If the preamble matches, the bit sequence is further decoded, otherwise, it is discarded and the next sequence is processed. This block outputs bit sequences (ignoring the idle times in the transmission) which are subsequently checked for the known preamble. The on-off keyed Manchester coding implies the bit selection block includes clock recovery. The received complex samples are amplitude demodulated by extracting their magnitude. The radio is tuned to a center frequency of 915 MHz for the entire simulation runtime. Since every packet is transmitted on each frequency hop, it is sufficient to monitor only one frequency for this example. The frequency hopping allows for increased reliability over time. For each frequency in the hopping pattern, every AMR data packet is transmitted. A sampling rate of 1.0 Msps is used to produce a sufficient number of samples per Manchester encoded data bit. The ADALM-PLUTO radio is capable of using a sampling rate in the range of 520 kHz-61.44 MHz. The RTL-SDR radio is capable of using a sampling rate in the range of 225-300 kHz or 900-2560 kHz.
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