Pulse or digital communications – Receivers – Angle modulation
Patent
1995-12-07
1998-03-24
Vo, Don N.
Pulse or digital communications
Receivers
Angle modulation
375373, 375375, 327 7, 327163, 327236, 327244, 331 25, H04L 2714, H04L 2716
Patent
active
057321094
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a phase detection apparatus used to detect the phase of a received signal in a carrier wave reproduction circuit for synchronous detection, a phase detection circuit, or a frequency detection circuit provided in, e.g., a digital mobile radio communication apparatus or a satellite communication apparatus.
BACKGROUND ART
Recently, with the development of semiconductor technologies, particularly digital IC technologies, a digital demodulation circuit is in many instances realized by a digital signal processing circuit in a radio communication apparatus for use in a digital cellular radio communication system or a satellite communication system. In a digital demodulation circuit of this type, a quadrature detector detects, e.g., a received radio signal and converts the signal into a complex baseband signal. An A/D converter converts this complex baseband signal into a digital complex baseband signal. A digital signal processing circuit performs synchronous detection, phase detection, or frequency detection for this digital complex baseband signal.
To realize the digital demodulation function as described above, it is necessary to detect the phase from the received complex baseband signal. The following various apparatuses have been developed as conventional phase detection apparatuses for performing this phase detection.
(1) A phase is the arc tangent (tan.sup.-1 (Q/I)) of a real-part component I and an imaginary-part component Q of a digital complex baseband signal. Accordingly, calculate the arc tangents of combinations of various I and Q values in advance, and prepare a table in a ROM. Input I and Q as addresses to the ROM, and output a phase corresponding to these input addresses from the table.
(2) Instead of calculating arc tangents in advance, calculate them by means of series expansion.
(3) Regard the value of the imaginary-part component Q as a phase.
(4) Calculate Q.times.sign(I), and regard the calculated value as a phase. Note that sign(X) is +1 when the sign of X is positive, and -1 when the sign is negative.
(5) Calculate Q.times.sign(I)-I.times.sign(Q), and regard the calculated value as a phase.
These conventional phase detection apparatuses have the following problems.
That is, system (1) using a table ROM requires a large-capacity ROM. This increases the circuit scale of the apparatus, leading to the difficulty in decreasing the size and weight of the apparatus. This degrades the portability of mobile communication apparatuses such as portable telephone sets whose most important objectives are a small size and a light weight. Therefore, system (1) is very undesirable in these apparatuses.
In system (2), calculations must be repetitively done a large number of times. Since this prolongs the calculation time, system (2) is unsuitable for real-time processing of communication apparatuses.
Systems (3) to (5) have the advantage that only relatively simple calculations need to be performed in these systems. However, these systems can detect only the polarity of the phase or the magnitude of the signal level, i.e., cannot detect the phase itself. In particular, because of variations in the calculation results these systems cannot calculate an accurate phase from a signal, such as a received signal modulated by a .pi./4 shift DQPSK system, which changes its amplitude level in accordance with the phase position.
The present invention has been made in consideration of the above situation and has its object to provide a phase detection apparatus which requires no large-capacity memory and can calculate an accurate phase, within a practical calculation time, independently of the amplitude value of an input signal.
It is another object of the present invention to provide a phase detection apparatus suited for use in mobile communication apparatuses.
DISCLOSURE OF INVENTION
To achieve the above objects, a phase detection apparatus of the present invention comprises phase rotating means for rotating a phase of an input signal point, rotational angle se
REFERENCES:
patent: 4253184 (1981-02-01), Gitlin et al.
patent: 4599732 (1986-07-01), LeFever
patent: 5109394 (1992-04-01), Hjerpe et al.
patent: 5315618 (1994-05-01), Yoshida
patent: 5386239 (1995-01-01), Wang et al.
patent: 5400366 (1995-03-01), Iwamatsu
patent: 5491729 (1996-02-01), Co et al.
Kabushiki Kaisha Toshiba
Vo Don N.
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