# How to solve this question on communication lines?

The Question asked is as follows:

A communication link operates at a bitrate of 20 Mbps. The receiver is expected to perform at a $$BER$$ of $$10^{-6}$$ or better using $$QPSK$$ modulation scheme.

[Note: $$BER$$ for $$QPSK$$ is given by $$Q(\sqrt{2Eb/ N_0})$$. Use the approximation $$Q(x)≈ \frac{1}{2} e^{\frac{{−x}^2}{2}}$$]

(a) Determine the minimum $$\frac{Eb}{N0}$$ in dB needed to achieve the desired $$BER$$ performance.

(b) Given that the noise figure of the receiver is 8 dB, determine the receiver sensitivity in dBm.

(c) If the required link margin is 20 dB and the transmit power $$P_{Tx} = 0.5 W$$, determine the maximum possible path-loss, $$L$$, in dB

(d) Using a carrier frequency of 5 GHz and assuming free-space propagation model, determine the maximum possible range in $$m$$ for this system.

I attempted to solve the question, but my answers didn't match with the given answers. Any help on how to go about solving this would be highly appreciated. Thanks.

• That’s awesome that you attempted the question, can you add details of your attempt so then we can more directly help you? – Engineer May 4 at 9:36