CN105071861B - A kind of MZM modulation index dynamic regulating methods of ROF system - Google Patents
A kind of MZM modulation index dynamic regulating methods of ROF system Download PDFInfo
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Abstract
The invention discloses a kind of MZM modulation index dynamic adjusting methods of ROF system, a MZM modulation index is initialized when initializing ROF system, then in communication process, when corresponding influence factor changes, optimal MZM modulation indexs are obtained from MZM modulation index table search according to current influence factor again；Or MZM modulation indexs are correspondingly adjusted according to the increase of number of users or reduction, until the bit error rate of user meets to require；Again or one set of maximum and composition for the MZM modulation indexs for allowing to use corresponding to each user, the MZM modulation indexs for then selecting a MZM modulation index of minimum to be used as emitter from the set is calculated in the interchannel noise estimate of the threshold value according to Signal to Interference plus Noise Ratio and each user's periodic feedback.The present invention realizes the dynamic regulation to MZM modulation indexs, adapts it to dynamic change of the ROF system in communication process.
Description
Technical field
The invention belongs to ROF communication technical fields, and more specifically, the MZM modulation indexs for being related to a kind of ROF system are moved
State adjusting method.
Background technology
With quickly propelling for informationization, communicate more and more important in the status of society.The quick popularization of internet, communication
Network traffics, especially data traffic greatly increase, and the bandwidth of backbone network is relatively sufficient due to a large amount of uses of optical fiber,
The main bottleneck of limitation bandwidth appears in access section.How to solve wireless high-speed rate data transfer and wireless access covering problem into
For key problem in technology in the urgent need to address.On the other hand, fiber optic communication has good electromagnetism interference, low-loss, can provide height
The advantages that bandwidth.ROF technologies (Radio Over Fiber, light carrier radio communication) are to answer High rate and large capacity wireless communication needs
The emerging wireless access technology for being combined fiber optic communication and radio communication to grow up.
Fig. 1 is ROF system structure chart.As shown in figure 1, ROF system is mainly by central station (CS), remote antenna unit
(RAU), Optic Fiber Transport Network and the part of user terminal four are formed.Connected between central station and remote antenna by optical fiber, and user terminal
It is still Radio Link between remote antenna.
The elementary tactics of ROF system is to connect CS with RAU with optical fiber, so as to realize two-way alternate communication, in uplink
Road, after RAU receives terminal signaling, by Laser Modulation, it can be then delivered to different RAU signal gathering to together
Central station is handled；In downlink, central station is transferred to RAU then in signal modulation to light carrier, then by optical fiber, so
RAU progress Photoelectric Detection radiate obtained millimeter-wave signal afterwards.
The method that useful signal is loaded on light carrier in ROF system has a variety of, is broadly divided into two classes：Directly modulate
And external modulation.Directly modulate simple and easy, but because the modulation bandwidth of laser is limited, therefore be not suitable for millimeter wave
Section.It is often more practical than directly modulating in higher frequency, such as more than 10GHz, external modulation.Wherein MZ Mach-Zehnder
(MZM, also referred to as MZ modulators) is a kind of the most frequently used device as external modulator.
MZ modulators can be by setting different bias voltage VDCPhase difference between the modulated signal of two-arm, according to
Need to realize different modulation systems.Due to the making material of MZ modulators and manufacture craft, added modulated signal
Voltage tend not to too big, be typically less than, which limits the modulation of MZ modulators twice of MZ modulator half-wave voltages
Index is only a smaller value.Assuming that the baseband signal for being loaded into MZ modulators is V1(t), by MZ modulators modulates
Transmitted on to optical signal, the relation between the output signal and input signal of modulator can be expressed as VOUT(t)=sin (m ×
V1(t)), m represents modulation index.In order to ensure the linear transfer of baseband signal, modulation index needs to use smaller value, to avoid
There is the nonlinear influence of MZ modulators modulates.But less modulation index can cause signal amplitude to reduce, and cause receiving terminal
The reduction of signal to noise ratio, influences signal receiving quality.Therefore, a suitable modulation index how is obtained, to based on MZ modulators
ROF system for it is extremely important.And in existing ROF system, the modulation index of MZ modulators is initialized in ROF system
When determine, but the system environments of ROF system and number of users are dynamic changes, and modulation index is difficult to adapt to these completely
Dynamic change.
The content of the invention
It is an object of the invention to overcome the deficiencies of the prior art and provide a kind of MZM modulation indexs of ROF system dynamic to adjust
Section method, the dynamic regulation to MZM modulation indexs is realized, adapt it to dynamic change of the ROF system in communication process.
For achieving the above object, the MZM modulation index dynamic adjusting methods of ROF system of the present invention, including following step
Suddenly：
S1：The influence factor of MZM modulation indexs is selected first, and ROF system is emulated, obtains influence factor in difference
In the case of MZM modulation indexs, save as MZM modulation index tables；
S2：When ROF system is initialized, according to current each influence factor in ROF system, from MZM modulation indexs
Table search obtains optimal MZM modulation indexs；
S3：In communication process, emitter is monitored to influence factor, if influence factor changes, basis
Current influence factor obtains optimal MZM modulation indexs from MZM modulation index table search again.
Present invention also offers a kind of MZM modulation index dynamic adjusting methods of ROF system, comprise the following steps：
S1：When ROF system is initialized, the modulation index of MZ modulators is initialized；
S2：In communication process, emitter monitoring number of users, if number of users increases, into step S3, otherwise enter
Step S4；
S3：Reducing MZM modulation indexs according to default step-length, the bit error rate of its reception signal is fed back to emitter by user,
All meet pre-provisioning request if not the bit error rate of all users, then continue to reduce MZM modulation indexs according to default step-length, until
Untill the bit error rate of all users is satisfied by pre-provisioning request；
S4：Increasing MZM modulation indexs according to default step-length, the bit error rate of its reception signal is fed back to emitter by user,
All meet pre-provisioning request if not the bit error rate of all users, then continue to increase MZM modulation indexs according to default step-length, until
Untill the bit error rate of all users is satisfied by pre-provisioning request.
Present invention also offers a kind of MZM modulation index dynamic adjusting methods of ROF system, comprise the following steps：
S1：When ROF system is initialized, the modulation index of MZ modulators is initialized；
S2：In communication process, each user is received the interchannel noise estimate of channel according to predetermined periodInstead
Feed emitter；
S3：According to below equation, the corresponding MZM modulation for allowing to use that each user is calculated respectively refers to emitter
Number m maximum：
Wherein, PSThe power of signal is sent for emitter, α represents default crosstalk coefficient, and TH represents that default letter is dry and made an uproar
Threshold value than SINR；
Thus a set M for allowing the MZM modulation index m maximums used to form by all users is obtained, from set M
The MZM modulation indexs that a minimum MZM modulation index of middle selection uses as emitter.
The MZM modulation index dynamic adjusting methods of ROF system of the present invention, a MZM is initialized when initializing ROF system
Modulation index, then in communication process, when corresponding influence factor changes, according to current influence factor again from
MZM modulation index table search obtains optimal MZM modulation indexs；Or correspondingly adjusted according to the increase of number of users or reduction
MZM modulation indexs, until the bit error rate of user meets to require；It is again or periodically anti-according to the threshold value of Signal to Interference plus Noise Ratio and each user
The maximum and composition of the corresponding MZM modulation indexs for allowing to use of each user is calculated in the interchannel noise estimate of feedback
One set, the MZM modulation indexs for then selecting a MZM modulation index of minimum to be used as emitter from the set.
Influence factor of the invention by monitoring MZM modulation indexs in ROF system, to enter Mobile state to MZM modulation indexs
Adjustment, enable the dynamic change of the adaptive ROF system of MZM modulation indexs, so that ROF system can keep good communication all the time
Performance.
Brief description of the drawings
Fig. 1 is ROF system structure chart；
Fig. 2 is that error rate of system performance curve corresponding to different modulation indexs is used under two-way active sub-carriers；
Fig. 3 is the error rate of system performance curve of different operating subcarrier number under fixed modulation index
Fig. 4 is the flow chart of the MZM modulation indexs dynamic adjusting method one of ROF system of the present invention；
Fig. 5 is the bit error rate performance curve map of each optimal MZM modulation indexs in table 1；
Fig. 6 is the flow chart of the MZM modulation indexs dynamic adjusting method two of ROF system of the present invention；
Fig. 7 is the flow chart of the MZM modulation indexs dynamic adjusting method three of ROF system of the present invention；
Fig. 8 be under 16QAM modulation systems error performance with SINR change curve.
Embodiment
The embodiment of the present invention is described below in conjunction with the accompanying drawings, so as to those skilled in the art preferably
Understand the present invention.Requiring particular attention is that in the following description, when known function and the detailed description of design perhaps
When can desalinate the main contents of the present invention, these descriptions will be ignored herein.
In order to which technical scheme is better described, the technical principle of foundation of the present invention is illustrated first.
For the user radio incoming radio frequency signal transmitted in ROF system, in order to meet multiple users share wireless communication
The demand in road, frequency division multiplexing (FDM) are most basic modes.Assuming that fkThe frequency used for k-th of subcarrier, total number of sub-carriers
For N, that is, there is N number of subcarrier to be used simultaneously for N number of user, each user's symbol waiting for transmission is Ai(t)=Ii(t)+jQi
(t), being multiplexed later baseband signal is：
The output signal obtained after MZM modulator is modulated is：
VOUT(t)=sin (m × VS(t))
(ignore three rank above signals) when modulation index m is smaller, can deploy to obtain：
It will be apparent that in output signal in addition to each sub-carrier signal comprising needs, in addition between each sub-carrier signal
Three rank crosstalk signals, its size is relevant with modulation index.
Fig. 2 is that error rate of system performance curve corresponding to different modulation indexs is used under two-way active sub-carriers.By Fig. 2
Analysis can obtain, and when modulation index increases to certain value (m ＞ 0.03), the performance of system becomes very poor.Because modulation index
When choosing excessive, MZM modulator output signal will be caused obvious nonlinear crosstalk signal occur, turning into influences systematic function
Principal element.When different active sub-carriers numbers in system be present, it may appear that similar systematic function becomes with modulation index
The situation of change.So key issue when to select suitable modulation index be system design.
For multiple access signal, the number of users that channel is at a time used is change.When solid
When determining MZM modulation index, from theory analysis before, during number of users increase, MZM Modulation and Nonlinear can be brought more
More inter-channel crosstalks.Fig. 3 is the error rate of system performance curve of different operating subcarrier number under fixed modulation index.Such as figure
Shown in 3, loading multiplexing signal can cause more crossmodulations between signal on a MZM, cause mission nonlinear
Distortion is more serious, is the non-linear of MZM to the principal element that systematic function impacts when active sub-carriers number is a lot
Inter-channel crosstalk caused by effect.
If using the MZM modulation indexs of fixation during system design, it is non-thread that the selection of the modulation index must take into consideration MZM
During property inter-channel crosstalk maximum, i.e., user job number maximum when, the maximum modulation index used can be allowed.It will be apparent that due to
Now number of users is a lot, it is necessary to selects a less modulation index, just can guarantee that and effectively suppress MZM nonlinear channel crosstalks
Size, but this can directly result in diminishing for user received signal intensity, and the letter of larger multiple at this moment must be used in receiving terminal
Number amplification, more noises and power consumption can be brought.On the other hand, it is contemplated that user accesses the dynamic of number of users in channel
Change, when number of users is smaller, crosstalk is smaller between the MZM nonlinear channels between user, at this moment allows to use larger modulation
Index is to strengthen received signal strength；When number of users increases, crosstalk change is big between the MZM nonlinear channels between user, at this moment
Modulation index can suitably be reduced to reduce crosstalk between nonlinear channel.Based on this, in order to obtain more preferable systematic function, this hair
Bright proposition MZM modulation indexs is set dynamically preferably to suppress the MZM nonlinear channel crosstalks in ROF system.
Embodiment
The MZM modulation index dynamic adjusting methods of three kinds of ROF systems are provided in the present invention.Fig. 4 is ROF system of the present invention
MZM modulation indexs dynamic adjusting method one flow chart.As shown in figure 4, the MZM modulation indexs dynamic adjustment side of ROF system
The specific steps of method one include：
S401：Emulation obtains MZM modulation index tables：
The influence factor of MZM modulation indexs is selected first, and ROF system is emulated, influence factor is obtained and is not sympathizing with
MZM modulation indexs under condition, save as MZM modulation index tables.
In addition to active sub-carriers number, the influence factors of MZM modulation indexs also include order of modulation (i.e. modulation system),
Particular location of subcarrier that the information quality of user, each user distribute etc..The influence factor selected in emulation is more, emulation
Also it is more complicated.In actual applications, influence factor can be selected as needed.Such as be found through experiments that, when solid
When determining order of modulation and number of users, the distribution of different user's sub-carrier positions, although have one to the optimum results of modulation index
Fixed influence, but influence is smaller, therefore the distribution of user's sub-carrier positions can be ignored when required precision is not high.
In the present embodiment, the influence factor of order of modulation and active sub-carriers quantity as MZM modulation indexs is selected.With
Exemplified by 16QAM modulation systems, the optimal modulation index under different operating number of subcarriers is emulated.Table 1 is that the MZM of the present embodiment is adjusted
Index table processed.
| Active sub-carriers number | 1 tunnel | 2 tunnels | 3 tunnels | 4 tunnels | 5 tunnels | 6 tunnels | 7 tunnels | 8 tunnels |
| Optimal modulation index | 0.029 | 0.026 | 0.024 | 0.022 | 0.020 | 0.018 | 0.017 | 0.016 |
Table 1
As it can be seen from table 1 with the increase of active sub-carriers number, the selection of modulation index value is less and less, with reason
It is consistent by the result of analysis.Fig. 5 is the bit error rate performance curve map of each optimal MZM modulation indexs in table 1.As shown in fig. 5, it is assumed that
The bit error rate of current system requirement is 10-3, under various receiver state of signal-to-noise, optimal modulation index can be by signal to noise ratio control
System is within the 3dB of ideal situation.In the present embodiment, it is assumed that modulation system will not change in whole communication process, therefore logical
The change for crossing active sub-carriers quantity is dynamically determined the size of modulation index.
S402：System initialization：
When ROF system is initialized, the modulation index of MZ modulators is initialized, i.e., according to current each in ROF system
Individual influence factor, optimal MZM modulation indexs are obtained from MZM modulation index table search.
S403：Monitor influence factor：
In communication process, emitter is monitored to influence factor.In the present embodiment, exactly to active sub-carriers
Quantity is monitored, and the quantity of active sub-carriers is number of users in ROF system, because user can be to transmitter requests point
With transmission channel, thus emitter is that can determine that transmitting number of users, so as to obtain the quantity of active sub-carriers.
S404：Judge whether influence factor changes, if do not changed, do not make any operation, return to step
S403；In the event of change, then into step S405.
S405：Redefine MZM modulation indexs：
Optimal MZM modulation indexs, return to step are obtained from MZM modulation index table search according to current influence factor again
S403。
It can be seen that MZM modulation indexs are dynamically adjusted according to influence factor, it is ensured that system always works in optimal shape
State.
It was found from technical principle analysis before, number of users represents active sub-carriers quantity, is to determine that MZM modulation refers to
A several important factor in order, therefore, method two adjusts modulation index based on number of users and user feedback.Fig. 6 is this
The flow chart of the MZM modulation indexs dynamic adjusting method two of invention ROF system.As shown in fig. 6, the MZM of ROF system of the present invention is adjusted
Index dynamic adjusting method two processed comprises the following steps：
S601：System initialization：
When ROF system is initialized, the modulation index m of MZ modulators is initialized.The initialization value of MZM modulation indexs
Determined according to the actual conditions of ROF system.In the present embodiment, the initial value of MZM modulation indexs is searched in MZM modulation index tables
Obtain, i.e., according to current each influence factor in ROF system, corresponding optimal MZM modulation is obtained from MZM modulation index table search
Exponent m.
S602：Monitor number of users：
In communication process, emitter monitoring number of users, when thering is new user to add or user exits, according to corresponding place
Reason mode adjusts MZM modulation indexs.
S603：Judge whether number of users changes, if it is, into step S604, if do not changed, do not make any
Operation, return to step S602.
S604：Judge whether number of users increases, if it is, into step S605, enter step S608 if reducing.
S605：Reduce MZM modulation indexs by step-length：
Reduce MZM modulation indexs according to default step-length, even m=m- Δs1, Δ1Represent default reduction step-length.Work as step-length
When setting smaller, more accurate modulation index can be obtained, but the number of iteration adjustment may be more, and step-length is larger
When, then it may reduce the Adjustment precision of modulation index.Therefore, it is necessary to set step sizes according to actual conditions.
S606：The user feedback bit error rate：
In communication process, the bit error rate of its reception signal is fed back to emitter by user according to predetermined period.
S607：Judge whether that the bit error rate of all users is satisfied by pre-provisioning request, i.e., less than or equal to default bit error rate threshold
Value, if it is, this adjustment finishes, return to step S602；If it is not, then return to step S605.
S608：Increase MZM modulation indexs：
Increase MZM modulation indexs according to default step-length, even m=m+ Δs2, Δ2Represent default increase step-length.Due to MZM
Modulation index and number of users are not linear relationship, therefore Δ1And Δ2It is general unequal.
S609：The user feedback bit error rate：
In communication process, the bit error rate of its reception signal is fed back to emitter by user according to predetermined period.
S610：Judge whether that the bit error rate of all users is satisfied by pre-provisioning request, i.e., default bit error rate threshold, if
It is that then this adjustment finishes, return to step S602；If it is not, then return to step S608.
In order to improve the speed of modulation index adjustment, the present invention also provides a kind of MZM based on Signal to Interference plus Noise Ratio (SINR) and adjusted
Index dynamic adjusting method processed, i.e., each user estimate in real time its receive channel noise estimation value, feed back to emitter, as
Adjust the foundation of MZM modulation indexs.Fig. 7 is the flow chart of the MZM modulation indexs dynamic adjusting method three of ROF system of the present invention.
As shown in fig. 7, the MZM modulation indexs dynamic adjusting method three of ROF system of the present invention comprises the following steps：
S701：System initialization：
When ROF system is initialized, the modulation index m of MZ modulators is initialized.The initialization value of MZM modulation indexs
Determined according to the actual conditions of ROF system.In the present embodiment, the initial value of MZM modulation indexs is searched in MZM modulation index tables
Obtain, i.e., according to current each influence factor in ROF system, corresponding optimal MZM modulation is obtained from MZM modulation index table search
Exponent m.
S702：User feedback interchannel noise estimate：
In communication process, the interchannel noise estimate that each user is received channel according to predetermined period feeds back to hair
Penetrate machine.Interchannel noise estimation is the conventional techniques of the current communications field, and its specific method will not be repeated here.
S703：Emitter calculates the MZM modulation index maximums that each user allows to use：
When the inter-channel crosstalk in system can be approximated to be Gaussian Profile, the error performance of each user is by each use in system
The SINR at family determines that is, SINR is bigger, and the bit error rate is smaller.Fig. 8 is that error performance is bent with SINR change under 16QAM modulation systems
Line.As shown in figure 8, for the predetermined bit error rate requirement of system, as long as the SINR of each user can be more than certain threshold value, then
The error performance of the user, which can be ensured, can reach system pre-provisioning request.
In the present invention, SINR is defined as SINR=received signal powers/(jamming power+noise power), its calculation formula
For：
Wherein, PSThe power of signal, σ are sent for emitterICIInter-channel crosstalk size caused by expression MZM is non-linear,
Represent the interchannel noise estimate of user.Analyzed according to technical principle before, the present invention only considers three rank crosstalk signals, then
σICI=α m3, the default crosstalk coefficient of wherein α expressions.Understand that the quantity of crosstalk coefficient α and active sub-carriers has according to analysis
Close, therefore crosstalk coefficient α corresponding to different operating number of subcarriers can be obtained using emulation, gone here and there when calculating corresponding to selection
Disturb coefficient.Table 2 is the crosstalk coefficient table of the present embodiment.
Table 2
So, the maximum of MZM modulation index ms that below equation obtains allowing corresponding to each user using is solved：
Wherein, TH represents default Signal to Interference plus Noise Ratio SINR threshold value, that is, the SINR allowed minimum value.
In actual applications, it is possible to a certain user occur because channel quality is poor, interchannel noise is larger, leads to not
The modulation index of SINR threshold values is met, i.e., can not solve the modulation index for meeting above-mentioned threshold formula.For these use
, it is necessary to use the modulation system of relatively low order of modulation instead, order of modulation is lower at family, and relatively low SINR threshold values corresponding to it are easier to obtain
The MZM modulation indexs of requirement must be met.
S704：Determine MZM modulation indexs：
The maximum for the MZM modulation index ms for allowing to use corresponding to each user being calculated in S703 is formed one
Set M={ m1,m2,…,mN, wherein, miRepresent that MZM modulation indexs allow the maximum used corresponding to i-th of user, i's
Span is i=1, and 2 ..., N, N represent number of users.Then a MZM modulation index of minimum is selected from set M
The MZM modulation indexs used as emitter, i.e., the MZM modulation indexs finally usedThe tune
Index processed, which can guarantee that, can meet above-mentioned SINR threshold requirements to all users.
Comparative approach three and method two are understood, in method three, it is determined that do not need iteration adjustment during MZM modulation indexs,
It is thus determined that the speed of optimal MZM modulation indexs is faster.
Although the illustrative embodiment of the present invention is described above, in order to the technology of the art
Personnel understand the present invention, it should be apparent that the invention is not restricted to the scope of embodiment, to the common skill of the art
For art personnel, if various change in the spirit and scope of the present invention that appended claim limits and determines, these
Change is it will be apparent that all utilize the innovation and creation of present inventive concept in the row of protection.
Claims (1)
1. the MZM modulation index dynamic adjusting methods of a kind of ROF system, it is characterised in that comprise the following steps：
S1：The influence factor of MZM modulation indexs is selected first, and ROF system is emulated, obtains influence factor in different situations
Under MZM modulation indexs, save as MZM modulation index tables；
S2：When ROF system is initialized, according to current each influence factor in ROF system, looked into from MZM modulation index tables
Find optimal MZM modulation indexs；
S3：In communication process, emitter is monitored to influence factor, if influence factor changes, according to current
Influence factor obtains optimal MZM modulation indexs from MZM modulation index table search again.
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| CN101964683A (en) * | 2010-09-21 | 2011-02-02 | 上海大学 | Serial-parallel connection modulation optical frequency multiplication millimeter-wave RoF (Radio Over Fiber) system and QPSK (Quadrature Phase Shift Keying) /16QAM (Quadrature Amplitude Modulation) modulation method thereof |
| CN102136864A (en) * | 2011-03-05 | 2011-07-27 | 西安电子科技大学 | Device for optically producing multiple frequency doubling millimetre wave signals |
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| CN101964683A (en) * | 2010-09-21 | 2011-02-02 | 上海大学 | Serial-parallel connection modulation optical frequency multiplication millimeter-wave RoF (Radio Over Fiber) system and QPSK (Quadrature Phase Shift Keying) /16QAM (Quadrature Amplitude Modulation) modulation method thereof |
| CN102136864A (en) * | 2011-03-05 | 2011-07-27 | 西安电子科技大学 | Device for optically producing multiple frequency doubling millimetre wave signals |
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