Thursday, 11 March 2010 10:20

Researchers say the Sun is awakening after a period of low activity, which does not bode well for a world ever more dependent on satellite navigation.

The Sun's irregular activity can wreak havoc with the weak sat-nav signals we use.

The last time the Sun reached a peak in activity, satellite navigation was barely a consumer product.

But the Sun is on its way to another solar maximum, which could generate large and unpredictable sat-nav errors.

It is not just car sat-nav devices that make use of the satellite signals; accurate and dependable sat-nav signals have, since the last solar maximum, quietly become a necessity for modern infrastructure.

Military operations worldwide depend on them, although they use far more sophisticated equipment.

Sat-nav devices now form a key part of emergency vehicles' arsenals. They are used for high-precision surveying, docking ships and plans are even underway to incorporate them into commercial aircraft.

Closer to home, more and more trains depend on a firm location fix before their doors will open.

Simple geometry

The satellite navigation concept is embodied currently by the US GPS system and Russia's Glonass network, with contenders to come in the form of Europe's Galileo constellation and China's Compass system.

It depends on what is - at its root - a simple triangulation calculation.

A fleet of satellites circling the Earth are constantly beaming a radio signal with two bits of exceptionally precise information: where exactly they are, and at exactly what time.

A sat-nav receiver on Earth - or on a ship or plane - is equipped with a fairly precise clock and the means to collect signals from the satellites that happen to be in its line of sight.

It then works out, based on how long it took those signals to arrive, how far it is from each of those satellites. Some simple geometry yields its position.

1. Satellites advertise their exact position, and the precise time at which they are sending it 2. The signal travels through the outer atmosphere, the ionosphere; its speed depends on how much the Sun's radiation and particle winds are affecting the ionosphere's composition 3. A receiver on Earth determines how long the signals took to arrive from a number of satellites, calculating the position from the time differences

But those signals are incredibly weak and, as researchers have only recently begun to learn, sensitive to the activity on the Sun.

Solar flares - vast exhalations of magnetic energy from the Sun's surface - spray out radiation across the electromagnetic spectrum, from low-energy radio waves through to high-energy gamma-rays, along with bursts of high-energy particles toward the Earth.

The radiation or waves that come from the Sun can make sat-nav receivers unable to pick out the weak signal from satellites from the solar flare's aftermath.

There is little that current technology can do to mitigate this problem, with the exception of complex directional antennas used in military applications.

Sat-nav receivers will be blinded for tens of minutes, probably a few times a year at the solar maximum.

Charged up

A further complication comes from the nature of the outermost layer of the Earth's atmosphere, the ionosphere.

That is composed in part of particles that have ionised, or been ripped apart by radiation from the Sun, with the composition dependent on how much radiation is coming from the Sun at a given time.

The problem comes about because sat-nav technology assumes that signals pass through at a constant speed - which in the ionosphere isn't necessarily the case.

"The key point is how fast the signals actually travelled," said Cathryn Mitchell of the University of Bath.

"When they come through the ionosphere, they slow down by an amount that is actually quite variable, and that adds an error into the system when you do the calculations for your position," Professor Mitchell told BBC News.

The amount of solar activity runs on many cycles; the ionisation will be different on the sun-lit side of the Earth from the night side, and different between summer and winter; each of these cycles imparts a small error to a sat-nav's position.

But the disruption caused by solar flares is significantly higher.

The increased radiation will ionise more molecules, and the bursts of particles can become trapped in the ionosphere as the Earth's magnetic field drags them in.

The effects that sat-nav users will face, however, are difficult to predict.

"We can look at the measurements from the last solar maximum," Professor Mitchell said.

"If we project those forward, it varies quite a lot across the Earth; looking at the UK it will be about 10-metre errors in the positioning."

The errors would be much more long-lasting than the "blindness" problem, lasting hours or even days.

"Ten metres out is probably going to be OK for a sat-nav system in a car, but if you're using the system for something safety-critical like ships coming into harbour for navigation or possibly in the future landing aircraft, you're looking for much greater accuracy and more importantly, much greater reliability."

Bob Cockshott, a director of the government-funded Digital Systems Knowledge Transfer Network, said that for most consumer applications such as sat-nav for cars, the problem will be more troublesome than dangerous.

"You might find for a number of hours or even a day or two you couldn't go out surveying or be able to dock your oil tanker at the deep-ocean oil well," he told BBC News.

"It's more at the annoyance level than something that's going to bankrupt your business."

A number of schemes have been proposed to do real-time corrections to the signals as the atmosphere changes, allowing for local adjustments that are broadcast to receivers by other means such as the mobile phone network.

However, Mr Cockshott said that it remains unclear whether such a correction makes sense economically for manufacturers of sat-nav-enabled technology.

So as the Sun builds up to its peak in a few years' time, be aware that your sat-nav may for a time give some strange results - or for a short while none at all.

Thursday, 11 March 2010 10:20

End of an era: Pioneer's BDP-320

The BDP-320 sits in the lower half of Pioneer's six-strong Blu-ray player range. The feature spec rises fairly gradually from model to model though – the BDP-320 offers 48-bit Deep Colour over the basic BDP-120's 36-bit, but step up to the BDP-LX5 and you’ll get the anti-jitter Precision Quartz Lock System. Otherwise, features and connections are very similar. A good-looking machine – slimline with a gloss black finish – it feels solidly constructed. While the higher end models might have a classier build on close inspection, the BDP-320 certainly doesn't look cheap.

The back is home to a single HDMI v1.3 port, Ethernet, component, optical and composite digital audio outputs, and a remote control input for custom instals. The USB port is for additional memory storage beyond the 1GB already on board for BD-Live content. As yet, there's no sign of Wi-Fi connectivity at this level from Pioneer, such as you'll find in the similarly priced LG BD390 or Sony BDP-S560.

There are no analogue multichannel audio outputs though, which may put you off if you're still using a pre-HDMI AV amp. It's a shame too that the USB interface is only for memory, and won't allow you to load pictures or video from a USB flash drive. However there’s a reasonable range of formats supported on disc, including DivX, MP3, WMA, AVCHD and JPEG.

Special mention needs to be made of the remote, but not for any good reasons. It's large, it's bulky, has ill-defined buttons and it's not backlit. This can make things awkward to find – even though the buttons glow in the dark, but not very clearly – especially since the buttons are black, on a black background. How did that idea get off the design shelf?

Visually, not the easiest remote to get to grips with

It's not the fastest loading player around – we never managed to get it below 1m 10secs. Once you're up and running, the user interface is solidly sober and businesslike and if not particularly attractive, it does, at least, have the advantage of being easy to navigate. Less enticing is that there's no picture-in-picture option when you want to access the main menu while you're watching a film – you'll need to come out of the movie to make your adjustments, and it won't automatically return you to the place you left. Grrr.

However, a separate list of options can be accessed from the Tools menu on the remote while a film's playing, including Audio Adjust (for audio dynamic range and manual lip sync adjustment) and Video Adjust (all sorts of things, including gamma correction, white and black level adjustment and hue), plus subtitles, audio track selection and HDMI output resolution.

Digital options, but no multichannel analogue audio outputs

The BDP-320 can upscale standard DVD to 1080p and has a decent range of video features including presets for different types of screen such as Professional, PDP, LCD and Projector, and there's Video Adjust, which allows you to tweak the picture to your taste across 13 parameters and store your settings in up to three different modes.

There's also 48-bit Deep Colour support and x.v.Colour and several noise reduction technologies: Component Frame Digital Noise Reduction, Block Noise Reduction and Mosquito Noise Reduction. It's not exactly clear what each of those exotically named noise reduction facilities actually do, but in practice the BDP-320 proved itself an extremely capable and nimble performer.

Blacks were deep and subtly graduated, edges were sharp and movement was precise with a minimum of jaggies – the destruction of the Millenium Bridge in Harry Potter and the Half-Blood Prince threw up no obvious artefacts throughout its swift-moving, effects-heavy length. Upscaling too proved no obstacle to the 320, with DVD images brushed up and polished to a shine clearly well above their natural state.

The BDP-320 packs a pretty decisive punch on the audio front too, delivering all the HD audio codecs into LPCM or outputting them as raw bitstream to HDMI. It's also a bit of a rarity in offering audio-only circuitry for stereo playback with its PQLS feature, designed to work with a compatible Pioneer amp connected through the analogue stereo outs. Playing CDs through stereo speakers it certainly matched the performance of a similarly priced dedicated CD player, though there's no option to play hi-res surround audio formats like SACD or DVD-Audio.

Verdict

The Pioneer BDP-320 doesn't have an overly impressive feature set, instead concentrating its resources on sound and picture quality. In this regard it doesn't disappoint, since both are very fine. But with other players offering good enough sound and vision, plus additional options like Wi-Fi, YouTube and other Internet content, USB playback and analogue audio outputs, as well as faster loading and navigation, often for less money, the Pioneer may not be doing enough to justify its cost.