Lecture Notes on Mobile Communication

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Lecture Notes on Mobile Communication A Curriculum Development Cell Project Under QIP, IIT Guwahati Dr. Abhijit Mitra Department of Electronics and Communication Engineering Indian Institute of Technology Guwahati Guwahati 781039, India November 2009Contents 1 Introductory Concepts 1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Evolution of Mobile Radio Communications . . . . . . . . . . . . . . 1 1.3 Present Day Mobile Communication . . . . . . . . . . . . . . . . . . 3 1.4 Fundamental Techniques . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.4.1 Radio Transmission Techniques . . . . . . . . . . . . . . . . . 5 1.5 How a Mobile Call is Actually Made? . . . . . . . . . . . . . . . . . 7 1.5.1 Cellular Concept . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.5.2 Operational Channels . . . . . . . . . . . . . . . . . . . . . . 8 1.5.3 Making a Call . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.6 Future Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2 Modern Wireless Communication Systems 11 2.1 1G: First Generation Networks . . . . . . . . . . . . . . . . . . . . . 11 2.2 2G: Second Generation Networks . . . . . . . . . . . . . . . . . . . . 11 2.2.1 TDMA/FDD Standards . . . . . . . . . . . . . . . . . . . . . 12 2.2.2 CDMA/FDD Standard . . . . . . . . . . . . . . . . . . . . . 12 2.2.3 2.5G Mobile Networks . . . . . . . . . . . . . . . . . . . . . . 12 2.3 3G: Third Generation Networks . . . . . . . . . . . . . . . . . . . . . 13 2.3.1 3G Standards and Access Technologies . . . . . . . . . . . . . 14 2.3.2 3G W-CDMA (UMTS) . . . . . . . . . . . . . . . . . . . . . 14 2.3.3 3G CDMA2000 . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.3.4 3G TD-SCDMA . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.4 Wireless Transmission Protocols . . . . . . . . . . . . . . . . . . . . 19 iii2.4.1 Wireless Local Loop (WLL) and LMDS . . . . . . . . . . . . 19 2.4.2 Bluetooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.4.3 Wireless Local Area Networks (W-LAN) . . . . . . . . . . . . 20 2.4.4 WiMax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.4.5 Zigbee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.4.6 Wibree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.5 Conclusion: Beyond 3G Networks . . . . . . . . . . . . . . . . . . . . 22 2.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3 The Cellular Engineering Fundamentals 23 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.2 What is a Cell? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.3 Frequency Reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.4 Channel Assignment Strategies . . . . . . . . . . . . . . . . . . . . . 27 3.4.1 Fixed Channel Assignment (FCA) . . . . . . . . . . . . . . . 27 3.4.2 Dynamic Channel Assignment (DCA) . . . . . . . . . . . . . 27 3.5 Hando Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.5.1 Factors In uencing Hando s . . . . . . . . . . . . . . . . . . 29 3.5.2 Hando s In Di erent Generations . . . . . . . . . . . . . . . 31 3.5.3 Hando Priority . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.5.4 A Few Practical Problems in Hando Scenario . . . . . . . . 33 3.6 Interference & System Capacity . . . . . . . . . . . . . . . . . . . . . 34 3.6.1 Co-channel interference (CCI) . . . . . . . . . . . . . . . . . . 34 3.6.2 Adjacent Channel Interference (ACI) . . . . . . . . . . . . . . 37 3.7 Enhancing Capacity And Cell Coverage . . . . . . . . . . . . . . . . 38 3.7.1 The Key Trade-o . . . . . . . . . . . . . . . . . . . . . . . . 38 3.7.2 Cell-Splitting . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.7.3 Sectoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.7.4 Microcell Zone Concept . . . . . . . . . . . . . . . . . . . . . 46 3.8 Trunked Radio System . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 ivChapter 1 Introductory Concepts 1.1 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. Its 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. 1.2 Evolution of Mobile Radio Communications The rst wireline telephone system was introduced in the year 1877. Mobile com- munication 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 1Figure 1.1: The worldwide mobile subscriber chart. costs and numerous technological drawbacks. But with the development of the cel- lular concept in the 1960s at the Bell Laboratories, mobile communications began to be a promising eld of expanse which could serve wider populations. Initially, mobile communication was restricted to certain ocial 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 rst 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. 1.1. 2Figure 1.2: Basic mobile communication structure. 1.3 Present Day Mobile Communication Since the time of wireless telegraphy, radio communication has been used extensively. Our society has been looking for acquiring mobility in communication since then. Initially the mobile communication was limited between one pair of users on single channel pair. The range of mobility was de ned by the transmitter power, type of antenna used and the frequency of operation. With the increase in the number of users, accommodating them within the limited available frequency spectrum became a major problem. To resolve this problem, the concept of cellular communication was evolved. The present day cellular communication uses a basic unit called cell. Each cell consists of small hexagonal area with a base station located at the center of the cell which communicates with the user. To accommodate multiple users Time Division multiple Access (TDMA), Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA) and their hybrids are used. Numerous mobile radio standards have been deployed at various places such as AMPS, PACS, 3Figure 1.3: The basic radio transmission techniques: (a) simplex, (b) half duplex and (c) full duplex. GSM, NTT, PHS and IS-95, each utilizing di erent set of frequencies and allocating di erent number of users and channels. 1.4 Fundamental Techniques By de nition, mobile radio terminal means any radio terminal that could be moved during its operation. Depending on the radio channel, there can be three di er- ent types of mobile communication. In general, however, a Mobile Station (MS) or subscriber unit communicates to a xed Base Station (BS) which in turn com- municates to the desired user at the other end. The MS consists of transceiver, control circuitry, duplexer and an antenna while the BS consists of transceiver and channel multiplexer along with antennas mounted on the tower. The BS are also linked to a power source for the transmission of the radio signals for communication and are connected to a xed backbone network. Figure 1.2 shows a basic mobile communication with low power transmitters/receivers at the BS, the MS and also 4the Mobile Switching Center (MSC). The MSC is sometimes also called Mobile Tele- phone Switching Oce (MTSO). The radio signals emitted by the BS decay as the signals travel away from it. A minimum amount of signal strength is needed in order to be detected by the mobile stations or mobile sets which are the hand-held personal units (portables) or those installed in the vehicles (mobiles). The region over which the signal strength lies above such a threshold value is known as the coverage area of a BS. The xed backbone network is a wired network that links all the base stations and also the landline and other telephone networks through wires. 1.4.1 Radio Transmission Techniques Based on the type of channels being utilized, mobile radio transmission systems may be classi ed as the following three categories which is also shown in Fig. 1.3:  Simplex System: Simplex systems utilize simplex channels i.e., the commu- nication is unidirectional. The rst user can communicate with the second user. However, the second user cannot communicate with the rst 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 rst user can communicate with the second user but the second user can commu- nicate to the rst user only after the rst user has nished 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 com- munications. 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): FDD supports two-way radio communication by using two distinct radio channels. One frequency chan- nel is transmitted downstream from the BS to the MS (forward channel). 5Figure 1.4: (a) Frequency division duplexing and (b) time division duplexing. A second frequency is used in the upstream direction and supports trans- mission from the MS to the BS (reverse channel). Because of the pairing of frequencies, simultaneous transmission in both directions is possible. To mitigate self-interference between upstream and downstream transmis- sions, a minimum amount of frequency separation must be maintained between the frequency pair, as shown in Fig. 1.4. Time 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 dedi- cated telephone line with a speci c 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. 6Figure 1.5: Basic Cellular Structure. 1.5 How a Mobile Call is Actually Made? In order to know how a mobile call is made, we should rst look into the basics of cellular concept and main operational channels involved in making a call. These are given below. 1.5.1 Cellular Concept Cellular telephone systems must accommodate a large number of users over a large geographic area with limited frequency spectrum, i.e., with limited number of chan- nels. If a single transmitter/ receiver is used with only a single base station, then sucient amount of power may not be present at a huge distance from the BS. For a large geographic coverage area, a high powered transmitter therefore has to be used. But a high power radio transmitter causes harm to environment. Mobile communication thus calls for replacing the high power transmitters by low power transmitters by dividing the coverage area into small segments, called cells. Each cell uses a certain number of the available channels and a group of adjacent cells together use all the available channels. Such a group is called a cluster. This cluster can repeat itself and hence the same set of channels can be used again and again. Each cell has a low power transmitter with a coverage area equal to the area of the 7cell. This technique of substituting a single high powered transmitter by several low powered transmitters to support many users is the backbone of the cellular concept. 1.5.2 Operational Channels In each cell, there are four types of channels that take active part during a mobile call. These are:  Forward Voice Channel (FVC): This channel is used for the voice trans- mission from the BS to the MS.  Reverse Voice Channel (RVC): This is used for the voice transmission from the MS to the BS.  Forward Control Channel (FCC): Control channels are generally used for controlling the activity of the call, i.e., they are used for setting up calls and to divert the call to unused voice channels. Hence these are also called setup channels. These channels transmit and receive call initiation and service request messages. The FCC is used for control signaling purpose from the BS to MS.  Reverse Control Channel (RCC): This is used for the call control purpose from the MS to the BS. Control channels are usually monitored by mobiles. 1.5.3 Making a Call When a mobile is idle, i.e., it is not experiencing the process of a call, then it searches all the FCCs to determine the one with the highest signal strength. The mobile then monitors this particular FCC. However, when the signal strength falls below a particular threshold that is insucient for a call to take place, the mobile again searches all the FCCs for the one with the highest signal strength. For a particular country or continent, the control channels will be the same. So all mobiles in that country or continent will search among the same set of control channels. However, when a mobile moves to a di erent country or continent, then the control channels for that particular location will be di erent and hence the mobile will not work. Each mobile has a mobile identi cation number (MIN). When a user wants to make a call, he sends a call request to the MSC on the reverse control channel. He 8also sends the MIN of the person to whom the call has to be made. The MSC then sends this MIN to all the base stations. The base station transmits this MIN and all the mobiles within the coverage area of that base station receive the MIN and match it with their own. If the MIN matches with a particular MS, that mobile sends an acknowledgment to the BS. The BS then informs the MSC that the mobile is within its coverage area. The MSC then instructs the base station to access speci c unused voice channel pair. The base station then sends a message to the mobile to move to the particular channels and it also sends a signal to the mobile for ringing. In order to maintain the quality of the call, the MSC adjusts the transmitted power of the mobile which is usually expressed in dB or dBm. When a mobile moves from the coverage area of one base station to the coverage area of another base sta- tion i.e., from one cell to another cell, then the signal strength of the initial base station may not be sucient to continue the call in progress. So the call has to be transferred to the other base station. This is called hando . In such cases, in order to maintain the call, the MSC transfers the call to one of the unused voice channels of the new base station or it transfers the control of the current voice channels to the new base station. Ex. 1: Suppose a mobile unit transmits 10 W power at a certain place. Express this power in terms of dBm. Solution: Usually, 1 mW power developed over a 100 load is equivalently called 0 dBm power. 1 W is equivalent to 0 dB, i.e., 10 log (1W ) = 0dB. Thus, 10 3 1W = 10 mW = 30dBm = 0dB. This means, xdB = (x + 30)dBm. Hence, 10W = 10 log (10W ) = 10dB = 40dBm. 10 Ex. 2: Among a pager, a cordless phone and a mobile phone, which device would have the (i) shortest, and, (ii) longest battery life? Justify. Solution: The `pager' would have the longest and the `mobile phone' would have the shortest battery life. (justi cation is left on the readers) 91.6 Future Trends Tremendous changes are occurring in the area of mobile radio communications, so much so that the mobile phone of yesterday is rapidly turning into a sophisticated mobile device capable of more applications than PCs were capable of only a few years ago. Rapid development of the Internet with its new services and applications has created fresh challenges for the further development of mobile communication systems. Further enhancements in modulation schemes will soon increase the In- ternet access rates on the mobile from current 1.8 Mbps to greater than 10 Mbps. Bluetooth is rapidly becoming a common feature in mobiles for local connections. The mobile communication has provided global connectivity to the people at a lower cost due to advances in the technology and also because of the growing competition among the service providers. We would review certain major features as well as standards of the mobile communication till the present day technology in the next chapter. 1.7 References 1. T. S. Rappaport, Wireless Communications: Principles and Practice, 2nd ed. Singapore: Pearson Education, Inc., 2002. 2. K. Feher, Wireless Digital Communications: Modulation and Spread Spectrum Applications. Upper Saddle River, NJ: Prentice Hall, 1995. 3. J. G. Proakis, Digital Communications, 4th ed. NY: McGraw Hill, 2000. 10Chapter 2 Modern Wireless Communication Systems At the initial phase, mobile communication was restricted to certain ocial 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. 2.1 1G: First Generation Networks The rst mobile phone system in the market was AMPS. It was the rst U.S. cellular telephone system, deployed in Chicago in 1983. The main technology of this rst generation mobile system was FDMA/FDD and analog FM. 2.2 2G: Second Generation Networks Digital modulation formats were introduced in this generation with the main tech- nology as TDMA/FDD and CDMA/FDD. The 2G systems introduced three popular TDMA standards and one popular CDMA standard in the market. These are as 11follows: 2.2.1 TDMA/FDD Standards (a) 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 rst fully digital system utilizing the 900 MHz frequency band. The initial GSM had 200 KHz radio 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. (b) 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. (c) Paci c Digital Cellular (PDC): This standard was developed as the counter- part of NADC in Japan. The main advantage of this standard was its low transmis- sion bit rate which led to its better spectrum utilization. 2.2.2 CDMA/FDD Standard Interim Standard 95 (IS-95): The IS-95 standard, also popularly known as CDMA- One, uses 64 orthogonally coded users and codewords 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. 2.2.3 2.5G Mobile Networks In an e ort to retro t 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 upgradation techniques are:  supporting higher data rate transmission for web browsing 12 supporting e-mail trac  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. 2.3 3G: Third Generation Networks 3G is the third generation of mobile phone standards and technology, supersed- ing 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 stan- dardization bodies worldwide, targets to implement a global frequency band that would support a single, ubiquitous wireless communication standard for all coun- tries,to provide the framework for the de nition of the 3G mobile systems.Several radio access technologies have been accepted by ITU as part of the IMT-2000 frame- work. 3G networks enable network operators to o er users a wider range of more ad- vanced services while achieving greater network capacity through improved spectral eciency. Services include wide-area wireless voice telephony, video calls, and broad- band wireless data, all in a mobile environment. Additional features also include HSPA data transmission capabilities able to deliver speeds up to 14.4Mbit/s on the down link and 5.8Mbit/s on the uplink. 3G networks are wide area cellular telephone networks which evolved to incor- porate high-speed internet access and video telephony. IMT-2000 de nes a set of technical requirements for the realization of such targets, which can be summarized as follows:  high data rates: 144 kbps in all environments and 2 Mbps in low-mobility and indoor environments  symmetrical and asymmetrical data transmission 13 circuit-switched and packet-switched-based services  speech quality comparable to wire-line quality  improved spectral eciency  several simultaneous services to end users for multimedia services  seamless incorporation of second-generation cellular systems  global roaming  open architecture for the rapid introduction of new services and technology. 2.3.1 3G Standards and Access Technologies As mentioned before, there are several di erent radio access technologies de ned within ITU, based on either CDMA or TDMA technology. An organization called 3rd Generation Partnership Project (3GPP) has continued that work by de ning a mobile system that ful lls the IMT-2000 standard. This system is called Universal Mobile Telecommunications System (UMTS). After trying to establish a single 3G standard, ITU nally approved a family of ve 3G standards, which are part of the 3G framework known as IMT-2000:  W-CDMA  CDMA2000  TD-SCDMA Europe, Japan, and Asia have agreed upon a 3G standard called the Universal Mobile Telecommunications System (UMTS), which is WCDMA operating at 2.1 GHz. UMTS and WCDMA are often used as synonyms. In the USA and other parts of America, WCDMA will have to use another part of the radio spectrum. 2.3.2 3G W-CDMA (UMTS) WCDMA is based on DS-CDMA (direct sequencecode division multiple access) tech- nology in which user-information bits are spread over a wide bandwidth (much larger than the information signal bandwidth) by multiplying the user data with 14the spreading code. The chip (symbol rate) rate of the spreading sequence is 3.84 Mcps, which, in the WCDMA system deployment is used together with the 5-MHz carrier spacing. The processing gain term refers to the relationship between the signal bandwidth and the information bandwidth. Thus, the name wideband is derived to di erentiate it from the 2G CDMA (IS-95), which has a chip rate of 1.2288 Mcps. In a CDMA system, all users are active at the same time on the same frequency and are separated from each other with the use of user speci c spreading codes. The wide carrier bandwidth of WCDMA allows supporting high user-data rates and also has certain performance bene ts, such as increased multipath diversity. The actual carrier spacing to be used by the operator may vary on a 200-kHz grid between approximately 4.4 and 5 MHz, depending on spectrum arrangement and the interference situation. In WCDMA each user is allocated frames of 10 ms duration, during which the user-data rate is kept constant. However, the data rate among the users can change from frame to frame. This fast radio capacity allocation (or the limits for variation in the uplink) is controlled and coordinated by the radio resource management (RRM) functions in the network to achieve optimum throughput for packet data services and to ensure sucient quality of service (QoS) for circuit-switched users. WCDMA supports two basic modes of operation: FDD and TDD. In the FDD mode, separate 5-MHz carrier frequencies with duplex spacing are used for the uplink and downlink, respectively, whereas in TDD only one 5-MHz carrier is time shared between the up- link and the downlink. WCDMA uses coherent detection based on the pilot symbols and/or common pilot. WCDMA allows many performance- enhancement methods to be used, such as transmit diversity or advanced CDMA receiver concepts.Table summaries the main WCDMA parameters. The support for handovers (HO) between GSM and WCDMA is part of the rst standard version. This means that all multi-mode WCDMA/GSM terminals will support measurements from the one system while camped on the other one. This allows networks using both WCDMA and GSM to balance the load between the networks and base the HO on actual measurements from the terminals for di erent radio conditions in addition to other criteria available. 15Table 2.1: Main WCDMA parameters Multiple access method DS-CDMA Duplexing method Frequency division duplex/time division duplex Base station synchronisation Asynchronous operation Chip rate 3.84 Mcps Frame length 10 ms Service multiplexing Multiple services with di erent quality of service requirements multiplexed on one connection Multi-rate concept Variable spreading factor and multicode Detection Coherent using pilot symbols or common pilot Multi-user detection, smart antennas Supported by the standard, optional in the implementation The world's rst commercial W-CDMA service, FoMA, was launched by NTT DoCoMo in Japan in 2001. FoMA is the short name for Freedom of Mobile Mul- timedia Access, is the brand name for the 3G services being o ered by Japanese mobile phone operator NTT DoCoMo. Elsewhere, W-CDMA deployments have been exclusively UMTS based. UMTS or W-CDMA, assures backward compatibility with the second generation GSM, IS-136 and PDC TDMA technologies, as well as all 2.5G TDMA technologies. The network structure and bit level packaging of GSM data is retained by W-CDMA, with additional capacity and bandwidth provided by a new CDMA air interface. 2.3.3 3G CDMA2000 Code division multiple access 2000 is the natural evolution of IS-95 (cdmaOne). It includes additional functionality that increases its spectral eciency and data rate capability.(code division multiple access) is a mobile digital radio technology where channels are de ned with codes (PN sequences). CDMA permits many simultaneous transmitters on the same frequency channel. Since more phones can be served by 16fewer cell sites, CDMA-based standards have a signi cant economic advantage over TDMA- or FDMA-based standards. This standard is being developed by Telecom- munications Industry Association (TIA) of US and is is standardized by 3GPP2. The main CDMA2000 standards are: CDMA2000 1xRTT,CDMA2000 1xEV and CDMA2000 EV-DV. These are the approved radio interfaces for the ITU's IMT-2000 standard. In the following, a brief discussion about all these standards is given. CDMA2000 1xRTT: RTT stands for Radio Transmission Technology and the designation "1x", meaning "1 times Radio Transmission Technology", indicates the same RF bandwidth as IS-95.The main features of CDMA2000 1X are as follows:  Supports an instantaneous data rate upto 307kpbs for a user in packet mode and a typical throughput rates of 144kbps per user,depending on the number of user, the velociy of user and the propagating conditions.  Supports up to twice as many voice users a the 2G CDMA standard  Provides the subscriber unit with upto two times the standby time for longer lasting battery life. CDMA2000 EV: This is an evolutionary advancement of CDMA with the following characteristics:  Provides CDMA carriers with the option of installing radio channels with data only (CDMA2000 EV-DO) and with data and voice (CDMA2000 EV-DV) .  The cdma2000 1xEV-DO supports greater than 2.4Mbps of instantaneous high-speed packet throughput per user on a CDMA channel, although the user data rates are much lower and highly dependent on other factors.  CDMA2000 EV-DV can o er data rates upto 144kbps with about twice as many voice channels as IS-95B. CDMA2000 3x is (also known as EV-DO Rev B) is a multi-carrier evolution.  It has higher rates per carrier (up to 4.9 Mbit/s on the downlink per carrier). Typical deployments are expected to include 3 carriers for a peak rate of 14.7 Mbit/s.Higher rates are possible by bundling multiple channels together. It 17

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