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@ -97,7 +97,13 @@ It is possible to use modem **in client mode** with other generic Linux ax25/apr
LoRa library, which is in use by this project does not implement CAD, but CSMAp is utilized by this project as per KISS specification. TX path is executed only when there is no incoming data returned by `LoRa::parsePacket` and TX path is executed with probability p (CSMA persistence), configured by const `Loraprs::Service::CfgCsmaPersistence` in `loraprs_service.h`. Random value is picked between 0 and 255 and TX is executed only when it is lower than `CfgCsmaProbBoundary`. To decrease TX probability in case of high traffic use lower value. `Loraprs::ServiceCsmaSlotTimeMs` configures the amount of time in milliseconds to wait if transmission was not performed due to persistence, select lower value for lower TOA (time on air). It is also possible to dynamically override these parameters with KISS P 0x02 and SlotTime 0x03 command codes from the client.
# Digital voice communication by using Codec2
This modem could be used in conjuction with [Android Codec2 Walkie-Talkie](https://github.com/sh123/codec2_talkie), when application connects to the modem, instead of sending AX25 APRS packets it sends Codec2 speech encoded frames. This enables digital voice communicaiton between one or multiple modems. Select appropriate lora spread factor `cfg.LoraSf` and bandwidth `cfg.LoraBw` depending on Codec2 speech rate from 450-3200 bps. For example, if you are using 450 bps mode and 20 kHz bandwidth then set spreading factor to 6,7 or 8. See data rate table above. When using modem for voice communication `Loraprs::Service::CfgCsmaPersistence` must be set to maximum 255 value to disable CSMA, otherwise real time voice communication won't be guaranteed. Android codec2_talkie application automatically sets this parameter to 255 by using KISS P command code.
This modem could be used in conjuction with [Android Codec2 Walkie-Talkie](https://github.com/sh123/codec2_talkie), when application connects to the modem, instead of sending AX25 APRS packets it sends Codec2 speech encoded frames. This enables digital voice communicaiton between one or multiple modems.
Select appropriate lora spread factor `cfg.LoraSf` and bandwidth `cfg.LoraBw` depending on Codec2 speech rate from 450-3200 bps. For example, if you are using 450 bps mode and 20 kHz bandwidth then set spreading factor to 6,7 or 8. See data rate table above.
When using modem for voice communication `Loraprs::Service::CfgCsmaPersistence` must be set to maximum 255 value to disable CSMA, otherwise real time voice communication won't be guaranteed. Android codec2_talkie application automatically sets this parameter to 255 by using KISS P command code.
Also, it might be useful to disable CRC check for LoRa packets with `cfg.LoraEnableCrc` parameter equal to `false`. Some broken bits in one speech frame will cause audio being scrambled, it might be better then longer gap when complete packet is dropped.
# Test Results
![alt text](images/setup.png)