CN102437978B - Method and device for balancing digital microwaves - Google Patents
Method and device for balancing digital microwaves Download PDFInfo
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- CN102437978B CN102437978B CN201010500631.1A CN201010500631A CN102437978B CN 102437978 B CN102437978 B CN 102437978B CN 201010500631 A CN201010500631 A CN 201010500631A CN 102437978 B CN102437978 B CN 102437978B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
- H04L25/03019—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception
- H04L25/03057—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception with a recursive structure
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
- H04L2025/03375—Passband transmission
- H04L2025/0342—QAM
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L2025/03592—Adaptation methods
- H04L2025/03598—Algorithms
- H04L2025/03611—Iterative algorithms
- H04L2025/03617—Time recursive algorithms
Abstract
The invention provides a method and device for balancing digital microwaves and relates to the field of communication. By utilizing the method and the device, the problem that the conventional balancer technology cannot meet the performance requirement of high-order quadrature amplitude modulation (QAM) is solved. The method comprises the following steps that: a transmitting end sends a signal to a receiving end; the receiving end acquires an output sign according to the signal and compares the output sign with a reference sign so as to acquire a sign absolute error e (n); and the receiving end substitutes the sign absolute error e (n) into an adaptive algorithm for adaptive training. The technical scheme provided by the invention is applicable to digital microwave communication systems.
Description
Technical field
The present invention relates to the communications field, particularly relate to a kind of digital microwave equalization methods and device.
Background technology
Digital microwave telecommunication is that one adopts Digital Signal Processing in the transmission, utilizes microwave frequency to realize the means of communication of information transmission.On the basis of the development of Digital Signal Processing, in order to improve the capacity of system digits microwave telecommunication system, 256QAM even 512QAM or the higher high-order QAM modulation of exponent number is applied in digital microwave systems, and this brings great challenge to digital microwave systems.
Digital microwave communication system is generally as primary transmission or the stand-by protection as trunk fiber, and therefore its bandwidth, transmission capacity are large, requires high to the transfer rate of system and reliability and stability.
Although microwave telecommunication system is point-to-point horizon communication, its wireless channel environment will be got well relative to GSM, and it still cannot avoid declining in wireless channel, noise, the impact of interference and multipath effect.The ISI (intersymbol interference) that particularly in wireless channel, multipath effect causes, cause frequency selective fading at frequency domain to received signal, time domain causes the expansion of symbol, thus causes amplitude and the phase distortion of Received signal strength, the performance of influential system.Therefore the measure of anti-ISI must be adopted to improve systematic function at receiving terminal.
In digital microwave systems, the general impact adopting diversity technique and balancing technique antagonism ISI.Wherein, adaptive equalizer technology has a wide range of applications.But the equalizer techniques now in microwave system generally adopts the method for blind equalization, more effectively can eliminate ISI, but when microwave channel worsening condition, cannot adapt to the performance requirement of high-order QAM modulation under low-order-modulated and the good situation of microwave channel.
Summary of the invention
The invention provides a kind of method and apparatus of digital microwave equilibrium, solve the problem that existing equalizer techniques cannot adapt to the performance requirement of high-order QAM modulation.
A method for digital microwave equilibrium, comprising:
Transmitting terminal sends signal to receiving terminal, and described receiving terminal obtains output symbol according to described signal, and described output symbol and reference symbol is contrasted, and obtains symbol absolute error e (n);
Described receiving terminal, by described symbol absolute error e (n), substitutes into adaptive algorithm, carries out adaptive training.
Further, described signal is specially training frames, corresponding described reference symbol is known training symbol, or described signal is specially leading (Preamble) part of Frame front end, described reference symbol is Frame front end known pilot symbols, described receiving terminal is by described symbol absolute error e (n), and substitute into adaptive algorithm, the step of carrying out adaptive training is specially:
Described receiving terminal, according to described symbol absolute error e (n), substitutes into adaptive algorithm, upgrades the coefficient of feedforward filter (FFF) and decision feedback filter device (DFE).
Further, described adaptive algorithm is specially LMS or RLS.
Further, described signal is specially the data division after the Preamble of Frame, described reference symbol is specially the data symbol that obtain of rear end after judgement receiving Frame, described transmitting terminal sends signal to receiving terminal, described receiving terminal obtains output symbol according to described signal, and described output symbol and reference symbol are contrasted, obtain symbol absolute error e (n) and be specially:
Transmitting terminal sends Frame to receiving terminal, during data division after the Preamble receiving Frame, described receiving terminal obtains output symbol according to this signal, and by described output symbol and the result of adjudicating this output symbol, contrast, compute sign absolute error e (n), described judgement comprises hard decision and soft-decision.
Further, described receiving terminal is by described symbol absolute error e (n), and substitute into adaptive algorithm, the step of carrying out adaptive training is specially:
Calculate according to each data symbol of described Frame or upgrade described symbol absolute error e (n) successively.
Further, described transmitting terminal sends signal to receiving terminal, and described receiving terminal obtains output symbol according to described signal, and described output symbol and reference symbol is contrasted, and obtains symbol absolute error e (n) and comprising:
According to expression formula
acquisition feedforward filter outputs signal, wherein,
for feedforward filter input signal vector, W (n)=[w
0(n), w
1(n) ... w
l-1(n)]
tbe the feedforward filter response in the n-th symbol moment, L is the exponent number of feedforward filter, and Ts is the sampled symbols cycle;
Two times of extractions are carried out to feedforward filter output signal, obtains sampled signal y (n)=y ' (2m), wherein, m=1,2 ...;
Obtain response B (n)=[b of decision feedback filter device in the n-th symbol moment
0(n), b
1(n) ... b
p-1(n)]
t, decision feedback filter device input signal D (n) in n moment=[d (n-1), d (n-2) ... d (n-P)]
t, wherein, P is the exponent number of decision feedback filter device, according to expression formula
obtain the decision feedback filter device output signal in n moment;
Get feedforward filter output signal and decision feedback filter device output signal with, as output symbol s (n) in n moment, s (n)=y (n)+z (n);
Obtain absolute symbol error e (n)=d (the n)-s (n) in n moment.
Further, above-mentioned digital microwave equalization methods also comprises:
Transmitting terminal sends training frames to receiving terminal, and described receiving terminal obtains output symbol according to this training frames, and described output symbol and known training symbol is contrasted, and obtains relative error vector magnitude (EVM);
Described receiving terminal is according to described EVM, and the modulation of certainty annuity and encoding scheme, and described scheme is notified described transmitting terminal by AMC feedback channel, described transmitting terminal carries out modulation and the coding of Frame according to described scheme.
Further, above-mentioned digital microwave equalization methods also comprises:
Transmitting terminal sends Frame to receiving terminal, and described receiving terminal obtains output symbol according to this Frame, and by described output symbol and the result of adjudicating this symbol, carry out contrast and obtain EVM, described judgement comprises hard decision or soft-decision;
Described receiving terminal, according to described EVM, redefines modulation and the encoding scheme of system, and the described scheme redefined is notified described transmitting terminal by AMC feedback channel, and described transmitting terminal carries out modulation and the coding of next Frame according to described scheme.
Present invention also offers a kind of digital microwave balancer, comprising:
Error calculating module, for obtaining output symbol according to described signal, and contrasts described output symbol and reference symbol, obtains symbol absolute error e (n);
Training module, for by described symbol absolute error e (n), substitutes into adaptive algorithm, carries out adaptive training.
Further, described error calculating module comprises:
Feedforward filter, for according to expression formula
acquisition feedforward filter outputs signal, wherein,
for feedforward filter input signal vector, W (n)=[w
0(n), w
1(n) ... w
l-1(n)]
tbe the feedforward filter response in the n-th symbol moment, L is the exponent number of feedforward filter, and Ts is the sampled symbols cycle;
Decision feedback filter device, for carrying out two times of extractions to feedforward filter output signal, obtains sampled signal y (n)=y ' (2m), wherein, m=1,2, ..., obtain response B (n)=[b of decision feedback filter device in the n-th symbol moment
0(n), b
1(n) ... b
p-1(n)]
t, decision feedback filter device input signal D (n) in n moment=[d (n-1), d (n-2) ... d (n-P)]
t, wherein, P is the exponent number of decision feedback filter device, according to expression formula
obtain the decision feedback filter device output signal in n moment;
Error signal calculation unit, for get feedforward filter output signal and decision feedback filter device output signal with, as output symbol s (n) in n moment, s (n)=y (n)+z (n), obtains absolute symbol error e (n)=d (the n)-s (n) in n moment.
Further, described error calculating module also comprises:
Qam symbol decision device, for adjudicating described output symbol, and court verdict is sent to error signal calculation unit, described judgement comprises hard decision or soft-decision;
Described error signal calculation unit, also for by described output symbol and the court verdict to this output symbol, contrasts, compute sign absolute error e (n).
Further, above-mentioned digital microwave balancer also comprises:
Signal EVM detection module, for described output symbol and reference symbol being contrasted, obtains EVM; With,
For according to described EVM, the modulation of certainty annuity and encoding scheme, and the described scheme determined is notified described transmitting terminal by AMC feedback channel, indicate described transmitting terminal to carry out modulation and the coding of Frame according to described scheme.
The invention provides a kind of digital microwave equalization methods and device, transmitting terminal sends signal to receiving terminal, described receiving terminal obtains output symbol according to described signal, and described output symbol and reference symbol are contrasted, obtain symbol absolute error e (n), described receiving terminal is by described symbol absolute error e (n), substitute into adaptive algorithm, carry out adaptive training, adaptive approach is used to complete digital microwave equilibrium, effectively improve the modulation /demodulation performance of high-order QAM under severe microwave channel environment, improve the capacity of digital microwave systems.
Accompanying drawing explanation
The structural representation of a kind of digital microwave balancer that Fig. 1 provides for embodiments of the invention;
The flow chart of a kind of digital microwave equalization methods that Fig. 2 provides for embodiments of the invention one;
The flow chart of a kind of digital microwave equalization methods that Fig. 3 provides for embodiments of the invention two;
The flow chart of a kind of digital microwave equalization methods that Fig. 4 provides for embodiments of the invention three;
Fig. 5 is EVM measuring principle figure;
Fig. 6 is untreated 512QAM modulated signal constellation;
The 512QAM modulated signal constellation of Fig. 7 for obtaining after the digital microwave equalization methods process that provides through embodiments of the invention.
Detailed description of the invention
Adopt the method for blind equalization, more effectively can eliminate ISI under low-order-modulated and the good situation of microwave channel, but when microwave channel worsening condition, the performance requirement of high-order QAM modulation cannot be adapted to.Order of modulation is higher, to distorted signals or error more responsive, and the source of distorted signals or error mainly channel.
In order to solve the problem, The embodiment provides a kind of method and apparatus of digital microwave equilibrium.
First, be described the digital microwave balancer that embodiments of the invention provide, its structure as shown in Figure 1, comprises error calculating module 101 and training module 102.Wherein, error calculating module 101 comprises again a feedforward filter (feed-forward filter, referred to as FFF) 1011, decision feedback filter device (decision feedback equalizer, referred to as DFE) 1012 and a signal errors computing unit 1013.
Further, error calculating module 101 also comprises a qam symbol decision device 1014.
This digital microwave balancer also comprises a signal errors vector magnitude (Error VectorMagnitude, referred to as EVM) detection module 103.
Error calculating module 101, for obtaining output symbol according to described signal, and contrasts described output symbol and reference symbol, obtains symbol absolute error e (n);
Training module 102, for by described symbol absolute error e (n), substitutes into adaptive algorithm, carries out adaptive training.
Feedforward filter 1011, for according to expression formula
acquisition feedforward filter outputs signal, wherein,
for feedforward filter input signal vector, W (n)=[w
0(n), w
1(n) ... w
l-1(n)]
tbe the feedforward filter response in the n-th symbol moment, L is the exponent number of feedforward filter, and Ts is the sampled symbols cycle;
Decision feedback filter device 1012, for carrying out two times of extractions to feedforward filter output signal, obtains sampled signal y (n)=y ' (2m), wherein, m=1,2, ..., obtain response B (n)=[b of decision feedback filter device in the n-th symbol moment
0(n), b
1(n) ... b
p-1(n)]
t, decision feedback filter device input signal D (n) in n moment=[d (n-1), d (n-2) ... d (n-P)]
t, wherein, P is the exponent number of decision feedback filter device, according to expression formula
obtain the decision feedback filter device output signal in n moment;
Error signal calculation unit 1013, for get feedforward filter output signal and decision feedback filter device output signal with, as output symbol s (n) in n moment, s (n)=y (n)+z (n), obtains absolute symbol error e (n)=d (the n)-s (n) in n moment.
Qam symbol decision device 1014, for adjudicating described output symbol, and court verdict is sent to error signal calculation unit 1013, described judgement comprises hard decision or soft-decision;
Described error signal calculation unit 1013, also for by described output symbol and the court verdict to this output symbol, contrasts, compute sign absolute error e (n).
Signal EVM detection module 103, for described output symbol and reference symbol being contrasted, obtains EVM; With,
For according to described EVM, the modulation of certainty annuity and encoding scheme, and the described scheme determined is notified described transmitting terminal by AMC feedback channel, indicate described transmitting terminal to carry out modulation and the coding of Frame according to described scheme.
Above-mentioned digital microwave balancer also can be described as balanced device, is positioned at receiving terminal.
Concrete, described FFF, for multiple symbol after eliminating current receiving symbol to the interference of current sign, it is the fractional order FIR filter of 1/2, namely every tap is 1/2 symbol period interval, and the extraction coefficient of wave filter is 2, namely inputs two sampled points, output is 1 sampled point, and the adaptive algorithm that feedforward filter is adopted by filter coefficient control module upgrades coefficient.
Described DFE, for multiple symbol before eliminating current receiving symbol to the interference of current sign, for baud rate interval FIR filter, namely every tap is 1 symbol period time interval, similar with feedforward filter, the adaptive algorithm that decision feedback filter device is adopted by filter coefficient control module upgrades filter coefficient.
Described training module, utilize dependent adaptive algorithm to control the renewal of filter coefficient, adaptive algorithm can take LMS, RLS scheduling algorithm, concrete relevant with system hardware ability, and LMS convergence rate is slow, and computing is simple, requires low to hardware implementing; RLS algorithm the convergence speed is fast but computing is complicated, high to hardware requirement.
Described qam symbol decision device (Slicer), symbol for exporting FFF wave filter is adjudicated, decision rule can adopt hard decision criterion, the criterion that namely Euclidean distance is minimum, is from the minimum symbol of standard constellation point Euclidean distance the judgement of wave filter output symbol; Also can adopt soft-decision criterion, with maximum likelihood probability, the output of FFF wave filter be detected.
Described error signal calculation unit, for the error of calculating filter output symbol and known symbol (training symbol or Frame leading), errors enters the training module before FFF and DFE wave filter, is used for controlling filter coefficient.
Described signal EVM detection module, be used for calculating the EVM of equalizer output signal relative to reference symbol, the EVM obtained is for the adjustment of AMC.
Below in conjunction with accompanying drawing, embodiments of the invention one are described.
Embodiments of the invention one provide a kind of digital microwave equalization methods, and the flow process using the equilibrium of the method settling signal as shown in Figure 2, comprising:
Step 201, transmitting terminal send signal to receiving terminal, and described receiving terminal obtains output symbol according to described signal, and described output symbol and reference symbol are contrasted, and obtain symbol absolute error e (n);
When described signal is specially training frames, corresponding described reference symbol is known training symbol; Or when described signal is specially leading (Preamble) part of Frame front end, described reference symbol is Frame front end known pilot symbols; Or when described signal is specially the data division after the Preamble of Frame, described reference symbol is specially the data symbol that obtain of rear end after judgement receiving Frame.
Step 202, described receiving terminal, by described symbol absolute error e (n), substitute into adaptive algorithm, carry out adaptive training;
Step 203, transmitting terminal send training frames to receiving terminal, and described receiving terminal obtains output symbol according to this training frames, and described output symbol and known training symbol are contrasted, and obtain relative EVM;
Step 204, described receiving terminal according to described EVM, the modulation of certainty annuity and encoding scheme, and described scheme is notified described transmitting terminal by AMC feedback channel, described transmitting terminal carries out modulation and the coding of Frame according to described scheme;
Step 205, transmitting terminal send Frame to receiving terminal, and described receiving terminal obtains output symbol according to this Frame, and by described output symbol and the result of adjudicating this symbol, carry out contrast and obtain EVM, described judgement comprises hard decision or soft-decision;
Step 206, described receiving terminal are according to described EVM, redefine modulation and the encoding scheme of system, and the described scheme redefined is notified described transmitting terminal by AMC feedback channel, described transmitting terminal carries out modulation and the coding of next Frame according to described scheme.
Below in conjunction with accompanying drawing, embodiments of the invention two are described.
Embodiments of the invention two provide a kind of digital microwave equalization methods, use the method to complete the flow process of microwave equilibrium as shown in Figure 3, comprising:
After step 301, system boot or system step-out, by MAC layer signaling scheduling physical layer, transmitting terminal can send out training frames some, and all transmitting symbols of this frame are all known at receiving terminal, now balanced device work in training mode, is trained filter coefficient adaptive algorithm.Meanwhile, EVM checkout gear contrasts equalizer output signal and known training symbol, calculates the error vector magnitude of output signal and actual transmit signal, i.e. EVM.
Step 302, according to the EVM value obtained in step 301, the modulation of certainty annuity and encoding scheme, and by order of modulation and encoding scheme by AMC feedback channel notice transmitting terminal;
Step 303, transmitting terminal start to utilize the order of modulation and encoding scheme determined in step 302, transmit data frames.Receiving terminal receives Frame, and leading (Preamble) part of Frame is used for sign synchronization and carrier synchronization, and the Preamble of transmitting is also known at receiving terminal.Therefore, at every frame frame head of Frame, balanced device also can utilize known Preamble to train filter coefficient;
Step 304, when with frame head symbol by after wave filter, balanced device turns to tracing mode work, with the adaptive algorithm adjustment filter coefficient of decision-feedback, follows the tracks of channel;
Step 305, Frame demodulation are complete, and when the EVM of present frame equalizer output symbol remains unchanged, balanced device repeats step 303 and step 304, carries out the equilibrium of next Frame; When the EVM of equalizer output symbol is less than certain thresholding, illustrates that channel condition is better, the Modulation and Coding Scheme of high spectral efficiency can be used, therefore adjust by the adjustment modulation of feedback channel notice transmitting terminal and encoding scheme.
When the error rate level of step 306, present frame or the EVM of equalizer output symbol are greater than certain thresholding, illustrate that now channel changes, channel becomes severe, and now receiving terminal is by the adjustment modulation of feedback channel notice transmitting terminal and encoding scheme, adopts the scheme compared with low frequency spectrum efficiency.When the modulation of system and encoding scheme drop to minimum QPSK, EVM or BLER is still very large, upper signal channel change do not followed the tracks of by balanced device, equalizer output symbol contains a large amount of ISI and error performance is raised, now balanced device turns to step 301, namely retransmit training frames, balanced device re-starts present channel and catches and follow the tracks of, and according to present channel adjustment modulation and encoding scheme.
Below in conjunction with accompanying drawing, embodiments of the invention three are described.
Embodiments provide a kind of method of digital microwave equilibrium, combine with the balancer of digital microwave shown in Fig. 1, the flow process realizing data transmission as shown in Figure 4, comprising:
Re-synchronization after step 401, system boot or system step-out, transmitting terminal transmitting training frames, receiving terminal utilizes known training symbol to train filter coefficient, make through training the input signal of postfilter through filtering, the output after twice extracts and the error between the known training sequence of transmitting as far as possible little.
Concrete, obtain FFF output signal by expression formula one.
Wherein,
for feedforward filter input signal vector, W (n)=[w
0(n), w
1(n) ... w
l-1(n)]
tbe the feedforward filter response in the n-th symbol moment, L is the exponent number of feedforward filter, and Ts is the sampled symbols cycle.
Then, two times of extractions are carried out to the output signal of feedforward filter, obtain sampled signal: y (n)=y ' (2m), m=1,2 ...,
B (n)=[b
0(n), b
1(n) ... b
p-1(n)]
tfor decision feedback filter device is in the response in the n-th symbol moment, D (n)=[d (n-1), d (n-2) ... d (n-P)]
tfor the decision feedback filter device input signal in n moment, wherein, P is the exponent number of decision feedback filter device.Therefore the decision feedback filter device output signal in n moment can obtain according to expression formula two, for:
Feedforward filter output signal and decision feedback filter device output signal with, be the output signal s (n) of balanced device in the n moment, the symbol absolute error in s (n)=y (n)+z (n), n moment is: e (n)=d (n)-s (n).
To use LMS algorithm, structure cost function J (n)=E [| e (n) |
2], utilize the method for iteration to find appropriate filter vector W (n) and B (n), make cost function J (n) minimum.Use steepest descent method iteration, iterative formula is:
W(n+1)＝W(n)-μX
*(n)e(n) B(n+1)＝B(n)-μ
2D
*(n)e(n)
Now, by symbol absolute error e (n) in feedforward filter and the every symbol period of decision feedback filter device, filter coefficient is adjusted by adaptive algorithm by filter coefficient regulator.
By analyzing above, through enough training symbols training after, filter adaptation microwave channel, after filtering the filtered signal of device can compensate for channel decline impact.
Step 402, carrying out while step 401 pair wave filter trains, the EVM of EVM measurement mechanism to equalizer output signal measures, obtain the residual error of equalized channel, to determine modulation and encoding scheme, EVM measuring principle as shown in Figure 5, S standard constellation point symbol vector in Fig. 5, R is equalizer output signal vector.
Step 403, transmitting terminal transmitting data frame signal, after completing frame synchronization and Timing Synchronization, balanced device is trained by the leading Preamble of mode identical in step 402 to Frame;
Step 404, when with frame head symbol Preamble by after wave filter, balanced device mode of operation is converted to tracing mode by training mode, channel is followed the tracks of, under tracing mode, basically identical under the more new algorithm of filter coefficient and training mode, unique difference is because receiving terminal does not know to need the concrete symbol of transmitting terminal transmitting data first to adjudicate data when error of calculation vector:
, wherein
for decision device is to the certainly result of current sign, decision device can take the soft-decision structure of hard decision or maximum likelihood probability, and the process of soft-decision is:
Suppose that current is M-QAM modulation system, M=2
m, putting in order as S=[s of the bit that each constellation point comprises
ms
m-1s
2s
1].Suppose that the kth symbol received is R
k, then the order of its bit comprised is R
k=[r
k, m, r
k, m-1..., r
k, 2, r
k, 1], calculate M=2
mindividual conditional probability P (R
k/ S
i) (i=1,2 ... M), from M conditional probability P (R
k/ S
i) in the middle of find out maximum conditional probability P (R/S
l), then current sign is adjudicated as S
l=[s
lms
lm-1s
l2s
l1].P (R
k/ S
i) computational methods be: first adopt and minimumly measure scheduling algorithm, obtain current receiving symbol R
ksoft bit information B
k=[b
k, m, b
k, m-1..., b
k, 2, b
k, 1], soft bit information b
k, m-1represent each bit of receiving symbol be 1 or be 0 probability, b
k, m-1more represent that the probability of 1 is larger close to 1, more represent that the probability of 0 is larger close to 0.Therefore,
then obtain receiving symbol R
kfor constellation map symbol S
iprobability, find out maximum probability P (R/S
l) current sign judgement is for S
l.
Step 405, current data frame demodulation are complete, and when the EVM of equalizer output symbol remains unchanged, balanced device repeats step 403 and step 404, carries out the equilibrium of next frame data; When the EVM of equalizer output symbol is less than certain thresholding, illustrates that channel condition is better, the Modulation and Coding Scheme of high spectral efficiency can be used, therefore adjust by the adjustment modulation of feedback channel notice transmitting terminal and encoding scheme;
When the error rate level of step 406, present frame or the EVM of equalizer output symbol are greater than certain thresholding, illustrate that now channel sends change, upper signal channel change do not followed the tracks of by balanced device, equalizer output symbol contains a large amount of ISI and error performance is raised, now balanced device turns to step 401, namely retransmit training frames, balanced device re-starts present channel and catches and follow the tracks of, and according to present channel adjustment modulation and encoding scheme.
Fig. 6 and Fig. 7 compared for the signal constellation (in digital modulation) figure of the 512QAM modulation before and after the digital microwave equalization methods process that provides through embodiments of the invention, as can be seen from the figure, the method of the digital microwave equilibrium that embodiments of the invention provide, the digital microwave balancer that can provide with embodiments of the invention combines, effectively inhibit the intersymbol interference in Received signal strength, improve system error performance.Compared with existing scheme, the algorithm that the embodiment of the present invention provides is simple, and performance is better simultaneously, is more suitable for and is applied in the digital microwave channel of point-to-point transmission.
Owing to have employed the adaptive algorithm of training method, the anti-ISI scheme that the embodiment of the present invention provides is more excellent than the scheme equalization performance of the existing blind equalizer generally adopted, and is particularly useful for the high-order QAM modulation compared with more than the 256QAM under severe channel conditions.
Further, the method of the digital microwave equilibrium that embodiments of the invention provide, is more applicable for digital microwave systems, because in microwave transmission, the position of transmitting-receiving two-end is fixed, therefore there is not the impact of Doppler effect in microwave channel, and microwave channel change is very slow.Therefore can think and send training frames, after device to be filtered has been trained, channel response is substantially constant or change slowly, need not need to send the change of training sequence by equalizer adaptation channel continually as in some time varying channel.
In the embodiment of the present invention, also channel equalization is combined with AMC, more effectively can ensure reliability and the validity of digital microwave systems, make system can be operated in the heap(ed) capacity adapting to present channel environment.
Compared with the adaptive equalizer of existing band decision-feedback structure, in embodiments of the invention, qam symbol decision device can adopt the mode of soft-decision, the court verdict obtained according to the mode of Euclidean distance hard decision adopted than existing scheme is more accurate, thus effectively reduces because mistake in judgment causes the phenomenon of error propagation.
One of ordinary skill in the art will appreciate that all or part of step of above-described embodiment can use computer program flow process to realize, described computer program can be stored in a computer-readable recording medium, described computer program (as system, unit, device etc.) on corresponding hardware platform performs, when performing, step comprising embodiment of the method one or a combination set of.
Alternatively, all or part of step of above-described embodiment also can use integrated circuit to realize, and these steps can be made into integrated circuit modules one by one respectively, or the multiple module in them or step are made into single integrated circuit module to realize.Like this, the present invention is not restricted to any specific hardware and software combination.
Each device/functional module/functional unit in above-described embodiment can adopt general calculation element to realize, and they can concentrate on single calculation element, also can be distributed on network that multiple calculation element forms.
Each device/functional module/functional unit in above-described embodiment using the form of software function module realize and as independently production marketing or use time, can be stored in a computer read/write memory medium.The above-mentioned computer read/write memory medium mentioned can be read-only storage, disk or CD etc.
Anyly be familiar with those skilled in the art in the technical scope that the present invention discloses, change can be expected easily or replace, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain described in claim.
Claims (11)
1. a digital microwave equalization methods, is characterized in that, comprising:
Transmitting terminal sends signal to receiving terminal, and described receiving terminal obtains output symbol according to described signal, and described output symbol and reference symbol is contrasted, and obtains symbol absolute error e (n);
Described receiving terminal, by described symbol absolute error e (n), substitutes into adaptive algorithm, carries out adaptive training;
Described method specifically comprises:
After step 301, system boot or system step-out, transmitting terminal sends some training frames, and all transmitting symbols of described training frames are that receiving terminal is known, and now balanced device work in training mode, is trained filter coefficient adaptive algorithm; , equalizer output signal and known training symbol are contrasted meanwhile, calculate the error vector magnitude EVM of output signal and actual transmit signal;
Step 302, according to the modulation of described EVM certainty annuity and encoding scheme, and by order of modulation and encoding scheme by AMC feedback channel notice transmitting terminal;
Step 303, transmitting terminal utilize described order of modulation and encoding scheme transmit data frames; Receiving terminal receives Frame, the leading Preamble part of Frame is used for sign synchronization and carrier synchronization, described Preamble part is also known at receiving terminal, makes balanced device that the known Preamble of every frame frame head of Frame can be utilized to train filter coefficient;
Step 304, when with frame head symbol by after wave filter, balanced device turns to tracing mode work, with the adaptive algorithm adjustment filter coefficient of decision-feedback, follows the tracks of channel;
Step 305, Frame demodulation are complete, and when the EVM of balanced device present frame output symbol remains unchanged, balanced device repeats step 303 and step 304, carries out the equilibrium of next Frame;
When the error rate level of step 306, present frame or the EVM of equalizer output symbol are greater than certain thresholding, show bad channel, receiving terminal is by the adjustment modulation of feedback channel notice transmitting terminal and encoding scheme; When modulate and encoding scheme drop to minimum QPSK but EVM or the bit error rate are still very large time, turn to step 301, namely retransmit training frames, balanced device re-starts present channel and catches and follow the tracks of, and modulates and encoding scheme according to present channel adjustment.
2. digital microwave equalization methods according to claim 1, it is characterized in that, when described signal is specially training frames, corresponding described reference symbol is known training symbol, or described signal is when being specially the leading Preamble part of Frame front end, described reference symbol is Frame front end known pilot symbols, and described receiving terminal is by described symbol absolute error e (n), substitute into adaptive algorithm, the step of carrying out adaptive training is specially:
Described receiving terminal, according to described symbol absolute error e (n), substitutes into adaptive algorithm, upgrades the coefficient of feedforward filter FFF and decision feedback filter device DFE.
3. digital microwave equalization methods according to claim 2, is characterized in that, described adaptive algorithm is specially LMS or RLS.
4. digital microwave equalization methods according to claim 1, it is characterized in that, described signal is specially the data division after the Preamble of Frame, described reference symbol is specially the data symbol that obtain of rear end after judgement receiving Frame, described transmitting terminal sends signal to receiving terminal, described receiving terminal obtains output symbol according to described signal, and described output symbol and reference symbol is contrasted, and obtains symbol absolute error e (n) and is specially:
Transmitting terminal sends Frame to receiving terminal, during data division after the Preamble receiving Frame, described receiving terminal obtains output symbol according to this signal, and by described output symbol and the result of adjudicating this output symbol, contrast, compute sign absolute error e (n), described judgement comprises hard decision and soft-decision.
5. digital microwave equalization methods according to claim 4, is characterized in that, described receiving terminal is by described symbol absolute error e (n), and substitute into adaptive algorithm, the step of carrying out adaptive training is specially:
Calculate according to each data symbol of described Frame or upgrade described symbol absolute error e (n) successively.
6. digital microwave equalization methods according to claim 1, it is characterized in that, described transmitting terminal sends signal to receiving terminal, described receiving terminal obtains output symbol according to described signal, and described output symbol and reference symbol are contrasted, obtain symbol absolute error e (n) and comprising:
According to expression formula
Acquisition feedforward filter outputs signal, wherein,
For feedforward filter input signal vector, W (n)=[w
0(n), w
1(n) ... w
l-1(n)]
tbe the feedforward filter response in the n-th symbol moment, L is the exponent number of feedforward filter, and Ts is the sampled symbols cycle;
Two times of extractions are carried out to feedforward filter output signal, obtain sampled signal y (n)=y'(2m), wherein, m=1,2 ...;
Obtain response B (n)=[b of decision feedback filter device in the n-th symbol moment
0(n), b
1(n) ... b
p-1(n)]
t, decision feedback filter device input signal D (n) in n moment=[d (n-1), d (n-2) ... d (n-P)]
t, wherein, P is the exponent number of decision feedback filter device, according to expression formula
obtain the decision feedback filter device output signal in n moment;
Get feedforward filter output signal and decision feedback filter device output signal with, as output symbol s (n) in n moment, s (n)=y (n)+z (n);
Obtain absolute symbol error e (n)=d (the n)-s (n) in n moment.
7. the method for digital microwave equilibrium according to claim 1, it is characterized in that, the method also comprises:
Transmitting terminal sends Frame to receiving terminal, and described receiving terminal obtains output symbol according to this Frame, and by described output symbol and the result of adjudicating this symbol, carry out contrast and obtain EVM, described judgement comprises hard decision or soft-decision;
Described receiving terminal, according to described EVM, redefines modulation and the encoding scheme of system, and the described scheme redefined is notified described transmitting terminal by AMC feedback channel, and described transmitting terminal carries out modulation and the coding of next Frame according to described scheme.
8. adopt a digital microwave balancer for digital microwave equalization methods as claimed in claim 1, it is characterized in that, comprising:
Error calculating module, for obtaining output symbol according to described signal, and contrasts described output symbol and reference symbol, obtains symbol absolute error e (n);
Training module, for by described symbol absolute error e (n), substitutes into adaptive algorithm, carries out adaptive training.
9. digital microwave balancer according to claim 8, is characterized in that, described error calculating module comprises:
Feedforward filter, for according to expression formula
Acquisition feedforward filter outputs signal, wherein,
For feedforward filter input signal vector, W (n)=[w
0(n), w
1(n) ... w
l-1(n)]
tbe the feedforward filter response in the n-th symbol moment, L is the exponent number of feedforward filter, and Ts is the sampled symbols cycle;
Decision feedback filter device, for carrying out two times of extractions to feedforward filter output signal, obtains sampled signal y (n)=y'(2m), wherein, m=1,2, ..., obtain response B (n)=[b of decision feedback filter device in the n-th symbol moment
0(n), b
1(n) ... b
p-1(n)]
t, decision feedback filter device input signal D (n) in n moment=[d (n-1), d (n-2) ... d (n-P)]
t, wherein, P is the exponent number of decision feedback filter device, according to expression formula
obtain the decision feedback filter device output signal in n moment;
Error signal calculation unit, for get feedforward filter output signal and decision feedback filter device output signal with, as output symbol s (n) in n moment, s (n)=y (n)+z (n), obtains absolute symbol error e (n)=d (the n)-s (n) in n moment.
10. digital microwave balancer according to claim 9, is characterized in that, described error calculating module also comprises:
Qam symbol decision device, for adjudicating described output symbol, and court verdict is sent to error signal calculation unit, described judgement comprises hard decision or soft-decision;
Described error signal calculation unit, also for by described output symbol and the court verdict to this output symbol, contrasts, compute sign absolute error e (n).
11. digital microwave balancers according to claim 10, it is characterized in that, this device also comprises:
Signal errors vector magnitude EVM detection module, for described output symbol and reference symbol being contrasted, obtains EVM; With,
For according to described EVM, the modulation of certainty annuity and encoding scheme, and the described scheme determined is notified described transmitting terminal by AMC feedback channel, indicate described transmitting terminal to carry out modulation and the coding of Frame according to described scheme.
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| CN108199992B (en) * | 2017-12-28 | 2020-12-29 | 西安电子科技大学 | Blind equalization system and method suitable for 4096-QAM in microwave communication |
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