This set of Wireless & Mobile Communications Multiple Choice Questions & Answers (MCQs) focuses on “Physical Layer of WLAN”.
1. Which IEEE standard defines the specifications and architecture of Wireless Local Area Network (WLAN)?
a) IEEE 802.6
b) IEEE 802.16
c) IEEE 802.11
d) IEEE 802.15
View Answer
Explanation: IEEE 802.11 standard defines the specifications and architecture of WLAN. Devices under IEEE 802.11 standard use high radio frequency waves instead of connections using cables in Local Area Networks (LAN). Users utilizing WLAN can move around within network coverage areas without any internet disruptions.
2. The physical layer of WLAN includes MAC sublayer, Security sublayer and transmission convergence sublayer.
a) True
b) False
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Explanation: WLAN (IEEE 802.11) architecture includes Stations, Basic Service Set, Extended Service Set and Distribution Systems. MAC sublayer, Security sublayer and transmission convergence sublayer are the components used within IEEE 802.16, which includes Wireless Metropolitan Area Networks (WMAN).
3. Which of the following statements regarding physical layer of WLAN is incorrect?
a) Extended Service Set (ESS) is a combination of all Basic Service Set
b) Each access point in ESS is connected using Distribution System
c) Every station in WLAN has network interface controller
d) Wireless Access Points include computers, printers, workstations and smart phones
View Answer
Explanation: The physical layer of WLAN includes stations, which is further classified into Wireless Access Points (WAP) and Clients. WAP’s includes multiple wireless routers which serves as base station points whereas clients include the interconnected devices like computers, printers, workstations and smart phones.
4. What frequency is utilized by Frequency Hopping Spread Spectrum technique for microwave transmission?
a) 2.4 GHz
b) 3.6 GHz
c) 28 GHz
d) 42 GHz
View Answer
Explanation: IEEE 802.11 based devices operates at data rates 1 Mbit/s to 2 Mbit/s. This includes Industrial Scientific Medical (ISM) band which operates at 2.4GHz frequency. Microwave transmission between several devices is based on Frequency Hopping Spread Spectrum technique which operates at 2.4 GHz.
5. What is the maximum data rate supported by the physical layer of WLAN?
a) 60 Mbps
b) 54 Mbps
c) 32 Mbps
d) 43 Mbps
View Answer
Explanation: The physical layer of WLAN essentially defined in IEEE 802.11a standard offers data rates upto 54 Mbps. Other popular IEEE 802.11 standards include IEEE 802.11b, IEEE 802.11g and IEEE802.11n standards. These standards support data rates very much lesser than IEEE 802.11a since Direct Sequence Spread Spectrum (DSSS) and Complementary Code Keying (CCK) is deployed.
6. Which modulation scheme is utilized within WLAN frame structure?
a) Quadrature Phase Shift Keying (QPSK)
b) Quadrature Amplitude Modulation (QAM)
c) Binary Phase Shift Keying (BPSK)
d) Frequency Shift Keying (FSK)
View Answer
Explanation: WLAN frame structure includes preamble, header and data parts. Preamble portion contains multiple training sequences interrupted by guard intervals, header portion includes 24 bits which are BPSK modulated signals and the data length is calculated in the header part itself.
7. Which of the following is not a characteristic feature of IEEE 802.11 physical layer (PHY)?
a) PHY uses spread spectrum modulation scheme to transfer data frames over the media
b) PHY provides carrier sense indication to Media Access Control (MAC) to verify activity on the media
c) PHY provides interface for exchanging frames with the upper MAC layer
d) PHY is responsible for describing frame formats and encapsulation frames
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Explanation: PHY serves as an interface between wireless media and MAC layer where the frames are transmitted and received. PHY provides 3 main functionalities: First and foremost, it provides interface for exchanging frames with the upper MAC layer. Secondly, it uses spread spectrum modulation scheme to transfer data frames over the media. Finally, it provides interface for exchanging frames with the upper MAC layer.
8. What is the correct sequential process involved in the header generation process of Wireless LAN?
a) Generating field bits → coding and interleaving → Mapping with frequency domain → pilot and guard insertion → Time domain transformation
b) Generating field bits → mapping with frequency domain → coding and interleaving → pilot and guard insertion → Time domain transformation
c) Generating field bits → Time domain transformation → mapping with frequency domain → coding and interleaving → pilot and guard insertion
d) Pilot and guard insertion → Generating field bits → mapping with frequency domain → coding and interleaving → Time domain transformation
View Answer
Explanation: Header generation in preamble portion involves the following sequential process: Initially, signal bits are generated, followed by coding and interleaving of signal bits. Further, these bits are mapped with frequency domain signals and later, pilot and guard bits are inserted. Finally, these field bits are transformed into time domain.
9. Why preamble is used within the physical layer of WLAN frame structure?
a) Interleaving
b) Interoperability
c) Enhanced packet size
d) Synchronization
View Answer
Explanation: WLAN frame is composed of 3 parts namely preamble, header and data. Preamble contains 12 symbols which are extensively utilized for synchronization of the data. Header’s main objective lies in transmitting the modulation code rate of signals. The data portion contains Cyclic Redundancy Check (CRC) code for detecting errors during transmission.
10. Which protocol is utilized by WLAN systems to gain access within the medium?
a) Carrier Sense Multiple Access (CSMA)
b) Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
c) Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
d) Persistent Carrier Sense Multiple Access
View Answer
Explanation: Management frames in WLAN systems are extensively utilized in transforming management related information. This entire procedure is defined using CSMA/CA which provides access to the medium. It also deploys carrier sensing and all the nodes begin transmission only after checking whether the channel is idle.
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