Abstract
Variable-length codes, using source statistical features, improve the encoding. However, using these codes can results in error propagation in bit string transmitted to noisy transmission environments. This paper has used reversible symmetrical codes in the bit string obtained from JPEG compressor in order to overcome this problem. several examples of reversible code design algorithm have been reviewed and a symmetrical code based on Huffman code has been analyzed and deigned for JPEG compressor Jpeg compressor has been simulated by Huffman standard code and by reversible symmetrical code and the amount of their compression has been compared for several pictures Also, optimization of detection trend in noisy condition has been displayed. © 2009 IEEE.

Abstract
Unmanned Aerial Vehicles (UAVs) offer promising potential as communications node carriers, providing on-demand wireless connectivity to users. While existing literature presents various wireless channel models, it often overlooks the impact of UAV heading. This paper provides an experimental characterization of the Air-to-Ground (A2G) and Ground-to-Air (G2A) wireless channels in an open environment with no obstacles nor interference, considering the distance and the UAV heading. We analyze the received signal strength indicator and the TCP throughput between a ground user and a UAV, covering distances between 50 m and 500 m, and considering different UAV headings. Additionally, we characterize the antenna’s radiation pattern based on UAV headings. The paper provides valuable perspectives on the capabilities of UAVs in offering on-demand and dynamic wireless connectivity, as well as highlights the significance of considering UAV heading and antenna configurations in real-world scenarios. © ICST Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2024.

Abstract