APPARATUS AND METHOD FOR TRANSMITTING OFDMA SYMBOLS

• US 20080117872A1
• Filed: 11/15/2007
• Published: 05/22/2008
• Est. Priority Date: 11/16/2006
• Status: Active Grant

• Current Assignee: LG-Ericsson Company Limited (Telefonaktiebolaget LM Ericsson)
• Original Assignee: LG-Ericsson Company Limited (Telefonaktiebolaget LM Ericsson)
• Inventors: Kang, Hyoung Chang, You, Kyoung Bong, KIM, Jong Kuk
• Granted Patent: US 8,027,294 B2
• Time in Patent Office: Days
• US Class Current: 370/329
• CPC Class Codes: H04L 25/03012 operating in the time domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 25/03834 using pulse shaping
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/2626 Arrangements specific to the transmitter only
• CPC Class Codes: H04L 27/26265 Arrangements for sidelobes suppression specially adapted to multicarrier systems, e.g. spectral precoding

Abstract

Embodiments of the present invention may provide an apparatus and a method for transmitting an orthogonal frequency division multiplexing access (OFDMA) symbol in an OFDMA system. A bandwidth limit parameter for generating an OFDMA symbol may be adaptively determined based on the received signal quality of a receiver. An OFDMA symbol may be generated based on the bandwidth limit parameter and transmitted to the receiver. According to embodiments, when the received signal quality of the receiver is bad, the bandwidth limit parameter may be first adjusted before the modulation scheme is changed to have a lower data rate. In such a case, the downlink date rate may be maintained with enhancing the received signal quality of the receiver.

Claims

1. An apparatus for transmitting an orthogonal frequency division multiplexing access (OFDMA) symbol in an OFDMA system, comprising:

a transceiver to monitor the received signal quality of a receiver; and

a controller to adaptively determine a bandwidth limit parameter based on the received signal quality;

wherein a transceiver generates an OFDMA symbol based on the bandwidth limit parameter to transmit to the receiver.

2. The apparatus of claim 1, wherein the controller determines the bandwidth limit parameter as a value to limit bandwidth more as the received signal quality is better and determines the bandwidth limit parameter as a value to limit the bandwidth less as the received signal quality is worse.

3. The apparatus of claim 1, wherein the controller determines a modulation scheme including a high data rate as the received signal quality is better and determines a modulation scheme including a low data rate as the received signal quality is worse for modulating the OFDMA symbol, and wherein the transceiver generates the OFDMA symbol based on the modulation scheme and the bandwidth limit parameter.

4. The apparatus of claim 3, wherein the controller determines whether a value to limit bandwidth less than previous bandwidth limit parameter violates bandwidth limit requirements for the OFDMA system when the current received signal quality is worse than the previous received signal quality, and

if the value to limit bandwidth less does not violate the bandwidth limit requirements, the controller determines the bandwidth limit parameter as the value to limit bandwidth less, and

if the value to limit bandwidth less violates the bandwidth limit requirements, the controller determines a modulation scheme including a low data rate and determines the bandwidth limit parameter based on the modulation scheme including the low data rate, and

the controller determines whether a value to limit bandwidth more than the previous bandwidth limit parameter violates the bandwidth limit requirements for the OFDMA system when the current received signal quality is better than the previous received signal quality, and

if the value to limit bandwidth more does not violate the bandwidth limit requirements, the controller determines the bandwidth limit parameter as the value to limit bandwidth more, and

if the value to limit bandwidth more violates the bandwidth limit requirements, the controller determines a modulation scheme including a high data rate and determines the bandwidth limit parameter based on the modulation scheme including the high data rate.

5. The apparatus of claim 4, wherein the bandwidth limit requirements have a bandwidth limit parameter such that the window is rectangular-shaped in time domain as a lower limit, and a maximal bandwidth limit parameter such that curved portion of the window is not overlapped with the OFDMA symbol in frequency domain as an upper limit.

6. The apparatus of claim 2, wherein the controller determines a modulation scheme including a high data rate as the received signal quality is better and determines a modulation scheme including a low data rate as the received signal quality is worse for modulating the OFDMA symbol, and wherein the transceiver generates the OFDMA symbol based on the modulation scheme and the bandwidth limit parameter.

7. The apparatus of claim 6, wherein the controller determines whether a value to limit bandwidth less than previous bandwidth limit parameter violates bandwidth limit requirements for the OFDMA system when the current received signal quality is worse than the previous received signal quality, and

if the value to limit bandwidth less does not violate the bandwidth limit requirements, the controller determines the bandwidth limit parameter as the value to limit bandwidth less, and

if the value to limit bandwidth less violates the bandwidth limit requirements, the controller determines a modulation scheme including a low data rate and determines the bandwidth limit parameter based on the modulation scheme including the low data rate, and

the controller determines whether a value to limit bandwidth more than the previous bandwidth limit parameter violates the bandwidth limit requirements for the OFDMA system when the current received signal quality is better than the previous received signal quality, and

if the value to limit bandwidth more does not violate the bandwidth limit requirements, the controller determines the bandwidth limit parameter as the value to limit bandwidth more, and

if the value to limit bandwidth more violates the bandwidth limit requirements, the controller determines a modulation scheme including a high data rate and determines the bandwidth limit parameter based on the modulation scheme including the high data rate.

8. The apparatus of claim 7, wherein the bandwidth limit requirements have a bandwidth limit parameter such that the window is rectangular-shaped in time domain as a lower limit, and a maximal bandwidth limit parameter such that curved portion of the window is not overlapped with the OFDMA symbol in frequency domain as an upper limit.

9. The apparatus of claim 1, wherein the OFDMA system is an wireless broadband (WiBro) system, and

the apparatus is located in a radio access system (RAS) for the WiBro system, and

the receiver is a mobile station or a base station for the WiBro system.

10. The apparatus of claim 1, wherein the controller determines the bandwidth limit parameter in response to receiving an automatic repeat request (ARQ) signal from the receiver at the transceiver.

11. A method of transmitting an orthogonal frequency division multiplexing access (OFDMA) symbol in an OFDMA system, comprising:

monitoring the received signal quality of a receiver;

determining a bandwidth limit parameter adaptively based on the received signal quality; and

generating an OFDMA symbol based on the bandwidth limit parameter to transmit to the receiver.

12. The method of claim 11, wherein determining the bandwidth limit parameter adaptively includes determining the bandwidth limit parameter as a value to limit bandwidth more as the received signal quality is better and determining the bandwidth limit parameter as a value to limit the bandwidth less as the received signal quality is worse.

13. The method of claim 11, wherein determining the bandwidth limit parameter adaptively includes:

determining if the current received signal quality is worse than the previous received signal quality;

if the current received signal quality is worse than the previous received signal quality, determining whether a value to limit bandwidth less than previous bandwidth limit parameter violates bandwidth limit requirements for the OFDMA system;

if the value to limit bandwidth less does not violate the bandwidth limit requirements, determining the bandwidth limit parameter as the value to limit bandwidth less,

if the value to limit bandwidth less violates the bandwidth limit requirements, determining a modulation scheme including a low data rate, and the bandwidth limit parameter based on the modulation scheme including the low data rate,

if the current received signal quality is better than the previous received signal quality, determining whether a value to limit bandwidth more than the previous bandwidth limit parameter violates the bandwidth limit requirements for the OFDMA system,

if the value to limit bandwidth more does not violate the bandwidth limit requirements, determining the bandwidth limit parameter as the value to limit bandwidth more, and

if the value to limit bandwidth more violates the bandwidth limit requirements, determining a modulation scheme including a high data rate, and the bandwidth limit parameter based on the modulation scheme including the high data rate.

14. The method of claim 13, wherein the bandwidth limit requirements have a bandwidth limit parameter such that the window is rectangular-shaped in time domain as a lower limit, and a maximal bandwidth limit parameter such that curved portion of the window does not overlap the OFDMA symbol in frequency domain as an upper limit.

15. The method of claim 12, wherein determining the bandwidth limit parameter adaptively includes:

determining if the current received signal quality is worse than the previous received signal quality;

if the current received signal quality is worse than the previous received signal quality, determining whether a value to limit bandwidth less than previous bandwidth limit parameter violates bandwidth limit requirements for the OFDMA system;

if the value to limit bandwidth less does not violate the bandwidth limit requirements, determining the bandwidth limit parameter as the value to limit bandwidth less,

if the value to limit bandwidth less violates the bandwidth limit requirements, determining a modulation scheme including a low data rate, and the bandwidth limit parameter based on the modulation scheme including the low data rate,

if the current received signal quality is better than the previous received signal quality, determining whether a value to limit bandwidth more than the previous bandwidth limit parameter violates the bandwidth limit requirements for the OFDMA system,

if the value to limit bandwidth more does not violate the bandwidth limit requirements, determining the bandwidth limit parameter as the value to limit bandwidth more, and

if the value to limit bandwidth more violates the bandwidth limit requirements, determining a modulation scheme including a high data rate, and the bandwidth limit parameter based on the modulation scheme including the high data rate.

16. The method of claim 15, wherein the bandwidth limit requirements have a bandwidth limit parameter such that the window is rectangular-shaped in time domain as a lower limit, and a maximal bandwidth limit parameter such that curved portion of the window does not overlap the OFDMA symbol in frequency domain as an upper limit.

17. The method of claim 11, wherein the OFDMA system is an wireless broadband (WiBro) system, and

the receiver is a mobile station or a base station for the WiBro system.

18. The method of claim 11, wherein monitoring the received signal quality includes receiving an automatic repeat request (ARQ) signal from the receiver.

19. A computer readable medium storing computer executable instructions thereon, the computer executable instructions, when executed in a computer, executing a method of transmitting an orthogonal frequency division multiplexing access (OFDMA) symbol in an OFDMA system, comprising:

monitoring the received signal quality of a receiver;

determining a bandwidth limit parameter adaptively based on the received signal quality; and

generating an OFDMA symbol based on the bandwidth limit parameter to transmit to the receiver.