UWB Product and System Design
There has been considerable interest in Ultra WideBand (UWB) technology since the FCC modified its rulings (Part 15 Subpart F) to allow UWB transmissions. This made 7.5GHz of spectrum available, albiet at very low transmit power levels, for license exempt use.
The FCC rulings define different types of UWB devices and specify technical requirements for each. The red trace in the graph below shows the spectral mask that the rulings specify for indoor devices. Allowable transmit power levels are maximum between 3.1 and 10.6GHz when the Effective Isotropic Radiated Power (EIRP) can be as high as –41.3dBm/MHz. The occupied bandwidth of UWB systems must be at least 20% fractional or 500MHz.
There was a significant delay before European legislation was introduced to to allow the use of UWB. In the UK OFCOM introduced regulations that came in to force on August 13th 2007. These regulations are harmonised and now in place throughout Europe, although the allowed frequency range is more restricted than in the US. The European spectral mask is depicted by the green trace in the graph below. The most useful part of the European UWB spectrum is from 6GHz to 8.5GHz, where an EIRP of –41.3dBm/MHz is permitted. This is the same level as allowed by the FCC regulations and means that common products can be developed for both the US and European markets. However, the full 3.1 to 10.6GHz of UWB spectrum made available by the FCC cannot be used in Europe.
Plextek is able to help clients wishing to make use of the large operating bandwidths made available by the UWB legislation. We can undertake component, product and system design and assist clients in the innovative exploitation of the license exempt UWB spectrum. Our skills in RF IC design, microwave frequency design, system design, software design and digital electronics make us well suited to providing a comprehensive range of UWB design services.
One of the main perceived applications for UWB is short-range, high data rate equipment such as wireless USB devices. The IEEE 801.15.3 task group was chartered to draft and publish a new standard for high-rate (20Mbit/s or greater) Wireless Personal Area Networks (WPANs). Sub-group 3a was tasked with attempting to provide a higher data rate Physical Layer (PHY) based on UWB technology. Two competing UWB implementations were considered: Multiband OFDM and Direct Sequence UWB (DS-UWB). A joint proposal was developed but the proponents of the two technologies could not agree and it was decided that the technologies should compete head-on in the market place.
Whilst short range, high data rate communications has been the main focus of the UWB development work undertaken to date, other innovative applications can also be considred. Impulse-radio based UWB, as used in DS-UWB, relies on the transmission of very narrow pulse width (hence wide bandwidth) signals. The use of such narrow pulses yields potential advantages in a range of systems:
Another potential benfit of short-pulse systems is that the hardware (in particular the transmitter hardware) can be very simple and therefore small and low-cost. More specifically the short transmit pulses used in UWB impulse-radio can be generated without the need for stable RF frequency sources. The shape of the pulse determines the modulated spectrum and, together with the filtering and antenna, the bandwidth of the transmitted signal. Gaussian modulated sinusoidal pulses are often (but not exclusively) used as they have a well contained spectrum and, perhaps most importantly, simple techniques exist for generating approximations to Gaussian modulated sinusoids. The plots below show a time domain representation of a Gaussian modulated sinusoid and its corresponding frequency domain representation.
If you would like to discuss your UWB product or system development
plans in more detail please contact us.
