Wireless Networks Viva Questions with Answers - Part 3

Q52) Define Ad-hoc Networks.
Answer: A wireless Ad-hoc networkis a collection of autonomous nodes or terminals that communicate with each other by forming a multi-hop radio network and maintaining connectivity in a decentralized manner.

Advantages of Ad-hoc networks:
• Wireless Ad-hoc networks can be set up very fast.
• No single point of failure, such as base station. Network still functions even if individual node fails.
• They are spectrally more efficient than cellular networks.
• Cheaper to deploy.

Q53) Define QoS.
Answer: Quality of service (QoS) refers to any technology that manages data traffic to reduce packet loss, latency and jitter on a network. QoS controls and manages network resources by setting priorities for specific types of data on the network.

Q54) What is femto cell ?
Answer: Femtocell is a very low-range, low-power base station, able to be deployed in a home or office. It is usually provided by a mobile network operator, and operates in licensed frequency bands.Improves the coverage area within the cell with or without cable.

Q55) Give the advantages of femto cell.
Answer:

★ Consumer Benefits:
• Reduced power consumption: since the distance between the user and the femtocell is small, the user will no longer need to transmit with high power. As the current drain from the battery will be small, resulting in longer standby times and increased talk times.
• Improved voice quality: because the users are so close to in proximity to the femtocell , a better communication link will be provided .This will allow the use of better –sounding, higher data rate speech vocoders to be used.
• Enhanced multimedia/IP services: Allow the user to have an enhanced experience with videos, home services, phones, computers, etc
• Security: Since the femtocell’s connection is via the public ISP and traffic will be routed to the private cellular network, the user must authenticate him to the network; the service provider can use IPsec. The users can rest at east knowing that personal or professional information will be secure

★ Operator Benefits:
• Increased revenue: having the femtocell capability with the service provider would attract additional users . Moreover, the femtocell application can be viewed as an additional feature/service, in which case the service providers would be able to charge the user for use of the service.
• Reduced cost: shrinking the public cell size from macro to micro and then to Pico has its capacity benefits, but it adds to network costs (deployment, maintenance, backhaul, recurring expenses, site rental, etc.). Using an already-available network such as the Internet, cost reduction is certainly feasible, given the communications move to the all-IP-based structure.
• Enhanced services Using the user’s access to the Internet, the service provider can reveal enhanced services tailored around the user’s phone, cellular network, and home, hopefully to improve the user’s efficiency and quality of life.
• Improved customer satisfaction With benefits of improved indoor coverage and high throughputs, service providers expect the user’s expectations to be satisfied.
• Supports Real-time and None Real-time application via IP based or non IP based backbone network.
• Increased Reward points due to reduced call drop probability.

Q56) What is Ultra-Wide Band (UWB) ?
Answer: UWB radios emit low-power, high-bandwidth pulses that deliver data rates comparable to wired ethernet(upto 100Mbps). Its high data rates and low power consumption make it ideal for WBANs. UWB is still in its first stages of commercial deployment.

Q57) What are the characteristics of MANET's ?
Answer:
Characteristics of MANETs:

Spontaneous established Network

Self-organizing and adaptive.

Devices can communicate directly with neighbor devices.

Single-hop or multi-hop communication may be employed.

Q58) What are the unique characteristics and application of VANET ?
Answer: VANETs are vehicular ad hoc networks is a collection of wireless node that forms a momentary network to communicate between vehicles. The main use of VANETs is for safety and comfort application. The moving vehicles in the roadside are considered as nodes and these nodes can communicate with each other.

Unique characteristics of VANETs:

Geographically constrained topology: Due to high node mobility and random speed of vehicles, the position of node changes frequently. As a result of this, network topology in VANETs tends to change frequently.

Unpredictability: The nodes in VANETs usually are moving at high speed. This makes harder to predict a node’s position.

Power consumption: No problem with power due to charging nature of batteries.

Critical Latency Requirements.

Q59) What are the full form of VANET, MANET, WiBro, MMDS, LMDS.
Answer:

• VANET: Vehicular Ad-hoc Network
• MANET: Mobile Ad-hoc Network
• WiBro: Wireless Broadband
• MMDS: Multi-point Multi-channel Distribution Service
• LMDS: Local Multipoint Distribution Service

Q60) Difference between FHSS and DSSS.
Answer:

FHSS	DSSS / CDMA
Multiple frequencies are used	Single frequency is used
Hard to find the user’s frequency at any instant of time.	User frequency, once allotted is always the same.
Frequency reuse is allowed	Frequency reuse is not allowed
Sender need not wait	Sender has to wait if the spectrum is busy
Power strength of the signal is high	Power strength of the signal is low
Stronger and penetrates through the obstacles	It is weaker compared to FHSS
It is never affected by interference	It can be affected by interference
It is cheaper	It is expensive
This is the commonly used technique	This technique is not frequently used

Q61) What is link budget ?
Answer: It measures all power gains and losses in antransmission network.

Q62) Define frequency reuse.
Answer: Frequency re-use is a technique used for utilizing a specific range of frequencies more than once within the same satellite sytem so that the total capacity of the system is increased without increasing its allocated bandwidth.

Q63) What is the purpose of frequency reuse ?
Answer:

• It improves the spectral efficiency and signal quality(QoS)
• In this total bandwidth devided into different sub-bands that are used by cells.

Q64) Define Erlang ?
Answer: Erlang is a unit of trafficdensity in a telecommunication system.

Q65) What are the features of GSM ?
Answer:

Features of GSM:
• Uplink frequency: 890-916MHz
• Downlink frequency: 936-960MHz
• Supports: Call forwarding, Call on hold, Configure facility.
• The encrypted conversation that can not be tapped.
• Rapid call setup.
• It has fully Internation roaming capability.
• It allows data transmission and reception across GSM network at 9.6kbps

Q67) What are the features of CDMA ?
Answer:

CDMA features:
• Transmit rate of one channel: 192kbps
• Uplink frequency: 824-849MHz
• Downlink frequency: 869-894MHz
• Average data rate: 3kbps
• Number of time slotes in one CDMA channel: 64
• Modulation method: QPSK/BPSK

Q68) What are the drawbacks of CDMA over GSM ?
Answer:

• CDMA can not offer international roaming.
• Requires more power.
• Time synchronization is also required.

Q69) Define Cell loading factor.
Answer: Foreach cell the load factor is defined asthe amount of resource consumption in a relation to that which is available in cell.

Q70) Define Cell radius.
Answer: Cells may varying radius from 1Km to 30Km.The boundry of a cells can be overlap between the adjacentcell and large cells.Which can be devided into smaller cells.

Q71) Why hexagonal cell structure is used.
Answer: Hexagonal cell shape is a perfect over square or triangular cell shapes in cellular architectire because it covers on entire area without overlapping. They can cover entire geographical region without any gaps.

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