• 专利附录
  • 专利说明
  • 权利要求
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    • 专利摘要:
    The present invention relates to a carrier recovery arrangement (100) for recovering an input modulated signal (R(t)), down- converted by a local oscillator with a frequency different from the carrier frequency of the input modulated signal (R(t)) such that a distorted down-converted signal (RQ(t)) is provided. It comprises a delay means (14) for introducing a time delay into the distorted signal (RQ (t)), a mixer (4) adapted to multiply the received distorted signal (RQ(t)) with the delayed distorted signal and to provide an adjusted output signal, (Radj(t)), with a distortion term, a low pass filter (5) adapted to extract a signal comprising the second harmonic of the distortion term from the adjusted output signal (R adj (t)) related to twice the frequency difference (2Deltaomega) between the local oscillator and the carrier frequency of the input modulated signal (R(t)), and means for removing modulated data from said signal to provide a recovery signal free from modulated data that can be used to eliminate the distortion.
    公开号:SE1250404A1
    申请号:SE1250404
    申请日:2012-04-24
    公开日:2013-10-25
    发明作者:Zhongxia He
    申请人:Zhongxia He；
    IPC主号:
    专利说明:

    Z5 P1SE AB/ej 2012-04-24 Title:AN ARRANGEMENT AND A METHOD FOR CARRIER SIGNAL RECOVERY TECHNICAL FIELD The present invention relates to an arrangement for carriersignal recovery having the features of the first part of claim1. The invention also relates to a næthod for carrier recovery having the features of the first part of claim 10.
    BACKGROUNDCarrier signal recovery and demodulation are needed to be ableto estimate and compensate for frequency and phase differencesbetween for example the local oscillator* of a receiver in acommunication system and the carrier wave of the received signaltransmitter, such that coherent modulated in a particularly demodulation can be provided.side of a. communication On the transmitting systen1 a carrier wave is modulated by a baseband signal. The baseband informationis extracted from the modulated waveform in a signal received atthe oscillator the receiver. In an ideal communication system, carrier frequencies of the transmitter and the receiver would be matched perfectly as far as both frequency and phase areconcerned, which in turn would allow for a perfect coherentdemodulation of the nwdulated baseband signal. Normally,however, the carrier frequencies of the oscillators of the transmitter and the receiver are not the same since the receivers and the transmitters normally are completely independent and they have their own oscillators with frequency lO and phase offsets, frequency instabilities, phase instabilities etc.
    In order to be able to permit coherent demodulation, all these frequency and phase variations have to be estimated using information in the received signal to reproduce or recover the carrier signal at the receiver.
    There are two major categories of methods for handling carrier recovery or compensation. One of the methods in a first category is based on using a closed-loop compensation structure with a phase extraction block and a loop filter LF, which is schematically illustrated in Fig. l, and by means of which phase and frequency offset are detected, and the offset is compensated for by tuning the local oscillator, VCO (Voltage Control Oscillator), of the receiver.
    Fig. 2 illustrates an example of the other category which is based on an open-loop compensation structure which, instead of implementing a feedback-loop, a closed-loop, uses an open loop, a forward feed-loop, for cancelling the frequency offset by means of a derotator.
    For the closed-loop structure (Fig. l) and the open-loop structure (Fig. 2), there is a phase extraction block which extracts the frequency offset from a received signal given as: I cos + + (pdata +(po] lO A0) being the frequency offset between transmitter and receiver,Qdæfi being the phase containing the modulated data information, and QO being a random phase caused by the propagation, LF being a loop filter.
    Since Qdæfi is a data related random parameter which changes with time, it is difficult to extract Am from r(t). There are different known methods for performing such a phase extraction.A first method is based on data aided extraction which comprises transmitting known data at certain time instants (pilot data), and to, based on this known information, enable extraction of A0). Other methods that do not use data aided extraction are also known. In one such method, here referred to as a multiply- filter-divide method, non-data-aided carrier recovery, a non- linear operation is applied. to a modulated signal to create harmonics of the carrier frequency with the modulation removed.
    The carrier harmonic is then band-pass filtered and frequency divided to recover the carrier frequency, a PLL (Phase Locked Loop) may then follow. Multiply-filter-divide is an example of open-loop carrier recovery, which is favored in burst transactions since the acquisition time is typically shorter than for closed-loop synchronizers.in a QPSK case, a For example, (Quadrature Phase Shift Keying) received signal given as RQPSK (t) = A(t) cos(o)RFt + när /2); n = 0,1,2,3 is multiplied by four in a frequency multiplier giving: lO RÉPSKU) = A40) coäímRFf + A40)= TB + 4cos (2wRFt + nflt)+ cos (4wRFt + 11211: )] By using this approach, the unknown data-related phase is normalized into n2n. The signal is then divided by four, and QRF can be obtained (see Fig. 3): HPF indicates a high pass filter, LPF low pass filter.
    Another method uses a so called Costas Loop. A Costas Loop is a phase-locked loop used for carrier phase recovery fromsuppressed-carrier modulation signals, such as from double-sideband suppressed carrier signals. The main application of Costas loops is i11 wireless receivers.
    PLL-based Its advantage over the (Phase Locked Loop) detectors is that at small deviations the Costas loop error voltage is sin(2(6i-9f)) instead of sin(9f6f). This doubles the sensitivity and also makes the Costas loop uniquely suited for tracking Doppler-shiftedcarriers.In modern DSP (Digital Signal Processor) based receivers a decision directed method is often adopted. In decision directed carrier recovery' the output of a symbol decoder* is fed. to a comparison circuit and the difference/error between a decoded phase symbol and. a received. signal is used. to control the local oscillator.
    A common form of decision directed carrier recovery begins with quadrature phase correlators producing' in-phase and. quadrature signals representing a symbol coordinate in the complex plane.
    This point should. correspond. to a location in the modulation constellation diagram. The phase error between the received value and nearest/decoded symbol is calculated using arctangent (or* an approximation). However, arctangent can only' compute aphase correction between O and n/2. Most QAM (QuadratureAmplitude Modulation) constellations also have H/2 phasesymmetry.
    In many systems it is not allowed to introduce pilots in transmitted data, which means that data aided methods cannot be used. For a multiply-filter-divide method, when carrierfrequency is high (for example over 15 GHz), frequencymultiplication by four is difficult to achieve, since means capable of doing that are very complicated to design inpractice. Furthermore, for higher modulation formats, i.e. 8-PSK(Phase Shift Keying), frequency multiplication by eight isrequired. Such components are extremely difficult to design inpractice.
    The complexity of a Costas Loop is increased dramatically for higher modulation formats, and it requires that all branches are symmetric, which also is difficult to design in practice.
    Decision-directed. methods are commonly' used. with. DSP (DigitalSignal Processing), however, when the carrier/IF (IntermediateFrequency) is high, it is difficult to find available ADCs (Analog to Digital Converter) for sampling at such frequencies.
    SUMMARY OF THE INVENTIONIt is therefore an object of the present invention to provide an improved. arrangement for carrier signal recovery' as initially referred through which one or more of the above mentioned problems can be overcome. It is particularly an object of theinvention to provide an arrangement for carrier signal recoverywhich is easy and cheap to design and fabricate. It is also anobject to provide an arrangement which is suitable for high datarates, communication with high data particularly for systems rates and for high carrier frequencies. It is particularly anobject to be able to provide an arrangement which can be used insystems which do not allow introduction of pilote signals, andwhich does not require symmetric branches. It is a particular an arrangement which is suitable for high which object to provide formats and imposes lower requirements on which modulation involved components than known arrangements and particularly' can be used for high. modulation formats without requiring modification.
    Therefore an arrangement as initially' referred. to is provided which has the features of the characterizing part of claim 1.
    A receiving arrangement including such an arrangement for carrier signal recovery is also provided, as well as a næthod for carrier signal recovery, which has the features of thecharacterizing part of claim 10.It is an advantage of the invention that an arrangement is provided which is capable of handling high data rates and high carrier frequencies while still being easy to design and fabricate. It is also an advantage that an arrangement is lO provided which can be used for high modulation formats without requiring any modification and which, in advantageousembodiments, even removes the need for using any frequencymultipliers and enables the use of comparatively simplefrequency dividers.
    BRIEF DESCRIPTION OF THE DRAWINGS The invention will in the following be more thoroughly described, in a non-limiting manner, and with reference to the accompanying drawings, in which: Fig. l shows a state of the art closed loop carrier recoverycompensation structure, Fig. 2 shows a state of the art open loop carrier recoverycompensation structure, Fig. 3 shows a state of the art carrier recovery' structure based on multiplication, filtering and division for performing a phase extraction,Fig. 4 shows a carrier signal recovery' arrangement according to a first embodiment of the invention, Fig. 5 shows a carrier signal recovery' arrangement accordingto a second embodiment of the invention,Fig. 6 shows a receiving arrangement with a carrier signal recovery arrangement according to one embodiment of the invention, Fig. 7 shows a recovery arrangement according to the inventionincluded in a closed loop structure, Fig. 8 shows a carrier recovery arrangement according to oneembodiment of the invention. included. in an open loopstructure, and Fig. 9 is a schematic flow diagram describing a procedure for carrier signal recovery according to one embodiment of the invention.
    DETAILED DESCRIPTION Fig. 4 shows a block diagram. of a first embodiment of the invention. wherein. a distorted. signal RQ(t) is received. in an arrangement 100. The distorted signal is here a signal which has been down-converted in (here) an IQ direct converting mixer and by means of a local oscillator a sinusoid source has been provided at. a receiver carrier frequency. Generally any down- converted, distorted, signal or particularly any output distorted signal from the mixer may form the input signal to the arrangement 100, i.e. it could also have been the R1(t) which had been input and it would then be recovered in a similar manner as shown in Fig. 4. In a delay means 14 RQ(t) is delayed (AI) and in a mixer 4 the time delayed signal is multiplied by the distorted down-converted signal RQ(t) giving an adjusted output signalRæü(t) which then is input to a low pass filter (LPF) 5. In anadvantageous embodiment the low pass filter' 5 is so designed that only one signal is selected, namely the second harmonic of the distortion term of the distorted signal, which is only related to 2Ao, Ao being difference between the frequency of the down-converted distorted signal od, the frequency of the received lO carrier signal oc and the frequency of the local oscillator of the receiver, omw i.e. the second. harmonic of the distortion term, the second order of the difference signal, which is achieved by giving the low pass filter a cut-off frequency whichis much lower than the data symbol rate so that the output only contains low frequency components and no data.
    An output signal R"æü(t) is thus obtained which only relates to twice the frequency' offset, 2Ao. This signal can be used to recover an undistorted signal, which can be done in different ways, some of which will be further explained and exemplified below.
    Fig. 5 shows an alternative implementation, similar means as in Fig. 4 are indicated. by the same reference numerals but are given an index l and will therefore not be described any furtherherein to the extent that they perform the same function. Thedifference is here that the requirements on the low pass filter 51 are somewhat less stringent, important being that it be given such a cut-off frequency that only the second harmonic of the distortion. tern1 of the noise (difference signal) is selected, but the output signal R'wj@) does still contain the modulated data. For the purpose of eliminating data, an envelope detector 61 is introduced which has a time constant which is longer than the symbol period and so the data will be eliminated, and an output signal R"a@(Ü as described. in the embodiment shown in Fig. 4 is provided which does not contain any data but only the second order difference signal. In this embodiment it is thus the envelope detector* 6 that it responsible for removing' the data, whereas in the embodiment of Fig. 4 the low pass filter 5 is carefully selected so that also the data is removed, avoidingthe need for any envelope detector.Fig. 6 shows a receiving arrangement 300A with a recovery arrangement 300 substantially as the arrangement shown in Fig.
    The receiver arrangement 300A contains an IQ direct down- converting mixer 12, and a local oscillator 22 providing asinusoid source at carrier frequency. Thus, a signal R(t) from atransmitter* with its local oscillator* is received (considered undistorted), down-converted in mixer 12 in a receiver with local oscillator* 22 and a frequency' om» The distortion. produced is Ao=o¿m%-om” od being the frequency of the down-converted distorted signal, wherein oc is the frequency of the receiver carrier signal, ufio the frequency of the receiver local oscillator. One output of the mixer 12 here RQ(t) and a delayed- by-T version thereof are both input to a mixer 42, where they are multiplied to provide an output signal Ræü(t). Passing RæÜ(t) through. a low-pass filter' 52, the output will be R'æü(t) as explained below. R'æü(t) is fed to an envelope detector 62. The output R"æü(t) from the low-pass filter 62 represents the second harmonic of the frequency' offset between. a transmitter oscillator, not shown, and which does not form. part of the present invention, and a receiver oscillator 22. To obtain the true frequency offset, a balun 82 is used to convert a single-end signal to two differential signals which are 180° out of phase.
    These out-of-phase signals are then input to frequency dividers 92,102, giving outputs cos(Aot) and sin(Aot). By using phase detectors 111,112 the modulated I and Q signals can be extracted, thus demodulation is achieved. To explain the behavior of this lO ll structure, a nwthematic expression of the demodulation process is given according to the following: It is assumed that the received signal can be represented as R(t) =cos[mt+(p] [l] where m=m0+mdæ3, wherein mois a propagation related slow change value, and mmma is data related and changing at symbol rate.
    After the IQ direct down-converting mixer lg, the output can be written as: RQ (t) = cos(mt + (p )>< cos[(m + Amy]= å{cos[(2m + Amy + cp]+ cos(Amf - cp)} R, (t) = cos(mr + where it is assumed that LO 22 gives a frequency fw (f) = coskw + Amy] .
    In the proposed næthod, either RQHQ or Rïüfl can be used for carrier recovery. Here RQ(t) is taken as input to the mixer 42.
    Another input RQ(t) of the mixer 42 is provided. to a delay element 32, which provides a real time delay to the signal, the output thus being: lO l2 RQ (f + T) = coskw + T) +< coskw + A@)(f + T)]= ficoskzw + Aw)(f + T) + wherein T is an certain fixed true time delay, which satisfies: T<<7" can be considered to be wm, so that (p in R@(t) and Rïüfl the same.
    The output of the mixer 42 can then be calculated as follows: RaaÛ-(t) = RQ(t)> = å{cos[(2o) + Aw)t + (p]+ cos(A0)t - (p)}>
    权利要求:
    Claims (13)
    [1] 1. A (100;200;300;400;500) for (R(t)), carrier recovery arrangement recovering an input modulated signal particularly down-converted by a local oscillator with a frequency different fromthe carrier frequency of the input modulated signal such (R@(t)) (R(t)),that a distorted down-converted signal is provided,c h a r a c t e r i z e d i n (l4;l41;l43;l4M that it comprises a delay means for introducing a time delay into the distorted mixer (4;4i;42;43;44)(Ro(t)) adjusted output signal, signal (RQ(t)), aadapted to multiply the received distorted signalwith the delayed distorted(Raaj(t)), (5;5i;52;53;54) signal and to provide an with a distortion term, a lowpass filter adapted to extract a signal comprisingthe second. harmonic of the distortion term. from. the adjusted(Raaj (U) between the local oscillator and the carrier frequency of output signal (2Ao) related to twice the frequency difference the input modulated signal (R(t)), and in that means are provided which are adapted to remove modulated data from saidsignal to provide a recovery' signal free from Inodulated. datathat can be used to eliminate the distortion.
    [2] 2. An arrangement (100) according to claim 1,c h a r a c t e r i z e d i n that the low pass filter (5) is adapted to select, extract, only the second harmonic of the distortion term, and hence is adaptedto remove also the modulated data.(100)
    [3] 3. An arrangement according to claim 1, c h a r a c t e r i z e d i n 18 that the low pass filter (5) has a cut off frequency which is much lower than a symbol rate at which data is transmitted in the input signal thus providing' a data free recovery signal(R"an(t))-
    [4] 4. An arrangement (200;300;400;500) according to claim 1, c h a r a c t e r i z e d i n that it further comprises an envelope detector (6;62;63;6@ adapted to remove modulated data from the signal output from the low pass filter (51;&fi53;5@ to generate a data free recoverysignal (R"æü(t)).
    [5] 5. An arrangement (400) according to any one of the precedingclaims, c h a r a c t e r i z e d i n that it is adapted to be arranged in a closed loop compensation structure (400A) comprising a loop filter (153) to receive the recovery signal and to tune the local oscillator (29.
    [6] 6. An arrangement (500) according to any one of claims 1-4, c h a r a c t e r i z e d i nthat it is adapted to be arranged in an open loop compensation(5OOA) and i11 that (154) structure it comprises a loop filter adapted to receive the recovery signal and to provide a filtered(169 control signal to a derotator adapted to use said low pass filtered control signal and the recovery signal for frequencydistortion cancellation.(300)
    [7] 7. An arrangement according to any one of claims 1-4, c h a r a c t e r i z e d i n 19 that the envelope detector* is adapted. to be connected. to, or (8),free from data to two differential signals which are 180° out of (92,lÛ2) comprise, a balun adapted to convert the recovery signal phase, and frequency dividers for dividing the out of phase signals by two.
    [8] 8. An arrangement according to claim 7, c h a r a c t e r i z e d i n that the first and a second frequency dividers (92,1O2) areadapted. to provide respective first and second signals terms(cos(Aot), sin(Aot)) to a first and a second. phase detector(11U]J¿) for comparing the respective signal terms withmodulating signals R1'(t) and RQ'(t) respectively to providemodulated output signals Imm(t), Qmm(t).
    [9] 9. A receiving arrangement in a communications system, c h a r a c t e r i z e d i n that it comprises a carrier recovery arrangement(100;200;300;400;500) according to any one of claims 1-8.
    [10] 10. A. method. for recovering' an input modulated. signal (R(t)) down-converted by a local oscillator with a frequency differentfrom the carrier frequency of the input modulated signal (R(t)) such that a distorted down-converted signal (RQ(t)) is provided,c h a r a c t e r i z e d i n that it comprises the steps of: - time delaying a distorted down-converted signal output from a(1): - nmltiplying the delayed distorted down-converted signal with (4;41;42;43;44) down-converting mixer the distorted signal in a mixer to provide an adjusted signal with a distortion term; - extracting, by means of a low pass filter (5;5U52;5y54), asecond harmonic of the distortion term related to twice the(2Aw) frequency difference between the frequency of the local oscillator and the carrier frequency of the input, modulated signal (R(t)); - removing data from the extracted signal to obtain a recoverysignal; - using the recovery signal to eliminate the distortion.
    [11] 11. A method according to claim 10, c h a r a c t e r i z e d i n that it comprises the step of: - removing the data by means of setting the cut off frequency ofthe low pass filter (5) lower than the data rate such that data is removed.
    [12] 12. A method according to claim 10, c h a r a c t e r i z e d i n that it comprises the step of: detector - removing the means of an (6i;62;63;64) data by envelope comprising: - inputting the extracted signal to the envelope detector; - removing the data from the extracted signal by setting thetime constant of the envelope detector* (61;62;63;6@ to a period which is longer than the symbol period.
    [13] 13. A method according to any one of claims 10-12,c h a r a c t e r i z e d i nthat it comprises the steps of:- converting' the recovery' signal to differential 180° (8): signals out of phase by using a balun 2l - dividing the frequency of the differential signals by two inrespective frequency dividers (92,lOfi; - using phase detectors (llUll¿) for, by means of the divideddifferential signals, demodulating the received, distorted down-converted signals.
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    同族专利:
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    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    JP2000298165A|1999-04-15|2000-10-24|Mitsubishi Electric Corp|Pulse modulation signal identifying device and radar signal identifying device|
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    SE1250404A|SE536593C2|2012-04-24|2012-04-24|An apparatus and method for recovery of carrier signals|SE1250404A| SE536593C2|2012-04-24|2012-04-24|An apparatus and method for recovery of carrier signals|
    PCT/SE2013/050386| WO2013162444A2|2012-04-24|2013-04-10|An arrangement and a method for carrier signal recovery|
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