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 & 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 in 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.
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.
Research
Projects that are currently underway 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 characterize the EVM of a number of different signal generators thereby breaking the link between generator and receiver EVM.
On-going 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
- Working with Agilent Technologies to measure EVM for W-CDMA signals;
- A secondment of a member of NPL staff to Fluke to work on use of an IQ referencing technique for Amplitude Modulation measurement;
- A secondment of a member of NPL staff to Bookham to work on laser chirp and jitter;
- A secondment of a member of NPL staff to Bristol University to work on using RF waveform metrology in the development of advanced wireless components.
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