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Cellular Networks: Structure, Components, and Communication, Schemes and Mind Maps of Mathematics

Kerala KalamandalamMathematics

Notes for mobile computing introduction

Typology: Schemes and Mind Maps

2023/2024

Uploaded on 11/16/2023

kavisha-kulshreshtha
kavisha-kulshreshtha 🇮🇳

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Define Cellular network and discuss its structure with basic components and communication.
Cellular network is an underlying technology for mobile phones, personal communication systems, wireless
networking etc. The technology is developed for mobile radio telephone to replace high power
transmitter/receiver systems. Cellular networks use lower power, shorter range and more t ransmitters for
data transmission.
Features of Cellular Systems
• Offer very high capacity in a limited spectrum.
• Reuse of radio channel in different cells.
• Enable a fixed number of channels to serve an arbitrarily large number of users by reusing
the channel throughout the coverage region.
• Communication is always between mobile and base station (not directly between mobiles).
• Each cellular base station is allocated a group of radio channels within a small geographic
area called a cell.
• Neighbouring cells are assigned different channel groups.
• By limiting the coverage area to within the boundary of the cell, the channel groups may be
reused to cover different cells.
• Keep interference levels within tolerable limits.
• Frequency reuse or frequency planning.
• Organization of Wireless Cellular Network.
Cellular network is organized into multiple low power transmitters each 100w or less.
Shape of Cells
The coverage area of cellular networks is divided into cells, each cell having its own antenna for transmitting the
signals. Each cell has its own frequencies. Data communication in cellular networks is served by its base station
transmitter, receiver and its control unit. The shape of cells can be either square or hexagon
A square cell has four neighbors at distance d and four at distance Root 2 d
• Better if all adjacent antennas equidistant
• Simplifies choosing and switching to new antenna
A hexagon cell shape is highly recommended for its easy coverage and calculations. It offers the following
advantages −
• Provides equidistant antennas
• Distance from centre to vertex equals length of side
Frequency reusing is the concept of using the same radio frequencies within a given area, that are separated by
considerable distance, with minimal interference, to establish communication.
Frequency reuse offers the following benefits −
• Allows communications within cell on a given frequency
• Limits escaping power to adjacent cells
• Allows re-use of frequencies in nearby cells
• Uses same frequency for multiple conversations
• 10 to 50 frequencies per cell
Structure with basic components
Of the units within the cellular network, the BTS provides the direct communication with the mobile phones.
There may be a small number of base stations then linked to a base station controller. This unit acts as a small
centre to route calls to the required base station, and it also makes some decisions about which of the base
station is best suited to a particular call. The links between the BTS and the BSC may use either land lines of even
microwave links. Often the BTS antenna towers also support a small microwave dish antenna used for the link
to the BSC. The BSC is often co-located with a BTS. The BSC interfaces with the mobile switching centre. This
makes more widespread choices about the routing of calls and interfaces to the land line based PSTN as well as
the HLR and VLR.
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Define Cellular network and discuss its structure with basic components and communication.

Cellular network is an underlying technology for mobile phones, personal communication systems, wireless networking etc. The technology is developed for mobile radio telephone to replace high power transmitter/receiver systems. Cellular networks use lower power, shorter range and more transmitters for data transmission. Features of Cellular Systems

  • Offer very high capacity in a limited spectrum.
  • Reuse of radio channel in different cells.
  • Enable a fixed number of channels to serve an arbitrarily large number of users by reusing the channel throughout the coverage region.
  • Communication is always between mobile and base station (not directly between mobiles).
  • Each cellular base station is allocated a group of radio channels within a small geographic area called a cell.
  • Neighbouring cells are assigned different channel groups.
  • By limiting the coverage area to within the boundary of the cell, the channel groups may be reused to cover different cells.
  • Keep interference levels within tolerable limits.
  • Frequency reuse or frequency planning.
  • Organization of Wireless Cellular Network. Cellular network is organized into multiple low power transmitters each 100w or less. Shape of Cells The coverage area of cellular networks is divided into cells , each cell having its own antenna for transmitting the signals. Each cell has its own frequencies. Data communication in cellular networks is served by its base station transmitter, receiver and its control unit. The shape of cells can be either square or hexagon A square cell has four neighbors at distance d and four at distance Root 2 d
  • Better if all adjacent antennas equidistant
  • Simplifies choosing and switching to new antenna A hexagon cell shape is highly recommended for its easy coverage and calculations. It offers the following advantages −
  • Provides equidistant antennas
  • Distance from centre to vertex equals length of side Frequency reusing is the concept of using the same radio frequencies within a given area, that are separated by considerable distance, with minimal interference, to establish communication. Frequency reuse offers the following benefits −
  • Allows communications within cell on a given frequency
  • Limits escaping power to adjacent cells
  • Allows re-use of frequencies in nearby cells
  • Uses same frequency for multiple conversations
  • 10 to 50 frequencies per cell Structure with basic components Of the units within the cellular network, the BTS provides the direct communication with the mobile phones. There may be a small number of base stations then linked to a base station controller. This unit acts as a small centre to route calls to the required base station, and it also makes some decisions about which of the base station is best suited to a particular call. The links between the BTS and the BSC may use either land lines of even microwave links. Often the BTS antenna towers also support a small microwave dish antenna used for the link to the BSC. The BSC is often co-located with a BTS. The BSC interfaces with the mobile switching centre. This makes more widespread choices about the routing of calls and interfaces to the land line based PSTN as well as the HLR and VLR.

Base transceiver station, BTS The base transceiver station or system, BTS consists of a number of different elements. The first is the electronics section normally located in a container at the base of the antenna tower. This contains the electronics for communicating with the mobile handsets and includes radio frequency amplifiers, radio transceivers, radio frequency combiners, control, communication links to the BSC, and power supplies with back up. The second part of the BTS is the antenna and the feeder to connect the antenna to the base transceiver station itself. These antennas are visible on top of masts and tall buildings enabling them to cover the required area. Finally, there is the interface between the base station and its controller further up the network. This consists of control logic and software as well as the cable link to the controller. Mobile switching centre (MSC) The MSC is the control centre for the cellular system, coordinating the actions of the BSCs, providing overall control, and acting as the switch and connection into the public telephone network. As such it has a variety of communication links into it which will include fibre optic links as well as some microwave links and some copper wire cables. These enable it to communicate with the BSCs, routing calls to them and controlling them as required. It also contains the Home and Visitor Location Registers, the databases detailing the last known locations of the mobiles. It also contains the facilities for the Authentication Centre, allowing mobiles onto the network. In addition to this it will also contain the facilities to generate the billing information for the individual accounts.

Explain channel allocation techniques in cellular network.

Channel allocation techniques are used in radio resource management for wireless and cellular networks to distribute bandwidth and communication channels to base stations, access points, and terminal devices. The objective of channel allocation is to maximize system spectral efficiency in bits/s/Hz/site through frequency reuse while maintaining a high level of service by minimizing co-channel and neighboring channel interference among neighboring cells or networks that share the bandwidth. Channel allocation techniques can be grouped into two categories: Fixed Channel Allocation and Dynamic Channel Allocation. Fixed Channel Allocation (FCA) is a technique in which cells are assigned a certain number of channels or voice channels. The channels cannot be altered after they have been assigned to certain cells. In FCA, channels are assigned in such a way that Frequency reuse is maximized. If a user makes a call and the cell is occupied, then the call is blocked. Borrowing the channels from other cells is a solution to this problem. Fixed channel allocation scheme is preferred in situations where there are a small number of fixed users having a steady flow of uniform network traffic. The allocation technique is simple and so it can avoid the overhead of complex algorithms. In addition, there is no interference between the users since each user is assigned a fixed channel which is not shared with others. Dynamic Channel Allocation is a channel allocation technique in which channels are not assigned to cells indefinitely. When a user requests a call, the Base Station (BS) sends the request to the Mobile Station Center (MSC) for channel or voice channel allocation. This reduces the chances of calls being blocked. As the volume of traffic grows, additional channels are assigned, and vice-versa. DCA adjusts the bandwidth allotment as per the traffic volume and hence it is particularly suitable for burst traffic. However, DCA schemes increase the computational as well as storage load on the system. The following table highlights the major differences between FCA and DCA. Key Fixed Channel Allocation (FCA) Dynamic Channel Allocation (DCA) Channel Allocation Cells are given a fixed number of channels or voice channels. Cells are not given a fixed number of channels. The number of channels to be allotted to each cell is not fixed initially. Blockage If all the channels are occupied, then user call is blocked. If all the channels are blocked, then the Base Station (BS) requests more channels from the Mobile Station Center (MSC).

Discuss architecture of GPRS (General Packet Radio System).

General Packet Radio System is also known as GPRS is a third-generation step toward internet access. GPRS is also known as GSM-IP that is a Global-System Mobile Communications Internet Protocol as it keeps the users of this system online, allows to make voice calls, and access internet on-the-go. Even Time-Division Multiple Access (TDMA) users benefit from this system as it provides packet radio access. GPRS also permits the network operators to execute an Internet Protocol (IP) based core architecture for integrated voice and data applications that will continue to be used and expanded for 3G services. GPRS supersedes the wired connections, as this system has simplified access to the packet data networks like the internet. The packet radio principle is employed by GPRS to transport user data packets in a structure way between GSM mobile stations and external packet data networks. These packets can be directly routed to the packet switched networks from the GPRS mobile stations. In the current versions of GPRS, networks based on the Internet Protocol (IP) like the global internet or private/corporate intranets and X.25 networks are supported. Following three key features describe wireless packet data:

  • The always online feature - Removes the dial-up process, making applications only one click away.
  • An upgrade to existing systems - Operators do not have to replace their equipment; rather, GPRS is added on top of the existing infrastructure.
  • An integral part of future 3G systems - GPRS is the packet data core network for 3G systems EDGE and WCDMA. GPRS attempts to reuse the existing GSM network elements as much as possible, but to effectively build a packet- based mobile cellular network, some new network elements, interfaces, and protocols for handling packet traffic are required. Therefore, GPRS requires modifications to numerous GSM network elements as summarized below:

GSM Network Element Modification or Upgrade Required for GPRS.

Mobile Station (MS) New Mobile Station is required to access GPRS services. These new terminals will be backward compatible with GSM for voice calls. BTS A software upgrade is required in the existing Base Transceiver Station (BTS). BSC The Base Station Controller (BSC) requires a software upgrade and the installation of new hardware called the packet control unit (PCU). The PCU directs the data traffic to the GPRS network and can be a separate hardware element associated with the BSC. GPRS Support Nodes (GSNs) The deployment of GPRS requires the installation of new core network elements called the serving GPRS support node (SGSN) and gateway GPRS support node (GGSN). Databases (HLR, VLR, etc.) All the databases involved in the network will require software upgrades to handle the new call models and functions introduced by GPRS.

GPRS Mobile Stations New Mobile Stations (MS) are required to use GPRS services because existing GSM phones do not handle the enhanced air interface or packet data. A variety of MS can exist, including a high-speed version of current phones to support high-speed data access, a new PDA device with an embedded GSM phone, and PC cards for laptop computers. These mobile stations are backward compatible for making voice calls using GSM. GPRS Base Station Subsystem Each BSC requires the installation of one or more Packet Control Units (PCUs) and a software upgrade. The PCU provides a physical and logical data interface to the Base Station Subsystem (BSS) for packet data traffic. The BTS can also require a software upgrade but typically does not require hardware enhancements. When either voice or data traffic is originated at the subscriber mobile, it is transported over the air interface to the BTS, and from the BTS to the BSC in the same way as a standard GSM call. However, at the output of the BSC, the traffic is separated; voice is sent to the Mobile Switching Center (MSC) per standard GSM, and data is sent to a new device called the SGSN via the PCU over a Frame Relay interface. GPRS Support Nodes Following two new components, called Gateway GPRS Support Nodes (GSNs) and, Serving GPRS Support Node (SGSN) are added: Gateway GPRS Support Node (GGSN) The Gateway GPRS Support Node acts as an interface and a router to external networks. It contains routing information for GPRS mobiles, which is used to tunnel packets through the IP based internal backbone to the correct Serving GPRS Support Node. The GGSN also collects charging information connected to the use of the external data networks and can act as a packet filter for incoming traffic. Serving GPRS Support Node (SGSN) The Serving GPRS Support Node is responsible for authentication of GPRS mobiles, registration of mobiles in the network, mobility management, and collecting information on charging for the use of the air interface. Internal Backbone The internal backbone is an IP based network used to carry packets between different GSNs. Tunneling is used between SGSNs and GGSNs, so the internal backbone does not need any information about domains outside the GPRS network. Signaling from a GSN to an MSC, HLR or EIR is done using SS7. Routing Area GPRS introduces the concept of a Routing Area. This concept is similar to Location Area in GSM, except that it generally contains fewer cells. Because routing areas are smaller than location areas, less radio resources are used While broadcasting a page message.