V.G. Baranov, V.R. Milov, L.M. Vdovin, T.I. Goriacheva

As a result of investigations and initial implementations of the aviation "Air-Ground" data link with VDL-2 and VDL-4 modes for support of new applications of Air Traffic Management (ATM), within of AMCP working group (WG)? proposals arisen about amendments for system parameters of the VDL-2 and VDL-4 modes, which are given in initial versions of Technical Specifications for this modes. In particular, for VDL-2 mode, which implements non-adaptive p-persistence Carrier Sense Multiple Access (p-CSMA)), on default system parameter of p-persistence CSMA is given in Doc.9776 and DO-224B as p = 13/256. WG recommends to replace this parameter by p = 39/256. At that maximal number of access to channel attempts M1, which given initially equal to 135, it is recommended to decrease to M1 = 45. Therefore, WG recommends (as design object, but no mandatory mode for all) to implements mode of ap-CSMA - adaptive predicted p-persistence CSMA. Also, wizards of American FAA recommend Prioritized CSMA (PCSMA), which they have been investigated by simulator of aviation communication channels OPNET [1], for rising effectiveness of the VDL-2 mode channel. For VDL-4 mode also gathered need to search new selection clot strategy for reservation. Given in the present tense into Doc. 9816 standard process of clots selection for Semi-organization Time Division Multiple Access (STDMA), based on random with equally probability slot selection into given window of slots (between minimum and maximum numbers of slots, which given by system parameters) is cause of slot selection large lateness, direct associated with large width of given slot window: larger width of slot window is cause of larger lateness of packet transmission. Reduction of width of slot selection window shall be appropriated (optimized) for definite condition of traffic (length of message, intensity of message transmission), but such reduction will be in practice non appropriated (non optimized) for other length of message and intensity of message transmission. There are no such set of parameter, which should be optimized simultaneously for wide range of operational situations for the VDL-4 mode. Analysis shown that other slot selection strategy may be provided for VDL-4 mode without radical change of the VDL-4 standard. For example, substitute of equal probable slot selection into slot window by p-persistence slot selection from adjacent slot candidates will reduce delay by preference for adjacent slot. In this paper detail research of р-CSMA algorithm is presented and proposed optimized algorithms of Multiple Access to the channel of VDL-2 and VDL-4 modes based on р-CSMA with predicted parameter of p-persistence is proposed.