The
original Base Station product is shown in the picture to the right.
Almost every aspect of this product presented a challenge which we
overcame. For example:Between 1993 and 2000, the TETRA digital PMR standard was written, developed and turned into product. Philips/Simoco were leaders in this area. Alister Bailey was responsible for managing and designing their Base Station product from research through to manufacture. This was a programme lasting several years with a multidisciplinary team of over 14 engineers at its peak. The first time this technology was demonstrated publicly was at the ITU95 exhibition in Geneva. The successors of these products are now available from Sepura (handsets), Frequentis and Simoco Digital UK Ltd.
The
original Base Station product is shown in the picture to the right.
Almost every aspect of this product presented a challenge which we
overcame. For example:
The power amplifier had to be highly linear (beyond the measuring capabilities of available analysers) which was achieved using a state-of-the-art cartesian loop. It also required efficient cooling to operate continuously and reliably over an industrial temperature range.
The receiver used triple diversity with maximum likelihood decoding to improve the balance of uplink to downlink in an omnidirectional manner.
The system was powered with switch mode power supplies, these are normally avoided in RF products but all the difficulties were resolved to fully meet EMC, receiver sensitivity and transmitter purity requirements.
The signal processing was at the limit of DSPs of the day, to combine the functions a state of the art processing card was built using 100kgate FPGA and MIPs processor. These were interconnected via a purely digital backplane. The modular design concept was used to allow upgrade of individual modules as technology and designs improved.
The
on-site networking used a dual redundant optical fibre ring for
low-latency interconnect and reference distribution. This had to be
custom designed.
The software aspect of this project was also of significant complexity. It is recognised that TETRA is significantly more complex than GSM in many respects, especially regarding it's real-time performance.
The software had to be tested in an incremental fashion as the suite of products evolved together. Eventually, this required testing against competitor equipment where solutions to incompatibilities had to be negotiated.
Production was all in-house and introduced large BGAs to solve some of the placement difficulties. Production test equipment was based upon prototypes from a collaboration with instrument suppliers.
A product such as a base station is useless without the ancillaries required to construct a complete RF site – the original prototype for this can be seen on the right. The low noise amplifier/splitters and low-intermod duplexers were also developed as part of this programme.
© AJ Bailey 2004