Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
  • H03L7/00—Automatic control of frequency or phase; Synchronisation
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H21/00—Adaptive networks
  • H03H21/0012—Digital adaptive filters
  • H03H21/0043—Adaptive algorithms
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
  • H03J7/00—Automatic frequency control; Automatic scanning over a band of frequencies
  • H03J7/02—Automatic frequency control
  • H03J7/04—Automatic frequency control where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant

Definitions

• the present invention relates generally to the field of communications and particularly to automatic frequency con ⁇ trol.
• U.S. digital cellular (USDC) communications uses digi ⁇ tized voice and data signals for communication between a mo ⁇ bile telephone and a base station.
• the mobiles and bases em- ploy time division multiple access (TDMA) modulation for the transmission of these signals.
• TDMA time division multiple access
• FIG. 5 A typical format for the TDMA data bursts is illustrated in FIG. 5. This data burst, as well as USDC in general, is discussed in more detail in the USDC specification EIA/TIA IS-54 available from Electronic Industries Association, Engineering Department, 2001 Eye
• FIG. 1 A typical adaptive filter is illustrated in FIG. 1.
• the in ⁇ put signal (106) is processed by the adaptive filter (101), pro ⁇ ducing the adaptive filter output signal (102).
• the output of the filter is then subtracted (105) from a reference signal (103), typically the unfiltered input signal (106), to produce an error signal (104).
• This error signal (104) is used by an adaptive al- gorithm with an update coefficient, ⁇ , in the adaptive filter to update the filter coefficients.
• the update coefficient is also re ⁇ ferred to as a tracking coefficient or memory coefficient.
• the memory of the adaptive algorithm increases as the value of ⁇ increases.
• the adaptive algorith may be a Kal an, Recursive Least Square, or Least Mean Square (LMS) algorithm.
• LMS Least Mean Square
• the typical goal of the adaptive algorithm is to minimize the mean square value of the error signal (104), fixed update coefficient. This value is typically designated mean square error (MSE).
• MSE mean square error
• a detrimental characteristic of adaptive channel equal ⁇ izers is that they can experience degraded performance in the presence of a frequency offset of more than approximately 10 Hz (in a system with a 24 kHz symbol rate). While the spe ⁇ fi- cation for a transmission system requires a certain frequency variation limit, the adaptive channel equalizer may require a stricter limit.
• An example is the USDC system. USDC re ⁇ quires the receiver operating frequency to be locked within 200 Hz of the transmitter.
• a coarse automatic frequency control is typically used to remove most of the offset. Any remaining offset, however, can detrimentally af ⁇ fect a detection algorithm and increase the detected bit error rate. There is a resulting need for an AFC that can reduce the frequency offset to an acceptably small level and track any variation of the offset as the environment changes when the mobile moves.
• the process of the present invention generates an opti ⁇ mum automatic frequency control signal in an apparatus that has a plurality of adaptive algorithms, each adaptive algo ⁇ rithm having a reference signal with an associated frequency dither.
• the process starts by comparing the performance of each of the plurality of adaptive algorithms then modifying the automatic frequency control signal in response to a difference in the performances.
• FIG. 3 shows a graph of mean square error versus residual frequency offset in accordance with the process of the present invention.
• the difference in performance of the adaptive filters is used to modify the AFC signal, thereby reducing the frequency offset.
• This signal is then operated on by a detection algorithm (10) that is driven by the ACE 2 output.
• the resulting symbol decision signal, ⁇ is input to the three ACE's (1 - 3).

Landscapes

• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
• Channel Selection Circuits, Automatic Tuning Circuits (AREA)
• Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
• Circuits Of Receivers In General (AREA)
• Feedback Control In General (AREA)
• Radio Relay Systems (AREA)

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Cited By (4)

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Citations (4)

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• 1992
  • 1992-05-08 GB GB9303663A patent/GB2263829B/en not_active Expired - Lifetime
  • 1992-05-08 DE DE4292274T patent/DE4292274T1/de active Pending
  • 1992-05-08 DE DE4292274A patent/DE4292274C2/de not_active Expired - Lifetime
  • 1992-05-08 WO PCT/US1992/003763 patent/WO1993000747A1/en active Application Filing
  • 1992-05-08 CA CA002089154A patent/CA2089154C/en not_active Expired - Fee Related
  • 1992-05-08 KR KR1019930700393A patent/KR960005386B1/ko not_active IP Right Cessation
  • 1992-05-08 JP JP5501452A patent/JP2830471B2/ja not_active Expired - Fee Related
  • 1992-06-25 MX MX9203307A patent/MX9203307A/es unknown

Patent Citations (4)

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