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68c0023631b9916756c4eab7052aaa7b | 102 991 | 5.6.1.5.1 FECFrame Headers | FECFrame headers include the L1 part 1 signalling information. They are applied for Data Slices of Type 2. The FECFrame header is prepended at each QAM modulated FECFrame and includes information on PLP_ID as well as used QAM modulation scheme and LDPC code rate of the following FECFrame packet. Furthermore the FECFram... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 5.6.1.6 BB-Frames | BB-Frames are the basic unit in the logical framing structure of DVB-C2: allocation and scheduling are performed in whole numbers of BB-Frames. Where packetized streams are being carried, the packets may be mapped to BB-frames either synchronously or asynchronously, i.e. each BB-Frame may contain a whole number of pack... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 5.6.1.7 Packets | PLPs may carry packets, including MPEG Transport Stream packets or other types of packets used by generic streams. They may also carry continuous, non-packetized streams. The BB-Frame header (see clause 5.1.6 in [i.1]) provides a mechanism for packets to be reconstructed at the receiver, but the framing of the DVB-C2 s... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 5.7 Overview of interleaving | There are three different interleavers in the DVB-C2 specification, occurring in the following order in the modulation chain: • Bit Interleaver. • Time Interleaver. • Frequency Interleaver. The Bit Interleaver interleaves the code-bits within an LDPC codeword in order to avoid undesirable interactions between the bits ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 5.8 Payload Capacity | This clause lists the important technical parameters influencing the available payload capacity of a C2_System. • Modulation and code rate used for PLPs Obviously the choice of modulation parameters and code rate has the strongest impact on the payload capacity. In annex A examples for the calculation of the payload ca... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 5.9 New concept of absolute OFDM | Figure 7: Absolute OFDM concept in DVB-C2 The concept of 'absolute OFDM' is unique to DVB-C2. The first L1 part 2 signalling block begins at the absolute frequency of 0 MHz and the further blocks are partitioned in steps of 7,61 MHz towards higher frequencies. In contrast to other DVB standards it is not possible to sh... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6 Choice of Basic Parameters | There are a large number of parameters defined in DVB-C2 for configuring a cable transmission system. This clause will discuss the choice of each of the main parameters in turn. |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.1 Choice of code rate, block length and constellation | A choice of five rectangular QAM constellations is available in DVB-C2: 16-QAM, 64-QAM, 256-QAM, 1 024-QAM and 4 096-QAM. Selection of the constellations required can be related back to the commercial requirements of a minimum 30 % increased throughput over DVB-C and reuse of all existing cable network architectures an... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.2 Choice of FFT size and Carrier Spacing | Table 7 lists some of the tradeoffs to be considered when selecting an appropriate FFT size in OFDM-based transmission systems. Table 7: Tradeoffs in FFT size Increasing FFT size - Benefits Decreasing FFT size - Benefits Smaller guard interval fraction for required maximum echo delay tolerance Reduced complexity (altho... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.4 Choice of Pilot Pattern | DVB-C2 uses three types of pilots to aid the processes of synchronisation and channel estimation in the DVB-C2 receiver. This clause covers the choice of pattern for scattered pilots. A DVB-C2 receiver typically makes measurements of the channel using scattered pilots (SPs) and then interpolates between these measureme... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.5 Choice of C2 frame and FECFrame length | Factors affecting choice of the C2 Frame length include: • A longer value for the frame length generally decreases the percentage overhead associated with the preamble symbols thus increasing the total bit-rate. • A shorter value for the frame length enables the L1 signalling to occur more frequently, allowing faster l... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.6 Choice of Time Interleaving Parameters | The time interleaver provides a variety of different interleaving depths and can also be switched off. Enabling the time interleaver for L1 part 2 may affect the data throughput, which depends on the selected mode (see table 11). The time interleaver may be enabled or disabled depending on the following factors: • Use ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.7 Choice of Mode Adaptation | There are a number of options for mode adaptation, described in clause 5.1 of EN 302 769 [i.1]: • Normal Mode (NM) or High Efficiency Mode (HEM). • Use of Input Stream Synchronisation (ISSY). • Use of Null Packet Deletion (NPD). It is recommended that the options are used as follows: • Where compatibility with DVB-S2 [... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.8 Choice of Signalling Schemes | Selection of appropriate signalling schemes for C2 are defined by consideration of the following aspects: • C2 system architecture. • The required rate of change of each signalling parameter. • Overhead on data throughput. • Compatibility with DVB family of standards. • Compatibility with the C2 commercial requirements... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.9 Number of Data Slices versus PLPs | The cable operator needs to consider how to segment the required downstream services into and across Data Slices and PLPs to maximise the efficiency and flexibility offered by the C2 physical layer in the HFC network. The following characteristics and features of DVB-C2 have been considered especially: • The most commo... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.10 Notches | Spectrum notches can be signalled in DVB-C2 to reduce the effect of emissions from cable systems into terrestrial frequency bands (e.g. aircraft radio or conversely ingress from high power interfering signals into the cable network. The notching features in [i.1] are intended to enable C2 to coexist with other transmis... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.10.1.1 Minimum Data Slice Width | The minimum width of a data slice is constrained by the presence of an adjacent broadband notch. The C2 receiver requires a minimum number of Continual Pilots (CPs) for signal processing (e.g. for Common phase error correction). Table 13 shows the relationship between numbers of CPs and the data slice/OFDM bandwidth. C... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.10.1.2 Static Data Slices | Decoding of the L1 part 2 signalling data from the preamble cannot be reliable in the case where a Data Slice with less than 3 408 carriers exists between broadband notches. This is a problem for a Data Slice Type 1 as a pointer, which points to the start of the first FECFrame packet, is normally decoded from the L1 pa... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.11 Choice of Layer 1 signalling parameters | |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 6.11.1 Choice of the "Data Slice Tuning Position" parameter | To avoid the ingression of spectral artifacts which are not part of the signal spectrum of the DVB-C2 signal itself the value of the parameter DSLICE_TUNE_POS of each Data Slice of the DVB-C2 system might be selected such that the amount of out-of-band interference within the spectrum preselected by the tuner window is... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7 Input Processing / Multiplexing | |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.1 Generation of the FECFrame Header | Two encoding schemes of the FECFrame Header are shown in the figures 9(a) and 9(b). Initially the 16 bits of the L1 signalling part 1 are FEC encoded by a Reed-Muller (32,16) encoder. Subsequently each bit of the 32 bit Reed-Muller codeword is split to form an upper and a lower branch. The lower branch applies a cyclic... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.2 Use of common PLPs | A common PLP is only required when multiple TSs are transmitted, and these TSs are called as 'group of 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. ETSI ETSI TS 102 991 V1.2.1 (2011-06) 46 Figure 10: ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.3 PLP bundling and Statistical Multiplexing | In case of input signals that exceed the capacity of a single Data Slice (e.g. 200 Mbit/s), the XFECFrames of the input signal has to distributed into different Data Slices with one PLP each. If the input signal consists of HDTV services encoded in statistical multiplexing, the size of those three Data Slices will vary... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.4 Use of the Null Packet Deletion mechanism | Null Packet Deletion is an option offered by DVB-C2 that removes the Null Packets (stuffing data) at the transmitter side from the MPEG-2 Transport Stream. However, the receiver is able to re-insert the deleted Null Packets at their original positions, as these positions are signalled within the transmitted data (see c... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.4.1 Use of Null Packet Deletion with Common PLP | The Common PLP allows for the transmission of Transport Stream packets, which are common for multiple Transport Streams. At the receiver side the Common PLP and the Data PLP are merged in order to obtain the fully syntactically correct Transport Stream. Therefore this requires sufficient Null Packets within the individ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.4.2 Use of Null Packet Deletion for Efficient Statistical Multiplexing | Statistical Multiplexing can improve the source coding gain. Normally, different services that are jointly encoded are transmitted within a single MPEG-2 Transport Stream. However, for Video on Demand services it is also possible to transmit these services using multiple PLPs (Data Slice Type 2 only), which e.g. allows... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.4.3 Null Packet Deletion for Reduced Power Consumption | The Null Packet Deletion mechanism can be applied for reduced power consumption within the receiver (Data Slice Type 2 only). Instead of using the Null Packets within the Transport Stream to obtain a specific bit-rate, these Null Packets can be removed using the Null Packet Deletion. Then Stuffing Data Slice Packets ar... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.5 Use of Issy Time Stamping | The use of the Input Stream Synchronizer subsystem is mandatory for bundled PLPs (see annex F of [i.1]). For non- bundled PLPs the use of the Input Stream Synchronizer subsystem is optional for PLPs carrying GSE, GCS or GFPS streams, but in the case of PLPs carrying Transport Streams (TS), it shall always be used, exce... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.6 Stuffing Mechanism | The DVB-C2 system offers multiple stuffing means. This stuffing is mainly required to adapt the bit rate of the incoming signal to the bit rate of the current C2 system settings. The different mechanisms are described in the following clauses. |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.6.1 Transport Stream Stuffing | The stuffing on Transport Stream level by means of Null Packets is a well-known technique to adapt the bit rate of an input stream to a fixed output bit rate. For details see [i.10]. |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.6.2 Base Band Frame Stuffing | The Base Band Frame Stuffing is the recommended stuffing mode for the lower layer stuffing if Data Slice type 1 is used. It may be necessary if the Data Slice bit rate is not adjustable to the payload bit rate ideally (e.g. due to the granularity of Data Slice bandwidth). Hence, the Base Band Frame Stuffing is a means ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.6.3 Data Slice Packet Stuffing (only Data Slice Type 2) | Data Slice Packet Stuffing is the recommended stuffing mechanism for lower layer stuffing if Data Slices type 2 is used, because it reduces the amount of data the LDPC decoder has to process. If the transmitter does not have any payload Data Slice Packet to transmit, it simply transmits a Stuffing Data Slice Packet (se... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.6.4 Data Slice Stuffing | DVB-C2 offers the possibility to adapt the bandwidth of the Data Slices between consecutive frames without service interruption, which is also a stuffing mechanism. Figure 15: Principle of Data Slice Stuffing The principle of Data Slice Stuffing is depicted in figure 15. The two (payload) Data Slices do not fill the co... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.7 Multiplexing, Dimensioning of PLPs and Data Slices | The following clauses list possible scheduling algorithms. These are based on the MPEG-2 Transport Stream. However, extensions to other protocol schemes are possible. For simplicity, it is assumed that the available cell rate within the Data Slice is always higher than the required cell rate of the multiplexed payload ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.7.1 Single PLP per Data Slice | When using a single PLP per Data Slice only, no complex multiplexing is required. However, as the available bit-rate of the Data Slice will not match the bit-rate of the input stream, stuffing is required. As already explained in clause 7.3, different possibilities exist. Their application depends on the used Data Slic... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.7.1.1 Data Slice Type 1 | Figure 16 depicts the scheduler for Data Slice Type 1. It is assumed that the available Data Slice bit-rate is sufficient to transmit the input data stream. As the output stream (i.e. Data Slice Packets) has to have a fixed output bit-rate, the application of Null Packet Deletion is not useful for this configuration. T... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.7.1.2 Data Slice Type 2 | The transmission within the Data Slice Type 2 can follow the same principle as for Data Slice Type 1. However, the stuffing does not take place within the BBFRAMEs, but uses Stuffing Data Slice Packets. The application of Null Packet deletion has not been considered for simplicity reasons. Figure 17: Block Diagram for ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.7.2 Multiple PLP | The transmission of multiple PLPs within one Data Slice is only possible using the Data Slice Type 2, because Data Slice Type 1 does not allow for the transmission of multiple PLPs. Figure 18 shows the block diagram of a possible scheduling algorithm. The associated pseudo code for the scheduling algorithm is listed in... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.8 Layer-2 signalling | Layer 2 signalling is provided differently for MPEG-2 Transport Streams and Generic Streams. DVB-C2 introduces the layer-1 concept of the "C2 System" (see clause 8 in [i.1]). The mapping of Transport Streams to PLPs and the C2-system is signalled in the C2_delivery_system_descriptor transmitted in the NIT. |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.8.1 Transport Streams | For the Transport-Stream case a single new PSI/SI signalling element is used: the C2 delivery-system descriptor (C2dsd): see figure 20. It is a mandatory element of the Network Information Table (NIT) that is provided for all Transport Streams of a C2 system. For each Transport Stream a single instance of the descripto... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 7.8.2 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 [i.9]. For cases a) and b) there is no layer 2 signalling... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8 Modulator | |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1 Preamble Generation | Figure 22 depicts the block diagram of the preamble generation. Firstly, the preamble data is encoded by means of the forward error correction and the QAM mapping. This is followed by the time interleaving. Then, the preamble header is inserted. The preamble data and the Preamble Header are cyclically repeated until al... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.1 Preamble Payload Data Processing | |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.1.1 Preamble Time Interleaving | Time interleaving (TI) for the preamble operates at constellation-mapped Layer 1 (L1) part 2 data level (see clause 8.5 of [i.1]). A L1 TI block is the set of OFDM cells within which L1 time interleaving is performed; there is no time interleaving between L1 TI blocks within one or multiple preamble(s). No time interle... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.1.2 Addition of Preamble Header | In addition to the LDPC encoded preamble data a preamble header is added to the preamble symbol. This preamble header does not change within a C2 preamble if it consists of multiple OFDM symbols. It carries information that is required for the decoding of the L1 signalling data. Details are given in clause 8.2 of [i.1]... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.1.3 Cyclic Repetition | After the addition of the preamble header there may be still some unused OFDM cells within the preamble. Therefore, the remaining parts are filled with a cyclic repetition of the signalling data (including the preamble header). Details are given in clause 8.4.1 of [i.1]. |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.1.4 Preamble Frequency Interleaving | The purpose of the preamble frequency interleaver is the separation of neighbouring data cells and to avoid error bursts caused by narrow band interferers or frequency selectivity. Therefore, the same frequency interleaver as used for the Data Slices (see clause 9.4.5), which works on the NL1=2 840 data cells of each L... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.2 Preamble Pilot Generation | The DVB-C2 preamble repeats itself cyclically in the frequency domain. As repetitions within the frequency domain lead to high peak-to-average power ratios it is desirable to avoid this direct repetition. For the DVB-C2 preamble this aim is reached by means of scrambling the preamble with two scrambling sequences. The ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.2.1 Data Scrambling Sequence | Figure 23 shows the block diagram for the generation of the data scrambling sequence. The sequence is obtained by using a linear feedback shift register with the generator polynomial: 1 2 11 + + X X . The output of the generator is the value of the most right shift register in the figure. Before the calculation all shi... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.2.2 Pilot Scrambling Sequence | Figure 24 depicts the block diagram of the pilot scrambling sequence generator. In contrast to the data scrambling sequence it employs only 10 shift registers. The polynomial of this linear feedback shift register is: 1 2 11 + + X X . Similar to the data sequence it is also initialized with all '1's at the beginning. F... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.2.3 Impact of long "0" or "1" sequences in the Preamble on the PAPR | Generally the presence of long "0" or "1" sequences within the Preamble leads to a bias on the OFDM subcarriers. This causes a high Peak to Average Power Ratio (PAPR) within the resulting time domain signal, i.e. the presence of very high signal peaks. Therefore, any repetition of sequences is avoided by scrambling of ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.2.4 Preamble Pilot Modulation Sequence | The modulation of the pilots is obtained by combining the pilot and the data scrambling sequence: ' i k P k w w w ⊕ = with ( ) P L D K k i / mod 1 = while k is the absolute OFDM sub-carrier index, KL1=3 408 is the number of OFDM sub-carriers per L1 Block, and DP=6 is the preamble pilot spacing. The value i is the requi... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.3 Mapping of the Preamble Pilots and Data | |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.3.1 Mapping of the Pilots | The pilots are mapped onto the preamble by using the equation: { } ( ) { } 0 Im 2 / 1 2 Re , , , , = − ⋅ = P k l m k PP P k l m P P c r A c while P k l c P c , , is the complex QAM cell of frame m, preamble OFDM symbol lP and absolute OFDM sub-carrier k, APP=1 is the amplitude of the preamble pilots, and rk is the prea... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.1.3.2 Mapping and Scrambling of the Preamble Data | The preamble data repeats itself cyclically within the frequency domain, i.e. every KL1 OFDM sub-carriers (7,61 MHz in 8 MHz operation). Additionally, the data is scrambled using the data scrambling sequence wk. This is described by: { } { } ( ) { } { } ( ) k P P k P P w P q l P k l m w P q l P k l m a c a c 1 Im Im 1 ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.2 Pilots (Scattered-, Continual- pilots) | |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.2.1 Purpose of pilot insertion | Pilots are inserted for several reasons; the scattered pilots are inserted mainly for channel estimation and subsequently equalisation. The pilot patterns for DVB-C2 are chosen so that channel estimation potentially can be done without any time-axis interpolation, however to get maximum performance from the given pilot... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.2.2 Pilot locations | Regarding pilot locations, particular care should be taken to the following points: • Preamble symbols do not have any of scattered, continual or edge pilots, instead they have preamble pilot. The preamble pilot locations are a superset of all scattered-, continual- and edge-pilots locations. • The scattered pilot patt... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.2.3 Number of pilot cells | Due to the unique definition of the pilot locations across the whole cable medium bandwidth the absolute number of pilot cells depend on the C2 bandwidth as well as its frequency location. The number of pilot cells is furthermore different for the 2 possible guard interval fractions as they result in different scattere... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.2.4 Pilot boosting | All scattered-, continual- and edge-pilots of data symbols have the same boosting value of 7/3. The amplitude of preamble pilots (App) is fixed to App=6/5 in case of 1/128 Guard Interval and fixed to App=4/3 in case of 1/64 Guard Interval. The given boosting values ensure that the average energy of the preamble and the... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.2.5 Use of reference sequence | All pilots (scattered-, continual- and edge-pilots) are modulated with the same reference sequence as the preambles. The reference sequence is defined for all carrier indices k, and has its origin at 0 RF. (Not left most carrier as DVB-T/H/T2 system.) |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.3 PAPR and Possible Implementation | When reserved carriers are activated by a relevant L1 signalling part 2, 'RESERVED_TONES', these reserved carriers defined in clause 9.7 of [i.1] can be used for PAPR reduction. Figure 25 shows the structure of OFDM transmitter with PAPR reduction using reserved carriers. Reserved carriers are allocated according to pr... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.3.1 Reserved carriers | In the Data Symbols excluding Preamble Symbols, the set of carriers corresponding to carrier indices defined in table 36 of [i.1] or their circularly shifted set of carriers shall be reserved depending on the OFDM Symbol index of the Data Symbol. Positions of reserved carriers within Notches shall be excluded from the ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.3.2 Reference kernel | Signal peaks in the time domain are iteratively cancelled out by a set of impulse-like kernels made using the reserved carriers. A reference kernel signal, is defined as: 0 1 1 (1 ) , ,..., FFT FFT TR N TR N IFFT p p p N − ⎡ ⎤ = = ⎣ ⎦ p where NFFT and NTR indicate the FFT size and the number of reserved carriers, respe... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.3.3 Algorithm of PAPR reduction using reserved carriers | Figure 26 shows the detailed block diagram of the peak-cancellation algorithm. The IFFT output (x) is fed into the peak-cancellation block, and the peak position and value of x are detected. Then the reference kernel, generated by the reserved carriers corresponding to the current OFDM symbol, is circularly shifted to ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.3.3.1 PAPR cancellation algorithm | Denote the vector of peak reduction signal by c, and the vector of time domain data signal by x, then the procedures of the PAPR reduction algorithm are as follows: Initialization: The initial values for peak reduction signal are set to zeros: ( ) [ ] 0 0 0 T = c L where c(i) means the vector of the peak reduction sign... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4 Signalling (L1 part 2, including FEC) | |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.1 Overview | The Layer-1 (L1) part 2 provides all information that receiver needs to access the Layer-2 signalling and the PLPs within the current C2 Frame. The L1 part 2 signalling structure is illustrated in figure 28. All information is conveyed in L1 signalling part 2 data part and it can be changed frame by frame. L1 part 2 da... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.2 L1 change-indication mechanism | The L1 signalling offers a change-indication mechanism, by means of the L1 _PART 2_CHANGE_COUNTER-field. It is used to indicate when the configuration (i.e. all fields in L1 signalling part 2 data except for PLP_START and L1_PART 2_CHANGE_COUNTER itself) will change. The change is indicated as the number of C2 Frame af... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.3 CRC insertion | The 32-bit CRC is applied only to the L1 signalling part 2 data if the length of L1 signalling part 2 data is a multiple of 2. Otherwise 1-bit L1 block padding is inserted following the L1 signalling part 2 data and CRC is applied to the L1 signalling part 2 data and L1 block padding. The length of the L1 signalling pa... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.4 Example of L1 signalling part 2 data | The details of the use of the L1 part 2 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. Table 15 gives a worked example of the signall... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.5 FEC for the L1 signalling part 2 | This clause gives an overview on protection of L1 signalling part 2 based on BCH and LDPC codes. In particular, this clause briefly introduces the shortening of the BCH information part and puncturing of the LDPC parity part according to the length of signalling information: these are L1-specific operations which are n... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.5.1 Shortening of BCH Information part | The information bits of L1 signalling part 2 are protected by a concatenation of a BCH outer code and an LDPC inner code. The L1 signalling part 2 is first BCH-coded and the BCH-coded word is then further protected by a shortened and punctured 16 K LDPC code. For the protection of the L1 signalling part 2, the BCH code... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.5.2 Example for shortening of BCH information | Assume that the pure L1 signalling part 2 consists of 11 956 bits, i.e. K L1part 2_ex_pad = 11 956. K L1part 2_ex_pad denotes the number of information bits of the L1 signalling part 2 excluding the padding field, L1_PADDING, as described in clause 8.3.3 in [i.1]. Then, the number of LDPC blocks needed for the protecti... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.5.3 BCH encoding | The Kbch information bits (including the Kbch - Ksig zero padding bits) are first BCH encoded according to clause 6.1.1 in [i.1] to generate Nbch = Kldpc output bits (i0… iNbch - 1). |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.5.4 LDPC encoding | The Nbch = Kldpc output bits (i0… iNbch - 1) from the BCH encoder, including the (Kbch - Ksig) zero padding bits and the (Kldpc - Kbch) BCH parity bits, form the Kldpc information bits I = (i0, i1, …, iKldpc - 1) for the LDPC encoder. Note that for the protection of L1 signalling part 2, the number of BCH parity bits, ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.5.5 Puncturing of LDPC parity bits | The 16 K LDPC code with Kldpc = 7 200 for L1 signalling part 2 has (Nldpc - Kldpc) = 9 000 parity bits. Since the code length of 16 K LDPC code, Nldpc is 16 200, its effective LDPC code rates (Reff) is 4/9. All LDPC parity bits, denoted by {p0, p1, …, p8999}, are divided into 25 (= Qldpc) parity bit groups where each p... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.5.6 Example for Puncturing of LDPC parity bits | Assume that the pure L1 signalling part 2 consists of 11 956 bits. Then, Ksig is 3 986 as calculated in clause 8.4.6.2. Note that the coded L1 part 2 is always transmitted using 16-QAM. For a given Ksig = 3 986 and modulation order 16-QAM, Npunc is determined by the following steps: Step 1) _ 6 6 ( ) (7032 3986) 3655 5... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.5.7 Removal of zero-padding bits | The (Kbch - Ksig) zero-padding bits are removed and are not transmitted. This leaves a word consisting of the Ksig information bits, followed by the 168 BCH parity bits and 9 000 - Npunc (= Nldpc - Kldpc - Npunc) LDPC parity bits without Npunc punctured bits, as illustrated infigure 33. Figure 33: Example of removal of... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.4.5.8 Bit Interleaving and constellation mapping after shortening and puncturing | The LDPC codeword of length NL1part 2, consisting of Ksig information bits, 168 BCH parity bits, and (9 000 - Npunc) LDPC parity bits, are bit-interleaved using a block interleaver as described in clause 8.4.3.6 in [i.1]. Each bit-interleaved LDPC codeword is mapped onto constellations as described in clause 8.4.4 in [... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.5 Interleaving | |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.5.1 Bit interleaving | Bit Interleaving is described in clause 6.1.3 of [i.1]. |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.5.2 Time interleaving | Time interleaving (TI) for Data Slice operates at Data Slice level as described in clause 9.4.4 of [i.1]. A TI block is the set of OFDM cells within which time interleaving is performed; there is no time interleaving between Data Slices or TI blocks. No time interleaving is allowed between Data Slice and preamble. The ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.5.3 Frequency Interleaving | The frequency interleaver in DVB-C2 is applied to the payload cells of a given Data Slice from one OFDM symbol to the next. The number of payload cells per Data Slice per OFDM symbol (NDS) can vary from symbol to symbol. NDS comprises the number of cells between (KDS,max - KDS,min ) minus the number of continual pilots... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.6 Framing | The OFDM based C2 Frame structure is shown in time and frequency direction in figure 34. The C2 Frame structure comprises LP Preamble Symbols (LP >=1) followed by Ldata Data Symbols in time direction. The beginning of the first Preamble Symbol marks the beginning of the C2 Frame. The number of Preamble Symbols LP depen... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7 OFDM Signal Generation | The DVB-C2 specification introduces the new concept of Absolute OFDM, in which all OFDM subcarriers are seen relative to the absolute frequency 0 MHz instead of a centre frequency as used in other systems, e.g. DVB-T2. This leads to the formulas given in clause 10.1 of [i.1] that mathematically define the transmitted s... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.1 OFDM Modulation Using the Equivalent Lowpass Representation | Generally, the generation of the OFDM signal in the passband is impractical, as this requires extremely high sampling rates. Hence, the generation in the equivalent lowpass representation is normally used [i.22]. Afterwards, the signal is shifted from the equivalent lowpass representation into the desired passband. The... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.2 Calculation using the Fast Fourier Transform | This clause describes two possible signal generations using the equivalent lowpass representation of the signal in the transmitter. The first approach uses the centre frequency with pre-distortion, while the second approach uses an optimised carrier frequency. It has to be noted that similar considerations are also val... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.2.1 Generation Using the Centre Frequency of the Signal with Predistortion | The centre frequency of the DVB-C2 signal can be described as: U c c T k f = (9), with 2 min max K K kc + = (10). However, this would lead to unwanted common phase rotations between consecutive OFDM symbols. Hence, these rotations have to be compensated for generating a standard compliant signal. Therefore, the signal ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.2.2 Generation Using the Optimum Carrier Frequency | As described in the previous clauses, a common phase rotation may be introduced to the system, depending on the carrier frequency. This common phase rotation can be compensated in order to obtain an output signal as defined in [i.1]. Alternatively, this common phase rotation can be avoided by carefully choosing the car... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.3 OFDM Generation Block Diagram | Figure 35 depicts the transmitter block diagram for the generation of the OFDM signal, which will be described in detail in the following clauses. Firstly, the signal is zero padded for preparation of the Inverse Fast Fourier Transform (IFFT). Then, the Guard Interval is added, the signal is converted from digital to a... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.3.1 Zero Padding | The Zero Padding is required to pre-condition the signal for the transformation of the frequency domain signal into the time domain using the Fast Fourier Transform. Firstly, the signal has to be stuffed in order to fit the FFT size N. Secondly, a realignment of the subcarrier positions is required to be able to use th... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.3.2 IFFT Calculation | The signal has been generated within the frequency domain. The task of the inverse Fast Fourier Transform is the calculation of the corresponding time signal. This is achieved by means of: ∑ − = ⋅ ⋅ = 1 0 2 , , ) ( 1 ) ( N k N n k j l m total l m e n X K k x π (20) for N k < ≤ 0 , where m is the OFDM symbol, l the C2 f... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.3.3 Guard Interval Insertion | Figure 37 depicts the insertion of the Guard Interval. This is a cyclic copy of the last part of the useful OFDM symbol part, which is copied to the beginning. Mathematically, the OFDM symbol ) (' k x including the Guard Interval is obtained as described in equation (21). ) 0 ( x )1 ( − N x )0 ('x )1 (' − Δ + UT N N x ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.3.4 Digital to Analogue Conversion and Low-pass Filtering | The previous calculations have been made in the digital domain. The task of this block is the conversion into an analogue signal. Therefore, the signal x'(k)m,l sampled with the sampling rate U T N / has to be converted from digital to analogue OFDM symbol by OFDM symbol. This causes alias at multiples of the sampling ... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.7.3.5 Frequency Shifting | Final step is the shifting of the equivalent lowpass signal into the wanted passband. This goal is reached by mixing the signal with the carrier frequency fc, which is similar to a complex multiplication of the signal by t f j c e π 2 and the transmission of its real part. |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 8.8 Spectral Shaping | The effective bandwidth of a DVB-C2 signal is calculated by the difference between the highest and the lowest sub-carrier frequency. Its minimal and maximal limits are defined by the signalling mechanism chosen. The minimal effective bandwidth amounts to some 7,61 MHz in a system based on 8 MHz channels and to some 5,7... |
68c0023631b9916756c4eab7052aaa7b | 102 991 | 9 Network | The network provides the transport and distribution capability to deliver the DVB-C2 and other signals to a number of customer receivers. Apart from the conveyance of the signals, the network will add distortion signals like thermal noise from the amplifiers, echo and intermodulation products associated with the non-li... |
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