10 Mobile Communication Interview Questions and Answers

This article presents a list of questions and answers related to Mobile Communication. This questionnaire will help candidates prepare for job interviews for various Mobile Communication skill-based positions and will also be useful during viva voce examinations for engineering students.

Mobile Communication Questions and Answers

Question 1: What is Mobile Communication, and how does it work?

Answer 1: Mobile communication refers to the technology that enables the transmission of voice, data, and multimedia over wireless networks using mobile devices such as smartphones, tablets, and laptops.

It works through a network of base stations (cell towers) connected to a core network, which routes data and voice traffic to its destination.

• When a user makes a call or sends data, the mobile device connects to the nearest base station using radio waves (Electromagnetic Waves). The base station then forwards the signal to the core network.
• The core network manages the communication process, including call setup, routing, and handover as the user moves.
• Mobile communication relies on various technologies like GSM, CDMA, LTE, and 5G to provide connectivity.

Question 2: What is Frequency Reuse, and why is it important in cellular networks?

Answer 2: Frequency reuse is a fundamental concept in cellular networks that allows the same frequency channels to be used in different cells within the network, separated by a sufficient distance to avoid interference. This concept increases the capacity of the network without requiring additional spectrum.

Importance of Frequency Reuse:

• Efficient Spectrum Utilization: It maximizes the use of the available frequency spectrum by reusing frequencies across multiple cells.
• Increased Network Capacity: By reusing frequencies, more calls or data sessions can be supported simultaneously, enhancing the network’s capacity to serve users.
• Reduced Interference: Proper planning of cell placement and frequency allocation minimizes interference between cells using the same frequencies.
• Frequency reuse allows cellular networks to efficiently support a large number of users with limited spectrum resources.

Question 3: Explain the concept of handover in mobile communication.

Answer 3: Handover (or handoff) is the process of transferring an active call or data session from one cell or base station to another without interruption as a mobile user moves through the network. This ensures continuous connectivity and quality of service.

Types of Handover:

• Intra-cell Handover: Occurs within the same cell, usually to balance traffic load between different sectors.
• Inter-cell Handover: Transfers the connection between different cells within the same network, either on the same frequency (intra-frequency) or different frequencies (inter-frequency).
• Inter-RAT Handover: Involves switching between different radio access technologies, such as from 4G LTE to 3G or 5G.
• Handovers are essential for maintaining uninterrupted service, especially during mobility, and they are managed by the network’s core components like the Mobility Management Entity (MME) in LTE or the Base Station Controller (BSC) in GSM.

Question 4: What is the difference between FDD and TDD in mobile communication?

Answer 4: FDD (Frequency Division Duplex) and TDD (Time Division Duplex) are two methods used to separate uplink and downlink transmissions in mobile communication.

• FDD (Frequency Division Duplex):
  • Uses two separate frequency bands for uplink (device to base station) and downlink (base station to device) transmissions.
  • Provides continuous transmission, suitable for symmetric traffic like voice calls.
  • Requires more spectrum, as each transmission direction needs its dedicated frequency band.
• TDD (Time Division Duplex):
  • Uses the same frequency band but separates uplink and downlink by time slots.
  • Allows for dynamic allocation of time slots based on traffic demand, making it suitable for asymmetric data traffic like internet browsing.
  • More flexible in terms of spectrum use and can be more efficient in scenarios with varying uplink and downlink requirements.

Both FDD and TDD have their applications depending on the specific needs of the network, such as spectrum availability and traffic patterns.

Question 5: What are the main components of a cellular network?

Answer 5: The main components of a cellular network include:

• Mobile Devices (User Equipment): Devices like smartphones, tablets, and laptops that connect to the cellular network.
• Base Stations (BTS/eNodeB/gNodeB): Radio towers that communicate with mobile devices and provide coverage for a specific area (cell).
• Core Network: The central part of the network that handles data routing, call management, subscriber authentication, and mobility management. Key components include the MME (Mobility Management Entity), HSS (Home Subscriber Server), and gateways like SGW (Serving Gateway) and PGW (Packet Gateway).
• Backhaul Network: Connects base stations to the core network, usually through fiber optic cables, microwave links, or other high-capacity connections.
• RAN (Radio Access Network): Connects mobile devices to the core network via base stations, managing radio resources and handovers.

These components work together to provide seamless voice, data, and multimedia services to users.

Question 6: What is GSM, and how does it differ from CDMA?

Answer 6: GSM (Global System for Mobile Communications) and CDMA (Code Division Multiple Access) are two different technologies used in mobile communication.

• GSM:
  • Uses Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) to divide frequencies and time slots among users.
  • Widely adopted globally and uses SIM cards to identify users on the network.
  • Operates in specific frequency bands such as 900 MHz and 1800 MHz.
• CDMA:
  • Uses spread spectrum technology, where multiple users share the same frequency channel but are separated by unique codes.
  • Offers better voice quality and capacity in the same bandwidth compared to GSM.
  • Does not use SIM cards, relying on the device’s built-in identification.

GSM and CDMA have evolved over time, but GSM’s global adoption and SIM-based identification have made it the dominant standard.

Question 7: Describe the role of SIM cards in mobile communication.

Answer 7: SIM (Subscriber Identity Module) cards are small, removable smart cards used in mobile devices to store subscriber information and authenticate users on the network.

Roles of SIM cards include:

• Subscriber Authentication: SIM cards store unique identifiers like the IMSI (International Mobile Subscriber Identity) and cryptographic keys used to authenticate the user on the mobile network.
• Storage: SIM cards store contacts, SMS messages, and network-related information such as the preferred network list and access point names (APNs).
• Roaming: SIM cards enable roaming by allowing users to connect to different networks while traveling, using agreements between operators.
• Security: SIM cards provide secure storage and execution of network authentication procedures, ensuring the privacy and security of user communications.
• SIM cards are essential for accessing mobile services and maintaining user identity across different devices and networks.

Question 8: What is a cell in mobile communication, and why is it important?

Answer 8: A cell in mobile communication is the basic geographic unit of a cellular network, defined by the coverage area of a base station (BTS/eNodeB/gNodeB). Each cell operates on a specific set of frequencies and serves users within its range.

Importance of cells:

• Coverage: Cells provide the radio coverage necessary to connect mobile devices to the network, allowing users to make calls and access data services.
• Capacity: By dividing the network into smaller areas (cells), the same frequencies can be reused in non-adjacent cells, increasing the overall capacity of the network.
• Mobility Management: Cells enable the network to track and manage the movement of users, facilitating seamless handovers and continuous connectivity as users move.

The concept of cells is fundamental to mobile communication, enabling efficient use of spectrum and robust coverage over large areas.

Question 9: What is the purpose of a base station controller (BSC) in GSM networks?

Answer 9: The Base Station Controller (BSC) in GSM networks is a critical component that manages multiple base stations (BTS) and handles various control functions.

Purpose of BSC:

• Resource Management: BSC manages radio resources, such as allocating channels for voice and data services and controlling power levels and frequency hopping.
• Handover Management: It coordinates handovers between base stations within its control, ensuring smooth transitions for users moving from one cell to another.
• Traffic Management: BSC handles call setup, termination, and traffic distribution among base stations, optimizing network performance and resource utilization.
• Connection to MSC: BSC connects to the Mobile Switching Center (MSC), which manages call routing and switching functions, facilitating communication between different parts of the network.

The BSC plays a vital role in ensuring efficient operation and management of the radio access part of GSM networks.

Question 10: Explain the concept of cell splitting in cellular networks.

Answer 10: Cell splitting is a technique used in cellular networks to increase capacity and manage growing traffic demands by dividing a larger cell into smaller cells, each with its own base station and reduced coverage area.

Concept of Cell Splitting:

• Purpose: Cell splitting is used to enhance network capacity by creating more cells in high-demand areas, allowing more users to be served simultaneously.
• Process: The original larger cell is split into smaller cells with lower power base stations, and the frequency plan is adjusted to maintain interference control and optimize frequency reuse.
• Benefits: This approach increases the number of available channels, reduces congestion, and improves service quality in densely populated areas.
• Cell splitting is a key strategy for network expansion and performance optimization, especially in urban environments with high mobile traffic.