Ultrawideband (UWB) signals originated in work on high resolution radar imaging several decades ago. Their application to short-range high data-rate communications was first proposed in the 1990s.
A signal is generally considered to be UWB if its bandwidth is comparable to its centre frequency. More precisely, under the current FCC regulations in the US, a signal is UWB if its absolute bandwidth exceeds 500 MHz or fractional bandwidth is over 20%. As shown in the FCC UWB frequency mask graph to the right, the band assigned to UWB indoor communications systems extends from 3.1 GHz to 10.6 GHz - a bandwidth of 7.5 GHz centred at 6.85 GHz.
At Oxford, we are currently working on applications for these very wideband signals in communications and medical imaging.
UWB Medical Imaging
The objectives of this project are
- To develop optimised antennas and transducers for medical imabing in appropriate immersion fluids (oils and saline solutions).
- To develop realistic UWB tissue simulant materials to enable construction of useful phantoms for further development of imaging.
- To demonstrate imaging acquisition using scanned antennas and switched antenna arrays with realistic phantoms.
- To explore physical optics based 3D imaging algorithms for conversion of measured phase and amplitude data into useful tomographic images.
The UWB propagation channel differs from the narrowband and wideband channel in its fundamental characteristics that are of great interest in communications. We are undertaking a collaborative EPSRC-funded research project on various aspects of the UWB communications channel. As a next step, we have applied this channel analysis to improved system design.
The major objectives of the propagation research are
Diffraction, reflection, refraction and path loss characteristics in terms of time, frequency and range will be studied and models developed
Polarisation behaviour through walls and structures of differing material content will be studied
Spatio-temporal characteristics will also be studied with a view to identifying advanced antenna configurations for diversity, adaptive systems and MIMO type operation.
Code families/pulse waveforms will be studied and simulated within the real channel data to ascertain an optimum waveform and modulation scheme.
Capacity limits for communications will be ascertained based on the channel behaviour and the candidate modulation schemes.