Radio Communication Device, Demodulation Method, and Frequency Deflection Correction Circuit

• US 20080279172A1
• Filed: 05/17/2004
• Published: 11/13/2008
• Est. Priority Date: 05/17/2004
• Status: Active Grant

• Current Assignee: Rakuten Group, Inc.
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: Suemitsu, Taisei
• Granted Patent: US 8,018,914 B2
• Time in Patent Office: Days
• US Class Current: 370/347
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657
• CPC Class Codes: H04L 27/2271 wherein the carrier recovery circuit uses only the demodulated signals

Abstract

A demodulation section 13 receives a TDMA-TDD based phase-modulated burst signal of mobile communications and demodulates the burst signal by a synchronous detection system (or a quasi-synchronous detection system). The demodulation section 13 includes a frequency deviation compensation section and a carrier recovery section each having a loop filter 14 with three or more stages of time constants. The time constants are switched by a selector switch 15 based on a control signal from a demodulation control section 16. This achieves quick pull-in and jitter after convergence is minimized, thereby allowing highly efficient performance of frequency deviation compensation, etc. that is required for synchronous detection (or quasi-synchronous detection) without increasing the size of circuit.

Claims

1. A radio communication apparatus comprising:

a demodulation section that receives a phase-modulated burst signal, and demodulates the burst signal using one of a synchronous detection system and a quasi-synchronous detection system; and

a demodulation control section that generates a control signal to control demodulation of the burst signal in the demodulation section based on a reception state of the burst signal at the demodulation section,

wherein the demodulation section includes,

a filter that filters a signal based on the burst signal using a set time constant, and

a time constant switching section that switches a time constant of the filter by the control signal based on a number of burst signals received.

2. The radio communication apparatus of claim 1, wherein the filter is a loop filter in a frequency deviation compensation section that compensates deviation of a frequency of the burst signal.

3. The radio communication apparatus of claim 1, wherein the filter is a loop filer in a carrier recovery section that recovers a carrier wave of the burst signal.

4. The radio communication apparatus of claim 1, wherein the filter is a loop filer in a bit timing recovery section that recovers bit timing of the burst signal.

5. The radio communication apparatus of claim 1, wherein the filter is a loop filer in a reception level conversion section that converts a reception level of the burst signal.

6. The radio communication apparatus of claim 1, wherein the demodulation section demodulates a digitally phase-modulated burst signal by a Time Division Multiple Access system.

7. The radio communication apparatus of claim 1, wherein the demodulation control section detects the reception state of the burst signal at the demodulation section to determine one of three states, a synchronous state, an asynchronous state, and an intermediate state between the synchronous state and the asynchronous state, and outputs the control signal indicating a detected reception state, and

wherein the switching section includes a time constant having a large value for the synchronous state, a time constant having an intermediate value for the intermediate state, and a time constant having a small value for the asynchronous state, and switches the time constants according to the reception state indicated by the control signal.

8. The radio communication apparatus of claim 7, wherein the demodulation control section determines as the intermediate state a reception state of a predetermined number of frames or slots of the burst signal at the demodulation section in transition from the asynchronous state to the synchronous state.

9. The radio communication apparatus of claim 7, wherein the demodulation control section determines as the intermediate state a reception state of a predetermined number of frames or slots of the burst signal at the demodulation section in transition from the synchronous state to the asynchronous state.

10. The radio communication apparatus of claim 1, wherein the demodulation control section detects the reception state of the burst signal at the demodulation section by a signal-to-noise ratio, and outputs the control signal indicating a detected reception state, and

wherein the switching section switches the time constants according to the reception state indicated by the control signal.

11. A modulation method in a radio communication apparatus including a demodulation section that receives a burst signal and demodulates the signal by a synchronous detection system using a filter, and a demodulation control section that controls the demodulation section, the method comprising:

the demodulation section;

receiving a digitally phase-modulated burst signal by a time division multiple access system;

the demodulation control section;

generating a control signal to control a time constant of the filter in the demodulation section based on a reception state of the burst signal at the demodulation section; and

the demodulation section;

switching the time constant of the filter based on the control signal and filtering a signal based on the burst signal.

12. The demodulation method of claim 11 comprising:

the demodulation control section;

detecting the reception state of the burst signal at the demodulation section to determine one of three states, a synchronous state, an asynchronous state, and an intermediate state between the synchronous state and the asynchronous state;

outputting the control signal indicating a detected reception state, and

the demodulation section;

switching time constants according to the reception state indicated by the control signal among a time constant having a large value for the synchronous state, a time constant having an intermediate value for the intermediate state, and a time constant having a small value for the asynchronous state.

13. The demodulation method of claim 12 comprising:

determining the reception state of the burst signal at the demodulation section as an intermediate state in transition from the asynchronous state to the synchronous state; and

determining the reception state of the burst signal at the demodulation section as an intermediate state in transition from the synchronous state to the asynchronous state.

14. A frequency deviation compensation circuit comprising:

a multiplier that receives phase information and amplitude information of a burst signal, multiplies the phase information by the amplitude information, and generates a complex signal;

a delayed detection circuit that processes by delayed detection the complex signal generated by the multiplier and obtains phase difference information;

an angle information extraction circuit that extracts angle information from the phase difference information obtained in the delayed detection circuit;

a subtractor that subtracts an amount of angle of frequency deviation from the angle information obtained in the angle information extraction circuit;

a modulated component removal circuit that obtains a difference of the angle information subtracted in the subtractor from a point at an angle of 45 degrees from both an I-axis and a Q-axis on an IQ plane, and outputs an amount of angular deviation so that the difference in angle becomes an amount of variation from the I-axis;

a limiter circuit that limits an excess amount of deviation when the amount of angular deviation from the modulated component removal circuit exceeds an acceptable amount of deviation;

a selector switch that selects one of a plurality of time constants;

a multiplier that multiplies the amount of angular deviation outputted from the limiter circuit by a selected time constant by the selector switch;

a first integrator that adds an amount of angular deviation multiplied by the time constant by the multiplier, and outputs a result as the amount of angle of frequency deviation;

a second integrator that adds the amount of angle of frequency deviation obtained at the first integrator, thereby restoring a phase difference obtained by the delayed detection circuit;

an angular information-complex information conversion circuit that converts angle information obtained at the second integrator to a complex signal; and

a frequency deviation compensator that multiplies complex data obtained at the multiplier by the complex signal of the angle information obtained at the angle information-complex information conversion circuit so as to eliminate deviation of a phase angle.