Pulse or digital communications – Repeaters – Testing
Patent
1980-06-13
1982-09-21
Safourek, Benedict V.
Pulse or digital communications
Repeaters
Testing
375 43, 329 50, H04L 2549
Patent
active
043510612
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for phase synchronization in a synchronous data transmission system, which transmits a binary pulse train from a transmitter to a receiver by means of an amplitude modulated carrier. Specifically, the modulation is of the type known as single-side band amplitude modulation (SSBAM) and the modulating signal, which is derived from the input data flow consists of superimposed pulses of the Partial Response Class IV type.
DESCRIPTION OF PRIOR ART
The above-mentioned type of modulation is often used for high-speed transmission of data over Band-Limited-channels (CCITT Recommendation V. 36, Doc. APVI number 44 1976, pp 139-147). The instantaneous signal amplitude in the modulating signal according to the above contains contributions from several coded input data bits, and conversely a Partial-Response Pulse thus extends over several periods of the input data signal. The Partial-Response concept is described in detail, inter alia in the U.S. Pat. No. 3,388,330.
In order that the binary data signal can be restored correctly at the receiver side, information about both carrier frequency and carrier phase as well as bit rate and bit phase must be available at the receiver.
Although the recovery of carrier frequency and bit rate at the receiver side does not usually create any problems, an optimum control of carrier phase and bit phase can cause greater difficulties. A phase error of some few degrees can namely result in heavy distortion with accompanying data loss.
The carrier frequency is usually recovered from a transmitted pilot signal via narrow band filtering, but it is often impossible to get usable information about the carrier phase at the transmitter side from the transmitted pilot signal due to phase distortion in the transmitting channel. With regard to the bit rate, this can be obtained via zero crossover detection of the demodulated signal, even for the case where demodulation takes place in an incorrect phase.
A method is previously known for directly deriving a control signal for the bit phase and carrier phase from the symmetry properties of the transmitted demodulated signal. (Ein Verfahren zur Datenubertragung auf Primargruppenverbindungen NTZ 29, 1976 H.6 s. 449-452). The method requires complicated analogue signal processing and is furthermore dependent on the transmitted binary data signal containing an average of just as many ones as zeroes. There is further required a mean value of the error signal over a large number of data bits, which results in long synchronization times.
A method is also known, which utilizes the equalizer tap settings for generating a control signal for the bit phase and carrier phase, in systems with adaptive equalizers of the transversal type. (IEEE Transactions on Communication, September 1975, pp. 976-979). This method is very suitable for transmission systems where channel equalizing by means of adaptive equalizers is required but becomes complicated and expensive when this is not the case.
SUMMARY OF THE INVENTION
An object of the present invention is to provide phase synchronization in the detection of data signals of the type mentioned above.
The proposed solution utilizes certain sorted-out zero crossovers in the base band signal obtained after demodulation on the receiver side, to create suitable control signals for the phase correction. Further distinguishing features of the invention are apparent from the characterizing parts of the accompanying patent claims.
The advantages with the proposed solution are, inter alia, a very rapid phasing-in sequence and large pull-in range without utilizing any special starting sequence or the like, and the possibility of entirely digital realisation.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in detail by an embodiment with reference to the appended drawing on which:
FIG. 1 illustrates a block diagram of a transmission system utilizing the invention:
FIG. 2 illustrates a so-called Partial-Response pulse;
FI
REFERENCES:
patent: 3860871 (1975-01-01), Hinoshita et al.
patent: 4010421 (1977-03-01), Lind
Ein Verfahren zur Datenubertragung auf Primargruppenverbindungen, NTZ 29, 1976 H.6p. 449-452.
IEEE Transactions on Communications, Feb. 1975, pp. 259-265, (The Effects of Equalization, Timing and Carrier Phase on Eye Patterns of Class-4 Partial-Response Data Signals).
Hedin Jan S.
Jarnestedt Goran A.
Safourek Benedict V.
Telefonaktiebolaget L M Ericsson
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