Device and method for the analysis of a measured signal transmitted via a multi-channel system

A device, in particular, a multi-channel oscilloscope, for the analysis of at least one measured signal transmitted via a multi-channel system, with several measurement channels. The device includes in each case a sampling device, a baseband mixing device, and a filter device, and an analysis device. The measured signal is supplied to the measurement channels and to the respective sampling devices for simultaneous sampling. The sampled measured signal is supplied to the baseband mixing devices connected downstream of the sampling devices for the mixing of the measured signal down into the baseband, to the filter devices connected downstream of the baseband mixing devices for the decimation of the sampled values of the measured signal in the baseband and to the analysis device connected to the filter devices for the analysis of the measured signal.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to PCT Application No. PCT/EP2007/006102, filed on Jul. 10, 2007, and German Patent Application No. 10 2006 042 114.0, filed on Sep. 7, 2006, the entire contents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a device, in particular, a multi-channel oscilloscope, and to a method for the analysis of a measured signal transmitted via a multi-channel system.

2. Discussion of the Background

In communications technology, a multi-channel system is used for the transmission of signals, in order to increase the data rate per bandwidth used and to reduce the bit-error rate. A multi-channel system can be used, for example, in a wireless communications system, which provides a so-called single-input multiple-output (SIMO) system via one transmission antenna and several reception antennas, or a so-called multiple-input multiple-output (MIMO) system via several transmission antennas and several reception antennas. DE 101 14 052 C1 describes a radio transmission method with multiple transmission and reception antennas operating simultaneously within the same frequency band.

As a prerequisite for a particularly high-quality and accurate analysis and/or recording of the measured signal transmitted via the multi-channel system, the measured signal must be simultaneously de-coupled at outputs of the multi-channel system and simultaneously processed. In this context, with a multi-channel system comprising transmission antennas and reception antennas, it has hitherto generally been the case that a measured signal de-coupled at the one reception antenna is processed with a time offset relative to the measured signal de-coupled at the other reception antenna, that is to say, for example, supplied in a time succession to a sampling device and sampled with a time offset relative to one another. A time-offset processing of the measured signal de-coupled at several reception antennas restricts the measurement rate and leads to an impairment of the analysis results.

SUMMARY OF THE INVENTION

Embodiments of the present invention advantageously provide a device and a method for the analysis of a measured signal transmitted via a multi-channel system, wherein the measured signal is conditioned for the implementation of the analysis at a particularly low technical cost and at a particularly high speed.

Accordingly, the device, which is preferably designed as a multi-channel oscilloscope, comprises several measurement channels, which provide in each case a sampling device, in each case a baseband mixing device and in each case a filter device. In this context, the respective filter device of the respective baseband mixing device and the latter are connected downstream of the respective sampling device. The device also comprises an analysis device connected to the filter device for the analysis, for example, modulation analysis, of the measured signal.

In the method according to the invention, the measured signal is simultaneously supplied to the measurement channels and the sampling devices disposed in the latter and simultaneously sampled in the latter on all measurement channels. A sampled, measured signal provided by the sampling devices is supplied to the baseband mixing devices and mixed synchronously down into a baseband. The sampled measured signal is supplied to the filter devices for decimation of the sampled values and to the analysis device connected downstream of the filter devices for analysis.

The advantages achieved with the invention consist, in particular, in that the measured-signal analysis and/or modulation analysis can be implemented more rapidly by means of the device according to the invention and the method according to the invention, because the sampled measured signal is provided at the end of all measurement channels at the same time. Moreover, a particularly good measurement accuracy can be achieved with the method according to the invention. Furthermore, a bandwidth and recording length available in the measurement device, in particular a multi-channel oscilloscope, is effectively utilized. No further hardware is required in addition to the measurement device, because the outputs of the multi-channel system designed, in particular, as a MIMO system can be coupled directly to the measurement channels of the measuring device. Moreover, the purchasing cost for a measuring device comprising several measurement channels is particularly low by comparison with the purchasing cost for cascaded measuring devices each comprising only one measurement channel.

The number of measurement channels preferably corresponds to the number of outputs of the multi-channel system, in particular, to the number of reception antennas formed as outputs within the multi-channel system, at which the measured signal can be de-coupled.

For the synchronous mixing down of the sampled measured signal on the measurement channels, the baseband mixing devices preferably operate in phase.

According to an advantageous embodiment, the measurement channels provide in each case a further baseband mixing device and in each case a further filter device. The respective, further baseband mixing device, which is preferably connected downstream of the respective further filter device, is connected downstream of the respective filter device. In an expedient further development, the respective first baseband mixing device is used for coarse mixing of the sampled signal, whereas the respective further baseband mixing device is designed for fine mixing of the sampled signal.

According to an advantageous further development, a buffer device for recording the sampled signal determined for the analysis is connected downstream of the filter devices provided on the measurement channels.

In order to achieve an adequate coherence of the measurement channels and to provide a common phase relationship between the measurement channels, the first and/or the further baseband mixing devices and the first and/or the further filter devices are expediently designed to be capable of delay-time calibration. For this purpose, a time-delay element, which is preferably controlled by a common pulse generator, is expediently connected in each case to the first and/or the further baseband mixing devices and to the first and/or the further filter devices.

In this context, a common pulse generator can be connected in each case preferably to the time-delay elements connected to the baseband mixing devices and to the filter devices and to the further baseband mixing devices and to the further filter devices.

In an expedient further development, the real component of the baseband signal and the imaginary component of the baseband signal are obtained in the baseband mixing devices from the sampled measured signal.

In order to mix the sampled measured signal down into the baseband, the baseband mixing devices preferably provide a digital oscillator generating a carrier frequency expediently specified for the mixing down of the sampled measured signal for the multi-channel system.

Corresponding components are provided with identical reference symbols in all the drawings.

FIG. 1shows a schematic circuit diagram of a device designed as an oscilloscope2, which is connected to a multi-channel system4. The multi-channel system4in the exemplary embodiment is a MIMO system (multiple-input multiple-output system) and comprises, for example, four transmission antennas6,8,10,12disposed on a device under test5and four reception antennas14,16,18,20, across which an analog, high-frequency measured signal22is transmitted wirelessly from the transmission antennas6,8,10,12to the reception antennas14,16,18,20.

At the input end, the oscilloscope2comprises four measurement channels24,26,28,30, the number of which corresponds with the number of reception antennas14,16,18,20of the multi-channel system4. Furthermore, for each measurement channel24,26,28,30, the oscilloscope2provides in each case one sampling device32,34,36,38, to which the high-frequency, analog measured signal22a, provided via the measurement channels24,26,28, to the oscilloscope2, is supplied for sampling, wherein the sampling is implemented at the same time in all measurement channels24,26,28,30. The respective sampling device32,34,36,38provides the sampled measured signal22bas a digital high-frequency signal to a baseband mixing unit40,42,44,46connected downstream of the respective sampling device32,34,36,38within the measurement channel, which is disposed in a function analyzer47of the oscilloscope2described in detail with reference toFIG. 2.

The baseband mixing device40,42,44,46mixes the sampled measured signal22bdown into the baseband and provides the sampled measured signal22bas a digital signal in the baseband position to a filter device48,50,52,54connected downstream of the baseband mixing device40,42,44,46. The filter device48,50,52,54implements a decimation, that is to say, a reduction of the sampled values of the sampled measured signal22band an anti-aliasing filtering for bandwidth reduction. With a comparatively-fast sampling rate of, for example, 10 GHz, the respective filter device48,50,52,54decimates the number of sampled values and decimates, for example, 999 of 1000 sampled values with simultaneous anti-aliasing filtering. After this, the measured signal22is supplied to a buffer device56disposed in the function analyzer47, connected downstream of the filter device48,50,52,54for buffering of the measured data comprising the measured signal22.

For the analysis, the digital multi-channel measured signal is removed from the buffer device56again and supplied to an analysis device58, for example, realised via software in the oscilloscope2. The analysis device58implements, for example, a modulation analysis, which investigates, for example, the EVM (Error Vector Magnitude) and/or the SNR (Signal Noise Ratio) and/or the modulation depth and/or the I/Q errors, such as I/Q offset or I/Q imbalance. The measured result is supplied via a signal line60to an evaluation and/or display device not illustrated inFIG. 1.

FIG. 2shows a more detailed schematic circuit diagram of a function analyzer62for the processing of the measured signal22transmitted via the MIMO system. The function analyzer62shown inFIG. 2differs from the function analyzer47according toFIG. 1in the number of measurement channels provided in the latter and in the number of baseband mixing devices and filter devices provided in the latter.

In the example presented, the function analyzer62provides three measurement channels24,26,28with signal lines64,66,68, across which the measured signal22b, sampled in the sampling devices not illustrated inFIG. 2, which is marked inFIG. 2with an arrow, is supplied to the respective baseband mixing device40,42,44. In the baseband mixing device40,42,44, the measured signal22is supplied via two signal lines70,72,74and76,78,80connected to the signal line64,66,68in each case to two mixers82,84,86and88,90,82. For mixing down the measured signal22from the intermediate-frequency level into the baseband, a carrier frequency, generated by a digital oscillator94,96,98, which is designed in the exemplary embodiment as a numerically-controlled oscillator (NCO), is supplied via signal lines100,102,104and106,108,110as a mixer frequency to the respective two mixers or digital multipliers82,84,86and88,90,82.

In this context, the baseband real component and the baseband imaginary component is generated in the first baseband mixing device40,42,44. For this purpose, a sinusoidal oscillation is generated by the oscillator94,96,99and supplied via the signal line100,102,104to the mixer82,8,86for the generation of the measured-signal real component. For the generation of the measured-signal imaginary component, the oscillator94,96,98provides a cosine-oscillation phase-displaced by 90° relative to the sinusoidal oscillation for the mixers82,84,86via the signal line106,108,110to the mixers88,90,92.

The real component and respectively the imaginary component of the measured signal22in the baseband position are provided at the output end via a signal line112,114,116or respectively via a signal line118,120,122to the baseband mixing device40,42,44. The measured signal22is from now on processed as a complex baseband signal and supplied via the signal lines112,114,116and180,120,122to the filter device48,50,52and for bandwidth reduction for decimation of the number of sampled values of the measured signal22in order to avoid aliasing.

A further, second baseband mixing device124,126,128, which corresponds in the exemplary embodiment with the structure of the first baseband mixing device40,42,44, but, by contrast with the first baseband mixing device40,42,44, which is used for coarse mixing, is used for fine mixing of the measured signal22, is connected at the output end downstream of each filter device48,50,52. Once again at the output end, a further, second filter device130,132,134for the further decimation of the sampled values and for the further bandwidth reduction of the measured signal22is connected downstream of the further baseband mixing device124,126,128. The further filter device130,132,134is connected at the output end via signal lines136,138,140and142,144,146to the buffer device56for the recording of the measured signal22. A signal line148connects the buffer device56to the analysis device58illustrated inFIG. 1.

The delay-time calibration with the time-delay elements and the pulse generators has the purpose of compensating the delay-time differences in the different measurement channels. The device according to the invention is used with a sampling rate of, for example, 10 GHz, that is to say, at the intermediate-frequency level, measured signals with up to 5 GHz are sampled. At these very high frequencies, even slight geometric differences in the signal lines in the individual measurement channels determine relatively large phase differences. It must therefore be assumed that the sampling in the individual sampling devices (analog/digital converters)32to38in the individual measurement channels is not implemented at the exactly-identical phase position of the measured signal. This must be compensated in the subsequent digital processing by adjusting the phase position of the digital oscillators94,96,98and respectively204,206and208accordingly with reference to the phase position of the digital sinusoidal or cosine signals generated by the latter. Accordingly, the pulse controlling the filters48,50,52and respectively130,132,134must be brought forward or held back, so that the timing of the processing there coincides exactly with the corresponding forward or return sampling in this measurement channel.

In order to process the measured signal22simultaneously sampled in the sampling devices in a coherent manner in the measurement channels24,26,28, the baseband mixing device40,42,44, the filter device48,50,52, the further baseband mixing device124,126,128and the further filter device130,132,134in this schematically-presented exemplary embodiment are each adjusted by a time-delay element150,152,154,156for the delay-time calibration of the measurement channels24,26,28. Pulse generators158,160,162,164are connected upstream of the time-delay elements150,152,154,156in such a manner that, in the example, in each case one pulse generator158,160,162,164is provided in the function analyzer62for the pulse specification for those time-delay elements150,152,154,156, which are connected to the first baseband mixing devices40,42,44, to the first filter devices48,50,52, to the further baseband mixing devices124,126,128or to the further filter devices130,132,134. Accordingly, in the case of the second baseband mixing devices124,126,128, corresponding mixers or digital multipliers201,202,203,205,207,208and corresponding digital oscillators204,206,208are provided.

The invention is not restricted to the exemplary embodiment presented in the drawings, in particular, not to an oscilloscope comprising three or four measurement channels. A single pulse generator only may, of course, be provided as an alternative. This is also advantageous, because the individual pulse generators need not then be synchronized with one another. All of the features described above and presented in the drawings can be combined with one another as required.