A multifrequency TDMA/TDM system for a VSAT terminal network operating in Ka band

FH-JFDA (Frequency Hopping-Jitter Free Demand Assignment) is a satellite access scheme suitable for VSAT systems and designed for the Ka band (20-30 GHz). It uses the FH-TDMA (Frequency Hopping-Time Division Multiple Access) technique on the in-bound link towards the hub station, and the TDM (Time Division Multiplexing) technique on the out-bound link, from the hub towards the traffic stations. Each traffic station is allowed to transmit to the hub in temporal slots assigned by the hub itself, generally hopping among different TDMA carriers at each data burst transmission. The hub station retransmits the data received by using two TDM carriers modulated at different bit rates. It tries to maintain the same temporal position of the real time data packets when it switches between the two carriers in order not to introduce any further jitter on data. The fade countermeasure system adopted is based on the up-link power control and on data bit rate changing. This paper describes the FH-JFDA MAC protocol, the algorithm for assigning the transmission temporal slots, the algorithm adopted by the hub station for mapping the TDMA transmissions onto the TDM links, and the fade countermeasure technique used. The results of the investigation on one particular parameter of the system, which influences the choice of the TDMA assignment procedure, are also presented. A possible realization of the system using two transponders of the Italsat National coverage payload is also included in the paper, and the performance of the fade countermeasure system is evaluated.