| Frequency Hopping Communication is a branch of Spread Spectrum Communication. Its characteristic of anti-interference is so strong that it can be widely used in military field. The data frame will be difficult to be intercepted during the transmission. Therefore, the security will be much better than the traditional Ad Hoc networks.The frequency hopping stations used in military use VHF (Very High Frequency) channel for data transmission. However, because of the characteristic of frequency hopping and VHF channel, the existing MAC protocol in traditional Ad Hoc, such as CSMA/CA can not be used in this MAC layer directly.In this paper, a new competitive MAC protocol is designed to adapt to this kind of network. In this protocol, several Micro Slots are compartmentalized so that the mechanism of competitive slot can be used in this protocol. If the traffic of the network is large, the node will be access the channel by a dynamical probability. All the nodes accessed will be back to a random micro slot. In the perfect state, there will be more than one node to compete the slot to send there own data and only one node is succeed to transmit the data. Obviously, the time-delay and the conflict will be reduced a lot in the two methods.As the time-delay is so large, and the length of the slot is so long that the transmission of short frames will bring a large delay. Therefore, in this protocol, the short frames, such as RTS, CTS will not be transmitted. The effect of hidden stations will be reduced by further adjusting the probability of transmitting the data frames dynamically. Furthermore, the ACK will not transmitted to affirm whether the data in the physical layer is transmitted correctly.At the same time, the protocol ensures that the nodes which contains data to transmit and did not transmit the data successfully in the prior slot could transmit the data frame by a higher probability, so that all the nodes can access the channel more equally.In the method of mathematical analysis and the simulation of OPNET, the protocol is proved to be much better than the protocol of S-ALOHA. In the method of the protocol of QBDSP, the collision will be less, and the throughput will be much better when the frames of the network is a lot while the slot will be used better when the frames don't appear quite often . |
