Wide receivers

Researchers at Warwick University are developing ways to optimise ultrawide bandwidth (UWB) devices by designing receivers that will extend battery life and reduce bit error rates.

Technologies such as Wi-Fi and Bluetooth have become popular by enabling devices such as PDAs to transfer data without needing wires, but their data transfer rate is still not as fast as a wired connection. Bluetooth transfers data at a rate of two megabits/sec, while the latest Wi-Fi technologies operate at 200 megabits/sec.

UWB uses an extremely large bandwidth spanning several gigahertz, providing short-range wireless interconnections with data rates of up to several gigabits/sec, which is high enough to render most cables in many home and office devices redundant.

The technology can also be used in wireless sensor networks (WSNs) used in surveillance and disaster area monitoring and wireless body area networks (WBANs) used in health monitoring. In these applications, power consumption is more important than data rate.

The Warwick research, led by Dr Yunfei Chen, hopes to enable devices to run on lower power and reduce the bit error rate (the ratio of received bits that contain errors) by shortening the time UWB devices take to synchronise their transmitters and receivers.

For a device to receive a signal it must know when it is going to arrive and so must synchronise. The team aims to optimise how the signal is recognised by the receiver, using algorithms to reduce the power needed to transmit a signal and allowing sensor networks in remote and hard-to-reach places to be easily implemented.

By aiming to minimise the bit error rate rather than maximising the signal-to-noise ratio Chen hopes to improve the speed and accuracy of the receivers, and believes he could improve current systems by 20 per cent.

‘The first part of our research is designing new ways of receiving signals,’ said Chen. ‘As the receiver doesn’t know when, or what, it will receive, the first thing it needs to do is synchronise with the transmitter. The requirement of the synchroniser is to be fast and accurate. if, say, the transmission is four nanoseconds long, a one nanosecond error will lose 20 per cent of the useful energy.

‘Previous synchronisers used a multi-dimensional search for the optimal values. This is time-consuming, so our synchroniser will use a computer science algorithm. There are many algorithms out there which have never been applied to this technology, and when we find a suitable one we will apply it to both optimise the technology and reduce the synchronisation time.’

The researchers are looking at the relationship between system performance and synchroniser error to give them an idea how much energy can be lost without damaging performance. This will give them a margin of error for a synchroniser and allow them to develop a simple receiver which will use less power.

‘We want the receiver to be as simple as possible to extend battery life,’ said Chen. ‘More complicated algorithms need more power, so our goal is to simplify the current low complexity receiver but still provide reasonably good performance.’

Chen believes WSNs and WBANs, such as sensors on a patient in a hospital, could benefit from the low-power receivers.

‘Battery life is key,’ said Chen. ‘If you air-drop a sensor in a forest not accessible to humans you want it to last for at least year rather than having to change it every week.

‘The advantage of UWB is it can operate with low power consumption. Current mobile cell phone systems, for example, use a transmission power of about 300 milliwatts, whereas UWB use a transmission power of 14 milliwatts.’

Although no industrial partners are involved in the project yet, a recent study by Mason Communications and DotEcon (for Ofcom) predicted the area of UWB will be worth more than £6bn to the UK economy by 2020.