Multipath fading generator aids wireless tests

New multipath fading generator software for the Yokogawa range of I/Q signal generators will simplify tests on wireless communication systems and 3GPP applications.

Yokogawa Martron has introduced multipath fading generator software for use with the Yokogawa range of I/Q (in-phase/quadrature) signal generators in tests on wireless communication systems and 3GPP applications.

The new software is designed to simulate the conditions that can affect mobile and wireless communications systems where there is no clear line of sight between the transmitter and receiver.

In such a situation, the signals received by the receiver are not direct signals, but multiple signals that are superimposed due to reflections and diffraction.

This causes an electromagnetic field distribution with standing-wave characteristics to form at the reception point owing to multiple signals arriving.

As a result, when the receiver is moving, the reception signal receives amplitude and phase fluctuations, which are referred to as multipath fading.

The multipath fading generator software can simulate two models: one where time-delay differences can be ignored, and one where they cannot.

When there is no time-delay difference between multiple arriving signals, the reception signal is a superimposition of multiple signals with different amplitude and phase.

An example would be Rayleigh fading in which the envelope amplitude of the reception signal follows a Rayleigh distribution, and the phase follows a uniform distribution.

In the case of multipath fading in which the time delay difference cannot be ignored, the frequency characteristics of the reception signal changes.

This is called frequency-selective fading.

The software will simulate Rayleigh, Rice or pure Doppler fading profiles for each path, corresponding, respectively, to situations where no line-of-sight signals exist but reflection and diffraction signals are present (Rayleigh); both sets of signals exist together (Rice); and only line-of-sight signals exist (pure Doppler).

AWGN (additive white Gaussian noise) can also be added to the output.

In addition, for 3GPP applications, there is a two-path moving propagation generator, where the delay in one of the paths fluctuates, and a 'birth/death' propagation generator, where paths appear with random delays, disappear and then reappear with different delays.

The new simulation software can be used with Yokogawa's current range of I/Q signal generators, including the VB8000 arbitrary waveform generator, which offers up to eight channels, each with a 64Mpoint memory, and the VG6000 synthesised vector signal generator, which combines arbitrary waveform capability with an upconvertor to offer transmission frequencies up to 6.2GHz.

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