Pulse or digital communications – Synchronizers – Synchronizing the sampling time of digital data
Patent
1994-07-26
1997-02-11
Bocure, Tesfaldet
Pulse or digital communications
Synchronizers
Synchronizing the sampling time of digital data
327299, H04L 700
Patent
active
056028792
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital demodulator for demodulating signal waves modulated by digital signals, and also relates to AFC (Automatic Frequency Control) circuits, clock recovery circuits and bit error estimation circuits respectively used for that digital demodulator.
2. Prior Art
Digitization of communication has been studied and realized in the field of data transfer for communication on wires, such as telephone circuits, microwave communication or optical communication between base stations. Also, digitization of mobile communication for automobile telephones or portable telephones whose development has been delayed so far is studied extensively.
As the well-known method of modulating or demodulating digital signals, there can be mentioned the amplitude modulation for changing the amplitude of carrier waves corresponding to state of each digital signal and the so-called angle modulation for changing its phase or frequency.
In the field of digital mobile communication, generally, the angle modulation method which is not susceptible to amplitude distortion due to the signal transfer route is used.
The angle modulation is now described in brief with respect to the so-called .pi./4 shift quadrature phase shift-keying (.pi./4 shift QPSK) method which is excellent in withstandability to distortion and suitable for the mobile communication.
FIG. 16 is a block diagram showing fundamental construction of the .pi./4 shift QPSK system.
Serial/parallel converter 1 converts a row of binary digital data into 2-bit unit data (X, Y). The unit data is called one symbol used as one cycle of data processing. Differential coding circuit 2 produces a base band signal consisting of I and Q channels to which the information of (X, Y) is given respectively corresponding to the change (difference) in signals. The band of the base band signal is limited by low-pass filters (LPF) 3, 4. Thus, amplitude modulation is carried out by multiplying the in-phase and quadrature phase components of carrier wave .omega..sub.c by the band-limited base band signal respectively, and a modulation wave is then obtained by synthesizing both the products.
In case of the phase modulation by the above .pi./4 shift QPSK system, amplitude values "A", "-A" are assigned respectively to the binary signals "1", "0", and four signal-point data (I, Q) are given for one symbol to perform the quadrature phase shift keying. Namely, as shown by the signal-point arrangement with respect to I, Q in FIG. 17, the phase modulation is performed using the signal-point arrangement of QPSK designated by blackened circles (.circle-solid.) and the corresponding .pi./4 shifted signal-point arrangement designated by normal circles (.largecircle.) alternately at each symbol interval. Accordingly, each phase difference .DELTA..PHI. between the two consecutive symbols always becomes odd times the shift of .pi./4 so that the relation between .DELTA..PHI. and the input unit data (X, Y) can be expressed as shown in FIG. 17(b).
As the method of demodulating a modulation wave, the synchronous detection method and delay detection method are well-known. Theoretically, the synchronous detection method has excellent properties, but is likely to generate disadvantageously high-speed fading. Thus, the delay detection method is more preferred, in particular, in case of digital mobile communication where a sudden phase change often occurs.
In the delay detection method, a new modulation wave is detected based on the previous modulation wave delayed by a delay circuit provided with a predetermined delay time. Therefore, these modulation waves should be modulated by a signal processed by the differential coding as described above. In addition, the regeneration of the carrier wave becomes unnecessary. Accordingly, as compared to the synchronous detection method, the delay detection method can be constructed more simply and more suitable for the mobile communication.
For example, in case of the aforementioned .pi./4 shift Q
REFERENCES:
patent: 4692931 (1987-09-01), Ohsawa
patent: 4815103 (1989-03-01), Cupo et al.
patent: 5016206 (1991-05-01), Shinonaga
patent: 5093841 (1992-03-01), Vancraeynest
patent: 5202901 (1993-04-01), Chennakeshu et al.
patent: 5255289 (1993-10-01), Tomita
patent: 5259005 (1993-11-01), La Rosa et al.
patent: 5283815 (1994-02-01), Chennakeshu et al.
patent: 5309482 (1994-05-01), Wright et al.
patent: 5311544 (1994-05-01), Park et al.
patent: 5343498 (1994-08-01), Toy et al.
patent: 5425057 (1995-06-01), Paff
patent: 5504785 (1996-04-01), Becker et al.
Bocure Tesfaldet
Toyo Communication Equipment Co., Ltd.
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