AU9169291A - Frequency and time slot synchronization using adaptive filtering - Google Patents

Frequency and time slot synchronization using adaptive filtering

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Publication number
AU9169291A
AU9169291A AU91692/91A AU9169291A AU9169291A AU 9169291 A AU9169291 A AU 9169291A AU 91692/91 A AU91692/91 A AU 91692/91A AU 9169291 A AU9169291 A AU 9169291A AU 9169291 A AU9169291 A AU 9169291A
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AU
Australia
Prior art keywords
signal
frequency
signals
determining
produce
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
AU91692/91A
Other versions
AU636263B2 (en
Inventor
Arvind S Arora
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Motorola Solutions Inc
Original Assignee
Motorola Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc filed Critical Motorola Inc
Publication of AU9169291A publication Critical patent/AU9169291A/en
Application granted granted Critical
Publication of AU636263B2 publication Critical patent/AU636263B2/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/0035—Synchronisation arrangements detecting errors in frequency or phase
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2662—Arrangements for Wireless System Synchronisation
    • H04B7/2671—Arrangements for Wireless Time-Division Multiple Access [TDMA] System Synchronisation
    • H04B7/2675—Frequency synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2662—Arrangements for Wireless System Synchronisation
    • H04B7/2671—Arrangements for Wireless Time-Division Multiple Access [TDMA] System Synchronisation
    • H04B7/2678—Time synchronisation
    • H04B7/2681—Synchronisation of a mobile station with one base station
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2662—Arrangements for Wireless System Synchronisation
    • H04B7/2671—Arrangements for Wireless Time-Division Multiple Access [TDMA] System Synchronisation
    • H04B7/2678—Time synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00—Arrangements for synchronising receiver with transmitter
    • H04L7/04—Speed or phase control by synchronisation signals
    • H04L7/041—Speed or phase control by synchronisation signals using special codes as synchronising signal
    • H04L2007/047—Speed or phase control by synchronisation signals using special codes as synchronising signal using a sine signal or unmodulated carrier

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Time-Division Multiplex Systems (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)

Description

FREQUENCY AND TIME SLOT SYNCHRONIZATION USING ADAPTIVE FILTERING
Field of the Invention
The present invention relates generally to the field of communications and particularly to frequency and time slot synchronization in a mobile communication environment. Background of the Invention
Since a mobile radiotelephone does not have an accurate enough frequency reference internally, it must make fine frequency adjustments to achieve the required frequency synchronization to a base station frequency. In a time domain multiple access (TDMA) system, multiple logical channels are transmitted on the same frequency, but separated in time, FIG 2. To communicate with a base station, the mobile radiotelephone must also find the boundaries of these time slots, called time slot synchronization.
The different base stations in a cellular radiotelephone system maintain very accurate frequency references, but utilize different transmission frequencies, and possibly different time slot alignments. When a mobile radiotelephone is handed off from one cell to another in a cellular
radiotelephone system, the mobile may need some minor frequency adjustment, as well as complete time slot
synchronization to communicate with the new base station.
To accomplish this in a digital cellular radiotelephone system, the radiotelephone first finds a frequency correction channel (FCCH), which is part of the broadcast control channel (BCCH). FIG. 2 illustrates the FCCH slots (201) and other data control channels that make up the multiframe
TDMA structure of the BCCH. This format is described in greater detail in the digital cellular standard specification GSM Recommendation 5.02, Version 3.3.1, October 13, 1989. The base band signal of the FCCH is a frequency correction burst (FCB), a pure tone (sine wave) at 67.5 kHz, consisting of 148 samples, sent priodically and it always occurs in time slot zero of the data stream. The offset between the carrier frequencies of the base station and the mobile radiotelephone is translated to the base band as a deviation from 67.5 kHz. The boundaries of the FCB delineate the time slots of the TDMA structure. From the FCCH detected, the mobile radiotelephone synchronizes its local oscillator frequency and time slot boundaries with those of the base station using the frequency correction burst in the FCCH time slot.
Since the burst is relatively short, the mobile must find it in the data stream and synchronize with it in this short period. There is a resulting need for a process that can detect the presence and boundaries of the FCB very rapidly, and estimate the frequency offset very accurately, even when signals are received in the presence of noise. Summary of the Invention
The synchronizing process of the present invention is comprised of the steps of filtering a received signal with adaptive filtering means, buffering this signal in storage means, and determining if the frequency correction tone is present, (the detection process). This also establishes the boundaries of the TDMA time slots. When this frequency correction tone is present, filtering the buffered signal and determining the difference between the frequency of this filtered signal and 67.5 kHz, (the carrier frequency offset estimation process).
Brief Description of the Drawings FIG. 1 shows a block diagram of the process of the present invention. FIG. 2 shows the TDMA, multiframe, broadcast control channel format.
FIG. 3 shows a typical radiotelephone, using the process of the present invention, for use in a TDMA type system.
Detailed Description of the Preferred Embodiment
The process of the present invention provides rapid frequency and time slot synchronization between a mobile radiotelephone and the base station with which it is
communicating. This is accomplished by detecting the presence and boundaries of the frequency correction burst and determining the frequency of this base band tone.
The preferred embodiment of the process of the present invention is illustrated in FIG. 1. The input to this process is one of the two base band quadrature signals, the I or Q data stream, sampled at one sample per bit-time, from the receiver of the radiotelephone. This signal, labeled xn in FIG. 1, is initially filtered by a second order, infinite impulse response
(IIR) bandpass filter (101). Both the gain and the pole of this filter are adaptive. The gain is adjusted in order to maintain substantially unity gain through the filter, that is, the energy at the output is equal to the energy at the input. The pole of the filter is moved so that the passband of the filter encompasses the received signal. The signal output from the filter is labeled yn. The filtering is performed as follows: yn+1 = bn xn+1 + an yn + (- r2 0) yn-1 The energy of the input signal and the energy of the filtered signal are then estimated in the energy estimation blocks (103 and 104). The estimation for the input energy is accomplished as follows: E(x)n+1 = (1-αe) E(x)n + αe x2 n+1 The estimate for the filtered signal energy is as follows: E(y)n+1=(1-αe)Eyn+αe yn 2 +1 where αe is the energy adaptation coefficient and is set equal to 0.091 for the estimation operations.
The input and the output energies, E(x)n+1 and E(y)n+1, are compared in the gain adaptation block (105) and the gain of the filter is adapted to match the input and filtered signal energies. This adapted gain is then fed back to the filter. This comparison and adaptation is performed as follows:
bn+1=bn (1+αb(gn+ι-1)) where bn+1 is the gain in the adaptive filter and αb is the gain adaptation coefficient and is set to 0.077 for the gain adaptation operation.
The pole adaptation block (102) estimates the
instantaneous frequency of the filtered signal. The pole of the adaptive filter is adapted toward this frequency and the new pole location is fed back to the filter (101). This operation is as follows:
If (yn 2>0.15E(y)n+1) then If ( |2yn| > lyn-1+yn+1l ) then θn+1=(yn-1+yn+1)/(yn)
an+1=αpan+(1-αp)rθn+1
End If
End if where θn is an instaneous pole estimate and αp is the pole adaptation coefficient and is set to 0.083 for the pole adaptation operation. When the adaptive filter tracks a pure tone, such as in the frequency correction burst, all the energy in the input signal is in the band of the bandpass filter. Unit gain can thus be achieved through the filter (101) with the lowest value of the filter gain. This condition is checked to determine the instantaneous presence of a tone in the tone detection block (106). If gn+1 is less than a threshold of 1.2 and bn+1 is less than a threshold of f(an), then the tone is present.
The timer block (107) measures the length of time for which the tone present condition persists. If this tone is present for at least 100 samples in the preferred embodiment, the presence of the frequency correction burst has been verified. This integration prevents the algorithm from falsely detecting a signal, that, for short periods, may appear like a narrowband signal.
The signal, xn, that was input to the filter (101), is also stored in a shift registered buffer (108). Once it has been determined that this stored signal is the frequency correction burst, the signal from the buffer (108) is input to the band-pass filter (101) again using optimum coefficients, a* and b*, determined during the detection process. Since the passband of the filter (101) is now tuned to the frequency of the frequency correction burst, after the above adaptation process, it passes this signal without attenuation, and filters out the background noise, thus improving the effective signal-to-noise ratio. yn+1 =b* Xn+1 + a* yn + (- r0 2) yn-1
The filtered signal, yn, is next processed using a Least Squared Error estimation process to generate a frequency estimate, q*, of the base band tone.
The difference between q* and p/2 (67.5 kHz) is the frequency offset between the carrier frequencies of the base station and the mobile radiotelephone. This is entered to the local oscillator circuit of the radiotelephone to compensate for the carrier frequency offset. The above described process is performed periodically to keep the mobile radiotelephone locked to the base station carrier frequency.
An example of the receive portion of a typical mobile radiotelephone for use in a TDMA system is illustrated in FIG. 3. The I and Q decoder block contains the
synchronization process of the present invention disclosed herein. This type of radiotelephone is discussed in greater detail in copending U.S. patent application serial No. 590,415 "Interference Reduction Using an Adaptive Receiver Filter, Signal Strength, and BER Sensing filed September 28, 1990 on behalf of Cahill.
In summary, a novel process has been shown that will synchronize a mobile radiotelephone's local oscillator frequency and time slot positioning with those of the received signal from a base station. This synchronization occurs in real time and with significantly enhanced accuracy.

Claims (6)

Claims
1. A method for frequency synchronization between a cellular communication base station that transmits a plurality of signals, at least one of the plurality of signals having a frequency correction tone, and a mobile communication device that receives the plurality of signals, the mobile
communication device having local oscillating means with a variable frequency, the method characterized by the steps of: a) filtering a first signal of the plurality of signals to produce a first filtered signal (101);
b) buffering the first signal to produce a buffered signal (108);
c) determining if the frequency correction tone is present in the first signal by determining an energy of the first signal and an energy of the filtered signal and a duration for which a relationship between these energies exists (102-107); d) when the frequency correction tone is present, filtering the buffered signal to produce a second filtered signal which contains carrier frequency offset information (110); and the method further characterized by the step of
e) when the frequency correction tone is present, determining from the second filtered signal a frequency difference between the carrier frequency of the signal from the base station and the frequency of the local oscillating means of the mobile communication device (109).
2. The method of claim 1 and further characterized by the step of adjusting the local oscillating means of the mobile
communication device in response to the frequency difference.
3. The method of claim 1 characterized in that the
relationship between the input and output energies is equality.
4. A method for frequency synchronization in a time division multiple access (TDMA) cellular communication system between a communication base station that transmits a plurality of TDMA signals at a plurality of frequencies, and a mobile communication device that receives the plurality of signals, each signal comprised of a plurality of samples and at least one of the signals having a frequency correction tone, the mobile communication device having local oscillating means with a variable frequency that varies in response to the frequency correction tone, the method characterized by the steps of:
a) filtering a first signal of the plurality of signals with an adaptive filter to produce a filtered signal, the adaptive filter having a variable gain and a variable pole (101);
b) buffering the first signal to produce a buffered signal
(108);
c) determining a first energy level of the first signal (103);
d) determining a second energy level of the filtered signal (104);
e) varying the gain of the adaptive filter in response to a difference between the first and second energy levels (105); f) varying the pole of the adaptive filter in response to the frequency of the second signal (102);
g) when the first energy level is equal to the second energy level, determining a quantity of samples of the first signal for which a relationship between the first and the second energies exists (106-107);
h) when the quantity of samples is substantially the predetermined number, filtering the buffered signal to produce a second filtered signal having carrier frequency offset information (110); and the method further characterized by the step of i) if the quantity of samples is substantially a
predetermined number, determining from the second filtered signal a frequency difference between the carrier frequency of the signal from the base station and the frequency of the local oscillating means of the mobile communication device (109).
5. The method of claim 4 and further characterized by the step of adjusting the local oscillating means of the mobile
communication device in response to the frequency difference.
6. A radiotelephone for use in a TDMA type cellular communication system, the radiotelephone having
demodulation means for generating I and Q signals, the radiotelephone characterized by:
a) means for transmitting a first signal;
b) means for receiving a second signal, coupled to the TDMA demodulation means, the TDMA demodulation means processing the second signal to generate the I and Q signals; and the radiotelephone further characterized by
c) processing means for processing the I or Q signals, the processing means performing the steps of:
filtering a first signal of the plurality of signals with an adaptive filter to produce a first filtered signal (101);
buffering the first signal to produce a buffered signal (108) ;
determining if the frequency correction tone is present in the first signal by determining an energy of the first signal and an energy of the filtered signal and a duration for which a relationship between these energies exists (102-107);
when the frequency correction tone is present, filtering the buffered signal to produce a second filtered signal containing carrier frequency offset information (110); and the processing means further performing the step of
when the frequency correction tone is present, determining from the second filtered signal a frequency difference between the carrier frequency of the signal from the base station and the frequency of the local oscillating means of the mobile communication device (109).
AU91692/91A 1990-12-17 1991-12-11 Frequency and time slot synchronization using adaptive filtering Ceased AU636263B2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US62853590A 1990-12-17 1990-12-17
US628535 1990-12-17

Publications (2)

Publication Number Publication Date
AU9169291A true AU9169291A (en) 1992-07-22
AU636263B2 AU636263B2 (en) 1993-04-22

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AU91692/91A Ceased AU636263B2 (en) 1990-12-17 1991-12-11 Frequency and time slot synchronization using adaptive filtering

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AU (1) AU636263B2 (en)
CA (1) CA2071552C (en)
DE (2) DE4193255C2 (en)
FR (1) FR2671248B1 (en)
GB (1) GB2256993B (en)
IL (1) IL100366A (en)
IT (1) IT1250962B (en)
SE (1) SE504792C2 (en)
WO (1) WO1992011706A1 (en)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2709894B1 (en) * 1993-09-10 1995-10-20 Alcatel Mobile Comm France Method for determining, by a mobile station of a cellular radiocommunication system, the type of cell to which it is attached, mobile station and base station.
US5761250A (en) * 1995-08-15 1998-06-02 Rockwell International Corporation Iterative filtering frequency estimator and estimation method
DE19722219A1 (en) * 1997-05-28 1998-12-03 Alsthom Cge Alcatel Radio communication system with a fixed and a movable radio device
JP3088338B2 (en) * 1997-05-28 2000-09-18 埼玉日本電気株式会社 Wireless telephone equipment
US6278699B1 (en) 1998-06-22 2001-08-21 Telefonaktiebolaget Lm Ericsson (Publ) Synchronization techniques and systems for spread spectrum radiocommunication
US6356608B1 (en) * 1998-06-29 2002-03-12 Telefonaktiebolaget Lm Ericsson (Publ) Method, apparatus, and system for determining a location of a frequency synchronization signal
US6473420B1 (en) * 2001-02-16 2002-10-29 Harris Corporation Wideband ranging process for frequency acquisition
GB2534603B (en) * 2015-01-29 2019-07-31 Michell Instruments Ltd System for analysing the frequency of a signal, a method thereof and a system for measuring the relative phase between two input signals

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4317220A (en) * 1979-02-05 1982-02-23 Andre Martin Simulcast transmission system
US4466130A (en) * 1982-10-04 1984-08-14 Ael Microtel Limited Two pilot frequency control for communication systems
DE3508069C2 (en) * 1985-03-07 1993-12-02 Aeg Mobile Communication Single-wave radio with re-adjusted transmitter frequency
GB8604981D0 (en) * 1986-02-28 1986-04-09 Mcgeehan J P Data transmission
CA1288878C (en) * 1988-08-15 1991-09-10 John D. Mcnicol Timing and carrier recovery in tdma without preamable sequence
DK0387720T3 (en) * 1989-03-16 1994-03-21 Siemens Ag Link for recognizing a frequency reference signal

Also Published As

Publication number Publication date
DE4193255C2 (en) 1997-02-20
SE9202350D0 (en) 1992-08-14
IT1250962B (en) 1995-04-24
GB2256993B (en) 1995-06-21
ITRM910944A1 (en) 1993-06-17
WO1992011706A1 (en) 1992-07-09
SE504792C2 (en) 1997-04-28
GB9216946D0 (en) 1992-10-07
IL100366A0 (en) 1992-09-06
DE4193255T (en) 1992-12-10
CA2071552A1 (en) 1992-06-18
ITRM910944A0 (en) 1991-12-17
IL100366A (en) 1995-05-26
FR2671248A1 (en) 1992-07-03
SE9202350L (en) 1992-08-14
FR2671248B1 (en) 1994-11-04
CA2071552C (en) 1997-02-25
GB2256993A (en) 1992-12-23
AU636263B2 (en) 1993-04-22

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MK14 Patent ceased section 143(a) (annual fees not paid) or expired