Telecom Interview Questions and Answers

This page covers a set of telecom/wireless questions and answers prepared by experienced specialists in the telecommunication domain. This field consistently demands expertise in design, testing, and installation. These top telecom interview questions and answers are designed to help engineers seeking telecom jobs to ace their interviews. These questions are also useful as viva questions.

Question 1: Explain the basic block diagram of a wireless system. Explain the function of a scrambler or randomizer.

Answer:

As we know, a wireless system consists of two main parts: the transmitter and the receiver.

A scrambler removes long streams of 1s and 0s. This helps distribute energy over a larger bandwidth rather than concentrating it around a narrow bandwidth.

Question 2: Explain the function of the forward error correction (FEC) module in a digital communication system.

Answer:

The FEC module helps in correcting errors at the receiver using the redundant bytes transmitted along with the original information bytes. This module helps in eliminating re-transmission of information bytes. In FEC, the transmit end will have a convolutional encoder, and the receiver end will have a Viterbi decoder.

Question 3: What is Bit Error Rate (BER) and how is it calculated?

Answer:

Bit Error Rate (BER) is used to measure the performance of a wireless or wired system in a channel or impaired environment.

BER is the ratio of received erroneous bits to the total number of bits transmitted.

Question 4: What is the difference between analog and digital modulation? Explain the QPSK modulation scheme.

Answer:

Analog modulation will have baseband information in analog form, and digital modulation will have baseband information in digital form.

QPSK stands for Quadrature Phase Shift Keying. It is a modulation technique that transmits 2 bits per carrier. It is the most robust digital modulation technique after BPSK modulation.

Question 5: What is delay spread? How can it be tackled in a communication chain?

Answer:

Delay spread is the time delay a signal incurs while traveling from the transmitter to the receiver. Delay spread results in ISI (Inter-Symbol Interference). The concept of the cyclic prefix is used to tackle ISI and delay spread.

Question 6: Explain multipath fading.

Answer:

The variation in received signal strength over time is referred to as fading. When the signal traverses from the transmit end to the receive end, it will encounter many reflections from buildings and walls until it reaches the receive end. This results in multipath fading.

Question 7: What is diversity? Explain types of diversity techniques.

Answer:

Diversity utilizes the effect of fading to recover information from a corrupted received packet. Various types of diversity are space diversity, time diversity, frequency diversity, polarization diversity, directional diversity, pattern diversity, transmit-receive diversity, etc.

Question 8: Explain RF link budget with equation.

Answer:

Question 9: What is the difference between coherence bandwidth and coherence time?

Answer:

The frequency range and time period over which a channel remains constant is referred to as coherence bandwidth and coherence time, respectively.

Question 10: What is the relation between wavelength and frequency?

Answer:

Wavelength and frequency are inversely proportional to each other.

$\lambda = \frac{C}{Frequency}$, where $C = 3 \times 10^8$ m/sec

Question 11: What is the difference between Erlang and GoS?

Answer:

Both Erlang and GoS are used in telephone exchanges for the measurement of calls, such as calls dropped, calls passed, etc.

Question 12: What is the difference between CAS and CCS?

Answer:

CAS stands for Channel Associated Signaling, and CCS stands for Common Channel Signaling. Both are associated with PCM used in telephony.

Question 13: Often it is asked to differentiate between single carrier and multiple carrier systems (i.e., OFDM, OFDMA)?

Answer:

SC (single carrier) systems carry less information, while multi-carrier systems occupy multiple bits simultaneously. Hence, the data rate is higher for multi-carrier systems compared to single-carrier systems.

In addition to the above telecom interview questions and answers, one needs to thoroughly prepare for the projects carried out during their academic curriculum. Also, prepare questions on the technologies related to the products of the company where the interview needs to be given.