KR100258960B1 - Tps start position detection apparatus and method of ofdm system - Google Patents

Abstract

PURPOSE: A device for detecting a TPS(Transmission Parameter Signalling) starting location in an OFDM(Orthogonal Frequency Division Multiplexer) system is provided to perform a phase quantization and a differential decoding of a receiving TPS signal, and to detect a synchronous word, by using a quantizer, a comparator, a cumulator and a TPS starting location detector. CONSTITUTION: An ADC(Analog-To-Digital Converter)(210) converts a received OFDM(Orthogonal Frequency Division Multiplexer) analog signal into a digital signal. An FFT unit(Fast Fourier Transform)(230) performs an FFT for samples outputted from the ADC(210). A TPS(Transmission Parameter Signalling) detector(240) extracts a TPS complex signal transmitted through a pre-assigned sub carrier wave, and multiplies complex values by a determined integer, then performs a phase quantization. A differential decoder(250) compares the two complex quantization values each other, and cumulates a compared result value, then decides bits of a receiving TPS signal by using a code of the cumulated value. A TPS starting location detector(260) compares two bit values of the TPS signal, and decides whether the bit values are the same each other, then cumulates a compared value, finally detects a location having a maximum cumulated value as a TPS starting location.

Description

TPS starting position detection device and method of OPDM system

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Orthogonal Frequency Division Multipexer (hereinafter, called OFDM) system, and more particularly, to an apparatus and method for detecting a start position of transmission parameter signaling (TPS) in an OFDM system.

In general, in the European terrestrial broadcasting OFDM transmission method, a specific subcarrier of N subcarriers is not used to transmit data, but instead transmits information related to a transmission side transmission method. The transmission side transmission method is information on a scheme used by the transmission side to transmit an OFDM signal, that is, a channel code rate, a constellation pattern, a length of a guard interval, and a transmission mode. mode), frame number, etc. In the European standard, a subcarrier used to transmit this information is called a TPS (Transmission Parameter Signaling) subcarrier.

The TPS transmission scheme specified in the European terrestrial broadcasting OFDM transmission scheme is as follows. Transmission modes are classified into two modes, 2K mode and 8k mode, according to the total number of subcarriers used for transmission. In order to transmit the TPS signal, 2k mode uses a total of 17 subcarriers, and 8k mode uses a total of 68 subcarriers.

The configuration of the TPS signal is as follows. The TPS signal has a total length of 68 bits and consists of one bit of initialization bits, 16 bits (one word) of sync bits, 37 bits of information bits, and 14 bits of error correction bits. The length of 68 bits is because one frame is composed of 68 OFDM symbols in the European OFDM scheme. Since each OFDM symbol transmits 1 bit of TPS information, it takes 1 frame to transmit all 68 bits of TPS information. Moreover, one super-frame consists of four frames. All TPS subcarriers in one OFDM symbol carry the same information. TPS signal s _n It is defined as N is the nth bit. Initialization bit, which is the first bit of TPS for each TPS subcarrier s ₀ Can be obtained from the nth bit generated from the PBS (Pseudo Random Binary Sequence) corresponding to each subcarrier number n. This bit initializes the differential code BPSK (Differential Binary Phase Shift Keying, DBPSK), which is a modulation method of TPS information. 16-bit synchronization bit following the initialization bit s _{1 to} s ₁₆ Is shown in Table 1. The next 37 bits of information bits s _17- s ₅₃ As described above, is composed of information on the transmission method of the transmitting side, and the remaining 14 bits of error correction bits s _{54 to} s ₆₇ Is used to detect and correct errors that occur during the transmission of the 68-bit TPS signal.

The modulation scheme of the TPS signal uses differential binary phase shift keying (DBPSK), and all TPS subcarriers in one OFDM symbol transmit the same information. DBPSK is used to determine the TPS signal s ₀ It is initialized by and modulated as shown in Equation 1.

here k Is the TPS subcarrier number, m Is the frame number, n Is an OFDM symbol number, s _n Is the nth bit in the TPS signal c Is a complex signal that modulates a TPS subcarrier and is a symbol number n> 0 Applied when The initialization process is determined from the first symbol of every frame, as shown in Equation 2.

here w _k Denotes the k th bit in the PRBS sequence, which corresponds to k subcarriers. Finally w _k Since the value has a value of 0 or 1, the complex point transmitted by modulating with DBPSK becomes {1,0} or {-1,0}.

FIG. 1 is a block diagram illustrating an apparatus for detecting a starting position of a TPS in a general OFDM system. The ADC unit 110 converts a received OFDM analog signal into a digital signal, and modulates data generated from the ADC unit 110 at high speed Fourier. A differential to decode the complex signal received through the TPS subcarrier of the TPS extractor 140 and the TPS extractor 140 to extract the TPS signal from the output of the FFT unit 130 to be converted The decoder 150 performs correlation on two sync words (word: 16 bits) in the TPS bit string decoded from the differential decoder 150 to obtain a maximum correlation value corresponding to the start point of the TPS. It is composed of a correlator 160 for detecting the position.

As shown in FIG. 1, the TPS extractor 140 extracts the TPS signal, performs differential decoding using the differential decoder 150, and uses the correlation unit 160 to determine the position of the sync bit. Detect. In particular, since multiple subcarriers are used for accurate transmission of the TPS signal, the same information is simultaneously transmitted in parallel (17 in 2k mode and 68 in 8k mode). Accordingly, in processing information received through a plurality of TPS subcarriers, a TPS signal reconstruction process for each TPS subcarrier is required. For example, the 8k mode adds complexity to 68 TPS signal reconstructors. In addition, since the synchronization bit can be received in four types according to the initialization bit and the frame number (1, 3 and 2, 4 frames in Table 1) corresponding to each TPS subcarrier, the correlation unit 160 for each type is There is a problem in that a large amount of computation is required because a correlation operation on 16 bits (synchronization words), which is the size of a sync bit, must be performed in the operation process.

The technical problem of the present invention is to perform phase quantization and differential decoding of a received TPS signal using a phase quantizer, a comparator, an accumulator, and a simplified TPS start position detector to recover a TPS signal in an OFDM system. The present invention provides an apparatus and a method for finding a correct starting position of a TPS signal by detecting a.

1 is a block diagram showing an apparatus for detecting a starting position of a TPS in a typical OFDM system.

2 is a block diagram showing an apparatus for detecting a TPS start position in an OFDM system according to the present invention.

3 illustrates output characteristics of the phase quantizer of FIG. 2.

In order to solve the above technical problem, the present invention provides an apparatus for detecting a starting position of a TPS in an OFDM system, comprising: an analog to digital conversion means for converting the received OFDM analog signal into a digital signal; FFT means for fast Fourier transforming samples output from the analog-to-digital conversion means; TPS detection means for extracting a TPS complex signal transmitted through a pre-allocated subcarrier from the FFT output of the FFT means, multiplying the complex values by a predetermined integer, and performing phase quantization; Differential decoding means for comparing the two complex quantization values output from the TPS detection means with each other, accumulating the resultant values, and determining the bits of the received TPS signal using the signs of the accumulated values; Comparing the two values of the TPS signal determined by the differential decoding means, determining whether the magnitudes are the same, accumulating the comparison values, and detecting the point at which the accumulated value is maximum as the TPS start position; TPS start position detection device of an OFDM system, characterized in that it comprises a.

In order to solve the above technical problem, the present invention provides a method for detecting a starting position of a TPS in an OFDM system, by extracting a TPS complex signal transmitted through a pre-allocated subcarrier from an FFT output obtained by fast Fourier transforming an OFDM signal. Multiplying the complex values by a predetermined integer and quantizing the phases; Comparing the two complex quantization values output in the above process, accumulating the resultant values, and determining a bit of the received TPS signal using a sign of the accumulated value; Comparing the two values of the TPS signal determined in the above process to determine whether the magnitudes are the same, accumulating the comparison values, and detecting a point at which the accumulated value is maximum as the TPS start position. TPS start position detection method of an OFDM system.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

2 is a block diagram showing an apparatus for detecting a TPS start position in an OFDM system according to the present invention.

The apparatus of FIG. 2 includes an ADC unit 210, an FFT unit 230, a TPS detector 240, a differential decoder 250, and a TPS start position detector 260. The TPS detector 240 is a TPS extractor. 242, a multiplier 243, a phase quantizer 244, and a first register 246, wherein the differential decoder 250 includes a first comparator 252, a first accumulator 254, and a determiner. And a second register 258, and the TPS start position detector 260 includes a second comparator 262, a second accumulator 264, and a maximum position detector 266.

FIG. 3 shows the output characteristics of the phase quantizer 244 of FIG. 2, where the x-axis is the real part Re [.] And the y-axis is the imaginary part Im [.].

First, when considering the symbol of the OFDM signal, when the FFT size is N, the symbol prevents interference between N effective data samples and symbols, which are outputs of the Inverse Fast Fourier Transform (IFFT). For this purpose, it consists of Guard Interval with G sample length inserted between symbols. That is, the transmitter sequentially transmits one OFDM symbol consisting of a total of (G + N) samples by copying the N complex values output from the IFFT and the last G of them.

Equation 3 shows an n th symbol composed of complex values output from the IFFT. Where n is the symbol number k Is the carrier number and p is the sample time X (·) Wow x (·) Denote the input complex value and output complex value of the transmission IFFT, respectively. In the second equation of Equation 3, the first term is the guard interval and the second term is the effective data interval.

As illustrated in FIG. 2, the analog-to-digital converter (ADC) 210 samples an OFDM signal, such as Equation 3, to be converted into digital data, such as Equation 2. Next, the FFT unit 130 removes the protection interval, which is the first term of Equation 3, from among the samples output from the ADC 210, and sequentially inputs and demodulates the second term.

The TPS detector 240 extracts a complex value transmitted through a subcarrier previously allocated for TPS signal transmission from the FFT output, multiplies the complex values by +1 or -1, and performs phase quantization. Processing is all possible. In more detail, the TPS extractor 240 extracts a reception complex value of a subcarrier with respect to a number previously assigned for TPS signal transmission from the FFT output of the FFT unit 230. Since each TPS signal extracted by the TPS extractor 242 is initialized by the corresponding bits of the PRBS, two signal patterns are generated. Therefore, the influence of PRBS should be removed for the convenience of processing the received TPS signal. The multiplier 243 multiplies the received complex value by -1 when the bit of the PRBS corresponding to the TPS subcarrier number is 0 and vice versa. In other words, the initialization bit corresponding to subcarrier k is the kth bit in the PRBS sequence ( w _k )to be. kth bit ( w _k ) Is 1, the output value for subcarrier k is multiplied by +1 and vice versa. w _k If) is 0, the output value for subcarrier k is multiplied by -1. When the transmitter modulates the TPS signal into DBPSK, the same information may be transmitted in two different forms according to an initialization bit corresponding to the TPS subcarrier number k. Therefore, on the receiving side, the kth bit ( w _k By multiplying the received complex point by +1 or -1, the same information can be easily processed by eliminating the influence of the initialization bit. output value of multiplier 243 for the kth TPS subcarrier of the nth symbol p (n, k) ) Is expressed as in Equation 4.

here Y (n, k) Is the output complex value of the FFT for the kth subcarrier of the nth symbol.

Phase quantizer 244 outputs the output value of multiplier 243 ( p (n, k) ) Is quantized with respect to the phase. An example of the characteristics of phase quantizer 244 is shown in FIG. 3. As shown in FIG. 3, a 2-bit phase quantization value, i.e., a ₀ (00), a ₁ (01), a ₂ (10), and a ₃ (11) is output with respect to the input complex value. The phase quantizer 244 outputs the output value of the multiplier 243 as shown in equation (5). p (n, k) ) Is 2-bit quantized.

here Q [⋅] Denotes phase quantization.

In another embodiment, the phase quantizer 244 may be quantized with 1 bit or 3 bits.

Since the first register 246 needs two consecutively received values for differential decoding, the output value of the phase quantizer 244 ( p '(n, k) Save).

The differential decoding unit 250 compares two complex quantization values output from the TPS detection unit 240, accumulates the resultant values, and determines the bits of the received TPS signal using the signs of the accumulated values. Referring to the differential decoder 250 in more detail, the first comparator 252 uses two complexes received through the k th TPS subcarrier from the (n-1) th symbol and the n th symbol output from the TPS extractor 240. The quantized value of the value p '(n-1, k) , p (n, k) Are compared to each other. At this time, the output values for the two input values are determined by Table 2. In other words, the differential decoding is determined based on whether there is a change in phase between two consecutively received signals. As shown in Equation 6, the first accumulator 254 accumulates output values output from the first comparator 252 during one OFDM symbol period. In particular, when the transmission mode is 2k, the number of TPS subcarriers is 17, and when 8k, the number of TPS subcarriers is 68.

는 제1비교기(252)의 출력값이다. 제1누적기(254)에서 각 전송 모드에 따라 누적을 수행한 후 판정기(256)는 수학 식7에 나타난 바와 같이 제1누적기(254)의 결과값이 양수 혹은 음수인지의 여부를 이용하여 n번째 심볼을 통하여 전송된 n번째 TPS 신호값이 0 혹은 1인지를 판정한다.here

Is the output value of the first comparator 252. After accumulating according to each transmission mode in the first accumulator 254, the determiner 256 uses whether the result value of the first accumulator 254 is positive or negative, as shown in Equation (7). It is determined whether the n th TPS signal value transmitted through the n th symbol is 0 or 1.

The second register 258 stores the output value of the determiner 256 for 68 output values for 68 OFDM symbols. The position of the sync bit is detected in the 68 bit strings.

,

,

,

,

,

,

,

이다. 따라서 제2비교기(262)는 통상적으로 이용하고 잇는 미끄럼 윈도우기(도시안됨)을 이용하며, 68개의 수신 TPS 비트에서 연속한 16 비트구간에 대해 대응되는 값을 비교하여 동기 비트의 위치를 검출한다. 이 때 표 3와 같이 비교되는 두 값이 같을 경우 1을 출력하고 다를 경우 -1을 출력한다. 다른 실시예로 제2비교기(262)의 출력값은 (+1, -1)이외에 (+1, 0) 혹은 (+2, -2)로 할 수있다. 누적기(264)는 수학 식8에 나타낸바와 같이 16비트 구간에 대한 제2비교기(262)의 결과값을 누적한다.The TPS start position detector 260 detects the position of the sync bit in the 68 bit strings, compares two corresponding values output from the differential decoder 250, determines whether the sizes are the same, and accumulates the comparison values. The point where the accumulated value is maximum is detected as the point where synchronization starts. In this case, since the sync bit is transmitted differently according to the predefined frame number (1, 3 frame and 2, 4 frame in Table 1), it is necessary to perform correlation on both types. However, the present invention makes it possible to extract the position of the sync bit regardless of the frame number by using the arrangement of the sync bits. The TPS start position detector 260 will be described in more detail as follows. Sync bits as shown in Table 1 s _{1 to} s ₁₆ Some are repeated. In other words s ₁ and s ₂ , s ₃ and s ₄ , s _5- s ₆ and s _7- s ₈ And s _9- s ₁₂ and s _13- s ₁₆ to be. Therefore, if you repeat a pair of repeated parts, you can make a total of 8 pairs as follows. In other words,

,

,

,

,

,

,

,

to be. Accordingly, the second comparator 262 uses a sliding window window (not shown) that is typically used, and detects the position of the sync bit by comparing corresponding values for consecutive 16-bit sections in 68 received TPS bits. . In this case, as shown in Table 3, if the two values being compared are the same, 1 is output and if it is different, -1 is output. In another embodiment, the output value of the second comparator 262 may be (+1, 0) or (+2, -2) in addition to (+1, -1). The accumulator 264 accumulates the result of the second comparator 262 for the 16-bit interval as shown in Equation (8).

Where n is the starting point of the sliding window in the 16-bit section of the received TPS signal. b Wow c Means the corresponding point. The maximum position detector 266 is a cumulative value accumulated in the second accumulator 264 as shown in equation (9). s (n) The maximum point is detected. In other words, this point means the start point of the sync word (16 sync bits) corresponding to the start point of the TPS (start point of the TPS). Therefore, since the sync bit is followed by the information bit of the TPS, the starting point of the TPS is automatically known. In another embodiment, when the output value of the second comparator 262 is used in reverse, that is, when the output value is output as (-1, + 1) instead of (+ 1, -1), it is detected as the position of the minimum value.

As described above, conventionally, each signal received through the TPS pilot is processed, but in the present invention, by using an accumulator, all TPS received signals can be accumulated and processed at one time regardless of the number of TPS pilots, and the FFT output value is 2-bit with a phase quantizer. Phase quantization by means of phase quantizer can be used to reduce the effect of FFT window position offset by comparing two values with each other, and by detecting the repeating pattern in the received TPS signal to detect the starting position of the TPS. Computation can be reduced to a quarter compared to correlation work using correlators.

Frame number classification 1, 3 frames 2, 4 frames Sync bit (s _{1 to} s ₁₆ ) 0011 0101 1110 1110 1100 1010 0001 0001

p '(n-1, k) p' (n, k) 0 One 10 11 0 +1 0 -One 0 One 0 +1 0 -One 10 -One 0 +1 0 11 0 -One 0 +1

tps (n + b) tps (n + c) 0 One 0 +1 -One One -One +1

Claims (9)

An apparatus for detecting a starting position of a TPS in an OFDM system, Analog to digital conversion means for converting the received OFDM analog signal into a digital signal; FFT means for fast Fourier transforming samples output from the analog-to-digital conversion means; TPS detection means for extracting a TPS complex signal transmitted through a pre-allocated subcarrier from the FFT output of the FFT means, multiplying the complex values by a predetermined integer, and performing phase quantization; Differential decoding means for comparing the two complex quantization values output from the TPS detection means with each other, accumulating the resultant values, and determining the bits of the received TPS signal using the signs of the accumulated values; TPS start position detection means for comparing two bit values of the TPS signal determined by the differential decoding means to determine whether the magnitude is the same, accumulating the comparison values, and detecting a point at which the accumulated value is maximum as the TPS start position. Apparatus for detecting a TPS start position of an OFDM system comprising a. The method of claim 1, wherein the TPS detecting means A TPS extractor for extracting a TPS complex signal transmitted through a TPS subcarrier among the complex values output from the FFT means; A multiplier multiplying a TPS reception complex value output from the TPS extractor by a predetermined integer by a PRBS corresponding to a subcarrier number; A phase quantizer for quantizing the phases of the TPS received complex signals output from the multiplier; And a register for storing quantization values output from the phase quantizer. The apparatus of claim 2, wherein the multiplier multiplies a received complex value by -1 when the bit of the PRBS corresponding to the TPS subcarrier number is 0, and multiplies by 1 when the bit is 0. . The method of claim 1, wherein the differential decoding means A first comparator for comparing TPS received quantized values in two consecutively received OFDM symbols for the same TPS subcarrier among the quantized values quantized in the phase quantizer; A first accumulator for accumulating a comparison value output from the first comparator; And a determiner for determining a TPS bit by the sign of the cumulative value of the first accumulator. 5. The apparatus of claim 4, wherein the first accumulator is to process the comparison value output from the first comparator at one time. 5. The apparatus of claim 4, further comprising a register for storing an output value output to the determiner for a predetermined number of OFDM symbols. 5. The method of claim 4, wherein the determiner determines whether the value of the n th TPS signal transmitted through the n th symbol is 0 or 1 using whether the result value of the first accumulator is positive or negative. TPS start position detection device of OFDM system. The method of claim 1, wherein the TPS start position detecting means To find the sync bit position located before the start point of the TPS in the TPS bit string generated by the determiner, compare two bit values corresponding to a predetermined predetermined bit and output corresponding values when the two values are the same or different. A second comparator; A second accumulator for accumulating the comparison values compared in the second comparator; TPS start of the OFDM system, characterized in that it comprises a maximum position detector for detecting the maximum point corresponding to the case where two bits of the cumulative value of the second accumulator is the same and the position as the starting point of the TPS Position detection device. In the method for detecting the starting position of the TPS in an OFDM system, Extracting a TPS complex signal transmitted through a pre-allocated subcarrier from the FFT output of the fast Fourier transformed OFDM signal, multiplying the complex values by a predetermined integer, and performing phase quantization; Comparing two phase quantization values output in the above process, accumulating the resultant values, and determining a bit of a received TPS signal using a sign of the accumulated value; And comparing the two bit values of the TPS signal determined in the process to determine whether the magnitudes are the same, accumulating the comparison values, and detecting a point at which the accumulated value is maximum as the TPS start position. TPS start position detection method of an OFDM system.

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