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RSSI Operation
Original Post: power control? (eGroups Msg. )
Date: 2000-08-21
As the Radio specs state (p26), an optional RSSI
feature can be built into bluetooth units.
To implement a link with power control the
transmitting module must support Transmit Power Control and the receiving
module must have a Receive Signal Strength Indicator (RSSI) and a defined
Golden Receiver range.These are optional components implemented at the
Radio level. The capability of each device is determined during link
establishment.
Changes in the local device's transmit power, up and
down a preset power table to higher and lower transmit powers, are
controlled by the remote device. The remote device has AGC upper and lower
limits
stored which define the "Golden Receiver" power band. The module
manufacturer must determine values for these limits. They only have to be
accurate to within a few dB (see Bluetooth Spec) and may, if
consistent enough, be programmed with a standard value for all modules,
otherwise each module must be configured individually.
The change is triggered by the remote LC layer noting
that the RSSI has moved outside its Golden Reciver power band and sending
a change request to its LM layer. The LM layer sends the appropriate
change request message to the Baseband, which transmits it to the
local device (LMP_incr_power_req or LMP_decr_power_req). The local LM
layer changes the transmit power level (for remote device that sent the
message only: each device has it's own transmit power setting) up or
down.The power steps are defined as a monotonic sequence, with a maximum
step size of 8 dB and a minimum step size of 2 dB. If it is already at an
upper or lower limit a response is sent to the remote device indicating
this (LMP_max_power or LMP_min_power).
The HCI RSSI commands (HCI_Read_RSSI) are for
information only. The Host is not involved in altering the transmit power
of the Bluetooth device (although the message does contain information
about whether the value is above or below the Golden Receiver power band).
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