Unit - 1

Introduction to Wireless Communication Systems

1.1 Evolution of mobile radio communications

The history of wireless follows following hierarchy. After the Second World War many national and International projects in the area of wireless communications were triggered off.

In ancient times the light was modulated either ON or OFF pattern used for wireless communication. Flags were used to signal code words. Smoke signals were used in wireless communication as early as 150 BC

• In 1982 the European Conference of Postal and Telecommunications Administrations founded working group.
• In 1987 the Global System for Mobile communications standard was available
• In 1991 in Switzerland the first devices are presented
• In 1995SMS was available
• In 1998, Universal Mobile Telecommunication Systems (UMTS) developed by Europeans.
• In 1999, the 802.11b, Bluetooth was standardized.
• In 2000, General Packet Radio Service (GPRS) IEEE802.11a was developed
• In 2001, International Mobile Telecommunications (IMT – d-2000) was standardized
• The year 2007, is the fourth generation the Internet based.

Key takeaway

The development in the wireless system is explained. Old times used light On and OFF for wireless communication.

1.2 Examples of wireless comm systems

WiFi

• Wifi (also WiFi, Wi-fi or wifi), is a brand originally licensed by the Wi-Fi Alliance to describe the underlying technology of wireless local area networks (WLAN) based on the IEEE 802.11 specifications.
• Wi-Fi was intended to be used for mobile computing devices, such as laptops, in LANs, but is now often used for increasingly more applications, including Internet and VoIP phone access, gaming, and basic connectivity of consumer electronics such as televisions and DVD player
• The typical Wi-Fi setup contains one or more Access Points (APs) and one or more clients. An AP broadcasts its SSID (Service Set Identifier, "Network name") via packets that are called beacons, which are broadcast every 100 ms. The beacons are transmitted at 1 Mbit/s, and are of relatively short duration and therefore do not have a significant influence on performance. Since 1 Mbit/s is the lowest rate of Wi-Fi it assures that the client who receives the beacon can communicate at least 1 Mbit/s.

Bluetooth

• Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances (using short wavelength radio transmissions) from fixed and mobile devices, creating personal area networks (PANs) with high levels of security
• It was originally conceived as a wireless alternative to RS-232 data cable
• Bluetooth is a high-speed, low-power microwave wireless link technology, designed to connect phones, laptops, PDAs and other portable equipment together with little or no work by the user
• Bluetooth is the name for a short-range radio frequency (RF) technology that operates at 2.4 GHz and is capable of transmitting voice and data
• It is also known as the IEEE 802.15 standards. 
• Bluetooth is more suited for connecting two point-to-point devices, whereas Wi-Fi is an IEEE standard intended for networking
• Operates at 2.4 GHz and is capable of transmitting voice and data. The effective range of Bluetooth devices is 32 feet (10 meters). Bluetooth transfers data at the rate of 1 Mbps

Satellite systems, mobile networks

Satellites are used to transfer information from one place to another using communication satellite on Earth’s orbit. Satellite communication began in 1957 and the first artificial satellite launched was Sputnik I by the USSR. The satellite communication can be one way as well. In this case the transmission of signal from the transmitter of first earth satellite and the receiver of the second earth satellite is in one direction.

In two-way communication the information is exchanged between the two earth stations. There are two uplinks and two downlinks required to achieve two ways communication.

The main elements of communication satellite are

i)                   Uplink

Ii)                 Transponders

Iii)              Downlink

The block diagram of satellite communication is shown below. A communication satellite is basically a R.F repeater.

Fig 1 Block Diagram of Satellite Communication

The uplink frequencies used are of range 5.9GHz-6.4GHz these frequencies are converted to lower frequencies and amplified. The mixers and local oscillators are used to convert the higher frequency uplink signals to lower frequency signals. The com satellite receives this signal amplifies it and then transmits it so that there is no interference in the uplink and down link signals.

The transponders provide the medium for two-way communication. The downlink frequency used for transmission is from the range of 3.7GHz to 4.2GHz. The number of transponders per satellite depends upon the task which the satellite needs to do. For television broadcast two transponders are used in a satellite.

Advantages

The advantages of satellite communication are

• They are easy to install.
• The communication can be set up in every part of earth with the help of satellites.
• The network is controlled by the user.
• The elasticity of these circuits is excellent

Applications

The applications of satellite communication are

• Telephone
• Television
• Digital cinema
• Radio broadcasting
• Amateur radio
• Internet access
• Military
• Disaster Management

Radio astronomy and remote sensing

• CORF has a substantial interest in this proceeding, as it represents the interests of the scientific users of the radio spectrum, including users of the RAS and the EESS bands. Both RAS and EESS observers perform extremely important, yet vulnerable research d by scientists to study our universe. It was through the use of radio astronomy that scientists discovered the first planets outside the solar system, circling a distant pulsar. Measurements of radio spectral line emission have identified and characterized the birth sites of stars in our own galaxy, and the complex distribution and evolution of galaxies in the universe. Radio astronomy measurements have discovered ripples in the cosmic microwave background, generated in the early universe, which later formed the stars and galaxies we know today.
• Observations of supernovas have allowed us to witness the creation and distribution of heavy elements essential to the formation of planets like Earth, and of life itself. The EESS is a critical and unique resource for monitoring Earth’s global atmospheric and surface state. Satellite-based microwave remote sensing represents the only practical method of obtaining uniform-quality atmospheric and surface data encompassing the most remote oceans as well as densely populated areas of Earth. EESS data have contributed substantially to the study of meteorology, atmospheric chemistry, oceanography, and global change.
• Currently, instruments operating in the EESS bands provide regular and reliable quantitative atmospheric, oceanic, and land measurements to support an extensive variety of scientific, commercial, and government (civil and military) data users. Applications of the data include aviation forecasts, hurricane and severe storm warning and tracking, seasonal and interannual climate forecasts, decadal scale monitoring of climate variability, medium-range forecasting, and studies of the ocean surface and internal structure, as well as many others. The emissions that radio astronomers study is extremely weak--a typical radio telescope receives only about one-trillionth of a watt from even the strongest cosmic source.
• Because radio astronomy receivers are designed to pick up such remarkably weak signals, such facilities are therefore particularly vulnerable to interference from spurious and out-of-band emissions from licensed and unlicensed users of neighboring bands, and those that produce harmonic emissions that fall into the RAS bands. Similarly, the emissions received by passive EESS radiometers in Earth orbit are weak by comparison with emissions from other services. In addition to the gains in scientific knowledge that result from radio astronomy and Earth sensing, CORF notes that such research enables technological developments that are of direct and tangible benefit to the public.
• For example, radio astronomy techniques have contributed significantly to major advances in the following areas: --Computerized tomography (CAT scans) as well as other technologies for studying and creating images of tissue inside the human body; --Abilities to forecast earthquakes by very-long-baseline interferometric (VLBI) measurements of fault motions; and --Use of VLBI techniques in the development of wireless telephone geographic location technologies, which can be used in connection with the Commission’s “E911” requirements.
• Continued development of new critical technologies enabled by passive scientific observation of the spectrum depends on scientists having continued access to interference-free spectrum. More directly, the underlying science undertaken by RAS and EESS observers cannot be performed without access to interference-free spectrum. Loss of such access constitutes a loss for the scientific and cultural heritage of all people, as well as for the practical civil and military applications arising from the information learned and the technologies developed.

ZigBee

Zigbee forms the upper layer for control and sensor applications. It is built above the IEEE 802.15.4. Zigbee can provide security and flexibility due to its design. It has now become an open alliance. Its setup was developed in 2002 by Zigbee Alliance.

Basic of Zigbee

As ZigBee forms the upper layer it offers services like messaging. In security aspects and application of profile layers also this configuration can be implemented. IEEE 802.15.4 mainly focuses on security, control and monitoring where low levels of data are needed. The star, mesh and cluster tree network topologies are supported by ZigBee.

The star networks are simple networks. In this topology the outer nodes communicate with the centre node. The mesh topology consists of nodes placed according to the requirements. They provide a high degree of reliability. Here different stations are formed as relays to transmit messages. In case of interference at one section another can be used. The combination of mesh and star network is a cluster network.

Zigbee is designed for plow power consumption purposes. This increases the battery life and reduces the frequent maintenance cost.

Zigbee protocol features 

• They support network topologies such as star, mesh and cluster.
• The design increases the battery life.
• Low latency
• It uses Direct Sequence Spread Spectrum (DSSS)
• 128-bit AES encryption for secure data connections
• It reduces collisions. 

Application of Zigbee

Sensors, lighting controls, security and many more applications are all candidates for the new technology. They are also implemented in fields such as smart grid, lighting controls, high voltage AC control and in few medical devices.

Key takeaway

The satellites can be passive and active. The passive satellites just reflect back the signal to the earth as it is without any amplification. Due to this the signal received is weak. On other hand the active satellites amplify the transmitted signal before re-transmitting it to the earth and thus the received signal is of good strength.

Every user has a frequency range allocated for transmission so that interference can be avoided during communication.

1.3 Paging systems

While mobile devices perform updates according to their location update scheme, the network needs to be able to precisely determine the current cell location of a user to be able to route an incoming call. This requires the network to send a paging query to all cells where the mobile device may be located, to inform it of the incoming transmission. It is desirable to minimize the size of this paging area, to reduce the cost incurred on the network with each successive paging message. Ideally the paging area will be restricted to a known group of cells, such as with the currently implemented location area scheme. An optimum paging area size calculation involves a trade-off between location update cost and paging cost. This technique is used in many location- management schemes to reduce the location management costs incurred. The most commonly used paging schemes are summarized below. These have seen extensive use in real world telecommunications networks.

Simultaneous Paging

The simultaneous paging scheme, also known as blanket paging, is the mechanism used in current GSM network implementations. Here all cells in the users’ location area are paged simultaneously, to determine the location of the mobile device. This requires no additional knowledge of user location but may generate excessive amounts of paging traffic. Implementations of simultaneous paging favour networks with large cells and low user population and call rates. This scheme does not scale well to large networks with high numbers of users, necessitating the development of more advanced paging techniques.

Sequential Paging

Sequential paging avoids paging every cell within a location area by segmenting it into a number of paging areas, to be polled one-by-one. It is found in that the optimal paging mechanism, in terms of network utilization, is a sequential poll of every cell in the location area individually, in decreasing probability of user residence. The individual delays incurred in this scheme may be unacceptable however, and hence it is suggested that paging areas are formed from a larger number of cells. The number of cells per paging area is a factor which needs to be optimized and may lead to excessive call delays, particularly in large networks. The order by which each area is paged is central to the performance of the sequential paging

1.4 Cordless telephone systems

Fig 3 Block Diagram of Cordless System

• Cordless telephone systems are full duplex communication systems that use radio to connect a portable handset to a dedicated base station, which is then connected to a dedicated telephone line with a specific telephone number on the public switched telephone network.
• First generation cordless telephone systems in the 1980s had the portable unit communicating only to the dedicated base unit and only over distances of a few tens of meters. Early cordless telephones operated solely as extension telephones to a transceiver connected to a subscriber line on the PSTN and were primarily for in-home use. Second generation cordless telephones allow subscribers to use their handsets at outdoor locations within urban centers.
• Modern cordless telephones are sometimes combined with paging receivers so that a subscriber may first be paged and then respond to the page using the cordless telephone.
• Cordless telephone systems provide the user with limited range and mobility as it is usually not possible to maintain a call if the user travels outside the range of the base station.
• Typical second-generation base stations provide a coverage of up to a few hundreds of meters.

Key takeaway

Early cordless telephones operated solely as extension telephones to a transceiver connected to a subscriber line on the PSTN and were primarily for in-home use. Second generation cordless telephones allow subscribers to use their handsets at outdoor locations within urban centers.

1.5 Overview of generations of cellular systems

First-generation analog cellular telephone

• First generation cellular and cordless telephone networks are based on analog circuit switching technology. The first 1Gmobile phone was introduced in the USA in 1980. FDMA was the multiple access technique used and worked mainly in the 800-900 MHz frequency bands. The 1Gmobile phone had only voice facility.
• Examples of 1G systems are AMPS (Advanced mobile phone service) and TACS (total access communication systems)
• The limitations of 1 Gare:
• Supports Speech only
• Low traffic capacity
• Unreliable handover
• Long call setup time
• Frequent call drops
• Inefficient bandwidth usage
• Poor battery life
• Poor voice quality
• Large size of handset
• Allowed users to make voice calls within a country only
• A typical example of a cellular telephone system is the Advance Mobile Phone Services (AMPS) system used in the United States. In 1971, Bell Telephone Laboratories in Murry Hill, New Jersey, proposed the cellular telephone concept as the Advanced Mobile Telephone System (AMPS). AMPS is a standard cellular telephone service (CTS) initially placed into operation on October 13, 1983, by Illinois Bell that incorporated several large cell areas to cover approximately 2100squaremilesin the Chicago area.
• Basically, all first-generation systems use the transport architecture shown in the figure

Fig 4 Architecture

Fig 5 Block Diagram of First-Generation Cellular System

The block diagram of a first-generation cellular telephone network is shown in the figure. The system control for each market resides in the MSC which maintains all mobile related information and controls each mobile handoff. The MSC also performs the functions of network management, call handling and processing, billing and fraud detection within the market.

The MSC is interconnected with the PSTN via the landline trunked lines and a tandem switch. MSCs are connected with other MSCs via dedicated signaling channels for exchange of location, validation and call signaling information. First generation wireless systems provide analog speech and inefficient low-rate data transmission between the base station and the mobile user. The speech signals are usually digitized using a standard TDM format for transmission between the base station and the MSC and are always digitized for distribution from the MSC to the PSTN.

Second-generation wireless telephone networks

• First-generation cellular telephone systems were designed primarily for a limited customer base, such as business customers and a limited number of affluent residential customers. The problems inherent with these cellular telephones were poor battery performance and channel unavailability. Improved batteries were also needed to reduce the size and cost of mobile units, especially those that were designed to be handheld. Weak signal strengths resulted in poor performance and ahigh rate of falsely initiated handoffs (false handoffs).
• It was determined that improved battery performance and higher signal quality were possible only by employing digital technologies.
• In the United States, the shortcomings of the first-generation cellular systems led to the development of several second-generation cellular telephone systems, such as narrowband AMPS (N-AMPS) and systems employing the IS-54, IS-136, and IS-95 standards.
• A second-generation standard, known as Global System for Mobile Communications (GSM), emerged in Europe. The U.S Standards of TDMA and CDMA also belong to this generation.
• Other second-generation wireless standard includes, the British Cordless telephone standard CT2, Personal access Communication System (PACS) and the European standard for cordless and office telephony Digital European Cordless telephone (DECT).
• 2 G technology supports data, speech, fax, sms and WAP services.
• The architecture employed in second generation networks have reduced the computational burden on the MSC.
• GSM for example uses a base station controller (BSC) which allowed the data interface between the BSC and MSC to be standardized. This allows carriers to use different manufacturers for MSC and BSC components.
• All Second-generation systems use digital voice coding and digital modulation. The systems employ dedicated control channels within the air interface for simultaneously exchanging voice and control information between the subscriber, the base station and the MSC while the call is in progress.
• Second generation networks also provide dedicated voice and signaling trunks between MSCs and between each MSC and the PSTN.
• The first-generation systems were designed primarily for voice whereas the second-generation systems are specifically designed to provide paging, Fax and high data rate internet access.
• The network controlling structure is more distributed in second generation networks since mobile stations assume greater control functions.
• The handoff process is more mobile controlled and is known as Mobile assisted handoff (MAHO). The mobile units perform additional functions of received power reporting, adjacent base station scanning, data encoding and encryption.
• DECT (Digital European Cordless telephone) is an example of a second-generation cordless standard. It allows each cordless phone to communicate with any number of base stations. The base station with the greatest signal level is selected. The base stations have greater control in terms of switching, signaling and controlling handoffs.
• In general, second-generation systems have been designed to reduce the computational and switching burden at the base station or MSC. They also provide more flexibility in the channel allocation scheme so that systems may be deployed rapidly and in a less coordinated manner.
• The limitations of 2Gare
• Low data rates ranging from 9.6 kbps to 28.8kbps
• Circuit switched network
• End systems are dedicated for the entire call duration
• Inefficient usage of bandwidth and resources

Interim 2.5 G -generation wireless telephone networks

• The need for increased throughput data rates in data transfer such as web browsing and email led to the evolution of 2.5 G which is between 2g and3G.
• The mobile technology using GPRS (General Packet Radio Service) has been termed as 2.5G.
• The 2.5 G was started in 1998 with added GPRS and enhanced data rates for GSM evolution (EDGE). In addition to the Hypertext transfer protocol (HTTP) it supports the Wireless Access Protocol (WAP) through which web pages can be viewed on the small screen of a mobile phone or a handheld device which led to the development of mobile commerce (m-commerce).
• 2.5 G is packet switched and can use some of the existing infrastructures of GSM and CDMA (Code division multiple access) networks.

Third-generation wireless telephone networks

• The aim of third generation wireless networks is to provide a single set of standards that can meet a wide range of wireless applications and provide universal access throughout the world.
• In 3 G networks the distinctions between cordless telephones and cellular telephones disappear and a universal personal communicator or personal handset provides access to a variety of voice, data and video communication services.
• 3rd generation systems use the Broadband ISDN to provide access to information networks such as the internet and other private and public databases.
• 3 G networks carry all types of information like voice, data and video.
• They operate in densely populated and sparsely populated areas.
• They serve both stationary users and vehicular users travelling at high speeds.
• Packet radio communication is used in the 3 G networks
• Personal communication System (PCS), International Mobile Telecommunication (IMT-2000) and Universal Mobile telecommunication System (UMTS) are examples of 3G wireless networks. UMTS is also known as W-CDMA (Wideband CDMA)

Fourth-generation wireless telephone networks

• 4th-generation networks emerged as a data-optimized technology with the promise of speed improvements up to 10-fold over existing 3G technologies.
• It is basically the extension in the 3G technology with more bandwidth and services offers in the 3G.
• The expectation for the 4G technology is basically the high-quality audio/video streaming over end-to-end Internet Protocol. The transmission rates of 4G will be up to 20Mbps higher than that of3G.
• The first two commercially available technologies billed as 4G were the WiMAX standard and the LTE standard. LTE – Advanced is the newest version of LTE.
• One of the main ways in which 4G differed technologically from 3G was in its elimination of circuit switching, instead employing an all-IP network. 4G utilizes packet switching over internet, LAN or WAN networks via VoIP.
• 4G technology is meant to provide what is known as “ultra-broadband” access for mobile devices. It is set to deliver 100 Mbps to a roaming mobile device and up to 1 Gbps to a stationary device.
• 4G will bring the perfect real-world wireless inter networking called World Wide Wireless Web.
• 4 G allows for video conferencing, streaming picture-perfect video for telemetric applications
• OFDMA multi-carrier transmission methods, frequency-domain equalization (FDE) methods, MIMO (Multiple Input Multiple Output) and Turbo Code techniques are used in 4 G networks.
• Peak data rates for 4G networks must be close to 100 megabit per second for a user on a highly mobile network and 1 gigabit per second for a user with local wireless access or a nomadic connection.
• True 4G must also be able to offer smooth hand overs across differing networks without data loss and provide high quality of service for next-gen media.
• One of the most important aspects of 4G technology is the elimination of parallel circuit-switched and packet-switched network nodes using Internet Protocol version 6 (IPv6). The currently used standard, IPv4, has a finite limitation on the number of IP addresses that can be assigned to devices

1.6 Comparison of various wireless systems

References:

1. Wireless Communications- Principles and Practice, T S Rappaport, Pearson Education India, Second Edition.

2. Wireless Communication and Networks, Upen Dalal, Oxford university Press, First Edition, 2015.

3. Wireless Communication and Networks 3G and Beyond, Iti Saha Misra, Tata McGraw Hill Education Pvt. Ltd, Second Edition, 2009.

4. Mobile Communication Engineering – Theory and Applications W C Y Lee, TMH Publication, Second Edition, 2008.

5. Wireless Communication, Andrea Goldsmith, Cambridge University Press, 2005

6. Fundamentals of Wireless Communication, David Tse and Pramod Viswanath, Cambridge University Press, 2005