Working in a Real Office Environment
In practice, a real office environment typically requires an antenna gain of 10 to 20 dB
because of the absorption and reflection from walls and furniture.
In practice, performance across the radio physical layer is very variable if distances
of a few feet are needed. If the link is just between a headset and a handset, then the
link budget is okay, but then arguably a wired connector could do the same job at a
faster, more robust, and more consistent data rate, and it avoids the problem of needing
a battery in the headset device.
Several voice codecs are supported, including continuously variable slope delta
modulation (CVSD)—a voice codec that can work in a high bit error rate channel (4
percent bit error rate). Connections can either be synchronous for voice or asynchronous
connectionless for packet data. There are two types of block encoding, 1/3 rate
and 2/3 rate, or simple ARQ (automatic repeat request).
Gross data rate achievable is 1 Mbps typically divided into 2 × 432.6 kbps symmetric
channels or a 721 kbps unidirectional channel with a 57.6 kbps return channel. Each
packet is transmitted at a different hop frequency. A single Bluetooth transceiver can
support seven simultaneous links, that is, up to eight connected devices that then share
the available bandwidth. Devices can be organized in a scatternet—a collection of multiple
and nonsymmetrical pico nets. Alternatively, one of the devices can be elected as
the master unit (usually the first device to be turned on). The master unit clock and hop
sequence is used to synchronize all other devices in the pico net.
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