OFDM receiving method and apparatus

• US 7,672,382 B2
• Filed: 04/09/2002
• Issued: 03/02/2010
• Est. Priority Date: 09/14/2001
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Tanaka, Yoshinori, Yoshida, Makoto
• Primary Examiner(s): Ghayour; Mohammad H
• Assistant Examiner(s): Malek; Leila
• Application Number:
  US10/118,710
• Publication Number:
  US 20030053412A1
• Time in Patent Office: 2,884 Days
• Field of Search: 375/260, 375/316, 370/208, 370/210, 370/343, 343/876, 455/10, 455/504, 455/506
• US Class Current: 375/260
• CPC Class Codes: H04B 17/3911 Fading models or fading generators
• CPC Class Codes: H04B 7/0814 based on current reception conditions, e.g. switching to different antenna when signal level is below threshold
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04B 7/088 using beam selection
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

In order to improve upon a degradation in performances due to inter-carrier interference without loss of transmission efficiency, antennas provided on a mobile body are made directional antennas. An antenna selection unit selects a directional antenna in such a manner that Doppler shift that is caused by movement of the mobile body will keep a constant sign that is positive or negative, a fading-variation calculation unit calculates the average value of fading variation on each path of a multipath environment, and a fading-variation compensation unit compensates the multipath fading variation based upon the average value.

Claims

1. An OFDM receiving method for receiving a signal multiplexed according to Orthogonal Frequency Division Multiplexing (OFDM) and applying Fast Frequency Transform (FFT) processing to the received signal to demodulate transmit data, comprising the steps of:

providing a mobile body with a plurality of directional antennas having directivities that differ from one another and include a directivity in a direction of moving or in a direction opposite the direction of moving;

selecting a directional antenna in such a manner that Doppler shift that is caused by movement of the mobile body will keep a constant sign that is positive or negative;

calculating, prior to FFT processing, an average value of fading-variation in a multipath environment using a received signal from the antenna that has been selected; and

compensating the fading-variation based upon the average value, wherein the average value is attenuated and fading-variation in the multipath environment is compensated based upon a value obtained by attenuation.

2. An OFDM receiving method for receiving a signal multiplexed according to Orthogonal Frequency Division Multiplexing (OFDM) and applying Fast Frequency Transform (FFT) processing to the received signal to demodulate transmit data, comprising the steps of:

providing a mobile body with a plurality of directional antennas having directivities that differ from one another and include a directivity in a direction of moving or in a direction opposite the direction of moving;

selecting a directional antenna in such a manner that Doppler shift that is caused by movement of the mobile body will keep a constant sign that is positive or negative;

calculating, prior to FFT processing, an average value of fading-variation in a multipath environment using a received signal from the antenna that has been selected;

compensating the fading-variation based upon the average value;

combining received signals from each of the directional antennas and halting compensation of fading when the mobile body is moving at a velocity lower than a threshold velocity; and

selecting a directional antenna, and performing the fading compensation, based upon reception power and/or Doppler spread when the mobile body is moving at a velocity equal to or greater than the threshold velocity.

3. An OFDM receiving apparatus for receiving a signal multiplexed according to Orthogonal Frequency Division Multiplexing (OFDM) and applying Fast Frequency Transform (FFT) processing to the received signal to demodulate transmit data, comprising:

a plurality of directional antennas having directivities that differ from one another and include a directivity in a direction of moving or in a direction opposite the direction of moving, provided on a mobile body;

a directional antenna selecting unit for selecting a directional antenna in such a manner that Doppler shift that is caused by movement of the mobile body will keep a constant sign that is positive or negative;

a fading-variation calculation unit for calculating, prior to FFT processing, an average value of fading-variation in a multipath environment using a received signal from the antenna that has been selected;

a fading-variation compensation unit for compensating the fading-variation based upon the average value;

an FFT unit for applying FFT processing to a signal obtained by the fading compensation; and

an attenuator for attenuating the average value by multiplying the average value by a weighting coefficient;

wherein fading-variation in the multipath environment is compensated based upon the average value that has been attenuated.

4. An OFDM receiving apparatus for receiving a signal multiplexed according to Orthogonal Frequency Division Multiplexing (OFDM) and applying Fast Frequency Transform (FFT) processing to the received signal to demodulate transmit data, comprising:

a plurality of directional antennas having directivities that differ from one another and include a directivity in a direction of moving or in a direction opposite the direction of moving, provided on a mobile body;

a directional antenna selecting unit for selecting a directional antenna in such a manner that Doppler shift that is caused by movement of the mobile body will keep a constant sign that is positive or negative;

a fading-variation calculation unit for calculating, prior to FFT processing, an average value of fading-variation in a multipath environment using a received signal from the antenna that has been selected;

a fading-variation compensation unit for compensating the fading-variation based upon the average value;

an FFT unit for applying FFT processing to a signal obtained by the fading compensation; and

a reception-power measurement unit for measuring reception signal power of the directional antennas;

wherein said directional antenna selecting unit selects a directional antenna for which Doppler spread is minimum from among directional antennas for which reception power exceeds a threshold value of power, and

wherein the directional antenna for which the Doppler spread is minimum is an antenna whose directivity coincides with a direction of moving of the mobile body.

5. An OFDM receiving apparatus for receiving a signal multiplexed according to Orthogonal Frequency Division Multiplexing (OFDM) and applying Fast Frequency Transform (FFT) processing to the received signal to demodulate transmit data, comprising:

a plurality of directional antennas having directivities that differ from one another and include a directivity in a direction of moving or in a direction opposite the direction of moving, provided on a mobile body;

a directional antenna selecting unit for selecting a directional antenna in such a manner that Doppler shift that is caused by movement of the mobile body will keep a constant sign that is positive or negative;

a fading-variation calculation unit for calculating, prior to FFT processing, an average value of fading-variation in a multipath environment using a received signal from the antenna that has been selected;

a fading-variation compensation unit for compensating the fading-variation based upon the average value;

an FFT unit for applying FFT processing to a signal obtained by the fading compensation; and

a velocity comparator for comparing velocity of the mobile state and a set velocity;

wherein said directional antenna selecting unit combines received signals from each of the directional antennas when the mobile body is moving at a velocity lower than the threshold velocity, and selects a directional antenna based upon reception power and/or Doppler spread when the mobile body is moving at a velocity equal to or greater than the threshold velocity;

wherein said fading-variation calculation unit halts fading compensation when the mobile body is moving at a velocity lower than the threshold velocity, and performs the fading compensation when the mobile body is moving at a velocity equal to or greater than the threshold velocity.

6. An OFDM receiving method for receiving a signal multiplexed according to Orthogonal Frequency Division Multiplexing (OFDM) and applying Fast Frequency Transform (FFT) processing to the received signal to demodulate transmit data, comprising the steps of:

providing a mobile body with a plurality of directional antennas having directivities that differ form one another and include directivity in a direction of moving or in a direction opposite the direction of moving;

selecting a directional antenna for which reception power is maximum;

in a case where the selected antenna has a directivity in a direction of moving or in a direction opposite the direction of moving, calculating, prior to FFT processing, an average value of fading variation in a multipath environment using a signal received by said selected antenna and compensating the fading variation based upon the average value; and

in a case where the selected antenna does not have a directivity in a direction of moving or in a direction opposite the direction of moving, performing the FFT processing without the compensation processing of the fading variation.

7. An OFDM receiving apparatus for receiving a signal multiplexed according to Orthogonal Frequency Division Multiplexing (OFDM) and applying Fast Frequency Transform (FFT) processing to the received signal to demodulate transmit date, comprising:

a plurality of directional antennas having directivities that differ from one another and include directivity in a direction of moving or in a direction opposite the direction of moving;

an antenna selecting unit for selecting a directional antenna for which reception power is maximum;

a fading-variation calculation unit for calculating, prior to FFT processing, an average value of fading variation in a multipath environment using a signal received by said selected directional antenna;

a fading-variation compensation unit for compensating the fading variation based upon the average value;

an FFT unit for applying FFT processing to a signal obtained by the fading compensation; and

a control unit for deciding whether the fading compensation needs to be performed or not based upon the fact that said selected antenna has a directivity in a direction of moving or in a direction opposite the direction of moving,

wherein in a case where said selected antenna has a directivity in a direction of moving or in a direction opposite the direction of moving, the control unit controls the fading-variation calculation unit and fading-variation compensation unit to perform the fading compensation and in a case where said selected antenna does not have a directivity in a direction of moving or in a direction opposite the direction of moving, the control unit controls the fading-variation calculation unit and fading-variation compensation unit not to perform the fading compensation.