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[[文件:LoRa-packet-structure.jpg | 800px]] == RSSI == Received Signal Strength Indication,接收信号强度指示 Antenna Diversity,天线分集 The RSSI information is available during CAD and there is no need to leave the receiver on for some additional time <br> == CAD == Channel Activity Detection. It's designed to detect a LoRa preamble on the radio channel with the best possible power efficiency. Once in CAD mode, the SX127x will perform a very quick scan of the band to detect a LoRa packet preamble. <br> == Preamble == LoRa 数据包前导码,用于接收机辩识 rx data flow。内容固定,长度可选。 默认 12 个 symbol(Bytes?), 0x8 (RegPreambleLsb) + 4 可写 RegPreambleMsb 和 RegPreambleLsb 这两个寄存器,将其改为 6 +4 ~ 65535 +4 10 symbol 的短前导码,通信够用但具有更短的接收周期。。。 当前系统一般皆适用 12 (4 + 8) 的长度: <source lang=bash> ...... ^$Get Preamble Length: state 0 ^$Preamble Length: 8 ...... </source> <br> == Header == Explicit Header & Implicit Header 可通过寄存器 RegModemConfig1 内的位 ImplicitHeaderModeOn 来控制 '''Explicit Header:''' Reset 默认的模式。其能提供的信息: * Payload 长度 * The forward error correction code rate * The presence of an optional 16-bits CRC for the payload The head is transmitted with maximum error correction code (4/8). It also has its own CRC to allow the receiver to discard invalid headers. '''Implicit Header:''' Header is removed from the LoRa Packet. Payload, Coding Rate and CRC presence are fixed. Be advantageous to reduce transmission time <br><br> == CRC == RegPayloadCrcOn: RegModemConfig2[2:2] * 0 ---> CRC disable * 1 ---> CRC enable In Implicit Header Mode: must be set on Tx and Rx side In Explicit Header Mode: on the Tx side alone (recovered from the header in Rx side) '''Explicit Header Mode Checking process:''' Rx 用户负责检查 CrcOnPayload (RegHopChannel[6:6], CRC information extracted from the rx packet header) 如果 CrcOnPayload == 1,需要检查 IRQ 标志位 PayloadCrcError,以确保没有 CRC 错误 '''Implicit Header Mode 则直接去检查 IRQ 标志位 PayloadCrcError,以确保没有 CRC 错误''' <br><br>
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