LLCC68 datasheet(37/111 Pages) SEMTECH

37 / 111 page

LLCC68

Data Sheet

Rev. 1.1

DS.LLCC68.W.APP

Dec 2024

37 of 111

Semtech

LLCC68

www.semtech.com

the interest of reducing the receiver duty cycle in receive intensive applications. The transmitted preamble length may vary from 10 to

65535 symbols, once the fixed overhead of the preamble data is considered. This permits the transmission of near arbitrarily long preamble

sequences.

The receiver undertakes a preamble detection process that periodically restarts. For this reason the preamble length should be configured

as identical to the transmitter preamble length. Where the preamble length is not known, or can vary, the maximum preamble length should

be programmed on the receiver side.

The preamble is followed by a header which contain information about the following payload. The packet payload is a variable-length field

that contains the actual data coded at the error rate either as specified in the header in explicit mode or as selected by the user in implicit

mode. An optional CRC may be appended.

Depending upon the chosen mode of operation two types of header are available.

6.1.3.1 Explicit Header Mode

This is the default mode of operation. The header is transmitted with maximum error correction code (4/8). It also has its own CRC to allow

the receiver to discard invalid headers. The header provides information on the payload, namely:

• The payload length in bytes

• The forward error correction coding rate

• The presence of an optional 16-bit CRC for the payload

6.1.3.2 Implicit Header Mode

In certain scenarios, where the payload, coding rate and CRC presence are fixed or known in advance, it may be advantageous to reduce

transmission time by invoking implicit header mode. In this mode the header is removed from the packet. In this case the payload length,

error coding rate and presence of the payload CRC must be manually configured identically on both sides of the radio link.

6.1.4 LoRa Time-on-Air

The Time-On-Air of the LoRa packet is shown in the SX126x drivers.

6.1.5 LoRa Channel Activity Detection (CAD)

The use of a spread spectrum modulation technique presents challenges in determining whether the channel is already in use by a signal

that may be below the noise floor of the receiver. The use of the RSSI in this situation would clearly be impracticable. To this end the channel

activity detector is used to detect the presence of other LoRa signals.

On the LLCC68, the channel activity detection mode is designed to detect the presence of a LoRa preamble or data symbols while the

previous generations of products were only able to detect LoRa preamble symbols.

Once in CAD mode, the LLCC68 performs a scan of the band for a user-selectable duration (defined in number of symbols) and then returns

with the Channel Activity Detected IRQ if LoRa symbols have been detected during the CAD.

The time taken for the channel activity detection is dependent upon the LoRa modulation settings used. For a given configuration (SF/BW)

the typical CAD detection time can be selected to be either 1, 2, 4, 8 or 16 symbols. Once the duration of the selected number of symbols

has passed, the radio remains for around half a symbol in Rx to post-process the measurement.

6.1.6 RSSI Calibration

The power seen by the LLCC68 analog front-end is affected by external components such as the matching network and RF switches. An

incorrect RSSI results in a sensitivity degradation in (G)FSK mode and an incorrect gain selection in LoRa and GFSK mode. An incorrect gain

can result in a missed detection (packet loss) or decreased resistance to interference.

LLCC68 датащи(PDF) 37 Page - Semtech Corporation

LLCC68 датащи(HTML) 37 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL