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Unformatted text preview: a2. One 16PPM symbol represents 4 bits. Therefore, the period for symbol
transmission is 4 µs. There is one pulse in each symbol, so the average time
between pulses is 4 µs.
a3. Each symbol consists of 16 pulse positions, with only one pulse present. If the
adjacent symbols are 0000000000000001 and 1000000000000000, then the time
between pulses is 4/16 = 0.25 µs.
a4. If the adjacent symbols are 1000000000000000 and 0000000000000001, then the
time between pulses is 31 × 0.25 = 7.75 µs
b1. The 4PPM scheme is for the 2Mbps data rate. Therefore, the period for bit
transmission is 1/(2 × 106 ) = 0.5 µs.
b2. One 4PPM symbol represents 2 bits. Therefore, the period for symbol
transmission is 1 µs. There is one pulse in each symbol, so the average time
between pulses is 1 µs.
b3. Each symbol consists of 4 pulse positions, with only one pulse present. If the
adjacent symbols are 0001 and 1000, then the time between pulses is 1/4 = 0.25
µs.
b4. If the adjacent symbols are 1000 0001, then the time between pulses is 7 × 0.25 =
1.75 µs
14.4 Each subcarrier can operate at 250 kbaud, that is, 0.25 × 106 signal elements per
second. For the first row in Figure 14.6d, BPSK is used, which corresponds to one
bit per signal element. With a code rate of 1/2, each data bit is encoded as 2 code
bits. Thus, the effective data rate on each subcarrier is 125 kbps. With 48
subcarriers, this results in a data rate of 48 × 125 kbps = 6 Mbps.
For the second row in Figure 14.6d, a code rate of 3/4 is used, meaning 3 data
bits are coded as 4 code bits. Thus, the effective data rate on each subcarrier is 0.75
× 250 = 187.5 kbps. The overall data rate is 48 × 187.5 = 9 Mbps.
For the third row, the use of QPSK allows two bits per signal element, so that the
250kbaud rate per subcarrier becomes 500 kbps. Using the same reasoning as for
the first row in the table, this results in a data rate of 12 Mbps.
The remaining rows can be easily calculated. 63 ...
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This note was uploaded on 02/20/2012 for the course ENC 3250 taught by Professor Dr.timothycerner during the Fall '11 term at UNF.
 Fall '11
 Dr.TimothyCerner

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