Remote radio head unit system with wideband power amplifier

Abstract

A remote radio head unit (RRU) system for multiple operating frequency bands, multi-channels, driven by a single or more wide band power amplifiers. More specifically, the present invention enables multiple-bands RRU to use fewer power amplifiers in order to reduce size and cost of the multi-band RRU. The present invention is based on the method of using duplexers and/or interference cancellation system technique to increase the isolation between the transmitter signal and receiver signal of the RRU.

Claims

1. An interference mitigation system for improving isolation between transmitters and receivers in wireless communications systems comprising: a power amplifier operable to receive and amplify a received signal at a predetermined frequency to provide a transmit signal; a feedback coupler coupled to the power amplifier and operable to provide a feedback signal based on the transmit signal, wherein a characteristic of the feedback signal is representative of a characteristic of the transmit signal; an interference cancellation unit coupled to the feedback coupler and operable to generate a processed signal; a circulator coupled to the power amplifier; an antenna coupled to the circulator and operable to broadcast the transmit signal at the predetermined frequency and to receive an intake signal at the predetermined frequency; a combiner that is operable to combine the processed signal with the intake signal from the antenna to generate a combined signal; and a low noise amplifier coupled to the combiner and operable to receive the combined signal.

2. The interference mitigation system of claim 1 further comprising a multi-band frequency filter coupled to the feedback coupler.

3. The interference mitigation system of claim 1 further comprising a second feedback coupler coupled to the combiner and operable to provide a second feedback signal to the interference cancellation unit.

4. The interference mitigation system of claim 3 wherein the interference cancellation unit is operable to process the second feedback signal in addition to the feedback signal.

5. The interference mitigation system of claim 1 further comprising a transmit switch coupled between the power amplifier and the antenna.

6. The interference mitigation system of claim 5 further comprising a receive switch coupled between the antenna and the combiner.

7. The interference mitigation system of claim 1 wherein the interference cancellation unit includes a plurality of delay blocks.

8. The interference mitigation system of claim 7 wherein each of the plurality of delay blocks is associated with a frequency band.

9. The interference mitigation system of claim 7 wherein the interference cancellation unit further includes a plurality of attenuators and a plurality of phase shifters.

10. An interference mitigation system for improving isolation between transmitters and receivers in wireless communications systems comprising: a power amplifier operable to receive and amplify a received signal at a predetermined frequency to provide a transmit signal at the predetermined frequency; a feedback coupler coupled to the power amplifier and operable to provide a feedback signal based on the transmit signal, wherein a characteristic of the feedback signal is representative of a characteristic of the transmit signal; an interference cancellation unit including a plurality of delay blocks and operable to process the feedback signal to generate a processed signal; an antenna operable to: broadcast the transmit signal at the predetermined frequency; and receive an intake signal at the predetermined frequency; a combiner that is operable to combine the processed signal with the intake signal from the receiver to generate a combined signal; and a low noise amplifier coupled to the combiner and operable to receive the combined signal.

11. The interference mitigation system of claim 10 further comprising a multi-band frequency filter coupled to the feedback coupler.

12. The interference mitigation system of claim 10 further comprising a second feedback coupler coupled to the combiner and operable to provide a second feedback signal to the interference cancellation unit.

13. The interference mitigation system of claim 12 wherein the interference cancellation unit processes the second feedback signal in addition to the feedback signal.

14. The interference mitigation system of claim 10 further comprising a transmit switch coupled between the power amplifier and the antenna.

15. The interference mitigation system of claim 14 further comprising a receive switch coupled between the antenna and the combiner.

16. The interference mitigation system of claim 10 wherein each of the plurality of delay blocks is associated with a frequency band.

17. The interference mitigation system of claim 16 wherein the interference cancellation unit further includes a plurality of attenuators and a plurality of phase shifters.

18. The interference mitigation system of claim 10 wherein the antenna is operable to transmit and receive concurrently at the predetermined frequency.

19. The interference mitigation system of claim 1 wherein the antenna is operable to transmit and receive concurrently at the predetermined frequency.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further objects and advantages of the present invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

(2) FIG. 1 is a block diagram of a TD-SCDMA dual-band single PA configuration in a remote radio head unit system in accordance with the present invention.

(3) FIG. 2 is a block diagram of the TD-SCDMA dual-band single PA with an Interference Cancellation System (ICS) configuration in a remote radio head unit system in accordance with the present invention.

(4) FIG. 3 is a FDD Modulation Agnostic Dual-Band Remote Radio Head with an Interference Cancellation System.

(5) FIG. 4 is an Interference Cancellation System using Power Detection.

(6) FIG. 5 is a TDD Modulation Agnostic Dual-Band Remote Radio Head with an Interference Cancellation System.

(7) FIG. 6 is an Interference Cancellation System using Correlation.

GLOSSARY OF TERMS

(8) ACLR Adjacent Channel Leakage Ratio

(9) ACPR Adjacent Channel Power Ratio

(10) ADC Analog to Digital Converter

(11) AQDM Analog Quadrature Demodulator

(12) ARM Analog Quadrature Modulator

(13) AQDMC Analog Quadrature Demodulator Corrector

(14) AQMC Analog Quadrature Modulator Corrector

(15) BPF Bandpass Filler

(16) CDMA Code Division Multiple Access

(17) CFR Crest Factor Reduction

(18) DAC Digital to Analog Converter

(19) DET Detector

(20) DHMPA Digital Hybrid Mode Power Amplifier

(21) DDC Digital Down Converter

(22) DNC Down Converter

(23) DPA Doherty Power Amplifier

(24) DQDM Digital Quadrature Demodulator

(25) DQM Digital Quadrature Modulator

(26) DSP Digital Signal Processing

(27) DUC Digital Up Converter

(28) EER Envelope Elimination and Restoration

(29) EF Envelope Following

(30) ET Envelope Tracking

(31) EVM Error Vector Magnitude

(32) FFLPA Feedforward Linear Power Amplifier

(33) FIR Finite Impulse Response

(34) FPGA Field-Programmable Gate Array

(35) GSM Global System for Mobile communications

(36) I-Q In-phase/Quadrature

(37) IF Intermediate Frequency

(38) LINC Linear Amplification using Nonlinear Components

(39) LO Local Oscillator

(40) LPF Low Pass Filter

(41) MCPA Multi-Carrier Power Amplifier

(42) MDS Multi-Directional Search

(43) OFDM Orthogonal Frequency Division Multiplexing

(44) PA Power Amplifier

(45) PAPR Peak-to-Average Power Ratio

(46) PD Digital Baseband Predistortion

(47) PLL Phase Looked Loop

(48) QAM Quadrature Amplitude Modulation

(49) QPSK Quadrature Phase Shift Keying

(50) RF Radio Frequency

(51) RRU Remote Radio Head Unit

(52) SAW Surface Acoustic Wave Filter

(53) UMTS Universal Mobile Telecommunications System

(54) UPC Up Converter

(55) WCDMA Wideband Code Division Multiple Access

(56) WLAN Wireless Local Area Network

DETAILED DESCRIPTION OF THE INVENTION

(57) The present invention is a novel RRU system that utilizes a wideband power amplifier. The present invention is a hybrid system of digital and analog modules. The interplay of the digital and analog modules of the hybrid system eliminates interference between the wideband power amplifier output and the receiver's inputs. The present invention, therefore, achieves higher Transmitter (Tx) to Receiver (Rx) isolation when using wideband power amplifiers with multiple frequency hands.

(58) Referring first to FIG. 1, an embodiment of some aspects of the invention is shown in block diagram form. FIG. 1 depicts the analog section of a dual channel RRU. In this embodiment a single wideband power amplifier 404 is used. The two distinct frequency band signals 401, 402 are combined in a duplexer 403 and input to the wideband power amplifier 404. The output of the wideband power amplifier 404 is sent to a diplexer 405 in order to separate the two frequency band signals. This configuration enables the individual transmitter frequency bands to be independently turned-off The Tx switches 406 and 407 are placed in the signal path after the diplexer 405. The signals are then passed through circulators 411 and 412 and a duplexer 413 in order to gain further isolation between the Tx signals and the Rx signals. The Rx switches 408 and 410 are placed on the third port of the circulators 411, 412. Alternatively, two or more frequency bands can be combined in one power amplifier using the same architecture as in FIG. 1.

(59) FIG. 2 illustrates a further alternative embodiment of the dual-band single wideband power amplifier RRU analog section. Although the embodiment in FIG. 2 shows a dual-band implementation, the invention can also be utilized in single band embodiments. In the embodiment of FIG. 2, an interference cancellation system (ICS) 520 is utilized to improve the isolation between the transmitter and receivers. The interference cancellation system 520 generates a replica of the unwanted feedback signal but in anti-phase so as to eliminate the interference. The interference cancellation system 520 comprises five primary blocks: Delay, variable attenuator, variable phase shifter. Down Converter (DNC) and DSP controller, alternative arrangements of which are shown in FIGS. 4 and 6, discussed hereinafter. The ICS 520 of FIG. 2 receives incoming signals through links 506 and 507. The anti-phase output of the ICS 520 is combined with the signals from switches Rx1 and Rx2, indicated at 510 and 511, respectively, by the use of adders 551 and 552, and the resulting signal provides the inputs to the LNA's 515 and 516. The ICS 520 is an adaptive control system which continuously adjusts the variable attenuator as well as the variable phase shifter so as to maintain good interference cancellation. Alternatively, an embodiment of the ICS can comprise a fixed attenuator and phase shifter setting, eliminating the need for DSP control, although in at least some cases this results in inferior performance compared to the adaptive ICS system of FIG. 2. The remaining elements of FIG. 2 correspond to those shown in FIG. 1, and are indicated by the same numerals except that the most significant digit has been changed from “4” to “5”.

(60) FIG. 3 shows another embodiment of the analog section of a dual-band single wideband power amplifier RRU in Frequency Division Duplex (FDD) mode. This embodiment is modulation agnostic for FM standard systems, and elements 601-604 operate analogously to elements 401-404 of FIG. 1. In FIG. 3, the triplexer 608 separates the transmitter bands from the receiver bands. FDD systems use different transmit and receive frequencies for each channel. The function of the triplexer 608 is to pass the output of power amplifier 604 to the antenna while isolating the receivers from the transmitter output. The ICS 609 system is utilized for increasing the isolation between the transmitter output and the receiver inputs as with FIG. 2, and in FIG. 3 receives the output of PA 604 through link 605. The output of the ICS 609 is combined with the appropriate triplexer outputs through adders 610 and 611, and the links 616, 617 feeding the LNA's 612 and 613.

(61) FIG. 4 is a depiction of one embodiment of an Interference Cancellation System (ICS). The function of the ICS is to generate a replicate of the interfering signal and place it in anti-phase to the interference, thereby eliminating the interfering signal. The input to the ICS system is a sample of the power amplifier output. Coupler 605 as illustrated in FIG. 3 is used to sample the power amplifier output. In FIG. 4, the power amplifier's output is sampled and sent to a diplexer 710. This separates the two frequencies into distinct sections. The delay block 701 time-aligns the feedback interfering signal with the sampled power amplifier output. The variable attenuator 702 is adjusted to insure that the interfering signal and the sampled signal have equal magnitude. The variable phase shifter 703 is adjusted to insure that the interfering signal and the sampled signal are in anti-phase. A Digital Signal Processor (DSP) 707 or Microprocessor is used to control the attenuator and phase shifter. A power detection based adaptive algorithm in the DSP continuously monitors the signal at the Down Converter (DNC) 708 output and minimizes the level of the interference based on the detected power level. The power level of the interference is measured at the receiver while that band is in the transmit mode of operation. The second band is similarly processed using elements 704, 705 and 706.

(62) FIG. 5 shows an embodiment of the analog section of a dual-band single wideband power amplifier RRU in Time Division Duplex (TDD) mode. This embodiment is modulation agnostic for TDD standard systems. The output of wide-band power amplifier 804 feeds a circulator 807. The circulator 807 provides some isolation between the transmitted signals and the receiver inputs. A multi-band filter 820 is placed between the circulator 807 and the output antenna in order to attenuate out-of-band emissions. The third port of the circulator 807 is delivered to a diplexer 808, which separates the two distinct operating bands. TDD mode requires the transmitter and receiver to operate using the same frequency band at distinct times. In order to provide isolation between the transmitter and receiver, switches 821, 822 are used. The switches 821, 822 can provide some isolation but additional isolation may be required depending on the system specifications. The ICS 809 can provide additional isolation between the transmitter output and the receiver inputs in the manner described above.

(63) FIG. 6 is a depiction of another embodiment of an Interference Cancellation System (ICS). The function of ICS is to generate a replicate of the interfering signal and place it in anti-phase to the interference, thereby eliminating the interfering signal. The input to the ICS system is a sample of the power amplifier output. The power amplifier's output is sampled and sent to a diplexer 910. This separates the two frequencies into distinct sections. The delay block 901 time aligns the feedback interfering signal with the sampled power amplifier output. The variable attenuator 902 is adjusted to insure that the interfering signal and the sampled signal have equal magnitude. The variable phase shifter 903 is adjusted to insure that the interfering signal and the sampled signal are in anti-phase. A Digital Signal Processor (DSP) 907 or Microprocessor is used to control the attenuator and phase shifter. A correlation-based adaptive algorithm in the DSP is used to minimize the level of interference. The DSP correlates the two signals by controlling the output of switch 911 and the output of switch 912 after the signals have been translated to baseband using the two Downconverters 920 and 909. The switches 911 and 912 alternate between the two channels. The objective of the algorithm is to minimize the correlation between the sampled power amplifier output and the interference at the receiver. The computed correlation coefficient is used as the error function in an adaptive algorithm such as a Least Mean Squared (LMS) algorithm.

(64) From the foregoing teachings, those skilled in the art will appreciate that the RRU system of the present invention enables the use of single wideband power amplifier for multi-band operation, which consequently saves hardware resources and reduces costs. The RRU system is also reconfigurable and field-programmable since the algorithms can be adjusted like software in the digital processor at anytime.

(65) Moreover, the RRU system is agnostic to modulation schemes such as QPSK, QAM, OFDM, etc. in CDMA, TD-SCDMA, GSM, WCDMA, CDMA2000, and wireless LAN systems. This means that the RRU system is capable of supporting multi-modulation schemes, multi-frequency bands and multi-channels.

(66) Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.