Patent Application
20120151547
This application claims priority under 35 U.S.C. 119(a) to an application filed in the UK Intellectual Property Office on Dec. 13, 2010, and assigned Serial No. 1021113.4, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to broadcast systems, and more specifically, to a method and apparatus relating to transmission and reception of data streams in digital video broadcast systems.
2. Description of Related Art
A broadcast system, such as a Digital Video Broadcasting (DVB) system, may transmit data in the form of a sequence of frames. A DVB system may operate according to, for example, a DVB Terrestrial 2nd Generation (DVB-T2) standard, or for example, the following families of standards: Advanced Televisions Systems Committee (ATSC), Integrated Services Digital Broadcasting (ISDB), or Digital Multimedia Broadcasting (DMB). Each frame typically includes a preamble section and a data section. The preamble section and the data section are time-multiplexed. The data section may carry data arranged in the form of a number of data streams, which may be referred to as Physical Layer Pipes (PLP). A PLP or a plurality of PLPs may carry, for example, a service such as a video channel that is to be provided to a user. Reception of data from the frames, and reception of the data streams, may be assisted by signalling, which may typically be carried in the preamble of the frame, in which case the signalling is referred to as Out-of-Band (OB) signalling. The signalling may also be carried in the data section, in which case the signalling is referred to as In-Band (IB) signalling. The signalling may be referred to as physical layer signalling, or Layer 1 (L1) signalling. The signalling may indicate a modulation or coding scheme to be used for decoding data, and it may, for example, indicate sections of a data field to be decoded, or the location of a data stream within the data section.
The use of signal compression techniques has increased, and lower data rate services, which may be more robust in particular in mobile environments, have been provided. Accordingly, the number of data streams carried by a sequence of frames is potentially large, but thinly spread in the sense that not every frame may carry all of the data streams. Because signalling is typically required relating to each data stream for each frame, the signalling may represent a large overhead per frame in terms of data capacity and receiver power consumption.
Furthermore, since data streams are typically frequency interleaved within symbols transmitted in a data frame, it is necessary for a receiver to receive the whole symbol bandwidth in order to receive a data stream. As a result, the sampling rate used at the receiver is typically required to be sufficient to receive the whole symbol bandwidth, which places demands on the power consumption of the receiver. The power consumption of the receiver is related to the sampling rate. Power consumption is a particularly important parameter, in particular for battery-powered digital broadcasting receivers.
The present invention has been made to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention provides data transmission and reception techniques in a broadcast system.
According to one aspect of the present invention, a method is provided for transmitting data comprising a data stream in a broadcast system. A frame is generated. The frame includes preamble section and a data section. The data section carries the data stream. The preamble section carries signalling information. The frame is transmitted to a receiver. In generating the frame, the data section of the frame is segmented into a plurality of frequency zones, and the data stream is mapped to a frequency zone of the plurality of frequency zones. The signalling information includes segmentation information of the frequency zones.
According to another aspect of the present invention, a method is provided for receiving data comprising a data stream in a broadcast system. A frame is received. The frame includes a preamble section and a data section. The data section carries the data stream. The preamble section carries signalling information. The data section is segmented into a plurality of frequency zones. The frame is demodulated. The data stream is mapped to a frequency zone of the plurality of frequency zones. The signalling information includes segmentation information of the plurality of frequency zones.
According to an additional aspect of the present invention, a transmitter is provided for transmitting data having a data stream in a broadcast system. The transmitter includes a segmenting and mapping unit for segmenting the data section carrying the data stream in a frame into a plurality of frequency zones and for mapping the data stream to a frequency zone of the plurality of frequency zones. The transmitter also includes a signalling generation block for delivering signalling information. The transmitter further includes an Orthogonal Frequency Division Multiplexing (OFDM) generation unit for mapping the data stream and the signalling information onto OFDM resources. Wherein the signalling information includes segmentation information of the plurality of frequency zones.
According to a further aspect of the invention, a receiver is provided for receiving data having a data stream in a broadcast system. The receiver includes a signal processing unit for processing a received signal for demodulation. The received signal has at least one frame. A frame includes a preamble section and a data section. The data section carries the data stream. The preamble section carries signalling information. The data section is segmented into a plurality of frequency zones. The receiver also includes a controller for controlling the signal processing unit to process the signalling information and the data stream. The data stream is received via a segmented frequency zone of the plurality of frequency zones. The receiver further includes a demodulator for demodulating the data stream and the signalling information. The signalling information includes segmentation information of the plurality of frequency zones.
The above and other aspects, features and advantages of the present invention will be more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:
FIG. 12 is a table showing the L1-dynamic-Ext signalling field, according to an embodiment of the present invention;
Embodiments of the present invention are described in detail with reference to the accompanying drawings. The same or similar components may be designated by the same or similar reference numerals although they are illustrated in different drawings. Detailed descriptions of constructions or processes known in the art may be omitted to avoid obscuring the subject matter of the present invention.
Embodiments of the present invention are described in the context of a Digital Video Broadcasting Next Generation Handheld (DVB-NGH) standard based on the 2nd generation terrestrial DVB-T2 system.
However, the above context is provided by way of example only, and other embodiments may involve other broadcast systems. The embodiments of the present invention are not limited to the use of transmitting digital video signals.
In an embodiment of the present invention, several data streams, which may be embodied as PLPs, are mapped onto a super-frame, which is made up of a series of frames.
Typically, the L1-Pre section 10 contains signalling information relating at least to the modulation and coding scheme needed to receive the remainder of the preamble. The remainder of the preamble section contains information necessary to receive the data section, and in particular, the PLPs within the data section. The information may contain, for example, the start address of a PLP within the data section. The signalling information within the preamble may be referred to as OB signalling.
The L1 Config section 12 typically carries information that is valid for each frame of the super-frame, and is typically the same for each frame of the super-frame. The L1-Dynamic section 14 typically varies from frame to frame, and relates to decoding the PLP within the frame. Typically, the L1-Dynamic section 14 will include a start address of the PLP, for example. As data compression techniques improve, and as lower data rates and more robust services are offered for reception by, in particular, handheld and mobile user equipment, the number of PLPs mapped onto a super-frame increases. However, each PLP may not be mapped to every frame. Carrying signalling information, and in particular L1-Dynamic information, relating to each PLP in each frame may involve a significant overhead in terms of signalling information.
A first signalling information field, L1-Dynamic section 14, is provided for assisting in the reception of a first number of data streams. If required, a second signalling information field, L1-Dynamic EXT 16, is provided for assisting in the reception of further data frames. The signalling information carried in the signalling information field typically includes L1-Dynamic information. The number of data streams for which signalling information is carried in the first signalling information field is less than or equal to a limit applicable to each of the frames in the super-frame. The first signalling information field is the same size for each of the frames in the super-frame.
When the first signalling information field is the same size for each of the plurality of frames, the size may be set at a value that is sufficiently large to give robustness due to frequency diversity. When information is included in a second signalling information field, which is dependent on the number of data streams for the given frame being greater than a limit, additional information may be transmitted beyond the capacity limit of the first signalling information field. Accordingly, the first signalling information field is maintained at a sufficient size to give robustness due to frequency diversity, while the second signalling information field may accommodate extra capacity if required. The second signalling information field may be less robust than the first information field, if the size of the second signalling information field is smaller than the first signalling information field.
The first signalling information field may carry an indication as to whether a second signalling information field is to be transmitted, and may also carry an indication as to a length of the second signalling information field. This allows a receiver to inhibit reception of the second signalling information field if it is not to be transmitted, and may prepare for reception of the second signalling information field if it is to be transmitted. The second signalling information field may carry an indication of data streams that are idle. A receiver may inhibit reception of a frame that does not carry a data stream that is required to be received, thereby saving power consumption.
The limit to the number of data streams for which signalling information is carried in the first signalling information field is typically determined based on statistical information relating to a number of active or idle data streams per frame for the plurality of frames, and/or based on at least a robustness of a scheme employed for the transmission of at least one of the first and second signalling information fields. The robustness scheme may include at least one of a modulation and coding scheme, a Multiple-Input Multiple-Output (MIMO) scheme, a Fast Fourier Transform (FFT) size, a pilot pattern, and a guard interval. The limit to the number of data streams for which information is carried in the first signalling information field is determined in accordance with the robustness of the transmission of the field, so that a lower limit to the size the first signalling information field may be set to a sufficient size to give adequate robustness taking into account frequency diversity and robustness of the transmission scheme. The first signalling information field may also be set to a size that is sufficiently large, such that it may accommodate an expected amount of signalling information related to active and passive data streams per frame, so that any overflow of signalling information beyond the expected amount may be carried in the second signalling information field. An indication of the limit may be carried in the preamble section of each frame, typically in the L1-Config section 12.
As described above, the first signalling information field may have a higher robustness than the second signalling information field, due to a greater degree of frequency diversity, since the first signalling information field is typically interleaved over a larger frequency range. Thus, it may be advantageous to include preferential signalling information in the first signalling information field that relates to data streams requiring higher robustness.
A preamble region 2 occupies the full frequency width of the symbol. The remainder of the frame, being the data section, carries a number of data streams. The data section is segmented into a number of frequency zones, referred to as frequency interleaving zones, shown as FIZ1 3a, FIZ2 3b and FIZNFIZ 3c. The preamble carries signalling information that is used to receive the data streams within the data section. Each frequency zone has the same position in a frequency domain for each of the plurality of frames in a super-frame.
The data streams are mapped to the frequency zones, and typically, a data stream is mapped to a single frequency zone. Specifically, PLP1 4a and PLP2 4b are mapped to FIZ1 3a, PLP3 4c and PLP4 4d are mapped to FIZ2 3b, and PLP5 6 and PLP6 6b are mapped to FIZNFIZ.
A signalling information word, which carries signalling relating to a position and bandwidth of at least the first frequency zone in a frequency domain to assist in the reception of the data stream, is carried in the preamble section of at least the first frame of super-frame. However, the signalling information word is typically carried in the L1-Config section of each frame.
Accordingly, the preamble, carrying the signalling information word is transmitted within a wider frequency bandwidth (i.e., the full symbol bandwidth) than each of the frequency zones. This allows the receiver to use a reduced bandwidth and also a reduced sampling rate to receive the data stream, saving power consumption. However, using the full symbol bandwidth to receive the preamble section may avoid the need to duplicate information in the preamble between frequency zones, which may be needed if the receiver were to use the bandwidth of the frequency zone throughout.
A further advantage arising from reducing the transmission bandwidth, and consequently increasing a transmission time period, may be in terms of increased robustness, particularly in a mobile environment. Specifically, it may be advantageous to trade-off time and frequency diversity by reducing bandwidth and increasing a transmission time period, thereby trading a reduction in frequency diversity for a gain in time diversity.
IB signalling may be included in the data streams of a frame. This allows the signalling information, and in particular the L1-Dynamic section, to be received within the bandwidth of a frequency zone. Accordingly, a receiver may maintain the second bandwidth for the reception of the data stream (after initially receiving the preamble in the wider bandwidth, typically in the first frame), thereby saving power consumption.
As illustrated in
Data is typically interleaved in frequency, and the frequency interleaving sequence may vary from one OFDM symbol to another. This may provide greater robustness. Typically, pilot tones are inserted into the transmission symbol in a pattern that is independent of the segmentation of the data section of each of the plurality of frames into frequency zones. This simplifies the transmitter and receiver implementation, because the segmentation may be carried out independently from the arrangement of the physical layer.
As part of the process of determining bandwidths to be used for a frequency zone, which is typically done for a super-frame, a lower limit may be determined based on an arrangement of pilot tones mapped to the frequency zone. In this way, a minimum robustness may be maintained for the transmission of the first frequency zone, since the robustness is dependent on the arrangement of the pilot tones. It may be required that a certain number of pilot tones fall within the part of a symbol to which the first frequency zone is mapped.
The segmenting of the data section of each frame may be done at logic frame level, so that the implementation of a transmitter and a receiver may be simplified and the bandwidth and position of frequency zones may be allocated flexibly.
If the data stream includes components of a scalable video coding scheme, it is preferable to map the components to the same frequency zone in a given frame. This mapping is performed so that a receiver may fall back to a more robust component, or select a higher rate component, without changing the bandwidth used by the receiver.
In addition to segmenting the data section of each frame into frequency zones, i.e., frequency interleaving zones, the data section may also be segmented into a number of time zones, or Time Interleaving (TI) Frame Segments (TIFSs). The data streams may first be mapped onto TI frames. As shown in
If a TI frame, or a number of TI frames, were to be mapped directly onto a frequency interleaving zone, then padding may need to be included in the frequency interleaving zone if the amount of data carried by the TI frame or frames is not the same as the capacity of the frequency interleaving zone. The padding would be wasted capacity, since it may not carry data. In an embodiment of the present invention, as a result of the mapping of TI frames to TIFSs, the need to add padding in a frequency zone may be avoided, since the capacity of each TIFS may be arranged to fill a remaining part of a frame efficiently. For example, in
The mapping of the TI frame 22 to the TIFSs 24a, 24b and to the frames 5a, 5b may be done in real time, so that flexible scheduling may be realized, in which it is not necessary to determine the number of TIFSs per frame, or over how many frames the TI frame is mapped. The TI frame may be mapped to start and end at any point within a frame and at any point within a super-frame, without the need to fix these points in advance.
The second signalling information word may carry information relating to a timing of a subsequent TIFS, so that a receiver may inhibit reception of periods between TIFSs, thereby saving on power consumption, and so that the receiver may be prepared to receive subsequent TIFSs.
A data stream consists of different PLPs 400, 420, 430, and each PLP consists of consecutive TI frames. For example, PLP1 400 includes TIF1.0 405, TIF1.1 410, . . . TIF1.N 415. The data of each TIF is interleaved according to the predefined time interleaver.
A TIFS Segmentation and FIZ Mapping block 440 arranges several PLPs 400, 415, 430 into a specific FIZ 460, 465, 470, 475. Different PLPs of the FIZ are interleaved by the predefined frequency interleaver, according to the FIZ.
A signalling generation block 450 contains the information of the logical frame structure related to PLP, TIF and FIZ.
An OFDM generation block 480 constructs the block of OFDM cells, thereby building of the OFDM grid. The OFDM generation block 480 receives signalling information and a data stream, and maps the signalling information and data stream onto the OFDM resource. Typically, OFDM generation block 480 includes a pilot insertion block, which adds pilots into the transmitted frame depending on pilot pattern, IFFT block, and Guard Insertion block.
A Logic Frame Assembly block 490 includes a logical frame structure by assembling the different TIFSs and FIZ. For example,
Each time an interleaved frame segment may be mapped to a single physical layer zone in a given frame.
Interleaving within a frequency interleaving zone and/or within a TIFS may be frequency-wise interleaving, so that successive parts of a data stream are mapped across parts of an OFDM symbol in frequency. The mapping may then moves on to map to parts of another orthogonal frequency division multiplexing symbol in frequency, and so on. Alternatively, the mapping may be time-wise interleaving, so that successive parts of a data stream are mapped in time across a succession of OFDM symbols, and then typically the mapping moves on to map in time to other frequency parts of the succession of OFDM symbols, and so on.
In a receiver, a bandwidth of an analog filter and a sampling frequency, appropriate to the second bandwidth, may be set based on the signalling information word, so that the receiver may be arranged for a minimum power consumption consistent with the bandwidth of the frequency zone to be received.
TIFS Mapping Mode A implies that the TI-Frame is transmitted through successive frames. TIFS Mapping Mode B infers that the TI-Frame is transmitted on a frame.
NUM_PLP_IN_L1DYN: The number of data streams signalled in the first signalling information in the current frame.
PLP_ID: An 8-bit field indicating the ID of the PLP carrying the data stream.
PLP_START: A 22-bit field indicating the start (location) of that PLP in the frame.
PLP_NUM_BLOCKS: A 10-bit field indicating the number of FEC blocks encapsulated in that PLP.
Reference numeral 34 refers to NUM_PLP_ext, which may indicate the number of PLPs for which signalling information is carried in the L1 dynamic_EXT word. Reference numeral 34 also refers to NUM_IDLE_PLP, which indicates a number of idle PLPs within the frame. The signalling definitions related to embodiments of the present invention are provided below.
NUM_PLP_ext: An 8-bit field indicating the number of active PLPs in the second signalling part (in case the number of PLPs in the frame exceeds the limit).
NUM_IDLE_PLP: An 8-bit field indicates the number of idle PLPs in the current frame.
PLP_ID, PLP_START, PLP_NUM_BLOCKS: Same as in the signalling definition in
PLP_DELTA: An 8-bit field indicates the relative timing to when the idle PLP will become active again.
NUM_FIZ: A 3-bit field indicating the number of FIZs.
NUM_TIFS_a: An 8-bit field indicating the number of TIFSs in the frame.
PLP_TIF_NUM_BLOCKS: A 10-bit field indicating the number of FEC blocks used in one time interleaving frame for a given PLP.
FIZ_LENGTH: A 10-bit field indicating the size of one FIZ in OFDM cells.
FIZ_MAPPING_TYPE: A 1-bit field indicating the mapping type of FIZ. This field is set to ‘1” if a TIFS Mapping Mode A is applied, and is set to “0” if a TIFS Mapping Mode B is applied
PLP_ID: An 8-bit field indicating the ID of the PLP carrying the data stream.
PLP_TIFS_START: A 21-bit field indicating the start position in the given TIFS.
PLP_TIFS_LENGTH: A 15-bit field indicating the size of the PLP in the given TIFS.
PLP_TIFS_TYPE: A 2-bit field indicating the type of the PLP in the given TIFS (PLP Type 1 or Type 2).
PLP_TIFS_DRAME_IDX: A 1-bit field indicating the frame index of the PLP mapped onto the given TIFS.
PLP_TUFS_DELTA: A 4-bit field indicating the relative timing from the current TIFS to the next TIFS which will carry the given PLP (PLP ID).
FIZ_ID: A 1-bit field indicating the ID of the FIZ carrying the TIFS.
NUM_PLP_ext: An 8-bit field indicating the number of active PLPs in the second signalling part (in case the number of PLPs in the frame exceeds the limit).
NUM_IDLE_PLP: An 8-bit field indicating the number of idle PLPs in the current frame.
PZ0_PILOT_PATTERN: A 4-bit field indicating the pilot pattern in the Physical Zone 0 (First physical zone).
PZ0_GUARD_INTERVAL: A 3-bit field indicating the guard interval used in the Physical Zone 0 (first Physical Zone).
NUM_PZ: A 3-bit field indicating the number of the Physical Zones.
Reference numeral 54 is same as reference numeral 40
FIZ_LENGTH: A 10-bit field indicating the number of cells (capacity of the frequency interleaving zone).
FIZ_MAPPING_TYPE: A 1-bit field indicating either frequency-wise or time-wise mapping is used (mode A and B).
PZ_FFT_SIZE: A 4-bit field indicating the FFT size of the Physical Zone.
PZ_PILOT_PATTERN: A 1-bit field indicating the pilot pattern used in the given physical zone.
PZ_GUARD_INTERVAL: A 1-bit field indicating the OFDM guard interval used in the given physical zone.
Reference numeral 60 is same as reference numeral 38.
While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1021113.4 | Dec 2010 | GB | national |
