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Technology Beyond the Standard
Published in Klaus Diepold, Sebastian Moeritz, Understanding MPEG-4, 2012
Klaus Diepold, Sebastian Moeritz
This is a reasonably sound approach for assessing the coding performance of codecs that are not too different in terms of coding techniques. The rate-distortion curve depicted in Figure 4.6 suggests that Codec 3 has only half the coding performance of Codec 2, (i.e., Codec 3 needs about twice the amount of data compared to Codec 2 to achieve the same level of quality). Codec 2 has a PSNR-measured quality of 31 dB at a bit rate of 1 Mbit/sec. Codec 3 requires a bit rate of 2 Mbit/sec to reach the 31 dB point. This observation indicates a 2:1 performance ratio.
QAM and PSK modulation performance analysis over narrow band HF channel
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Real transceiver is implemented using Hack RF one (1 MHz to 6 GHz operating frequency) half-duplex transceiver and 20 million samples per second and open-source hardware (Greatscottgadgets 2019) using the (GNU) radio program. At the transmitter side, a wave voice file is queued and resampled using rational resampler, then Encoded using CODEC2 algorithm. CODEC2 is used to compress speech using sinusoidal coding and it is a method specialized for human speech. The output of coding is streamed and packed before being modulated using the different modulations that are to be compared and studied later in this paper. The tested modulation are 16 QAM, 32 QAM, 64 QAM also QPSK, 8 PSK and 16 PSK. After that the signal sent to the Osmocom sink which is a block in GNU radio that is responsible for converting the signal to the target RF frequency (4, 8, 11 and 18 MHz). Finally, the signal is transferred through the real sloping VEE Antenna from Tehran to Semnan city (receiver location). Figure 4 shows the block diagram of a real 16-QAM transmitter Using Hack RF.