SPIRIT1 datasheet(64/94 Pages) STMICROELECTRONICS

64 / 94 page

Transmission and reception

SPIRIT1

64/94

Doc ID 022758 Rev 3

9.10.5

SQI

The synchronization quality indicator (SQI) is a measurement of the best correlation

between the received synchronization word and the expected one. The value representing a

perfect match is 8×SYNC_LENGTH.

This indicator is calculated as the peak cross-correlation between the received data stream

and the expected synchronization word.

It is possible to set a synchronization quality threshold in such a way that, if SQI is below the

threshold, the packet demodulation is automatically aborted.

If the synchronization quality indicator check is enabled (field SQI_EN of the QI register set

to '1'), the running peak SQI is compared to a threshold value and the sync valid IRQ is

asserted as soon as the threshold is passed. The preamble quality threshold is equal to 8 ×

SYNC_LEN - 2xSQI_TH with SQI_TH = 0..3. When SQI_TH is 0, a perfect match is

required; when SQI_TH = 1, 2, 3 then 1, 2, or 3-bit errors are respectively accepted.

It is recommended to always enable the SQI check.

RX timeout mechanism

In order to reduce power consumption, a few automatic RX timeout modes are supported.

RX timeout applies both to normal receive mode and to the LDCR mode.

Infinite timeout: in this mode RX is stopped when the packet ends or the SABORT command

strobe is issued (default).

Carrier sense timeout: RX is aborted if the RSSI never exceeds a programmed threshold

within Trx timeout.

SQI timeout: in this mode RX is aborted if the synchronization quality indicator (SQI) never

exceeds a programmed threshold within Trx timeout.

PQI timeout: in this mode RX is aborted if the preamble quality indicator (PQI) never

exceeds a programmed threshold within Trx timeout.

The value of Trx timeout can be programmed ranging from ~1 µs to ~3 sec.

9.11

Antenna diversity

The device implements a switching based antenna diversity algorithm. The switching

decision is based on a comparison between the received power level on antenna 1 and

antenna 2 during the preamble reception.

The antenna switching function allows to control an external switch in order to select the

antenna providing the highest measured RSSI.

When antenna switching is enabled, the two antennas are repeatedly switched during the

reception of the preamble of each packet, until the carrier sense threshold is reached(c)

(static carrier sense mode must be used). From this point on, the antenna with the highest

power is selected and switching is frozen. The switch control signal is available on GPIO and

in the MC_STATE[1] register.

The user should make sure to provide a preamble sufficiently long to allow the algorithm to choose the final

antenna.

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