Wideband time-varying systems can be found in many applications, in particular in orthogonal frequency division multiplexing (OFDM) technologies . The time variation due to Doppler scaling effects, coupled with dispersive scattering due to multipath propagation and diffuse scattering from foliage, can severely limit the performance of wideband systems. Just as the discrete time-frequency model can efficiently improve narrowband processing, a discrete time-scale system characterisation is important in processing wideband time-varying systems . Vegetation effects can severely limit the performance of wideband systems operating at microwave and millimetre wave wavelengths . Attenuation due to single or groups of trees varies significantly with species, whether trees are in leaf or not, and wind speed conditions [3-6].
The objective of this research is to improve the existing 38 GHz narrowband (CW) system developed under the project POSC/EEA-CPS/57481/2004, in order to measure the channel impulse response in addition to the dynamic effects, including Doppler spectra, due to wind movement induced on leaves and branches caused by trees interfering in the radio path. The proposed topology for the channel sounder has the portability to be quickly and easily re-located to various measurement sites, as well as the flexibility to characterise a wide variety of frequencies, e.g. 18 GHz.
The objectives at the outset are as follows:
1. Construction of the swept-time delay cross correlation (STDCC) radio channel sounder (IF stage) to be built upon the existing 38 GHz narrowband (CW) system developed under the project POSC/EEA-CPS/57481/2004, in order to measure the dynamic effects (including Doppler) due to wind movement induced on leaves and branches caused by trees interfering in the radio path;
2. Extension of the resulting 38 GHz STDCC channel sounder to 18 GHz, including construction of specific enclosure to house the measurement system including the antennas. Most of the RF components already exist for this extension.
The methodology to be followed under this task consists of:
(i) Matlab (and/or Simulink) implementation and simulation of the proposed STDCC channel sounder and assessment of the underlying theoretical principles inherent to the proposed topology;
(ii) Development of PN generators (minimum of 3) using a programmable hardware platform, e.g. high speed DACs and drivers;
(iii) Construction of the channel sounder extension, integration on the existing system and preliminary bench testing, including appropriate anechoic chamber and outdoor measurements.
This measurement facility is a combined continuous wave (CW) and swept-time delay cross-correlation (through the IF stage herein proposed) and multi-frequency channel sounder system essential to conduct research in propagation through vegetation. The proposed combined solution comprises of highly stable phase lock loop (PLL) oscillators operating at 18 and 38 GHz which are synchronised via GPS reference signal, antennas, amplifiers, mixers, Wi-Fi enables accessories, data acquisition and control unit. A simplified block diagram of the proposed system can be found in Figure 1. The system is sought to provide reliable measurement data in both time and frequency domains. In the former, it is expected to be able to measure the channel impulse response with a time resolution better than 2 ns and Doppler spectra.
Finally, it is intended with this project to build a rather compact and highly portable channel sounder (as an alternative to the VNA approach at IF stage) which is a major advantage to researchers that wish to study the channel across a variety of radio links. The mobility of such a system eliminates the need to disassemble, stow the equipment for transport, and then re-assemble at the new site or measurement position. This is a lengthy process that requires time consuming and painstaking adjustments when setting up the equipment at the new location, and results in a significant amount of downtime during a measurements campaign.
 ”Time dynamic channel model for broadband fixed wireless access systems, Michael Cheffena, Lars Erling Bråten, Terje Tjelta, COST Action 280 “Propagation Impairment Mitigation for Millimetre Wave Radio Systems”, PM9-110 3rd International Workshop, June, 2005;
 ” Recommendation on Time Varying Radio Propagation Channel Models and Study of System Performance for LMDS”, P Soma, Y W M Chia and L C Ong, IEEE 802.16.1pc-00/24r1, 2000.
 “A generic model of 1-60GHz radio propagation trough vegetation – Final report”, N.C. Rogers et al., Radiocommunications Agency, UK, May 2002;
 ''Radio charaterisation of single trees at micro- and millimetre wave frequencies”, Ph.D Thesis, R.F.S. Caldeirinha, University of Glamorgan, UK, April, 2001;
 ''A discrete RET Model for Micro- and Millimetre Wave Propagation through Vegetation'', Ph.D Thesis, T.R. Fernandes, University of Glamorgan, June, 2007.
 ITU-R P.833-5 – Attenuation in vegetation, International Telecommunication Union, Radiocommunications Study Group 3, Agosto, 2005.
 W. G. Newhall, T. S. Rappaport, and D. G. Sweeney, “A Spread Spectrum Sliding Correlator System for Propagation Measurements,” RF Design, pp 40-54, April 1996.
 T. S. Rappaport, Wireless Communications: Principles and Practice, 2nd Edition. New Jersey: Prentice-Hall, 2002.
 J. D. Parsons, D. A. Demery, A. M. D. Turkamani, “Sounding Techniques for Wideband Mobile Radio Channels: A Review,” IEE Proceedings, vol. 138, no. 5, pp. 437-446, October 1992.
 R. C. Dixon, Spread Spectrum Systems, 2nd Edition. New York: John Wiley and Sons Inc., 1984.
 D. C. Cox, “Delay Doppler characteristics of multipath delay spread and average excess delay for 910 MHz urban mobile radio paths,” IEEE Transactions on Antennas and Propagation, vol. AP-20, No. 5, pp. 625-635, 1972.
|Start Date: 01-05-2009|
|End Date: 01-04-2010|
|Team: Rafael Ferreira da Silva Caldeirinha, Telmo Rui Carvalhinho Cunha Fernandes, Diogo Ferreira|
|Groups: Antennas and Propagation – Lr|
|Local Coordinator: Rafael Ferreira da Silva Caldeirinha|
|Links: Internal Page|