CN101083508B - OFDM modulation system performance test method based on low peak-valley ratio sequence transmission - Google Patents

OFDM modulation system performance test method based on low peak-valley ratio sequence transmission Download PDF

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CN101083508B
CN101083508B CN2007101192704A CN200710119270A CN101083508B CN 101083508 B CN101083508 B CN 101083508B CN 2007101192704 A CN2007101192704 A CN 2007101192704A CN 200710119270 A CN200710119270 A CN 200710119270A CN 101083508 B CN101083508 B CN 101083508B
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low peak
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宋健
毛嵩
杨昉
王劲涛
潘长勇
王军
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Tsinghua University
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Abstract

The invention belongs to digital transmission technology area. Its characteristic is: it put forward a new test model for the OFDM multi-carrier modulation system. This model sees the data stream from the inchoation of the modulation system and the data stream from the receiver as linear channel with the white Gaussian noise. Namely, we can describe the data stream from the inchoation x(n) and the data stream from the receive r(n) by r(n)=h(n)*x(n)+v(n). Here, '*' stand for linearity convolution operation. h(n) stand for test model channel's impulse response. v(n) stand for the linear convolution system's noise and the data disturbance. Propose a precise measuring model method according to this model. Its characteristic is that it carries on model parameter estimate when using LPVR testing system to transmit data.

Description

OFDM modulation system performance test method based on the low peak-valley ratio sequence transmission
Technical field
The invention belongs to digital information transmission technical field, be particularly related to OFDM (Orthogonal FrequencyDivision Multiplexing, OFDM) multicarrier (Multi Carrier, MC) in the modulating system based on low peak-valley ratio sequence system for transmitting performance test methods.
Background technology
The problem that modulation system performance test mainly solves be how constructing system performance test model reflecting this modulating system characteristic, and based on this test model measurement model parameter how accurately.
The OFDM multicarrier modulation system has been widely used in the Digital Television Terrestrial Broadcasting transmission technique field.(can be referring to European standard (can referring to ETSI EN 300744: " Digital Video Broadcasting (DVB): Framing structure; channelcoding and modulation for digital terrestrial television ") and national standard referring to GB20600-2006, digital television ground broadcast transmission system frame structure, chnnel coding and modulation, 2006-08-18).Accurately the systematic function of test OFDM multicarrier modulation system is essential.
At present the parameter of test OFDM multicarrier modulation system performance mainly comprise Modulation Error Rate (Modulation ErrorRatio, MER), the aims of systems error (System Target Error, STE) and quadrature error (Quadrature Error, QE) etc.Referring to (ETSI TR 101290: " Digital Video Broadcasting (DVB); Measurement guidelinesfor DVB systems ").
OFDM multicarrier modulation system modulated output signal is difficult to accurately measure this small distortion owing to be subjected to the influence of process such as ripple and digital-to-analogue conversion in the filter band can produce small distortion with existing multicarrier modulation system performance parameter.The present invention is directed to the OFDM multicarrier modulation system and propose a kind of new system performance testing model, and propose a kind of new based on this test model based on low peak-to-valley ratio (Low Peak-to-Volley, LPVR) method of measurement of the above-mentioned small distortion of accurate measurement of sequence transmission.
Summary of the invention
The objective of the invention is to propose a kind of system performance testing model, and propose a kind of method of accurate measurement model parameter at this model at the OFDM multicarrier modulation system.This performance test model can be used for all OFDM multicarrier modulation systems.
The present invention has defined a kind of performance test model at the OFDM multicarrier modulation system.The transmission course that this model is made a start OFDM multicarrier modulation system to be measured between base-band data stream and the test macro receiving end base-band data stream is modeled as a linear channel that has white Gaussian noise, be that make a start base band data t (n) and test macro receiving end base band data r (n) of OFDM multicarrier modulation system to be measured can be described by r (n)=h (n) * t (n)+v (n), wherein, symbol * represents the linear convolution computing, h (n) is the impulse response of this performance test model neutral line channel, and v (n) is the white Gaussian noise in this performance test model.By modeled transmission course comprise OFDM multicarrier modulation system to be measured analog-to-digital conversion and on fade to process such as radio frequency transmission and test macro downconvert to base band, digital-to-analogue conversion, carrier wave recover, regularly recover and process such as synchronous.As shown in Figure 1.
The present invention has defined a kind of new transfer sequence, promptly low peak-valley ratio sequence (Low Peak-to-Volley Ratio, LPVR).Discrete Fourier transform (DFT) (the Discrete Fourier Transform of definition LPVR sequence, DFT) amplitude peak of sequence is not more than 3 with the ratio of valley, as pseudorandom or pseudo noise sequence (Pseudo Noise, PN), referring to (Muquet B, Wang Z, Giannakis G.B, Courville M.de, and Duhamel P, Cyclic Prefixing or Zero Padding forWireless Multicarrier Transmissions, IEEE Trans.on Communications, 2002,50 (12): 2136-2148) with (GB 20600-2006, the digital television ground broadcast transmission system frame structure, chnnel coding and modulation, 2006-08-18).(Inverse Discrete FourierTransform, what obtain after IDFT) is the LPVR sequence through anti-discrete Fourier transform (DFT) through the sequence of QPSK and 16QAM mapping.
The present invention is directed to above-mentioned OFDM multicarrier modulation system performance test model and proposed method of estimation, it is characterized in that adopting the LPVR sequence as the transmission data for the treatment of examining system based on the performance test model parameter h (n) of LPVR sequence.This method realizes in digital integrated circuit or computer successively as follows:
At end to be measured
Figure G2007101192704D00021
Step (1), according to the transmission data block length N of OFDM multicarrier modulation system to be measured, selecting a group length arbitrarily is the LPVR sequence x (n) of N
Figure G2007101192704D00022
Step (2) is treated examining system, fills its transmission data block with this LPVR sequence x (n);
Figure G2007101192704D00023
Step (3), the transmission data block that protection interval and LPVR sequence are filled obtains the base-band data stream of making a start successively after framing and back-end processing; The Frame of being filled as data block with x (n) is designated as t (n), and its length is M;
Figure G2007101192704D00024
Step (4), the base-band data stream of will making a start obtains delivering to test lead behind the radio frequency transmissions through digital-to-analogue conversion and analog-modulated;
At test lead
Figure G2007101192704D00025
Step (1 '), with treat radiofrequency signal that examining system is launched through analog demodulator and analog-to-digital conversion and early stage data recover to obtain the receiving end base-band data stream, data were recovered to guarantee this receiving end base-band data stream and were treated that examining system is made a start and keep frame synchronization between the base-band data stream, regularly reach carrier synchronization synchronously early stage; Note is r (n) with t (n) for the receiving end base band data of base band data of making a start;
Figure G2007101192704D00026
Step (2 ') obtains the circular convolution y (n) of channel impulse response h (n) in LPVR sequence x (n) and the performance test model according to above-mentioned receiving end base-band data stream:
y ( n ) = h ( n ) ⊗ x ( n ) + w ( n ) ,
Wherein, symbol
Figure G2007101192704D00028
The computing of expression circular convolution, the impulse response of this test model channel of h (n), w (n) are that the white Gaussian noise and the data of circular convolution result stack are disturbed;
Step (3 '), calculate LPVR sequence x (n) and the circular convolution discrete Fourier transform (DFT) of y (n) as a result:
X(k)＝DFT(x(n))，
Y(k)＝DFT(y(n))，
According to the LPVR sequence character, X (k) is a peak amplitude and the ratio of valley amplitude is not more than 3 sequence;
Figure G2007101192704D00031
Step (4 ') obtains the estimated value of the discrete Fourier transform (DFT) H (k) of test model channel impulse response h (n) by division
Figure G2007101192704D00032
H ^ ( k ) = Y ( k ) / X ( k ) ,
X (n) is the LPVR sequence, and the peak amplitude of its DFT sequence X (k) is not more than 3 with the ratio of valley amplitude, thereby this division arithmetic precision is guaranteed;
Figure G2007101192704D00034
Step (5 '): calculate Anti-discrete Fourier transform (DFT), obtain the estimated value of test model channel impulse response h (n): h ^ ( n ) = IDFT ( H ^ ( k ) ) ;
Figure G2007101192704D00037
Step (6 '): according to
Figure G2007101192704D00038
Calculate Noise Estimation
Description of drawings
Fig. 1 explanation is at the modeled transmission course of performance test model of OFDM multicarrier modulation system;
Fig. 2 illustrates the frame format of DTMB multicarrier modulation system and the base band data stream format of making a start:
The frame format of Fig. 2 .a explanation DTMB multicarrier modulation system;
The base band data stream format of making a start of Fig. 2 .b explanation DTMB multicarrier modulation system;
Fig. 3 illustrates the test result at the DTMB multicarrier modulation system of the QPSK mapping of reality:
Fig. 3 .a illustrates the amplitude spectrum of h (n) parameter that records at actual DTMB multicarrier modulation system;
Fig. 3 .b illustrates the planisphere mapping situation of the output signal of actual DTMB multicarrier modulation system;
Planisphere mapping situation behind h (n) equalization parameter among signal process Fig. 3 .a among Fig. 3 .c key diagram 3.b;
Embodiment
The objective of the invention is to propose a kind of performance test model of new OFDM multi-carrier modulating system.The present invention will treat that the transmission course that examining system is made a start between base-band data stream and the test macro receiving end base-band data stream is modeled as a linear channel of being with white Gaussian noise.The present invention is directed to above-mentioned model has proposed a kind of based on low peak-valley ratio sequence (Low Peak-to-VolleyRatio, LPVR) Chuan Shu model parameter method of measurement.
With current national standard (can be referring to GB 20600-2006, digital television ground broadcast transmission system frame structure, chnnel coding and modulation, 2006-08-18) adopting the DTMB multicarrier modulation system of QPSK mapped mode is example.This modulating system adopts OFDM (the Timing Domain Synchronous Orthogonal Frequency DivisionMultiplexing of Domain Synchronous; TDS-OFDM) multi-carrier modulation; the protection gap length is 420 in its framing process; data block length is 3780, shown in Fig. 2 .a.Referring to national standard (GB 20600-2006, digital television ground broadcast transmission system frame structure, chnnel coding and modulation, 2006-08-18).The present invention's embodiment in digital integrated circuit or computer is as follows in this example:
At end to be measured
In this modulating system, data flow through QPSK mapping and after 3780 IDFT computing, be packed into data block again with protection framing at interval.Remember that protection interval padding sequence is p in the i frame i(n), 1≤n≤420 remember that the sequence of filling in the i frame data piece is x i(n), 1≤n≤3780, then x i(n) DFT sequence amplitude peak is 1 with the ratio of valley, and this sequence is the LPVR sequence.
With above-mentioned data block as the required LPVR sequence padding data piece of test and protection at interval successively through framing and back-end processing, obtain the base-band data stream of making a start, obtain the radio frequency transmissions emission through digital-to-analogue conversion and analog-modulated again.Remember that the base-band data stream of making a start is t (n), shown in Fig. 2 .b.
Aforesaid operations and this modulating system modulated process are identical, need not this system is changed.
At test lead
Figure G2007101192704D00041
Step 1, the radiofrequency signal that the DTMB multicarrier modulation system of above-mentioned employing QPSK mapped mode is launched through analog demodulator and analog-to-digital conversion and early stage data recover to obtain the receiving end base-band data stream, data were recovered to comprise regularly and were recovered early stage, carrier wave recovery and frame synchronization keep frame synchronization, timing to reach carrier synchronization synchronously to guarantee the receiving end base-band data stream with respect to the base-band data stream of making a start; Note receiving end base-band data stream is r (n); According to the performance test model hypothesis, r (n)=h (n) * t (n)+v (n); Wherein, symbol * represents the linear convolution computing, and h (n) is the impulse response of this performance test model neutral line channel, and v (n) is the white Gaussian noise in this performance test model;
Figure G2007101192704D00042
Step 2 is by receiving end base-band data stream r (n) the i frame data piece x in the base-band data stream that obtains making a start i(n) and the circular convolution of test model channel impulse response y as a result i(n):
y i ( n ) = h ( n ) ⊗ x i ( n ) + w ( n ) , 1 ≤ n ≤ 3780 ,
Wherein, symbol
Figure G2007101192704D00044
The computing of expression circular convolution, the impulse response of this test model channel of h (n), w (n) are circular convolution noise superimposed and data interference as a result;
Figure G2007101192704D00045
Step 3, sequence of calculation x i(n) and circular convolution y as a result i(n) discrete Fourier transform (DFT):
X i(k)＝DFT(x i(n))，1≤n≤3780，1≤k≤3780，
Y i(k)＝DFT(y i(n))，1≤n≤3780，1≤k≤3780，
According to the DTMB modulating system structure of this QPSK mapping, X i(k) be peak amplitude and the ratio of valley amplitude is 1 sequence;
Step 4 obtains the estimated value of the discrete Fourier transform (DFT) H (k) of test model channel impulse response h (n) by division
Figure G2007101192704D00047
H ^ ( k ) = Y i ( k ) / X i ( k ) , 1 < k < 3780 ,
x i(n) be the LPVR sequence, then the peak amplitude of sequence X (k) equals 1 with the ratio of valley amplitude, and this division arithmetic precision is guaranteed;
Step 5: calculate Anti-discrete Fourier transform (DFT), obtain the estimated value of test model channel impulse response h (n):
Figure G2007101192704D000411
1≤n≤3780,1≤k≤3780;
Figure G2007101192704D000412
Step 6: according to Can estimate estimation of white Gaussian noise in the test model
Figure G2007101192704D000414
Energy because above-mentioned computing is all the time at i frame data piece, thereby the estimation range of this white Gaussian noise Energy Estimation also is limited in the i frame frame;
Figure G2007101192704D00051
Step 7: repeat above-mentioned steps, conversion i value, the test model channel estimating and the noise energy that can obtain are frame by frame estimated.
Fig. 3 .a is h (n) parameter according to this measured performance test model of the DTMB modulating system of the QPSK mapping of reality, here only drawn near the channel situation in the main footpath of h (n) at 100, and can obtain according to further calculating, main footpath energy accounts for 99.92% of gross energy.Fig. 3 .b is the planisphere mapping situation of this modulating system output signal, and its MER value is 31.086dB.Fig. 3 .c is that this modulating system output signal is shone upon situation through the balanced planisphere afterwards of above-mentioned test model parameter h (n), and its MER value is 43.874dB.Comparison diagram 3.b and Fig. 3 .c as can be seen because the influence of small multipath h (n) of the equivalence in the transmission course makes the MER of output signal worsen near 13dB.The OFDM multicarrier modulation system itself has very strong ability of anti-multipath, and the MER deterioration that above-mentioned small equivalent multipath brought is not sufficient to influence the modulating system performance, adopts h (n) described then more accurate.
The present invention carries out in the performance test process the DMBT modulating system that adopts the QPSK mapping in this example, this system is not done any change, has the efficient of enforcement height, the characteristics that operational precision is high.
Above concrete embodiment of the present invention is had been described in detail, but the present invention is not restricted to above-mentioned embodiment, under the spirit and scope situation of the claim that does not break away from the application, those skilled in the art can make various modifications or remodeling.

Claims (1)

1. OFDM modulation system performance test method based on low peak-valley ratio sequence transmission, it is characterized in that: OFDM multicarrier modulation system originating data stream to be measured and test macro are received that the transmission course between the data flow is modeled as the linear channel of a band white Gaussian noise, be that relation between modulating system originating data x (n) and the test macro receiving end data r (n) can be described by r (n)=h (n) * x (n)+v (n), wherein, symbol * represents the linear convolution computing, h (n) is the impulse response of this test model channel, and v (n) is that the noise and the data of linear convolution system are disturbed; This method realizes in the end to be measured of digital integrated circuit or Computer Simulation and test lead successively as follows:
At end to be measured
Figure F2007101192704C00011
Step (1), according to the transmission data block length N of OFDM multicarrier modulation system to be measured, selecting a group length arbitrarily is the low peak-valley ratio sequence x (n) of N, the amplitude peak of its discrete Fourier transform sequence is not more than 3 with the ratio of valley;
Figure F2007101192704C00012
Step (2) is treated examining system, fills its transmission data block with this low peak-valley ratio sequence x (n);
Figure F2007101192704C00013
Step (3), the transmission data block that protection interval and low peak-valley ratio sequence are filled obtains the base-band data stream of making a start successively after framing and back-end processing; The Frame of being filled as data block with x (n) is designated as t (n), and its length is M;
Figure F2007101192704C00014
Step (4), the base-band data stream of will making a start obtains delivering to test lead behind the radio frequency transmissions through digital-to-analogue conversion and analog-modulated;
At test lead
Figure F2007101192704C00015
Step (1 '), with treat radiofrequency signal that examining system is launched through analog demodulator and analog-to-digital conversion and early stage data recover to obtain the receiving end base-band data stream, data were recovered to guarantee this receiving end base-band data stream and were treated that examining system is made a start and keep frame synchronization between the base-band data stream, regularly reach carrier synchronization synchronously early stage; Note is r (n) with t (n) for the receiving end base band data of base band data of making a start;
Figure F2007101192704C00016
Step (2 ') obtains the circular convolution y (n) of channel impulse response h (n) in low peak-valley ratio sequence x (n) and the performance test model according to above-mentioned receiving end base-band data stream:
y ( n ) = h ( n ) &CircleTimes; x ( n ) + w ( n ) ,
Wherein, symbol
Figure F2007101192704C00018
The computing of expression circular convolution, h (n) is the impulse response of this test model channel, w (n) is circular convolution noise superimposed and data interference as a result;
Step (3 '), calculate low peak-valley ratio sequence x (n) and the circular convolution discrete Fourier transform (DFT) of y (n) as a result:
X(k)＝DFT(x(n))，
Y(k)＝DFT(y(n))；
Step (4 ') obtains the estimated value of the discrete Fourier transform (DFT) H (k) of test model channel impulse response h (n) by division
Figure F2007101192704C000111
H ^ ( k ) = Y ( k ) / X ( k ) ;
Figure F2007101192704C000113
Step (5 '): calculate
Figure F2007101192704C000114
Anti-discrete Fourier transform (DFT), obtain the estimated value of test model channel impulse response h (n):
h ^ ( n ) = IDFT ( H ^ ( k ) ) ;
Figure F2007101192704C000116
Step (6 '): according to
Figure F2007101192704C000117
Calculate Noise Estimation
CN2007101192704A 2007-07-19 2007-07-19 OFDM modulation system performance test method based on low peak-valley ratio sequence transmission Expired - Fee Related CN101083508B (en)

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