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--- network_protocol_programming_lab:15.3_5_exercise [2020/05/15 11:22] – rathke
+++ network_protocol_programming_lab:15.3_5_exercise [2020/06/11 09:16] (current) – rathke
@@ Line 10: / Line 10: @@
 In practice, it is not easy to build such systems. Especially the synchronization problems are hard to takle and introduces a large amount of overhead. To alleviate the synchronization problem, asynchronous frequency hopping systems are introduced. A simple system has been proposed by Texas Instruments (look at).
-In that system, the sender selects an arbitrary frequency from a set of available channels and transmits a packet as usual. But the packet has a huge and very large preamble. The receiver will be sensing the channel for some time. If he does not recognize a signal, he will change the channel and sense this new channel again and if there is also no signal, he will change again and so on. But, if there is signal on a channel, he will start receiving the packet. The idea behind this system is, that receiver will sense all chanels during the time he sender is transmitting the preamble of the packet. In that case, the receiver is able to always find the frequency the sender is using. In this system, receiver need not be synchronized with the sender and always finds the channel on which the sender will send its packet.
+In that system (see Fig. 1), the sender selects an arbitrary frequency from a set of available channels and transmits a packet as usual. But the packet has a huge and very large preamble (green part in Fig. 1). The receiver will sense a channel for some time (blue boxes in Fig. 1). If he does not recognize a signal, he will change the channel and sense this new channel again and if there is also no signal, he will change again and so on. But, if there is signal on a channel, he will wait for a sync word (orange boxes in Fig. 1) and after a sync word has been found, he will start receiving the packet.
-<imgcaption 1| TI Asynchronous Channel Hopping System>{{:network_protocol_programming_lab:FH-TI.png?950%}}</imgcaption>
+The idea behind this system is, that the receiver will sense all channels during the time the sender is transmitting the preamble of the packet. In that case, the receiver is able to always find the frequency the sender is using. In this system, receiver need not to always synchronized with the sender and always finds the channel on which the sender will send its packet.
-This system has also some drawbacks. E.g. if the receiver detects a signal on a channel, but this signal is was not generated by sender (e.g. from an microwave owen). In that case, the receiver is blocked. He will wait receiving a packet, that will never come. But vor our purposes this system is best fit for a small project. To implement such system, we will divide it in multiple parts:
+<imgcaption 1| TI Asynchronous Channel Hopping System>{{:network_protocol_programming_lab:FH-TI.png?650%}}</imgcaption>
+This system has also some drawbacks. E.g. if the receiver detects a signal on a channel, but this signal was not generated by sender (e.g. from an microwave owen). In that case, the receiver is blocked. He will wait receiving a packet, that will never come. But for our purposes this system is best fit for a small project. To implement such system, we will divide it in multiple parts:
+  * [[network_protocol_programming_lab:change_frequency|Exercise: Changing the frequency]]
+  * [[network_protocol_programming_lab:channel_sensing|Exercise: Sensing a channel]]
+  * [[network_protocol_programming_lab:scanning|Exercise: Scanning the channel and packet reception]]
+  * [[network_protocol_programming_lab:robust|Exercise: Making the system robust against disturbances]]
+  * [[network_protocol_programming_lab:fast_scan|Exercise: Scanning faster]]
+  * [[network_protocol_programming_lab:fh_sender|Exercise: Finalizing the FH system by implementing the sender]]
-  * Changeing a frequency
-  * Sensing a channel
-  * Receiving a packet
-  * Optimizing the system
 Each part consists of some exercises. For some exercises you can use previous already done exercises.