hash stringlengths 32 32 | doc_id stringlengths 7 13 | section stringlengths 3 121 | content stringlengths 0 2.2M |
|---|---|---|---|
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.2.2 BBFRAMEs, FECFrames and FEC blocks | There is a 1:1:1 correspondence between these three objects, but there is a subtle difference between them and all three terms are used in [i.1]. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.2.2.1 BBFRAMEs. | BBFRAMEs are the basic unit in the logical framing structure of DVB-T2: allocation and scheduling are performed in whole numbers of BBFRAMEs. Where packetised streams are being carried, the packets may be mapped to BBFRAMEs either synchronously or asynchronously, i.e. each BBFRAME may contain a whole number of packets,... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.2.2.2 FECFRAMES | The baseband frame, complete with header, is treated as an information word to which BCH and LDPC coding are applied. The resulting codeword always contains either 64 800 bits or 16 200 bits and is known as a FECFRAME. The two different lengths correspond to the choice of long or short FEC blocks respectively. Short FE... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.2.2.3 FEC Blocks | The bits of a FECFRAME are interleaved and arranged into words, which are then mapped onto constellation points, or OFDM cells; the set of constellation points corresponding to one FECFRAME is known as a FEC block. The number of cells in a FEC block therefore depends on both the QAM modulation and the choice of long or... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.2.3 Interleaving Frames | The Interleaving Frame is an important concept in DVB-T2, but one that causes a certain amount of confusion, and a proper understanding is essential to the understanding of many of the other parts of the specification [i.1]. To begin with, the name "Interleaving Frame" is somewhat misleading. Although the need for this... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.2.4 TI blocks | A TI-block is the set of OFDM-cells within which Time Interleaving is performed; there is no interleaving between TI-blocks. Each TI-block contains a dynamically variable whole number of FEC blocks. An Interleaving Frame in turn contains an integer number of TI-blocks, this number being statically configurable. The tot... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.2.5 Mapping to physical frame structure | Each Interleaving Frame is mapped to one or more (PI) T2-frames. Following time interleaving, each Interleaving Frame consists of a series of OFDM cell values. These cells are partitioned into equal parts to be carried in each of the corresponding T2-frames; the cells allocated to a particular T2-frame are described as... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.2.6 The concept of a T2-system | The DVB-T2 specification [i.1] uses the phrase "T2 System" in different senses. In some places it is used in a general way to refer to the DVB-T2 standard and the various elements which make it up. However, "T2-System" is also used in a specific way to refer to a particular layer-1 concept, which is a generalisation of... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.3 Capacity | This clause explains how the total capacity of the T2 system can be calculated. The total capacity depends on a number of different factors: • FFT size. • Guard interval. • Pilot pattern. • Bandwidth and use of Normal or Extended carrier mode. • Use of reserved tones (TR). • Existence of Future-Extension Frames. • Use ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.3.1 Capacity in cells and FEC blocks per frame | The total capacity in cells per frame of the T2 system can be calculated as: FC data data P P tot C C L C N C + × − + × = )1 ( 2 2 . where CFC = Cdata for cases where no frame-closing symbol is used. To find the capacity available for transmission of PLPs and auxiliary services, the number of cells needed to carry L1 s... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.3.2 Total bit-rates of the T2 system | When a Transport Stream is carried by a data PLP together with a common PLP, the maximum useful bit rate which can be carried, assuming FEFs are not used, is given by: ⎟⎟ ⎠ ⎞ × − − × × + ⎜⎜ ⎝ ⎛ + × − − × × + = jump_cplp I_cplp IB_cplp bch_cplp cplp max_ _ B MA_cplp jump_data I_data IB_data bch_data data max_ _ B MA_dat... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.3.3 Examples of bit-rates | In an 8 MHz channel, the highest data rate is achieved with the 32 K, GI=1/128, extended-carrier mode and no tone reservation, for which pilot-pattern PP7 is always used. The first few columns of table 17 give the maximum achievable bit rate for each combination of constellation and code-rate, together with the corresp... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 6.4 Overview of interleaving | There are four different interleavers in the DVB-T2 specification, occurring in the following order in the modulation chain: • Bit Interleaver. • Cell Interleaver. • Time Interleaver. • Frequency Interleaver. The Bit Interleaver interleaves the code-bits within an LDPC codeword in order to avoid undesirable interaction... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 7 Modulator Interface (T2-MI) and network topology | The DVB-T2 Modulator-Interface Specification (T2-MI) is defined by TS 102 773 [i.20]. An outline of a typical network topology based on the use of the T2-MI specification is given below. 7.1 Overview As described in clause 4.4.2, it is assumed that networks, particularly SFNs, will make use of a central network functio... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 7.2 Statistical multiplexing and service splitting | We consider the case where a number of video services are statistically multiplexed within the limits of a constant total capacity. This total capacity could be the total capacity of the DVB-T2 signal or a subset of this. In the latter case the remaining capacity would be used for some other purpose. Depending on the w... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 7.3 The T2 gateway and T2-Modulator Interface (T2-MI) | The T2-Gateway accepts one or more TSs (and/or GSE streams) at the input and generates, based on the input streams, a sequence of T2-MI packets at the T2-MI interface (Interface B of clause 4.4.2) at the output. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 7.3.1 The Basic T2-Gateway | The reference model of clause 4.4.2 defines the Basic T2-Gateway. From the point of view of this reference model any required splitting, PSI/SI handling apart from that related to the use of the common PLP, and PCR restamping of MPEG-2 TSs are assumed to have been done before the input to the Basic T2-Gateway. The Basi... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 7.3.2 Practical T2-Gateways | A practical T2-Gateway might correspond exactly to the Basic T2-Gateway described in clause 7.3.1. However, it might be convenient for real implementations to include additional functionality. Possible examples are: • Generation of one transport stream per data PLP (see clause 8.2). If a multiplex is generated by a non... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 7.4 Distribution of T2-MI packets to transmitters | The stream of T2-MI packets being output from the T2 gateway has to be encapsulated into appropriate lower protocol layers. The T2-MI specification [i.20] describes a way to carry the packets in an MPEG Transport Stream, which can in turn be carried over an ASI circuit as for DVB-T. The T2-MI specification also provide... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 7.5 Over-air distribution | Where a master transmitter acts as the distribution mechanism for a separate SFN on a different frequency (see figure 33), all the information required to generate identical co-timed SFN signals needs to be carried over air. Figure 33: Use of Main Transmitter to feed SFN Relays This topology has been successfully deplo... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 7.6 Regional/local content insertion | Regional or local services could be inserted in a distributed way after the T2 gateway, provided the corresponding capacity has been prepared in the T2-MI stream using one or more dedicated PLPs carrying dummy data. If e.g. a constant number (per T2 frame) of Baseband frames are reserved (e.g. by using "dummy" Baseband... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 7.7 Networks carrying composite T2-base/T2-lite signals | T2-lite signals (see clause 16) can be combined with T2-base signals to form a composite on-air signal in which the FEF parts of one profile contain the T2-frames of the other profile and vice versa. The signals of the two profiles are described by separate T2-MI streams with different values of t2mi_stream_id. The res... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8 T2-gateway | This clause gives guidance on the implementation of the functions associated with a T2-gateway, as described in clause 4.4.2, or with other equipment expected to be co-sited with the T2-gateway. In simple applications or networks these functions may be carried out by the modulator itself. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.1 Input interface | Formats for the input interface to the T2 gateway itself are expected to include: • one or more MPEG-2-TS multiplexes (see ISO/IEC 13818-1 [i.16]); and/or • one or more GSE streams (see TS 102 606 [i.9]). Enc #1 Enc #2 #n PSI/SI A/V + some A/V + some PSI/SI A/V + some PSI/SI PSI/SI For Common PLP Common control T2 Gate... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.2 Generation of one Transport Stream per data PLP | In input mode B a number (N) of transport streams may be input to the DVB-T2 system and allocated to N data PLPs (and a common PLP, where applicable). Two different approaches to generate these TSs are outlined below. In both approaches, when the common PLP is used a statistical multiplexer should take into account the... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.2.1 Separate TSs with common control | One way of generating the N TSs is to use N variable-bit-rate encoders, each producing a constant-bit-rate TS containing one service (video+audio+other possible components), where the proportion of null packets varies depending on the instantaneous bit rate (see figure 35). A central control ensures that the total amou... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.2.2 From one big TS | Another way to generate the N TSs is to use a normal statmux and then split this into the N TSs. N TSs would first be generated as above, but without the requirement for same bit rate and co-timed common data, and then fed to a multiplexer. The multiplexer then assembles a big TS, containing all services of the element... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.2.3 Discussion | The difference in end result between the two methods is only in the TS bit-rate and proportion of null packets, which is much higher in the second case. It should be noted that since Deletion of Null Packets (DNP) is limited to sequences of 255 null packets (signalling limited to 8 bits) and the bit rate of the big TS ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.3 Use of common PLPs | The common PLP of a group of PLPs is transmitted in such a way that a receiver can receive simultaneously any data PLP of the group as well as the common PLP. Since the common PLP typically benefits from much less time interleaving than the data PLPs it may be sent with a more robust MODCOD. When the DVB-T2 system is f... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.4 PLP grouping and statistical multiplexing | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.4.1 PLP groups with the same modulation and coding | The most straightforward way of performing statistical multiplexing between PLPs is to start with a conventional statmux of constant total bit-rate and allocate each of the services to a PLP, using the same coding and modulation for all the PLPs. All the PLPs would therefore have the same number of cells and the same n... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.4.2 T2-aware statistical multiplexing | More advanced statistical multiplexing could in principle be performed between PLPs with different code rates or modulation. In the case of different code-rates, the statistical multiplexer would need to allocate bits to each service in proportion to the code-rate of the associated PLP, so that the total gross bit-rate... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.5 Mode adaptation | The choice of options for Mode Adaptation were discussed in clause 5.12. The following points should be noted by implementers of the mode adaptation: • Where applicable, including for Transport Streams, the sync bytes are always removed, both in HEM and NM. This means that, in HEM, a (188-byte) TS packet will occupy on... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.6 Scheduling | The scheduler has two main tasks: • Allocating sections of the input bit-streams to Baseband Frames within particular Interleaving Frames. • Allocating the slices and sub-slices of each PLP to cells of the T2-frame. There is a degree of flexibility in the way that both tasks are carried out, and the T2 specification [i... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.6.1.1 Mode A | When a single PLP is used (Mode A), there will be a constant number of FEC blocks per Interleaving Frame and each Interleaving Frame will correspond to one T2 frame. This in turn will correspond to a fixed number of input bits, and the scheduler need only count these bits and map them into the BBFRAMEs. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.6.1.2 Mode B | When multiple PLPs are used (Mode B), with potentially variable bit-rates in each PLP, the situation is more complicated, because of the following: PLP data is quantised into BBFRAMEs - there have to be a whole number of FEC blocks, and therefore BBFRAMEs, in each Interleaving Frame. Even where the PLPs have constant b... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.6.1.2.1 Allocation model 1 | Allocation model 1 is the more efficient model, but imposes additional constraints, in particular on minimum data rate. In the normal run of operation, the sub-system behaves as follows. Each time one of the FIFOs contains one BBFRAME's worth of data, another BBFRAME in the current Interleaving Frame is allocated to th... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.6.1.2.2 Allocation model 2 | Allocation model 2 is much simpler, at the expense of wasted capacity. In this model, the collection window for each interleaving frame is defined to correspond to exactly TIF, with no overlap. At the end of each collection window, any data in each of the FIFOs is allocated to a baseband frame, with padding inserted if... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.6.1.2.3 Other allocation strategies | In addition to the two models described above, the following possibilities should be considered: • Intermediate strategies between model 1 and model 2 could be used. The total input bit-rate would be set somewhat below the total capacity of the frame, and padding used if the entire frame had not been allocated at the e... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.6.1.2.4 Use of the allocation models with FEFs | As explained in clause 8.6.1.2.1, the spacing between the ends of the collection windows is equal to the Interleaving Frame duration TIF. In allocation model 2 (clause 8.6.1.2.2), this is also equal to the duration of the collection windows. Where FEFs are used, TIF is longer than Ijump×PI×TF because each Interleaving ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.6.1.2.5 Timing and alignment of collection windows | The alignment and timing of the collection windows requires care, particularly when FEFs, multi-frame interleaving or frame skipping are used. We will specify the timing of the collection windows by defining the transmission delay TTX as the time interval from the end of the collection window for an Interleaving Frame ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.6.2 Scheduling of sub-slices | As explained, the second role of the scheduler is to decide where in the frame each of the sub-slices for each PLP will go. The number of sub-slices is statically configurable and is the same for all Type-2 PLPs; the factors affecting the choice of this parameter were discussed in clause 5.8. The locations of the sub-s... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.7 Padding methods | For a number of reasons, the capacity of the T2 system might exceed the amount of data to be carried. Possible reasons are: • The TS input bit-rate has been deliberately set slightly below the theoretical capacity. • Statistical multiplexing, particularly a T2-aware variant, might require some headroom to be left for s... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8 Managing the de-jitter buffer | [i.1] provides a receiver-buffer model which includes both the time de-interleaver memory and the de-jitter buffer, as well as the frequency/L1-de-interleaver. It is the responsibility of the modulator or T2-gateway to manage these buffers and to ensure that they neither under- nor over-flow. The buffer occupancy is ma... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.1 The receiver-buffer model | Time de- Interleaver (TDI) - Data De- modul- ation RF input Output stream (Data PLP) Time de- Interleaver Common Output stream (Common PLP) L1 cells Freq / L1 de-inter- leaver FEC chain De-jitter buffer (DJB) De-jitter buffer (DJB) Figure 43: Receiver buffer model The receiver-buffer model from annex C is shown in figu... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.2 Principles of buffer management | The general principle for managing the buffers is as follows. The end-to-end chain will have a constant delay, since the output TS will emerge at the same bit-rate as the input. The one parameter to be chosen is what this delay is. In the following discussion, we will define a number of terms. For the purpose of this c... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.3 Choice of design delay | Having defined the terms, the next step is to choose the design delay. If the design-delay value is too great, there will not be enough memory in the de-jitter buffer to provide the delay, and overflow will occur in the TDI (recall that the DJB itself cannot overflow according to the receiver buffer model). If the desi... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.3.1 Single PLP modes with multiple TI-blocks per Interleaving Frame | For single PLP modes, there will often be more than one TI block per Interleaving Frame (NTI>1). ISSY is not generally mandatory in such modes, unless one or more of the other criteria for ISSY applies, e.g. FEFs are used. In such cases the design delay should be set according to the following steps (from [i.28]): ETSI... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.3.2 Type 2 PLPs in multiple PLP modes | For type 2 data PLPs in multiple PLP cases using null packet deletion and with NTI= 1, together with allocation model 2, the recommended value (from [i.28]) is: { } { } )) , ( GCD , mod( ) , mod( )1 ( 1 )1 ( 3 1 1 ) ( I JUMP FEF JUMP FF FEF FF JUMP I FEF FEF JUMP I F basic L P cell common cells packet basic design P I ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.3.3 Common PLPs in multiple PLP modes | For common PLPs for which NTI=PI=Ijump=1, the most straightforward choice is to set Tdesign to be the same as for the associated data PLPs. This is not the optimum as a shorter design delay would reduce the DJB requirements, but as long as the common PLP has a relatively low bit-rate, the impact on the DJB budget is mi... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.3.4 Other cases | • The cases discussed in the preceding clauses only cover a subset of the possible DVB-T2 configurations. Other configurations are possible but the implications for the receiver buffer model have not yet been studied in detail. In particular, these include: Modes using multiple PLPs with dynamic bit-rate variation toge... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.4 The de-jitter buffer budget | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.4.1 Multiple PLP cases with variable bit-rate | Analysis of the DJB budget for multiple PLPs (with variable bit-rate) is rather involved, since it is necessary to identify the worst possible combination of incoming cells and outgoing packets. Broadly speaking, the worst case occurs when the data to be output in a particular frame is all concentrated at the end of th... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.4.2 Constant bit-rate | For single PLPs, or indeed PLPs as part of a group of multiple PLPs where the output bit-rate is known to be constant, the DJB budget calculation is generally simpler. Broadly speaking, it can be derived by calculating the bits delivered during one frame (or TI-block in the case of multiple TI-blocks), and subtracting ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.5 Receiver Buffer Management in T2-Lite | The parameters of the Receiver Buffer Model are slightly different in the T2-Lite profile (see clause 16). In particular, the value of Rcell depends on the constellation and, except for QPSK, is lower than the value in T2-Base (7,6 × 106 cells/s). As a result, cells could potentially arrive from the T2-Frame more quick... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.6 Other parameter checks required | In addition to the design delay and DJB budget, there are a few other features of the receiver buffer model that need to be checked. ETSI ETSI TS 102 831 V1.2.1 (2012-08) 90 |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.6.1 Avoiding TDI overflow during P2 | There is a possibility of overflow in the TDI during the P2 symbols, for single-PLP modes using multiple TI-blocks. This occurs because the PLP cells can be written to the TDI faster than they can be read. To avoid overflow, designers should ensure that: ( ) ( ) FIFO cell s extraBlock S cell post sig small big small sm... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.6.2 Avoiding TDI overflow during the first TI-block | There is also a possibility of TDI overflow during the normal symbols for single-PLP modes using multiple TI-blocks. The problem arises principally because the first TI-block can be smaller than the other TI-blocks and so there is a risk that the first TI-block will be written before the last TI-block of the previous f... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.6.3 Avoiding DJB underflow / TDI overflow during common PLP decoding | There is a danger that the requirement for the data and common PLPs to share a single FEC chain could prevent data from being transferred between the TDI and the DJB in the required time. For more information please see [i.28]. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.8.7 Further guidance in Receiver Buffer Management | Derivations and further explanation of the design rules presented in the preceding clauses are presented in [i.28]. The rules are also encoded in the dvbt2bl_VV_parameter_check simulation, which is part of the Common Simulation Platform [i.27] (see clause 4.4.5). This allows a complete configuration to be checked for c... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.9 Compensating Delay | A compensating delay is required if common PLPs are used and the data PLP uses different interleaving parameters to its associated common PLP. The relevant interleaving parameters are NTI, PI and Ijump; if any of these differ then a compensating delay is required. The purpose of the compensating delay is to ensure that... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10 Layer-1 signalling | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.1 Overview | 8. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.1 Overview | The Layer-1 (L1) signalling has two main functions. First, it provides receiver a means for fast signal detection and hence enables fast signal scanning. Secondly, it provides all information that receiver needs to access the Layer-2 signalling and the services themselves within the current (and possibly also the next)... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.2 Repetition of L1-dynamic signalling | To obtain increased robustness for the dynamic part of the L1-post signalling, the information may be repeated in the P2 symbols of two successive T2-frames. The use of this repetition is signalled by the L1-pre parameter L1_REPETITION_FLAG. If the flag is set to '1', dynamic L1-post signalling for the current and next... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.3 L1 change-indication mechanism | The L1 signalling offers a change-indication mechanism, by means of the L1_CHANGE_COUNTER-field in the dynamic part of the L1-post signalling. It is used to indicate when the configuration (i.e. the contents of the L1-pre signalling or the configurable part of the L1-post-signalling) will change. The change is indicate... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.4 Use of the L1 extension field | The L1 extension field may be defined for future applications. Possible applications include signalling to professional receivers for control of network operation, e.g. for control and synchronisation of relay sites. The L1 extension field, if present, should be ignored by receivers. In version 1.2.1 of [i.1], the firs... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.5 Example of L1 signalling | The details of the use of the L1 signalling are specified in [i.1]. This clause gives a full worked example of the construction of the fields of the L1 signalling for the simple case of a single PLP, together with comments to explain the chosen meaning in each case. The mode corresponds to the DVB reference stream case... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.6 In-band L1-dynamic signalling | In Input Mode B, the PADDING field in BBFRAME may be used to carry in-band signalling. Two types of in-band signalling are defined: type A and type B. Type A was defined in version1.1.1 of [i.1], whilst type B was introduced from version 1.2.1 of [i.1] in a backward-compatible way. Type B is optional in the T2-Base pro... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.6.1 Generation of the in-band type A signalling message | In-band type A signalling blocks carry L1 update information and co-scheduled information. When the IN_BAND_FLAG field in the L1-post signalling, defined in clause 7.2.3.1 of [i.1], is set to '0', the in-band type A is not carried in the PADDING field. The use of in-band type A is mandatory for PLPs that appear in ever... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.6.2 Insertion of L1-dynamic information of other PLPs | If NUM_OTHER_PLP_IN_BAND > 0, the in-band signalling carries L1-dynamic information for other PLPs as well as L1-dynamic information for its own PLP. The L1-dynamic information for other PLPs can be carried only when the values of PI and IJUMP for the current PLP are both equal to '1'. In other words, NUM_OTHER_PLP_IN_... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.6.3 Which frame is signalled for same PLP and other PLPs | The following points should be noted: • The dynamic signalling for the current PLP always applies to the next, rather than the current, Interleaving Frame, i.e. the in-band L1 dynamic information for the current PLP for Interleaving Frame n + 1 is carried in Interleaving Frame n. • The L1 dynamic signalling for the cur... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.6.4 Example of in-band signalling | An example of the contents of the padding field when carrying in-band signalling is given in table 22. Table 22: Example of the use of the in-band signalling fields In-band signalling field Contents Explanation PADDING_TYPE 00 This is in-band signalling type A PLP_L1_CHANGE_COUNTER 00000000 There are no changes foresee... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.10.6.5 In-band type B signalling | In-band type B signalling was introduced in a backward-compatible way in version 1.2.1 of [i.1]. It is used to give extra information related to the input streams, in particular allowing several pieces of ISSY information related to the first User Packet that begins in the BBFRAME. ETSI ETSI TS 102 831 V1.2.1 (2012-08)... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.11 Layer-2 signalling | Layer 2 signalling is provided differently for MPEG-2 Transport Streams and Generic Streams. DVB-T2 introduces the layer-1 concept of the "T2 System" (see clause 6.2.6). The mapping of Transport Streams to PLPs and the T2-system is signalled in the T2_delivery_system_descriptor transmitted in the NIT. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.11.1 Transport Streams | For the Transport-Stream case a single new PSI/SI signalling element is used: the T2 delivery-system descriptor (T2dsd): see figure 52. It is a mandatory element of the Network Information Table (NIT) that is provided for all Transport Streams of a T2 system. For each Transport Stream a single instance of the descripto... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.11.2 Generic Streams. | Generic Streams might occur in one of the following three variants: a) Generic Fixed Packet size Stream (GFPS). b) Generic Continuous Stream (GCS), also covering the case of a Generic Variable Packet size Stream. c) Generic Stream Encapsulated (GSE) according to TS 102 606 [i.9]. For cases a) and b) there is no layer 2... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.12 Generation of the T2-MI stream | The generation of BBFRAMEs and their allocation to Interleaving frames, together with the generation of the L1 dynamic data for each frame has been described in the previous clauses. This provides all of the information required for generation of the T2-MI packets containing BBFRAMEs and L1 signalling. Each time a BBFR... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.13 Generation of the T2-MIP | If over-air distribution is used as described in clause 7.5, the T2-Gateway should also generate the T2-MIP. This indicates the transmission time for the T2 super-frame in which it is carried. The T2-gateway is the easiest place to generate this for two reasons. Firstly, the T2-gateway generates the SFN information con... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.14 L1 Bias Balancing | It was realised, after version 1.1.1. of [i.1] was published and receivers had been manufactured, that the lack of energy dispersal scrambling for the L1-signalling could, under some circumstances, result in large peaks in the time domain signal, during the P2 symbols. The underlying cause of this was the fact that, al... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.14.1 L1 Bias balancing Techniques | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.14.1.1 P2 Tone Reservation | The reserved tones are always available in the P2 symbols, and so even when TR PAPR (see clause 9.3.8.3) is not being applied to the rest of the signal, it is worthwhile to apply it to the P2 symbols alone. Since no peaks in the rest of the signal are being cancelled, it only really makes sense to try to cancel the pea... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.14.1.2 L1 reserved bits and extension field | There are several fields in the L1 signalling "reserved for future use". Originally, these were set to '0's, but they could equally well be set to '1's. This is doubly effective since it reduces the number of '0's and adds '1's at the same time. The L1 signalling itself can be extended by adding an extension field, and... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.14.1.3 Bias balancing cells | Additional cells may be inserted between the L1-signalling and the PLPs (see clause 8.3.6.3.1 of [i.1]). The sole purpose of these cells is to reduce the bias and so they are called bias balancing cells - they can be thought of as being a little like reserved tones, although their modulation is set directly depending u... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.14.1.4 L1-ACE | A modified form of the ACE algorithm may be applied to the modulated cells of the L1 signalling. With this technique, the modification is calculated directly from the bias, to simplify the implementation (see clause 7.3.3.3 of [i.1]). The use of L1-ACE will cause a slight increase in the power of the P2 symbols, but ha... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 8.14.2 Approach to bias balancing | A good approach to bias balancing would comprise the following steps: 1) Set all of the reserved bits in the best possible way, either using the algorithm from [i.1] or a better one if available. 2) If appropriate to the FFT size, and capacity is available, add an L1 extension field. However, it will usually be more ef... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9 Modulators | This clause assumes that the modulator is fed with a T2-MI stream as defined in [i.20], generated by the T2 gateway. In some applications, some or all of the functions of the T2 gateway may be included in the modulator. See clause 8 for details of those functions. ETSI ETSI TS 102 831 V1.2.1 (2012-08) 110 |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1 Operation with T2-MI input stream | This clause describes how a modulator might work when operating with a T2-MI input stream. Details of the individual processing stages are given later in the later clauses of clause 9, whereas this clause discusses how the various blocks work together in terms of delays and relative timings. This clause is subject to c... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.1 Overview | Figure 56 is a top-level block diagram of a modulator operating with T2-MI input. Firstly the headers of the incoming T2-MI packets should be decoded to determine which of the defined packet types it is. The majority of packets will contain BBFRAMEs; in this case the PLP index should also be decoded from the header and... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.2 Buffering and timing relationships | When a T2-gateway is used, BBFRAMEs are formed and immediately sent to the modulators via T2-MI as soon as they are ready. Delays are required in the modulator both to hold up the data until the scheduling has been performed, and also to enable the L1 signalling, both in P2 and in-band, to be inserted at the appropriat... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.3 Generation of L1-signalling from T2-MI packets | The L1-signalling packets serve two purposes: they are used by the modulator to provide the dynamic information needed to perform the BICM processing on the BBFRAMEs. They are also needed to provide the signalling bits to be inserted into the T2-frame. The arrows at the bottom of figure 57 show how the L1 information i... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.4 Generation of the PLP data from the T2-MI input | Generating and encoding the PLP data for a given T2-frame from the T2-MI input packets is entirely deterministic. For a given T2-frame index, the modulator can determine from the configurable L1 signalling the following pieces of information: 1) Whether a given PLP is mapped to the T2-frame at all. The PLP is mapped to... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.5 Start-up behaviour | At start-up, or when the T2-MI input is restored following an outage, the modulator needs to wait until it has received a complete Interleaving Frame for each PLP. The worst case is that it just misses the beginning of one, so has to wait most of one Interleaving Frame to get the start of the next one, then receive all... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.6 Modulator synchronisation | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.6.1 Single-Frequency Network operation | When operating in Single Frequency Networks (SFNs) the need for modulators to be synchronised both in time and centre frequency is well known already from DVB-T and other COFDM systems. Typically a GPS receiver is used to provide timing signals in the form of a 10MHz frequency reference and a one-pulse-per-second (1PPS... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.6.2 Modulator test modes for SFN operation | A modulator test mode has been defined for operation in Single Frequency Networks (SFNs). In this mode, the first P1 preamble of each superframe is replaced by zero modulation at the modulator output (a "null P1 preamble"). This can be used in the laboratory to compare the timing of different modulators using the same ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.6.3 Testing SFN synchronisation using a spectrum analyser | A method has also been developed to verify SFN synchronisation at the T2-frame level without using the test mode described in the previous clause. The P1 preamble only occupies 6,83 MHz of the 7,61 MHz of the DVB-T2 System bandwidth (see clause 10.2.2.2). Therefore approximately 400 kHz at the edges of the DVB-T2 spect... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.6.4 Multiple-frequency network operation | In Multiple Frequency Networks (MFNs), the need for absolute synchronisation of the transmitters in a network is less critical. In DVB-T, one method used is to lock the modulator to the incoming Transport Stream, since for a given mode this has a fixed relationship to the fundamental clock rate of the DVB-T system. The... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.1.6.5 Operation with a composite signal with multiple profiles | Modulators may support the generation of signals made up of a combination of T2-Base and T2-Lite profiles (see clause 16). In this case separate T2-MI input streams will be provided, each having different values of t2mi_stream_id. The T2-MI streams can be carried in the same transport stream on different PIDs, or on di... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 9.2 Bit-interleaved coding and modulation |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.