Unit-1 Introduction to Wireless Communication

Q 1: Explain in brief Basic Cell Fundamentals in wireless communication.

1. The early mobile radio systems achieved a large coverage area by using a single, high-powered transmitter with an antenna mounted on a tall tower.
2. This approach achieved very good coverage, but it was impossible to reuse the frequencies.
3. The cellular concept offered very high capacity in a limited spectrum by reusing frequencies.
4. In cellular system the coverage area is divided into (conceptually hexagonal) cells. A low power transmitter provides coverage to a cell. The actual radio coverage of a cell is known as the footprint and is amorphous in nature.
5. Each base station is allocated a portion of the total number of channels available to the entire system. Nearby base stations are assigned different groups of channels to reduce interference. All the available channels are assigned to a small number (called cluster size) of neighboring base stations.
6. The channel groups may be reused as many times as necessary, as long as the interference between co-channel stations is kept below acceptable levels.
7. As the demand for service increases (i.e., as more channels are needed within a particular market), the number of base stations may be increased(along with a corresponding decrease in transmitter power to avoid added interference),
   thereby providing additional radio capacity without additional radio spectrum. Any regular polygon, such as an equilateral triangle, a square or a hexagon can be used for cell design.

Criteria for shape of a cell: –

• Area without overlap
• Geometric shape and
• Area of cell

The hexagon is used for two reasons:
• First a hexagonal layout requires fewer cells and therefore, fewer transmitter sites
and
• Second a hexagonal cell layout is less expensive compared to square and
triangular cells.

Q 2: Explain the following terms used in wireless communication

• Mobile Station (MS): A mobile station or simply mobile is a radio terminal that may be attached to a high speed mobile platform (e.g. a cell phone in a fast moving vehicle). It is also called User Equipment (UE).
• Subscriber: A mobile or a portable user.
• Cell: The area of coverage is divided into cells. Each cell has a base station usually located at its center or at the edge.
• Control Channel: Radio channels used for transmission of call setup, call request and call initiation. Control channels intended to carry signaling and synchronization data between base station and mobile user.
• Forward Channel (downlink): Radio channel used for transmission of information from the base station to the mobile.
• Reverse Channel (uplink): Radio channel used for transmission of information from the mobile to the base station.
• Base Station : A base station is a common term used in telecommunications for a radio receiver with one or more antennae. While the base station has many other applications, it’s often used for mobile telephony, wireless communications, and even wireless computer networking. A base station works as the main communication point for one or more wireless mobile devices. It is a fixed transceiver capable of sending and receiving wireless signals via the radio frequency (RF) base station antennas to transmit RF signals
  to other devices.

• Page: Page is a brief message that is broadcast over the entire service area by many base stations at the same time primarily to locate where the mobile station is.
• Transceiver: A device capable of transmitting and receiving radio signals.
• Forward Voice Channel (FVC): Used for voice transmission from BS to MS.
• Reverse Voice Channel (RVC): Used for voice transmission from MS to BS.
• Mobile Switching Center(MSC): The MSC is used to provide route to all the calls in large service area. It is the base of cellular communication system as it manage or control all the services within the system

Functions:

1. Switching of calls between subscriber
2. Switching sms between subscriber
3. Tracking of BSC location of subscriber
4. Subscriber authentication and info.
5. Billing management of each subscriber

Q 3: Describe the operation of basic cellular system with neat sketch.

In a cellular system, the entire region is divided into regular hexagonal patterns called as cells. The area covered by the cell is called Cell Size and there is no standard fixed value defined for this. It varies from service provider to service provider. The cell size ranges from 10 Km to 50 Km based on the population in that area. Figure shows the basic structure and elements of a cellular system.

Elements Of a Cellular system

1. A cellular system consists of three important elements. They are: Mobile Stations (MS), Base Stations (BS) and Mobile Switching Centre (MSC).
2. Mobile Station commonly called as cell phone is a transmitting/receiving portable station in the cellular Radio service used for communication. Mobile stations may be hand held (portable units) or installed in vehicles (mobiles).
3. A base Station/Cell site refers to a fixed station used for radio communication with mobile stations. Base stations are located at the center or edge of the cell. It consists of transmitter and receiver antennas mounted on a tower and some circuitry to process the mobile signals.
4. Initially the cell sites were designed to cover a radius of 10 miles (16 Kms) or more. The transmitted signal power and height of the antenna determines the final cell size.
5. Mobile Switching Centre/ Mobile Telephone Switching Office (MSC/MTSO): In a cellular radio system, MSC is very important element which connects the cellular Base Stations and the mobiles to the Public Switched Telephone Network (PSTN). MSC coordinates the routing of calls in a large service area and does very important functions such as finding frequency channels, provides billing information etc.

Control and Voice Channels

1. The BS, MSC and PSTN communicate with each other using wired connectivity. The wireless connection is only between the Base Station and Mobile Station. A full Duplex communication exists between these two entities. Both are connected to each other by a pair of voice channels or control channels.
2. Control Channels refer to the radio channels used for transmission or reception of call set up, call requests, call initiation and other beacon or control purposes.
3. Voice Channels are radio channels used for transmission or reception of actual information from subscriber (user).
4. Bandwidths of these channels vary from technology to technology. For example, 1G technology AMPS uses 30 KHz as each channel’s bandwidth. 2G technology GSM uses 200 KHz as each channel’s bandwidth.
5. The channels used for transmission from Base station to the mobile are called Forward Channels or Downlink Channels. The channels used for transmission from Mobile station to the Base Station are called Reverse Channels or Uplink Channels.

The forward channel frequency is always higher than the Reverse channel
frequency by 45 MHz.

This is due to the reason that higher frequencies require higher processing power. The mobile station side which is portable has to work on limited power levels. Hence the lower spectrum out of the two bands is assigned for the mobile station transmission. Also, Duplexers available in those days could separate out the transmitted and received frequencies with minimum interference only if both were at a minimum frequency separation of 45 MHz Channel connectivity between MS and BS is illustrated in Figure.

There are four channels using which a mobile can communicate with the Base station. They are namely, FCC, RCC, FVC, RVC. The Reverse Control Channel carries signaling information like call requests or call termination from Mobile Station to Base station.

The Forward Control channel carries signaling information like Power control, information of channels etc. from Base station to Mobile station.

The Forward and Reverse Voice Channels carry the desired voice signals
between MS and BS.

Advantages of cellular system:

1. Higher capacity-Smaller the size of the cell more the number of concurrent users i.e. huge cells do not allow for more concurrent users.
2. Less transmission power-Huge cells require a greater transmission power than small cells.
3. Local interference only-For huge cells there are a number of interfering signals, while for small cells there is limited interference only.
4. Robustness-As cellular systems are decentralized, they are more robust against the failure of single components.

Q 4: Explain in brief Evolution of Mobile Communication.

Mobile communications standards had to evolve to support more users.

1. First Generation (1G)

• In 1979, the Japanese telecommunications provider Nippon Telephone and Telegraph Company (NTT) deployed the first generation of wireless communication, known today as 1G.
• In this technology voice call get modulated to higher frequency of about 150 MHz .
• Because 1G network used analog signals, the technology was severely limited. Rather than encoding voice calls into digital signals, the audio was modulated to a higher frequency that degraded the quality of the signal over time and space.
• In 1G technology voice channel is transmitted with FM modulation.
• Access method of 1G technology is FDMA(Frequency division multiple access)
• It allows users to make voice calls only
• This technology commercially introduced in US in1980s as AMPS (Advanced Mobile Phone Service).

Key Features of 1G

• Bandwidth: 10MHz
• Speed: 2.4Kbps
• Frequency: 800MHz, 900MHz
• Channel capacity: 30KHz

Disadvantages of 1G

• Unable to interoperate between countries
• Unreliable handoff
• Signal interference issues
• Little protection against hackers
• Poor voice quality, poor battery life
• Large phone size
• No security

2. Second Generation (2G)

• The second generation in the evolution of wireless communication introduced a new digital technology known as Global System for Mobile communication (GSM), which became the standard in future generations of wireless communication.
• This technology is fully digital.
• GSM technology enabled digital voice and data to be sent across the network, rather than relying on analog radio signals, in the early 1990s.
• 2G technology uses TDMA and few uses CDMA

Key Features of 2G

• Bandwidth: 30–200KHz
• Speed: Up to 64Kbps
• SMS and MMS messaging
• Roaming
• Billing based on services used, e.g., long-distance calls

Disadvantages of 2G

• Low data rate
• Few features on mobile phones and devices
• Limited number of users

2.5G and 2.75G

• Between the year 2000 and 2003, an upgrade in technologies introduced the packet network which provided high speed data transfer and internet and became known as 2.5G and 2.75G.
• The standards included GPRS (General Packet Radio Service) and EDGE(enhanced Data Rates in GSM).
• GPRS supports flexible data transmission rates and provides continuous connection with the network. It also allows for the service provider to charge for the amount of data that is sent rather than their connection time.

3. Third Generation (3G)

• 2G network were built mainly for voice calls, sms, data and slow transmission. But due to rapid changes in user expectation they do not meet today’s wireless need.
• 3G network provides the ability to transfer voice data and non voice data over the same network simultaneously.
• The introduction of UMTS (Universal Mobil Telecommunication Systems) launched the third generation of wireless communications, which could transmit more significant amounts of data at higher speeds.
• 3G mobile communication enabled the global popularity of smartphones. Specific applications were developed to utilize newer capabilities, such as multimedia chat, email, video calling, social media and mobile games.
• The access method Uses W-CDMA.

Key Features of 3G

• Bandwidth: 15–20 MHz
• Speed: Up to 14Mbps
• Higher data rate
• Video calling
• Mobile app support
• Multimedia message support
• Location tracking
• Improved web browsing
• TV streaming

Disadvantages of 3G

• Costly infrastructure, equipment and implementation
• Expensive mobile devices
• Higher bandwidth requirements to enable faster data transmission

4. Fourth Generation (4G)

• The 4G network is an enhanced version of 3G networks, developed by the Institute of Electrical and Electronics Engineers (IEEE) to provide even higher data rates while handling more advanced multimedia features.
• In addition, 4G networks also use a cutting-edge technology known as Long-Term Evolution (LTE) while remaining compatible with previous generations of mobile communication for easier deployment.
• 4G is a very different technology as compared to 3G and was made possible practically only because of the advancements in the technology in the last 10 years.
• Its purpose is to provide high speed , high quality and high capacity to users while improving security

Key Features of 4G

• Bandwidth: 15–20 MHz
• Speed: Up to 1Gbps
• Interactive multimedia, voice and video calling
• High definition video streaming and gaming
• Enhanced security and mobility
• Reduced latency

Disadvantages of 4G

• Costly infrastructure, hardware
• Expensive mobile devices compatible with 4G required
• Time-consuming deployment and upgrade

5. Fifth Generation (5G)

• As the latest stage in the evolution of mobile communication, 5G addresses one of the biggest challenges of wireless technology: latency, or the time it takes for an amount of data to be transmitted from one point to another.
• 5G technologies allows for high-speed data transmission to support the Internet of Things (IoT), which describes physical objects that use sensors, processing ability, software and other technologies to connect with other devices and exchange data.
• It enables a new kind of network design to connect virtually everyone and everything together including machines, object and devices.

Key Features of 5G

• Speed: 1–10Gbps (in lab conditions)
• Interactive multimedia, voice and video calling
• High-definition video streaming and gaming
• Enhanced security and mobility
• Reduced latency in milliseconds

Disadvantages of 5G

Costly infrastructure, hardware
Expensive mobile devices compatible with 4G required
Time-consuming deployment and upgrade

Uses of 5G

• Industrial automation,
• Doctors using robots to perform surgery remotely,
• Smart TVs that need a very high amount of data,
• Internet of Things,
• Autonomous vehicles

Q 5: Explain
i) Fixed channel assignment strategy.
ii) Dynamic channel assignment strategy.

An optimum Frequency Reuse scheme helps in increasing Capacity and reducing interference. The Radio Spectrum has to be efficiently utilized. To meet these objectives, a number of channel assignment strategies have been suggested. They are: Fixed Channel and Dynamic Channel assignment strategies.

1. Fixed Channel Assignment Strategies:

● In the fixed channel assignment method, each cell is assigned a predetermined set of voice channels.
● Any call attempt can only be served by the unused channels within the same cell.
● If all the channels in the cell are occupied, the call is blocked and the subscriber does not receive any service.
● However, in a particular version of fixed channel assignment strategy, called as the borrowing strategy, a cell is allowed to borrow channels from its neighboring cells in case of scarcity of the channels.
● The MSC supervises such borrowing procedures and ensures that this
procedure does not interfere with any of the calls in progress.

2. Dynamic Channel Assignment Strategies:
● In this strategy, permanent allocations of voice channels to individual cells are not done. The entire pool of channels is in the MSC’s control.
● Whenever there is a call request, the base station requests a channel from the MSC.

A channel is allotted after monitoring the following: -Likelihood of future blocking within the cell. -The reuse distance of the channel. -Rate at which the channel is being allotted and other cost functions.

● The MSC only allocates a given frequency if that frequency is not presently in use in the cell or any other cell which falls within the minimum restricted distance of frequency reuse to avoid co-channel interference.
● Thus, this channel assignment strategy reduces the likelihood of blocking.
● Dynamic channel assignment strategies require the MSC to collect real-time data on channel occupancy, traffic distribution, and Radio Signal Strength Indications (RSSI) of all channels on a continuous basis. As number of subscriber’s increases, the storage and computational load on the system also increases. However, it provides the advantage of increased channel utilization and decreased probability of a blocked call. Most of the 1G cellular operators, opt for a static channel assignment scheme with channel borrowing provisions.

Comparison between FCA and DCA channel assignment strategies

Q 6: Compare 1G, 2G, 3G and 4G of cellular mobile system

Q 7: Difference between Simplex, Half duplex and Full Duplex Transmission Modes

S. No.	Parameters	Simplex	Half Duplex	Full Duplex
1.	The direction of communication	Simplex mode is a uni-directional communication.	Half Duplex mode is a two way directional communication but one at a time.	Full Duplex mode is a two way directional communication simultaneously.
2.	Sender and Receiver	In simplex mode, Sender can send the data but that sender can’t receive the data.	In Half Duplex mode, Sender can send the data and also can receive the data but one at a time.	In Full Duplex mode, Sender can send the data and also can receive the data simultaneous.
3.	Channel usage	Usage of one channel for the transmission of data.	Usage of one channel for the transmission of data.	Usage of two channels for the transmission of data.
4.	Performance	The simplex mode provides less performance than half duplex and full duplex.	The Half Duplex mode provides less performance than full duplex.	Full Duplex provides better performance than simplex and half duplex mode.
5.	Bandwidth Utilization	Simplex utilizes the maximum of a single bandwidth.	The Half Duplex involves lesser utilization of single bandwidth at the time of transmission.	The Full Duplex doubles the utilization of transmission bandwidth.
6.	Suitable for	It is suitable for those transmissions when there is requirement of full bandwidth for delivering data.	It is suitable for those transmissions when there is requirement of sending data in both directions, but not at the same time.	It is suitable for those transmissions when there is requirement of sending and receiving data simultaneously in both directions.
7.	Examples	Example of simplex mode is: Keyboard and monitor.	Example of half duplex mode is: Walkie-Talkies.	Example of full duplex mode is: Telephone.