Communications MCQ Set 1
1. Bit error rate provides the information about the type of error.
Answer: b [Reason:] Bit error rate does not provide information about the type of error. However, bit error rate (BER) evaluation gives a good indication of the performance of a particular modulation scheme.
2. Which of the following is specified by a specific number of bit errors occurring in a given transmission?
a) Bit error rate
b) Equally likely event
c) Outage event
d) Exhaustive events
Answer: c [Reason:] Outage event is specified by a specific number of bit errors occurring in a given transmission. Evaluating the probability of outage is one of the means to judge the effectiveness of the signalling scheme in a mobile radio channel.
3. Irreducible BER floor is created in frequency selective channels due to ____________
a) Intersymbol interference
b) Random spectral spreading
c) Time varying Doppler spread
d) Blind speed
Answer: a [Reason:] Frequency selective fading is caused due to multipath delay spread which causes intersymbol interference. It results in an irreducible BER floor for mobile systems.
4. Irreducible BER floor is created in non frequency selective channels due to ____________
a) Intersymbol interference
b) Multipath time delay
c) Time varying Doppler spread
d) Blind speed
Answer: c [Reason:] Even if a mobile channel is not frequency selective, the tie varying Doppler spread due to motion creates an irreducible BER floor. It is caused due random spectral spreading.
5. The performance of BPSK is best is term of BER because _______
a) Symbol offset interference does not exist
b) Existence of cross rail interference
c) No multipath delay
d) Doppler spread
Answer: a [Reason:] BER performance of BPSK is best among all the modulation schemes compared. This is because symbol offset interference does not exist in BPSK. Symbol offset interference is also called cross rail interference due to the fact that the eye diagram has multiple rails.
6. High capacity mobile systems are interference limited. State whether True or False.
Answer: a [Reason:] High capacity mobile systems are interference limited, but they are not noise limited. It was clearly seen that when carrier to interference ratio (C/I) is large, the errors are primarily due to fading, and interference has very little effect. However, as C/I drops below a certain level, interference dominates the link performance.
7. Which of the following do not impact bit error rate in mobile communication systems?
a) Mobile velocity
b) Channel delay spread
c) Modulation format
d) Base station
Answer: d [Reason:] The mobile velocity, channel delay spread, interference levels and modulation formats all independently impact the raw bit error rate in mobile communication systems. And simulation is a powerful way to design or predict the performance of wireless communication links.
8. Coherence time refers to ___
a) Time required attaining a call with the busy base station
b) Time required for synchronization between the transmitter and the receiver
c) Minimum time for change in magnitude and phase of the channel
d) None of the above
Answer: c [Reason:] Coherence time is the time required for synchronization between the transmitter and receiver. It is the over which a propagating wave is said to be coherent.
9. Doppler spread refers to _________
a) Signal fading due to Doppler shift in the channel
b) Temporary failure of message transfer
c) Large coherence time of the channel as compared to the delay constraints
d) All of the above
Answer: a [Reason:] Doppler spread refers to signal fading due to Doppler shift in the channel. It is a measure of spectral broadening caused by time rate of change of the mobile radio channel.
10. A rake receiver uses multiple ______
a) Delay circuits
d) Flip flops
Answer: b [Reason:] A rake receiver uses multiple correlators to separately detect multiple strongest components. It is designed to counter the effects of multipath fading.
Communications MCQ Set 2
1. MIMO stands for _______
a) Many input many output
b) Multiple input multiple output
c) Major input minor output
d) Minor input minor output
Answer: b [Reason:] MIMO stands for Multiple Input and Multiple Output. It refers to the technology where there are multiple antennas at the base station and multiple antennas at the mobile device.
2. In MIMO, which factor has the greatest influence on data rates?
a) The size of antenna
b) The height of the antenna
c) The number of transmit antennas
d) The area of receive antennas
Answer: c [Reason:] By increasing the number of receiving and transmitting antennas, it is possible to linearly increase the throughput of the channel with every pair of antennas added to the system.
3. MIMO was initially developed in the year _____
Answer: b [Reason:] Since the initial development in the year 1990, MIMO Wireless Communications have become integral part of the most forthcoming commercial and next generation wireless data communication systems.
4. MIMO is a smart antenna technology.
Answer: a [Reason:] MIMO is one of several forms of smart antenna technology, the others being MISO (multiple input, single output) and SIMO (single input, multiple output). It is an antenna technology for wireless communications in which multiple antennas are used at both the source and the destination.
5. MIMO technology makes advantage of a natural radio wave phenomenon called _______
Answer: b [Reason:] MIMO technology makes use of multipath phenomenon to maximize transmission by receiving bounced signals from obstructions. Multipath is a phenomenon in wave propagation.
6. Which of the following technology does not use MIMO?
Answer: d [Reason:] MIMO is used in mobile radio telephone standards such as recent 3GPP and 3GPP2. In 3GPP, High-Speed Packet Access plus (HSPA+) and Long Term Evolution (LTE) standards take MIMO into account. Moreover, MIMO is also used in Wifi and WiMax.
7. MIMO means both transmitter and receiver have multiple antennas.
Answer: a [Reason:] MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. It uses multiple antennas at the transmitter and receiver along with some complex digital signal processing.
8. _______ is a technique of transmit diversity used in UMTSS third-generation cellular systems.
c) Collaborative Uplink MIMO
Answer: a [Reason:] Space Time Transmit Diversity (STTD) is a technique of transmit diversity used in UMTSS third-generation cellular systems. Space Time Transmit Diversity is optional in the UTRANN air interface, but compulsory for user equipment.
9. _______ is a transmission method used in MIMO wireless communications to transmit encoded data signals independently.
c) Collaborative Uplink MIMO
Answer: b [Reason:] Spatial multiplexing is a transmission method used in MIMO wireless communications to transmit encoded data signals independently and separately (so-called streams) from each of the multiple transmit antennas.
10. _______ is an additional open-loop MIMO technique considered by the WiMAX vendors.
c) Collaborative Uplink MIMO
Answer: c [Reason:] Collaborative MIMO is an open-loop MIMO technique considered by the WiMAX vendors to surge the spectral efficiency and capacity of the uplink communications path. It is compared with the regular spatial multiplexing, wherein data streams are transmitted multiplying from multiple antennas on the same device.
Communications MCQ Set 3
1. Several protocols for upper layers in bluetooth use _________
Answer: d [Reason:] L2CAP is Logical Link, Control Adaptation Protocol Layer. The logical unit link control adaptation protocol is equivalent to logical link control sub layer of LAN. The ACL link uses L2CAP for data exchange. The various function of L2CAP is segmentation and reassembly, multiplexing and quality of service.
2. Protocols are set of rules to govern ______
c) Metropolitan communication
Answer: a [Reason:] A protocol is a set of rules that governs the communications between computers on a network. These rules include guidelines that regulate the characteristics of a network including access method, allowed physical topologies, types of cabling, and speed of data transfer.
3. An internet is a ______
a) Collection of WANS
b) Network of networks
c) Collection of LANS
d) Collection of identical LANS and WANS
Answer: b [Reason:] Internet is a massive network of networks, a networking infrastructure. It connects millions of computers together globally, forming a network in which any computer can communicate with any other computer as long as they are both connected to the Internet.
4. Checksum is used in Internet by several protocols although not at the ______
a) Session layer
b) Transport layer
c) Network layer
d) Data link layer
Answer: d [Reason:] The checksum is used in the Internet by several protocols although not at the data link layer. Like linear and cyclic codes, the checksum is based on the concept of redundancy. Several protocols still use the checksum for error detection.
5. In version field of IPv4 header, when machine is using some other version of IPv4 then datagram is ______
d) Interpreted incorrectly
Answer: a [Reason:] A 4 bit field defines the version of IPv4 protocol. This field tells the software running in the processing machine that the datagram has the format of version 4. If the machine is using some other version of IPv4, the datagram is discarded rather than interpreted incorrectly.
6. Network layer at source is responsible for creating a packet from data coming from another ________
Answer: d [Reason:] ‘The network layer at the source is responsible for creating a packet from the data coming from another’ protocol (such as a transport layer protocol or a routing protocol). The network layer is responsible for checking its routing table to find the routing information.
7. Header of datagram in IPv4 has _________
a) 0 to 20 bytes
b) 20 to 40 bytes
c) 20 to 60 bytes
d) 20 to 80 bytes
Answer: c [Reason:] IP header length is a minimum of 20 bytes and a maximum of 60 bytes. The minimum value for this field is 5, which is a length of 5×32 = 160 bits = 20 bytes. Being a 4-bit value, the maximum length is 15 words (15×32 bits) or 480 bits = 60 bytes.
8. In IPv4 layer, datagram is of ________
a) Fixed length
b) Variable length
c) Global length
d) Zero length
Answer: b [Reason:] ‘IPv4 is a connectionless protocol used for packet switched networks. It operates on best effort delivery model, in which neither delivery is guaranteed, nor proper sequencing or avoidance of duplicate delivery is assured. The size of the datagram header can be of variable length from 20 bytes to 60 bytes.’
9. In IPv4, service type of service in header field, first 3 bits are called ______
a) Type of service
b) Code bits
c) Sync bits
d) Precedence bits
Answer: d [Reason:] The 8-bit ToS (type of service) in IPv4 uses 3 bits for IP Precedence, 4 bits for ToS with the last bit not being used. The 4-bit ToS field, although defined, has never been used.
10. Which is a link layer protocol?
Answer: b [Reason:] ‘In computer networking, the link layer is the lowest layer in the Internet Protocol Suite. It is commonly known as TCP/IP, the networking architecture of the Internet. It is described in RFC 1122 and RFC 1123.’
11. Which protocol is commonly used to retrieve email from a mail server?
Answer: b [Reason:] ‘The Internet Message Access Protocol (IMAP) is a mail protocol used for accessing email on a remote web server from a local client. IMAP is the most commonly used Internet mail protocols for retrieving emails. It is supported by all modern email clients and web servers.’
Communications MCQ Set 4
1. OFDMA stands for ________
a) omnidirectional frequency division multiple access
b) orthogonal frequency duplex multiple access
c) orthogonal frequency divider multiple access
d) orthogonal frequency division multiple access
Answer: d [Reason:] Orthogonal frequency-division multiple access (OFDMA) is a multi-user version of the popular orthogonal frequency-division multiplexing (OFDM) digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users.
2. Why is a cyclic prefix required in an OFDMA?
a) To ensure symbol time is an integer number
b) To help overcome multipath and ISI
c) To maintain orthogonality
d) To make OFDMA scalable
Answer: b [Reason:] 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.
3. What does the DC subcarrier indicate?
a) Identity of the cell
b) Antenna configuration
c) Center of OFDM channel
d) Format of data channel
Answer: c [Reason:] All the subcarriers of an OFDM symbol do not carry useful data. In OFDM and OFDMA PHY layers, the DC subcarrier is the subcarrier whose frequency is equal to the RF centre frequency of the transmitting station.
4. What processing step combines multiple OFDM subcarriers into a single signal for transmission?
c) RF combining
d) Channel mapping
Answer: b [Reason:] IFFT combines multiple OFDM subcarriers into a single signal for transmission. These transforms are important from the OFDM perspective because they can be viewed as mapping digitally modulated input data (data symbols) onto orthogonal subcarriers.
5. Which property of OFDMA system allows adjacent subcarriers to be used without interference?
Answer: a [Reason:] Orthogonality of sub-carriers simply means their correlation is zero. Orthogonality in OFDMA system allows adjacent subcarriers to be used without interference.
6. In OFDMA, what is the relationship between the subcarrier spacing f and symbol time t?
d) no relation
Answer: c [Reason:] In OFDMA, relationship between the subcarrier spacing f and symbol time t is f=1/t. They are inversely proportional.
7. OFDM is a technique for 3G mobile communication. State whether True or False.
Answer: b [Reason:] OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G mobile communications.
8. OFDM uses complex equalizers.
Answer: b [Reason:] ODMA does not use complex equalizers. In OFDM, the equalizer only has to multiply each detected sub-carrier (each Fourier coefficient) in each OFDM symbol by a constant complex number, or a rarely changed value.
9. When we divide band of Orthogonal Frequency Division Multiplexing (OFDM) into sub bands, it diminishes effects of ____
d) signals absence
Answer: c [Reason:] OFDM uses the same bandwidth to deliver roughly the same data rate as a single carrier modulation by introducing multiple lower-bandwidth channels. Each of the lower-bandwidth channels has a lower rate, and by combining them together, the original rate is achieved.
10. Common data rates of IEEE 802.11 OFDM are ______
a) 18 Mbps
b) 200 Mbps
c) 50 Mbps
d) 54 Mbps
Answer: a [Reason:] The IEEE 802.11a standard specifies a modulation that divides a high-speed serial information signal into multiple lower-speed sub signals. Common data rates of IEEE 802.11 OFDM is 18 Mbps.
Communications MCQ Set 5
1. PCS/PCN provides only wired communication.
Answer: b [Reason:] The objective of personal communication systems (PCS) or personal communication networks (PCNs) is to provide ubiquitous wireless communications coverage, enabling users to access telephone network and Internet.
2. Concept of PCS/PCN is based on _________
a) Advanced intelligent network
b) Artificial intelligent network
Answer: a [Reason:] The concept of PCS/PCN is based on an advanced intelligent network (AIN). The mobile and fixed networks will be integrated to provide universal access to the network and its databases.
3. AIN has different telephone numbers for both wireline and wireless services.
Answer: b [Reason:] AIN (advanced intelligent network) allow its users to have a single telephone number to be used for both wireless and wireline services.
4. Circuit switching has more advantage than packet switching for PCS.
Answer: b [Reason:] Packet switching technology will have more advantages for PCS/PCN than circuit switching. PCS is required to serve a wide range of services including voice, data, e-mail and digital video.
5. ______ is used for transmission of packets in the cellular switched architecture.
a) Packet switching techniques
b) Circuit switching techniques
c) Packet and circuit switched technique
d) Datagram technique
Answer: a [Reason:] Packet switching techniques are used for transmission of packets in the cellular switched architecture. Packet switching is attractive for wireless networks because the addresses and other information in packet headers make it possible for dispersed network elements to respond to a mobile user without intervention central controllers.
6. Which of the following has the function to accept information from PSTN?
Answer: a [Reason:] The function of TIU (Trunk interface unit) is to accept information from the PSTN. TIU acts as the physical layer and transforms the standard format of the PSTN into the wireless access physical layer.
7. PTI is the address of ___
Answer: a [Reason:] PTI (Permanent terminal identifier) is the address of TIU. It is the address from where he call is originated.
8. _______ is the information contained in the packet header of TIU.
Answer: b [Reason:] VCI (virtual circuit identifier) is the information contained in the packet header of TIU. It is used to identify the route through which the transmission will take place.
9. Transmission protocol, PRMA stands for _________
a) Pocket reservation multiple access
b) Packet register multiple access
c) Pocket register multiple access
d) Packet reservation multiple access
Answer: d [Reason:] Transmission protocol, PRMA stands for packet reservation multiple access. PRMA is a time division multiplex (TDM) based multiple access protocol that allows a group of spatially dispersed terminals to transmit packet voice and low bit rate data over a common channel.
10. UMTS stands for ____________
a) Universal mobile telecommunication system
b) Universal mobile telephone system
c) United multiplex telecommunication system
d) Universal mobile telecommunication system
Answer: d [Reason:] UMTS stands for Universal mobile telecommunication system. It is a system that is capable of providing a variety of mobile services to a wide range of global mobile communication standards.