Mobile Communication CAT Maasai Mara University 2024/2025

 Define the following terms:(2 marks)

• Cellular network - A cellular network is a communication network where the coverage area is divided into smaller regions called cells. Each cell has its own base station that communicates with mobile devices within that region. Cellular networks allow mobile devices to move freely across different cells while maintaining a continuous connection.

• Frequency reuse- Frequency reuse refers to the practice of using the same frequency bands in different geographic areas (cells) to maximize the use of available bandwidth. Cells are designed to not interfere with each other by using different frequencies or employing advanced techniques like directional antennas.

• Handoff (handover) in mobile communication -Handoff (or handover) is the process of transferring an ongoing call or data session from one cell to another as a mobile device moves across the network. This ensures uninterrupted service as the user moves between different coverage areas. 

• Bandwidth and its significance in mobile communication- Bandwidth refers to the data transmission capacity of a network, measured in bits per second (bps). In mobile communication, sufficient bandwidth is crucial for supporting high data rates, enabling faster download/upload speeds, and reducing latency for a better user experience.

What are the key differences between 4G and 5G mobile communication technologies? Explain the major advantages of 5G over 4G. (2 marks)

Speed: 5G offers significantly faster speeds (up to 100x) compared to 4G, enabling faster downloads and lower latency.

Latency: 5G has a much lower latency (less than 1 ms) compared to 4G (which is around 30-50 ms).

Capacity: 5G supports more devices simultaneously, allowing for better scalability, particularly in dense urban areas.

Use Cases: 5G supports advanced applications like autonomous vehicles, IoT, and smart cities, which require ultra-reliable, low-latency communication.

Explain the concept of "cellular reuse" in mobile networks. Why is it important for efficient spectrum usage? (2 marks)

Cellular reuse refers to reusing the same frequencies in different cells (with sufficient distance between them) to maximize spectrum efficiency. This technique is crucial for efficient spectrum usage as it allows for the optimization of available bandwidth across large geographic areas, improving overall capacity and coverage.

What is the role of a base station (BS) in a cellular system? How does it interact with mobile devices and the central network? (2 marks)

A base station (BS) provides wireless communication to mobile devices within a particular cell. It handles tasks such as:

• Transmission: Sending and receiving signals from mobile devices.

• Connection to the network: It communicates with the core network to route calls and data.

• Coordination: The base station manages radio resources and handoff processes when users move between cells.

What is the process of handoff in a cellular network? Describe two types of handoff used in mobile communication. (2 marks)

Handoff is the process of transferring an active call or data session from one base station to another without disconnecting the service. There are two main types:

• Hard Handoff: A break-before-make handoff where the connection with the old cell is terminated before the new connection is established.

• Soft Handoff: A make-before-break handoff where the device simultaneously maintains connections to both the old and new cells until the new connection is established.

Why is QPSK preferred over BPSK in mobile communications? (2 marks)

QPSK (Quadrature Phase Shift Keying) is preferred over BPSK (Binary Phase Shift Keying) because it can transmit twice the amount of data using the same bandwidth. While BPSK transmits 1 bit per symbol, QPSK transmits 2 bits per symbol, offering improved spectral efficiency and higher data rates, which is essential for mobile communications.

Explain how a mobile operator can optimize the placement of base stations to reduce signal interference and improve network performance in a densely populated urban area. (2 marks)

In densely populated urban areas, a mobile operator can optimize base station placement by:

• Conducting a site survey to identify high-traffic areas.

• Using small cells to improve coverage and capacity in localized areas, reducing interference.

• Employing advanced antenna technologies like MIMO (Multiple Input, Multiple Output) to maximize signal strength and reduce interference.

• Placing base stations at higher elevations to improve line-of-sight and coverage, especially in crowded city environments.

What is the concept of "network slicing" in 5G? How does it enhance the flexibility and efficiency of mobile networks? (2 marks)

Network slicing in 5G refers to the creation of multiple virtual networks (slices) on top of a single physical network infrastructure. Each slice can be customized to meet specific needs, such as low latency, high throughput, or reliability, for different use cases (e.g., IoT, autonomous vehicles). This enhances the flexibility and efficiency of mobile networks by optimizing resources for diverse applications.

Explain the difference between circuit-switched and packet-switched networks. How are these two types of networks used in mobile communication? (2 marks)

Circuit-Switched Network: Establishes a dedicated communication path for the entire duration of a call or session, commonly used in traditional voice calls (e.g., GSM, PSTN).

Packet-Switched Network: Data is broken into packets and sent over the network independently, with no dedicated path. This is more efficient for data transfer and is used in modern data communication networks (e.g., 4G, 5G, internet).

Describe the architecture of a 4G LTE network. What are the key components and how do they interact? (2 marks)

The 4G LTE network architecture consists of several key components:

• User Equipment (UE): Devices like smartphones or tablets.

• Evolved Node B (eNB): The base station in 4G LTE that communicates directly with the UE.

• Evolved Packet Core (EPC): The core network responsible for managing data sessions, mobility, and routing.

• Serving Gateway (SGW): Routes data between the eNB and the core network.

• Packet Data Network Gateway (PGW): Connects to external networks such as the internet.

• Policy and Charging Rules Function (PCRF): Manages data traffic and billing.

These components work together to provide high-speed data, voice services, and mobility support for users in the 4G network.