Wireless base station and communication method therefor

• US 20070072646A1
• Filed: 02/06/2006
• Published: 03/29/2007
• Est. Priority Date: 09/29/2005
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Kuwahara, Mikio, Taira, Masanori
• Granted Patent: US 8,068,874 B2
• Time in Patent Office: Days
• US Class Current: 455/561
• CPC Class Codes: H04W 88/085 Access point devices with remote components

Abstract

In a wireless base station comprising a center unit, and a remote unit provided with an array antenna and connected to the center unit through an optical fiber, the center unit outputs to the optical fiber a transmission signal in a base band state prior to array processing, the remote unit performs the array processing of transmission signals in accordance with array weights and converts the transmission signals into RF signals, thereby to localize the compensation for transmission signal deviations occurring among the antenna elements on the remote unit side.

Claims

1. A wireless base station including a center unit and a remote unit provided with an array antenna having a plurality of antenna elements, the center unit being coupled with the remote unit through an optical fiber,

the center unit comprising:

a modulator for modulating a transmission signal to a base band signal; and

a first interface for converting the base band signal output from the modulator into an optical signal and transmitting the optical signal to the optical fiber, and

the remote unit comprising;

a second interface for converting the optical signal received from the optical fiber into an electric base band signal and outputting the electric base band signal;

a signal processor unit for converting the base band signal received from the second interface into a plurality of transmission signals corresponding to the antenna elements of the array antenna and outputting the transmission signals;

a radio frequency (RF) unit for converting the respective transmission signals output from the signal processor unit into transmission signals in an RF band and supplying the transmission signals to the antenna elements of the array antenna; and

a deviation detector for detecting deviations among the transmission signals supplied to the respective antenna elements of the array antenna,

wherein the signal processor unit performs compensation on the transmission signals to be output to the RF unit in accordance with the deviations detected by the deviation detector.

2. The wireless base station according to claim 1, wherein:

the signal processor unit of the remote unit converts the base band signal received from the second interface into a plurality of transmission signals including probe signals, and outputs the transmission signals; and

the deviation detector extracts the probe signals from the transmission signals supplied to the respective antenna elements of the array antenna, and detects the deviations among the transmission signals based on the probe signals.

3. The wireless base station according to claim 2, wherein the signal processor unit of the remote unit adds the probe signals to the respective transmission signals by using any one of time multiplexing, code multiplexing, and frequency multiplexing.

4. The wireless base station according to claim 1, wherein:

the modulator of the center unit outputs array weight information with the base band signal;

the first interface transmits to the optical fiber an optical signal formed by time multiplexing the base band signal and the array weight information output from the modulator;

the second interface converts the optical signal received from the optical fiber into an electric signal, separates the electric signal into the base band signal and the array weight information, and outputs the base band signal and the array weight information; and

the signal processor unit converts the base band signal received from the second interface into a plurality of transmission signals weighted in accordance with the array weight information, and optimizes the array weight information in accordance with the deviations detected by the deviation detector.

5. The wireless base station according to claim 1, wherein:

the modulator of the center unit outputs array weight information with the base band signal;

the first interface transmits to the optical fiber an optical signal formed by time multiplexing the base band signal and the array weight information output from the modulator;

the second interface converts the optical signal received from the optical fiber into an electric signal, separates the electric signal into the base band signal and the array weight information, and outputs the base band signal and the array weight information;

the remote unit includes a weight compensation unit for optimizing the array weight information output from the second interface in accordance with the deviations detected by the deviation detector; and

the signal processor unit weights the base band signal received from the second interface in accordance with the array weight information compensated by the weight compensation unit, and converts the base band signal into the plurality of transmission signals.

6. The wireless base station according to claim 1, wherein:

the modulator of the center unit converts the transmission signals into a plurality of base band transmission signals for orthogonal frequency division multiplexing (OFDM), wherein frequency channels for the transmission signals are different from one another, and the modulator outputs the transmission signals and array weight information;

the first interface transmits to the optical fiber an optical signal formed by time multiplexing the base band signal and the array weight information output from the modulator;

the second interface converts the optical signal received from the optical fiber into an electric signal, separates the electric signal into the base band signals and the array weight information, and outputs the base band signal and the array weight information;

the remote unit includes a weight compensation unit for optimizing the array weight information output from the second interface in accordance with the deviations detected by the deviation detector; and

the signal processor unit weights the plurality of base band signals received from the second interface in accordance with the array weight information compensated by the weight compensation unit, and converts the base band signal into the plurality of transmission signals corresponding to the antenna elements.

7. The wireless base station according to claim 6, wherein the signal processor unit of the remote unit includes:

an array processor unit for weighting the base band signals on the respective frequency channels received from the second interface, in accordance with the compensated array weight information and outputting the base band signals in the form of two-dimensional transmission signals comprised of a frequency domain signal component and a time domain signal component each including a probe signal; and

an OFDM terminating unit for converting the frequency domain signal component output from the array processor unit to the time domain signal component by inversed Fourier transform, thereby to convert the base band signals into the plurality of transmission signals corresponding to the antenna elements.

8. The wireless base station according to claim 7, wherein the modulator of the center unit intermittently outputs the array weight information in accordance with an update cycle thereof.

9. The wireless base station according to claim 1, wherein:

the modulator of the center unit converts the transmission signal into a plurality of modem signals corresponding to the respective antenna elements of the array antenna, and outputs the modem signals,

the first interface transmits to the optical fiber an optical signal formed by time multiplexing the plurality of modem signals output from the modulator;

the second interface converts the optical signal received from the optical fiber into an electric signal, separates the electric signal into the plurality of modem signals, and outputs the modem signals;

the remote unit includes a measurement unit for generating complex vector information corresponding to the respective antenna elements in accordance with the deviations detected by the deviation detector; and

the signal processor unit performs compensation on the plurality of modem signals received from the second interface based on the complex vector information output from the measurement unit, and outputs the modem signals as a plurality of transmission signals, corresponding to the respective antenna elements, together with probe signals.

10. The wireless base station according to claim 1, wherein:

the modulator of the center unit converts the transmission signal into a plurality of modem signals corresponding to the antenna elements of the array antenna and to frequency channels, and outputs the modem signals;

the first interface transmits to the optical fiber an optical signal formed by time multiplexing the plurality of modem signals output from the modulator;

the second interface converts the optical signal received from the optical fiber into an electric signal, separates the electric signal into the plurality of modem signals corresponding to the antenna elements of the array antenna and to the frequency channels;

the remote unit includes a measurement unit that generates complex vector information corresponding to the respective antenna elements in accordance with the deviations detected by the deviation detector; and

the signal processor unit performs compensation on the plurality of modem signals received from the second interface based on the complex vector information output from the measurement unit, and outputs the plurality of modem signals as a plurality of transmission signals, corresponding to the respective antenna elements, together with probe signals.

11. A communication method for a wireless base station including a center unit and a remote unit provided with an array antenna having a plurality of antenna elements, the center unit being coupled with the remote unit through an optical fiber,

the center unit executing the steps of:

modulating a transmission signal to a base band signal;

converting the base band signal into an optical signal; and

transmitting the optical signal to the optical fiber, and

the remote unit executing the steps of;

converting the optical signal received from the optical fiber into an electric base band signal;

converting the base band signal into a plurality of transmission signals corresponding to the antenna elements of the array antenna;

converting the respective transmission signals into transmission signals in a radio frequency (RF) band, thereby supplying the transmission signals to the antenna elements of the array antenna;

detecting deviations among the transmission signals supplied to the respective antenna elements of the array antenna; and

performing compensation on any one of the transmission signals to be output to the RF band in accordance with the deviations.

12. The communication method according to claim 11, wherein:

the remote unit converts the base band signal into a plurality of transmission signals including probe signals, extracts probe signals from the transmission signals supplied to the respective antenna elements of the array antenna, and detects deviations among the transmission signal in accordance with the probe signals.

13. The communication method according to claim 11, wherein:

the center unit generates array weight information, and transmits to the optical fiber an optical signal formed by time multiplexing the base band signal and the array weight information; and

the remote unit converts the base band signal received from the from the optical fiber into a plurality of transmission signals weighted in accordance with the array weight information, converts the respective transmission signals into transmission signals in the RF band, supplies the transmission signals to the antenna elements of the array antenna, and optimizes the array weight information in accordance with the deviations.

14. The communication method according to claim 11, wherein:

the center unit converts the transmission signal into a plurality of base band transmission signals for orthogonal frequency division multiplexing (OFDM), wherein frequency channels for the transmission signals are different from one another, time multiplexes the transmission signals and the array weight information, and transmits the time multiplexed signal to the optical fiber, and

the remote unit optimizes the array weight information output from the center unit in accordance with the deviations, weights the plurality of base band signals received from the center unit in accordance with either the array weight information received from the center unit or the compensated array weight information, and converts the base band signal into the plurality of transmission signals corresponding to the antenna elements.

15. The communication method according to claim 11, wherein:

the center unit converts the transmission signal into a plurality of modem signals corresponding to the respective antenna elements of the array antenna, time multiplexes the plurality of modem signals, and transmits the time multiplexed signal to the optical fiber, and

the remote unit generates complex vector information corresponding to the respective antenna elements in accordance with the deviations, performs compensation on the plurality of modem signals received from the center unit based on the complex vector information, and converts the plurality of modem signals to a plurality of transmission signals, corresponding to the respective antenna elements, to gether with probe signals.

16. The communication method according to claim 11, wherein:

the center unit converts the transmission signal into a plurality of modem signals corresponding to the antenna elements of the array antenna and to frequency channels, time multiplexes the plurality of modem signals, and transmits the time multiplexed signal to the optical fiber, and

the remote unit generates complex vector information corresponding to the antenna elements in accordance with the deviations, performs compensation on the plurality of modem signals received from the center unit based on the complex vector information, and converts the plurality of modem signals into a plurality of transmission signals, corresponding to the respective antenna elements, together with probe signals.