Wireless Communication MCQ || Wireless Communication Questions and Answers

Answer.4. Erlang

Explanation

Traffic intensity is a measure of the average occupancy of a server or resource during a specified period, normally a busy hour. It is measured in traffic units (erlangs) and defined as the ratio of the time during which a facility is cumulatively occupied to the time this facility is available for occupancy

Answer.4. All of the mentioned

Explanation

Wireless communications have enabled the connection of billions of people to the Internet so that they can reap the benefits of today’s digital economy.

It also enables economies of scale by reducing the cost of network equipment and user devices enabling affordable services.

It also allows for economies of scale by lowering the cost of network infrastructure and user devices, making services more inexpensive.

Answer.4. Multiple access technique

Explanation

Multiple access is a technique that lets multiple mobile users share the allotted spectrum in the most effective manner. Since the spectrum is limited, sharing is necessary to improve the overall capacity over a geographical area.

The type of multiple access technique used is an important factor in determining the spectral efficiency of the system. It strongly influences the choice of speech codec.

There are four main multiple access schemes that are used in cellular systems ranging from the very first analog cellular technologies to those cellular technologies that are being developed for use in the future. The multiple access schemes are known as FDMA, TDMA, CDMA, and OFDMA.

Answer.3. Shadowing

Explanation

Shadowing is a type of large-scale fading in wireless communication.

• Shadowing is caused by obstacles between the transmitter and receiver that attenuate signal power through absorption, reflection, scattering, and diffraction. When the attenuation is strong, the signal is blocked.
• Received power variation due to path loss occurs over long distances (100–1000 m), whereas variation due to shadowing occurs over distances that are proportional to the length of the obstructing object (10–100 m in outdoor environments and less in indoor environments).
• Since variations in received power due to path loss and shadowing occur over relatively large distances, these variations are sometimes referred to as large-scale propagation effects.
• Large scale fading or shadowing is fading that occurs on several meters or more; it reflects conditions that may vary as one turns a corner, moves behind a large building, or enters a building.

Answer.4. 100

Explanation

Assume the system is interference limited. i.e,

$\frac{{{E_b}}}{{{N_0} + {I_0}}} \approx \frac{{{E_b}}}{{{I_0}}}$

The number of users per cell is:

M ≈ G_p(d – E_b/I₀(d

$\frac{{{E_b}}}{{{I_O}}} = \frac{{{G_p}}}{{M – 1}}$

Processing gain is defined as:

G_P = R_dh/R

R_ch: Chip rate

R: Data rate

Calculation:

The given chip rate is 1 Mbps and the data rate is 1 Kbps.

The processing gain will be 1000.

A maximum number of users is:

M – 1 = 100

M ≈ 100

Answer.1. Real-Time Text Messaging

Explanation

RTT stands for Real-Time Text Messaging.

It is a technology that allows text to be sent immediately as it is created through wireless handsets that use IP-based technology on networks that support RTT. With RTT, there is no need to press a “send” key as there generally is for SMS, chat, or other types of texting.

A recipient can read a message while the sender types it. Instant text transmissions are similar to the instantaneous exchange of information in voice conversations over the phone and can be critical for emergency calls to 911.

Answer.3. SM

Explanation

Spatial multiplexing in wireless communications is based on multi-input and multiple-output (MIMO) technology where multiple antennas at both the transmitter and receiver are used to carry multiple data streams simultaneously within the same frequency band.

Spatial multiplexing takes advantage of the differences in the channels between transmitting and receiving antenna pairs to provide multiple independent streams between the transmitting and receiving antennas, increasing throughput by sending data over parallel streams.

Answer.3. Discrete cosine transform

Explanation

Discrete Cosine Transform is a technique applied to image pixels in the spatial domain in order to transform them into a frequency domain in which redundancy can be identified. DCT (discrete cosine transform) is one of the most attractive and frequently used transforms for speech coding. Fast algorithms developed for computing the DCT in a computationally efficient manner are used.

Answer.4. 165

Explanation

Minimum sampling rate to avoid aliasing f_s = 2f_m= (Nyquist rate)

ω_m = max {100π, 200π, 300π} = 300π

f_m = 150 Hz = maximum frequency of signal

Sampling frequency or Nyquist rate; f_s = 2 × 150 = 300 Hz

Answer.2. Number of times a cluster is replicated

Explanation

To understand the frequency reuse concept, consider a cellular system that has a total of S duplex channels available for use.

If each cell is allocated a group of k channels (k < S), and if the S channels are divided among N cells into unique and disjoint channel groups which each have the same number of channels, the total number of available radio channels can be expressed as

S = kN

The N cells which collectively use the complete set of available frequencies is called a cluster.

If a cluster is replicated M times within the system, the total number of duplex channels, C, can be used as a measure of capacity and is given by

C = MkN = MS

If the cluster size N is reduced while the cell size is kept constant, more clusters are required to cover a given area, and hence more capacity is achieved.

Conclusion:

The capacity of a cellular system is directly proportional to the number of times a cluster is replicated in a fixed area.