OFDM transmitting/receiving device and method

• US 6,345,036 B1
• Filed: 06/29/2000
• Issued: 02/05/2002
• Est. Priority Date: 11/06/1998
• Status: Expired due to Term

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Sudo, Hiroaki, Ishikawa, Kimihiko
• Primary Examiner(s): Hsu, Alpus H.
• Assistant Examiner(s): Qureshi, Afsar M.
• Application Number:
  US09/582,613
• Time in Patent Office: 586 Days
• Field of Search: 375/222, 375/260, 375/261, 375/262, 375/263, 375/264, 375/265, 375/285, 375/346, 375/348, 375/349, 375/266, 375/267, 375/268, 375/269, 370/203, 370/209, 370/210, 370/213, 370/480, 370/481, 370/485, 370/419, 455/63, 455/522
• US Class Current: 370/203
• CPC Class Codes: H04L 27/2614 Peak power aspects
• CPC Class Codes: H04L 27/2637 with direct modulation of individual subcarriers
• CPC Class Codes: H04L 27/2646 using feedback from receiver for adjusting OFDM transmission parameters, e.g. transmission timing or guard interval length
• CPC Class Codes: H04L 27/2653 with direct demodulation of individual subcarriers
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0046 Determination of how many bits are transmitted on different sub-channels
• CPC Class Codes: H04W 52/346 distributing total power among users or channels
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

An average value of reception power of subcarriers A to D is calculated by a control circuit 162, and the average value is divided by envelops of received signals of subcarriers A to D, respectively, so as to calculate a coefficient signal of each subcarrier. Multipliers 106 to 109 multiply transmitting signals of subcarriers A to D output from mapping circuits 102 to 105 by the coefficient signals, respectively. Whereby, power between the subcarriers at a reception time can be maintained substantially constant so as to improve an error rate characteristic.

Claims

1. An OFDM transmitting and receiving apparatus comprising:

coefficient calculating means for calculating a coefficient for each subcarrier based on reception power of the received signals from a partner station of each subcarrier;

a plurality of weighting means for multiplying a transmitting signal to said partner station of each subcarrier by said coefficient to perform weighting; and

information selecting means for outputting the received signal only when important information is transmitted, wherein said coefficient calculating means calculates the coefficient only when the received signal is input from said information selecting means.

2. An OFDM transmitting and receiving apparatus comprising:

coefficient calculating means for calculating a coefficient for each subcarrier based on reception power of the received signals from a partner station of each subcarrier;

a plurality of weighting means for multiplying a transmitting signal to said partner station of each subcarrier by said coefficient to perform weighting; and

second symbol selecting means for outputting only a pilot symbol of the received signal to said coefficient calculating means, wherein said coefficient calculating means calculates a coefficient based on power of the pilot symbol of the received signal.

3. An OFDM transmitting and receiving apparatus comprising:

coefficient calculating means for calculating a coefficient for each subcarrier based on reception power of the received signals from a partner station of each subcarrier;

a plurality of weighting means for multiplying a transmitting signal to said partner station of each subcarrier by said coefficient to perform weighting; and

fourth determining means for determining whether or not the link quality is larger than a second threshold value preset every user, wherein said coefficient calculating means calculates a coefficient with respect to only the weighting means corresponding to the user in which the link quality is larger than the second threshold value based on a determination result of said fourth determining means.

4. The OFDM transmitting and receiving apparatus according to claim 3, further comprising third averaging means for averaging the link quality every user, wherein said fourth determining means determines whether or not the average value of the link quality is larger than the second threshold value every user.

5. The OFDM transmitting and receiving apparatus according to claim 3, wherein said fourth determining means determines whether or not the link quality is smaller than a third threshold value preset every user, and said coefficient calculating means calculates a coefficient with respect to only the weighting means corresponding to the user in which the link quality is larger than the second threshold value and smaller than the third threshold value.

6. The OFDM transmitting and receiving apparatus according to claim 3, further comprising error detecting means for providing error detection to a demodulation signal;

and fifth determining means for determining whether or not the number of error bits detected by said error detecting means for a predetermined period is smaller than a fourth threshold value preset every user, wherein said coefficient calculating means determines weighting means for calculating a coefficient based on the determination result of said fourth determining means only when said fifth determining means determines that the number of error bits is smaller than the fourth threshold value.

7. An OFDM transmitting and receiving apparatus comprising:

coefficient calculating means for calculating a coefficient for each subcarrier based on reception power of the received signals from a partner station of each subcarrier;

a plurality of weighting means for multiplying a transmitting signal to said partner station of each subcarrier by said coefficient to perform weighting; and

sixth determining means for determining whether or not a link variation value is smaller than a fifth threshold value preset every subcarrier, wherein said coefficient calculating means outputs the calculated coefficient to only the weighting means corresponding to the subcarrier in which a difference in coefficient between this time and previous time is smaller than a fifth threshold value based on a determination result of said sixth determining means.

8. An OFDM transmitting and receiving apparatus comprising:

coefficient calculating means for calculating a coefficient for each subcarrier based on reception power of the received signals from a partner station of each subcarrier;

a plurality of weighting means for multiplying a transmitting signal to said partner station of each subcarrier by said coefficient to perform weighting; and

branch selecting means for selecting a branch whose reception power is large as a transmission branch every subcarrier, wherein a diversity function is provided.

9. The OFDM transmitting and receiving apparatus according to claim 8, further comprising seventh determining means for determining whether or not the number of subcarriers transmitted from one branch is smaller than a sixth threshold value preset, wherein said coefficient calculating means outputs a calculated coefficient to the weighting means only when the number of subcarriers is smaller than the sixth threshold value based on a determination result of said seventh determining means.

10. The OFDM transmitting and receiving apparatus according to claim 8, further comprising upper limit value setting means for setting an upper limit value to be high when the number of subcarriers transmitted from one branch is small, and for setting the upper limit value to be low when the number of subcarriers transmitted from one branch is large, and ninth determining means for determining whether or not the coefficient is smaller than the upper limit value set by said upper limit setting means every subcarrier, wherein said coefficient calculating means outputs the upper limit value to the weighting means corresponding to the subcarrier in which the coefficient exceeds the upper limit value.

11. The OFDM transmitting and receiving apparatus according to claim 8, further comprising combining means for combining reception power of the respective branches every subcarrier.

12. The OFDM transmitting and receiving apparatus according to claim 11, wherein said combining means maximal-ratio combines reception power of the respective branches every subcarrier.

13. An OFDM transmitting and receiving method wherein an average value of reception power of each subcarrier is calculated, and said average value is multiplied by reception power of each subcarrier to calculate a coefficient.