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Wireless Communication : Cellular Telephony
WIRELESS COMMUNICATTION AND INTERNET OF THINGS
WIRELESS COMMUNICATION
Author - Asst. Prof. G. A. Darandale
1.1 Overview of Wireless Communication
Wireless Communication:
Electromagnetic transfer of information between two or more points not connected by an electrical conductor.
Involves transmission of information over a distance without wires, cables, or other electrical conductors.
Common Technologies:
Most common wireless technologies use radio waves.
Cellular network or mobile network is a communication network where the last link is wireless, distributed over land areas called "cells".
CDMA System:
Cellular system based on CDMA (Coded Division Multiple Access) developed by Qualcomm, Inc.
Standardized by the Telecommunications Industry Association (TIA) as Interim Standard IS-95.
In the early 1990s, a new specialized Mobile Radio Service (MRS) was developed to compete with U.S. cellular radio carriers.
Mobile Internet Services:
Increasing penetration of laptop computers used by mobile users to access Internet services like E-mail and WWW.
Support of Internet services in a mobile environment is an emerging requirement.
Mobile IP is an Internet Protocol (IP) that allows IP nodes to change physical location without changing IP address, offering 'Nomadicity' to Internet users.
IMT-2000 Standard:
International Mobile Telecommunications-2000 (IMT-2000) standard developed by ITD for the third generation of mobile communication systems.
Consolidates different wireless environments (e.g., cellular mobile, cordless telephony, satellite mobile services) under a single standard.
Ensures global mobility with seamless roaming and delivery of services.
European Telecommunication Standards Institute (ETSI) developed Universal Mobile Telecommunication System (UMTS), part of the IMT-2000 family.
Chapter Content:
Explains cellular telephony system, cellular telephony generations, and GSM, GPRS systems.
1.2 Introduction of Cellular Telephony System
Development:
Developed by AT&T Bell Laboratories, USA in 1947.
First tests conducted in 1962 for commercial applications.
Cellular Radio Systems:
Rely on intelligent allocation and reuse of channels throughout a coverage region.
Each base station is allocated a group of radio channels within a small geographic area called a cell.
Cell:
A small geographic coverage area of a base station with a diameter of 2 to 50 km.
Represents the coverage area of a base station.
Channel Allocation:
Base stations in adjacent cells are assigned different channel groups to avoid interference.
Antenna Design:
Base station antennas are designed to achieve desired coverage within the cell.
Frequency Reuse:
Limiting the coverage area to within the boundaries of a cell allows the same group of channels to be used in different cells.
Cells are separated by distances large enough to keep interference levels within tolerable limits.
Geometric Shape of a Cell:
Should cover the entire region of radio coverage without overlap and have equal area of coverage.
Sensible choices: square, equilateral triangle, hexagon.
Hexagon is the best choice as it covers the largest area and approximates a circular radiation pattern.
Universally adopted for easy and manageable analysis of cellular measurements or propagation prediction models.
1.2.1 Frequency Reuse
Frequency Reuse:
Technique for using a specified range of frequencies more than once in the same radio system.
Increases the total capacity of the system without increasing its allocated bandwidth.
Space Division Multiplexing (SDM):
Used in mobile communication systems.
Three-dimensional SDM allows frequency reuse.
Interference Range:
If one transmitter is far away from another (outside the interference range), it can reuse the same frequencies.
Frequency Assignment:
Frequencies are assigned to certain users and blocked for others.
Frequencies are a scarce resource, and the number of concurrent users per cell is limited.
Cell Size:
Huge cells do not allow for more users; they are limited to fewer possible users per square kilometer.
Very small cells are used in cities where many more people use mobile phones.
1.2.2 Handoff Strategies
Call Transfer:
Automatic transfer of a call from one cell to another.
Provides mobility and continuous call service even when moving, e.g., in a car.
Roaming:
Movement of a wireless station from one access point to another for uninterrupted service.
Term "handover" or "handoff" refers to the change of the active cell.
Mobile Telephone Switching Office (MTSO):
Controls all cells and provides the interface between each cell and the main telephone office.
Routes telephone calls through MTSO and the standard telephone system.
Cell Transceiver:
Serves the mobile phone during a call.
System automatically switches from one cell to the next as the mobile phone owner moves.
Handling:
Transfer of a call in progress from one cell to another.
Receiver in each cell base station continuously monitors the signal strength of the mobile unit.
Optimum transmission and reception monitored by the computer at MTSO.
Channel Allocation:
Cellular carriers and frequencies are allocated with channels.
Control channels are used to allocate noise channels to mobile phones.
Call Setup:
When a user dials a phone number, the phone scans all control channel frequencies to find the strongest frequency.
Control channel is associated with the closest cell site.
Mobile phone transmits on its corresponding channel, and the cell site assigns a clear voice channel once the call is set up.
Signal strength is continuously monitored to ensure the strongest signal during the conversation, similar procedure for incoming calls.
1.2.3 Co-channel and Adjacent Channel Interference
Cellular System:
High-capacity land mobile system.
Frequency spectrum partitioned into discrete channels assigned in groups to geographic cells covering a Geographic Service Area (GSA).
Discrete channels can be reused in different cells within the service area.
Large geographic service area divided into cells with diameters from 2 to 50 km, each allocated a number of Radio Frequency (RF) channels.
Transmitters in adjacent cells operate on different frequencies to avoid interference.
Cells far apart can reuse the same set of frequencies without causing co-channel interference.
Theoretical coverage range and capacity of a cellular system are unlimited.
Additional cells can be added as demand for cellular mobile service grows.
Cells can be split to accommodate additional traffic.
Handoff Capability:
Cellular system provides the capability to handoff calls in progress as the mobile terminal (or user) moves between cells.
Co-channel Interference:
Occurs in mobile communications using time division multiplexing (TDM).
If two transmissions overlap in time, it is called co-channel interference.
Precise synchronization between different senders is required to avoid co-channel interference.
Adjacent Channel Interference:
Frequency division multiplexing (FDM) subdivides the frequency dimension into several non-overlapping frequency bands.
Each channel is allotted its own frequency band, allowing continuous use by senders.
Multiple signals sent simultaneously, each allocated a separate frequency band or channel.
Possibility of frequency band overlapping, called adjacent channel interference.
Guard spaces used in TDM and FDM to reduce co-channel and adjacent channel interference.
Guard spaces represent time gaps used to separate different periods when senders use the channel.
1.2.4 Block Diagram of Mobile Handset
Transmitter and Receiver:
Operate simultaneously with a single antenna.
Antenna types: quarter-wave monopole and half-wave dipole, connected through a matching inductor.
Duplexer separates transmitting and receiving signals.
Mobile Phone Antenna:
Wide 45 MHz frequency separation between transmit and receive frequencies simplifies frequency synthesizer design.
Microprocessor controls channel switching and power levels.
Additional functions: call timings, message storage, phone locking, storing called numbers, reminders.
FM Signal Processing:
Received FM signal is de-emphasized and expanded to drive the speaker.
Microphone transmits speech through compression and pre-emphasis with FM transmission.
Cellular Telephone Unit Components:
Transmitter
Receiver
Frequency synthesizer
Logic unit
Control unit
Transmitter:
Carrier generated by frequency synthesizer is phase modulated by amplified voice signal.
Phase modulator output is translated by a mixer and fed to power amplifiers.
Automatic Power Control (APC) circuit controls output power.
Duplexer circuit allows shared antenna for transmission and reception.
Receiver:
Dual conversion super heterodyne receiver.
Input signal translated to IF of 82.2 MHz, then to 10.7 MHz or 455 kHz.
Signal demodulated, filtered, amplified, and applied to speaker.
Receive Signal Strength Indicator (RSSI) sent back to cell site for handoff decisions.
Frequency Synthesizer:
Develops signals for transmitter and receiver.
Uses PLL circuits and mixer.
Reference frequency from crystal oscillator.
Produces a wide range of frequencies with high stability.
Logic Unit:
Contains main control circuitry: CPU, RAM, ROM, I/O interface, control logic.
Number Assignment Module (NAM) holds Mobile Identification Number (MIN).
Control Unit:
Interface unit for speaker, microphone, and LCD display.
1.3 Overview of Cellular Telephony Generations
1.3.1 Mobile Technology 1G to 5G
1G (First Generation):
Introduced in the early 1980s in the US.
Used analog signals for voice communication.
Characteristics: Speed up to 2.4 kbps, poor voice quality, large phones, limited battery life, no data security.
2G (Second Generation):
Launched in 1991 in Finland using GSM technology.
Used digital signals for the first time.
Characteristics: Data speed up to 64 kbps, text and multimedia messaging, better quality than 1G.
Introduction of GPRS technology enabled web browsing and email services, referred to as 2.5G.
3G (Third Generation):
Began in the early 2000s.
Characteristics: Data speed of 144 kbps to 2 Mbps, high-speed web browsing, video conferencing, multimedia emails.
Enhanced developments: Fast transfer of audio and video files, 3D gaming, but higher costs and infrastructure requirements.
Intermediate generation 3.5G grouped dissimilar mobile telephony and data technologies.
4G (Fourth Generation):
Introduced in 2011.
Characteristics: Speed of 100 Mbps to 1 Gbps, mobile web access, high-definition mobile TV, cloud computing, IP telephony.
5G (Fifth Generation):
Emerging technology, implemented in some countries.
Designed to connect virtually everyone and everything, including machines, objects, and devices.
Characteristics: Higher multi-Gbps peak data speeds, ultra-low latency, more reliability, massive network capacity, increased availability.
1.3.2 3G (W-CDMA, UMTS)
3G UMTS:
Uses WCDMA technology.
Provides mobile data connectivity and circuit-switched voice.
Two kinds: Wideband Code Division Multiple Access (W-CDMA) and Universal Mobile Telecommunications System (UMTS).
UMTS adds a new radio interface but relies on the same core network as GSM/GPRS.
1.3.3 4G (LTE)
LTE (Long-Term Evolution):
Standard for wireless broadband communication for mobile devices and data terminals.
Based on GSM/EDGE and UMTS/HSPA technologies.
Increases capacity and speed using a different radio interface and core network improvements.
LTE is the upgrade path for carriers with both GSM/UMTS and CDMA2000 networks.
Advantages: Fast download speeds, seamless web browsing, HD quality video and music streaming.
1.4 GSM (Global System for Mobile Communication)
Introduction:
GSM stands for Global System for Mobile Communication.
It is a European standard intended to replace analog systems in Europe.
Developed by the Group Special Mobile, an initiative of the Conference of European Post and Telecommunications (CEPT) administrations.
Work on the standard began in 1982, with the first full set of specifications (Phase 1) available in 1990.
Services:
Supports a range of basic and supplementary services, defined similarly to those for ISDN (Integrated Services Digital Network).
The most important service supported by GSM is telephony.
Other services include emergency calling and voice messaging.
Frequency Bands:
Uplink (mobile-to-base) frequency band: 890-915 MHz.
Downlink (base-to-mobile) frequency band: 935-960 MHz.
45 MHz spacing for duplex operation.
Uses TDMA (Time Division Multiple Access) and FDMA (Frequency Division Multiple Access).
The available 25 MHz spectrum is partitioned into 124 carriers (carrier spacing 200 kHz), each divided into 8 time slots (radio channels).
Popularity and Usage:
GSM is one of the most popular mobile communication standards.
Uses cellular networks.
Developed to solve fragmentation problems of the first cellular systems.
World's first cellular system to specify digital modulation and network-level architectures and services.
Development:
The Conference of European Postal and Telecommunications Administrations (CEPTA) began developing GSM standards for TDMA systems in June 1982.
1.4.1 Architecture
GSM System Architecture:
GSM is a hierarchical, complex system architecture with many entities, interfaces, and acronyms.
Consists of three subsystems: Radio Subsystem (RSS), Network and Switching Subsystem (NSS), and Operation Subsystem (OSS).
Mobile Station (MS) is also a subsystem, usually considered part of the BSS for architecture purposes.
Mobile stations communicate with the BSS over the radio air interface.
RSS consists of Base Station Controllers (BSCs) connected to Base Transceiver Stations (BTSs).
NSS consists of Mobile Services Switching Centers (MSCs), Home Location Registers (HLRs), and Visitor Location Registers (VLRs).
OSS consists of the Authentication Centre (AuC), Equipment Identity Register (EIR), and Operation and Maintenance Centre (OMC).
Frame Structure:
GSM uses Frequency Division Multiplexing (FDM) and Time Division Multiple Access (TDMA) frame structures.
FDM is used for simultaneous access to the medium by base station and mobile station.
Duplex channel allows simultaneous transmission in both directions, separated using different frequencies (Frequency Division Duplex, FDD).
Basic frequency allocation scheme for GSM is fixed and regulated by national authorities.
Uplink band: 890.2 to 915 MHz, Downlink band: 935.2 to 960 MHz.
Each channel (uplink and downlink) has a bandwidth of 200 kHz.
TDMA frame subdivides each 200 kHz carrier into frames repeated continuously.
Frame duration: 4.615 ms, subdivided into 8 time slots (577 µs each).
Data transmitted in small portions called bursts (546.5 µs long, 148 bits).
Guard space (30.5 µs) avoids overlapping with other bursts.
Each physical TDM channel has a raw data rate of about 33.8 kbit/s, each radio carrier transmits approximately 270 kbit/s over the Um interface.
Mobility Management:
GSM specifies two basic groups of logical channels: Traffic Channels (TCH) and Control Channels (CCH).
TCH used to transmit user data (e.g., voice, fax).
CCH used to control medium access, allocation of traffic channels, and mobility management.
Three groups of control channels: Broadcast Control Channel (BCCH), Common Control Channel (CCCH), and Dedicated Control Channel (DCCH).
BCCH transmits information like cell identifier, frequency hopping options, and available frequencies.
CCCH responsible for transferring control information between mobiles and BTS.
DCCH is bidirectional, used for call setup, authentication, location updating, and SMS point-to-point.
1.5 GPRS (General Packet Radio Services)
Introduction:
GPRS provides packet mode transfer for applications with traffic patterns like frequent transmission of small volumes.
It is a flexible and powerful data transmission scheme.
Uses existing network resources efficiently for packet mode applications.
Allows for broadcast, multicast, and unicast services.
Main benefit: No connection setup necessary before data transfer, but requires additional hardware and software.
Time Slots:
GSM system can allocate between one and eight time slots within a TDMA frame for GPRS radio channels.
Time slots are allocated on demand, not in a fixed manner.
GPRS concept is independent of channel characteristics and does not limit the maximum data rate.
All GPRS services can be used in parallel with conventional services.
Services:
Offers point-to-point (PTP) packet transfer services.
Users can specify quality of service profile, determining service precedence, reliability class, and delay class of transmission.
Includes security services like authentication, access control, user identity confidentiality, and user information confidentiality.
Allows for anonymous services, e.g., road toll systems charging users via MS independent of their identity.
1.5.1 Architecture
GPRS Architecture:
Packet data transmitted from a PDN, via the GGSN and SGSN, to the BSS and finally to the MS.
MSC used for signaling in GPRS, not for data transport.
Additional interfaces to further network elements and other PLMNs.
MS attached by following mobility management procedures before sending data over GPRS.
Attachment procedure includes assigning a temporary logical link identity (TLLI) and a ciphering key sequence number (CKSN) for data encryption.
GPRS context set up and stored in the MS and corresponding SGSN, including status, CKSN, compression flag, and routing data.
Mobility Management:
Functions for authentication, location management, and ciphering.
In idle mode, MS is not reachable, and all context is deleted.
In standby state, only movement across routing areas is updated to the SGSN.
In ready state, every movement of the MS is indicated to the SGSN.
Characteristics:
Mobility: Constant voice and data communications while on the move.
Immediacy: Connectivity when needed, regardless of location, without lengthy login sessions.
Localization: Information relevant to the current location.
1.5.2 Applications
Communications:
E-mail, fax, unified messaging, intranet/internet access.
Value-added services like information services and games.
E-commerce:
Retail, ticket purchasing, banking, financial trading.
Location-based Applications:
Navigation, traffic conditions, airline/rail schedules, location finder.
Other Applications:
Freight delivery, fleet management, sales-force automation.
Advertising: Location-sensitive advertising for shops, malls, dispensaries, and hotels.
SMS, MMS, and voice calls.
Closed User Group (CUG) and supplementary services like Call Forwarding Unconditional (CFU) and Call Forwarding on Mobile Subscriber Not Reachable (CFNRc).
THINK OVER IT...
A. Applications of GPRS in Day-to-Day Life
GPRS (General Packet Radio Services) has opened up a wide range of applications for mobile users. Here are some common uses:
Communications:
E-mail, fax, unified messaging, and intranet/internet access.
Non-voice services like SMS, MMS, and voice calls.
Value-Added Services:
Information services and games.
E-commerce:
Retail, ticket purchasing, banking, and financial trading.
Location-Based Applications:
Navigation, traffic conditions, airline/rail schedules, and location finder.
Vertical Applications:
Freight delivery, fleet management, and sales-force automation.
Advertising:
Location-sensitive advertising, such as receiving ads specific to stores in a mall.
B. Characteristic Features and Technical Specifications of Mobile Phones
To find the characteristic features and technical specifications of mobile phones, you can refer to the manual provided with your device. Here are some common specifications to look for:
Processor:
Speed (GHz) and number of cores.
Memory:
RAM and internal storage capacity.
Display:
Screen size, resolution, and type (e.g., AMOLED, LCD).
Camera:
Megapixels, aperture, and additional features like optical image stabilization.
Battery:
Capacity (mAh) and estimated battery life.
Connectivity:
Support for 2G, 3G, 4G, and 5G networks, Wi-Fi, Bluetooth, and NFC.
Operating System:
Version of Android, iOS, or other operating systems.
C. Mobile Network Information in India
India has several mobile service providers offering various network services. Some of the major providers include:
Jio:
Offers 4G LTE services and is the largest mobile network provider in India.
Airtel:
Provides 2G, 4G LTE, and 4G+ data services.
Vodafone Idea (VI):
Offers 2G, 4G LTE, and 4G+ data networks.
BSNL:
Government-owned, providing mobile voice and internet services.
D. Similarities and Advanced Features in 4G and 5G Networks
Similarities:
Both 4G and 5G networks provide high-speed data transfer and support for mobile internet access.
Both use OFDM (Orthogonal Frequency Division Multiplexing) for signal modulation.
Advanced Features of 5G:
Higher Speeds: 5G offers significantly faster data speeds compared to 4G.
Lower Latency: 5G has much lower latency, making it ideal for real-time applications like gaming and video conferencing.
Increased Capacity: 5G can support a larger number of connected devices simultaneously.
Enhanced Connectivity: 5G enables new applications like IoT (Internet of Things), smart cities, and autonomous vehicles.
E. Justification: "Smart Mobile Phone is the Ultimate Electronic Application Device"
Smart mobile phones have become indispensable in modern life due to their versatility and wide range of applications. Here are some reasons why they are considered the ultimate electronic application device:
Communication:
Instant messaging, voice and video calls, and social media connectivity.
Productivity:
Access to emails, calendars, document editing, and collaboration tools.
Entertainment:
Streaming services for music, movies, and TV shows, as well as gaming.
Navigation:
GPS and mapping services for real-time directions and traffic updates.
Photography and Videography:
High-quality cameras for capturing photos and videos.
Health and Fitness:
Apps for tracking fitness activities, monitoring health metrics, and providing workout routines.
E-commerce:
Online shopping, banking, and financial transactions.
Smart Home Integration:
Control of smart home devices like lights, thermostats, and security systems.
# Summary of Wireless Technologies and Cellular Networks
Wireless Technologies:
Most common wireless technologies use radio waves.
Cellular networks are communication networks where the last link is wireless.
Cellular Network Structure:
Relies on intelligent allocation and reuse of channels.
Uses hexagon geometry for efficient coverage.
Cell sites are connected by copper cable, fibre optics, or microwave links to a Mobile Switching Centre (MSC) or Mobile Telephone Switching Office (MTSO).
Calls between mobiles go through a cell site and MSC; landline communications go through PSTN.
Frequency Reuse and Roaming:
Frequency reuse increases system capacity without increasing bandwidth.
Roaming allows uninterrupted service as users move between access points.
Handoff transfers calls in progress from one cell to another.
Cellular System Principles:
Divides large geographic areas into cells with diameters from 2 to 50 km.
Uses guard spaces in TDM and FDM to reduce interference.
Theoretical coverage range and capacity are unlimited.
Mobile Communication:
Uses time division multiplexing (TDM) to avoid co-channel interference.
Mobile phones are full duplex transceivers with quarter-wave monopole and half-wave dipole antennas.
Mobile units have a Programmable Read Only Memory (PROM) chip called Number Assignment Module (NAM) with a Mobile Identification Number (MIN).
Evolution of Cellular Networks:
1G: First generation, analog signals.
2G: Second generation, digital signals, introduction of GPRS (2.5G).
3G: Data speeds of 144 kbps to 2 Mbps, high-speed web browsing, video conferencing.
4G: Speeds of 100 Mbps to 1 Gbps, mobile web access, high-definition mobile TV, cloud computing.
5G: Higher multi-Gbps speeds, ultra-low latency, massive network capacity, increased availability.
3G and 4G Technologies:
3G UMTS: Uses WCDMA technology, provides mobile data connectivity and circuit-switched voice.
UMTS: Successor to GSM, uses wideband CDMA.
LTE: Standard for wireless broadband communication, upgrade path for GSM/UMTS and CDMA2000 networks.
4G LTE: Fast download speeds, seamless web browsing, HD video and music streaming.
GSM and GPRS:
GSM: Global System for Mobile, supports telephony and supplementary services.
GPRS: Provides packet mode transfer for applications with frequent small data transmissions, no connection setup needed, supports parallel conventional services.
Exercises
Q1. Short answer questions:
What is mobile communication?
Mobile communication refers to the technology that allows users to communicate with each other wirelessly using mobile devices such as smartphones and tablets.
What are the limitations of conventional mobile telephone systems?
Limited coverage area, poor voice quality, limited data transmission capabilities, and high susceptibility to interference.
What is a cell in a cellular radio system?
A cell is a geographic area covered by a base station in a cellular network. It is the basic unit of a cellular system.
Why is the hexagonal cell preferred over others in the cellular concept?
The hexagonal cell is preferred because it provides the largest area coverage for a given distance between the center and the farthest perimeter points, allowing efficient coverage with fewer cells.
Explain the basic principle of the cellular system.
The basic principle of the cellular system is to divide a large geographic service area into smaller cells, each with its own base station, to efficiently use the available radio frequencies and provide seamless communication.
State the advantage of frequency reuse in mobile network cells.
Frequency reuse allows the same range of frequencies to be used multiple times within the same network, increasing the system's capacity without requiring additional bandwidth.
What are the advantages of handover?
Handover ensures uninterrupted service by transferring an ongoing call or data session from one cell to another as the user moves, maintaining a strong signal and connection quality.
What is call handling in a mobile communication system?
Call handling refers to the process of managing calls, including call setup, maintenance, and termination, as well as transferring calls between cells during handover.
What is the role of guard spaces used in TDM?
Guard spaces in Time Division Multiplexing (TDM) are used to prevent overlapping of signals from different time slots, reducing interference and ensuring clear communication.
List the salient features of GSM.
Digital modulation, support for voice and data services, international roaming, encryption for security, and efficient use of spectrum through TDMA and FDMA.
List the characteristics of the GSM standard.
High-quality voice calls, support for SMS and MMS, international roaming, secure communication, and compatibility with various frequency bands.
What is a 4G mobile network?
A 4G mobile network is the fourth generation of mobile communication technology, offering high-speed data transfer, improved network capacity, and support for advanced services like HD video streaming and mobile internet.
State features of the LTE network.
High data transfer speeds, low latency, increased capacity, improved spectral efficiency, and support for seamless handover between different network types.
Which wide channel is used by UMTS?
UMTS uses a wideband version of CDMA occupying a 5 MHz wide channel.
"4G LTE network provides fast download speed", Comment.
4G LTE networks offer significantly faster download speeds compared to previous generations, enabling quick access to large files, seamless streaming of high-definition content, and improved overall user experience.
What is GPRS? Write its salient features.
GPRS (General Packet Radio Services) is a packet-based data service for mobile networks. Salient features include efficient use of network resources, support for point-to-point and point-to-multipoint services, and the ability to use GPRS services alongside conventional services.
“All GPRS services can be used in parallel to conventional services”, Comment.
GPRS services can be used simultaneously with conventional voice and SMS services, allowing users to access data services without interrupting ongoing calls or messages.