What is claimed is:
1. A demodulation method for demodulating a transmission signal having a guard interval and a data interval, comprising the steps of:
receiving said transmission signal;
delaying said received signal by said data interval;
calculating difference between said received signal and said delayed signal;
detecting a reference position of said guard interval based upon the result of the calculation of said difference; and
demodulating said received signal based upon said reference position of said guard interval.
2. A demodulation method according to claim 1, wherein:
said transmission signal is a repetition signal of a symbol including said guard interval and said data interval; and
the step for detecting said reference position of said guard interval comprises the steps of generating a predetermined threshold and generating a reference signal corresponding to a starting point of the incorporation of data to be demodulated based upon the result of the calculation of said difference and said predetermined threshold.
3. A demodulation method according to claim 2, further comprising the step of setting a type of the modulation of said transmission signal, wherein:
said predetermined threshold is controlled based upon said modulation type.
4. A demodulation method according to claim 3, wherein said predetermined threshold is set to a value according to at least either one of modulation technique and an error correction method used for said transmission signal.
5. A demodulation method according to claim 2, wherein said predetermined threshold is set to a value calculated based upon the received signal.
6. A demodulation method according to claim 2, wherein the step of demodulating said received signal is provided with an FFT calculation window for incorporating said received signal in a predetermined interval, and the position of said FFT calculation window is controlled based upon said reference position of said guard interval.
7. A demodulation method according to claim 6, wherein:
said transmission signal includes a main wave and a reflection wave; and
if said reference position of said FFT calculation window detected in the preceding symbol is W, the quantity of displacement between the reference position W and a reference position of the main wave detected in a current symbol is m, the detection frequency of reflection waves is n and a constant of the control of the position of said FFT calculation window is K, the position of said FFT calculation window is so controlled that the reference position W of the current symbol is Wm when the main wave is detected and the position of said FFT calculation window is so controlled that said reference position W of said current symbol is WnK when the reflection wave is detected.
8. A demodulation method according to claim 1, wherein said transmission signal is an OFDM modulated signal.
9. A receiving apparatus for receiving a transmission signal having a guard interval and a data interval, comprising:
a receiving unit for receiving said transmission signal;
a delay unit for delaying said transmission signal from said receiving unit by the data interval;
a differential value calculating unit for calculating difference between said transmission signals from said receiving unit and said delay unit;
a guard interval reference position detecting unit for detecting a reference position of said guard interval based upon the result of the calculation of said difference; and
a demodulating unit for demodulating said transmission signal based upon said reference position of said guard interval.
10. A receiving apparatus according to claim 9, wherein:
said transmission signal is a repetition signal of a symbol including said guard interval and said data interval; and
said guard interval reference position detecting unit comprises a threshold generator for generating a predetermined threshold and a reference signal generator for generating a reference signal corresponding to a starting point of the incorporation of data to be demodulated based upon the result of the calculation of said difference and said predetermined threshold.
11. A receiving apparatus according to claim 10, further comprising:
a type setting unit for setting a type of the modulation of said transmission signal, wherein:
said predetermined threshold is controlled based upon the output of said type setting unit.
12. A receiving apparatus according to claim 11, wherein:
the output of said type setting unit is output according to at least either one of modulation technique and an error correction method used for the transmission signal.
13. A receiving apparatus according to claim 10, wherein:
said threshold generator receives said transmission signal and generates a threshold calculated based upon said transmission signal.
14. A receiving apparatus according to claim 10, wherein:
said demodulating unit includes an FFT calculation window generator for incorporating said transmission signal in a predetermined interval and controls a position of an FFT calculation window generated by said FFT calculation window generator based upon said reference position of said guard interval.
15. A receiving apparatus according to claim 14, wherein:
said transmission signal includes a main wave and a reflection wave; and
said FFT calculation window generator is so designed that if said reference position of said FFT calculation window detected in the preceding symbol is W, the quantity of displacement between said reference position W and a reference position of said main wave detected in a current symbol is m, the detection frequency of reflection waves is n and a constant of the control of the position of said FFT calculation window is K, the position of said FFT window is so controlled that said reference position W of said current symbol is Wm when the main wave is detected and the position of said FFT window is so controlled that the reference position W of the current symbol is WnK when said reflection wave is detected.
16. A receiving apparatus according to claim 9, wherein:
said tranmission signal is an OFDM modulated signal.
17. A signal transmission system having a transmitting apparatus and a receiving apparatus, wherein:
said transmitting apparatus for transmitting a transmission signal being a repetition signal of a guard interval and a data interval comprises:
a modulating unit for modulating said transmission signal according to predetermined modulation technique;
a guard interval inserting unit for inserting said guard interval into a modulated signal from said modulating unit and generating said transmission signal made by the repetition of the guard interval and said data interval; and
an antenna for transmitting the output of said guard interval inserting unit; and
said receiving apparatus comprises:
a receiving unit for receiving said transmission signal;
a delay unit for delaying said transmission signal from said receiving unit by said data interval;
a differential value calculating unit for calculating difference between signals from said receiving unit and said delay unit;
a guard interval reference position detecting unit for detecting a reference position of said guard interval based upon the result of the calculation of said difference; and
a demodulating unit for demodulating said transmission signal based upon said reference position of said guard interval.
18. A signal transmission system according to claim 17, wherein:
said guard interval reference position detecting unit comprises a threshold generator for generating a predetermined threshold and a reference signal generator for generating a reference signal corresponding to the boundary between symbols based upon the result of the calculation of said difference and said predetermined threshold.
19. A signal transmission system according to claim 18, further comprising:
a type setting unit for setting a type of the modulation of said transmission signal, wherein:
said threshold is controlled based upon the output of said type setting unit.
20. A signal transmission system according to claim 19, wherein:
the output of said type setting unit is output according to at least either one of modulation technique and an error correction method used for the transmission signal.
21. A signal transmission system according to claim 18, wherein:
said threshold generator receives said transmission signal and generates a threshold calculated based upon said transmission signal.
22. A signal transmission system according to claim 18, wherein:
said demodulating unit comprises an FFT calculation window generator for incorporating said transmission signal in a predetermined interval and controls a position of a FFT calculation window generated by the FFT calculation window generator based upon said reference position of said guard interval.
23. A signal transmission system according to claim 17, wherein:
said transmission signal is an OFDM modulated signal.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A system for inspecting a workpiece, comprising:
an ultrasonic inspection system comprising an ultrasonic transducer that directs sound waves to the workpiece, wherein the sound waves contact the workpiece surface at a first workpiece surface location; and
a laser pointer connected to the ultrasonic inspection system, wherein the laser pointer directs a laser beam against the workpiece surface to visually annunciate the first workpiece surface location;
wherein the laser beam is one of a plurality of laser beams directed from the laser pointer against the workpiece surface by the laser pointer, wherein each laser beam contacts the workpiece surface at a respective second workpiece surface location, and wherein the first workpiece surface location is centered between the second workpiece surface locations.
2. The system of claim 1, wherein the laser pointer comprises a water-resistant laser pointer.
3. The system of claim 1, wherein the laser pointer comprises a laser pointer housing mounted to the ultrasonic transducer.
4. The system of claim 3, wherein the laser pointer further comprises a plurality of lasers connected to the laser pointer housing, and arranged circumferentially around the ultrasonic transducer.
5. The system of claim 1, wherein the ultrasonic transducer is connected to a manipulator system.
6. The system of claim 5, wherein the manipulator comprises a robotic multi-axis manipulator system.
7. A system for non-contact inspecting a workpiece that includes a workpiece surface, comprising:
a manipulator system;
an ultrasonic inspection system comprising an ultrasonic transducer that is connected to the manipulator system, that directs sound waves into the workpiece, and that senses reflected sound waves to detect a workpiece defect, wherein the sound waves intersect the workpiece surface at a first workpiece surface location; and
a laser pointer connected to the ultrasonic transducer, wherein the laser pointer directs a laser beam against the workpiece surface to visually mark the first workpiece surface location associated with and indicative of the workpiece defect;
wherein the laser beam is one of a plurality of laser beams directed against the workpiece surface by the laser pointer, wherein each laser beam contacts the workpiece surface at a respective second workpiece surface location, and wherein the first workpiece surface location is located between the second workpiece surface locations.
8. The system of claim 7, wherein the laser pointer comprises a water-resistant laser pointer.
9. The system of claim 7, wherein the laser pointer comprises a plurality of lasers connected to a laser pointer housing, and arranged circumferentially around the ultrasonic transducer.
10. The system of claim 7, wherein the manipulator system comprises a robotic multi-axis manipulator.