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5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.1 FFT | The considerations for the use of the Fast Fourier Transform (FFT) algorithm in a receiver are essentially the same as those for the use of the IFFT in the modulator (see clause 9.3.6). |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2 Channel equalisation | Channel equalisation comprises the processes of common phase-error correction, channel estimation and equalisation. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.1 Common Phase-Error correction | As explained in reference [i.10], phase noise (whether introduced by local oscillators in the transmitter or the receiver) can be shown to introduce two distinct kinds of imperfection in OFDM: • Inter-Carrier Interference (ICI): crosstalk between carriers of a more-or-less noise-like nature. • Common Phase Error (CPE):... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.2 Locating the CPs | The number and locations of the Continual Pilots vary depending on FFT size, Scattered Pilot Pattern and the use of Extended Carrier mode. Receiver implementers should refer to clauses 9.3.4.2 and 9.3.4.3 which list a number of important points to be noted as well as tabulating numbers of pilots of various types as a c... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.3 SISO channel estimation | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.3.1 Overview | 10.3.2.3.1.1 The need for channel estimation The received carrier amplitudes output by the receiver FFT are not in general the same as transmitted - they are affected by the channel through which the signal has passed on its way from the transmitter. Consider the channel extent, which could be variously described as: t... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.3.2 Fundamental limits | The channel response Hk,l in general varies with both time (symbol index l) and frequency (carrier index k). The temporal variation corresponds to external causes such as Doppler shift and spread, but also to instantaneous error in the receiver's frequency tracking. The variation with frequency is a symptom of channel ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.3.3 Interpolation | 10.3.2.3.3.1 Limitations In principle, channel variations within the Nyquist supported area described in the previous section can be measured. However, the Nyquist limit can only be very closely approached when using an interpolator having a very large number of taps. This is unattractive on grounds of cost and complex... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.3.4 P2 symbols | The P2 symbols are different from the main payload data symbols since they always use a relatively dense pilot pattern. There are two versions: one in which every sixth carrier is a pilot, which is used with 32 K FFT in SISO mode; the other one has every third carrier as a pilot and is used for all other FFT sizes (and... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.3.5 Other special cases | The foregoing clauses have outlined a strategy for channel estimation for the main body of payload symbols and also for the P2 symbol(s). There are some other special cases pertaining to data near the start and finish of the frame, where the sequence of Scattered Pilots is inevitably in some sense disturbed, and thus r... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.3.6 Further observations | The procedure outlined in the previous clause derives all channel estimation for data cells within a T2 frame from measurements made within the same the T2 frame. This has the merit of being undisturbed when T2 frames are separated by FEFs (whose internal format is currently undefined, apart from the need to start with... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.2.4 MISO channel estimation | The basic principle of MISO channel estimation is that the pilots can be partitioned into two subsets: in one subset the pilots are transmitted in the same phase from both sets of transmitters, allowing the sum of the two channel responses to be estimated; in the other subset the pilots are inverted from transmitters i... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.3 MISO decoding | This clause describes MISO decoding in the receiver for a MISO processed transmission signal, according to clause 9.1 of [i.1]. Figure 106: System model for MISO diversity scheme The diversity scheme used in DVB-T2 is based on the methodology described by Alamouti in [i.8]. Figure 106 depicts the system model for the m... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.3.1 ZF and MMSE Alamouti matrix inversion | The analysis above assumes that the channel response is the same on both cells of an Alamouti pair. In real-world channels the variation of the channel response is likely to be significant, and this assumption is not valid. It is therefore recommended that a more sophisticated Alamouti decoding process be used. In the ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.3.3.2 Separation of Alamouti pairs by pilot cells | In normal data and frame-closing symbols, the cells making up a MISO pair will sometimes be separated by a pilot, since no special measures are taken in those symbols to avoid this. Care should therefore be taken to ensure that the correct channel estimates are used in the Alamouti decoding process. In frequency-select... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4 De-interleaving and de-mapping | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.1 Frequency/L1 de-interleaver | To minimise memory use the frequency de-interleaver may be implemented with a single memory comprising Nmax locations. Nmax is the maximum number of data cells in an OFDM symbol of the given FFT size. It is envisaged that practical implementations of DVB-T2 receivers should support all the FFT sizes included in [i.1]. ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.1.1 Implementation of L1/Frequency de-interleaver 32 K | For odd-even interleaving as used in 32 K, the de-interleaver should read data cells from even symbols (symbol number of form 2n) into its memory in a sequential order. For odd symbols (symbol number of form 2n + 1) the data cells are read into memory in a permuted order, the permuted order addresses H(p) being provide... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.1.2 Implementation of the basic frequency de-interleaver in 1 K-16 K | Similarly for modes other than 32 K that use odd-only interleaving, with symbol 2n at its input the de-interleaver steps for the basic frequency de-interleaver are as follows. Modifications to implement the combined L1/Frequency de-interleaver are described in clause 10.4.1.3. 1) p = 0; wptr = rptr = 0; 2) generate add... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.1.3 Implementation of the L1/ Frequency De-interleaver in 1 K-16 K | Figure 107 shows how the combined de-interleaver can be implemented in memory. The figure is for 8 K, with two P2 symbols, but the principle can easily be extended to other modes. The red and green cells are L1-pre- and post- cells respectively, and the blue cells are data cells. Figure 107: Combined L1/Frequency de-in... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2 Frame extraction | Following the frequency de-interleaving, the cells will be in the correct order to reverse the function of the frame builder, and so extract the L1 signalling and the PLPs. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.1 Extraction of the PLPs | The PLP (or PLPs) to be received should be extracted based on the PLP_START and PLP_NUM_BLOCKS parameters as described in clause 7.2.3.2 of [i.1]. These parameters are carried in the P2 symbol(s) and may also be signalled using in-band signalling (see clause 10.4.2.4). The specification describes how the slices or sub-... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.2 Extraction of the L1 signalling cells | The L1 signalling cells are carried in the P2 symbols as described in clause 8.5.3 of [i.1]. When the cells are extracted, the zig-zag order should be undone; this can be considered as a de-interleaving process, and should be implemented as part of the frequency de-interleaver as described in clause 10.4.1. This is bot... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.3 Timing of L1 and PLP extraction and decoding in the P2 symbols | The timing of signal flows during the P2 symbols can be quite critical, because of the way each of the L1-pre, L1-post and PLP extraction and decoding depends on the previous stage. Figure 108 shows a timeline of the process, with the time taken for each stage according to the receiver buffer model. Some of the stages ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.4 Use of in-band dynamic signalling | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.4.1 Interleaving over one T2 frame or less | The T2 receiver can obtain L1-dynamic signalling from in-band signalling as well as P2 symbols. The in-band signalling is carried in the PADDING field of the first BBFRAME of each PLP, when IN-BAND_FLAG field in L1-post signalling, defined in EN 302 755 [i.1], is set to '1' and one Interleaving Frame is mapped to one T... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.4.2 In-band signalling when interleaving over multiple T2 frames | When multi-frame interleaving is used, i.e. PI > 1 so that one Interleaving Frame is mapped to more than one T2 frame, in-band L1-dynamic signalling can still be used. In this case the in-band signalling of a PLP carries only its own L1 dynamic information, and the information applies to the T2 frames to which the next... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.4.3 In-band signalling for PLPs not present in every T2-frame | In-band signalling can also be used for PLPs which are not present in every T2 frame. In this case, the signalling applies to the T2 frame to which the next Interleaving Frame is mapped. If each Interleaving Frame is mapped to one T2 frame, the signalling therefore applies to the next T2 frame to which the PLP is mappe... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.4.4 Reading the P2 symbols on reconfiguration | It can be signalled in the in-band signalling where the configuration (i.e. the contents of the fields in the L1-pre signalling or the L1-post signalling) will change in a way that affects the PLPs referred to by this in-band signalling field. This is indicated by PLP_L1_CHANGE_COUNTER field in the in-band signalling o... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.4.5 PLPs with zero FEC blocks in a given Interleaving Frame | EN 302 755 [i.1] explains that PLPs might be allocated no FEC blocks at all in a given Interleaving Frame, and there is therefore no BBFRAME frame to carry the in-band L1 signalling. The receiver will already know that this is the case from the in-band L1 signalling in the previous frame. There are two options for the ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.5 Power saving | Receivers may save power by switching off some of the circuitry while signals for the PLP of interest are not being transmitted. This is most likely to be applicable to Type-1 PLPs, since they only have one sub-slice per T2 frame, and furthermore this sub-slice generally appears near the beginning of the T2 frame, clos... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.6 FEFs | The receiver can detect the presence of FEF parts by looking for P1 symbols and by decoding the L1-post signalling (in the P2 symbols). In the initial scan the receiver will look for P1-symbols. If the first P1-symbol found is from a T2-frame, P2 can be decoded normally. The receiver will also see from the P1 if FEFs a... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.2.7 Auxiliary streams | Auxiliary streams are for future definition. A receiver may completely ignore them if they are present. However, a useful feature for a receiver chip would be the ability to output the complex cell values for a particular range of cell addresses, either on the main output or by reading a register. This could then be us... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.3 Time de-interleaver | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.3.1 Phase of Time de-interleaving | The receiver need not wait until the beginning of a superframe to start de-interleaving. Instead it should deduce, from the L1 signalling, which T2 frame is the first of the next Interleaving Frame and begin de-interleaving from that point. In many cases one Interleaving Frame will be mapped to one T2 frame so the de-i... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.3.2 Memory-efficient implementation of time de-interleaver | The permutation function for the time interleaver is the same for each TI-block and so it might appear that two blocks of memory are required in the de-interleaver. However, a more efficient method exists using only one TI-block's worth of memory. NOTE: The maximum size of a TI-block is smaller in the T2-Lite profile t... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.3.2.1 De-interleaver for constant bit-rate | The de-interleaving method for a constant bit-rate will be described, as this forms the core of the method for the variable bit-rate case. The de-interleaver for the constant bit-rate case is almost identical. The basic de-interleaver is shown in the block diagram shown in figure 109. Figure 109: De-interleaver block d... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.3.2.2 Implementation details | A practical implementation to generate the above address sequence is straightforward. At the start of each frame, the address generator is reset to 0. Subsequent addresses are then calculated by modulo M addition of the increment for that frame, kj, with an extra 1 to be added if M is exceeded. The value of kj can easi... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.3.2.3 Adaptation for variable bit-rates | The same basic structure can be used for the variable bit-rate case, dimensioned according to the maximum number of FEC blocks per TI-block. This is simply given by ⎥⎥ ⎤ ⎢⎢ ⎡ = TI N MAX BLOCKS NUM PLP N _ _ _ max . Since the de-interleaver writes in rows, there will in general be unused columns, which the write sequenc... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.3.3 Disabled Time Interleaving | The time de-interleaving may be disabled in cases where the receiver is expected to perform data-directed demodulation. In this case, it may still be useful to use the de-interleaver memory as a buffer, but the read and write sequences will both be identical. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.3.4 Relationship to the receiver buffer model | The Time De-interleaver forms part of the receiver buffer model (see annex C of [i.1] and clause 8.8.1 of the present document). Implementers should pay attention to the assumptions described in the model, including the rate and timing of reading from the memory and the interaction with the de-jitter buffer. Implemente... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.4.4 Cell de-interleaver | The cell de-interleaver simply performs the inverse of the cell interleaver function (see clause 9.2.4). The cell de-interleaver on its own would require two FEC-blocks' worth of memory. However, it may be possible to use the same memory as for the preceding or following stages (Time de-interleaver or bit de-interleave... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5 Channel decoding | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.1 LLR demapping for non-rotated constellations | LDPC decoding should be performed using Log Likelihood-Ratios (LLRs), also known as soft decisions or metrics. When rotated constellations are not used, the LLRs can be derived in the normal one-dimensional way well-known from DVB-T. The derivation of LLRs in the case of rotated constellations is discussed in clause 10... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.2 Removal of cyclic Q-delay | When rotated constellations are used, the cyclic Q delay needs to be removed. This can be done simply by delaying the 'I' component by one cell, to re-unite it with the corresponding 'Q' value; this requiring only one cell of memory. The 'Q' component of the first cell also needs to be stored until the end of the FEC b... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.3 De-mapping for rotated constellations | This clause describes the main implications on the receiver of the use of rotated constellations. Rotated constellations require the receiver to form metrics - Log Likelihood-Ratios (LLRs) - as a function of two dimensions, rather than the conventional, variables-separable 1-D approach appropriate to conventional, unro... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.3.1 2D LLR demapping | At the receiver, the classical demapper is replaced by the structure shown in figure 112: QAM demapper α-rotated constellation LLR(b0) LLR(b1) LLR(bm-2) LLR(bm-1) I Q : Figure 112: 2D LLR demapper for rotated constellations |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.3.1.1 Computation of perfect LLR | We define as follows the LLRs that we wish the de-mapper of figure 112 to form from the received constellation I,Q; this expression describes the LLR for the ith bit bi: LLR bi( )= ln Pr(bi =1| I,Q) Pr(bi = 0 | I,Q) ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ A positive LLR would indicate that bi was more probably transmitted as a 1, a negative value... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.3.1.2 Computation of simplified LLR (suitable for hardware implementation) | The LLR computation can be simplified by applying the Max-Log approximation: ln ea1 + L + eak ( )≈max i=1Lk ai ( ) The LLR becomes: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ⎥⎥ ⎦ ⎤ ⎢⎢ ⎣ ⎡ − + − − − + − ≈ ∈ ∈ 2 x Q 2 x I C x 2 x Q 2 x I C x 2 i Q Q I I min Q Q I I min 2 1 b LLR 1 i 0 i ρ ρ ρ ρ σ |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.3.2 2D LLR demapper with iterative demapping and decoding | When Iterative Demapping (ID) is applied, the demapper has to be slightly modified in order to take extrinsic bit information coming from the LDPC decoder into account as shown in figure 113. QAM demapper α-rotated constellation LLR(b0) LLR(b1) LLR(bm-2) LLR(bm-1) I Q : A priori information from the LDPC decoder Figure... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.3.2.1 Computation of perfect LLR with ID | With iterative demapping, the metric for bit bi should be calculated in the light of a priori knowledge of the likely state of the m - 1 other bits, obtained from the LDPC decoder in the previous iteration. Because of this knowledge, we should no longer assume that all states x of the constellation are equiprobable. To... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.3.2.2 'Genie-aided' demapping | 'Genie-aided' demapping is the assumed limiting case of the benefits of iterative decoding and demapping. In this case we assume that the LDPC decoding of all the bits except bi is error-free and known to be so. It follows that only two constellation points could possibly have been transmitted, which two points of cour... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.3.2.3 Computation of simplified LLR with ID (suitable for hardware implementation) | While we trust that iterative demapping will eventually converge on the 'Genie-aided' scenario (where the state of the other bits bk k≠i is deemed to be known with absolute certainty), during the iterations we do need to take into account the relative certainty about these bits expressed by the probabilities ( ) k k LD... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.3.3 Impact on complexity | The main added complexity for the receiver, when rotated constellations are used, arises in the calculation of metrics, i.e. the LLRs for each coded bit carried by each OFDM constellation. Whether rotated or not, 2m-QAM conveys m bits per cell, and thus requires the calculation of m LLRs per cell. The difference arises... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.4 PAPR-aware demapping | The ACE PAPR technique (see clause 9.3.8.2) makes modifications to the outer transmitted-constellation points in order to reduce the peak-to-mean ratio of the transmitted signal. This could potentially affect the LLR demapping process in the receiver, since the assumption built into the traditional LLR is that the tran... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.5 LDPC decoding | The most general decoding algorithm of LDPC code is an iterative message passing algorithm called belief propagation [i.12]. This algorithm is naturally suitable for parallel message computation. The structure of the parity check matrices of the LDPC codes adopted in DVB-T2 implies a partly-parallel decoder architectur... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.6 BCH decoding | For the purpose of removing any possible error floor, use of bounded-distance decoding [i.11] is sufficient. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.7 Decoding of the L1 signalling | The extraction of the L1 signalling cells was described in clause 10.4.2.2. Subsequent processing stages are similar to the corresponding stages in the PLP decoding chains, with the following differences: • No Time or Cell de-interleaving is applied to the L1 signalling, but the zig-zag mapping constitutes a form of in... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.7.1 FEC decoding of the L1 signalling | This clause gives an overview of the procedure of decoding of L1 dynamic signalling. Figure 117 illustrates the L1 signalling structure, which is split into three main sections: the P1 signalling, L1-pre-, and L1-post signalling. Then the L1-pre signalling should be decoded by using the BCH code with Kbch = 3 072 and 1... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.7.2 Extraction of the L1-signalling fields | The L1-post signalling contains the configurable, dynamic and (optional) extension part as illustrated in figure 117. The configurable part of L1-post signalling has a variable length which depends not only on the numbers of RFs, PLPs, and auxiliary streams but also on the use of FEF. That is, the length of configurabl... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.5.7.3 Storage required in L1 decoding | If the decoding of the Layer-1 signalling information carried in the P2 symbol(s) is to take more than one symbol time, then the data symbols received during the decoding time need to be stored until the Layer-1 signalling is decoded to extract the Layer-1 post-signalling parameters. The amount of storage required depe... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.6 Output processing | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.6.1 De-/Re-multiplexing | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.6.1.1 Construction of output TS | Construction of the output TS will make use of the following pieces of information: • The SYNCD, SYNC and UPL fields of the BB-Header: Used to regenerate the user packets (where applicable). See clause 10.6.1.2. • The TTO variable of ISSY: used to set the initial occupancy of the DJB (see clause 10.6.1.4). • The DNP by... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.6.1.2 Mode adaptation | Given the decoded baseband frames from the BCH decoder (clause 10.5.6), the receiver should partially reverse the process of mode adaptation performed in the T2-Gateway (clause 8.5) and so recover the input packets. The receiver should first determine whether Normal or High Efficiency Mode is being used. If the PLP_MOD... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.6.1.3 Determination of output-TS bit-rate | The receiver needs to know the exact bit-rate of the output transport stream, in order to be able to output the stream. If ISSY is used, this can be calculated from the ISCR values. Following null-packet re-insertion, the bit stream will consist of a sequence of TS packets, some of which will have associated ISCR value... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.6.1.4 De-jitter buffer | The de-jitter buffer itself can be implemented using a FIFO more or less as described in annex C of [i.1]. ETSI ETSI TS 102 831 V1.2.1 (2012-08) 210 The data should be read out using a clock derived from the recovered modulator sampling clock taking into account the calculation of output bit rate described in clause 10... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.6.1.5 Re-insertion of deleted null packets | Conceptually, the deleted null packets are re-inserted before the de-jitter buffer as illustrated in annex I of [i.1]. The de-jitter buffer would then consist of a simple FIFO as shown. However, the de-jitter buffer memory will generally not be large enough to accommodate all of the null packets, since the scheduler is... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.6.1.6 Re-combining the Common and Data PLPs | When a particular input TS has been split and is sent in a data PLP and a common PLP (see clause 8.3) the original TS can be recreated in the receiver by combining the contents of the data PLP and the common PLP. The operations required to re-combine the common and data PLPs, together with recommendations for receiver ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 10.6.2 Output interface | For TS input, the output from a demodulator should be the relevant complete Transport Stream. For generic streams, the output format will depend on the type of stream. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 11 Transmitters | Many considerations for the implementation and use of transmitters for DVB-T2 will be similar to those for DVB-T, since the occupied bandwidth and signal spectra are broadly similar. One area in which DVB-T2 is significantly different is in the availability of two techniques for PAPR reduction (see clause 9.3.8). Futur... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 12 Network planning | Network planning for DVB-T2 will have much in common with planning for DVB-T, but the availability of a wider range of technologies and options in DVB-T2 gives more flexibility. In particular, the larger FFT sizes and wider choice of guard intervals will give greater scope for optimisation of networks. The use of MISO ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 13 Tuners | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 13.1 Phase noise requirements | Generally phase-noise considerations are the same as for DVB-T. Phase noise added to an OFDM signal causes two distinct effects: CPE and ICI. CPE is a common rotation of all the constellations transmitted in one OFDM symbol. Because it is common for all carriers, it is possible to measure it and cancel it out. ICI is a... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 13.2 AGC, headroom and FEFs | Considerations for the dynamics of the AGC, together with the setting of the backoff to allow headroom for the OFDM signal, are likely to be similar to the DVB-T case. As was explained in clause 10.4.2.6, the AGC of a receiver should be locked during any FEF part. If the tuner has its own analogue AGC loop, this should... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14 Performance | This clause presents simulation results indicating the performance of DVB-T2 in a range of terrestrial channels. The results are based on the simulation and validation effort carried out during and following the development of the DVB-T2 standard [i.1]. The following information will be presented: • Description of the ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1 Channel models for simulations | |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.1 Introduction | During the development of the DVB-T2 specification [i.1], different channel models have been used to provide simulated performance results. In addition to the well-known channels from DVB-T, some other channels have been added, some specific to DVB-T2. The channels have been chosen to verify the performance in a wide r... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.2 Gaussian Channel | In this channel model only white Gaussian noise (AWGN) is added to the signal, and there is only one path. |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.3 Ricean Channel | The same F1 Ricean fading channel defined in the DVB-T specification is used to describe the fixed, outdoor rooftop-antenna reception conditions. The channel does not include any Doppler and should therefore be considered as a snapshot of the real time-variant channel. The model has 21-taps. ETSI ETSI TS 102 831 V1.2.1... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.4 Rayleigh Channel | The same P1 Rayleigh-fading channel defined in the DVB-T specification is used to describe the portable indoor or outdoor reception conditions. The channel does not include any Doppler and should therefore be considered as a snapshot of the real time-variant Rayleigh channel. The model has 20 taps. The model is defined... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.5 Mobile Channel, TU-6 | This profile reproduces the terrestrial propagation in an urban area. It has been defined by COST 207 as a typical urban (TU6) profile and is made of 6 paths having wide dispersion in delay and relatively strong power. The profile parameters are given in table 40. Table 40: Typical Urban profile (TU6) Tap number Delay ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.6 Simple two path profile, 0 dB Echo | This profile only includes two paths. Each path, 'i', is defined by αi, τi, Δfi which denote the amplitude, delay and frequency shift of the particular path 'i', respectively. The profile parameters are given in table 41. Table 41: 0 dB Echo profile i αi (dB) τi (μs) Δfi (Hz) 1 0 0 0 2 0 0,9Δ 1 The parameter 'Δ' denote... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.7 MISO channel | As MISO transmission is used from different transmit antennas, the simulation of MISO channels requires at least two independent fading channels, one for each transmitter. For the first transmitter, the values defined in table 39 are used, whereas the values for the second transmitter are defined in table 42. Table 42:... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.7.1 Ricean MISO Channel | The Ricean MISO fading channel is very similar to the normal SISO F1 Ricean Channel, except that a second path is added. The Ricean MISO channel is defined by: ∑ ∑ ∑ ∑ = = ⋅ ⋅ ⋅ = − = − + ⋅⎥ ⎦ ⎤ ⎢ ⎣ ⎡ Δ − − + Δ − + − + = Δ N i i N i i t f j N i i j i N i i j i A e t x e t x A t x e t x t y i i 0 2 , 2 2 0 2 ,1 2 1 2 , ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.7.2 Rayleigh MISO Channel | The Rayleigh MISO channel is very similar to the SISO P1 Rayleigh channel, except that a second path is added. The MISO Rayleigh channel is: ∑ ∑ ∑ ∑ = = = ⋅ − = − + ⋅ Δ − − + − = Δ N i i N i i N i f j i j i N i i j i A e t x e A t x e t y i i 1 2 , 2 2 1 2 ,1 1 2 2 , 2 2 , 2 1 ,1 1 ,1 ) ( ) ( ) ( , 2 , 1 ρ ρ τ ρ τ ρ π ... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.1.8 Memoryless Rayleigh Channel with erasures | This channel model is used to simulate the behaviour of the BICM module of DVB-T2 system over terrestrial multipath channels. As described in figure 119, the principle consists in modelling the concatenation of the frame builder, OFDM generator, wireless channel, OFDM demodulator and frame extraction as an equivalent f... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.2 Simulated system performance for 8 MHz channel | Table 44 and table 45 give simulated performance, assuming perfect channel-estimation, perfect synchronization and without phase noise, of channel coding and modulation combinations, and are subject to confirmation by testing. These results are given for the Gaussian channel, Ricean channel (F1), Rayleigh channel (P1),... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.2.1 Correction values for pilot boosting | The values of required (C/N)0 given in table 44 and table 45 are raw and do not taken into account the reduction in data C/N resulting from the presence of boosted pilots, since this depends on the pilot pattern in use. Net values of C/N can be derived from the raw values (C/N)0 by computing a correction factor BP Δ su... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.4 Simulation results for TU6 channel | Figure 121, Figure 122, Figure 123 and Figure 124 are the result of simulations in the TU6 channel for different configurations of time interleaving. Additional simulation results can be found in [i.23]. The selected Doppler frequencies are 10 Hz and 80 Hz, which correspond to 18 km/h and 144 km/h with an RF carrier of... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.5 Penalty for real channel estimation | The simulations reported in the previous clause were made under the assumption that the receiver has perfect, noiseless knowledge of the channel. This is an ideal which cannot be realised, but at least sets a clear single system-performance criterion. Receivers may use various practical implementations, the choice of w... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.6 P1 performance | The figures presented in this clause are the results of simulations of P1 performance run under critical conditions. These include not only the cases defined in clause 14.1 to test data performance, but also cases using different parameter values. The figures show the robustness behaviour in terms of probability of mat... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.6.1 Figure description | In the following results, each figure shows five curves for a particular scenario. The meaning of these curves is: • T2 OK: This shows the probability of detecting a P1 preamble when it is expected to be received. • Lost: This shows the probability of not detecting a P1 preamble when it should. In this case, the preamb... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.6.2 P1 performance results | The simulations were run for various channels, assuming a guard interval of 1/8 with FFT-size=2 K for the data OFDM symbols, and a CW-interference in place (CW-interference was not added in the 0 dB 180º channel). |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.6.2.1 Gaussian channel | Figure 128: P1 robustness in Gaussian channel ETSI ETSI TS 102 831 V1.2.1 (2012-08) 229 |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.6.2.2 Rayleigh channel (P1) | Figure 129: P1 robustness in Rayleigh channel (P1) |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.6.2.3 TU-6@200Hz | Figure 130: P1 robustness in Tu-6@200Hz channel |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 14.6.2.4 0 dB 180º Echo, Echo with opposite sign | The worst case of a 0 dB-echo channel for the P1 symbol, are those in which the echo is destructive. This means that the echo is rotated 180 degrees. The following figure shows the probability of detection for every delay in this channel (from 0 to 2 000 samples delay) at an SNR of 0 dB. ETSI ETSI TS 102 831 V1.2.1 (20... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 15 Examples of possible uses of the system | The DVB-T2 system is designed to be highly flexible, allowing different trade-offs to be made in terms of capacity and ruggedness, as well as flexibility and overhead. For example, the system may be used in a very simple configuration to carry a few HDTV services within a single PLP, intended for fixed rooftop receptio... |
5c408ecfef3e523a192afe3fd7249eaf | 102 831 | 16 T2-Lite | T2-Lite is a new profile which was added to the DVB-T2 specification [i.1] in version 1.3.1. The profile is targeted at mobile and handheld receivers, and consequently contains only the modes likely to be suitable for reception under those conditions. Furthermore, the profile has been designed in order to reduce the co... |
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