Wireless communication system and transmit power and data rate control method therefor

• US 20040176033A1
• Filed: 08/15/2003
• Published: 09/09/2004
• Est. Priority Date: 03/03/2003
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Yano, Takashi, Tamaki, Satoshi
• Granted Patent: US 7,301,989 B2
• Time in Patent Office: Days
• US Class Current: 455/59
• CPC Class Codes: H04W 52/24 using SIR [Signal to Interference Ratio] or other wireless path parameters
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

When channel-coded data is transmitted in a wireless communication system, coded data is divided into a plurality of bandwidths and the signal power is distributed to the bandwidths so that the communication channel capacity is increased. In addition, the transmission power is controlled on a time basis in such a way that the average power becomes larger when the channel quality is poorer so that the quality of each code word is stabilized. Alternatively, the coding rate is controlled in such a way that the data rate is decreased when the channel quality is poorer.

Claims

1. A wireless communication system transmitting data from a transmitting station to a receiving station using a plurality of subcarriers in parallel,

wherein said transmitting station comprises:

a channel quality judgment module judging the quality of a channel between said transmitting station and said receiving station for each of said plurality of subcarriers;

a channel coding module coding data signals into a code word;

a subcarrier modulation module dividing the code word into a plurality of subcarriers for modulation and modulating the subcarriers each composed of a plurality of symbols;

a multi-carrier modulation module combining the plurality of subcarrier-modulated symbols into transmission signals via frequency-time conversion; and

a data power setting module setting a transmission power for each of the plurality of subcarriers according to an output from said channel quality judgment module,

wherein said receiving station comprises;

a demodulation module demodulating signals received from said transmitting station; and

a channel decoding module decoding the demodulated received signals, and

wherein the transmission power is determined by a first control rule stipulating that, for the plurality of symbols transmitted at the same time, a transmission power for symbols corresponding to a first subcarrier whose channel quality is judged to be good is set higher than a transmission power for symbols corresponding to a second subcarrier whose channel quality is judged to be poor.

2. The wireless communication system according to claim 1,

wherein said channel quality judgment module judges the channel quality based on a received power of signals transmitted from said receiving station to said transmitting station.

3. The wireless communication system according to claim 1,

wherein said receiving station further comprises a channel quality measuring module,

wherein said channel quality measuring module measures the channel quality based on an output of said demodulation module demodulating signals transmitted from said transmitting station to said receiving station,

wherein said receiving station notifies said transmitting station of the measurement result, and

wherein said channel quality judgment module judges the channel quality based on the measurement result.

4. The wireless communication system according to claim 1,

wherein the coding rate of the code word is changed according to the channel quality.

5. The wireless communication system according to claim 1,

wherein said channel quality judgment module determines a reference power based on a noise power for signals transmitted via a plurality of subcarriers between said transmitting station and said receiving station and outputs a value, generated by subtracting the noise power in each subcarrier from the reference power, as a signal transmission power and

wherein the reference power is determined by a second control rule stipulating that the reference power is equal in each code word.

6. The wireless communication system according to claim 5,

wherein the reference power of a first code word transmitted when the total of the noise power is high is set larger than the reference power of a second code word transmitted when the total of the noise power is low.

7. The wireless communication system according to claim 5,

wherein the reference power is a value common to a plurality of continuous code words.

8. A data transmission control method for use by a transmitting station in a wireless communication system transmitting data from the transmitting station to a receiving station using a plurality of subcarriers in parallel, said method comprising the steps of:

judging the quality of a channel between said transmitting station and said receiving station for each of said plurality of subcarriers;

coding, by said transmitting station, data signals, which is to be transmitted to said receiving station, for generating a code word;

dividing the code word into a plurality of subcarriers for modulation and generating a plurality of symbols;

combining the plurality of symbols into transmission signals via frequency-time conversion; and

setting a transmission power for each of the plurality of subcarriers according to the judged channel quality and transmitting the transmission signals to said receiving station,

wherein the transmission power is determined by a first control rule stipulating that, for the plurality of symbols transmitted at the same time, a transmission power for symbols corresponding to a first subcarrier whose channel quality is judged to be good is set higher than a transmission power for symbols corresponding to a second subcarrier whose channel quality is judged to be poor.

9. The data transmission control method according to claim 8,

wherein the channel quality is judged based on a received power of signals transmitted from said receiving station to said transmitting station.

10. The data transmission control method according to claim 8,

wherein the channel quality is measured by said receiving station and is notified to said transmitting station.

11. The data transmission control method according to claim 8,

wherein the channel quality is judged using a reception-to-noise ratio power of signals transmitted between said transmitting station and said receiving station.

12. The data transmission control method according to claim 8,

wherein the transmission power is a value generated by subtracting a noise power in each subcarrier from the reference power determined based on the noise power for signals transmitted via a plurality of subcarriers between said transmitting station and said receiving station and

the reference power is determined by a second control rule stipulating that the reference power is equal in each code word.

13. The data transmission control method according to claim 12,

wherein the reference power of a first code word transmitted when the total of the noise power is high is larger than the reference power of a second code word transmitted when the total of the noise power is low.

14. The data transmission control method according to claim 12,

wherein the reference power is a value updated for each a plurality of code words.

15. The data transmission control method according to claim 8,

wherein when the channel quality is higher than a predetermined criterion, the transmission power is set lower than a transmission power used when the channel quality is the predetermined criterion.

16. The data transmission control method according to claim 8,

wherein the coding rate of the code word is controlled according to the channel quality.

17. A transmitting station transmitting data to a receiving station using a plurality of subcarriers in parallel, comprising:

a channel quality judgment module judging the quality of a channel between said transmitting station and said receiving station for each of said-plurality of subcarriers;

a channel coding module coding data signals into a code word;

a subcarrier modulation module dividing the code word into a plurality of subcarriers for modulation and modulating the subcarriers each composed of a plurality of symbols;

a multi-carrier modulation module performing frequency-time conversion for the plurality of subcarrier-modulated symbols to generate transmission signals; and

a data power setting module setting a transmission power for each of the plurality of subcarriers according to an output from said channel quality judgment module, and

wherein the transmission power is determined by a first control rule stipulating that, for the plurality of symbols transmitted at the same time, a transmission power for symbols corresponding to a first subcarrier whose channel quality is judged to be good is set higher than a transmission power for symbols corresponding to a second subcarrier whose channel quality is judged to be poor.

18. The transmitting station according to claim 17,

wherein said channel quality judgment module judges the channel quality based on a received power of signals transmitted from said receiving station to said transmitting station.

19. The transmitting station according to claim 18, wherein

said channel quality judgment module judges the channel quality based on reception quality information in said receiving station notified by said receiving station.

20. The transmitting station according to claim 17,

wherein said channel quality judgment module determines a reference power based on a noise power for signals transmitted via a plurality of subcarriers between said transmitting station and said receiving station and outputs a value, generated by subtracting the noise power in each subcarrier from the reference power, as a signal transmission power and

the reference power is determined by a second control rule stipulating that the reference power is equal in each code word.