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Examination of a digital radio link

A digital radio link is designed to carry a T1 rate digital signal (1.544 Mbps). The transmitter and receiver have ideal RRC bandpass filters with roll off factor (r) = 0.2.

a. What RF bandwidth must the radio link provide if the modulation is binary phase shift keying (BPSK)?

b. The link is unchanged but the modulator and demodulator in the transmitter and receiver are changed to transmit and receive QPSK. The link has the bandwidth you found in part (a) above. What is the maximum bit rate that the link can carry using QPSK modulation?

c. If the filters in the transmitter and receiver are changed for ideal RRC filters with roll off factor (r) = 0.5, what is the maximum symbol rate for this link?

Solution Preview

(a) Bit rate (R) = Symbol Rate {SR} x Bits/Symbol {m}

R = m*SR (1)

Since BPSK is only two levels (M = 2) we get the number of Bits/Symbol (m) determined from (2) as

m = log2{M} (2)

m(BPSK) = log2(2) = 1

Therefore symbol rate for the BSPK case, using (1), is

SR (BPSK) = R/m(BPSK) = 1.544/1 = 1.544 MSymbols/s

The Symbol rate of a modulation set occupies a Bandwidth that is the real RF Bandwidth (B) reduced by a factor of (1+r) where (r) represents ...

Solution Summary

Examination of a digital radio link and determination of some of its parameters including RF bandwidth, bit rate and sysmbol rate for known parameters calculated

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