Active antenna system and methods of determining intermodulation distortion performance

An active antenna test system comprising an active antenna unit comprising: a test signal generator arranged to generate at least a first test signal and at least one second test signal; a plurality of transmitter modules operably coupled to the test signal generator wherein the plurality of transmitter modules are arranged to simultaneously process the first test signal and at least one second test signal to produce at least one radio frequency test signal therefrom; and at least one receiver module arranged to process one or more signals falling in at least one spectral band determined to be susceptible to intermodulation distortion products caused by the at least one radio frequency test signal being generated from the first test signal and at least one second test signal; and an intermodulation determination module operably coupled to the at least one receiver module and arranged to determine a first received intermodulation performance. A first transmitter module of the plurality of transmitter modules is operably uncoupled from the test signal generator and at least a first test signal and at least one second test signal re-applied to the remaining transmitter modules, such that the intermodulation determination module determines a second received intermodulation performance in order to determine an intermodulation distortion contribution of the first transmitter module therefrom.

CLAIM OF PRIORITY

This application is a U.S. National Stage Filing under 35 U.S.C. § 371 from International Patent Application No. PCT/EP2015/057598, titled “ACTIVE ANTENNA SYSTEM AND METHODS OF DETERMINING INTERMODULATION DISTORTION PERFORMANCE,” filed on Apr. 8, 2015, which claims the benefit of priority of United Kingdom Patent Application No, 1406330.9, titled “ACTIVE ANTENNA SYSTEM AND METHODS OF DETERMINING INTERMODULATION DISTORTION PERFORMANCE,” filed Apr. 8, 2014, the benefit of priority of each of which is hereby presently claimed, and each of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The field of this invention relates to an antenna arrangement and methods of testing, and in particular an antenna arrangement and a method of determining an intermodulation distortion performance of one or more components and compensation therefor.

BACKGROUND OF THE INVENTION

In a traditional radio network comprising a base station and passive antenna system, for example, at least one connectorised 50Ω port is generally located on the passive antenna system and at least one connectorised 50Ω port is generally located on the basestation. These connectorised 50Ω ports allow signals to be passed there between via at least one 50Ω connectorised cable. The connectors on the base station are typically 7/16 DIN radio frequency (RF) connectors or N-type RF connectors.

Wireless communication systems are prone to intermodulation distortion (IMD), affecting performance of desired communications, which is often an artefact of non-linear behaviour of signal processing elements within transmitters/receivers of passive antenna systems. Intermodulation can be generated by both active components, for example solid state electronics, and passive components, for example antennae, filters and connectors.

Passive intermodulation (PIM), is a known issue in passive antenna systems and is caused by signal, or signals, undergoing an undesired non-linear mixing to generate an interference frequency component as an artefact.

Due to the non-linear nature of some signal processing elements within the passive antenna system, fundamental frequency components can become distorted, thereby leading to a decaying series of higher order harmonic frequency components in the frequency domain. If these generated (undesired) harmonic frequency components mix again with the fundamental frequencies the resultant artefact signal may fall within a receive band of that processed by the passive antenna system, they can effectively block real communications/communication channels, for example by making a base station receiver believe that a real carrier is present when there is not. Generally, the IMD components of concern are 3rd, 5thand 7thorder, where the third order is of greatest signal strength and, therefore, often of primary concern.

Network operators have stipulated that antenna suppliers guarantee a certain level of PIM performance, which must be maintained over the lifetime of the supplied antennas. PIM performance can be affected after deployment by, for example, oxidation of connectors and/or printed circuit boards (PCBs). In the case of degraded PIM performance, network operators have forced many antenna manufacturers to replace entire networks of antenna installations at the antenna manufacturers cost. As a result, network operators need to test and maintain their network of antenna installations in order to highlight any degradation in PIM performance. Existing PIM testing techniques rely on the at least one connectorised 50Ω port for inserting test signals into the passive antenna system.

Passive antenna systems are often tested for PIM performance by inputting two fixed high power carrier frequencies into at least one connectorised 50Ω port and measuring the resultant IMD artefact presented on the same connectorised 50Ω port.

Regarding active antenna systems (AASs), similar PIM and IMD issues exist. However, traditional IMD testing techniques cannot be utilised as AASs do not provide at least one connectorised 50Ω port.

Referring toFIG. 1, a simplified block diagram of a traditional active antenna system100is illustrated. The example AAS100comprises a common public radio interface (CPRI)102, for interfacing to a baseband processing unit of a cellular base station, such as a third generation partnership project (3GPP™) evolved NodeB (eNodeB). The cellular base station comprises base band circuits that perform demodulation decoding in the receive path and modulation encoding in the transmit path. Multiple-in/multiple-out (MIMO) data for example is transferred between the base station and the AAS100in LTE mode operation. The AAS100further comprises one or more of its own baseband processing circuits104, which are arranged to perform functions including but not limited to for example system control, beamform manipulation and additional signal processing.

The AAS100comprises a plurality of parallel transceiver circuits106operably coupled via a switched coupler structure108to an antenna arrangement110comprising an array of cross-polarised antenna elements. At least one transmit module112and at least one receive module114within the transceiver106are also operably connected to the antenna arrangement110, as shown. A further transceiver path114provides a dedicated common calibration transceiver path to a calibration transceiver116.

In a transmit mode, the output from transmit module112is fed into the antenna arrangement110via a duplexer118and coupler structure120. In a receive mode, each receive circuit114is operably coupled, via the coupler structure120, to the antenna arrangement that is capable of receiving signals.

The inventors of the present invention have recognised and appreciated a desire to validate IMD and PIM performance in such an AAS, as well as provide a field-deployable test regime so that a performance over the lifetime of the AAS can be monitored.

Furthermore, the inventors of the present invention have recognised and appreciated a desire to provide self-test modes within such an AAS. In this manner, external test equipment may not be required if the AAS is serviced when installed at a cellular site. In addition, the inventors of the present invention have recognised and appreciated a desire to be able to remotely invoke self-test modes, or schedule them locally for a particular AAS, so that service personnel may not be required to visit installed cellular sites.

Also, if it is determined that the AAS is not performing correctly or within predefined performance limits, the inventors of the present invention have recognised and appreciated a desire to provide a system for an AAS that allows self-healing (e.g. determination that a problem exists and a solution to remotely and independently resolve that problem). This alleviates a need to replace the AAS in the field if there is degraded IMD performance.

SUMMARY OF THE INVENTION

In a first aspect of the invention, an active antenna test system comprises: an active antenna unit comprising: test signal generator arranged to generate at least a first test signal and at least one second test signal; a plurality of transmitter modules operably coupled to the test signal generator wherein the plurality of transmitter modules are arranged to simultaneously process the first test signal and at least one second test signal to produce at least one radio frequency test signal therefrom; at least one receiver module arranged to process one or more signals falling in at least one spectral band determined to be susceptible to intermodulation distortion products caused by the at least one radio frequency test signal being generated from the first test signal and at least one second test signal; and an intermodulation determination module operably coupled to the at least one receiver module and arranged to determine a first received intermodulation performance. A first transmitter module of the plurality of transmitter modules is operably uncoupled from the test signal generator and at least a first test signal and at least one second test signal re-applied to the remaining transmitter modules, such that the intermodulation determination module determines a second received intermodulation performance in order to determine an intermodulation distortion contribution of the first transmitter module therefrom.

In this manner, an intermodulation distortion performance of individual transmit (and receive) modules can be determined. In examples, a comparison of the respective contribution of individual transmit (and receive) modules, when coupled (enabled) and uncoupled (disabled) from the test signal generator.

In an optional example, the first transmitter module of the plurality of transmitter modules may be re-coupled to the test signal generator and a second transmitter module of the plurality of transmitter modules may be operably uncoupled from the test signal generator and at least a third test signal and at least one fourth test signal applied to the remaining coupled transmitter modules, such that the intermodulation determination module determines a further received intermodulation performance in order to determine an intermodulation distortion contribution of the second transmitter module therefrom.

In an optional example, the at least one further transmitter module of the plurality of transmitter modules may be re-coupled to the test signal generator and the at least one further transmitter module may be operably uncoupled from the test signal generator, such that an intermodulation performance of the at least one further transmitter module(s) is sequentially determined. In this manner, a benchmark IMD performance for a plurality (or all) of the transmit modules can be determined and a number (or each) of the of individual transmit (and receive) modules can be successively uncoupled (disabled) to determine their respective contribution, with the re-coupling (re-enabling) included to revert to the benchmark set up.

In an optional example, the first test signal may substantially equal the third test signal and/or the second test signal may substantially equal the fourth test signal. In this manner, the test signals to be applied may be the same in each successive iteration of the testing routine, with the coupling/uncoupling of respective transmit modules, or the test signals to be applied may be different.

In an optional example, the test signal generator may be arranged to at least generate the first test signal and the at least one second test signal following the test signal generator being arranged to disable normal traffic being routed through the active antenna unit.

In this manner, the same transmit (and/or receive) modules for normal operation may be re-used, with their use for normal traffic being temporarily disabled (before being re-enabled in order to re-commence working with normal traffic, subject to any optimisation that may have been applied to the respective transmit (and/or receive) modules.

In an optional example, the active antenna unit may comprise an inbuilt at least one test signal source arranged to perform one or more of the following: generate at least one standardised test signal; generate at least one test signal with at least one characteristic of the air interface being operated by the active antenna unit. In this manner, antenna units may be provided that support internal IMD calibration/performance determination, thereby removing a need for a plurality of external ports. In this manner, specialist or standardised test signals may be employed to meet defined regulatory requirements.

In an optional example, the intermodulation determination module may be further arranged to measure a power level and frequency of intermodulation components of the at least one radio frequency test signal and determine therefrom a resultant impact on receiver performance for at least one order of intermodulation distortion. In this manner, a simplified measurement mechanism may be employed, and/or the IMD contribution for plurality of orders of IMD can be determined.

In an optional example, the at least one receiver may be tuned to select a predetermined frequency spectrum susceptible to at least one of the intermodulation components from an artefact of the at least one radio frequency test signal and the intermodulation determination module may be arranged to determine whether the selected at least one intermodulation component exceeds an intermodulation distortion acceptable range or falls above or below a threshold value.

In this manner, a mechanism is provided that may automatically enable the selected receiver to tune to portions of frequency spectrum that are determined as susceptible to various orders of IMD.

In an optional example, at least one processor may be arranged to rank a plurality of transmitter modules in response to their respective determined intermodulation performance. In this manner, the more problematic transmit (and receive) modules can be highlighted and, for example, removed from service.

In an optional example, at least one processor may be arranged to adjust a parameter of at least one of: the at least one transmitter module, the at least one receiver module in response to the determined intermodulation performance thereby reducing an intermodulation level of signals processed by the active antenna unit. In an optional example, the at least one processor may be arranged to adjust a parameter by applying at least one of: an attenuation factor, a gain factor, a beamform weight adjustment, to a live air interface traffic signal processed by the active antenna unit. In this manner, a means of compensating and correction of transmit (and/or receive) modules that contribute to IMD can be effected.

In an optional example, the at least one processor may be arranged to offset an effect of the applied attenuation or gain factor by applying at least one beam weight compensation value to another transmit module or receiver module. In this manner, a means of compensating for a problematic transmit (and/or receive) module may be achieved by adjustment of, say, a beamform weight compensation value on another transmit module or receiver module.

In an optional example, an interface may be operably coupled to the test signal generator such that the test signal generator and intermodulation determination module are remotely controllable via the interface. In an optional example, the test signal generator and intermodulation determination module may be remotely controllable via the interface by a software program located in the cloud.

In accordance with a second aspect of the invention, a method of determining intermodulation performance in an active antenna test system comprising an active antenna unit having a plurality of transmitter modules is described. The method comprises: generating by a test signal generator at least a first test signal and at least one second test signal; applying the first test signal and the at least one second test signal to the plurality of transmitter modules; simultaneously processing the first test signal and the at least one second test signal output from the plurality of transmitter modules to produce at least one radio frequency test signal therefrom; processing one or more signals falling in at least one spectral band determined to be susceptible to intermodulation distortion products caused by the at least one radio frequency test signal being generated from the first test signal and at least one second test signal in at least one receiver module; determining a first received intermodulation performance of the processed one or more signals; uncoupling a first transmitter module of the plurality of transmitter modules from the test signal generator; re-applying the first test signal and the at least one second test signal to the remaining transmitter modules; determining a second received intermodulation performance for the remaining transmitter modules; and determining an intermodulation distortion contribution of the first transmitter module therefrom.

In a third aspect of the invention, a non-transitory computer program product comprises executable program code for performing the method of the second aspect when the executable program code is executed at an active antenna unit.

DETAILED DESCRIPTION

Example embodiments of the invention are described with reference to smart (or active) antenna technology used in a wireless communication system.

The following description focuses on embodiments of the invention that are applicable to active antenna arrays employed in Universal Mobile Telecommunication System (UMTS) cellular communication systems and in particular to a UMTS Terrestrial Radio Access Network (UTRAN) operating in a 3rdgeneration partnership project (3GPP™) system, and evolutions to this standard such as HSPA+ or long term evolution (LTE) system. However, it will be appreciated that the invention is not limited to this particular cellular communication system, but may be applied to any wireless communication system, including satellite communication systems, employing antenna arrangements.

Example embodiments are described where a processor or multiple processors are arranged to perform a number of functional operations. In some examples, dedicated modules are described to perform a number of functional operations. Thus, hereafter, the terms should be considered as interchangeable, and implementation-dependent, such that the physical component performing the functional operation may be a signal processor or module implemented using hardware, firmware or software.

Example embodiments are described where an active antenna unit of an active antenna test system comprises an intermodulation modulation distortion (IMD) determination module. However, in other examples, it is envisaged that the active antenna unit may be connectable to a remote IMD determination module or a distinct IMD determination module that is operably coupleable to the active antenna unit. In some examples, the IMD module may be a software module, comprising connectable circuits that may be used in the signal processing of the array.

Referring toFIG. 2, an example of an AAS architecture200comprising an active antenna test system according to aspects of the invention is illustrated.

In one example, a CPRI interface201is coupled to a CPRI decode/encode logic module203that may be operable to decode a signal(s) from a baseband unit (not shown). Alternative interfaces, such as ORI (Open Radio Interface), may be considered, and this should be considered as being within the teachings of this application. The signal from the CPRI decode/encode logic module203is input to a switching module205. In a first mode, switching module205is operable to pass the signal output from the CPRI logic203to at least one transmit baseband processing circuit207, which may be arranged to perform functions including, but not limited to, for example, system control, beamform manipulation and additional signal processing. In a second mode, switching module205is operable to isolate the at least one transmit baseband processing circuit207from the signal output from the CPRI decode/encode logic module203. In the second mode, the switching module205may be operable to couple a test signal source209to the at least one transmit baseband processing circuit207. This transition may occur if the AAS architecture200is in a test-mode operating state. The test signal source209may generate a test signal, for example, a tonal signal as used in conventional IP3 and IMD testing, or a signal comprising characteristics similar to an air interface being utilised. In some examples, at least one processor202may be arranged to function as a test signal generator/test signal source209arranged to perform one or more of the following: generate at least one standardised test signal; generate at least one test signal with at least one characteristic of the air interface being operated by the active antenna unit. In some examples, the test signal source209may synthesise the test signal form on-board logic, or load the test signal from a memory, for example a read only memory (ROM).

In this example, transmit baseband processing circuit207may receive at least two signals from test signal source209or a signal from CPRI decode/encode logic203. In some cases the first baseband signal can be the same or the second baseband signal. In either case, beamform weights may be applied via complex multiplication stages211,213to the signal to each signal respectively. In one example, the complex multiplication stages211,213may adjust the amplitude and phase of the signal passing there through to each signal respectively. In this context, a complex multiplier is one that uses a complex number in Cartesian format in order to multiply another signal represented in Cartesian format (namely the IQ signal) on the logical channel. The outputs from the two complex multiplication stages211,213are then passed through filter and interpolation stages. Thus, the outputs from the two complex multiplication stages211,213are passed through first low pass filters215,217, interpolation functions219,221, and second low pass filters223,225. The purpose of the first215,217and second223,225low pass filters is to spectrally filter the signals to conform to spectral mask requirements of the transmitter and limit aliasing as part of the interpolation. The interpolation functions219,221are used to transform the sample rate to that required by subsequent signal processing functions, such as digital-up-converters (DUC)227,229, and digital pre-distorter (DPD)231.

The filtered and interpolated signals output from second low pass filters223,225are then processed by latency adjustment blocks233,235using correction adjustment. The latency adjustment blocks233,235could be for example an integer sample delay line circuit or a Lagrange sample interpolator. In one example, a combination of both schemes could be applied in implementing the latency adjustment function. A Lagrange sample interpolator is a means of achieving non-integer clock delays of adjustment on the signal processing path. The latency adjustment blocks (e.g. Lagrange sample interpolator)233,235, interpolation functions219,221and second low pass filters233,225process signals in the Cartesian digital domain. In this manner, digital ‘I’ and ‘Q’ paths may be processed independently.

The output of latency adjustment blocks233,235are input to the DUCs227,229. One example purpose of the DUCs227,229is to convert the digital signals at the input, to a complex intermediate frequency (IF) output. For example, an input baseband signal centred at 0 Hz, may be up-converted to be centred at, for example, −50 MHz. Since the signals are in Cartesian IQ format, the carrier can be a centred positive or negative frequency about 0 Hz.

The signals in Cartesian format from the DUCs227,229are then summed in summation logic237. The output of the summation logic is then processed by a Crest Factor Reduction (CFR) signal processing block239. One example purpose of the CFR signal processing block239is to reduce a peak-to-average level of the signal being processed by subsequent signal processing chains. For example, LTE and wideband code division multiple access (WCDMA) filtered signals would generally have a peak-to-average ratio of approximately 14 dB. It is known that power amplifiers (PAs) operating with a back-off of 14 dB run inefficiently. Hence, the CFR signal processing block239is arranged to minimise the peak to average ratio often to something in the order of 8 dB, without substantially degrading the signal's quality figure of merit, such as its error vector magnitude (EVM) or spectral mask. In this manner, the PA may be allowed to run closer to its optimum efficiency point. Since the signal potentially going to each of the antenna element feeds will not be identical, by virtue of different beam weights applied per element, a common CFR block cannot be employed for all signals of a particular polarisation. As such, an independent CFR signal processing block239(and consequently digital predistorter (DPD) function231) is applied per signal processing chain basis, and/or on a per radio frequency path basis.

The output of the CFR signal processing block239is input to the DPD function231, which applies digital correction to the signal(s) based on a determined distortion caused by PA247. The DPD function231corrects for power amplification distortions such as AM-AM, AM-PM and memory effects of the PA247. A feedback point is required to sense the distortion caused by PA247, which is not shown inFIG. 2for the purposes of clarity. The output of the DPD function231is routed to a transmitter240comprising a pair of IQ digital to analogue convertors (DACs)241, filters243and the signals up-converted to the radio frequency using IQ mixers245. The up-converted signal is amplified at RF frequencies by PA247prior to routing via duplexer118, coupler structure120and antenna arrangement110, as described with respect toFIG. 1. In some examples, the output of PA247may optionally be coupled off (not shown) for DPD purposes.

One example of a receive circuit249is also shown, with the receive circuit249operably coupled, via the coupler structure120to the antenna arrangement110. The received signals detected by the antenna arrangement110are forwarded by the coupler structure120, and processed in respective duplexer118, and respective low-noise amplifiers (LNA)251. The LNAs251provide amplified versions of the received signals to a quadrature mixer253in order to generate respective quadrature and ‘Q’) down-converted signals. The quadrature mixers253are arranged to down-convert the respective amplified received signals based on a frequency down-conversion by selecting a local oscillator signal frequency255. The quadrature mixer output of quadrature down-converted amplified received signals are input to respective low-pass filters257and thereafter to respective analogue-to-digital converters259in order to transform the quadrature down-converted received signal to a digital form. The resultant digital signals are passed to a receive baseband processing circuit261.

The receive baseband processing circuit261receives the resultant signals via a digital-down-converter (DDC)263. One example purpose of the DDC263is to convert the complex intermediate frequency (IF) signal into a digital signal, before passing the digital signal into a latency adjustment block265, first receive low pass filter267, decimation function269, second receive low pass filter271and complex multiplication stage273, which is operable to adjust the phase and or amplitude of the signal such as for example apply beamform weights and or correct for amplitude and phase mismatches between that of a plurality of receivers of the AAS. The resultant signal is output to a beamformer module275, which outputs a resultant signal to a second switching module277, which either passes the signal to the CPRI decode/encode logic203or to a measurement module279. The beamformer module275may aggregate the signal received from a plurality of receive paths with the appropriate beamform weights to generate one aggregated output signal, for example a beam signal.

In this example, a control module281, for example a microprocessor or microcontroller, may be operably coupled to at least the measurement module279, the test signal source209and a memory283. The control module281may be operable to invoke a test mode operating state to generate at least one test signal, and at least two test signals in a case of intermodulation distortion (IMD) performance testing, and be further operable to determine the effects on the test signal(s) once routed through the transmit modules and a receive module. In some examples, the memory283may store test result values.

In one example, the measurement module279may be a type of power measurement module that may be operable to determine if a received signal is within a defined range or above/below a threshold level. For example, the measurement module279may be a power squared meter module utilising a multiplication function in order to determine a power level of a received signal. An equation to determine the power level may then be determined by, for example, using the equation in [1].

In some other examples, the measurement module279may be operable to perform Fast Fourier Transforms (FFTs) on a received signal. Thus, the measurement module279may comprise, or be configured to perform the operation of, an intermodulation determination module that may comprise a Fast Fourier Transform (FFT) module. The FFT module may be arranged to determine at least a magnitude of identified intermodulation components from the one or more signals falling in at least one spectral band determined to be susceptible to intermodulation distortion products caused by the at least one radio frequency test signal being generated from the first test signal and at least one second test signal. By being able to perform FFTs, the measurement module279may be able to identify any IMD components from other spurious signals and noise from a received signal. This may have an advantage of allowing a more accurate reading of signal degradation caused by IMD, for example, thereby allowing for more efficient mechanisms to reduce the effects of IMD on received signals.

In some examples, the control module281and/or the measurement module279may be operably coupled to the transmit baseband processing circuit207and the receive baseband processing circuit261to facilitate self-healing (not shown for clarity), for example IMD self-healing.

In some examples, a processor202may be operably coupled to test signal source209in the active antenna unit200and may comprise an IMD spectrum determination module that is arranged to determine a frequency spectrum range that is susceptible to at least one order of intermodulation component based on at least one radio frequency test signal created by routing at least the first and second test signals from test signal source209through at least one of a plurality of transmit modules. The test signal spectral profile may allow for the calculation of a deterministic receive spectrum, which may be susceptible to IMD components. The processor202may also be couplable to at least one selected receiver to tune the selected receiver to the predetermined frequency spectrum.

In some examples, a test mode of operation may be initiated periodically by the AAS architecture200. In other examples, a test mode of operation may be initiated remotely by a remote operator, for example via a communications link and/or a dedicated interface, or by service personnel when on site.

In this example, if a test mode of operation has been initiated, for example via a remote operator, the first switching module205may couple test signal source209to at least one transmit baseband processing circuit207, wherein a plurality of transmit baseband processing circuits for a plurality of antenna arrangements110are envisaged. A second switching module277may couple the measurement module279to at least one corresponding receive baseband processing circuit261, wherein a plurality of receive baseband processing circuits for the plurality of antenna arrangements110are envisaged.

It should be appreciated by skilled artisans that the switching to a test signal source209need not be performed within the AAS200, and could be performed on a baseband processing unit coupled to an end of the CPRI interface201.

In accordance with examples of the invention, a first transmitter module of the plurality of transmitter modules is operably coupled and then uncoupled from the test signal generator, for example test signal generator/source209, where at least a first test signal and at least one second test signal of the test signal can be generated from source209in order to perform two distinct IMD measurements. In examples of the invention, the two distinct IMD measurements comprise a first IMD determination for signals passing through the remaining transmitter modules, when the first transmitter module is uncoupled (or disabled) and a second IMD determination for signals passing through the first transmitter module and the other transmitter modules, when the first transmitter module is coupled (or enabled). In this manner, by comparison of the two distinct measurements, an intermodulation determination module275may be operable to facilitate a determination of intermodulation distortion contribution of the first transmitter module.

After switching module205has coupled test signal source209to at least one transmit baseband processing circuit207, the test signal source209may output at least one test signal to the relevant transmit baseband processing circuit207, and in the case of IMD testing, output at least two test signals capable of generating an RF test signal defined by having disparate spectral content between the at least two test signals. The test signals may be, as discussed above, tonal test signals or test signals or with characteristics similar to an air interface being operated on by the AAS in network operational mode. The test signals pass through to a plurality of transmitter modules, wherein the plurality of transmitter modules are arranged to simultaneously process a first test signal and at least one second test signal to produce at least one radio frequency test signal therefrom, to be output by a relevant antenna arrangement110.

In some examples, the same (e.g. tonal) test signal may be repeatedly applied as the first and second test signals wherein, however, the test signal may be up-converted in such a way that they are spectrally disparate as transformed to the radio frequency test signal. In other examples, it is envisaged that different (e.g. tonal) test signals may be applied as the first and second test signals, for example a subsequent iteration of the test signals applied to a further transmit module may be a third test signal and a fourth test signal.

In response to this, at least one relevant receiver may be configured to receive a spectrum determined to be susceptible to IMD components from the outputted radio frequency test signal and pass the received signal through a relevant receive baseband processing circuit261to the measurement module279via beamformer module275and second switching module277.

In some examples, the same circuits/modules may be used for live normal traffic. In such a situation, when a test mode of operation is to be initiated, the test signal generator209may be arranged to at least generate the first test signal and the at least one second test signal following a disabling of normal traffic being routed through the active antenna unit.

In this example, the test signal output from test signal generator209may comprise two separate test frequencies that may be combined in summation logic237. An advantage of using two separate test frequencies may be that PIM and IMD effects can be closely simulated. The signals from the test signal generator209may be the same signals that are output from the test signal generator209. However, in some examples, a difference in the subsequent transformation process, for example digital up conversion stage229,227, of these signals can be converted to that of being spectrally disparate as amalgamated in the at least one radio frequency test signal. The combined test signal may be passed through the relevant transmit baseband processing circuit207and transmitter240before being output by the relevant antenna arrangement110. Due to inherent non-linear effects introduced by the transmit circuitry and the receive circuitry, the combined test signal may allow the formation of artefact IMD component signals that may interfere with the receive circuitry249or signals processed there through. As a result, during the test mode, the receive circuitry249may be tuned or configured to receive spectrum that is determined to be susceptible to one of the spectral artefacts generated by the combined test signal as processed by non-linear circuits. Further, the DUC227,229DDC263and receive RF LO frequencies may be tuned to receive the relevant of the determined to be susceptible spectrum.

In one example, the measurement module279may be, or comprise, an intermodulation determination module operably coupled to the at least one receiver module, and arranged to determine a received intermodulation performance. In one example, the measurement module279may facilitate determination of whether (or not) the received intermodulation performance is within a specified range or above/below a specified or threshold value. The specified range or value may be pre-programmed. If the measurement module279determines that the received intermodulation performance is within a specified range or above/below a specified or threshold value, it may signal this to the control module281. In some examples, the control module281may store the result in memory283.

Thus, an active antenna test system200comprises an active antenna unit comprising: a test signal generator209, arranged to generate at least a first test signal and at least one second test signal; a plurality of transmitter modules operably coupled to the test signal generator wherein the plurality of transmitter modules are arranged to simultaneously process the first test signal and at least one second test signal to produce at least one radio frequency test signal therefrom; at least one receiver module arranged to process one or more signals falling in at least one spectral band determined to be susceptible to intermodulation distortion products caused by the at least one radio frequency test signal being generated from the first test signal and at least one second test signal; and an intermodulation determination module operably coupled to the at least one receiver module and arranged to facilitate determination of a first received intermodulation performance, wherein a first transmitter module of the plurality of transmitter modules is operably uncoupled from the test signal generator and at least a first test signal and at least one second test signal re-applied to the remaining transmitter modules, such that the intermodulation determination module determines a second received intermodulation performance in order to determine an intermodulation distortion contribution of the first transmitter module therefrom.

If the measurement module279is used to determinate that the received signal artefact is not within a specified level, the measurement module279may signal this to the control module281. In response to this, the control module may initiate an optimisation procedure in order to attempt to bring the received component frequency within the specified level.

In this example, all of the transmit processing circuits240may be tested in turn. In one example implementation, at least two test signals are generated and applied to the plurality (or all) of transmitter modules. The test signals output from the plurality of transmitter modules are simultaneously processed to produce at least one (combined) radio frequency test signal. At310, at least one processor202processes one or more signals falling in at least one spectral band determined to be susceptible to intermodulation distortion products caused by the at least one radio frequency test signal being generated from the first test signal and at least one second test signal as observed through at least one receiver module. At311, a first received intermodulation performance of the processed one or more RF signals is determined. This sets a bench mark for the IMD performance when test signals are applied to a plurality (e.g. a majority or all) of the transmit modules. Thereafter, transmit modules are successively uncoupled to determine their effect on the IMD performance, and then re-coupled to receive test signals (to return to the benchmark state) and a next transmit module uncoupled.

This may have an advantage that the measurement module279is able to rank each of the transmit baseband processing circuits according to their contribution to IMD. In some examples, the ranking data may be stored in a memory, for example memory283.

An optimisation procedure may be performed on the transmit baseband processing circuits that contribute most in terms of IMD products based on the stored ranking data. In some examples, the ranking data may optionally include details of the IMD levels measured, time of the tests and frequencies used in the tests.

In some examples, if the measurement module279determines that the performance of the received resultant signal(s) is still outside the specified desired value, after the relevant transmit baseband processing circuits have been optimised, based on their rank, for example, the measurement module may perform a similar test regime on receive circuits. In this mode of operation, each receive circuit may be tested in turn, and separately combined with beamformer module275. A rank based on each of the receiver's impact on IMD may also be generated by the measurement module279and stored in memory.

In some examples, optimisation procedures may include reducing gain of analogue or RF gain stages, and/or disabling some or all of the worst performing transmit and/or receive circuits within the AAS architecture200. As a result, in some examples, some of the better performing receive and transmit circuits within the AAS architecture200may be modified to compensate for any disabled or badly performing receive and transmit architectures. Further, in some examples, it may be necessary to alter beamform weights of the AAS architecture200to compensate for the resultant beam shape of the AAS architecture200due to IMD effects created by one or more transmit or receive modules.

Since, for example, third order intermodulation products increase three decibels for every one decibel of increased power applied to a non linear circuit, output power of a transmitter(s) could be adapted to minimised the effects of generating IMD components by decreasing the power generated by such circuits. Other optimisations could include adapting the performance of onboard algorithms such as DPD (digital predistortion) to linearize the transmitter over a larger dynamic range essentially improving the linearity and minimising IMD.

In some examples, it may be possible to adapt a frequency selective filter to shape the response in the receive circuit or transmit circuit, thereby potentially allowing for a suppression of the signals generated as IMD products from the test signals.

In some other examples the frequency plan of the AAS in terms of the frequencies used may be adapted to allow for the avoidance of IMD product artefacts from disrupting live traffic.

Referring toFIG. 3, a simplified test procedure300is illustrated, for example that may be utilised in the AAS architecture ofFIG. 2. In this example, the test procedure300may be initiated302by a remote user via a communications link and/or a dedicated interface, for example by a user present at the installed AAS architecture ofFIG. 2, or by an internal test scheduler within the AAS architecture ofFIG. 2. The flowchart300commences by initiating a start of the test and optimisation at302with a method of determining intermodulation distortion (IMD), and optionally inclusive of PIM, performance in an active antenna test system comprising an active antenna unit having a plurality of transmitter modules. Hereafter, the term IMD performance encompasses additionally or alternatively determining a PIM performance of the various transmit or receive modules or combinations thereof.

At304, at least a first test signal and at least one second test signal are generated. At306, the first test signal and the at least one second test signal are applied to the plurality (or all) of transmitter modules. At308, the first test signal and the at least one second test signal output from the plurality of transmitter modules are simultaneously processed to produce at least one radio frequency test signal. At310, at least one processor (e.g. processor202fromFIG. 2) in conjunction with at least one receiver circuit249processes a spectral band determined to be susceptible to intermodulation distortion products caused by the at least one radio frequency test signal being generated from the first test signal and at least one second test signal in at least one transmitter module and at least one receiver module. At311, a first received intermodulation performance of the at least one transmitter module and at least one receiver module is determined. This sets a bench mark for the IMD performance when test signals are applied to a plurality (e.g. a majority or all) of the transmit modules and a plurality of receive modules (e.g. a majority or all). Thereafter, if the IMD performance is not within a specified threshold level as determined in316the contribution of each of the transmit or receiver as selected in380modules are ranked through being successively uncoupled to determine their effect on the IMD performance, and then re-coupled to receive test signals (to return to the benchmark state) and a next transmit module uncoupled.

Thus, at312, if the IMD is not within specified limits as determined in316and a decision to optimize the transmitter performance of the array is determined in380, a first transmit module of the plurality of transmitter modules is uncoupled from the test signal generator, and the first test signal and the at least one second test signal re-applied to the remaining transmit modules at313. At314, a second received intermodulation performance is determined for the remaining transmit modules, i.e. notably measured without the uncoupled first transmit module in order to determine an intermodulation distortion contribution of the first transmitter module.

At386, a determination may be made as to whether the IMD performance of the uncoupled transmit module is the final one of the plurality of transmit modules, wherein the result of the IMD performance may be stored in a ranked system with the largest contributor to IMD being at the top of the ranking for any optimisation. If it is determined at386that the IMD measurement ranking of transmit modules is not complete, the test procedure300may then transition to312and another transmit module uncoupled and the previous uncoupled transmit module re-coupled in order to receive the first and second test signals.

If it is determined at386that the IMD level is ranked for a plurality of transmit modules, the test procedure300may determine that an optimisation routine should be performed on one or more of the transmit modules, for example including the uncoupled transmit module, at318. For example, such an optimisation routine may comprise one or more of: varying gain/attenuation levels, adjusting power supply levels, enhancing modules within the transmit and/or the receive circuits, disabling badly performing transmit and/or receive circuits, etc. If it is determined that all possible optimisations have been performed at320, then the newly optimised IMD performance of the AAS can be measured in311. If the IMD is determined to be within acceptable specified thresholds, or if no more optimisations are available to the algorithm, the algorithm can end at382. If, however, the IMD is still outside specification having completed the transmit optimisations, a determination can be made at316to pursue more optimisations.

At380, since the transmit optimisation has been previously performed, an optimisation on receiver performance may be determined based on380.

In this example, in much the same way as that pursued for transmit ranking of contributors to IMD, a first receive module of the plurality of receive modules may be uncoupled from forming an aggregated signal392as part of a beamforming process, and first test signal and the at least one second test signal re-applied to the transmit modules at393. At394, a second received intermodulation performance may be determined for the remaining receive modules, i.e. notably measured without the uncoupled first receive module in order to determine an intermodulation distortion contribution of the first receiver module.

At384, a determination may be made as to whether the IMD performance of the uncoupled receive module is the final one of the plurality of receive modules. The result of the IMD performance may be stored in a ranked system with the largest contributor to IMD being at the top of the ranking for any optimisation. If it is determined at384that the IMD measurement ranking of receive modules is not complete, the test procedure300may then transition to392and another receive module uncoupled and the previous uncoupled receive module re-coupled in order to receive the first and second test signals. If it is determined at384that the ranking is complete an optimisation routine may be performed. A receive optimisation routine may be performed at318. This may include increasing the current or voltage of one or more receiver circuits to influence its IMD performance. Further enhancements could include optimisation of filter responses, in order to suppress the RF test signals or IMD component artefacts generated therefrom. A further optimisation may be to decrease the gain in a receiver or uncouple a receiver from being aggregated with other signal in the beamforming process.

Thus, in some examples, each transmit module may be tested successively, thereby allowing a transmit module rank to be determined based on IMD performance. If the IMD level is still not within the threshold level, which may be predefined or vary during tests for example, each receive circuit may be tested in turn, thereby providing a rank of receive circuits based on IMD performance.

Referring toFIG. 4, a more detailed test and self-healing procedure400is illustrated, which may be utilised for example in the AAS architecture ofFIG. 2. In this example, the test and self-healing procedure400may, for example, be initiated402by a remote user via a communications link, by a user present at the installed AAS architecture ofFIG. 2, or by an internal test scheduler within the AAS architectureFIG. 2.

The test procedure commences at402. At404the test and self-healing procedure400selects at least two test signals/frequencies to be used for IMD testing and the test signals are applied to a plurality of transmit modules. At least one receiver is also selected and configured to receive spectrum determined to be susceptible to the IMD products of the at least two test signals/frequencies output of the plurality of (or all) transmit modules. The spectrum susceptible to IMD products may be determined by, for example, selecting a separation of “f”, knowing the first “f1” lower and the at least second “f2” higher signal frequencies of the at least one radio frequency test signal as located in the RF spectrum. For example in third order IMD, the band susceptible to this third order IMD, as known in the art, is located at “f2+f” in the spectrum or “f1−f”. Depending on the IMD order of the test, the first “f1” lower and the at least second “f2” higher signal frequencies may be selected in conjunction with the receiver spectrum selection to carry out the IMD test. At406, all transmit modules are disabled, and the selected receiver(s) samples the receive power level to determine an ambient RF noise level, thus allowing for an accurate assessment of the IMD signal artefact related to the overall signal processed by the receiver. In some examples, the receiver may be arranged to sample signals in a portion of a frequency spectrum that is determined as being susceptible to at least one intermodulation component artefact of at least one of the processed radio frequency test signal created by the at least two test signals. In this manner, the receiver may be tuned to a predetermined frequency spectrum in order to, say, determine whether the selected spectrum contains at least one intermodulation component exceeding an intermodulation threshold value. In some examples, an intermodulation determination module or a processor configured to calculate intermodulation distortion may perform such a determination when operably coupled to the receiver or forming part of the selected receiver. In one example, an intermodulation determination module, as part of the processor or operably coupled to the processor may comprise a Fast Fourier Transform module arranged to determine at least a magnitude of identified intermodulation components from the one or more signals falling in at least one spectral band determined to be susceptible to intermodulation distortion products.

At408, the transmit module is re-enabled and the selected receiver(s) again samples the receive power level from the all transmit modules with the at least two test signals were applied to. The receiver(s) may again be arranged to sample signals in a portion of a frequency spectrum that is determined as being susceptible to at least one intermodulation component from an artefact of at least one radio frequency test signal created by the at least two test signals. Advantageously, the power level may be compared to the previously sampled receive power level in406, in order to determine a level of interference induced by the previously disabled transmit modules. Thereby allowing for the effect of the transmission of the at least two test signals impact on the received signal performance of the receiver modules.

Optionally, a further step could be added that allows the procedure, or algorithm, to determine410if the determined interference in408is a characteristic of IMD. For example, if the receiver is tuned to receive spectrum susceptible to a third order IMD component, reducing the transmit power by 1 dB, as shown in410, should result in a 3 dB decrease in interference if the interference is indeed a product of third order IMD. This may ensure that any IMD performance algorithms that are run may follow predictable performance.

At412, the test and self-healing algorithm determines whether the IMD level of the received signal is within specification. In some examples, the specification may be dictated by a programmed value, or determined by an optional threshold level detection step. If it is determined that the IMD level is within specification, the algorithm may determine at414if other tests are required, for example whether other IMD orders should be checked, say by re-tuning the receiver to other spectral band determined to be susceptible to intermodulation distortion products. If the algorithm determines that no more testing is required at414, the algorithm may store, at416, the results of the test before the algorithm terminates at418. In some examples, the algorithm may store the time of the test and/or the levels measured and/or frequencies used in the test. In some other examples, the algorithm may transfer these parameters to another network element, such as an Operations and Management Centre (OMC).

If, at412, it is determined that the IMD level of the received signal is not within specification, the algorithm may, at420, perform at least one transmit optimisation routine and determine whether all transmit optimisations have been completed. If it is determined, at420, that not all transmit optimisations have been completed, the process may transition to422. At422, a sequence is initiated to test each transmit circuit to determine each transmit module's individual contribution to IMD. In this example, all bar one of the plurality of power amplifiers within the transmit circuit may be successively enabled and the resultant receive power level is sampled. In this example, disabling the power amplifier allows the entire transceiver module to substantially eliminate any signal being output from the power amplifier to the antenna arrangement. Thus in this way any the disabled power amplifier will not substantially contribute to any IMD signals measurements results. This sampled value may then be stored at424in a memory.

At426, a determination is made as to whether there are more transmit modules (including, for example, power amplifiers) to test. If there are more transmit modules/power amplifiers to test within the transmit circuit, the algorithm transitions to428and disables a further transmit module/power amplifier (and typically re-enables a previously disabled transmit module/power amplifier), before sampling the received power level at422. If it is determined at426that all transmit modules/power amplifiers have been tested for the transmit circuit, the algorithm may transition to430, and rank the tested power amplifiers by their received power level, which may take into account respective IMD level contributions from each of the transmit modules/power amplifiers.

At432, a modification may be applied to some transmit modules/power amplifiers based on their rank, in order to reduce their respective contribution in terms of IMD product artefacts. For example, power levels may be altered on a per transmitter basis to reduce the impact on IMD performance.

As is known in the art, backing the signal amplitude processed to IMD artefact level is not a linear scaling. For example, for 3rdorder IMD component artefacts, for every 1 dB power reduction of the transmitter output power, around a 3 dB reduction in the IMD products generated would ensue. Further, for 5thorder IMD, around a 5 dB reduction would manifest. Thus modest changes to output powers of certain power amplifiers in the array may have a disproportionate impact on the overall IMD performance. In some examples, transmitters may be limited to operate up to a certain power level. In this example, an amplitude for each transmitter module and its associated power amplifier profiles may be determined at432and fed to a beamform optimisation routine, for use in configuring, for example, beamformer module211,213fromFIG. 2. The beamform optimisation routine would, for example, trade off reduced RF power processing capability of a particular transmit module of the array with the need to maintain beam shape conformance of the AAS. The algorithm may then transition back to404and re-test the performance of the system as discussed above.

If, at412, the IMD is still outside specification, and all transmit optimisations have been completed at420, the algorithm may transition to434and determine whether receive circuit optimisations may be performed and if so whether they are complete. If it is determined that all receiver optimisations have been completed at434, the process may transition to416and store the results as discussed above, before the process terminates at418.

If it is determined at434that not all receiver optimisations have been completed, the algorithm may transition to436and test each receiver in turn, for example in a similar manner to that performed on the earlier transmit modules. Thus, at436, the algorithm may enable all bar one of the receivers and sample and measure the receive power level of any IMD component artefact. This measured result of the IMD component artefact pertaining to this receive modules may then be stored at438in a memory.

At440, a determination is made as to whether there are more receivers to test. If there are more receiver modules/receivers to test, the algorithm may transition to442to select a new receive module to test and disable a further receiver module/receiver, before sampling and measuring the received IMD component artefact power level at436. If it is determined by the procedure at440that all receivers have been tested, the procedure may transition to444and rank the receiver module/receiver based on their impact on IMD performance.

At446, a modification may be applied to some receiver modules/receivers based on their rank to mitigate their contribution in terms of intermodulation products. For example, the gain of analogue or RF amplifier stages may be reduced for receivers that have a disproportionate impact on IMD performance, which may be determined from the determined ranked measurement result data. In this example, receive beamform weights may be determined for each required receiver and fed to a beamform optimisation module, for example beamformer module275fromFIG. 2. In some examples, the signal applied to the beamform optimisation module may be attenuated first to suppress its capability to generate IMD component artefacts. In some examples, this attenuation may be offset, for example, by altering other receiver beamform weights in order to compensate for the offset.

Subsequently, the algorithm may transition back to414to determine whether there are any more IMD tests to perform. The test may include optionally testing for third, fifth or seventh order IMD component artefacts. If there are no more different order IMD tests and optimisations to complete, the routine or algorithm may proceed to416. The results of the test, any optimisations, and the date and time of carrying out the test may be stored in416. This result may be stored in the AAS or in any device operably connected to it. The optimisation routine can then terminate in418.

Referring now toFIG. 5, there is illustrated a typical computing system500that may be employed to implement signal processing functionality in embodiments of the invention. Computing systems of this type may be used in network elements/wireless communication units. In some examples, the computer program and storage media may be located in the cloud or somewhere in the network of the operator environment, for example at an Operations and Management Centre (OMC). Those skilled in the relevant art will also recognize how to implement the invention using other computer systems or architectures. Computing system500may represent, for example, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment. Computing system500can include one or more processors, such as a processor504. Processor504can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control logic. In this example, processor504is connected to a bus502or other communications medium.

Computing system500can also include a main memory508, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by processor504. Main memory508also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor504. Computing system500may likewise include a read only memory (ROM) or other static storage device coupled to bus502for storing static information and instructions for processor504.

The computing system500may also include information storage system510, which may include, for example, a media drive512and a removable storage interface520. The media drive512may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media518may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive512. As these examples illustrate, the storage media518may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, information storage system510may include other similar components for allowing computer programs or other instructions or data to be loaded into computing system500. Such components may include, for example, a removable storage unit522and an interface520, such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory) and memory slot, and other removable storage units522and interfaces520that allow software and data to be transferred from the removable storage unit518to computing system500.

Computing system500can also include a communications interface524. Communications interface524can be used to allow software and data to be transferred between computing system500and external devices. Examples of communications interface524can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via communications interface524are in the form of signals that can be electronic, electromagnetic, and optical or other signals capable of being received by communications interface524. These signals are provided to communications interface524via a channel528. This channel528may carry signals and may be implemented using a wireless medium, wire or cable, fibre optics, or other communications medium. Some examples of a channel include a phone line, a cellular phone link, an RF link, a network interface, a local or wide area network, and other communications channels.

In this document, the terms ‘computer program product’ ‘computer-readable medium’ and the like may be used generally to refer to media such as, for example, memory508, storage device518, or storage unit522. These and other forms of computer-readable media may store one or more instructions for use by processor504, to cause the processor to perform specified operations. Such instructions, generally referred to as ‘computer program code’ (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system500to perform functions of embodiments of the present invention. Note that the code may directly cause the processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system500using, for example, removable storage drive522, drive512or communications interface524. The control logic (in this example, software instructions or computer program code), when executed by the processor504, causes the processor504to perform the functions of the invention as described herein.