Introduction to Microservice Architecture Using SpringBoot - Part 1

1]Cellular concepts-Cell structure

Cellular Concepts refers to the use of a group of cells to provide communication from one place to another place when the user is mobile.

2]frequency reuse

Frequency Reuse is the scheme in which allocation and reuse of channels throughout a coverage region is done. Each cellular base station is allocated a group of radio channels or Frequency sub-bands to be used within a small geographic area known as a cell.

Silent Features of using Frequency Reuse:

· Frequency reuse improve the spectral efficiency and signal Quality (QoS).

· In Frequency Reuse scheme, total bandwidth is divided into different sub-bands that are used by cells.

To find the total number of channel allocated to a cell:

S = Total number of duplex channels available to use
k = Channels allocated to each cell (k<S)
N = Total number of cells or Cluster Size

Then Total number of channels (S) will be,

S = kN

Frequency Reuse Factor = 1/N

The distance between any two Co-Channels can be calculated by the following formula:

D = R * (3 * N)^(1/2)

Where,
R = Radius of a cell
N = Number of cells in a given cluster

3]cell splitting

Cell splitting in mobile communication is the process in which the bigger cells split up into smaller ones. In mobile communication we use cell splitting so that we can expand the capacity of the system. Cell splitting also helps to increase the number of channels.

4]Concept of Macro Cell

In a large area we need not to split all the cells in all clusters. Some of the base stations are capable of handling the traffic well when cells are split up.

The cells which are already split can be further split up into smaller cells. Therefore the efficiency of the BS also increases by doing so.

The cell which is again splits into smaller ones is called the master cell. The splits smaller cells are called Marco cells. The further splitting of these macro cells results in Pico cells.

5]Hand Off

When the mobile unit travels along a path it crosses different cells. Each time it enters into a different cell associated with f = different frequency, control of the mobile is taken over by the other base station. This is known as ‘Hand off’.

Hand off is decided based on −

· Received signal strength information if it is below a threshold value.

· Carrier to interference ratio is less than 18 dB.

6]What is channel assignment?

Channel assignment is the process of assigning separate orthogonal channel to all the nodes in the communication range.

The channel assignment problem can be categorised into three different forms,

1. Fixed Channel Assignment
2. Dynamic Channel Assignment
3. Hybrid Channel Assignment

7] What is interference in communication example?

Interference in communication is commonly referred to as "noise." Physical sources of noise, such as a loud hallway conversation

8] What are the 4 types of interference?

The common types of interference in cellular networks are:

1. self-interference,
2. multiple access interference,
3. co-channel interference (CCI)
4. adjacent channel interference (ACI)

9] What is capacity in mobile communication?

Capacity is the ultimate 'speed limit' of information transmission over any communication channel.

10] Power Control

power control refers to the process of controlling the power of a transmitter to achieve better communication signal or overall quality of service.

11]Wireless Standards

1. PAN (Personal Area Network)
2. LAN (Local Area Network)
3. MAN (Metropolitan Area Network)
4. WAN (Wide Area Network)

12] 2G and 3G Technology

Second Generation (2G) technology was launched in the year 1991 in Finland. It is based on the technology known as global system for mobile communication or in short we can say GSM. This technology enabled various networks to provide services like text messages, picture messages and MMS.

3G technology generally refers to the standard of accessibility and speed of mobile devices. This technology enables use of various services like GPS (Global Positioning System), mobile television and video conferencing.

13] Difference between 2G and 3G Technology

·Cost: The license fee to be paid for 3G network is much higher as compared to 2G networks. The network construction and maintenance of 3G is much costlier than 2G networks. Also from the customers point of view the expenditure for 3G network will be excessively high if they make use of the various applications of 3G.

Data Transmission: The main difference between 2G and 3G networks is seen by the mobile users who download data and browse the Internet on the mobile phones. They find much faster download speeds, faster access to the data and applications in 3G networks as compared to 2G networks. 2G networks are less compatible with the functions of smart phone. The speed of data transmission in 2G network is less than 50,000 bits per sec while in 3G it can be more than 4 million bits per sec

Function: The main function of 2G technology is the transmission of information via voice signals while that of 3G technologies is data transfer via video conferencing, MMS etc.

Features: The features like mobile TV, video transfers and GPS systems are the additional features of 3G technology that are not available with 2G technologies.

 14. Explain different types of fading and the sub- categories.

Large Scale Fading: This refers to the attenuation of signal power due to obstacles between the transmitter and receiver. It also covers the attenuation and fluctuations of signal when the signal is transmitted over a long distance (usually in kilometres).

Path Loss: It refers to the attenuation when a signal is transmitted over large distances. Wireless signals spread as they propagate through the medium and as the distance increases, the energy per unit area starts decreasing. This is a fundamental loss that is independent of the type of transmitter and medium. Although, we can minimize its effects by increasing the capture area/dimension of the receiver.

Shadowing: This refers to the loss in signal power due to the obstructions in the path of propagation. There are a few ways in which shadowing effects can minimize signal loss. One that is most effective, is to have a Line-Of-Sight propagation.

Small Scale Fading: This refers to the fluctuations in signal strength and phase over short distance and small duration of time. It is also called Rayleigh Fading. Small Scale Fading affects almost all forms of wireless communication and overcoming them is a necessity to increase efficiency and decrease error.

 15. What is cell splitting and cell Sectoring?

Cell splitting is a method of subdividing cell into the smaller sized cell. The parent cell that was originally congested is called as macro cells and the smaller cell called as microcells.

Cell sectoring is a method of decreasing the co-channel interference and enhancing system performance by using a directional antenna.

Cell splitting and sectoring are the two cellular design techniques for increasing system capacity and improving coverage Cell splitting subdivides a congested cell into smaller cells, each with its own base station and a corresponding reduction in antenna height and transmitter power. In the sectoring approach, omni directional antennas at the base station are replaced by directional antennas, each radiating in a specific sector.

For instance, if a subscriber moves out of the coverage area of a particular cell while entering another, a handoff takes place between the two cells. The cell that served the call prior to the handoff is relieved of its duties, which are then transferred to the second cell. A handoff may also be triggered when the number of subscribers using a particular cell has already reached the cell's maximum limit (capacity).

Such a handoff is possible because the reach of the cell sites serving these cells can sometimes overlap. Thus, if a subscriber is within an overlapping area, the network may opt to transfer one subscriber's call to the cell involved in the overlap.

Handoffs may be classified into two types:

Hard Handoff: Characterized by an actual break in the connection while switching from one cell or base station to another. The switch takes place so quickly that it can hardly be noticed by the user. Because only one channel is needed to serve a system designed for hard handoffs, it is the more affordable option. It is also sufficient for services that can allow slight delays, such as mobile broadband Internet.

Soft Handoff: Entails two connections to the cell phone from two different base stations. This ensures that no break ensues during the handoff. Naturally, it is more costly than a hard handoff.

16. What is channel assignment and its types?

Channel assignment strategies deal with the efficient utilization of radio spectrum through a frequency reuse scheme whose objective is to increase capacity as well as keep interference level as low as possible. In fixed assignment, each cell is assigned a predetermined set of voice channels. In this assignment scheme, if all the channels in the cell are occupied, a newly generated call is blocked and the subscriber does not receive the service until a channel becomes free.In another approach, a cell is allowed to borrow channels from a neighboring cell if all its own channels are already occupied. The mobile switching center (MSC) supervises such borrowing and also ensures that services in the donor cell are not disrupted due to borrowing. In dynamic channel assignment, channels are not assigned to the cells permanently. Instead, serving base station, on receipt of a call request, asks for a channel in the MSC. MSC based on certain considerations allocates channel Dynamic channel assignment reduces the likelihood of blocking. However in this scheme MSC is required to collect real time data on channel occupancy and traffic distribution.

17. What are the shape of cells in cellular concept in mobile communication?

In a cellular network, total area is subdivided into smaller areas called "cells". Each cell can cover a limited number of mobile subscribers within its boundaries. Each cell can have a base station with a number of RF channels.

For analytical purposes, a "Hexagon" cell is preferred to other shapes on paper due to the following reasons.

1. A hexagon layout requires fewer cells to cover a given area. Hence, it envisages fewer base stations and minimum capital investment.

2. Other geometrical shapes cannot effectively do this. For example, if circular-shaped cells are there, then there will be overlapping of cells.

3. Also for a given area, among square, triangle and hexagon, radius of a hexagon will be the maximum which is needed for weaker mobiles.

In reality cells are not hexagonal but irregular in shape, determined by factors like propagation of radio waves over the terrain, obstacles, and other geographical constraints. Complex computer programs are required to divide an area into cells. One such program is "Tornado" from Siemens.

The group of cells where the available frequency spectrum is totally consumed is called a cluster of cells. Two cells having the same number in the adjacent