Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Reexamination Certificate
1999-04-06
2001-08-21
Trost, William (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
C455S182300, C455S067700
Reexamination Certificate
active
06278865
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of measuring the frequency difference in a radio receiver generating for synchronization purposes a tuning frequency corresponding as accurately as possible to a transmission frequency, and in which an estimated impulse response for the channel used by a received signal is generated.
The invention also relates to a method of measuring the frequency difference in a radio receiver generating for synchronization purposes a tuning frequency corresponding as accurately as possible to a transmission frequency, and in which the strength and phase of a received signal is measured in relation to the tuning frequency.
The invention further relates to a receiver, arranged to generate for synchronization purposes a tuning frequency corresponding as accurately as possible to a transmission frequency, and to generate an estimated impulse response for the channel used by a received signal.
The invention also relates to a receiver, arranged to generate for synchronization purposes a tuning frequency corresponding as accurately as possible to a transmission frequency, and to measure signal strength and signal phase.
BACKGROUND ART
A basic requirement for the operation of a radio system is that the connection between a transmitter and receiver is synchronized. In conventional radio technology, a PLL receiver (Phase Lock Loop) is employed to achieve and maintain synchronization. However, this method is not very useful in the CDMA system (Code Division Multiple Access).
In the CDMA method, a narrowband user data signal is multiplied to a relatively broad band by a spreading code having a considerably higher frequency than that of the data signal. The aim is to select spreading codes that are mutually substantially orthogonal, i.e. have minimal mutual correlation. Upon transmission, a broadband signal is multiplied, i.e. modulated, by a continuous carrier having a considerably higher frequency than that of the spreading code. Owing to orthogonal spreading codes, the signals of several users can be transmitted on the same carrier.
In a conventional CDMA receiver, the signal carrier is demodulated by multiplying the signal by the tuning frequency of the local oscillator of the receiver. The tuning frequency is intended to have the same frequency as the carrier employed in transmission. The data signal again is returned in the receiver to the original band by multiplying it again by the same spreading code as at the transmission stage.
However, there is usually frequency difference between the tuning frequency of a local oscillator and the carrier employed in transmission. It can be seen as a phase shift between the receiver and the spreading code employed in transmission. Without corrective measures, this phase shift increases the longer the connection between the transmitter and the receiver lasts. In a fading multi-path environment, the change caused by the difference between the transmission carrier and the receiver tuning frequency in the code phase is called a group shift. In a typical multi-path environment of a radio system this increasing group shift cannot be detected reliably with prior art measurements.
DISCLOSURE OF THE INVENTION
It is the object of the present invention to provide a method for reliably detecting a group shift in a multipath environment.
This is achieved with a method of the kind described in the preamble, characterized by generating at least two temporally successive estimated impulse responses, comparing the mutual temporal shift of said impulse responses in relation to one another, generating a phase shift between the estimated impulse responses on the basis of the comparison, and forming a frequency difference between the transmission frequency and the tuning frequency on the basis of the phase shift.
The method of the invention is also characterized by measuring the phase of a received signal at least two temporally successive times, comparing the measured phases with one another, generating a signal phase shift on the basis of the comparison, and forming a frequency difference between the transmission frequency and the tuning frequency on the basis of the phase shift.
The receiver of the invention is characterized in that the receiver comprises means for generating at least two temporally successive estimated impulse responses, means for comparing the temporal shift of said impulse responses in relation to one another, and for generating a phase shift on the basis of the comparison, and means for forming a frequency difference between the transmission frequency and the tuning frequency on the basis of the phase shift.
The receiver of the invention is further characterized in that the receiver comprises means for measuring the phase of a received signal at least two temporally successive times, means for comparing the phases of the received signal with one another, and for generating a phase shift on the basis of the comparison, and means for forming a frequency difference between the transmission frequency and the tuning frequency on the basis of the phase shift.
Considerable advantages are achieved with the method of the invention. The frequency error between the tuning frequency of the receiver and the carrier frequency employed in transmission can be determined exactly and easily, and the error can be corrected. This makes the connection more reliable than before.
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Nokia Telecommunications Oy
Perez-Gutierrez Rafael
Pillsbury & Winthrop LLP
Trost William
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