Ordonnancement ad hoc facilitant le saut rapide de fréquence avec des durées et à des moments pseudo-aléatoires

Abstract

The Techniques of frequency hopping scheduling are very popular in military networks operating in ad hoc mode. Most scheduling techniques for frequency hopping used in existing systems offer a fixed subdivision of the resource, which is not always consistent with the application of network users. In addition, the rate offered on each link is fixed, a user with a queue of packets to transmit could be allocated a flow which is not sufficient to prevent packet loss. This often occurs with low priority queues. The latency thus remains a challenge. To improve latency in scheduling for frequency hopping, we propose a new algorithm with variable frequency width per hop. It provides the frequency hopping with variable data rates and packet sizes. We propose two approaches; a less complex, which subdivides randomly the resource and a more complex, which uses the size and priority of queue to determine the subdivision of the resource. The first solution is proposed for queues with the same priority whereas the second one relates to systems with several types of files. Combining this variation to the changing users’ demand, we improve the network latency. Thus, packet loss is reduced. The limit we have encountered is about the "Bit Error Rate," BER, which is higher in the variable rates. The theoretical BER for traditional frequency hopping is assumed to be satisfying so that the error correcting code recovers the majority of errors. Then, exceeding the BER can cause packet retransmissions, which may increase latency of variable frequency hopping. So, to circumvent this problem, we vary the signal power as a fonction of the variable rates. The BER obtained with this approach is identical to the theory. The variation of power combined with low latency of variable frequency hopping, allows to have energy savings.

Date	11 Dec 2012
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	François Gagnon (Supervisor)