It's all related by sample rate and IFFT size. For PRIME, it's a 250 kHz
sample rate and an IFFT size of 512.
Carrier spacing = sample rate / IFFT size = 250,000 / 512 = 488.28125 Hz
OFDM symbol time = IFFT size / sample rate = 512 / 250,000 = 2.048
milliseconds.
However, only 97 carriers out of the possible 512 are used. 96 carry
data and one is used as a pilot.
Bandwidth = active carriers * carrier spacing = 97 * 488.28125 Hz =
47363.28125 Hz. The signal occupies a little over 47 kHz from 42 to 89 kHz.
There is also a guard interval of 48 samples. So an OFDM symbol takes
2.048 + 0.192 = 2.24 milliseconds to transmit.
So you get to send 96 DBPSK, QQPSK or D8PSK symbols (1 per carrier) for
each OFDM symbol every 2.24 milliseconds.
This gives an uncoded throughput of 1 / 0.00224 * 96 * 1 = 42847 bps for
DBPSK
This gives an uncoded throughput of 1 / 0.00224 * 96 * 2 = 85714 bps for
DQPSK
This gives an uncoded throughput of 1 / 0.00224 * 96 * 3 = 128571 bps
for D8PSK
Ron
On 04/03/2016 05:00 AM, Paul Creaser wrote:
With regards to OFDM I have one question.
I have a 8 channel OFDM using 8PSK. To me a single symbol using 8PSK means 8
bits, hence one byte of data. Since I have 8 channels, that would mean 64
bytes. This would equate to a single OFDM symbol of 64 bytes?
Going on further a payload of 16 OFDM symbols would mean 16*64 bytes of
data.
I'm not too sure of the relationship between bits, symbols and OFDM symbols
even though it appears to be simple.
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