· 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.

考虑到数据包在高传播因子下的潜在长时间, 该选项用于提高传输到数据包传输和接收期间的频率变化的鲁棒性。LowDataRateOptimize位开启后可以增强Lora 连接在低速率条件下的鲁棒性。当单个符号传输时间超过16毫秒时，必须使能LowDataRateOptimize位。请注意，发射机和接收机都必须具有相同的LowDataRateOptimize设置。

· Symbol Duration

Symbol Duration其实就是Rs的倒数:

RS.png

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作为低速优化，是针对Symbol Rate（简称Rs）需要大于16ms/per symbol情况下。当SF设置较低，BW设置较大情况下，Ts会很大，此时必须开启这个优化功能。
那TS小于16ms情况下，是否也可以打开？是可以的，但是传送时间会增加不少，设计时请注意。

· 举例分析：

1. 以BW=500K，SF=10为例：
   此时RS = 500kHz / 1024，TS = 1 / RS = 1024/500 (ms) = 2 ms
   这种情况下，不一定需要开启Low Data Rate Optimization，但是也可以开启。
2. 以BW=25K，SF=10为例：
   此时RS = 25kHz / 1024，TS = 1 / RS = 1024/25 (ms) = 40.96 ms
   这种情况下，必须开启Low Data Rate Optimization。