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Wireless Communication Interview Questions | Page 3



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Wireless Communication

Not Example of wireless media

A. Wired communication. Co-axial cable (bandwidth is around 200MHz) is a famous example of a wired communication medium. Fiber optics can also be an excellent example of a non-wireless communication medium. Other examples are twisted pair cables (bandwidth is around 600MHz), etc. 


Who created the first wireless communication device? What is it named?

A. Jagadish Chandra Bose first studied millimeter-length electromagnetic waves in the 1890s. The earliest work on millimeter wave frequency band may also be dated back to the 1890s by, e.g., Bose and Lebedev.  


What is the battery capacity of drumroar magnetic wireless earphones?

A. The battery rating of a typical magnetic wireless earphone is 65 mAh.


Which device is used in towers to provide wireless signals to our home routers?

A. At the base station, it sends or receives data streams from different users using antennas. On the other hand, there may be sensing devices. There may be a lot of complex circuitries to allocate bandwidth to individual users, etc. A typical large base station transmits a power of 40 watts.


Q. Explain briefly the services provided by the 802.11 protocol in wireless communication 

A. IEEE 802.11 protocol was developed by IEEE for LAN Technologies. 


Q. Which wireless technology can provide a metropolitan area with up to 100 Mbps bandwidth?

A. WLAN


Q. Steps to connect devices in wireless media

A. If you want to connect PDAs, like mobile laptops, to the cell tower, you need a modem. 'modem' is an abbreviation of 'modulator-demodulator.' If we want to connect our PDAs to WLAN, then we need a router at our home to connect to the core network. 

 

Q. What is an even channel in communication?


Q. What is the use of process ID during communicating over the Internet?

A. See answer


Q. Why do e companies spend a lot on secure data transmission?


Antenna and wave propagation interview questions and MIMO system

What are dB and dBm?

A. dB is an abbreviation of decibel. In dB calculation, the ratio of noise power to signal power is logarithmic scale because logarithmic is more convenient in this context.

dB = log[10](signal power / noise power)

log[10] indicates log with base 10

dBm = log[10] (signal power / 1 milliwatt noise power)

By calculation 1 dB = 30 dBm

Use dB to dBm calculator and vice versa


What do you know about a MIMO system's spatial multiplexing (SM), rank, and condition number?

A. Want to know about the Rank and Condition Number of the Channel Matrix? [click here]


Let's assume there are 1 transmitter antenna and 2 receiver antenna. How do you communicate with 2 receiver antennas simultaneously from the transmitter antenna?


What is spatial division multiplexing or SDM?


How many simultaneous data streams are possible between 2 X 2 MIMO antennas?

A. 2


How many individual antennas are required for the Alamouti scheme?

A, Two transmitter antennas and a receiver antenna. (2 X 1 MIMO). read more about alamouti scheme


MIMO technology is used in wireless systems to archive

A. MIMO technology in wireless communication increases capacity by sending data from multiple antennas and receiving it from multiple receivers. In MIMO, we can send multiple parallel data streams by spatial multiplexing through a single channel.


What is the optimum isolation in the MIMO antenna system?

A. Antenna isolation is a process to keep interference between antennas medium or reduced to an acceptable level. Usually, measurement of power transfer from one ant nana to another. It is measured in decibels (dB). Isolation should be as large as possible to reduce interferences. The popular methods to reduce interference are the physical separation of the antenna, polarization, optimization of antenna patterns, filtering, etc.    


How many types of MIMO CSI transmission are categories available based on the amount of CSI?

A. There may be two cases. The transmitter may be aware of CSI. In another case, the transmitter may need to be mindful of CSI. In the first case, we can apply SVD to the channel matrix and benefit from spatial multiplexing of MIMO. In the second scenario, channel estimate via pilot signal retrieval may be helpful.


What is the electric power consumption of a massive MIMO antenna?

The 64T 64R or 64 X 64 massive MIMO antennas consume about 1,500 watts maximum.


What is an outage in a wireless communication system?  

A. As per Shannon's law, every communication channel can transfer data from transmitter to receiver. For Example, we assume the capacity of a wireless system is C bits/s/Hz. Again, we are sending a data rate of R bits/s/Hz. Primarily, we must choose a data rate o to communicate between the transmitter and receiver. If our data rate selected R > C, then an outage occurs. No communication is possible between TX and RX. However, the MIMO system reduces the probability of an outage because multiple simultaneous data streams are potential between the transmitter and receiver. On the other hand, multiple independent data streams multiply the capacity of a system. 


(MIMO) What are the advantages of clustering instead of MIMO antenna?


What is the process of beam framing the MIMO system?


Identify the challenges in the control of the MIMO system.


Q. What is the future scope of spectral efficiency improvement in UL massive MIMO using space-time block? Coding?


Q. What is the process of beam framing the MIMO system?

A. See answer


What are the s11 and s21 of the MIMO antenna?

We can reduce interfaces between multiple antenna elements by using sound inter-element isolation. We must design the MIMO antenna element accordingly to achieve high gain. That is also recommended for higher WLAN frequencies.

When designing MIMO antennas, we generally get the terms like S11, S21, S31, etc. Here, S21 represents the reflected signal power from element or antenna no due to transmission from element or antenna 1. Obviously, that causes interference if the intensity is above the acceptable level. Usually, isolation less than -20 dB is considered sound isolation for typical MIMO systems.   

Usually, power transfer between an antenna and an antenna is measured in dB or decibels. It is a logarithmic scale. In our case, it is 10* og(reflected power / total transmission power). Here, the base of the log is 10.


Types of antennae used for coverage and interference reduction

A. You can use a MIMO system or closely placed antenna elements to produce a stronger main lobe to focus the signal towards a particular receiver. You know, beamforming dramatically reduces interference. On the other hand, the MIMO system shows spatial multiplex property, which leads to independent data streams between transmitter and receiver receivers.


An antenna operates single-frequency or multiple-frequencies

A. An antenna may operate simultaneously at multiple frequencies, e.g., MIMO system.


#beamforming

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