LoRa——關於Low Data Rate Optimization功能分析

原文鏈接：https://www.jianshu.com/p/6763ec8ad80e

· Low Data Rate Optimization

Given the potentially long duration of the packet at high spreading factors the option is given to improve the robustness ofthe transmission to variations in frequency over the duration of the packet transmission and reception. The bit LowDataRateOptimize increases the robustness of the LoRa link at these low effective data rates. Its use is mandated when the symbol duration exceeds 16ms. Note that both the transmitter and the receiver must have the same setting for LowDataRateOptimize.

考慮到數據包在高傳播因子下的潛在長時間, 該選項用於提高傳輸到數據包傳輸和接收期間的頻率變化的魯棒性。LowDataRateOptimize位開啓後可以增強Lora 連接在低速率條件下的魯棒性。當單個符號傳輸時間超過16毫秒時，必須使能LowDataRateOptimize位。請注意，發射機和接收機都必須具有相同的LowDataRateOptimize設置。

· Symbol Duration

Symbol Duration其實就是Rs的倒數:

 

 

where BW is the programmed bandwidth and SF is the spreading factor. The transmitted signal is a constant envelopesignal. Equivalently, one chip is sent per second per Hz of bandwidth.

LowDataRateOptimize作爲低速優化，是針對Symbol Rate（簡稱Rs）需要大於16ms/per symbol情況下。當SF設置較低，BW設置較大情況下，Ts會很大，此時必須開啓這個優化功能。那TS小於16ms情況下，是否也可以打開？是可以的，但是傳送時間會增加不少，設計時請注意。

舉例分析：

1. 以BW=500K，SF=10爲例：
   此時RS = 500kHz / 1024，TS = 1 / RS = 1024/500 (ms) = 2 ms
   這種情況下，不一定需要開啓Low Data Rate Optimization，但是也可以開啓。
2. 以BW=25K，SF=10爲例：
   此時RS = 25kHz / 1024，TS = 1 / RS = 1024/25 (ms) = 40.96 ms
   這種情況下，必須開啓Low Data Rate Optimization。