net/gnrc_lorawan: implement uplink redundancy

This commit implements uplink redundancy in GNRC LoRaWAN. Uplink
redundancy is used to retransmit unconfirmed uplink frames. The
retransmission stops when either a downlink message is received or the
number of uplink retransmissions is reached.

This functionality doesn't affect confirmed uplinks.

sys/include/net/gnrc/lorawan.h

@@ -24,6 +24,7 @@
 #define NET_GNRC_LORAWAN_H
 
 #include "gnrc_lorawan_internal.h"
+#include "assert.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -320,6 +321,21 @@ void gnrc_lorawan_set_timer(gnrc_lorawan_t *mac, uint32_t us);
  */
 void gnrc_lorawan_remove_timer(gnrc_lorawan_t *mac);
 
+/**
+ * @brief Set unconfirmed uplink redundancy
+ *
+ * @pre   @p redundancy <= 14
+ *
+ * @param[in] mac pointer to the MAC descriptor
+ * @param[in] redundancy number of unconfirmed uplink retransmissions
+ */
+static inline void gnrc_lorawan_set_uncnf_redundancy(gnrc_lorawan_t *mac,
+                                                     uint8_t redundancy)
+{
+    assert(redundancy <= (0xF - 1));
+    mac->mcps.redundancy = redundancy;
+}
+
 #ifdef __cplusplus
 }
 #endif

sys/net/gnrc/link_layer/lorawan/gnrc_lorawan.c

@@ -58,6 +58,7 @@ static inline void gnrc_lorawan_mcps_reset(gnrc_lorawan_t *mac)
     mac->mcps.waiting_for_ack = false;
     mac->mcps.fcnt = 0;
     mac->mcps.fcnt_down = 0;
+    gnrc_lorawan_set_uncnf_redundancy(mac, CONFIG_LORAMAC_DEFAULT_REDUNDANCY);
 }
 
 void gnrc_lorawan_set_rx2_dr(gnrc_lorawan_t *mac, uint8_t rx2_dr)
@@ -164,8 +165,11 @@ void gnrc_lorawan_timeout_cb(gnrc_lorawan_t *mac)
         case LORAWAN_STATE_JOIN:
             gnrc_lorawan_trigger_join(mac);
             break;
+        case LORAWAN_STATE_IDLE:
+            gnrc_lorawan_event_retrans_timeout(mac);
+            break;
         default:
-            gnrc_lorawan_event_ack_timeout(mac);
+            assert(false);
             break;
     }
 }

sys/net/gnrc/link_layer/lorawan/gnrc_lorawan_mcps.c

@@ -331,16 +331,33 @@ static void _transmit_pkt(gnrc_lorawan_t *mac)
     last_snip->iol_next = NULL;
 }
 
-void gnrc_lorawan_event_ack_timeout(gnrc_lorawan_t *mac)
+void gnrc_lorawan_event_retrans_timeout(gnrc_lorawan_t *mac)
 {
     _transmit_pkt(mac);
 }
 
 static void _handle_retransmissions(gnrc_lorawan_t *mac)
 {
+    /* Check if retransmission should be handled.
+     *
+     * If there was a confirmed uplink, follow the standard retransmission
+     * procedure.
+     * If it was an unconfirmed uplink, perform retransmissions only if
+     * there's redundancy > 0 */
     if (mac->mcps.nb_trials-- == 0) {
+        if (mac->mcps.waiting_for_ack) {
+            /* If we are here, the node ran out of confirmed uplink retransmissions.
+             * This means, the transmission was not successful. */
             _end_of_tx(mac, MCPS_CONFIRMED, -ETIMEDOUT);
-    } else {
+        }
+        else {
+            /* In this case, we finished sending one or more unconfirmed
+             * (depending on the redundancy) */
+            _end_of_tx(mac, MCPS_UNCONFIRMED, GNRC_LORAWAN_REQ_STATUS_SUCCESS);
+        }
+    }
+    else {
+        /* Schedule a retransmission */
         gnrc_lorawan_set_timer(mac, 1000000 + random_uint32_range(0, 2000000));
     }
 }
@@ -358,14 +375,7 @@ void gnrc_lorawan_event_no_rx(gnrc_lorawan_t *mac)
         return;
     }
 
-    /* Otherwise check if retransmission should be handled */
-
-    if (mac->mcps.waiting_for_ack) {
     _handle_retransmissions(mac);
-    }
-    else {
-        _end_of_tx(mac, MCPS_UNCONFIRMED, GNRC_LORAWAN_REQ_STATUS_SUCCESS);
-    }
 }
 
 void gnrc_lorawan_mcps_request(gnrc_lorawan_t *mac,
@@ -416,7 +426,7 @@ void gnrc_lorawan_mcps_request(gnrc_lorawan_t *mac,
     mac->mcps.waiting_for_ack = waiting_for_ack;
     mac->mcps.ack_requested = false;
 
-    mac->mcps.nb_trials = CONFIG_LORAMAC_DEFAULT_RETX;
+    mac->mcps.nb_trials = waiting_for_ack ? CONFIG_LORAMAC_DEFAULT_RETX : mac->mcps.redundancy;
 
     mac->mcps.msdu = pkt;
     mac->last_dr = mcps_request->data.dr;

sys/net/gnrc/link_layer/lorawan/include/gnrc_lorawan_internal.h

@@ -153,6 +153,7 @@ typedef struct {
     int nb_trials;                      /**< holds the remaining number of retransmissions */
     int ack_requested;                  /**< whether the network server requested an ACK */
     int waiting_for_ack;                /**< true if the MAC layer is waiting for an ACK */
+    uint8_t redundancy;                 /**< unconfirmed uplink redundancy */
     char mhdr_mic[MHDR_MIC_BUF_SIZE];   /**< internal retransmissions buffer */
 } gnrc_lorawan_mcps_t;
 
@@ -393,11 +394,11 @@ void gnrc_lorawan_mlme_no_rx(gnrc_lorawan_t *mac);
 void gnrc_lorawan_event_no_rx(gnrc_lorawan_t *mac);
 
 /**
- * @brief Mac callback for ACK timeout event
+ * @brief Mac callback for retransmission timeout event
  *
  * @param[in] mac pointer to the MAC descriptor
  */
-void gnrc_lorawan_event_ack_timeout(gnrc_lorawan_t *mac);
+void gnrc_lorawan_event_retrans_timeout(gnrc_lorawan_t *mac);
 
 /**
  * @brief Get the maximum MAC payload (M value) for a given datarate.