Modifys imec iDLab's ns-3 implementation of LoRaWAN to include Class B mode.

This is temporarily not a fork because I already have one fork of the imec ns-3 implementation.

The original repository can be found here:

https://github.com/imec-idlab/ns-3-dev-git/tree/lorawan

Just the modified LoRaWAN ns-3 library can be found in the master branch. The library as part of a full ns-3 install (which can be downloaded and ran straight away) can be found in the lorawan branch.

An extention of imec iDLab's ns-3 implementation of LoRaWAN to include Class B mode, including:

For the Network Server

• generation and sending of beacon frames

• calculation of ping slots for each Class B device

• the transmission of downlink frames in those slots when data is pending and the duty cycle limits allow.

• the detection of the Class B bit in the uplink frame header to signify to the NS whether to calculate ping slots and send downlink frames to a device

For the End Devices:

• the waking up and reception of beacon frames when in Class B mode

• the use of the timestamp in the beacon frame to calculate a device's own ping slots (in the same way as the NS)

• the waking up in those ping slots to potentially receive additional downlink frames

LoRaWAN in general (TODOs inherited from imec library):

• The LoRaWAN Join Procedure

• Encryption / Decryption

• Class C

• many other things - see imec original repository for details

Class B related:

• Class B transition (i.e. all nodes start in Class A mode, have to detect beacon frames in order to transition). Currently devices just either start in Class A or Class B mode.

• The widening of RX slots in Class B beaconless mode.

• A satisfactory way of modeling time drift in the internal clocks of end devices in ns-3 (right now, if a certain number of beacon frames are missed, the device is just presumed to have gone out of sync)

• multicast support

Also have TO DO:

• more Class B-specific examples

• more Class B-specific tests

• an update of the documentation

• move this whole repository to be a fork of the imec one.