HK1230352A - System for improving isolation between transmitters and receivers - Google Patents

Description

System for improving isolation between a transmitter and a receiver

The application is a divisional application of an invention patent application with the application date of 21/12/2010, the application number of 201080064329.4 (international phase application number of PCT/IB2010/003452) and the name of a remote radio frequency head unit with a broadband power amplifier and a method.

RELATED APPLICATIONS

This application claims the benefit of the following applications:

U.S. patent application 61/288,840, entitled "REMOTE RADIO HEAD UNIT SYSTEM WITHWIDEBAND POWER AMPLIFIER AND METHOD", filed 12/21/2009, and filed by the inventors of Chengxun Wang and Shawn PatrickStapleton, which is incorporated herein by reference for all purposes.

Technical Field

The present invention relates generally to wireless communication systems using power amplifiers and remote radio head units (RRUs or RRHs). More particularly, the present invention relates to RRU as part of a distributed base station, where all radio frequency related functions are contained in a small single unit that can be arranged at a location remote from the main unit.

Background

Wireless and mobile network operators face a continuing challenge to establish networks that effectively manage high data traffic growth rates. The mobility and increased magnitude of end-user multimedia content requires end-to-end network adaptivity that supports new services and increased demand for broadband and flat-rate internet access. Furthermore, network operators must consider the most cost-effective solutions for expanding network capacity and evolving towards and above 4G.

Wireless and mobile technology standards are evolving towards higher frequency band requirements for peak rates and cell throughput growth. The latest standards supporting wireless and mobile technologies are HSPA +, WiMAX, TD-SCDMA and LTE. Network updates required to deploy networks based on these standards must balance the limited availability of new spectrum, leverage existing spectrum, and ensure operation of all desired standards. These must all occur at the same time as the transition phase, which typically spans many years.

The distributed open base station architecture concept has evolved in parallel with the evolution of standards to provide a flexible, inexpensive and more scalable (scalable) modular environment for managing the evolution of radio frequency access. For example, the Open Base Station Architecture Initiative (OBSAI), Common Public Radio Interface (CPRI), and IR interface standards introduce standardized interfaces that separate the base station server and the remote radio head portion of the base station over optical fiber.

The remote radio head (RRU) concept is an essential part of the prior art base station architecture. The 2G/3G/4G base station is typically connected to the RRU by optical fiber. The CPRI, OBSAI, or IR interfaces may all be used to carry data to the RRH to cover a three sector cell. The RRU incorporates a number of digital interface connections and processing functions. Traditionally, multi-channel RRU implies the use of multiple antennas, typically two power amplifiers for two different frequency bands. A duplexer is used to combine the two power amplifier outputs. A switch is used to isolate a transmit signal from a receive signal present in time division synchronous code division multiple access (TD-SCDMA) modulation. To extend the prior art architecture to multiple frequency bands (i.e., two or more frequency bands), implementations should include adding additional parallel channelized power amplifiers. The outputs of the further power amplifiers are typically combined in an N x1 duplexer and fed to a single antenna.

While conventional RRU architectures provide certain advantages, current RRUs are power inefficient, costly, and inflexible. Furthermore, the poor DC to RF power conversion of the RRU makes it to have a large mechanical enclosure. In addition, current RRU designs have poor flexibility. As standards evolve, there is a need for multi-band RRUs that can accommodate two or more operating channels using a single wideband power amplifier. Since the broadband power amplifier is usually on, this creates isolation problems at the individual receivers. In case a single power amplifier is used to develop multi-band RRU, isolation between the wideband transmitter and receiver is a problem with any modulation standard (HSPA +, WiMAX, LTE, etc.). This is a problem common to all communication systems using broadband power amplifiers in the multi-band case.

Disclosure of Invention

Accordingly, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a high-performance and cost-effective technique for implementing an RRU system serving multiple frequency bands. Furthermore, the present disclosure enables RRU to be field reconfigurable and support multiple modulation schemes (modulation agnostic), multiple carriers, multiple bands and multiple channels. The invention also provides multiple frequency bands within a single RRU to save the cost of radio network deployment. In particular, the present invention solves the isolation problem of RRUs in case the number of power amplifiers is smaller than the number of operating frequency bands. Multimode radio frequencies capable of operating in accordance with GSM, HSPA, LTE, TD-SCDMA and WiMAX standards and advanced software configurability are key features for the deployment of more flexible and energy efficient radio frequency networks.

The present invention achieves the above objects using techniques that are generally based on methods and techniques for maximizing isolation between a transmit signal (Tx signal) and a receive signal (Rx signal). The Tx signal may include noise generated at the output of the power amplifier or it may include an undesired transmitter band leaking into the receiver. By using the present invention, a conventional RRU can be extended to a multi-band multi-channel configuration. Multi-band means that more than one frequency band is used in RRU, while multi-channel means that more than one output antenna is used. Various embodiments of the invention are disclosed.

One embodiment of the present invention utilizes a duplexer, switch and circulator to maximize isolation between the transmitter and receiver. Another embodiment of the present invention utilizes an Interference Cancellation System (ICS) along with a duplexer, switch, and circulator.

According to one aspect of the disclosure, there is provided a system for improving isolation between a transmitter and a receiver in a multi-band wireless communication system, the system comprising: a wideband power amplifier operable to receive a plurality of input signals, wherein each input signal is adapted for wireless transmission, and the wideband power amplifier is operable to provide an amplified output signal; a feedback sensor operable to provide a feedback signal representative of an interference characteristic of the amplified output signal; a receiver operable to receive a plurality of received signals; a plurality of feedback sensors operable to provide a plurality of feedback signals representative of interference characteristics of the plurality of received signals; cancellation logic operable to receive the feedback signal and the plurality of feedback signals, wherein the cancellation logic is configured to generate a plurality of inverted signals corresponding to interference characteristics of the plurality of received signals; and a plurality of combiners operable to combine the plurality of inverted signals with the plurality of received signals to remove the interference characteristic from the plurality of received signals.

Applications of the present invention are suitable for use with all wireless base stations, remote radio heads, distributed base stations, distributed antenna systems, access points, repeaters, mobile devices and wireless terminals, portable wireless devices, and other wireless communication systems such as microwave and satellite communications. The present invention also enables field upgrades via a link such as an ethernet connection to a remote computing center.

Drawings

Further features and advantages of the present invention will be more fully understood from the following detailed description, given in conjunction with the accompanying drawings, in which:

fig. 1 is a block diagram of a TD-SCDMA dual band single power amplifier configuration in a remote radio head unit system according to the present invention.

Fig. 2 is a block diagram of a TD-SCDMA dual band single power amplifier with Interference Cancellation System (ICS) configuration in a remote radio head unit system according to the present invention.

Fig. 3 is a FDD modulation agnostic dual band remote radio head with an interference cancellation system.

Fig. 4 is a dual-band interference cancellation system using power detection.

Fig. 5 is a TDD modulation agnostic dual band remote radio head with an interference cancellation system.

Fig. 6 is a dual band interference cancellation system using correction.

Glossary

ACLR adjacent channel leakage ratio

ACPR adjacent channel power ratio

ADC analog-to-digital converter

AQDM analog quadrature demodulator

AQM analog quadrature modulator

AQDMC analog quadrature demodulation corrector

AQMC analog quadrature modulation corrector

BPF band-pass filter

CDMA code division multiple access

CFR crest factor reduction

DAC digital-to-analog converter

DET detector

DHMPA digital mixed mode power amplifier

DDC digital down converter

DNC down converter

DPA Doherty power amplifier

DQDM digital quadrature demodulator

DQM digital quadrature modulator

DSP digital signal processing

DUC digital up-converter

EER envelope elimination and restoration

EF envelope following

ET envelope tracking

EVM error vector magnitude

FFLPA feed-forward linear power amplifier

FIR finite impulse response

FPGA field programmable gate array

GSM global mobile communication system

I-Q in-phase-quadrature

IF intermediate frequency

Linear amplification using non-linear components for LlNC

LO local oscillator

LPF low pass filter

MCPA multi-carrier power amplifier

MDS multidirectional search

OFDM orthogonal frequency division multiplexing

PA power amplifier

Peak-to-average power ratio (PAPR)

PD digital baseband predistortion

PLL phase-locked loop

QAM quadrature amplitude modulation

QPSK quadrature phase shift keying

RF radio frequency

RRU remote radio head unit

SAW surface acoustic wave filter

UMTS universal mobile communication system

UPC up converter

WCDMA wideband code division multiple access

WLAN wireless local area network

Detailed Description

The present invention is a new RRU system using a broadband power amplifier. The invention is a hybrid system of digital and analog modules. The interaction of the digital and analog modules of the hybrid system eliminates interference between the wideband power amplifier output and the input of the receiver. Thus, the present invention achieves higher transmitter (Tx) to receiver (Rx) isolation in the case of using a wideband power amplifier with multiple frequency bands.

Referring initially to FIG. 1, an embodiment of certain aspects of the present invention is shown in block diagram form. Fig. 1 depicts the analog portion of a dual channel RRU. In this embodiment, a single wideband power amplifier 404 is used. The two different frequency band signals are combined in the duplexer 403 and input to the wide band power amplifier 404. The output of the wideband power amplifier 404 is sent to a diplexer 405 to separate the two band signals. This configuration enables individual transmitter bands to be independently disconnected. Tx switches 406 and 407 are provided in the signal path after diplexer 405. The signal then passes through circulators 411 and 412 and duplexer 413 to obtain further isolation between the Tx and Rx signals. Rx switches 408 and 410 are provided on the third port of the circulator. Alternatively, two or more frequency bands may be combined in one power amplifier using the same structure as that of fig. 1.

Fig. 2 shows a further alternative embodiment of the analog part of a dual-band single wideband power amplifier RRU. Although the embodiment of fig. 2 shows a dual band implementation, the present invention may also be used in a single band implementation. In the embodiment of fig. 2, an Interference Cancellation System (ICS)520 is utilized to improve isolation between the transmitter and receiver. An interference cancellation system generates an inverted replica of the undesired feedback signal to cancel the interference. The interference cancellation system comprises five main modules: a delay, a variable attenuator, a variable phase shifter, a down converter (DNC) and a DSP controller, alternative arrangements of which are shown in fig. 4 and 6 and discussed below. The ICS receives input signals over links 506 and 507. The inverted output of the ICS is combined with the signals from switches Rx1 and Rx2 (represented by 510 and 511) using adders 551 and 552, respectively, and the resulting signals provide inputs to LNA515 and LNA 516. ICS is an adaptive control system that continuously adjusts a variable attenuator and a variable phase shifter to maintain good interference cancellation. Alternatively, to eliminate the need for DSP control, implementations of ICS may include fixed attenuator and phase shifter settings, although this results in poor performance compared to the adaptive ICS system of fig. 2, at least in some cases. The remaining elements of fig. 2 correspond to those shown in fig. 1 and are designated by the same reference numerals, except that the most significant digit is changed from "4" to "5".

Fig. 3 shows another embodiment of the analog part of a dual-band single wideband power amplifier RRU in Frequency Division Duplex (FDD) mode. The present embodiment is a modulation agnostic FDD standard system, and elements 601 and 604 operate similarly to elements 401 and 404 of fig. 1. Triplexer 608 separates the transmitter band from the receiver band. FDD systems use different transmit and receive frequencies for each channel. The function of the triplexer 608 is to pass the output of the power amplifier 604 to the antenna while isolating the receiver from the transmitter output. As with fig. 2, the ICS 609 system is used to increase isolation between the transmitter output and the receiver input, and to receive the output of PA 604 over link 605. The output of the ICS 609 is combined with the appropriate triplexer output by adders 610 and 611 and fed to LNA 612 and LNA 613 by link 605.

Fig. 4 is a depiction of one embodiment of an Interference Cancellation System (ICS). The function of the ICS is to generate a replica of the interference signal and to make it opposite in phase to the interference signal, thereby canceling the interference signal. The input to the ICS system is a sample of the power amplifier output. Coupler 605 is used to sample the power amplifier output. The output of the power amplifier is sampled and sent to diplexer 710. A diplexer (diplexer)710 separates the two frequencies into different portions. The delay module 701 time aligns the feedback interference signal with the sampled power amplifier output. The variable attenuator 702 is adjusted to ensure that the interfering signal and the sampled signal have equal amplitudes. The variable phase shifter 703 is adjusted to ensure that the interfering signal is in phase opposition to the sampled signal. A Digital Signal Processor (DSP)707 or microprocessor is used to control the attenuators and phase shifters. Adaptive algorithm based power detection in the DSP continuously monitors the signal at the output of the down-converter (DNC)708 and minimizes the interference level based on the detected power level. When the frequency band is in a transmit mode of operation, a power level of the interference is measured at the receiver. Similarly, elements 704, 705 and 706 are used to process the second frequency band.

Fig. 5 shows an embodiment of the analog part of a dual-band single wideband power amplifier RRU in Time Division Duplex (TDD) mode. The present embodiment is a modulation agnostic TDD standard system. The output of the wide band power amplifier 804 is fed to a circulator 807. The circulator provides some isolation between the transmit signal and the receiver input. A multiband filter 820 is placed between the circulator and the output antenna to attenuate out-of-band emissions. The third port of circulator 807 is connected to diplexer 808, diplexer 808 separating the two different operating bands. TDD mode requires that the transmitter and receiver operate using the same frequency band at different times. To provide isolation between the transmitter and receiver, switches 821, 822 are used. These switches may provide some isolation, but depending on the system specifications, additional isolation may be required. The ICS 809 can provide additional isolation between the transmitter output and the receiver input in the manner described above.

Fig. 6 is a depiction of another embodiment of an Interference Cancellation System (ICS). The function of the ICS is to generate a replica of the interference signal and to make it opposite in phase to the interference signal, thereby canceling the interference signal. The input to the ICS system is a sample of the power amplifier output. The output of the power amplifier is sampled and sent to diplexer 910. Diplexer 910 splits the two frequencies into different portions. The delay module 901 aligns the feedback interference signal in time with the sampled power amplifier output. The variable attenuator 902 is adjusted to ensure that the interfering signal has the same amplitude as the sampled signal. The variable phase shifter 903 is adjusted to ensure that the interfering signal is in phase opposition to the sampled signal. Digital Signal Processor (DSP)907 or a microprocessor is used to control the attenuators and phase shifters. A correlation-based adaptive algorithm in the DSP is used to minimize the interference level. After converting the signals to baseband using the two downconverters 920 and 909, the DSP correlates the two signals by controlling the output of switch 911 and the output of switch 912. Switches 911 and 912 alternate between the two channels. The purpose of the algorithm is to minimize the correlation between the sampled power amplifier output and the interference at the receiver. The calculated correlation coefficient is used as an error function in an adaptive algorithm, such as the Least Mean Square (LMS) algorithm.

Based on the above teachings, it can be appreciated by those skilled in the art that the RRU system of the present invention enables a single wideband power amplifier to be used for multi-band operation, thus saving hardware resources and reducing costs. The RRU system is also capable of reconfiguration and field programming since the algorithm can be adjusted at any time as software in the digital processor.

Furthermore, RRU systems are modulation scheme agnostic like QPSK, QAM, OFDM etc. in CDMA, TD-SCDMA, GSM, WCDMA, CDMA2000 and wireless LAN systems. This means that RRU systems can support multiple modulation schemes, multiple frequency bands and multiple channels.

Further, the techniques provided by the present disclosure may be configured as follows:

scheme 1. an interference cancellation system for improving isolation between a transmitter and a receiver in a wireless communication system, the interference cancellation system comprising: an input signal adapted for wireless transmission; at least one power amplifier for receiving the input signal and providing an amplified output; a feedback sensor for providing a feedback signal representative of at least one disturbance characteristic of the amplified output; cancellation logic to receive the feedback signal and to generate an inverted signal corresponding to the interference characteristic of the amplified output; a received signal comprising the interference characteristic; and a combiner for combining the inverted signal with the received signal to remove the interference characteristic from the received signal.

Although the invention has been described with reference to preferred embodiments, it is understood that the invention is not limited to the details described. Various alternatives and modifications are suggested in the foregoing description, however, other alternatives and modifications will occur to those skilled in the art. Accordingly, all such alternatives and modifications are intended to be included within the scope of the invention as defined in the appended claims.

Claims (10)

1. A system for improving isolation between a transmitter and a receiver in a multi-band wireless communication system, the system comprising:

a wideband power amplifier operable to receive a plurality of input signals, wherein each input signal is adapted for wireless transmission, and the wideband power amplifier is operable to provide an amplified output signal;

a feedback sensor operable to provide a feedback signal representative of an interference characteristic of the amplified output signal;

a receiver operable to receive a plurality of received signals;

a plurality of feedback sensors operable to provide a plurality of feedback signals representative of interference characteristics of the plurality of received signals;

cancellation logic operable to receive the feedback signal and the plurality of feedback signals, wherein the cancellation logic is configured to generate a plurality of inverted signals corresponding to interference characteristics of the plurality of received signals; and

a plurality of combiners operable to combine the plurality of inverted signals with the plurality of received signals to remove the interference characteristic from the plurality of received signals.

2. The system of claim 1, further comprising: a multiplexer operable to combine the plurality of input signals, wherein the multiplexer provides the combined input signal to the broadband power amplifier.

3. The system of claim 1, further comprising: a circulator operable to isolate the amplified output signal from the receive signal.

4. The system of claim 3, further comprising:

a duplexer operable to separate a combined receive signal into the plurality of receive signals; and

a plurality of switches operable to isolate the amplified output signal from the plurality of receive signals;

wherein an output of the diplexer is connected to an input of the diplexer.

5. The system of claim 1, further comprising: a triplexer operable to isolate the amplified output signal from the received signal.

6. The system of claim 1, further comprising: a multiband filter operable to attenuate out-of-band emissions.

7. The system of claim 1, wherein the cancellation logic comprises:

a duplexer operable to receive the amplified output signal and operable to divide the amplified output signal into a plurality of portions;

a plurality of delay modules, wherein each delay module is configured to receive an output of the duplexer and is operable to align the feedback signal with one portion from the plurality of portions;

a plurality of variable attenuators, wherein each variable attenuator is configured to receive an output from one of the plurality of delay blocks and is operable to adjust the feedback signal to be of equal magnitude to one of the plurality of portions;

a plurality of variable phase shifters, wherein each variable phase shifter is configured to receive an output from one of the plurality of variable attenuators and is operable to adjust the feedback signal to be in anti-phase with one of the plurality of portions;

a digital signal processor operable to control the plurality of attenuators and the plurality of variable phase shifters; and

a plurality of downconverters, wherein each downconverter is operable to receive a received signal from one of the plurality of received signals;

wherein the digital signal processor is operable to monitor an output of each of the plurality of downconverters.

8. The system of claim 7, wherein the digital signal processor is operable to detect a power level of each of the plurality of received signals, and is operable to minimize a level of interference between the amplified output signal and the plurality of received signals based on the detected power levels.

9. The system of claim 7, wherein the cancellation logic further comprises:

a plurality of switches, wherein each switch is configured to receive one of the plurality of portions and one of the plurality of receive signals and is operable to provide a signal to one of the downconverters from the plurality of downconverters.

10. The system of claim 9, wherein the digital signal processor is operable to correlate the plurality of receive signals and the amplified output signal by controlling the plurality of switches.