiment of claim 4 provides changing the radio channels for transmitting the service related data, which may be advantageous for user terminals (e.g. conventional set top boxes) that are not able to perform channel hopping.

The embodiment of claim 5 may be relevant in case that the service related data comprises entitlements for accessing one or more encrypted services. The broadcast may then be controlled such that at the time that the conditional access data are broadcast on a radio channel, the coinciding service content data at one or more different radio channels does not require conditional access data, e.g. the service content data are free- to-air bursts.

Various radio channels may carry complementary service related data, as defined in claims 6 and 7.

The embodiment of claim 9 may also be relevant in case the service related data comprises conditional access data for accessing one or more encrypted services. The user terminal may have built-in intelligence to detect that a service (or service content data) is encrypted and does not possess the information (keys/entitlements) for decryption. The user terminal may then be switched to the radio channel carrying the conditional access information.

Hereinafter, embodiments of the invention will be described in further detail. It should be appreciated, however, that these embodiments may not be construed as limiting the scope of protection for the present invention.

In the drawings:

FIG. 1 provides a schematic illustration of a DVB broadcasting network for providing service content data from a broadcasting system transmitting content over multiple radio channels to a plurality of user terminals according to an embodiment of the invention;

FIG. 2 is a schematic illustration of multiple radio channels according to the prior art;

FIGS. 3A-3C are schematic illustrations of multiple radio channels according to embodiments of the invention;

FIGS. 4A and 4B display schematic illustrations of a portion of a DVB broadcasting system and a user terminal accord- ing to an embodiment of the invention;

FIG. 5 provides a schematic illustration of a CMMB broadcasting system; and

FIGS. 6A and 6B display schematic illustration of a portion of a CMMB broadcasting system and a user terminal ac- cording to an embodiment of the invention.

FIG. 1 shows an illustration of a DVB broadcasting system 1 configured for broadcasting service content data to a plurality of mobile user terminals 2 (e.g. mobile telephone, portable computer) over a wireless network- The service content data may comprise video, audio, files etc.

The broadcasting system 1 comprises an antenna 3 via which the service content data are broadcast over the air to the mobile terminals 2. Broadcasting system 1 may e.g. be a DVB-H broadcasting system, described in detail and incorporated in its entirety in the present application in ETSI EN 301 192 Vl .4.1 (2004-6) . Alternatively, broadcasting system 1 may be a system having implemented the China Multimedia Mobile Broadcasting (CMMB) standard as will be illustrated further in FIG. 5. The CMMB broadcasting system is further specified in GY/T220.1-2006 and GY/T220.2-2006. It is known that broadcasting system 1 may be used to transmit service content data and service related data to the mobile terminals. The service content data are provided to the antenna 3 by a head-end system 4. Head-end system 4 may also provide or include service related data in the broadcast signal. Examples of such service related data include conditional access (CA) data and electronic service guide (ESG) data. Particularly, the CA data are entitlement management messages (EMMs), comprising private conditional access information which specifies the authorization levels or the services for specific decoder Head-end system 4 is configured to provide service content data over a plurality of radio channels ("carriers") using modules 5A, 5B, 5C in the head end system. Each of the modules 5A-5C is responsible for providing data for a single radio channel RC. Head-end system 4 provides data frames as time-slices.

The video data and service related data are sent in high bit rate bursts. Within a burst, also the time before the start of the next burst (delta-t) is indicated. Between the bursts of one service, bursts with data of other services can be inserted. The relevant data are stored in a buffer of the mobile terminal 2. This enables a mobile terminal 2 to stay active only for the fragment of time during which bursts of a requested service can be received. Data can be played continuously making use of the buffered data during the off-times. FIG. 2 provides a schematic diagram illustrating parts of three radio channels RCl, RC2 and RC3. A CA system 7 provides EMM's A, B, C to a system 8 for copying the EMM' s to each of the radio channels RCl, RC2 and RC3. The service content data comprises video data. Radio channel RCl carries video VIi and video Vlii frames. Radio channel RC2 carries video V2i, V2ii and V2iii frames. Radio channel RC3 carries video V3i and V3ii frames. Clearly, considerable bandwidth is consumed by the service re- lated data occupying all channels. The letters i, ii and iii indicate content data of different services.

Returning to FIG. 1, broadcasting system 1 may transmit a data structure 6 informing mobile user terminals 2 of the ap- plication of a method for reducing the bandwidth requirements for service related data, thereby freeing bandwidth for service content data.

Data structure 6 may be a network information table (NIT) broadcast over the wireless network. The NIT 6 signals e.g. information on the location of the service related data bursts to the user terminals 2. Other information that may be present in the NIT relates to the time slicing of the service content data. In case of EMM's. the data structure 6 (or a part thereof) may be obtained from a conditional access system. The data structure 6 is e.g. put on the radio channels RCl, RC2, RC3 (e.g. at particular frames of such a radio channel) known to the user terminal. The user terminal 2 may then be tuned to this radio channel to obtain the information on the radio channels and the frames carrying the EMM's. Subsequently, the user terminal can be controlled to switch to the radio channel (s) carrying the EMM's during available time slots.

The data structure 6 comprises information for the mobile terminals 2 that the service related data is only present on some of the available radio channels RC1-RC3, as shown in FIGS. 3A-3C, thereby indicating the bursts comprising the service related data.

Generally, the system may be operated for implementing the invention as follows. A multi-service data stream is transported on a radio channel in a time-sliced fashion. The user terminals 2 are signalled on all channels which time slices carry service related data. The allocation of the service related data to specific time slices may be computed in advance at e.g. the head end. The head end 4 uses an appropriate algorithm, e.g. a deterministic distribution algorithm, for distributing the service related data over the signalled time slices of the channels. The user terminals 2 are configured for tuning to the appropriate time slices of the channels quickly enough to re- ceive these time slices carrying the service related data. The allocation algorithm and location signalling of the service related data are designed such that normally, the user terminals 2 will receive the service related data in time. Multiple embodiments can be envisaged with the scope of the invention for distributing service related data bursts over various radio channels using a distributor 9. Distributor 9 uses an appropriate distribution algorithm for distributing the service related data bursts over the radio channels such that bandwidth is saved.

FIGS. 3A-3C schematically illustrate three exemplary embodiments, wherein the reduced lengths of the series of bursts in indicative of bandwidth savings as compared to the prior art situation of FIG. 2. Generally, for FIGS. 3A and 3B, the number of radio channels carrying service related data A, B, C is less than the number of radio channels carrying service content data V. In other words, distributor 9 distributes the service related data over only some of the available radio channels RCl, RC2 and RC3. In FIG. 3A, radio channels RCl and RC2 carry service related data A, B, C, whereas all radio channels RC1-RC3 carry service content data V. In other words, the service related data is broadcast over two of the three carriers. The service related data A, B, C are broadcast such that these bursts do not overlap. As schematically shown in FIG. 3A, the application of the distribution results in bandwidth gain for radio channel RC3. Mobile terminal 2 being tuned to radio channel RC3 for receiving video V3i, will only be able to obtain service related data bursts B and C by switching to radio channel RC2. However, the bandwidth savings will still be sufficient when taking into account the reduction of the response time of the mobile terminal 2, i.e. the time the mobile terminal 2 must wait before receiving the required data.

In FIG. 3B, service related data bursts A, B, C are carried by a single radio channel RCl as a result of distribution by distributor 9 to only this channel. This is particularly feasible when the service content data bursts V to be received by the user terminal 2 do not coincide with the service related data bursts. Bandwidth savings are obtained in radio channels RC2 and RC3, as schematically indicated. The user terminal 2 may be controlled such that priority is given to receiving the ser- vice content data when the service related data bursts coincide with the service content data bursts.

Whereas in FIGS. 3A and 3B, the service related data are shown to be transmitted continuously on RCl and RC2 (FIG. 3A) and only RCl (FIG. 3B), head-end system 4 may be configured such that the service related data are transmitted dynamically over the available radio channels. As an example, at time tl, service related data A are transmitted over radio channel RC3 only. At a subsequent time t2, service related data A may be broadcasted only on radio channel RCl. At still a later time t3, service related data A may be transmitted only on radio channel RC2 etc. At any point in time t, however, the number of radio channels RC over which a particular service related data burst is broadcast is less than the total number of available radio channels . The head-end 4 may be controlled such that the broadcast service content data V coincides with service related data A, B, C required by the service content data. The service content data may e.g. comprise conditional access data for accessing one or more encrypted services. The broadcast may then be controlled such that at the time that the conditional access data are broadcasted on radio channel RCl in FIG. 3A, the coinciding service content data video V2iii of RCl (and possible also of radio channel RC3) , do not require these entitlements data. Video V2iii may e.g. relate to a free-to-air service con- tent data burst,

In FIG. 3A, the service related data bursts on radio channels RCl and RC2, may be complementary data. Mobile device 2, tuned to RC3 for receiving video 2C, may be tuned to RC3 in advance and to RCl afterwards to receive the service related data.

FIG. 3C, on the other hand, is a schematic illustration of an embodiment wherein the total amount of service related data is distributed over all of the available radio channels. However, by distributing the load, bandwidth savings are obtained. In particular, distributor 9 distributes all service related data bursts A, B, C to radio channels RCl and RC2, while transmitting only bursts A and C on radio channel RC3. The partial allocation of service related data bursts to the radio channel provide for a (minimum) bandwidth savings, as schematically indicated in the Figure.

FIGS. 4A and 4B illustrate schematically a DVB archi- tecture of a part of the head-end system 4 and a mobile terminal 2, respectively.

FIG. 4A shows components of a head-end system 4 for a one or more radio channels. Head-end system 4 comprises an ESG section 10, a service content data section 11 and a CA section 12. Schedule data 13 are provided to indicate the time-slices to be used for carrying ESG data and EMMs respectively. The user terminal 2 uses information in the stream (e.g. CAT, NIT, SDT) to point to CA and ESG data bursts. Each burst contains information to reference to the exact location and time of the next burst.

ESG section 10 comprises an ESG generator 14 providing ESG data to a File Delivery over Unidirectional Transport (FLUTE) server 15 allowing for the delivery of files as transport objects to the mobile terminal 2. FLUTE server may also receive an SDP input (not shown) describing how a user terminal 2 should access a session/event, which media codecs are in use and other configuration information.

Service content data section 11 comprises a standard H.264 video encoder 16 providing MPEG-2 TS packets to a scram- bier 11 to be scrambled using control words CW from ECM generator 18. The scrambled data is transferred to an RTP pack- etizer 19. The ECM' s carry encrypted control words in a manner well known to the skilled person. It should be appreciated, however, that other data than video data may be used for performing the present invention.

Apart from the ECM generator 18, CA section 12 also comprises an EMM generator 20 providing encryption keys for en- crypting the control words in the ECM' s. EMMs may be generated using data from subscriber management system 21.

It should be appreciated that head-end system 4 may also be configured for connecting to a mobile wireless telecom- munication network. This network may be used for receiving requests from mobile terminals 2 to the subscriber management system 21 for subscribing to services.

The outputs of the ESG section 10, the service content data section 11 and CA section 12 are subsequently fed to IP en- capsulator 22. IP encapsulator 22 provides the service content data and the service related data (ESG data and EMMs) to a OFDM modulator 23 for broadcasting on the radio channel (s) in a manner shown in FIGS. 3A-3C.

The data are received by a user terminal 2 comprising tuner, demodulation unit and demultiplexer 30. User terminal 2 is configured for hopping between various radio channels RCl- RC3. User terminal 2 may also comprise a detector, possibly implemented in unit 30, for service content data to be decrypted and switching the tuner receiver to another radio channel in re- sponse to obtain the service related data, i.e. the conditional access data.

The output of block 30 comprises an encapsulated IP data stream that is further processed by an IP stack unit 31. The IP stack unit 31 removes the IP encapsulation and forwards the IP packets to applications that request data packets from a particular IP address. IP stack unit 31 is configured for tuning to different frequencies in order to receive IP data streams on different channels.

An ESG client 32 processes data from the ESG generator 14 and interfaces with a terminal application, ESG client may also process the SDP data and transmit SDP data to a conditional access agent 33 configured for cooperating with a smart card 34 in a manner known as such. Conditional access agent 33 receives ECM' s and EMM' s from IP stack unit 31. IP stack unit 31 provides a H.264-RTP output to a de- scrambler 35. Descrambler 35 receives control words CW for secure device 33 to provide descrambled data to a H.264 decoder 36.

As mentioned above, FIG. 5 provides a schematic illustration of a CMMB broadcasting system 1. Service content data and service related data is provided from a head-end system 4 via a satellite 50 to user terminals 2. Signals are transmitted to the satellite 50 over the Ku band, whereas signals are transmitted from the satellite 50 towards the user terminals 2 using the S band. In rural areas the signals are received by the user terminals 2 in the S band. In urban areas, repeaters 51 may be required that forward the service content data and service related data via the S band or UHF band. The NIT 6 is also received over these bands,

FIGS. 6A and 6B display schematic illustration of a portion of a CMMB broadcasting system of FIG. 5 and a user terminal 2 according to an embodiment of the invention.

FIG. 6A shows components of a head-end system 4 for a one or more radio channels. Head-end system 4 comprises an ESG Section 60, a Service Content Data Section 61 and a CA Section 62. Schedule data are provided to indicate the time-slices to be used for carrying ESG data and EMMs respectively. The user terminal 2 uses information in the stream to point to CA and ESG data bursts. Each burst contains information to reference to the exact location and time of the next burst. The ESG Section 60 comprises an ESG Generator providing

ESG data to an ESG Carousel (typically a File Delivery over Unidirectional Transport (FLUTE) server) allowing for the delivery of files as transport objects to the mobile terminal 2. The ESG Carousel may also receive an input (not shown) describing how a user terminal 2 should access a session/event, which media codecs are in use and other configuration information. This information forms part of the Control Logic Channel of the CMMB physical layer, which is used for transmitting system control information and channel parameters. The Service Content Data Section 61 comprises one or more audio/video encoders providing elementary stream packets to an Audio/Video Scrambler to be scrambled using control words CW from an ECM generator of the CA section 62. The scrambled data is transferred to an XPE-FEC for forward error coding. The ECM' s carry encrypted control words in a manner well known to the skilled person. It should be appreciated that other data, origi- nating from a data server and scrambled by a data scrambler may also be processed.

Apart from the ECM generator, CA section 62 comprises an EMM generator providing encryption keys for encrypting the control words in the ECM' s . EMMs may be generated using data from a business operation support system.

It should be appreciated that head-end system 4 may also be configured for connecting to a mobile wireless telecommunication network. This network may be used for receiving requests from mobile terminals 2 to the business operation sup- port system for subscribing to services.

The outputs of the ESG section 60, the service content data section 61 and CA section 62 are subsequently fed to a multiplexer. The multiplexer provides the service content data and the service related data (ESG data and EMMs) to a COFDM modula- tor for broadcasting on the radio channel (s) in a manner shown in FIGS. 3A-3C.

The data are received by a user terminal 2 comprising a CMMB receiver. User terminal 2 is configured for hopping between various radio channels RC1-RC3. User terminal 2 may also com- prise a detector, possibly implemented in the CMMB receiver, for service content data to be decrypted and switching the tuner receiver to another radio channel in response to obtain the service related data, i.e. the conditional access data.

The output of the CMMB receiver comprises an encapsu- lated IP data stream that is further processed by an IP stack unit. The IP stack unit removes the IP encapsulation and forwards the IP packets to applications that request data packets from a particular IP address. IP stack unit is configured for tuning to different frequencies in order to receive IP data streams on different channels. An ESG client processes data from the ESG generator and interfaces with a terminal application. ESG client may also process the SDP data and transmit SDP data to a conditional access agent configured for cooperating with a smart card in a manner known as such. Conditional access agent receives ECM' s and EMM's from IP stack unit.

IP stack unit provides a H.264-RTP output to a descram- bler. Descrambler receives control words CW for secure device to provide descrambled data to a H.264 decoder.

Claims

1. A method of wirelessly transmitting time-sliced service content data and service related data in a transmission system configured for transmitting service content data over a plurality of radio channels, the method comprising the steps of: - transmitting said service content data as bursts over a plurality of radio channels;

- transmitting said service related data by distributing said service related data as bursts over said plurality of radio channels .

2. The method according to claim 1, wherein said service content data bursts are transmitted over a first number of radio channels and said service related data bursts are transmitted over a second number of radio channels, wherein said second number of radio channels is less than said first number of radio channels.

3. The method according to claim 1 or 2, further comprising the step of broadcasting service related data over at least a first radio channel and a second radio channel of said second number of radio channels at different times.

4. The method according to one or more of the claims 1- 3, further comprising the step of varying the radio channels over which said service related data are broadcast.

5. The method according to one or more of the preceding claims, further comprising the step of controlling transmission of at least one of said service content data and said service related data to avoid said service related data on a first radio channel of said second number of radio channels to coincide with said service content data, requiring said service related data, on a first radio channel of said first number of radio channels.

6. The method according to one or more of the preceding claims, wherein said service related data on a first radio channel and a second radio channel carry complementary service related data.

7. The method according to claim 6, wherein said service related data on said first radio channel and said complementary service related data on said second radio channel are broadcasted at different times.

8. A broadcasting system configured for performing the method according to one or more of the claims 1-7.

9. A data structure for transmission by a broadcasting transmission system according to claim 8, said data structure comprising information for user terminals for obtaining said service related data from said radio channels.

10. A method for wirelessly receiving time-sliced broadcast service content data and service related data in a user terminal comprising a single receiver, from a broadcast transmission system configured for broadcasting said service content data over a plurality of radio channels, the method comprising the steps of: - tuning said receiver for receiving said service content data over a first radio channel of said plurality of radio channels during a first time slot; - tuning said receiver for receiving said service related data over a second radio channel of said plurality of radio channels during a second time slot, preceding or following said first time slot.

11. The method according to claim 10, wherein said second radio channel comprises service content data bursts and service related data bursts, further comprising the step of obtaining said service related data bursts from said second readio channel during said second time slot.

12. The method according to claim 10 or 11, wherein said service content data comprises encrypted service content data and said service related data comprises entitlement manage- ment messages for authorizing decryption of said encrypted service content data, further comprising the step of detecting said service content data to be encrypted and switching said receiver to said second radio channel.

13. A user device configured for executing the method according to one or more of the claims 10-12.