Here is the solution to the Advance Wireless Communication exam solution of the Islamic University of Bangladesh.

2. 1Q. What is Wireless communication?
2Q. Write the features of Wireless Communication.
Wireless communications is a type of data communication that is performed and delivered
wirelessly. This is a broad term that incorporates all procedures and forms of connecting and
communicating between two or more devices using a wireless signal through wireless
communication technologies and devices.
The features of Wireless Communication: The evolution of wireless technology has brought
much advancement with its effective features.
• The transmitted distance can be anywhere between a few meters (for example, a television's
remote control) and thousands of kilometers (for example, radio communication).
• Wireless communication can be used for cellular telephony, wireless access to the internet,
wireless home networking, and so on.
• Other examples of applications of radio wireless technology include GPS units, garage door
openers, wireless computer mice, keyboards and headsets, headphones, radio receivers,
satellite television, broadcast television and cordless telephones.
Wireless Advantages: Cost effectiveness, Flexibility, Convenience, Speed, Accessibility, Constant
connectivity.

3. 3Q. What is flat fading and frequency selective fading?
4Q. Write the difference between coherence time and coherence bandwidth?
Flat fading: In flat fading, the coherence bandwidth of the channel is larger than
the bandwidth of the signal. Therefore, all frequency components of the signal will
experience the same magnitude of fading. In frequency-selective fading, the
coherence bandwidth of the channel is smaller than the bandwidth of the signal.
Frequency selective fading: Selective fading or frequency selective fading is a
radio propagation anomaly caused by partial cancellation of a radio signal by itself
— the signal arrives at the receiver by two different paths, and at least one of the
paths is changing (lengthening or shortening).
The difference between coherence time and coherence bandwidth: Coherence
time is the time duration over which the channel impulse response is considered to
be not varying. Such channel variation is much more significant in wireless
communications systems, due to Doppler effects.
Coherence bandwidth is a statistical measurement of the range of frequencies over
which the channel can be considered "flat", or in other words the approximate
maximum bandwidth or frequency interval over which two frequencies of a signal
are likely to experience comparable or correlated amplitude fading.

4. 5Q. What are the factors influencing small scale fading?

5. 6Q. What is large scale fading in wireless communication?
8Q. What is meant by inter symbol interference?
Large Scale Fading: Large Scale Fading occurs when an obstacle gets positioned
between the wireless device and the signal transmitter. This interference causes
significant reduction in signal strength because the wave is shadowed or blocked by
the obstacle. It is the result of signal attenuation due to signal propagation over
large distances and diffraction around large objects in the propagation path.
Intersymbol interference: In telecommunication, intersymbol
interference (ISI) is a form of distortion of a signal in which one symbol
interferes with subsequent symbols. This is an unwanted phenomenon
as the previous symbols have similar effect as noise, thus making the
communication less reliable.

6. 7Q. Describe the single-carrier baseband communicate on system model.
It conveys two analog message signals, or two digital bit streams, by
changing (modulating) the amplitudes of two carrier waves, using the
amplitude-shift keying (ASK) digital modulation scheme or amplitude
modulation (AM) analog modulation scheme.

7. 9Q. What do you mean by Nyquist criterion for zero ISI?
11Q. Show the basic structure of multicarrier system.
In communications, the Nyquist ISI criterion describes the conditions which, when satisfied by a
communication channel, result in no intersymbol interference or ISI. It provides a method for
constructing band-limited functions to overcome the effects of intersymbol interference. Nyquist
Criterion for Zero-ISI. A pulse that satisfies the above condition at multiples of the bit period Tb will
result in zero– ISI if the whole spectrum of that signal is received. The square pulse required a lot of
bandwidth to be transmitted.
The basic structure of multicarrier system:

8. 10Q. What is the limitation of Single-Carrier Transmission for High Data Rate?
• High data rate is desired in many data communications. However, as the symbol
duration reduces with the increase of data rate, the systems using single-carrier
modulation suffer from more severe ISI caused by the dispersive fading of
wireless channels, thereby needing more complex equalization. In order to
support the symbol rate of Rs symbols per second, the minimum required
bandwidth is the Nyquist bandwidth, which is given by Rs=2½Hz. It implies that
wider bandwidth is required to support a higher data rate in a single-carrier
transmission. So far, it has been assumed that the channel is perfectly
compensated by the equalizer. However, as the symbol rate increases, the signal
bandwidth becomes larger. When the signal bandwidth becomes larger than the
coherence bandwidth in the wireless channel, the link suffers from multi-path
fading, incurring the inter-symbol interference (ISI). In general, adaptive
equalizers are employed to deal with the ISI incurred by the time-varying multi-
path fading channel. Furthermore, the complexity of an equalizer increases with
the data rate. More specifically, adaptive equalizers are implemented by finite
impulse response (FIR) filters with the adaptive tap coefficients that are adjusted
so as to minimize the effect of ISI. In fact, more equalizer taps are required as the
ISI becomes significant, for example, when the data rate increases.

9. 12Q. Write the comparison between the single-carrier and
multi-carrier transmission schemes.

10. 13Q. What is OFDM?
14Q. What is OFDM and how it works?
OFDM: Orthogonal frequency-division multiplexing (OFDM) is a method of digital
signal modulation in which a single data stream is split across several separate
narrowband channels at different frequencies to reduce interference and crosstalk.
In telecommunications, orthogonal frequency-division multiplexing is a type of
digital modulation, a method of encoding digital data on multiple carrier
frequencies.
OFDM working procedure: Orthogonal Frequency Division Multiplexing (OFDM) is
a technique for transmitting large amounts of digital data over a radio wave the
technology works by splitting the radio signal into multiple smaller sub-signals that
are then transmitted simultaneously at different frequencies to the receiver. The
OFDM concept is based on spreading the high speed data to be transmitted over a
large number of low rate carriers. The carriers are orthogonal to each other and
frequency spacing between them are created by using the fast Fourier transform
(FFT).

11. 15Q. What is the purpose of the guard interval in OFDM?
16Q. What is cyclic prefix in OFDM?
• These transmissions may belong to different users (as in TDMA) or to the same
user (as in OFDM). The purpose of the guard interval is to introduce immunity to
propagation delays, echoes and reflections, to which digital data is normally very
sensitive. In telecommunications, guard intervals are used to ensure that distinct
transmissions do not interfere with one another, or otherwise cause overlapping
transmissions. These transmissions may belong to different users (as in TDMA) or
to the same user (as in OFDM). The purpose of the guard interval is to introduce
immunity to propagation delays, echoes and reflections, to which digital data is
normally very sensitive.
• Cyclic prefix in OFDM: The cyclic prefix used in Frequency Division Multiplexing
schemes including OFDM to primarily act as a guard band between successive
symbols to overcome intersymbol interference, ISI. Use of cyclic prefix is a key
element of enabling the OFDM signal to operate reliably. In telecommunications,
the term cyclic prefix refers to the prefixing of a symbol, with a repetition of the
end.

12. 17Q. Why cyclic prefix is added in OFDM?
18Q. What is the use of zero padding?
• Cyclic prefix is added in OFDM: OFDM Orthogonal Frequency Division
Multiplexing Includes: Use of cyclic prefix is a key element of enabling the
OFDM signal to operate reliably. The cyclic prefix acts as a buffer region or
guard interval to protect the OFDM signals from intersymbol interference.
The cyclic prefix used in Frequency Division Multiplexing schemes including
OFDM to primarily act as a guard band between successive symbols to
overcome intersymbol interference, ISI. Use of cyclic prefix is a key element
of enabling the OFDM signal to operate reliably.
• Use of zero padding: Zero padding in the time domain is used extensively
in practice to compute heavily interpolated spectra by taking the DFT of the
zero-padded signal. Such spectral interpolation is ideal when the original
signal is time limited (nonzero only over some finite duration spanned by
the orignal samples). Zero-padding a signal increases its period. This
decreases the spacing(the inverse of the fundamental period) between the
DFS(Discrete Fourier Series)

13. 19Q. What is BER performance?
21Q. What is MIMO Systems?
BER performance: The bit error ratio (also BER) is the number of bit errors divided
by the total number of transferred bits during a studied time interval. Bit error ratio
is a unit less performance measure, often expressed as a percentage. This estimate
is accurate for a long time interval and a high number of bit errors. The bit error
ratio (also BER) is the number of bit errors divided by the total number of
transferred bits during a studied time interval. Bit error ratio is a unitless
performance measure, often expressed as a percentage. The bit error probability
pe is the expectation value of the bit error ratio.
MIMO Systems: MIMO (multiple input, multiple output) is an antenna technology
for wireless communications in which multiple antennas are used at both the
source (transmitter) and the destination (receiver). The antennas at each end of
the communications circuit are combined to minimize errors and optimize data
speed. In radio, multiple-input and multiple-output, or MIMO, is a method for
multiplying the capacity of a radio link using multiple transmission and receiving
antennas to exploit multipath propagation. MIMO technology can be used in non-
wireless communications systems.

14. 20Q. How the BER is calculated in OFDM Scheme?
As the name implies, a bit error rate is defined as the rate at which errors occur in a
transmission system. This can be directly translated into the number of errors that
occur in a string of a stated number of bits. The definition of bit error rate can be
translated into a simple formula:
Signal to noise ratios and Eb/No figures are parameters that are more associated with
radio links and radio communications systems. In terms of this, the bit error rate, BER,
can also be defined in terms of the probability of error or POE. The determine this,
three other variables are used. They are the error function, erf, the energy in one bit,
Eb, and the noise power spectral density, No. It is possible to define the bit error rate
in terms of a probability of error-
Where,
• erf = error function
• Eb = energy in one bit
• No = power spectral density (noise in 1Hz bandwidth).
It is important to note that Eb / No is a form of signal to noise ratio.

15. 22Q. What are the two basic types of MIMO technology?
MIMO or Multiple Input Multiple Output is a wireless technology that helps in
transmitting wireless signals over multiple antennas. MIMO is generally used to
improve the Wireless Range, Bandwidth, Interference and ECHO handling features
of the new generation of wireless routers. Generally, there are three different types
of MIMO techniques:
• The first type is to maximize spatial diversity by improving transmitting power and
efficiency.
• The second type includes spatial multiplexing where multiple independent data
signals are transmitted over antennas to increase data transfer rate.
• The third type uses channel knowledge at the transmitter to obtain capacity
gains.

16. 23Q. Write the some Benefits of Beamforming.
Beamforming controls the directionality of the transmission or reception of a signal on an antenna
array. Beamforming improves the spectral efficiency by providing a better signal-to-noise ratio
(SNR). Working with other antenna technologies such as smart antennas and MIMO, beamforming
boosts cell range and capacity.

17. 24Q. Draw the block diagram of MIMO Transmitter and MIMO Receiver.

18. 25Q. Compare FDMA, TDMA & CDMA?

19. 26Q. Calculate channel capacity of TDMA in cell system.

20. 27Q. Write the comparison of 1G to 5G Technologies.

21. 28Q. What is difference between 5G and 6G?
• In simple words, 6G is widely believed to be smarter, faster and more
efficient than 5G. It promises mobile data speeds 100 times faster
than 5G network currently available in limited countries. With speeds
of up to 100 times of 100 gigabits per second, 6G is set to be as much
as 100 times faster than 5G.
• 5G is the fifth generation wireless technology for digital cellular
networks that began wide deployment in 2019. The frequency
spectrum of 5G is divided into millimeter waves, mid-band and low-
band. Low-band uses a similar frequency range as the predecessor,
4G.
• A few of the key motivating trends behind the evolution of 6G
communication systems are as follows: high bit rate, high reliability,
low latency, high energy efficiency, high spectral efficiency, new
spectrums, green communication, intelligent networks, network
availability, and convergence of communications.

22. 29Q. How fast will 6G be?
• How 6G will be faster than 5G?
Ultra high frequency bands, such as mmWave band, terahertz band, and
even visible-light frequency of the radio spectrum.
The higher you go up the radio spectrum, the more data you can carry.
Reach extremely high frequency levels of 300 GHz, or even terahertz
ranges
• 6G will improve weaknesses and limitations of 5G.
6G will be transformative with more requirements specified as follows:
Very high data rates, up to 1 Tb/s;
Very high energy efficiency, with the ability to support battery-free IoT
devices;
Massive low-latency control (less than 1 msec);
Very broad frequency bands (e.g., 73GHz-140GHz and 1THz-3THz);
Broadband global network coverage by integrating terrestrial wireless with
satellite systems;
Connected intelligence with machine learning capability.