Using Bluetooth to revolutionise landlines

The remarkable status of mobile handsets as must-have fashion accessories, has made the fixed line telephone business look as if it's been standing still in the last few years. Now, a new concept that allows mobile handsets to be used to receive and make fixed-line calls, appears to be about to inject fresh life into the market. This '3-in-1' communications capability allows you to make calls as:

• Cellular-to-mobile network, when you're out and about
  
• Bluetooth-to-fixed-network, when at home or in the office
  
• Bluetooth-to-local-handset, for intercom calls

I say a 'new' concept, but of course it's not. The Cordless Telephony Profile (CTP) was one of the first profiles to be specified and developed by the Bluetooth community. And, the idea had been floating around the industry for a long time before that, attached to standards like DECT.

What's brought it to the fore now is not just the recent move by a major telco to launch the concept, but the cost reduction progress of Bluetooth silicon. Single chip solutions such as CSR’s BlueCore - now available with on-chip peripherals such as voice codecs - have brought the BOM of a cordless phone implementation to the kind of level that is highly attractive, and unmatchable by other current technologies. Comparing BOM estimates for a typical domestic cordless handset-plus-basestation pair shows that Bluetooth is a highly attractive solution:

Suitability
Cost is only one element of suitability, however. How well does Bluetooth stack up when measured against other parameters?

The range capability is not spectacular but certainly adequate. In terms of audio quality, it's beaten by DECT, but on a par with digital spread-spectrum communication schemes. There's been criticism of Bluetooth audio quality, but it's pretty good already - better than GSM certainly - and the v1.2 spec introduces more robust error-corrected packet types that push quality even higher.

In terms of functionality, the relevant CTP and Intercom Profiles provide a comprehensive suite of call control and connection management features and services as well as the all-important security features. The current Bluetooth specification can also be used to provide ‘value-added’ services over fixed-line cordless telephones, such as Caller-ID and SMS.

Where it really scores though is on power consumption. In power save mode, waiting for an incoming call, the BlueCore chip consumes just 1mW. The very best GSM phones require 2-5mW for example, and our survey of chipsets for other personal-area wireless standards (DECT and 802.11a, b, g) shows levels starting at 80mW and spiralling up to nearly 2W. Along with BOM, this parameter is absolutely crucial, as a 3-in-1 phone will effectively be a constant always-on companion.

Product potential
So, pushing the argument forward - just what phone products can be achieved with Bluetooth? 3-in-1 functionality is easy; as existing Bluetooth equipped mobiles only need the addition of software and possibly also some minor additional voice routing circuitry - a fairly modest design iteration.

Also technically feasible is the idea of using Bluetooth to act as a cellular connection when in range, running GSM protocols over a Bluetooth link to a basestation; this would be ideal for the emerging pico-basestation coverage scenarios. As this is not currently specified by the Bluetooth SIG, building such an architecture would not be without problems but would give some very interesting advantages in terms of coverage, quality, cost, and 1-handset/1-number capability.

Roaming between basestations (hand-over capability), even though it's not part of the current Bluetooth specification, is a real possibility for commercial CTP-based solutions, as proven proprietary solutions are already available.

The figure shows that low cost hardware and ready-made software solutions could be used to implement a very attractive home cordless telephone product. Not only would it cost less than a DECT phone, but also it would do a great deal more, offering dial-up network access and use with a Bluetooth headset. Plus, a simple and very low cost handset implemented on a single BlueCore chip equipped with Intercom and CTP Profiles is all that's required for additional home handsets.

The Mezoe Interface Express Bluetooth software already offers all the fundamental features required for any of the added-value variants outlined. It is also possible to deliver these feature rich solutions, as ‘host-less’ single-chip solutions, through the combined services of Mezoe's parent Cambridge Consultants - who were selected by CSR as its partner for delivering custom on-chip BlueCore projects.

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