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Wireless Communication Interview Questions | Page 1


 

Q. Sampling's importance in signal processing

A. To convert an analog signal to a digital one, sampling is required.

Q. Describe the Nyquist criterion.

A. When a message signal's highest available frequency component is Fm, the sampling rate must be 2*Fm. If not, we cannot recover the original message signal at the receiver.   

Q. Why do we need "signal quantization"?

A. By quantization, we allocate the signal to specific symbols based on their amplitude in volts or map the call to particular levels. In that case, there will be endless signal levels if quantization is avoided. They are indistinguishable from one another.

Q. Modulation definition

A. See the answer

Q. Why is modulation necessary?

A. View the answer to the previous question.

Q. What are heterodyne or super-heterodyne receivers?

A. 

Q. What is a communication channel's capacity?

A. Capacity, C = BW * (1 + SNR) bits/s/Hz
     when, BW = bandwidth
In simple terms, capacity refers to the highest feasible data rates between TX and RX. 

Q. A constellation diagram is what?

A. See the answer

Q. Draw the BPSK constellation diagram (binary phase shift keying).

A. See the answer to the previous question.

Q. Draw the 16 QAM constellation diagram (quadrature amplitude modulation).

A. See the answer

Q. What do baud rate and bit rate mean?

A. Baud rate is the number of symbols sent and received each second.

     Bit rate is the number of bits sent and received each second.

Q. Coherence bandwidth: what is it?

A. See the answer

Q. Which QAM format—32 QAM, 64 QAM, 128 QAM, and 256 QAM—has the most bits per symbol?

A. 32 QAM -----> 5 bits per symbol
64 QAM -----> 6 bits per symbol 
128 QAM -----> 7 bits per symbol
256 QAM -----> 8 bits per symbol

Q. Which modulation scheme—4 QAM or BPSK—will you choose in a noisy channel?


Q. Assume you are using two different modulation techniques. Both BPSK and QPSK modulation are used in the first. Please tell us what the SNR for QPSK should be when the SNR for BPSK is 5 dB to have the same BER (bit error rate) for both modulation techniques.


Q. OFDM modulation: what is it? What are the benefits of OFDM modulation?


Q. Alamouti scheme: what is it?

A. Alamouti scheme is a space-time block coding technique that sends two orthogonal symbols from two transmitters at two different time slots. It requires 2 X 1 MIMO systems.



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