High efficiency, remotely reconfigurable remote radio head unit system and method for wireless communications

Abstract

A remote radio head unit (RRU) system is disclosed. The present invention is based on the method of adaptive digital predistortion to linearize a power amplifier inside the RRU. The power amplifier characteristics such as variation of linearity and asymmetric distortion of the amplifier output signal are monitored by a wideband feedback path and controlled by the adaptation algorithm in a digital module. Therefore, embodiments of the present invention can compensate for the nonlinearities as well as memory effects of the power amplifier systems and also improve performance, in terms of power added efficiency, adjacent channel leakage ratio and peak-to-average power ratio. The present disclosure enables a power amplifier system to be field reconfigurable and support multi-modulation schemes (modulation agnostic), multi-carriers, multi-frequency bands and multi-channels. Consequentially, the remote radio head system is particularly suitable for wireless transmission systems, such as base-stations, repeaters, and indoor signal coverage systems.

1 . (canceled) 
     
     
         2 . A remote radio head unit comprising:
 an input interface configured to receive an input signal;   a digital module comprising digital predistortion logic configured to predistort the input signal;   a power amplifier configured to output an amplified output signal that is a representation of the predistorted input signal; and   a feedback path comprising:
 a directional coupler for sampling the amplified output signal; 
 a mixer for frequency translating the sampled output signal to an intermediate-frequency (IF) signal comprising nonlinear distortions of the amplified output signal including in-band distortions and out-of-band distortions; and 
 a band pass filter for capturing the out-of-band distortions, 
   wherein the digital module determines dynamic parameters of the predistorted input signal in response to the out-of-band distortions.   
     
     
         3 . The remote radio head unit of  claim 2 , further comprising a temperature sensor configured to provide a temperature signal representing a temperature of the power amplifier. 
     
     
         4 . The remote radio head unit of  claim 2 , further comprising a clipping error restoration path coupled to the amplified output signal for compensating the in-band distortions of the amplified output signal. 
     
     
         5 . The remote radio head unit of  claim 2 , wherein the digital module further comprises a crest factor reduction block configured to reduce a crest factor of the input signal prior to providing the crest factor reduced signal to the digital predistortion logic. 
     
     
         6 . The remote radio head unit of  claim 5 , wherein the input interface comprises:
 a radio frequency input path comprising an analog downconverter;   a baseband input path comprising I-Q input; and   an optical input path comprising an optical-to-electrical interface, a serializer/deserializer (SERDES) device and a Framer/Deframer device.   
     
     
         7 . The remote radio head unit of  claim 2 , wherein the power amplifier comprises an analog quadrature modulator for modulating the predistorted input signal. 
     
     
         8 . The remote radio head unit of  claim 2 , further comprising a bias control path configured to stabilize linearity fluctuations of the power amplifier caused by temperature changes in the power amplifier. 
     
     
         9 . The remote radio head unit of  claim 2 , wherein the digital module comprises a field programmable gate array (FPGA). 
     
     
         10 . A dual-channel remote radio head unit comprising:
 a first transmit path including a first power amplifier configured to receive a first input signal at a first frequency band and output a first amplified output signal;   a second transmit path including a second power amplifier configured to receive a second input signal at a second frequency band separated from the first frequency band and output a second amplified output signal;   a duplexer configured to combine the first and second amplified output signals and provide the combined first and second amplified output signals to an antenna;   a first feedback path including a first feedback signal associated with first distortions of the first amplified output signal;   a second feedback path including a second feedback signal associated with second distortions of the second amplified output signal;   digital logic configured to predistort the first input signal in response to the first feedback signal and predistort the second input signal in response to the second feedback signal.   
     
     
         11 . The dual-channel remote radio head unit of  claim 10 , further comprising:
 a first switch configured to isolate the first transmit path from a first receive path; and   a second switch configured to isolate the second transmit path from a second receive path, wherein the digital logic synchronizes the first switch and the second switch to support a time division synchronous code division multiple access (TD-SCDMA) modulation.   
     
     
         12 . The dual-channel remote radio head unit of  claim 11 , further comprising:
 a first circulator having a first port coupled to the first power amplifier, a second port coupled to the duplexer, and a third port coupled to the first switch; and   a second circulator having a fourth port coupled to the second power amplifier, a fifth port coupled to the duplexer, and a sixth port coupled to the second switch.   
     
     
         13 . The dual-channel remote radio head unit of  claim 12 , further comprising:
 a first temperature sensor coupled to the first power amplifier and configured to provide a first temperature signal associated with the first power amplifier;   a second temperature sensor coupled to the second power amplifier and configured to provide a second temperature signal associated with the second power amplifier;   a temperature switch coupled to the first temperature sensor and the second temperature sensor,   wherein the digital logic synchronizes the temperature switch with the first switch and the second switch such that the first temperature signal and the first feedback signal are provided to the digital logic for calibrating the first power amplifier and the second temperature signal and the second feedback signal are provided to the digital logic for calibrating the second power amplifier.   
     
     
         14 . The dual-channel remote radio head unit of  claim 10 , further comprising an interface port comprising:
 a digital input interface configured to provide first digital signals to the digital logic; and   an optical-to-electrical interface configured to convert optical signals to second digital signals and provide the second digital signals to the digital logic.   
     
     
         15 . The dual-channel remote radio head unit of  claim 10 , further comprising:
 a first digital-to-analog converter configured to convert the first input signal to a first analog signal;   a second digital-to-analog converter configured to convert the second input signal to a second analog signal;   a first analog quadrature modulator configured to modulate the first analog signal and provide a first modulated analog signal to the first power amplifier; and   a second analog quadrature modulator configured to modulate the second analog signal and provide a second modulated analog signal to the second power amplifier.   
     
     
         16 . The dual-channel remote radio head unit of  claim 10 , further comprising:
 a first bias control path configured to stabilize linearity fluctuations of the first power amplifier caused by temperature changes in the first power amplifier; and   a second bias control path configured to stabilize linearity fluctuations of the second power amplifier caused by temperature changes in the second power amplifier.   
     
     
         17 . A method comprising:
 receiving an input signal;   predistorting the input signal by digital predistortion logic;   amplifying the predistorted input signal by a power amplifier to obtain an amplified output signal;   obtaining a feedback signal including in-band distortions and out-of-band distortions of the amplified output signal;   determining dynamic parameters of the digital predistortion logic in response to the out-of-band distortions.   
     
     
         18 . The method of  claim 17 , further comprising:
 reducing a crest factor of the input signal by a crest factor reduction block prior to predistorting the input signal.   
     
     
         19 . The method of  claim 18 , further comprising:
 compensating the in-band distortions caused by the crest factor reduction block by coupling a clipping error restoration signal to the amplified output signal.   
     
     
         20 . The method of  claim 17 , further comprising:
 stabilizing linearity fluctuations of the power amplifier caused by temperature changes in the power amplifier by biasing the power amplifier.   
     
     
         21 . The method of  claim 17 , further comprising, prior to amplifying the predistorted input signal:
 digital-to-analog converting the predistorted input signal to obtain an analog predistorted signal; and   modulating the analog predistorted signal by an analog quadrature modulator.