WO2006067680A1 - Procede et dispositif d'estimation de l'etalement doppler - Google Patents

Procede et dispositif d'estimation de l'etalement doppler Download PDF

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Publication number
WO2006067680A1
WO2006067680A1 PCT/IB2005/054228 IB2005054228W WO2006067680A1 WO 2006067680 A1 WO2006067680 A1 WO 2006067680A1 IB 2005054228 W IB2005054228 W IB 2005054228W WO 2006067680 A1 WO2006067680 A1 WO 2006067680A1
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WIPO (PCT)
Prior art keywords
signal sequence
sequence
signal
doppler spread
processing
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Application number
PCT/IB2005/054228
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English (en)
Inventor
Xia Zhu
Yan Li
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Koninklijke Philips Electronics N.V.
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Publication of WO2006067680A1 publication Critical patent/WO2006067680A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/002—Reducing depolarization effects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset

Definitions

  • the present invention relates to a mobile communication system, and more particularly to a method and apparatus for estimating Doppler spread in a receiver of a mobile communication system.
  • Radio signals are usually blocked by barriers during propagation, which cause reflection, diffusion, and attenuation, etc, thereby resulting in multi-path effect, and consequently, the signal received by the antenna end of a receiver is actually a linear superposition of multi-path signals from various paths. Furthermore, multi-path signals from various paths have different time delays, amplitudes, phases and frequencies.
  • there may be Doppler effect for radio signal during propagation when the radio signal receiver is in a motion state i.e. the signal frequency will vary when the mobile receiver is moving relative to a transmitter, and the phase relationship among the signals with various incidence path may vary with time, resulting in spreading the frequency spectrum of the received signal, i.e. resulting in Doppler spread.
  • the Doppler spread essentially describes the change speed of time varying channels in a mobile communication system, in general rayleigh fading or rapid fading can be used to indicate the statistical characteristic of signal fading of the radio signal in a motion state being propagated in a multi-path environment.
  • the third generation terrestrial cellular mobile communication system requires the system design and device specification to support data transfer for mobile terminals with a speed of up to 120-500km/hour.
  • the Doppler spread caused by high-speed motion of a signal receiver relative to a signal transmitter inevitably results in signal change and signal distortion and affects the receiving performance of the system and even the correct reception of data. Therefore, in a mobile communication system, it is very necessary to estimate Doppler spread to track the dynamic change of channels efficiently, in particular when the mobile terminals are in a high-speed motion state.
  • the estimated information of Doppler spread can be used to improve the performance of the decoder of a receiver, and to decrease the bit error ratio;
  • the estimated information of Doppler spread can be used to improve the efficiency of radio resource management, e.g. in a layered cellular cell, said information can be used by the network to infer the motion speed of a mobile terminal, thereby adjusting the policy of channel allocation and cell switching to decrease the signaling overhead of dynamic resources and improve the operating efficiency of a system.
  • the estimated information of Doppler spread can also be used to optimize the parameters of a communication system, e.g. to optimize the data interleaving interval to decrease reception delay, etc.
  • Fig. 1 shows the mutual relationship between the Doppler spread estimate means and other functional means in a mobile communication receiver in a conventional method.
  • the receiver shown in Fig. 1 mainly consists of radio frequency signal processing means 100, baseband signal processing means 200 and application processing means 300.
  • the radio frequency signal processing means 100 is mainly for completing the function of converting a radio frequency signal down to a baseband signal
  • the baseband signal processing means 200 is mainly for completing channel estimate and decoding the encoded signal
  • the application processing means 300 is mainly for completing the function of signal interaction between a communication system and users.
  • the baseband signal processing means 200 comprises baseband signal pre-processing means 220, channel estimate means 240 and decoding means 260, wherein the channel estimate means 240 can be disassembled into frequency offset estimate means 242, Doppler spread estimate means
  • Fig. 1 it is serial processing relationship between the frequency offset estimate means 242 and the Doppler spread estimate means 244, i.e. the estimate of Doppler spread must be performed after the estimate of frequency offset has been completed and the frequency offset has been compensated.
  • the methods of such kind have a common disadvantage, i.e. the estimate of Doppler spread can only be performed after the frequency offset has been compensated, resulting in the estimate of Doppler spread being much dependent on accuracy and speed of the estimate of frequency offset, meanwhile serial processing will delay the estimate time of other parameters of the channel and thus decrease the overall performance of data reception.
  • An object of the present invention is to provide a method and apparatus for estimating Doppler spread in a mobile communication receiver.
  • Said method and apparatus separate the effect of Doppler spread on signal reception from the effect of frequency offset on signal reception and eliminate the effect of frequency offset on signal reception by processing the training sequences extracted from received signals, and thereby estimate Doppler spread directly from received signals, solving the problems about the dependency of Doppler spread estimate on the accuracy and speed of the frequency offset estimate and the delay of estimate time of other parameters of the channel, caused by the serial processing of the frequency offset and Doppler spread in conventional methods.
  • the invention provides a method for estimating Doppler spread in a receiver of a mobile communication system, comprising the steps of: extracting an initial signal sequence comprising channel characteristics from received signals; processing said initial signal sequence to obtain a first signal sequence based on frequency offset and Doppler spread; processing said first signal sequence to eliminate the frequency offset of said first signal sequence, thereby obtaining a second signal sequence based on said Doppler spread; and estimating and acquiring said Doppler spread based on said second signal sequence.
  • the invention provides an apparatus for estimating Doppler spread in a receiver of a mobile communication system, comprising: signal extracting means for extracting an initial signal sequence comprising channel characteristics from received signals; first signal processing means for processing said initial signal sequence to obtain a first signal sequence based on frequency offset and Doppler spread; second signal processing means for processing said first signal sequence to eliminate the frequency offset of said first signal sequence, thereby obtaining a second signal sequence based on said Doppler spread; and estimate processing means for estimating and acquiring said Doppler spread based on said second signal sequence.
  • signal extracting means for extracting an initial signal sequence comprising channel characteristics from received signals
  • first signal processing means for processing said initial signal sequence to obtain a first signal sequence based on frequency offset and Doppler spread
  • second signal processing means for processing said first signal sequence to eliminate the frequency offset of said first signal sequence, thereby obtaining a second signal sequence based on said Doppler spread
  • estimate processing means for estimating and acquiring said Doppler spread based on said second signal sequence.
  • Doppler spread in a mobile communication receiver can estimate Doppler spread directly from the received signals by separating and eliminating the effect of frequency offset.
  • the estimate of Doppler spread can be performed in parallel with the estimate of the frequency offset by utilizing the method and apparatus proposed by the present invention, without the prerequisite of acquiring the estimate of frequency offset and performing frequency offset compensation.
  • the dependency of Doppler spread estimate on the accuracy of frequency offset estimate is overcome, the reception delay caused by the delay of Doppler spread estimate is decreased, and the overall performance of a receiver in a mobile communication system is improved effectively.
  • Fig. 1 is a schematic diagram of a mobile communication receiver comprising conventional Doppler spread estimate means.
  • Fig. 2 is a schematic diagram of a mobile communication receiver comprising Doppler spread estimate means of an embodiment of the invention.
  • Fig. 3 is a schematic diagram of Doppler spread estimate means according to an embodiment of the invention.
  • Fig. 4 is a schematic diagram of first signal processing means in the Doppler spread estimate means according to an embodiment of the invention.
  • Fig. 5 is a schematic diagram of second signal processing means in the Doppler spread estimate means according to an embodiment of the invention.
  • Fig. 6A and 6B are schematic diagrams of estimate processing means in the Doppler spread estimate means according to an embodiment of the invention.
  • Fig. 7 is a flow chart of a Doppler spread estimate method according to an embodiment of the invention.
  • the method and apparatus for estimating Doppler spread in a mobile communication receiver modify the conventional serial processing of the estimate of frequency offset and the estimate of Doppler spread into parallel processing, i.e. to estimate Doppler spread directly from the received signals by signal processing.
  • Fig. 2 is a schematic diagram of a mobile communication receiver comprising Doppler spread estimate means of an embodiment of the invention.
  • one of the major improvements of the invention is: the relationship between the frequency offset estimate means 242 and the
  • Doppler spread estimate means 246 is parallel processing, and thus the dependency of Doppler spread estimate on the frequency offset estimate is eliminated, the delay of estimate time for other parameters of the channel and reception delay arising therefrom are decreased, thereby improving the overall performance of the receiver.
  • Fig. 3 shows Doppler spread estimate means 246 provided by an embodiment of the invention. As shown in Fig. 3, the Doppler spread estimate means 246 comprises signal extracting means 10, first signal processing means 20, second signal processing means 30 and estimate processing means 40.
  • the signal extracting means 10 extracts an initial signal sequence comprising channel characteristics from the received signal; then, the first signal processing means 20 processes said initial signal sequence, thereby obtaining a first signal sequence based on the frequency offset and Doppler spread; next, the second signal processing means 30 processes said first signal sequence to eliminate the frequency offset of said first signal sequence, thereby obtaining a second signal sequence based on said Doppler spread; finally, the estimate processing means 40 estimates and acquires the estimate value of Doppler spread based on the acquired second signal sequence.
  • correlative demodulation is always achieved by inserting known training sequences in the signal to be transmitted and estimating time varying channels using the change of known training sequence at the receiving end.
  • g(t) is an impulse waveform
  • 1/T C is a data transfer rate
  • dj is a random variable of independent uniform distribution and its amplitude is 1
  • the phase can be selected as one of
  • r(t) c(t)e j2 ⁇ Af t s(t) + n(t) (2)
  • c(t) is a time varying complex value channel gain
  • ⁇ f is a frequency offset caused by the difference between local oscillators of the transmitter and the receiver
  • n(t) is a complex value additive white noise with variance of N 0 .
  • the fading of the radio signal in a motion state propagating in a multi- path environment presents a rayleigh distribution in statistical characteristic.
  • the time varying channel traveled by the signal can be supposed as a rayleigh fading channel
  • a complex gauss random process with mean of 0 can be used as c(t) in equation (2)
  • its auto-correlation function is :
  • J o ( # ) is a zero-order Bessel function of the first kind
  • fo is Doppler spread.
  • nk is a complex gauss random process with means of 0 and variance of N 0 .
  • X k comprises the information related to the frequency offset and Doppler spread on the transmission channel.
  • the signal extracting means 10 of the Doppler spread estimate means 246 as shown in Fig. 3 performs match filtering on the output signal r(t) of the baseband signal pre-processing means 220 shown in Fig. 2 and then performs sampling to obtain an initial signal sequence X k as described in equation (4), the initial signal sequence comprises the information of the frequency offset and Doppler spread indicating the characteristics of the transmission channel.
  • the obtained initial signal sequence will be further processed by the first signal processing means 20.
  • Fig. 4 shows first signal processing means 20 of the Doppler spread estimate means 246 provided by an embodiment of the invention.
  • the first signal processing means 20 comprises training sequence generating means 22, conjugate means 24 and first signal computing means 28, wherein the first signal computing means 28 can be composed of multiplying means 26 and auto-correlation means 27.
  • the first signal processing means 28 can be composed of multiplying means 26 and auto-correlation means 27.
  • the problems to be solved by the invention can be stated as: estimating Doppler spread fo without knowing the amount of the frequency offset ⁇ f for a certain sampling sequence ⁇ yk
  • k k l5 k2,...,kL ⁇ . It has a certain obstacle to estimate fo directly from ⁇ yk ⁇ , since the estimate of the phase 2 ⁇ k ⁇ Af ⁇ T c is involved.
  • a scheme can be employed that Doppler spread fb is estimated after the auto-correlation function of yk has been processed .
  • the auto-correlation function R yy (m) of yk can be expressed as:
  • R yy (m) E ⁇ y k y k * +m ⁇
  • R yy (m) is a function with the frequency offset ⁇ f and Doppler spread fo as parameters, its output sampling points depend on the time interval m of received signals instead of the received signals themselves.
  • the auto-correlation function of yk can also be calculated according to the method provided in "Further Results in Carrier Frequency Estimation for Transmission Over Flat Fading Channels" by M. Morelli, U. Mengali, IEEE Comm. Letter, Vol. 2, No. 12, Dec. 1998, pp. 327-330, obtaining:
  • R yy (m) J 0 (2 ⁇ mf D T c )e- j2 ⁇ m Af ⁇ ⁇ z F[li -m TM 2i (( ⁇ f fB T T c ⁇ f 1]e --J>2 2 ⁇ "m"- ⁇ Af-T L (8)
  • the training sequence generating means 22 generates a training sequence signal identical to that at the transmitting end based on a known training sequence coding, the resulting training sequence signal is processed by the conjugate means 24 to obtain a complex conjugate training sequence signal d k * .
  • the multiplying means 26 performs multiply operation as described in equation (5) on the complex conjugate training sequence signal d k * and the initial signal sequence Xk acquired by the signal extracting means 10, thereby obtaining a corresponding signal sequence yk.
  • the auto-correlation means 27 performs auto-correlation processing as described in equation (7) on the signal sequence yk, thereby obtaining the first signal sequence R yy (m) as described in equations (7) and (8).
  • the signal sequence R yy (m) is a signal sequence with the frequency offset and Doppler spread as parameters.
  • the acquired first signal sequence is further processed by the second signal processing means 30.
  • Fig. 5 shows a block diagram of second signal processing means 30 in the Doppler spread estimate means provided by an embodiment of the invention.
  • the second signal processing means 30 shown in Fig. 5 comprises conjugate means 32, setting means 34 and eliminating means 36.
  • conjugate means 32 for setting the second signal processing means 30
  • setting means 34 for eliminating the second signal processing means 30
  • eliminating means 36 for eliminating the second signal processing means 30
  • various functional means and the characteristics of their output signals in the second signal processing means 30 will be described in detail in combination with mathematical expressions. Using the intermediate variable as described in the following expression:
  • the conjugate means 32 firstly performs conjugate processing on the first signal sequence R yy (m) outputted by the first signal processing means 20, resulting in the conjugate signal sequence R * yy (m) of R yy (m).
  • the setting means 34 performs the processing as described in equation (11) on the first signal sequence R yy ( m ) and its conjugate signal sequence R * yy (m) to acquire a signal sequence X n , wherein said signal sequence X n comprises the same frequency offset term.
  • the value of the first sequence point of said signal sequence X n is set as the value of the first point of said signal sequence R * yy (m)
  • the value of the nth sequence point of said signal sequence X n is set as the product of the nth point of said signal sequence R * yy (m) and the (n-l)th point of said first signal sequence R yy (m)
  • n is a natural number greater than 2 but less than half of the length L of said observation window.
  • the signal sequence B n is a signal sequence that only takes Doppler spread as parameters and eliminates the effect of the frequency offset.
  • the acquired second signal sequence is further processed by the estimate processing means 40.
  • Fig. 6A and 6B show a block diagram of estimate processing means in the Doppler spread estimate means provided by an embodiment of the invention. As shown in Fig. 6A and 6B, there are two different methods for implementing the estimate processing means 40, both of them are composed of computing means 42 and numerical estimate means 44, the accomplished processing functions of which are same, but the processed signal sequences have minor difference due to the different orders of these two functional means.
  • the numerical estimate means 44 can be designed according to various numerical estimate methods, such as the method of mean evaluation and the method of digital approximation, etc.
  • various functional means and the characteristics of their output signals in the estimate processing means 40 will be described in detail in combination with mathematical expressions.
  • the Doppler spread sequence fo, n can also be calculated directly according to equation (12), and then fo, n is estimated numerically to acquire an estimated value of Doppler spread f D . Up to now, the estimated value of Doppler spread has been acquired from the received signals.
  • the signal sequence B n acquired by equation (12) is firstly numerically estimated by the numerical estimate means 44 according to equation (13), resulting in the numerical estimate value B of the signal sequence B n , and then the estimated value of Doppler frequency f D is calculated by the computing means 42 according to equations (9) and (14).
  • Fig. 7 shows a flow chart of a Doppler spread estimate method provided by an embodiment of the invention. As shown in Fig. 7, the method comprising:
  • Step SlO extracting an expected training sequence suffering from the radio channel fading (an initial signal) from the received signals
  • the received signals are processed, an initial signal sequence Xk comprising the characteristics of the channel is extracted, the initial signal sequence Xk comprises the information of the frequency offset and Doppler spread, moreover, said initial signal sequence is an expected training sequence suffering from the radio channel fading, said expected training sequence is already known.
  • Step S20 processing the initial signal sequence to acquire a first signal sequence based on the frequency offset and Doppler spread
  • a known training sequence signal is generated based on the known training sequence coding; next, the conjugate of said known training sequence is taken to obtain a signal sequence d k * .
  • the signal sequence R yy (m) is a signal sequence with the frequency offset and Doppler spread as parameters.
  • Step S30 processing said first signal sequence to eliminate the frequency offset in said first signal sequence, thereby acquiring a second signal sequence based on said Doppler spread
  • the first signal sequence R yy (m) acquired in step S20 is simplified to acquire the signal sequence as described in equation (10).
  • a conjugate multiply operation as described in equation (11) is performed on the acquired signal sequence to obtain a corresponding signal sequence X n , wherein, each sequence point of the signal sequence X n comprises the same amount of frequency offset.
  • the elimination operation as described in equation (12) is performed on the signal sequence X n to acquire a second signal sequence B n .
  • the signal sequence B n is a signal sequence that eliminates the effect of the frequency offset and only takes Doppler spread as parameters. Up to now, the effect of the frequency offset has been eliminated, the relation between Doppler spread and the received signals has been established, i.e. a second signal sequence based on Doppler spread has been acquired.
  • Step S40 processing the second signal sequence to acquire an estimated value of Doppler spread
  • the second signal sequence B n acquired by step S30 is computed to acquire the Doppler spread sequence fb, n .
  • a numerical estimate processing is performed on said Doppler spread sequence fo, n to acquire said estimated value of Doppler spread f D .
  • Said numerical estimate processing can be either simple mean evaluation, or complicated digital approximation.
  • the method and apparatus for estimating Doppler spread in a mobile communication receiver can be used for not only a cellular communications system but also a radio LAN communication system as well as various communication systems in which there is relative motion between transmitters and receivers.

Abstract

Procédé et un dispositif d'estimation de l'étalement Doppler dans un récepteur de communication mobile qui permettent de séparer l'effet de l'étalement Doppler sur les signaux reçus de l'effet du décalage de fréquence sur ces même signaux. A cette fin, on traite les séquences d'apprentissage extraites des signaux reçus, ce qui permet d'estimer directement l'étalement Doppler à partir de ces signaux et de résoudre les problèmes propres aux procédés classiques, à savoir: dépendance de l'estimation de l'étalement Doppler de la vitesse et la précision de l'estimation du décalage de fréquence ainsi que du retard dans le temps d'estimation d'autres paramètres de canal provoqués par le traitement sériel du décalage de fréquence et de l'étalement Doppler.
PCT/IB2005/054228 2004-12-24 2005-12-14 Procede et dispositif d'estimation de l'etalement doppler WO2006067680A1 (fr)

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CN200410104487.4 2004-12-24

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007003715A1 (fr) * 2005-07-04 2007-01-11 Nokia Corporation Procede de detection de vitesse dans un systeme de communication, recepteur, element de reseau et processeur
CN102546495A (zh) * 2012-01-29 2012-07-04 中兴通讯股份有限公司 频偏补偿方法及装置
WO2013066260A2 (fr) * 2011-11-04 2013-05-10 Zte Wistron Telecom Ab Procédé et appareil pour estimer la vitesse d'un terminal mobile
CN110809870A (zh) * 2018-08-20 2020-02-18 深圳市大疆创新科技有限公司 频点偏移的估计方法、装置、无人机及遥控器

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020172307A1 (en) * 2001-03-27 2002-11-21 David Sandberg Method and apparatus for estimating doppler spread
US6606363B1 (en) * 1999-12-28 2003-08-12 Telefonaktiebolaget Lm Ericsson (Publ) Method and apparatus for estimating a frequency offset by combining pilot symbols and data symbols

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6606363B1 (en) * 1999-12-28 2003-08-12 Telefonaktiebolaget Lm Ericsson (Publ) Method and apparatus for estimating a frequency offset by combining pilot symbols and data symbols
US20020172307A1 (en) * 2001-03-27 2002-11-21 David Sandberg Method and apparatus for estimating doppler spread

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007003715A1 (fr) * 2005-07-04 2007-01-11 Nokia Corporation Procede de detection de vitesse dans un systeme de communication, recepteur, element de reseau et processeur
WO2013066260A2 (fr) * 2011-11-04 2013-05-10 Zte Wistron Telecom Ab Procédé et appareil pour estimer la vitesse d'un terminal mobile
WO2013066260A3 (fr) * 2011-11-04 2013-07-11 Zte Wistron Telecom Ab Procédé et appareil pour estimer la vitesse d'un terminal mobile
US9736626B2 (en) 2011-11-04 2017-08-15 Zte Wistron Telecom Ab Method and apparatus for estimating speed of a mobile terminal
CN102546495A (zh) * 2012-01-29 2012-07-04 中兴通讯股份有限公司 频偏补偿方法及装置
CN110809870A (zh) * 2018-08-20 2020-02-18 深圳市大疆创新科技有限公司 频点偏移的估计方法、装置、无人机及遥控器

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