As is known reliable multicast transmission is not addressed in WLANs. Multicast packets are sent over wireless channels without using medium access control (MAC) layer automatic repeat request (ARQ) mechanism. Therefore, packet error rates will be very high. This paper investigates reliable video multicasting, which became a very popular application, over WLANs. To this end, application layer forward error correction (AL-FEC) codes based on Raptor Q can be used as a means to provide reliable delivery of the multicast video encoded with the H.264/Advanced video coding (AVC) codec. Since video streaming applications have very stringent Quality of Service requirements (low delay and error free transmission of packets), the Raptor Q and the H.264/AVC parameters have to be determined depending on the QoS of the video. Therefore, in this work an advanced cross-layer simulator was developed to analyse the performance of the end-to-end system. Simulation results show that using AL-FEC significantly improve the received video quality, i.e., the mean peak signal to noise ratio (PSNR) is improved over 34 dB. Further that it is shown that frequently inserting intra-frame results in poor video quality. Therefore, it is suggested to send intra frame at longer intervals.
Millimeter wave (mmWave) communication is a key enabling technology with the potential to deliver high capacity, high peak data rate communications for future railway services. Knowledge of the radio characteristics is of paramount importance for the successful deployment of such systems. In this paper mmWave channel measurements are reported for a railway environment using a wideband channel sounder operating at 60GHz. Highly directional antennas are deployed at both ends of the link. Data is reported for path loss, root mean square (RMS) delay spread and K-factor. Static and mobile measurements are considered. Analysis shows that the signal strength is strongly dependent (up to 25dB) on the azimuth orientation of the directional transmit and receive antennas. A path loss exponent of = .was extracted from the Line-of-Sight measurements with optimally aligned antennas. RMS delay spreads ranged from 1ns to 22ns depending on antenna alignment. 50% of the measured K-factors were found to be less than 6dB. We conclude this is the result of ground reflections in the vertical Tx-Rx plane.
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