100 Technical Interview Questions on Wireless communication, LTE and 5G.

This document covers most of the basic concepts related to wireless communication.

In total, i have compiled 100 fundamental questions.

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1. What is a Communication system and How is it classified?
A communication system is a system model that describes communication exchange taking place between
two stations, transmitter and receiver. The purpose of a communication system is to carry information from
one point to another.

Communication system is classified into wired and wireless, and the medium used for communication can be
guided or unguided.

In Wired communication, the medium is a physical path like co-axial cables, twisted pair cables, optical fiber
links etc. which guides the signal to propagate from one point to another. Such type of medium is called guided
medium.

Wireless communication doesn’t require any physical medium but propagates the signal through space. Since,
space only allows for signal transmission without any guidance, the medium used in wireless communication
is unguided.

2. What are the 3 major components of a communication system?
A typical communication system consists of 3 components – Source (Generates Information), Channel and
Destination (Reads Information).

3. What is Wireless Communication?
Wireless Communication is a method of transmitting information from one point to another over a distance,
without using any physical medium like wires, cables etc.

4. If there is no physical medium, how does wireless communication transmit signals from source to destination?
The transmission and reception of signals is accomplished with antennas placed at the source and destination.

5. What is an Antenna?
Antenna is an electrical device which transforms the electrical signals to radio signals in form of EM waves and
Vice versa. The EM Waves propagate through space. Hence, both to send the receive the EM Waves antennas
are placed at the transmitter and receiver.

6. What are the advantages of Wireless Communication?
• Cost - Wireless Communication does not require elaborate physical infrastructure or maintenance.
The cost of installing wires, cables and other physical infrastructure is eliminated in wireless
communication and hence the overall cost of the system is reduced compared to wired
communication system. Installing wired network in building, digging up the Earth to lay the cables and
running those wires across the streets is extremely difficult, costly and time-consuming job.
• Mobility – It is the main advantage of wireless communication system. It offers the freedom to move
around while still connected to network.
• Flexibility – Can be accessed from anywhere, anytime. Enables people to communication irrespective
of their locations.
• Ease of Installation - The setup and installation of wireless communication network’s equipment and
infrastructure is very easy as we need not worry about the hassle of cables. Also, the time required to
setup a wireless system like a Wi-Fi network for example, is very less when compared to setting up a
full cabled network.

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• Reliability - Since there are no cables and wires involved in wireless communication, there is no chance
of communication failure due to damage of these cables which may be caused by environmental
conditions, cable splice and natural diminution of metallic conductors.
• Disaster Recovery - In case of accidents due to fire, floods or other disasters, the loss of communication
infrastructure in wireless communication system can be minimal
• Data is transmitted faster and at a high speed.

7. What are the basic elements of a wireless communication system?
A typical wireless communication system consists of 3 elements – Transmitter, Channel and Receiver.



8. What is Source Encoding?
Source coding is all about studying the structure of the information that is to be stored or sent over a channel
and representing the data using minimum number of bits. A source encoder converts the signal into a suitable
form for applying signal processing techniques. The redundant bits from the signal are removed in this process
in order to maximise the utilization of resources.

9. What is Channel Encoding?
Channel Encoding is a technique that is applied to the signal to reduce the impairments like noise,
interference etc. During this process, a small amount of redundancy is introduced to the signal so it becomes
robust against noise.

10. What is a channel?
A channel in wireless communication indicates the medium of transmission of the signal i.e. open space. A
wireless channel is unpredictable and also highly variable and random in nature. A channel is subjected to
interference, distortion, noise, scattering etc. and the result is that the received signal may be filled with
some errors.

11. What is Modulation?
Modulation is the process of varying one or more properties of a steady periodic waveform called carrier
signal, in accordance with the instantaneous values of a modulating signal that typically contains the
information to be transmitted.

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12. What is Demodulation?
Demodulation is the process of extracting the original information bearing signal from a carrier wave.

13. What is Amplitude Modulation (AM)?
Amplitude modulation is a process in which the amplitude of the carrier signal is varied in accordance with the
message signal being transmitted.



14. What is Digital Amplitude Modulation?
The digital amplitude modulation is referred to as Amplitude Shift Keying (ASK). It is also called as ‘on-off
Keying’ (OOK). Digital amplitude modulation involves varying the amplitude of a carrier wave in discrete
sections according to binary data.

In an ASK system, the binary symbol 1 is represented by transmitting s fixed amplitude carrier wave and fixed
frequency for a bit duration of T Seconds.

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15. What is Frequency Modulation (FM)?
Frequency modulation is a process in which the frequency of the carrier signal is varied in accordance with the
message signal being transmitted.



16. What is Phase Modulation?
Phase modulation is a process in which the phase of the carrier signal is varied in accordance with the message
signal being transmitted.

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17. What is digital frequency modulation?
The Digital frequency modulation is called Frequency Shift Keying (FSK). With digital frequency modulation the
frequency of the carrier or a baseband signal is varied in discrete sections according to binary data. The digital
information is transmitted through discrete frequency changes of a carrier signal.


18. What is Digital Phase Modulation?
The Digital Phase modulation is called Phase Shift Keying (PSK). PSK is a process which conveys the data by
changing the phase of a constant frequency reference signal (carrier signal). The modulation is accomplished
by varying the sine and cosine inputs at a precise time.


19. What is BPSK (Binary Phase Shift Keying)?
BPSK is the most straightforward type of PSK, where the 0’s and 1’s in binary message are represented by use
of two-phase states in the carrier signal (θ = 0° for logic high, and θ = 180° for logic low).

20. What is QPSK (Quadrature Phase Shift Keying)?
QPSK is a form of phase modulation technique, in which two information bits (combined as one symbol) are
modulated at once, selecting one of the four possible carrier phase shifts (0, 90, 180, 270 degrees). QPSK
allows the signal to carry twice as much information as ordinary PSK using the same bandwidth. QPSK is also
called as 4-QAM.

21. What is QAM (Quadrature Amplitude Modulation)?
QAM is a form of modulation that is a combination of phase modulation and amplitude modulation. The QAM
scheme represents bits as points in a quadrant grid known as a constellation map.

22. What is a Constellation map?
Constellation map is a graph of the phase and amplitude modulation points in a given modulation scheme.
Shown below is the Constellation map of 16-QAM.

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23. What is the difference between QPSK and QAM?
QPSK is a specific symbol set (of the PSK family, where all symbols lie on the unit circle) that uses 4 symbols.
QAM is the family of symbols all lie on straight lines that form a square.

24. What is DPSK?
DPSK is a modulation technique in which the phase of the modulated signal is shifted relative to the previous
signal element. This technique doesn’t need a reference oscillator.

25. What is Electromagnetic Spectrum?
Electro-magnetic radio frequency is used to carry mobile signals. Low frequency spectrum is where the
distance/time between one wave and another is very long, whereas the distance/time is very short in high
frequency spectrum.

26. What is frequency?
Number of waves that pass a fixed point in unit time. The standard unit of frequency is hertz, abbreviated as
Hz. The time period is reciprocal of frequency.

27. What is wavelength?
Wavelength is the distance between identical points in the adjacent cycles of a waveform signal propagated
in space or along wire. It is typically measured in terms of millimeters or centimeters. The wavelength is
inversely proportional to frequency.

28. What is the range of Radio waves?
Radio waves are a type of EM radiation with wavelengths in EM spectrum longer than infrared light. They have
frequencies from 300GHz to as low as 3KHz, and the corresponding wavelengths from 1 millimeter to 100
killometers.

29. What is BER?
Bit error rate (BER) is defined as the percentage of bits that have errors relative to the total number of bits
received in a transmission. BER is usually expressed as 10 to a negative power.

30. What is SNR?
Signal to noise ratio (SNR) is a measure that compares the level of a desired signal to the level of background
noise. SNR is defined as the ratio of signal power to the noise power, it is often expressed logarithmically in
terms of decibels (dB). Ideally you want to aim for a higher SNR. A ratio higher than 1:1 (i.e., greater than 0
dB) indicates more signal than noise. SNR of zero indicates that the desired signal is virtually indistinguishable
from unwanted noise.

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31. What is network capacity?
The maximum data volume a network can support at one time in a given geography.

32. What is Density?
The maximum number of connections a network can handle in a given area at the same time. As more and
more devices connect and work together, the experience will be rich and data-driven.

33. What is network Bandwidth?
- Network bandwidth is the capacity of a wired or wireless network communications link to transmit the
maximum amount of data from one point to another over a computer network or internet connection in
a given amount of time – usually, one second.
- Amount of data that can be transmitted in a fixed amount of time. Measured in terms of number of bits
transmitted per second (bps). Less the bandwidth, slower the transmission. More the bandwidth faster
is the transmission.

34. Bandwidth vs. speed
The terms bandwidth and speed are often used interchangeably- but not correctly. Speed refers to the rate at
which data can be sent, while definition of bandwidth is the capacity for that speed.

35. What is latency?
Latency is the time it takes for data from your device to be uploaded and reach its target. It measures the time
it takes for data to go from source to destination in milliseconds (ms).

36. What is Multiplexing?
Multiplexing (Muxing) is the process of combining multiple signals into one signal over a shared medium. If
the analog signals are multiplexed, then it is called as analog multiplexing. Similarly, if the digital signals are
multiplexed, then it is called as digital multiplexing.

A common kind of multiplexing merges a number of low speed signals to send over a high-speed link. The
entire process is done using a multiplexer device. The main function of the device is to unite n-input lines for
generating a single output line. Thus, a multiplexer has multiple inputs and a single output.

37. What is Demultiplexing?
Demultiplexing (Demuxing) is a term relative to multiplexing. It is the reverse of the multiplexing
process. Demultiplexing is a process of reconverting a signal containing multiple analog or digital signal
streams back into the original separate and unrelated signals.

38. What are the types of multiplexing techniques?
The are 3 types of multiplexing techniques are: Frequency Division Multiplexing (FDM), Wavelength Division
Multiplexing (WDM) and Time Division Multiplexing (TDM).

39. What is FDM?
Frequency division multiplexing (FDM) is a scheme in which numerous signals are combined for transmission
on a single communications line or channel. Each signal is assigned a different frequency (sub channel) within
the main channel.

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40. What is TDM?
Time division multiplexing (TDM) is a method of putting multiple data streams in a single signal by separating
the signal into many segments, each having a very short duration. Each individual data stream is reassembled
at the receiving end based on the timing.

41. What is simplex transmission?
In simplex transmission mode, the communication between sender and receiver occurs in only one direction.
The sender can only send the data, and the receiver can only receive the data. The receiver cannot reply to
the sender
Simplex transmission can be thought of as a one-way road in which the traffic travels only in one direction- no
vehicle coming from the opposite direction is allowed to drive through.
To take a keyboard/monitor relationship as an example, the keyboard can only send the input to the monitor,
and the monitor can only receive the input and display it on the screen. The monitor cannot reply, or send any
feedback to the keyboard.

42. What is Full duplex transmission?
In full duplex transmission mode, the communication between sender and receiver can occur simultaneously.
The sender and receiver can both transmit and receive at the same time. Full duplex transmission mode is like
a two-way road, in which traffic can flow in both directions at the same time.
For example, in a telephone conversation, two people communicate, and both are free to speak and listen at
the same time.

43. What is Half duplex transmission?
The communication between sender and receiver occur in both directions in half duplex transmissions, but
only one at a time. The sender and receiver can both send and receive the information, but only one is allowed
to send at any given time. Half duplex is still considered a one-way road, in which a vehicle travelling in the
opposite direction of the traffic has to wait till the road is empty before it can pass through.
For example, in walkie-talkie, the speakers at both ends can speak, but they have to speak one by one. They
cannot speak simultaneously.

44. What is TDMA?
Time division multiple access (TDMA) is a digital cellular telephone communication technology. It facilitates
many users to share the same frequency without interference. Its technology divides a signal into different
timeslots, and increases the data carrying capacity.

45. What is FDMA?
Frequency division multiple access (FDMA) is the oldest of all multiple access schemes. In FDMA, the available
channel bandwidth is divided into may nonoverlapping frequency bands, where each band is dynamically
assigned to a specific user to transmit data. In an FDMA system, signals, while occupying their assigned
frequency bands, can be transmitted simultaneously and continuously without interfering with each other.

46. What is CDMA?
Code division multiple access (CDMA) is a sort of multiplexing that facilitates various signals to occupy a single
transmission channel. It optimizes the use of available bandwidth.
In this system, a user has access to the whole bandwidth for the entire duration. The basic principle is that
different CDMA codes are used to distinguish among the different users.

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47. What is OFDMA?
Orthogonal frequency division multiple access (OFDMA) is the multi-user variant of the OFDM scheme where
multiple access is achieved by assigning subsets of sub-carriers to different users, allowing simultaneous data
transmission from several users.

48. What is SC-FDMA?
Single Carrier FDMA is a FDMA scheme. It is also called as linearly precoded OFDMA (LP-OFDMA). Like other
above-mentioned multiple access schemes, it deals with assignment of multiple users to a shared
communication resource. SC -OFDMA is interpreted as a linearly precoded OFDMA scheme, in the sense that
it has an additional DFT processing step proceeding the conventional OFDMA processing.

49. What are the advantages of SC-FDMA over OFDMA?
- Low PAPR with performance close to OFDMA.
- Low sensitivity to carrier frequency offset.
- Less sensitive to non-linear distortion and hence, it allows the use of low-cost power amplifiers.
- Greater robustness against nulls.

50. What is TDD?
Time Division Duplexing (TDD) refers to duplex communication links where the uplink is separated from
downlink by allocation of different time slots in the same frequency band. It is a transmission scheme that
allows asymmetric flow for uplink (UL) and downlink (DL) data transmission. Any data transmitted can be 1
byte long, or a frame of multiple bytes.

Time slots can be dynamically allocated and variable based on the network needs. A guard period is needed
to ensure that UL and DL transmissions do not collide. Swapping capacities in UL and DL degrades the
performance of the network.

51. What is FDD?
Frequency Division Duplexing (FDD) is a technique where the transmission and reception (uplink and downlink)
takes place at different carrier frequencies. If the frequencies are adjacent, a guard band is used between
them to reduce interference. A large guard band does not impact capacity.

The frequency allocation for UL/DL capacity is predetermined based on the system needs so that it is same in
either direction. It is not possible to dynamically change the capacity. Continuous transmission and high
performance is guaranteed with FDD.

52. What is 1G?
1G is the first generation of mobile networks. Cell phones begin with 1G technology of wireless cellular
technology. 1G supports voice only calls.
1G was analog technology, and the phones using it had poor battery life and voice quality, little security, and
were prone to dropped calls.

53. What was the maximum speed achieved by 1G networks?
The maximum speed of 1G technology is 2.4Kbps.

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54. What is 2G?
2G is the second generation of mobile networks. Cell phones received their first major upgrade when their
technology went from 1G to 2G. The 2G telephone technology introduced call and text encryption, along with
data services such as SMS, picture messages and MMS.

55. What was the maximum speed achieved by 1G networks?
The maximum speed of 2G with General Packet Radio Service (GPRS) is 50Kbps. The data speed is 1Mbps with
Enhanced Data Rates for GSM Evolution (EDGE).

56. What is 2.5G and 2.75G?
Before taking a major leap from 2G to 3G wireless networks, the lesser known 2.5G and 2.75G were interim
standards that bridged the gap to make data transmission (Slow data transmission) possible.

2.5G introduced a new packet switching technique that was more efficient than 2G. This led to 2.75G, which
provided a theoretical threefold speed increase.
*2.5G and 2.75G were not defined formally as wireless standards. They served mostly as marketing tools to
promote new cell phone features to public.

57. What is EDGE?
EDGE is an acronym for Enhanced Data GSM Environment. It is an improved wireless technology over GSM
• EDGE is used for wireless data transfer via mobile phone connection
• Data transfer rates up to 4 times more than GSM networks
• With the advent of Blackberry and iPhone, faster data transfer is sought
• Using more sophisticated coding, usually without high end hardware, wireless carrier’s base stations are
supported for data transfer speeds up to 384 KBPS
• EDGE is an alternative to replacing wireless technology, such as GPRS
• EDGE is eventually be replaced by 3G technology such as WCDMA.

58. What is 3G?
3G is the third generation of mobile networks. The introduction of 3G networks in 1998 ushered in faster data
transmission speeds, so the users can use the cell phone in more demanding ways such as video calling and
instant mobile internet access.
The term “Mobile Broadband” was first applied to 3G mobile technology.

59. What Are 3G Standards?
UMTS: Universal Mobile Telecommunications System – One of the 3G mobile telecommunications
technologies, also being developed into a 4G technology.
• Most common form of UMTS uses W-CDMA as an underlying air interface.
• UMTS also covers Radio Access Network – UMTS Terrestrial Radio Access Network (UTRAN), and Mobile
Application Part (MAP).
• Users are authenticated via USIM cards (Universal Subscriber Identity Module).
CDMA2000: Also known as IMT Multi-Carrier (IMT-MC), uses CDMA channel access for sending voice, data
and signaling data between mobile phones and cell sites.
The standards are CDMA2000 IX, CDMA2000 EV-DOR Rev.0, CDMA2000 EV-DO Rev.A and CDMA2000 EV-
Rev.B. They are approved radio interfaces for the ITU’s IMT-2000.

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60. What was the maximum speed achieved by 3G networks?
The maximum speed of 3G is around 3Mbps for non-moving devices, 384Kbps in moving devices and 125Kbps
in fast moving devices.

61. What is 4G?
4G is the fourth generation of mobile networks. 4G supports mobile web access like 3G does and also gaming
services, HD mobile TV, Video conferencing, 3D TV and other features that demand high speeds.

62. What was the maximum speed achieved by 4G networks?
The maximum speed of a 4G network when the device is moving is 100Mbps. The speed is 1Gbps for low-
mobility communication.

63. What is the average latency in 4G networks?
Around 50 milliseconds.

64. What is 5G?
5G is the next generation of mobile networking technology following 4G. 5G promises faster data rates, higher
connection density, much lower latency, high reliability, energy savings and many more improvements.

65. What is the maximum expected speed of 5G?
Theoretical speeds: 10 to 50Gbps

66. What is the expected latency in 5G networks?
Theoretically less than 1 millisecond.

67. Why 5G?
Unlike in the past, when mobile networks only needed to support cell phones that were just for browsing the
web and text messaging, we now have all sorts of bandwidth demanding devices like our HD streaming
smartphones, smartwatches with data plans, always-on security cameras, self-driving and internet connected
cars, and other promising devices like health sensors and untethered AR and VR hardware.
As billions more devices connect to the web, the entire infrastructure needs to accommodate the traffic to
not only support faster connections but also better handle simultaneous ones and provide broader coverage
for these devices. This is what 5G is all about.

68. How 5G benefits you?
- Minimal lag when streaming videos and playing games
- Safer cities with smart, interconnected vehicles
- Near-instant access to most files online
- Smaller devices that offload hardware requirements to remote servers
- Explosion of new products and applications that require ultrafast speeds
- Reliable internet in remote areas

69. What are the 5 functional key drivers of 5G Wireless Networks?
The 5 Key functional drivers of 5G Wireless Networks are: eMBB, URLLC, mMTC, Security and Power efficiency.

➢ eMBB (Enhanced Mobile Broadband)

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• Description – Faster Connections, Higher throughput and greater capacity (Upto 10Gbps).
• Added value – Allows for an extension in cellular coverage into diverse structures (Large venues,
buildings etc) and the ability to handle a large number of devices using high amounts of data.
➢ URLLC (Ultra Reliable Low Latency Communication)
• Description – Reduced time for data to be uploaded on a device and reach its target (extended to
be <1ms in 5G compared to 10ms in 4G/LTE).
• Added value – Enables time sensitive Wireless connectivity.
➢ mMTC (Massive Machine Type Communication)
• Description – Increased spectral efficiency + Small cell deployment.
• Added value – Allows for a large number of connections to support data-intensive applications.
➢ Security
• Description – Robust security properties leading to high reliability and availability.
• Added value – Creates an ultra-reliable connection to support applications where failure is not an
option.
➢ Power Efficiency
• Description – Efficient Power requirements for Massive MIMO, Small cell Implementation.
• Added value – Leads to lower costs and enables massive internet of things.

70. What can 5G do that 4G can’t do?
5G still lets you send text messages, make phone calls, browse the internet, and stream videos. In fact, nothing
you currently do on your phone, in regards to the internet, is taken away when you’re on 5G they’re just
improved.

Websites load faster, online multiplayer games don’t lag as much, there’s smooth and realistic video when
using skype or facetime etc. 5G is so fast that everything you do on the internet now that seems relatively
quick might even appear to be instant. If you end up using 5G at home to replace your cable, you’ll find that
you can connect more of your devices to the internet at the same time without bandwidth issues. Some home
internet connections are so slow that they simply don’t support all the new interconnected tech coming out
these days.

5G at home lets you connect your smartphone, wireless thermostat, videogame console, smart locks, virtual
reality headset, wireless security cameras, tablet, and laptop all to the same router without worrying that
they’ll stop working when they’re all on at the same time.

When 4G fails at providing all the data needs to a growing number of mobile devices, 5G opens the airways
for more internet-enabled tech like smart traffic lights, wireless sensors, mobile wearables, and car-to-car
communication.

Vehicles that receive GPS data and other instructions that help them navigate the road, like software updates
or traffic alerts and other real-time data, require fast internet to always be on top – it isn’t realistic to think
that all of this could be supported by 4G networks.

Since 5G can carry data so much quicker than 4G networks, it isn’t out of the realm of possibility to expect to
see more raw, uncompressed data transfers. What this will do is ultimately allow foe even quicker access to
information since it won’t need to be uncompressed before being used.

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71. What is another name for 5G?
IMT 2020 is the official name for 5G as decided by International Telecommunication Union (ITU). IMT stands
for ‘International Mobile Telecommunications’ and 2020 refers to the roadmap that’s also been agreed by the
union, as it aims for the 5G standard to be finished by 5G.

72. What is NR?
New Radio as defined by 3GPP Release 15. This is a best suited marketing name for 5G.

73. What is LTE?
Long Term Evolution (LTE) is a 4G communication standard that sets the ground work of 5G technology. The
LTE Network offered increased data transfer speeds upto 10 times faster than 3G networks. LTE Supports
various types of traffic including voice, video and messaging.

74. What is LTE-Advanced?
LTE Advanced is a mobile communication standard that introduced new functionalities such as carrier
aggregation, enhanced multi antenna techniques and support for relay nodes.
LTE Advanced completely fulfils the requirement set for IMT Advanced, also referred to as 4G.
• Increased peak data rate – Downlink 3Gbps and Uplink 1.5Gbps.
• Higher Spectral efficiency 30bps/Hz
• Increased number of simultaneously active subscribers.
• Improved performance at cell edges.

75. What is 3GPP?
The 3
rd
generation partnership project (3GPP) is the collaboration between different groups that work on
setting telecom standards internationally. 3GPP was established in 1998 with the goal of setting the standard
of 3G. Since its establishment, it has evolved to encompass 4G and is now working on defining 5G Standards.

76. What is ITU?
The International Telecommunication Union (ITU), originally the international telegraph union, is a specialized
agency of the United States that is responsible for issues that concern information and communication
technologies. ITU coordinates telecom operations and services throughout the world. It is responsible for
allocation of global radio spectrum and satellite orbits, and development of technical standards that ensure
the interconnectivity of networks and enable telecom services to be provided on a worldwide scale.

77. What are the 3 sectors of ITU that cover specific areas of ICT activity?
The 3 sectors of ITU that cover specific areas of ICT activity are –
• Radio Communication (ITU-R)
• Telecommunication Standards (ITU-T) and
• Telecommunication Development (ITU-D).

78. What is FCC?
Federal Communications Council (FCC) is an independent federal regulatory agency of the United States
government that regulates interstate and international communications by radio, television, wire, satellite
and cable. FCC maintains the jurisdiction over the areas of broadband access, fair competition, radio frequency
use, media responsibility, public safety and homeland security.

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79. What is mmWave Spectrum?
The mmWave Spectrum corresponds to band of frequencies between 30GHz to 300GHz, and sometimes it is
also known as Extremely High Frequency (EHF).
Wedged between the super high frequency band and the far infrared band, it is the subset of microwave
radio frequencies.
The high frequency of millimeter waves as well as their propagation characteristics make them useful for
variety of applications which includes transmitting large amounts of data. Thus, this spectrum is currently
used for high speed wireless communications as seen in IEEE 802.11ad Wi-Gig Standard (operating at
60GHz).

80. Why the name millimeter waves?
As we know, wavelength (??????) can be calculated using the frequency (f) and speed of light in vacuum (c).
??????=
??????
??????

When,
f=30GHz, Wavelength will be approximately 10mm since the speed of light is 3.8×10
8
m/sec.
f=300GHz, Wavelength will be approximately 1mm since the speed of light is 3.8×10
8
m/sec.

As shown above, high frequencies mean narrow wavelengths. The wavelength of mmwaves range between 1
millimeter to 10 millimetres whereas the wavelengths of radio waves currently used are mostly several dozen
centimeters in length. Hence the name ‘millimetre Waves’.

81. What are the advantages of using mmwaves in 5G?
The advantages of using millimeter waves in 5G are:
• Large Bandwidth
- The large bandwidth available in mmwaves translate to better data transfer rates, attaining speeds
of about 10Gbps or more compared to the 1Gbit/s limit when using the microwave frequencies. This makes
high-quality video streaming, real-time gaming, and other bandwidth intensive applications a reality.

• Higher resolution
- The narrow beam width allows the ability of mmwaves to achieve greater resolutions. For Same
antenna size, when frequency increases, the beam width decreases.
• Low interference (High immunity to cramming)
- The narrow beam width and short range can be a benefit since there is less interference from nearby
radios.
• Small components sizes
- The components and antennas for the higher millimeter waves are usually very small compared to
those for lower frequencies. This makes it possible to design physically smaller circuitry and equipment.
Higher the frequency, Smaller is the antenna size (Large no. of antennas can be packed in small area).
• Increased security
- In addition, it is much harder to intercept the signals and there is also increased security since the
signal is only restricted to a small area.
• Cost efficiency

82. What are the disadvantages of using mmwaves?
The disadvantages of using mmwaves are:

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• High manufacturing costs
- Manufacturing the small components require high precision and care, hence increased costs.
• Limited range.
- Due to the short wavelength, mmwaves have a short transmission range of about 10 meters for
most low power applications. However, the range is extended by using high transmit power and antenna
gains, and receivers with high sensitivity.
• Requires Line of Sight (LOS)
- Physical objects such as trees, buildings, even humans will block the waves, leading to weak wave
signals and a reduced range.
• Vulnerability to atmosphere and meteorological conditions
- The short wavelengths between 1 to 10mm suffer high atmospheric attenuation; with fog, rain and
moisture attenuating the waves the highest, and shortening the transmission distances. All these factors
reduce the possible range to about one kilometre. Use of high-gain antenna arrays can boost the
effective radiated power and increase the transmission range.
• Over sensitivity of mmwaves can be a problem at certain instances, leading to false alarm even when
there was no real threat.
• In some instances, the mmwaves receiving system may be less sensitive due to less energy collected by
smaller size antennas.

83. What is SISO?
SISO is an antenna configuration which means single input and single output. With one antenna on either side,
SISO provides no diversity protection against fading.
The use of multiple antennas on the transmitter side, the receiver side, or both, can improve reliability,
capacity, or both.

84. What is SIMO?
SIMO is an antenna configuration which means single input and multiple output. This configuration creates
receiver diversity, uses smart antennas to implement beamforming, and provides an improved SINR (signal-
to-interference-plus-noise ratio).

85. What is MISO?
MISO is an antenna configuration which means multiple input and single output. This configuration creates
transmitter diversity, uses smart antennas to implement beamforming, and improves SINR.

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86. What is MIMO?
MIMO is an antenna configuration which means multiple input and multiple output. This configuration
creates both transmitter & receiver diversity, uses smart antennas to implement beamforming on both
sides, improves SINR, and provides greater spectral efficiency.

87. What is single user MIMO?
In single-user MIMO, the transmitter multiplexes the data for one user across two or more independent radios
and antennas. Each receive antenna will see a combination of the signals from all of the transmit antennas.

Part of the transmitted data will be a known sequence of pilot signals or a preamble. The receiver will
use the known data to calculate the channel matrix, H, and once that matrix is known, the receiver can then
use it to decode the unknown data transmission.

The transmitter does not need to have any knowledge about the channel. All of the required extra
computation is done in the receiver—and putting this heavy computational burden on battery-powered user
equipment (UE) is not ideal.

In the example case shown in figure, the receiver de-multiplexes the two data streams based on knowledge
of the channel [H].

We can use matrix math to express the direct and cross interactions within this system:

From this,

Single-user MIMO requires a multipath environment to allow the receiver to correctly generate the H matrix,
which is needed to decode the received signals.

88. What is multi user MIMO?
Multi-user MIMO has several differences from single-user MIMO. It uses multiple antennas on a single
transmitter and there can be several independent receivers, each with one antenna. Another difference: the
transmitter pre-codes the data, shown as the W matrix in the figure.

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We can use matrix math to express the direct and cross interactions within this system on the transmitter and
receiver sides:

As shown in the matrix, the signal transmitted on each antenna, x0 and x1, is a combination of the symbols
for each user, s0 and s1. On the receiver side, the basic process proceeds as follows:
– For user 0, the components of s0 from all antennas arrive in phase, and thus add. The components of s1
arrive out of phase and thus cancel, leaving only s0 at the first receiver.
– For user 1, the s0 signals cancel and the s1 signals add, leaving only s1 at the second user’s input.
In single-user MIMO, the knowledge of the channel is in the receiver; in multi-user MIMO the knowledge of
the channel is in the transmitter. Because all of the power-consuming calculations are performed in the
transmitter, this approach is more attractive for any system in which the receivers are battery-powered.

89. What is Massive MIMO?
Massive MIMO is a useful and scalable version of Multiuser MIMO. There are three fundamental distinctions
between Massive MIMO and conventional Multiuser MIMO.
• First, only the base station learns G (The Channel Matrix).
• Second, M (No. of antennas) is typically larger than K (No. of users).
• Third, Simple linear signal processing is used both on the uplink and the downlink.
All these feature render Massive MIMO scalable with respect to the base station antennas (M).

Massive MIMO is a multi-user MIMO system with M antennas and K users per Base station. The system is
characterized by M>>K and operates in TDD mode using linear uplink and downlink processing.

A more precise definition can be written as such:
“Massive MIMO is a multi-user MIMO system that serves multiple users through spatial multiplexing over a
channel with favourable propagation (when users being mutually orthogonal) in time-division duplex, and
relies on channel reciprocity & uplink pilots to obtain channel state information.”

90. What are the most popular 5G frequency bands?
700MHz, 3.5GHz and 28GHz.

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91. What is range of 3GPP defined FR1 and FR2 for 5GNR?
FR1 – 410MHz to 7.125GHz and FR2 – 24.25GHz to 52.6GHz

92. What is a base station?
A base station is a wireless transceiver at a fixed location, which is part of a wireless communications network.

93. Why small cells are required in 5G?
This is because 5G will use higher frequencies, which don’t travel as far and don’t travel as well through
obstacles, such as buildings so prevalent in concrete jungles (cities). This means Mobile Network Operators
must install 5G radios, and a lot of them, closer to end users. Small cells won’t be required day one, as they
can be installed over time. But there’s no getting around the fact that rolling out 5G to large geographic areas
will require a tremendous number of new small cells.

94. What is the difference between NodeB and eNodeB?
Node B is the radio base station for UMTS (Universal Mobile Telecommunications System) networks,
while eNodeB is the radio base station for LTE (Long Term Evolution) networks. These nodes are installed at
the cell sites of mobile operators and can be seen as tall masts also known as cellular towers.

95. What is gNB?
gNB - Next Generation Node B. The gNB is a 3GPP 5G Next Generation base station which supports
the 5G New Radio. The equivalent of which was called NodeB in 3G-UMTS and eNodeB or eNB in 4G LTE.

96. What is C-band?
ITU-R defines C-band as 3.4 - 4.2, 4.5 - 4.8, 5.85 - 7.075GHz. For 5G, the C band is generally referred to as 3.4
to 4.2GHz.

97. What is Network Slicing?
5G network slicing is a network architecture that enables the multiplexing of virtualized and independent
logical networks on the same physical network infrastructure. Each network slice is an isolated end-to-end
network tailored to fulfil diverse requirements requested by a particular application.

98. What are the multiple access techniques does LTE system use in DL and UL?
LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) in Downlink and Single Carrier-Frequency
Division Multiple Access (SC-FDMA) in Uplink.

99. What is Beamforming?
Beamforming is a technique by which an array of antennas can be steered to transmit radio signals in a specific
direction. Rather than simply broadcasting energy/signals in all directions, the antenna arrays that use
beamforming, determine the direction of interest and send/receive a stronger beam of signals in that specific
direction.

100 . What is DSS?
Dynamic Spectrum Sharing (DSS) is a technology that allows the deployment of both 4G LTE and 5G NR in the
same frequency band and dynamically allocates spectrum resources between the two technologies based on
user demand.
500+ more related technical questions will be available in my upcoming eBook.