CN1205770C - Orthogonal frequency division multiplex transmission system for digital surface broadcasting - Google Patents

Abstract

The present invention discloses a signal transmitting method of a transmission system of digital terrestrial broadcasting COFDM. The sampling rate of baseband digital modulation signals is 10MHz, a frame of OFDM signals are composed of 64 OFDM symbols, each OFDM symbol is composed of a plurality of carrier signals whose persistent period is Ts, wherein the carrier signals comprise a plurality of data signal sub carriers, mobile pilot frequency sub carriers, continuous pilot frequency sub carriers and TPS pilot frequency sub carriers, and various carriers are regularly arranged. Continuous pilot frequency and mobile pilot frequency sub carrier reference signals are obtained by a pseudo random binary sequence which is also used for the 2DPSK modulation and initialization of the TPS pilot frequency sub carriers. 64 bits of each TPS block comprise 1 initialization bit, 16 synchronization bits, 34 information bits and 13 redundancy bits which are used for error code protection. The signal transmitting method of the present invention obviously increase the performance of COFDM transmission systems, and simultaneously enables receivers to be realized simply.

Description

A Coded Orthogonal Frequency Division Multiplexing Transmission System Suitable for Digital Terrestrial Broadcasting

Technical Field The present invention belongs to the field of signal transmission, in particular to a signal transmission method in a digital terrestrial broadcasting system using Orthogonal Frequency Division Multiplexing Modulation Mode (OFDM).

Background Art A typical digital terrestrial broadcasting transmission system includes a transmitter and a receiver. Digital modulation technology usually performs channel coding on the digital signal and then modulates it, then adds necessary auxiliary information such as pilot signal, and then forms and filters the channel spectrum to become a baseband digital modulation signal. The digital signal is modulated to a corresponding frequency band and sent through a digital-to-analog converter and an up-converter. At the receiving end, the down-converter converts the RF signal into a baseband signal, and then passes through an analog-to-digital converter to obtain a digital signal. After digital demodulation and channel decoding, the digital signal is restored to the same information as the source. Figure 1 shows a typical digital terrestrial broadcast transmission system block diagram.

The digital coding modulation unit of the digital terrestrial broadcasting COFDM transmission system performs a series of digital processing on the input data. It includes data randomization, outer coding (usually Reed-Solomon codes), outer interleaving (usually convolutional interleaving), inner coding (usually convolutional or trellis codes), inner interleaving (usually time and frequency two-dimensional interleaving), mapping, adding pilot signals, system information, orthogonal frequency division multiplexing (usually implemented with IFFT), adding guard intervals (usually cyclic extension), shaping filtering, etc. The flow chart of its processing module is shown in Figure 2.

In the digital terrestrial broadcasting COFDM transmission system, besides the data signal, the transmission signal also includes the mobile pilot signal and continuous pilot signal for channel estimation, synchronization acquisition and tracking, and the transmission parameters for transferring the service type system information signaling (TPS) signal. The proportion and position arrangement of each pilot subcarrier in the subcarrier have an important impact on the performance of the COFDM transmission system.

SUMMARY OF THE INVENTION The purpose of the present invention is to provide a signal transmission method for the COFDM transmission system of digital terrestrial broadcasting. The method improves the performance of the COFDM transmission system by rationally arranging the structure of the data subcarrier and each pilot subcarrier, and at the same time reduces the reception machine complexity.

The signal transmission method designed by the present invention is as follows: in the digital terrestrial broadcasting COFDM transmission system, the sampling rate of the baseband digital modulation signal is 10MHz, and the signal bandwidth occupied by the OFDM signal is 7.62MHz. The OFDM transmission signal is composed of frames, and one frame of OFDM signal is composed of 64 OFDM symbols. Each OFDM symbol consists of multiple carrier signals with duration Ts. The symbol duration Ts includes a useful part of duration Tu and a guard interval part of duration _ΔT . Each OFDM symbol consists of multiple subcarrier signals. In the working mode of Inverse Fast Fourier Transform (IFFT) block size of 2048 (commonly known as "2K working mode"), the number of subcarriers is 1561; in the working mode of IFFT block size of 4096 (commonly known as "4K working mode") Among them, the number of subcarriers is 3121; in the working mode with the IFFT block size of 8192 (commonly known as "8K working mode"), the number of subcarriers is 6241. In addition to subcarrier signals carrying data, each OFDM symbol also contains mobile pilot subcarrier signals and continuous pilot subcarrier signals for channel estimation, synchronization acquisition and tracking, and TPS for transmitting service type system information subcarrier signal. For the 2K working mode, the number of data signal subcarriers is 1392, the number of mobile pilot subcarriers is 130, the number of continuous pilot subcarriers is 41, and the number of TPS subcarriers is 8. For the 4K working mode, the number of data subcarriers is 2784, the number of mobile pilot subcarriers is 260, the number of continuous pilot subcarriers is 81, and the number of TPS subcarriers is 16. For the 8K working mode, the number of data subcarriers is 5568, the number of mobile pilot subcarriers is 520, the number of continuous pilot subcarriers is 161, and the number of TPS subcarriers is 32.

Data subcarriers are modulated by multilevel quadrature amplitude (MQAM) or phase shift keying (MPSK), continuous pilot and moving pilot subcarriers are modulated by binary phase shift keying (BPSK), TPS subcarriers are binary differential Phase Shift Keying (2DPSK) modulation.

Continuous pilot and moving pilot subcarrier reference signals are obtained by a pseudo-random binary sequence w _k . The pseudo-random binary sequence w _k is also used to initialize the 2DPSK modulation of the transmission parameter signaling TPS subcarrier.

The modulation of all data elements is normalized so that the average power level is 1. All pilot (continuous and moving) subcarriers and TPS subcarriers are transmitted at boosted power, resulting in an average power level of 16/9.

Transmission Parameter Signaling (TPS) is defined on 64 consecutive OFDM symbols of an OFDM signal frame. Each OFDM symbol conveys one TPS bit. Each TPS block (corresponding to an OFDM frame) consists of 64 bits, including: 1 initialization bit, 16 synchronization bits, 34 information bits and 13 redundant bits for error protection. For the 34 information bits, only a part of them can be used, and the rest can be used as spares. The pseudo-random binary sequence w _k corresponding to the TPS subcarrier position of the first symbol of each OFDM frame is applied to the 2DBPSK modulation initialization of the TPS subcarrier signal at this position.

The signal transmission method designed by the present invention has many beneficial effects as follows: the signal bandwidth occupied by the OFDM signal is 7.62MHz, and the sampling rate of 10MHz is beneficial to frequency domain filtering and spectrum shaping; the OFDM frame signal is composed of 64 OFDM symbols, and the input code length is 50. The binary original Bosch-Chadhoury-Hokungum (BCH) code with an output code length of 63 is used to transmit parameter signaling signals with strong error protection and is more suitable for differential two-phase modulation; Symmetric configuration between frequency and center can simplify receiver implementation; transmission signaling parameters contain a variety of information, which can flexibly realize mixed, single, and hierarchical working modes for mobile reception and fixed reception services; the power of each pilot frequency is greater than that of the signal The power is 3dB, which can realize various synchronization and channel estimation functions; the reference signal is generated by a 13th-order pseudo-random sequence generator, and there will be no periodic repetition for 2K, 4K, and 8K modes.

Embodiments of the present invention are further described below in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a typical digital terrestrial broadcasting transmission system.

Fig. 2 is a flow chart of the digital coding and modulation functional module of the digital terrestrial broadcasting COFDM transmission system.

Fig. 3 is the PRBS sequence generator.

FIG. 4 is a schematic diagram of a frame structure of an OFDM transmission signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the COFDM transmission system of digital terrestrial broadcasting, the sampling rate of the baseband digital modulation signal is 10 MHz, and the signal bandwidth occupied by the OFDM signal is 7.62 MHz. The OFDM transmission signal consists of frames, and each frame signal contains 64 OFDM symbols. Each OFDM symbol consists of multiple carrier signals with duration Ts. The symbol duration Ts includes a useful part of duration Tu and a guard interval part of duration _ΔT . The guard interval is inserted before the useful part, and it has multiple values that can be selected, such as Tu/4, Tu/8, Tu/16, Tu/32, but not limited to these values. The 8K working mode Tu is 819.2 microseconds, the 4K working mode Tu is 409.6 microseconds, and the 2K working mode Tu is 204.8 microseconds. In addition to subcarrier signals carrying data, each OFDM symbol also contains mobile pilot and continuous pilot subcarrier signals for channel estimation, synchronization acquisition and tracking, and system transmission service types (such as single, mixed and Layered modulation) TPS subcarrier signal of information. The data subcarrier signal is modulated by multilevel amplitude modulation (MQAM) or phase shift keying (MPSK), the continuous pilot and moving pilot subcarrier signals are modulated by binary phase shift keying (BPSK), and the TPS subcarrier signal is binary Phase Shift Keying (2DPSK) modulation.

Continuous pilot and moving pilot subcarrier reference signals are obtained by a pseudo-random binary sequence w _k . The pseudo-random binary sequence w _k is generated according to Fig. 3, and the connection polynomial used by the generator for generating the pseudo-random binary sequence is: x ¹³ +x ⁴ +x ³ +x+1. It is initialized to 11111111111, so that the first output bit of the pseudo-random binary sequence coincides with the first valid subcarrier. A new value is generated from this sequence on each carrier used (whether pilot or not). The pseudo-random binary sequence w _k is also used to initialize the 2DPSK modulation of the transmission parameter signaling TPS subcarrier.

The 64 OFDM symbols constituting one frame are sequentially defined as the 0th, 1st, ..., 63rd OFDM symbols. The positions of the mobile pilot subcarriers of these 64 OFDM symbols are different, and their distribution is related to the symbol index i (0-63). For the ith OFDM symbol, the set of mobile pilot subcarrier positions S _i is: k=K _min +3×(i mod4)+12p, p is an integer ≥ 0, i∈[0,63], k∈[K _min , K _max ], wherein, K _min =0, for the 2K working mode, K _max =1560; for the 4K working mode, K _max =3120; for the 8K working mode, K _max =6240.

The position of the mobile pilot subcarrier is shown in Fig. 4 . The reference information obtained from the pseudo-random binary sequence _wk is transmitted in mobile pilot elements interspersed within each symbol. A moving pilot unit always transmits at a "boosted" power level, and the corresponding modulation is:

Re(C _m,k )=4/3·(1-2·w _k )

Im(C _{m, k} )=0 In the formula, m is an OFDM symbol time indication, and k is a subcarrier frequency indication.

The number of consecutive pilot subcarriers varies with system operating modes. In the 2K working mode, the number of continuous pilot subcarriers is 41; in the 4K working mode, the number of continuous pilot subcarriers is 81; and in the 8K working mode, the number of continuous pilot subcarriers is 161. The positions and values of the continuous pilot subcarriers of the 64 OFDM symbols in the OFDM transmission signal frame are the same. The locations of consecutive pilot subcarriers are symmetrical about the center frequency location (the sum is 0 with respect to the center location). Tables 1, 2, and 3 give a set of consecutive pilot subcarrier positions that are symmetrical about the central frequency position.

Table 1 2K working mode continuous pilot subcarrier position set 0, 15, 69, 162, 177, 216, 270, 351, 375, 414, 429, 480, 516, 537, 594, 603, 639, 666, 741, 768, 780, 792, 831, 852, 882, 921, 966, 1023, 1050, 1095, 1146, 1185, 1200, 1209, 1278, 1344, 1383, 1437, 1479, 1545, 1560

Table 2 4K working mode continuous pilot subcarrier position set 0, 15, 69, 162, 177, 216, 270, 351, 375, 414, 429, 480, 516, 537, 594, 603, 639, 666, 741, 768, 780, 792, 831, 852, 882, 921, 966, 1023, 1050, 1095, 1146, 1185, 1200, 1209, 1278, 1344, 1383, 1437, 1479, 1545, 1560, 1575, 1629, 1722, 1737, 1776, 1830, 1911, 1935, 1974, 1989, 2040, 2076, 2097, 2154, 2163, 2199, 2226, 2301, 2328, 2340, 2352, 2391, 2412, 2442, 2481, 2526, 2583, 2610, 2655, 2706, 2745, 2760, 2769, 2838, 2904, 2943, 2997, 3039, 3105, 3120

Table 3 8K working mode continuous pilot subcarrier position set 0, 15, 69, 162, 177, 216, 270, 351, 375, 414, 429, 480, 516, 537, 594, 603, 639, 666, 741, 768, 780, 792, 831, 852, 882, 921, 966, 1023, 1050, 1095, 1146, 1185, 1200, 1209, 1278, 1344, 1383, 1437, 1479, 1545, 1560, 1575, 1629, 1722, 1737, 1776, 1830, 1911, 1935, 1974, 1989, 2040, 2076, 2097, 2154, 2163, 2199, 2226, 2301, 2328, 2340, 2352, 2391, 2412, 2442, 2481, 2526, 2583, 2610, 2655, 2706, 2745, 2760, 2769, 2838, 2904, 2943, 2997, 3039, 3105, 3120, 3135, 3189, 3282, 3297, 3336, 3390, 3471, 3495, 3534, 3549, 3600, 3636, 36573714, 3723, 3759, 3786, 3861, 38088, 39 3912, 3951, 3972, 4002, 4041, 4086, 4143, 4170, 4215, 4266, 4305, 4320, 4329, 4398, 4464, 4503, 4557, 4599, 4665, 4680, 4695, 4749, 4842, 4857, 4896, 4950, 5031, 5055, 5094, 5109, 5160, 5196, 5217, 5274, 5283, 5319, 5346, 5421, 5448, 5460, 5472, 5511, 5532, 5562, 5601, 5646, 5703, 5730, 5775, 5826, 5865, 5880, 5889, 5958, 6024, 6063, 6117, 6159, 6225, 6240

All continuous pilots are modulated according to the reference sequence given by the pseudo-random binary sequence _wk . Consecutive pilots are always transmitted at a "boosted" power level, and the corresponding modulation is

Re(C _m,k )=4/3·(1-2·w _k )

Im(C _{m, k} )=0 In the formula, m is an OFDM symbol time indication, and k is a subcarrier frequency indication.

The TPS subcarrier is used to give parameters related to the transmission scheme, namely channel coding and modulation parameters and system information. For 2K working mode, TPS signaling is transmitted in parallel on 8 carriers; for 4K working mode, TPS signaling is transmitted in parallel on 16 carriers; for 8K working mode, TPS signaling is transmitted in parallel on 32 carriers. Each TPS subcarrier in the same symbol conveys the same differentially encoded information bits. Tables 4, 5, and 6 show a carrier position set of a TPS subcarrier.

TPS subcarrier units are transmitted at "boosted" power levels. Each TPS subcarrier conveys the same information with 2DBPSK modulation. 2DBPSK is initialized with a reference sequence provided by a pseudo-random binary sequence w _k at the beginning of each TPS block.

Table 4 Carrier position set of TPS subcarrier in 2K working mode 40, 346, 569, 700, 790, 1155, 1219, 1469

Table 5 Carrier position set of TPS subcarrier in 4K working mode 40, 346, 569, 700, 790, 1155, 1219, 1469, 1600, 1906, 2129, 2260, 2350, 2715, 2779, 3029

Table 6 Carrier position set of TPS subcarrier in 8K working mode 40, 346, 569, 700, 790, 1155, 1219, 1469, 1600, 1906, 2129, 2260, 2350, 2715, 2779, 3029, 3160, 3466, 3689, 3820, 3910, 4275, 4339, 4589, 4720, 5026, 5249, 5380, 5470, 5835, 5899, 6149

Each OFDM symbol transmits one TPS bit, and each TPS block (corresponding to an OFDM frame) consists of 64 bits, including: 1 initialization bit, 16 synchronization bits, 34 information bits and 13 for error protection redundant bits. For the 34 information bits, only a part of them can be used, and the rest can be used as spares. If 27 are used, the remaining 7 are used as spares and set as "1010101". The reference symbol sequence w _k corresponding to the TPS subcarrier position of the first symbol of each OFDM frame is used for 2DBPSK modulation initialization of the TPS subcarrier signal at this position.

TPS information is transmitted according to Table 7. The first bit S ₀ of 2DPSK modulation is an initialization bit. The TPS initialization bit S ₀ is derived from the pseudo-random binary sequence w _k .

The 1st-16th bits in TPS are a synchronization word, each frame takes sw ₀ and sw ₁ in turn, here sw ₀ is 0011010111101110, sw ₁ is 1100101000010001

The TPS error code protection adopts the binary primitive Bosch-Chadhuri-Hokungum (BCH) code with an input code length of 50, an output code length of 63, and an error correction capability of 3. The code generation polynomial is: g(x)=x ¹³ +x ¹² +x ¹¹ +x ¹⁰ +x ⁹ +x ⁸ +x ⁶ +x ³ +x+1

Table 7 TPS signaling information and format number of bits Format purpose/content S ₀ w _k 2DBPSK modulation initialization S ₁ -S ₁₆ 0011010111101110, sync word S ₁₇ -S ₁₈ See Table 8 Operating mode S ₁₉ -S ₂₁ See Table 9 transfer mode S ₂₂ -S ₂₄ See Table 10 Non-layered single or layered HP code stream or mixed mode first intra-channel encoding rate S ₂₅ -S ₂₇ See Table 10 Layered LP code stream or mixed mode second intra-channel coding rate S ₂₈ -S ₂₉ See Table 11 Non-hierarchical single or hierarchal HP stream or mixed mode 1st channel out-of-weave depth S ₃₀ -S ₃₁ See Table 11 Layered LP stream or mixed mode 2nd interleaving depth S ₃₂ -S ₃₃ See Table 12 Single or mixed mode first channel signal constellation S ₃₄ -S ₃₅ See Table 12 Mixed Mode Second Channel Signal Constellation S ₃₆ See Table 13 Mixing working mode of current frame S ₃₇ See Table 13 Next frame mixed working mode S ₃₈ See Table 13 Bottom and bottom frame mixed working mode S ₃₉ See Table 13 Up and down down frame mixed working mode S ₄₀ See Table 13 Up and down down and down frame mixed working mode S ₄₁ -S ₄₃ See Table 14 guard gap S ₄₄ -S ₅₀ set to "1010101" Reserved in the future S ₅₁ -S ₆₃ BCH code error protection

Table 8 Signaling format of working mode Bits S ₁₇ -S ₁₈ Operating mode 00 2K 01 4K 10 8K 11 spare

Table 9 Signaling format of transmission mode Bits S ₁₉ -S ₂₁ transfer mode 000 non-hierarchical single 001 non-stratified mix 010 Layer α = 1 011 Layer α = 2 100 Layer α = 4 101 spare 110 spare 111 spare

Table 10 Signaling format of code rate Bits S ₂₂ -S ₂₄ , S ₂₅ -S ₂₇ code rate 000 1/2 convolutional code 001 2/3 convolutional code 010 3/4 convolutional code 011 5/6 convolutional code 100 7/8 convolutional code 101 1/2 turbo code 110 spare 111 spare

Table 11 Signaling format of outer interleaver interleaving depth Bits S ₂₈ -S ₂₉ , S ₃₀ -S ₃₁ Convolutional Interleaver Parameters 00 4 01 32 10 64 11 192

Table 12 Signaling formats for possible types of constellations Bits S ₃₂ -S ₃₃ , S ₃₄ -S ₃₅ Constellation Properties 00 DQPSK 01 QPSK 10 16QAM 11 64QAM

Table 13 Mixed working mode signaling format Bits S36, S37, S38, S39, S40 Hybrid working mode 0 first road 1 second road

Table 14 Signaling format of the guard interval Bit S ₄₁ -8 ₄₃ guard interval value 000 1/32 001 1/16 010 1/8 011 1/4 100 spare 101 spare 110 spare 111 spare

Claims (5)

1. Coded Orthogonal Frequency Division Multiplexing (COFDM) transmission system that is suitable for DTB Digital Terrestrial Broadcasting, it is characterized in that: base-band digital modulation signal sample rate is 10MHz, ofdm signal Seize ACK message bandwidth is 7.62MHz;

One frame ofdm signal is made up of 64 OFDM symbols, and each OFDM symbol is that M the carrier signal of Ts formed by the duration, comprising N ₁Number it is believed that work song carrier wave, N ₂Individual mobile pilot sub-carrier, N ₃Individual continuous pilot subcarrier and N ₄Individual TPS subcarrier;

Symbol duration Ts comprises that the duration is that useful part and duration of Tu is Δ _TThe protection compartment, protection is inserted in before the useful part at interval;

Be that the sub-carrier number M of each OFDM symbol equals 1561, data-signal sub-carrier number N under 2048 the mode of operation at the IFFT block size ₁Equal 1392, mobile pilot sub-carrier is counted N ₂Equal 130, continuous pilot sub-carrier number N ₃Equal 41, TPS sub-carrier number N ₄Equal 8; Tu is 204.8 microseconds; For i OFDM symbol, mobile position set of pilot subcarriers S _iFor:

K=3 * (i mod4)+12p, p is 〉=0 integer, i ∈ [0,63], k ∈ [0,1560]

Be that the sub-carrier number M of each OFDM symbol equals 3121, data-signal sub-carrier number N under 4096 the mode of operation at the IFFT block size ₁Equal 2784, mobile pilot sub-carrier is counted N ₂Equal 260, continuous pilot sub-carrier number N ₃Equal 81, TPS sub-carrier number N ₄Equal 16; Tu is 409.6 microseconds; For i OFDM symbol, mobile position set of pilot subcarriers S _iFor:

K=3 * (i mod4)+12p, p is 〉=0 integer, i ∈ [0,63], k ∈ [0,3120]

Be that the sub-carrier number M of each OFDM symbol equals 6241, data-signal sub-carrier number N under 8192 the mode of operation at the IFFT block size ₁Equal 5568, mobile pilot sub-carrier is counted N ₂Equal 520, continuous pilot sub-carrier number N ₃Equal 161, TPS sub-carrier number N ₄Equal 32; Tu is 819.2 microseconds; For i OFDM symbol, mobile position set of pilot subcarriers S _iFor:

K=3 * (i mod4)+12p, p is 〉=0 integer, i ∈ [0,63], k ∈ [0,6240]

The position of continuous pilot subcarrier is about centre frequency position symmetry, and the continuous pilot sub-carrier positions of 64 OFDM symbols is identical with value in the OFDM transmission signal frame;

Continuous pilot and mobile pilot sub-carrier reference signal are obtained by a pseudo-random binary sequence, and this pseudo-random binary sequence also is used for the TPS subcarrier is carried out 2DPSK modulation initialization;

Each OFDM symbol transmits a TPS bit; each TPS subcarrier in the prosign transmits the information bit of identical differential coding; corresponding to an OFDM frame; each TPS piece is made up of 64 bits, comprises 1 initialization bit, 16 synchronization bits, 34 information bits and 13 redundant bits that are used for error protection.

2. Coded Orthogonal Frequency Division Multiplexing (COFDM) transmission system according to claim 1 is characterized in that: the modulation of all data cells is through normalization, and making average power level is 1; Continuous pilot, mobile pilot tone and TPS subcarrier are all launched on the power that promotes, and making average power level is 16/9.

3. Coded Orthogonal Frequency Division Multiplexing (COFDM) transmission system according to claim 1 is characterized in that: the connection multinomial that pseudo-random binary sequence generator is used is: x ¹³+ x ⁴+ x ³+ x+1 presets 11111111111, and the first output bit of this pseudo-random binary sequence is overlapped with first effective subcarrier, produces a new numerical value by this sequence on the carrier wave of each use.

4. Coded Orthogonal Frequency Division Multiplexing (COFDM) transmission system according to claim 1 is characterized in that: the 2nd～17 bit in the TPS piece is a synchronization character, and every frame gets 0011010111101110 and 1100101000010001 successively.

5. Coded Orthogonal Frequency Division Multiplexing (COFDM) transmission system according to claim 1; it is characterized in that: the TPS error protection adopts that the input code length is 50, the output code length is 63, error correcting capability is binary system basis Bo Si-Cha Dehuli-Huo Kun lattice nurse sign indicating number of 3, and a sign indicating number generator polynomial is: g (x)=x ¹³+ x ¹²+ x ¹¹+ x ¹⁰+ x ⁹+ x ⁸+ x ⁶+ x ³+ x+1.

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