updated 10:00 pm EDT, Tue October 4, 2011
Lower power use, lower latency
Apple's just-announced iPhone 4S is the first iPhone to utilize the Bluetooth 4.0 specification (though it is already in use in the latest MacBook Air and Mac mini), which focuses on making the wireless protocol use dramatically less power, and offers lower latency and tougher encryption. The standard Bluetooth used in most recent Apple devices is now referred to as "classic" Bluetooth, while the new 4.0 specification features the option of using as little as one one-hundredth as much power in its most idle state.
Overall, the low-power variant uses less than half the energy of classic Bluetooth, leading to the development of single-mode chips (less expensive but limited to low-power mode only) or dual-mode chips (which can switch back to classic Bluetooth whenever needed). Apple is using dual-mode chips for the iPhone 4S, as it has done with the previous Mac models that use it.
The newer technology also lowers the latency of Bluetooth down to six milliseconds compared to the current 100ms, making Bluetooth much more viable for multimedia use when synchronization is vital. Bluetooth 4.0 also ramps up security, improves robustness of signal and reduces even peak power consumption by one-third, down to less than 20 milliamps in some devices. In standby mode, a Bluetooth 4.0 chip could run off a coin-sized feature-phone battery for over a year.
The new protocol's low "pulsing" method of communication is expected to be of even more benefit to small accessories or appliances that could use Bluetooth to communicate wirelessly. It is expected to open up a wide range of new Bluetooth-enabled devices, from medical sensors and "find me" type applications to more detailed exercise-statistic apps and even proximity alarms that could deter theft.
Among the manufacturers of dual-mode Bluetooth controllers are Atheros, CSR, Broadcom and Texas Instruments. A teardown of components in the new iPhone 4S should reveal exactly which vendor Apple went with for its dual-mode Bluetooth technology.
Single-mode Bluetooth chips, which can be used in a wide variety of other devices but are not well suited to audio use, make a few compromises to lower cost (such as not being voice capable). Single-mode Bluetooth chips lower the working range down from 330 feet to 160 ft, along with a slower over-the-air data rate (1Mb per second steady rather than 1-3Mb per second in classic Bluetooth) and lower application throughput (0.26Mb per second rather than 0.7-2.1Mb per second). None of these limitations are serious concerns for most Bluetooth-enabled accessory devices.
The use of Bluetooth 4.0, despite its own lower battery usage, does not appear to have significantly improved the iPhone 4S's reported battery life. Although Apple has raised the average talk time on the new phone up to eight hours (up from seven on the iPhone 4) on 3G, Apple now rates standby time on the 4S as 200 hours (down from 300 hours on the iPhone 4), and typical internet use at 9 hours (down from 10 hours on the iPhone 4). The revised figures could simply be down to more accurate reporting based on real-world experience with the iPhone 4.