Pulse or digital communications – Receivers – Automatic frequency control
Patent
1996-03-14
1998-01-20
Chin, Stephen
Pulse or digital communications
Receivers
Automatic frequency control
375316, 375371, H03K 900, H04L 2714, H04L 2722
Patent
active
057107963
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/F195/00212, filed Apr. 12, 1995.
BACKGROUND OF THE INVENTION
The invention relates to a method for determining a phase error in a received radio-frequency signal, wherein an impulse response of a received signal is calculated, measuring points are chosen from the signal, and samples are taken from areas surrounding the measuring points, the samples are filtered with a complex adapted filter, the phase error in the samples is measured from the filtering result, and the total phase error in the received signal is calculated on the basis of the measured phase error. The invention also relates to a receiver for receiving a radio-frequency signal, the receiver comprising: means for calculating an impulse response for a received signal, sampling means for taking samples of the signal at chosen measuring points, complex adapted filtering means for filtering the samples, measuring means for measuring a phase error in the filtered samples, calculating means responsive to the measuring means for calculating the total phase error in the received signal on the basis of the measured phase error, and compensation means for compensating for the phase error in the received signal.
The present invention relates especially to digital mobile communication systems, such as the GSM (Groupe Special Mobile) and DCS systems (Digital Cellular System). A subscriber station of e.g., the GSM system uses a signal received from a base station as its frequency reference. With a stationary subscriber station the frequency synchronization works well, but when the subscriber station is moving, the Doppler effect causes a frequency error directly proportional to the speed of the mobile phone. The frequency error detected by the base station is double compared with that seen by the subscriber unit, wherefore the frequency error is more problematic as regards the base station. Additionally, in the DCS system, the problem is double that of the GSM system because of the double carrier frequency.
In addition to the Doppler effect, a frequency error in the transmitter of a subscriber station may cause an additional frequency error at the receiving side of the base station. GSM specifications allow a 90 Hz frequency error in the transmitter of a subscriber station, the corresponding value being 180 Hz in the DCS system. In defective subscriber units, the allowable frequency error value may, however, be significantly exceeded.
A prior art solution to measuring and compensating for a frequency error in a subscriber station is a method wherein the frequency error is calculated on the basis of phase errors at the beginning and at the end of a burst. Once the phase error is known, it may be used to calculate the frequency error in the received signal. In measuring, this prior art solution utilizes the characteristics of a complex adapted filter. After this filter the phase error in the signal equals zero, and where a fixed frequency error is concerned, the phase error will grow linearly towards the edges of the received burst.
The drawback of the above described prior art method is a narrow measuring band. Large frequency errors cause a large phase error at the edges of a burst, and large phase errors (>60.degree.) cause measuring errors due to an excessive convolving of the signal state diagram. Only small frequency errors (below 400-500 Hz) may thus be measured by this known method. Practice has shown that with too large a frequency error, the measuring algorithm has detected the wrong frequency, which has resulted in failure to correct the frequency error.
SUMMARY OF THE INVENTION
The object of the present invention is to solve the above problem and provide a method for measuring significantly larger phase errors than by known methods. This object is achieved with the method of the invention, which is characterized in that the measuring points are chosen on the basis of phase errors measured from signals received earlier so that the phase errors at the measuring points will re
REFERENCES:
patent: 4847869 (1989-07-01), Labedz et al.
patent: 5136616 (1992-08-01), Dent
patent: 5151936 (1992-09-01), Chennakeshu et al.
patent: 5245611 (1993-09-01), Ling et al.
patent: 5283815 (1994-02-01), Chennakeshu et al.
Jarvela Mikko
Suonvieri Jukka
Chin Stephen
Deppe Betsy Lee
Nokia Telecommunications Oy
LandOfFree
Method and receiver for determining a phase error in a radio-fre does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and receiver for determining a phase error in a radio-fre, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and receiver for determining a phase error in a radio-fre will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-731142