Improve multichannel support for Cooja.

* Fix CCA detection in Cooja in the case when the receiver swicthes on the right channel during an ongoing transmission. Always add a connection on transmission, even when the channel is not correct. Initially the connection is in a dormant state; this mimics what Cooja is doing when the receiver radio is turned off;
when the receiver is turned on and switched to the right channel, `updateSignalStrengths()` is called, and the connection starts to recieve PHY-level traffic.

* Add "channel" property for DGRM edges.

* Avoid cross-channel interference on DGRM and MRM radio mediums

tools/cooja/apps/mrm/java/org/contikios/mrm/MRM.java

@@ -169,6 +169,7 @@ public class MRM extends AbstractRadioMedium {
       if (sender.getChannel() >= 0 &&
           recv.getChannel() >= 0 &&
           sender.getChannel() != recv.getChannel()) {
+        newConnection.addInterfered(recv);
         continue;
       }
       final Radio recvFinal = recv;
@@ -313,15 +314,15 @@ public class MRM extends AbstractRadioMedium {
     /* Interfering/colliding radio connections */
     for (RadioConnection conn : conns) {
       for (Radio intfRadio : ((MRMRadioConnection) conn).getInterfered()) {
-        double signalStrength = ((MRMRadioConnection) conn).getInterferenceSignalStrength(intfRadio);
-        if (intfRadio.getCurrentSignalStrength() < signalStrength) {
-                intfRadio.setCurrentSignalStrength(signalStrength);
-        }
         if (conn.getSource().getChannel() >= 0 &&
             intfRadio.getChannel() >= 0 &&
             conn.getSource().getChannel() != intfRadio.getChannel()) {
           continue;
         }
+        double signalStrength = ((MRMRadioConnection) conn).getInterferenceSignalStrength(intfRadio);
+        if (intfRadio.getCurrentSignalStrength() < signalStrength) {
+                intfRadio.setCurrentSignalStrength(signalStrength);
+        }
 
         if (!intfRadio.isInterfered()) {
           /*logger.warn("Radio was not interfered: " + intfRadio);*/

tools/cooja/java/org/contikios/cooja/radiomediums/AbstractRadioMedium.java

@@ -236,8 +236,9 @@ public abstract class AbstractRadioMedium extends RadioMedium {
 				case RECEPTION_STARTED:
 				case RECEPTION_INTERFERED:
 				case RECEPTION_FINISHED:
+					break;
+
 				case UNKNOWN:
-					return;
 				case HW_ON: {
 					/* Update signal strengths */
 					updateSignalStrengths();
@@ -322,8 +323,11 @@ public abstract class AbstractRadioMedium extends RadioMedium {
 					COUNTER_RX += connection.getDestinations().length;
 					COUNTER_INTERFERED += connection.getInterfered().length;
 					for (Radio intRadio : connection.getInterferedNonDestinations()) {
+
+					  if (intRadio.isInterfered()) {
 					    intRadio.signalReceptionEnd();
 					  }
+					}
 					
 					/* Update signal strengths */
 					updateSignalStrengths();

tools/cooja/java/org/contikios/cooja/radiomediums/DGRMDestinationRadio.java

@@ -42,6 +42,7 @@ public class DGRMDestinationRadio extends DestinationRadio {
 	public double signal = AbstractRadioMedium.SS_STRONG; /* RSSI */
 	public long delay = 0; /* EXPERIMENTAL: Propagation delay (us). */
 	public int lqi = 105;
+	public int channel = -1; /* not set by default */
 
 	public DGRMDestinationRadio() {
 		super();
@@ -50,12 +51,17 @@ public class DGRMDestinationRadio extends DestinationRadio {
 		super(dest);
 	}
 
+	public int getChannel() {
+		return channel;
+	}
+
 	protected Object clone() {
 		DGRMDestinationRadio clone = new DGRMDestinationRadio(this.radio);
 		clone.ratio = this.ratio;
 		clone.delay = this.delay;
 		clone.signal = this.signal;
 		clone.lqi = this.lqi;
+		clone.channel = this.channel;
 		return clone;
 	}
 	
@@ -75,11 +81,14 @@ public class DGRMDestinationRadio extends DestinationRadio {
 		element.setText("" + lqi);
 		config.add(element);
 		
-		
 		element = new Element("delay");
 		element.setText("" + delay);
 		config.add(element);
 		
+		element = new Element("channel");
+		element.setText("" + channel);
+		config.add(element);
+
 		return config;
 	}
 	
@@ -96,6 +105,8 @@ public class DGRMDestinationRadio extends DestinationRadio {
 				lqi = Integer.parseInt(element.getText());
 			} else if (element.getName().equals("delay")) {
 				delay = Long.parseLong(element.getText());
+			} else if (element.getName().equals("channel")) {
+				channel = Integer.parseInt(element.getText());
 			}
 		}
 		return true;

tools/cooja/java/org/contikios/cooja/radiomediums/DirectedGraphMedium.java

@@ -166,6 +166,19 @@ public class DirectedGraphMedium extends AbstractRadioMedium {
       DGRMDestinationRadio dstRadios[] =  getPotentialDestinations(conn.getSource());
       if (dstRadios == null) continue; 
       for (DGRMDestinationRadio dstRadio : dstRadios) {
+
+        int activeSourceChannel = conn.getSource().getChannel();
+        int edgeChannel = dstRadio.channel;
+        int activeDstChannel = dstRadio.radio.getChannel();
+        if (activeSourceChannel != -1) {
+          if (edgeChannel != -1 && activeSourceChannel != edgeChannel) {
+            continue;
+          }
+          if (activeDstChannel != -1 && activeSourceChannel != activeDstChannel) {
+            continue;
+          }
+        }
+
         if (dstRadio.radio.getCurrentSignalStrength() < dstRadio.signal) {
           dstRadio.radio.setCurrentSignalStrength(dstRadio.signal);
         }
@@ -254,6 +267,20 @@ public class DirectedGraphMedium extends AbstractRadioMedium {
         continue;
       }
 
+      int srcc = source.getChannel();
+      int dstc = dest.radio.getChannel();
+      int edgeChannel = dest.getChannel();
+
+      if (edgeChannel >= 0 && dstc >= 0 && edgeChannel != dstc) {
+      	/* Fail: the edge is configured for a different radio channel */
+        continue;
+      }
+
+      if (srcc >= 0 && dstc >= 0 && srcc != dstc) {
+        /* Fail: radios are on different (but configured) channels */
+        newConn.addInterfered(dest.radio);
+        continue;
+      }
 
       if (!dest.radio.isRadioOn()) {
         /* Fail: radio is off */
@@ -269,13 +296,6 @@ public class DirectedGraphMedium extends AbstractRadioMedium {
         continue;
       }
      
-      int srcc = source.getChannel();
-      int dstc = dest.radio.getChannel(); 
-      if ( srcc >= 0 && dstc >= 0 && srcc != dstc) {
-    	/* Fail: radios are on different (but configured) channels */
-        continue;
-      }
-      
       if (dest.radio.isReceiving()) {
          /* Fail: radio is already actively receiving */
          /*logger.info(source + ": Fail, receiving");*/

tools/cooja/java/org/contikios/cooja/radiomediums/UDGM.java

@@ -192,6 +192,13 @@ public class UDGM extends AbstractRadioMedium {
       if (sender.getChannel() >= 0 &&
           recv.getChannel() >= 0 &&
           sender.getChannel() != recv.getChannel()) {
+
+        /* Add the connection in a dormant state;
+           it will be activated later when the radio will be
+           turned on and switched to the right channel. This behavior
+           is consistent with the case when receiver is turned off. */
+        newConnection.addInterfered(recv);
+
         continue;
       }
       Position recvPos = recv.getPosition();