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

Definitions

• the present invention relates generally to the field of communications and particularly to frequency and time slot synchronization in a mobile communication environment.
• TDMA time domain multiple access
• 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.
• a mobile radiotelephone is handed off from one cell to another in a cellular
• the mobile may need some minor frequency adjustment, as well as complete time slot
• FCCH frequency correction channel
• BCCH broadcast control channel
• 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.
• FCB frequency correction burst
• 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.
• 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).
• 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.
• 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
• 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 x n in FIG. 1, is initially filtered by a second order, infinite impulse response
• IIR bandpass filter 1031
• 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 y n .
• 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 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:
• b n+1 b n (1+ ⁇ b (g n+ ⁇ -1)) where b n+1 is the gain in the adaptive filter and ⁇ b is the gain adaptation coefficient and is set to 0.077 for the gain adaptation operation.
• the pole adaptation block (102) estimates the
• 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:
• a n+1 ⁇ p a n +(1- ⁇ p )r ⁇ n+1
• ⁇ n is an instaneous pole estimate and ⁇ p is the pole adaptation coefficient and is set to 0.083 for the pole adaptation operation.
• 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 g n+1 is less than a threshold of 1.2 and b n+1 is less than a threshold of f(a n ), 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, x n 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.
• y n+1 b * X n+1 + a * y n + (- r 0 2 ) y n-1
• the filtered signal, y n 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.
• the I and Q decoder block contains the

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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)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Cited By (7)

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Citations (4)

Family Cites Families (2)

• 1991
  • 1991-12-11 DE DE4193255A patent/DE4193255C2/de not_active Expired - Lifetime
  • 1991-12-11 GB GB9216946A patent/GB2256993B/en not_active Expired - Lifetime
  • 1991-12-11 DE DE19914193255 patent/DE4193255T/de active Pending
  • 1991-12-11 CA CA002071552A patent/CA2071552C/en not_active Expired - Fee Related
  • 1991-12-11 WO PCT/US1991/009409 patent/WO1992011706A1/en active Application Filing
  • 1991-12-11 AU AU91692/91A patent/AU636263B2/en not_active Ceased
  • 1991-12-13 IL IL10036691A patent/IL100366A/en not_active IP Right Cessation
  • 1991-12-17 FR FR9115662A patent/FR2671248B1/fr not_active Expired - Lifetime
  • 1991-12-17 IT ITRM910944A patent/IT1250962B/it active IP Right Grant
• 1992
  • 1992-08-14 SE SE9202350A patent/SE504792C2/sv not_active IP Right Cessation

Patent Citations (4)

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