National Physical Laboratory

Digital Communication Parameters

Measurements of a wide variety of wireless and optical telecommunications systems, from A(MPS) to Z(igBee).

The Digital Communications Parameters Group is concerned with the accurate measurement of the types of modulated signal used in RF and optical communications systems and the various parameters used to classify the signal fidelity.

Modulation is the process by which a high frequency electromagnetic wave is varied at a lower frequency inĀ order to encode analogue or digital data in the signal. If the signal is degraded during its transmission through a fibre, cable or free-space or the transmitter or receiver add or remove signal components, the ability to transmit data is reduced and the error rate increases.

DCP Image
Constellation diagram of a W-CDMA signal,
used to view the quality of the signal

Each telecommunications system has its own set of important measurands and accurate and traceable measurement of these can help to:

  • Prove compliance with a regulatory system
  • Improve the guaranteed specification of a test instrument
  • Diagnose problems in a particular component or sub-system
  • Reduce inter-system interference
  • Make full use of the available bandwidth in a crowded spectrum

To enable these measurements, methods of signal capture and processing need to be understood to appreciate their traceability to national (and thereby international) standards and the associated uncertainties and error mechanisms.


Projects that are currently under way aim to deliver:

  • Traceable waveform capture, demodulation and data retrieval
  • Traceability and uncertainty analysis for instruments
  • Techniques to measure beyond the capability of current instruments to support instrument development

This is achieved using new approaches to the capture and analysis of communications signals in the time and frequency domains such as fast A-to-D conversion and electro-optic sampling.

The recent focus has been on the 3G telecommunications format Wideband-CDMA and NPL have worked with major instrument manufacturers to

  • Establish a low uncertainty, traceable Error Vector Magnitude (EVM) measurement capability
  • Accurately characterise the EVM of a number of different signal generators thereby breaking the link between generator and receiver EVM

Ongoing work aims to consider similar types of measurement on OFDM, ultra-wideband (UWB) and TETRA systems as well as covering parameters such as time and frequency masks and bit error rate.

Recent Collaborations

For further details of the methods by which NPL can work with your company, see the Measurement for Innovators scheme

For more information please contact: James Miall

Last Updated: 2 Nov 2015
Created: 12 Jun 2007


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