| Motivated by the increasing request of providing the battlefield data dissemination and communications relay, we presents the design of an unmanned aerial vehicle (UAV) platform's applications of tactical communications for providing beyond-line-of-sight (BLOS) communications capability. Providing a description of the UAV platform's development, we conduct a deeply study on the wireless asymmetric data link structure, communication protocols and the algorithm of data dissemination. The main works can be summarized as follows.1. The transfer architecture of the UAV's BLOS communication is studied. Based on the layered structure, we presented a new topic design of the UAV platform based BLOS communications relay, which includes backbone layer, tactical layer and mission layer.2. We designed a wireless asymmetric physical layer link model with a direct sequence spread spectrum system as a transmitted reference. Uplink and downlink are both one-way links connected by an IP tunneling. Uplink is consisted with the narrowband radio data link of the warfighter information networks (WIN). The design simplified the synchronization of the downlink and can be realized in practical project. We presented an applicable demonstrated circuit based on commercial-off-the-shelf integrated circuit, and with the tool of SystemView some computer simulations verified the performance of this circuit.3. We analyzed the anti-jam and band inside anti-interfere performance of the system, and the Low Probability Intercept (LPI) of the traditional Direct Sequence Spread Spectrum (DSSS) modulations in the UAV platform's applications. So a new modulation technique using a multi-level Pseudo Noise (PN) code has been presented. The new multi-level PN code is built from a high speed PN code through a low passed filter (LPF). As a result, the computer simulations show that the LPI capability of the new DSSS modulation become more effective within the same bandwidth and Spread Spectrum gain.4. We study and analyze the problems of wireless asymmetric network applications using the original TCP/IP as system transport layer protocols. It is the high error rate in wireless asymmetric link, high-latency, TCP/IP performance deteriorated because of the asymmetric data streams that depressed the efficiency of the utilization coefficient of the wireless link. We studied many methods to improve the TCP/IP in wireless environment, such as TCP/IP Initial Slow Start Algorithm, Initial Window and Retransmission Time Out (RTO) estimate. Finally, we consider the Round-trip time (RTT) with the physical layer and the transfer layer combined together. Physical layer using RTT related to the channel state and transfer layer using the constant RTT, the interference between the two layers can be eliminated, and so the effectiveness of the wireless data link can be enhanced.5. The length or the capacities of the tactical data are always different, and so the conventional data scheduling algorithm which consisted "first in first service" and "shore message first service " are not appropriate in the tactical communication applications. To meet the requirement of the information service priority, we presented a dynamic priority scheduling algorithms, which working on the order programming mode, can improve the efficiency of the asymmetric broadcast channel.
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