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The PC Pro guide to wireless

Posted on 28 Nov 2005 at 12:13

The standard issue

The solution may well lie in MIMO (multiple input, multiple output) technology. This forms part of the as-yet unratified standard 802.11n, which is set to replace 11b and 11g. MIMO splits one incoming data stream into multiple lower-rate streams, transmitting simultaneously via two or more aerials on the same channel. It improves both range and transmission speed by relying on a phenomenon known as multipath, where signals arrive at different times because of reflections. That's usually considered a problem, but here it effectively creates virtual radio channels along which more than one stream of data can be fed on the same frequency. Receiving the differing signals on multiple aerials, the two data streams can be reconstructed. Current WLAN MIMO technology has a maximum theoretical speed of 108Mb/sec - twice as fast as 802.11g and more than enough to cater for multiple users streaming multi-media files around a large house. MIMO offers higher speeds over longer range than conventional WLAN, so you'll be able to connect from further away without needing to spend extra on wireless bridges or repeaters.

You'll need to spend more on the router itself, though. Not just because a pre-N router such as the Belkin costs around £75 to the £40 of a typical 802.11g router, but because you'll also need to buy matching PC Cards (or USB adaptors) to upgrade the wireless radios in your notebook or PC.

Apart from the inevitably high cost of buying a new technology, the chief drawback of MIMO is that until it's ratified by the IEEE the way in which it's implemented by manufacturers will be proprietary. This means there's no guarantee MIMO products from different manufacturers will work together at 108Mb/sec; it's more likely that everything will slow to standard 802.11g speeds. But having been using MIMO products - in particular, Belkin's Pre-N router and network card - for the last couple of months, we're big fans of the technology. Range and, more importantly, reliability of the connection are hugely improved.

Transfer big files, fast

Four months ago, we tested 15 wireless routers in a group test and saw clearly the benefits of MIMO technology over standard 802.11g. Although the MIMO-based routers were generally faster than 802.11g routers at close range, the real difference came when we moved our test notebook further away from the router: while many routers struggled to make a connection, the MIMO routers kept transferring at 9Mb/sec. At close range, the Belkin hit almost 17Mb/sec, so even a 100MB file transferred in less than a minute. We've included the full group test on the cover disc this month (click on the Editorial tab).

Streaming DVDs

Media streaming is one of the big selling points of home wireless networking; devices such as the Sonos Digital Music System spread audio around the house. The bandwidth demands of streaming MP3 audio are pretty modest; the standard data rate is just 128Kb/sec (or, to put it another way, less than 0.2Mb/sec). But video is a different matter, and high-quality DVD- Video in MPEG2 format is different again.

There are various systems and proprietary setups on the market that claim to transmit video over a standard 802.11g connection, and this they certainly do. What they can't do, however, is transmit DVD- Video in its original form without reducing its quality or its resolution. There are no magic solutions to the problem of bandwidth - a system either has enough for a given application or it must strip out some information in order to transmit a given data stream. The minimum bit rate for DVD-Video is 4Mb/sec and can extend up to almost 10Mb/sec for short, high-quality movies. This is only the bitrate required for the raw data - transmitting it over the network adds the significant data overhead of network communication protocols and error correction.