Note for Wireless and Mobile Communication - WMC By UPTU Risers
- Wireless and Mobile Communication - WMC
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Wireless & Mobile Communication (EEC-801) UNIT-I Evolution of mobile radio communication fundamentals.Large scale path loss: propagation models, reflection, diffraction,scattering,Practical link budget design using path loss model.Small scale fading & multipath propagation and measurements,impulse response model and parameters of multipath channels.Small scale Multipath Measurements, Parameters of Mobile MultipathChannels types of small scale fading. INTRODUCTION Communication is one of the integral parts of science that has always been a focus point for exchanging information among parties at locations physically apart. After its discovery, telephones have replaced the telegrams and letters. Similarly, the term `mobile' has completely revolutionized the communication by opening up innovative applications that are limited to one's imagination. Today, mobile communication has become the backbone of the society. All the mobile system technologies have improved the way of living. It’s main plus point is that it has privileged a common mass of society. In this chapter, the evolution as well as the fundamental techniques of the mobile communication is discussed. EVOLUTION OF MOBILE RADIO COMMUNICATIONS The first wire line telephone system was introduced in the year 1877. Mobile communication systems as early as 1934 were based on Amplitude Modulation (AM) schemes and only certain public organizations maintained such systems. With the demand for newer and better mobile radio communication systems during the World War II and the development of Frequency Modulation (FM) technique by Edwin Armstrong, the mobile radio communication systems began to witness many new changes. Mobile telephone was introduced in the year 1946. However, during its initial three and a half decades it found very less market penetration owing to high costs and numerous technological drawbacks. Fig: 1.The worldwide mobile subscriber chart Fig. 2 Basic mobile communication structure But with the development of the cellular concept in the 1960s at the Bell Laboratories, mobile communications began to be a promising field of expanse which could serve wider populations. Initially, mobile communication was restricted to certain official users and the cellular concept was never even dreamt of being made commercially available. Moreover, even the growth in the cellular networks was very slow. However, with the development of newer and better technologies starting from the 1970s and with the mobile users now connected to the Public Switched Telephone Network (PSTN), there has been an astronomical growth in the cellular radio and the personal communication systems. Advanced Mobile Phone System (AMPS) was the first U.S. cellular telephone system and it was deployed in 1983. Wireless services have since then been experiencing a 50% per year growth rate. The number of cellular telephone users grew from 25000 in 1984 to around 3 billion in the year 2007 and the demand rate is increasing day by day. A schematic of the subscribers is shown in Fig. 2. MODERN WIRELESS COMMUNICATION SYSTEMS At the initial phase, mobile Communication was restricted to certain official users and the cellular concept was never even dreamt of being made commercially available. Moreover, even the growth in the cellular networks was very slow. However, with the development of newer and better technologies starting from the 1970s and with the mobile users now connected to the PSTN, there has been a remarkable growth in the cellular radio. However, the spread of mobile communication was very fast in the 1990s when the government throughout the world provided radio spectrum licenses for Personal Communication Service (PCS) in 1.8 - 2 GHz frequency band. By:Ms. SHALINI MISHRA email:shalini.mishra.06@gmail.com Page 1
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1G: FIRST GENERATION NETWORKS The first mobile phone system in the market was AMPS. It was the first U.S. cellular telephone system, deployed in Chicago in 1983. The main technology of this first generation mobile system was FDMA/FDD and analog FM.Ex:-AMPS,ETACS etc. 2G: SECOND GENERATION NETWORKS Digital modulation formats were Introduced in this generation with the main technology as TDMA/FDD and CDMA/FDD. The 2G systems introduced three popular TDMA standards and one popular CDMA standard in the market. EX:-GSM,CDMA etc. These are as follows: TDMA/FDD STANDARDS GLOBAL SYSTEM FOR MOBILE (GSM): The GSM standard, introduced by Groupe Special Mobile was aimed at designing a uniform pan-European mobile system. It was the first fully digital system utilizing the 900 MHz frequency band. The initial GSM had 200 KHz audio channels, 8 full-rate or 16 half-rate TDMA channels per carrier, encryption of speech, low speed data services and support for SMS for which it gained quick popularity. INTERIM STANDARD 136 (IS-136): It was popularly known as North American Digital Cellular (NADC) system. In this system, there were 3 full-rate TDMA users over each 30 KHz channel. The need of this system was mainly to increase the capacity over the earlier analog (AMPS) system. PACIFIC DIGITAL CELLULAR (PDC): This standard was developed as the Counter part of NADC in Japan. The main advantage of this standard was its low transmission bit rate which led to its better spectrum utilization. CDMA/FDD STANDARD INTERIM STANDARD 95 (IS-95): The IS-95 standard, also popularly known as CDMA One uses 64 orthogonally coded users and code words are transmitted simultaneously on each of 1.25 MHz channels. Certain services that have been standardized as a part of IS-95 standard are: short messaging service, slotted paging, over-the-air activation (meaning the mobile can be activated by the service provider without any third party intervention), enhanced mobile station identities etc. 2.5G MOBILE NETWORKS In an effort to retrofit the 2G standards for compatibility with Increased Throughput rates to support modern Internet application, the new data centric standards were developed to be overlaid on 2G standards and this is known as 2.5G standard. Here, the main up gradation techniques are: supporting higher data rate transmission for web browsing supporting e-mail traffic enabling location-based mobile service 2.5G networks also brought into the market some popular application, a few of which are: Wireless Application Protocol (WAP), General Packet Radio Service (GPRS), High Speed Circuit Switched Dada (HSCSD), Enhanced Data rates for GSM Evolution (EDGE) etc. 3G: THIRD GENERATION NETWORKS 3G is the third generation of mobile Phone standards and technology,superseding 2.5G. It is based on the International Telecommunication Union (ITU) family of standards under the International Mobile Telecommunications-2000 (IMT-2000). ITU launched IMT-2000 program, which, together with the main industry and standardization bodies worldwide, targets to implement a global frequency band that would support a single, ubiquitous wireless communication standard for all countries, to provide the framework for the definition of the 3G mobile systems. Several radio access technologies have been accepted by ITU as part of the IMT-2000 framework RADIO TRANSMISSION TECHNIQUES By:Ms. SHALINI MISHRA email:shalini.mishra.06@gmail.com Page 2
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Based on the type of channels being utilized, Mobile radio transmission systems may be classified as the following three categories which is also shown in Fig: Fig:The basic radio transmission techniques:(a) simplex,(b) half duplex(c) full duplex. Simplex System: Simplex systems utilize simplex channels i.e., the communication is unidirectional. The first user can communicate with the second user. However, the second user cannot communicate with the first user. One example of such a system is a pager. Half Duplex System: Half duplex radio systems that use half duplex radio channels allow for non-simultaneous bidirectional communication. The first user can communicate with the second user but the second user can communicate to the first user only after the first user has finished his conversation. At a time, the user can only transmit or receive information. A walkie-talkie is an example of a half duplex system which uses `push to talk' and `release to Listen' type of switches. Full Duplex System: Full duplex systems allow two way simultaneous communications. Both the users can communicate to each other simultaneously. This can be done by providing two simultaneous but separate channels to both the users. This is possible by one of the two following methods. Frequency Division Duplexing (FDD): By:Ms. SHALINI MISHRA email:shalini.mishra.06@gmail.com Page 3
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FDD supports two-way radio communication by using two distinct radio channels. One frequency channel is transmitted downstream from the BS to the MS (forward channel). A second frequency is used in the upstream direction and supports transmissionfrom the MS to the BS (reverse channel). Because of the pairing of frequencies, simultaneous transmission in both directions is possible. To mitigate selfinterference between upstream and downstream transmissions, a minimum amount of frequency separation must be maintainedbetween the frequency pair, as shown in Fig. ime Division Duplexing (TDD): TDD uses a single frequency band to transmit signals in both the downstream and upstream directions.TDD operates by toggling transmission directions over a time interval. This toggling takes place very rapidly and is imperceptible to the user. A full duplex mobile system can further be subdivided into two category: a single MS for a dedicated BS, and many MS for a single BS. Cordless telephone systems are full duplex communication systems that use radio to connect to a portable handset to a single dedicated BS, which is then connected to a dedicated telephone line with a specific telephone number on the Public Switched Telephone Network (PSTN). A mobile system, in general, on the other hand, is the example of the second category of a full duplex mobile system where many users connect among themselves via a single BS. Fig. Basic Cellular Structure BASIC METHODS OF PROPAGATION Reflection, diffraction and scattering are the three fundamental phenomena that cause signal propagation in a mobile communication system, apart from LoS communication. The most important parameter, predicted by propagation models based on above three phenomena, is the received power. The physics of the above phenomena may also be used to describe small scale fading and multipath propagation. The following subsections give an outline of these phenomena. Reflection: Reflection occurs when an electromagnetic wave falls on an object, which has very large dimensions as compared to the wavelength of the propagating wave. For example, such objects can be the earth, buildings and walls. When a radio wave falls on another medium having different electrical properties, a part of it is transmitted into it, while some energy is reflected back. Let us see some special cases. If the medium on which the e.m. wave is incident is a dielectric, some energy is reflected back and some energy is transmitted. If the medium is a perfect conductor, all energy is reflected back to the first medium. The amount of energy that is reflected back depends on the polarization of the e.m. wave. Another particular case of interest arises in parallel polarization, when no reflection occurs in the medium of origin. This would occur, when the incident angle would be such that the reflection coefficient is equal to zero. By:Ms. SHALINI MISHRA email:shalini.mishra.06@gmail.com Page 4
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