Unit-1 Introduction to mobile communication 1 Introduction to wireless comm J.C BOSE put the concept of wireless communication In 1897 Guglietmo marconi demonstrated radios ability to provide continuous contact with ships

Then new wireless communication methods & services have been adopted by people throughout the world : 1960 & 1970s - bell laboratories developed the cellular concept The wireless era was born in 1970s with the development of highly reliable ,miniature ,solid state radio frequency hardware Future growth of consumer based mobile communication will tied closely to: 1. radio spectrum allocation 2. regulatory decision 3. support to new & extended services 4. advance technology signal processing 5. access & networking areas V Evolution of mobile radio communicationmjvs In 1934 , 194 municipal police radio system & 58 state police station had developed AM mobile comm system In 1935 edwin armstrong demonstrate FM 4 Examples of wireless communication systems Garage door openers Remote controller for home equipment Cordless telephone Walkie-talkie Pager Cellular phones 5 Dept of E& TC, SCOE,Pune 416 Mobile radio transmission system: Simplex Half duplex Full duplex-provide separate channnel FDD & TDD 7 Frequency division duplex(FDD): FDD provides simultaneous radio transmission channels for the subscriber & BS so that they may constantly txmit & Rx the signals At the BS separate Txmit & Rx antennarused to accommodate the 2 separate channels At the subscriber unit single antenna is used for both Txmission & receptions This device called duplex unit Duplex unit is used inside the subscriber unit to enable the same antenna for Txmission or Rx 2channels- fwd & reverse 8 Time division duplexing(TDD) TDD is possible only in digital Txmission formats & digital modulation is very sensitive to time TDD is used recently for indoor , small area wireless n/w, physical distance is very small

9 Paging system Paging Systems are wireless communication systems that are designed to send brief messages to a subscriber. It's a one-way messaging system in which Base Station send messages to all subscribers. The Paging System transmits the message also known as Page, along with Paging System access number, throughout the service area using Base Station, which broadcast the page on a radio link. 10 Types of Paging Systems The Paging Systems can be of two types. Manual Paging System: In a manual paging system, a message is sent to the paging operator through telephone call by the caller. The message is then delivers to the pager through paging network by the operator. Automatic Paging System: In an automatic paging system, the incoming requests are automatically processed by the paging terminal and then this information is delivers to the pager. Automatic Paging Systems are mostly used. 11 Wide area paging system 12 Paging system 13 Cordless telephone A cordless telephone or portable telephone is a telephone with a wireless handset that communicates via radio waves with a base station connected to a fixed telephone line, usually within a limited range of its base station (which has the handset cradle). The base station is on the subscriber premises, and attaches to the telephone network the same way a corded telephone does. 14 Cordless telephone 15 cordless telephone 16 Cordless telephone 17 Cellular telephone system 18 Cellular telephone system Cellular telephone system provides a wireless connection to PSTN for any user location within the radio range A cellular system offers 1.high quality of service 2.high capacity3.same radio channelmay be reused 4.handoff Each BShave limited coverage area called cell 19 Communication between BS & MS is defined by common air interfaces (CAI) that specifies 4 channel FVC BS to MS RVC MS to BS FCC RCC FCC & RCC responsible for initiating mobile call 20 Timing diagram illustrating how a call to a mobile user initiated by a landline subscriber is established. 21 22 Timing diagram illustrating how a call initiated by a mobile is established 23 Dept of E& TC, SCOE,Pune 4124 Modern wireless communication systems Dept of E& TC, SCOE,Pune 4125 First Generations 1G Analog modulation(FM) FDMA/FDD A cell-phone carrier typically gets 832 radio frequencies to use in a city. Therefore, each cell has about 56 voice channels available, which allows 56 people to be talking on their cell phone at one time. 395 voice channels per carrier/2 frequencies per call (The other 42 frequencies are used for control channels) Dept of E& TC, SCOE,Pune 4126 First Generations 1G Shortcomings Cell phones Limited battery life (typically 8 hours) Limited range could have more powerful cell phone mounted in cars Security None easy to listen in Very limited number of voice channels Dept of E& TC, SCOE,Pune 4127 Second Generation 2G Voice (data) channels are digital-1990 Control channels the same Modulation scheme used-GMSK GSM uses frequency duplex communication & each call is allotted a duplex channel(TDMA/FDD) Duplex channels are separated by a 45MHz Every channel is of 200KHz BW so GSM uses FDM to separate the channel Downlink frequency (BS to MS)- 935 t0 960 MHz Uplink frequency (MS to BS)- 890 t0 915 MHz 28 2G cellular networks 2G popular std includes 3TDMA std 1. Global system Mobile(GSM): - supports 8 time slotted user for 200KHz - deployed widely by Europe,Asia,Australia,South America & some US 2. Intrim standard 136(IS-136) : - also called north American digital cellular - supports 03 time slotted users for 30KHz - deployed by North America,Australia Dept of E& TC, SCOE,Pune 4129 2G cellular networks 3. Specific Digital Cellular(PDC): - A Japanese TDMA std. - Similar to IS-136 4. 2G-CDMA - also called as cdma-one - supports 64 users that are orthogonally coded - simultaneous txed on 1.25 MHz channel - deployed by Korea,Japan,Chaina ,south America& Australia 30 Specification of 2G services 31 Shortcomings of 2G Single ckt sw voice channel Less data txmission Limited data throughput rate 2Gn/w designed to support only single user data rate (10kbps) Too slow for email & internet Generally used for SMS Dept of E& TC, SCOE,Pune 4132 Various upgrade paths for 2G technologies 33 Evolution of 2.5G Higher data rate Web browsing Email traffic Mobile commerece Location based mobile services 2.5G uses : upgrades 1 . High speed ckt sw data(HSCSD) 2. General packet Radio service(GPRS) 3. Enhanced data rates for GSM evolution(EDGE)

Dept of E& TC, SCOE,Pune 4134 Evolution of 2.5G High-speed circuit-switched data (HSCSD), is an enhancement to Circuit Switched Data (CSD) One innovation in HSCSD is to allow different error correction methods to be used for data transfer Data rate archives 14.4 kbps It can provides up to 57.6 Kbps Dept of E& TC, SCOE,Pune 4135 . General packet Radio service(GPRS) GPRS was designed to make mobile data faster, cheaper, and user-friendlier than ever before. By introducing Internet Protocol (IP) and packet switching to mobile networks, it gives mobile users faster data rate For subscribers, GPRS enables voice and data calls simultaneously. Setting up a Connection is almost instantaneous, and users can be always connected to the mobile Internet, enjoying Web surfing, high-speed delivery of e-mails with large file attachments, and access to corporate LANs. 36 . General packet Radio service(GPRS) Packet based nw use for -Non-real time internet usage - retrival of email,fax, & web browser - user can download data It is always onto access nw Data rate -172.2kbps Dept of E& TC, SCOE,Pune 4137 . General packet Radio service(GPRS) GPRS supports-Short message services( SMS) - Wireless application protocol(WAP) - multimedia messaging services(MMS) Dept of E& TC, SCOE,Pune 4138 Application of GPRS Chat Multimedia services Virtual private nw Personal information management Vehicle positioning Dept of E& TC, SCOE,Pune 4139 WHAT IS EDGE

EDGE (Enhance data rate for GSM evolution) is a radio signaling technology for 3G mobile networks.

EDGE use for mobile service such as -downloading of video and music clips - full multimedia messaging - high- speed colors internet access - e-mail on the move 40 Enhance data rate for GSM evolution Enhance data rate for GSM evolution (EDGE) is a digital mobile phone technology. It is generally classified as a 2.75G network technology. EDGE has been introduced into GSM networksince 2003 initially in north America It can be used for any packet switching application such as an internet connection. EDGE circuit switching is a possible for future development. Introduces a new modulation technique (8PSK) and channel coding. p. p. p. p. p. p. p. p. p. p. p. p. p. p. p. p. p. p. More from this user PreviousNext 3 p. 3 p. 3 p. 56 p. 64 p. 3 p. 9 p. 20 p. 17 p. Recent Readcasters Add a Comment Submit Characters: 400 p. p. p. p. p. p. p. p. p. p. p. p. p. p. p. p. p. p. More from this user PreviousNext 3 p. 3 p. 3 p. 56 p. 64 p. 3 p. 9 p. 20 p. 17 p. Recent Readcasters Add a Comment Submit Characters: 400 41 Enhance data rate for GSM evolution Increase data rates up to 384 kbps Introduces a new modulation technique (8PSK) and channel coding. In addition to Gaussian minimum- shift keying (GMSK),EDGE uses higher-order PSK/8 phase shift keying (8PSK). EDGE produces a 3-bit word for every change in carrier phase. 43 Dept of E& TC, SCOE,Pune 4144 HOWDOES EDGE WORK ? Edge work by improving the signaling interface used to communicate over the radio wave. Typically edge enhance three time the performance of GPRS achieving an data rate 80 to 160 kbps per user with mobile terminals Dept of E& TC, SCOE,Pune 4145 Impact of EDGE on existing GSM/GPRS networks : Hardware upgrade to the BSS (new transceiver in each cell) Software upgrade to the BS and BSC No change in the core networks New terminals -Terminal which provides 8PSK in the uplink and the downlink -Terminal which provides GMSK in the uplink and 8PSK in the downlink 46 Advantage of EDGE Faster data transfer rates up to384 kbps Higher data throughput increase Capacity and performance Easy implementation on a GSM/GPRS network Cost effective Increase the capacity and triples the data rate of GPRS Enabling new multimedia services Dept of E& TC, SCOE,Pune 4147 3G wireless networks 3G provides - multimegabit bits internet access - communication using VOIP - voice activated call- always on access It Receives - live music - interactive web - simultaneous voice & data access - multiple parties on single handset irrespective on location 48 3G W-CDMA-Universal mobile telecom services(UMTS) 3GPP body developing W-CDMA for - wide area mobile cellular coverage(FDD) - indoor cordless application(TDD) W-CDMA provides always on packet based services Supports packet data rate up to 2.048 mbps per user with high quality data multimedia streaming audio video videoconferencing virtual home entertainment It requires min BW of 5Mhz 49 3G CDMA 2000 It provides a seamless & evolutionary high data rate up to 2Mbps Total BW is 12Mhz & channel BW is 1.25Mhz Previous cdma20001xprovides data rate of up to 307kbps for user in packet mode Total throughput rate of up to 144kbps per user depending upon the no.of users & the velocity of user cdma20001xEV ( evolutionary) originally developed byto provides data rate greater than 2.4Mbps - web browsing- email accessDept of E& TC, SCOE,Pune 4150 Cellular concept Dept of E& TC, SCOE,Pune 4151 Cellular network Regions divided into cells modeled as hexagons. Each cell has a base station that all cell phones within the cell communicate with. Communication uses both dataand control channel. Dept of E& TC, SCOE,Pune 4152 IDEAL ACTUAL DIFFERENT CELL MODEL Dept of E& TC, SCOE,Pune 4153 CELL SHAPE Cellular network Why hexagon 1) it avoids dead spots & full area coverage is achieved 2) it requires fewer cell3) it requires less transmitter sites 4) less expensive Group of cells is called cluster Dept of E& TC, SCOE,Pune 4154 55 Clusters Cluster size N = 7 1 1 2 3 4 5 6 7 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 In TDMA and FDMA cells are grouped into clusters. The total number of channels are equally distributed among all cells in a cluster.The channel allocation pattern is repeated in every cluster.

56 Clusters (2) 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 4 3 2 1 4 3 2 1 Cluster size N = 4 57 Clusters (3) We cannot select cluster size arbitrarily. Cluster sizes must satisfy the following: N = i2+ij+j2 where i and j are non-negative integers. Thus N = 1, 3, 4, 7, 9, 12 1.Frequency reuse Users in different geographical areas (in different cells) may simultaneously use the same frequency Frequency reuse drastically increases user capacity and spectrum efficiency Dept of E& TC, SCOE,Pune 4158 4/22/201359 Process of selecting& allocating channel groups for all of the cellular base stations within a system is called frequency reuse or frequency planning. To keep interference level within tolerable limits. FREQUENCY REUSE 4/22/201360 FREQUENCY REUSE The frequency spectrum is a limited resource. Therefore, wireless telephony, like radio, must reuse frequency assignments. For example, two radio stations might transmit at 91.3 FM. There is no interference as long as the radio stations are far enough apart. Problem: Limited frequency spectrum

Solution: Based on the idea of splitting up coverage region into small areas referred to as cellsFrequency reuse Each cellular BS station allocated a group of radio channel to be used within small geographic area called as cell Adjacent BS are allocated different group of channel Antenna at BS are designed to achieves desired coverage in same cell The same group of channel may be used to cover different cell that are separated from one another by distance large enough to keep interference level min The process of selecting & allocating channel groups for all cellular BS is called frequency re-use 61 Frequency reuse distance Dept of E& TC, SCOE,Pune 4162 Frequency reuse Dept of E& TC, SCOE,Pune 4163

Consider a cellular system which has a total of S duplex channels. Each cell is allocated a group of k channels, . The S channels are divided among N cells. The total number of available radio channels S=KN The N cells which use the complete set of channels is called cluster. The cluster can be repeated M times within the system. The total number of channels, C, is used as a measure of capacity C=MKN=MS The capacity is directly proportional to the number of replication M. The cluster size, N, is typically equal to 4, 7, or 12. Small N is desirable to maximize capacity. The frequency reuse factor is given by 1/N 64 Fixed channel assignment strategies: Each cell is allocated a predetermined set of voice channel Any call attempt within the cell can only be served by the unused channel in that particular cell If all the channel in that cell are occupied, the call is blocked& subscriber does not Rx call Dept of E& TC, SCOE,Pune 4165 2.channel assignment Why we need channel assignment ? - to utilize the spectrum efficiently - reuse the frequency- increase the capacity- minimize interference There are Two types ofchannel assignment strategies - fixed or dynamic - borrowing strategies Dept of E& TC, SCOE,Pune 4166 Borrowing strategies: A cell is allowed to borrow channel from a neighboring cell if all of its own channel are already occupied MSC supervised the borrowing procedure Borrowing does not disrupt or interfere with any of the calls in progress in the donor cellDept of E& TC, SCOE,Pune 4167 Dynamic channel assignment: Voice channels are not allocated to different cell permanently Instead each time a call request is made the BS request a channel from MSC The switch then allocates a channel to be requested cell following the algorithm Dept of E& TC, SCOE,Pune 4168 3.Handoff When a mobile moves into a different cell while a conversation is in progress, the MSC automatically transfers the call to a new channel belonging to the new base station. Dept of E& TC, SCOE,Pune 4169 70 BSMobile DeviceNetworkBSNetworkBS BSMobile DeviceNetworkBS BSMobile DeviceBefore During AfterBS = Base-StationHard Handoff :Dept of E& TC, SCOE,Pune 4171 BSMobile DeviceNetworkBSNetworkBS BSMobile DeviceNetworkBS BSMobile DeviceBefore During AfterBS = Base-StationSoft Handoff : 1G handoff Signal strength measured by BS & supervised by MSC BS monitors strength of RVC & location Spares receiver in each BS called locator receiver Locator receiver determines signal strength ofuser in other cell Location Rxver reports RSSI to MSC MSC will decide if handoff is necessary or not Locator receiver controlled by MSC Dept of E& TC, SCOE,Pune 4172 73 2G TDMA Handoffs In second generation systems which use digital TDMA technology, handoff decisions are assisted by the MS (MAHO). MS monitor control channels of other BSs. MS reports all signal strengths to serving BS. When received power from a neighboring BS is stronger than the serving one (and this increase is of significant duration), MS signals MSC (through BS) that a handoff may be needed. Handoff Strategies When a mobile moves into a different cell while a conversation is in progress, the MSC automatically transfers the call to a new channel belonging to the new base station. Handoff operation identifying a new base station re-allocating the voice and control channels with the new base station. Handoff Threshold Minimum usable signal for acceptable voice quality (-90dBm to -100dBm) Handoff margin =Pr handoff Pr minimumusable cannot be too large or too small. If is too large, unnecessary handoffs burden the MSC If is too small, there may be insufficient time to complete handoff before a call is lost. Dept of E& TC, SCOE,Pune 4174 Handoff Strategies Dept of E& TC, SCOE,Pune 4175 76 Practical Handoff Considerations With frequency reuse, a cellular provider can increase system capacity by decreasing cell sizes. With more cells in the same area, and by using the same frequency reuse pattern, the number of effective channels over the same area is increased. However, as the cells decrease in size, the number of handoffs increase. More channels must be reserved for handoffs. As cells decrease in size, high speed users may require many handoffs per call, which increases probability of call being cut off. 77 Practical Handoff Considerations Low speed users, such as pedestrians, may not need a handoff, even in very small cells. The rate of decrease in the received power (which is usually a function of the velocity of the MS), determines the priority of a handoff. How can we support both high speed and low speed users while maintaining a high system capacity and low number of handoffs? Umbrella cell approach. 78 Umbrella Cell Approach Low speed users can be handled by microcells or picocells. High speed users are handled by a larger cell macrocell which is co-located with smaller cells. Speed of MS can be estimated by MSC by observing the rate of change of signal strength. 4/22/201379 Macrocell Microcell Macro-cellularMicro-cellular Large cells(5-20km radius) Higher TX power BS is expensive Lesser back-haul cost Low capacity Supports mobility Low bit rates Smaller cells(200m to 2km) Lower TX power BS is much cheaper Higher back-haul cost High capacity possible Pedestrian & fixed use High bit rates Practical Handoff Consideration Different type of users High speed users need frequent handoff during a call. Low speed users may never need a handoff during a call. Microcells to provide capacity, the MSC can become burdened if high speed users are constantly being passed between very small cells. Minimize handoff intervention handle the simultaneous traffic of high speed and low speed users. Large and small cells can be located at a single location (umbrella cell) different antenna height different power level Cell dragging problem: pedestrian users provide a very strong signal to the base station The user may travel deep within a neighboring cell 80 Practical Handoff Consideration Dept of E& TC, SCOE,Pune 4181 4/22/201382 Omnidirectional ANTENNAS 4/22/201383 ANTENNAS coaxial portable broadband 4/22/201384 CELLULAR Interference and System Capacity Sources of interference another mobile in the same cell a call in progress in the neighboring cell other base stations operating in the same frequency band noncellular system leaks energy into the cellular frequency band Two major cellular interference co-channel interference adjacent channel interference Co-channel Interference and System Capacity Frequency reuse - there are several cells that use the same set of frequencies these cell called co-channel cells Interference between signal from these cell called co-channel interference To reduce co-channel interference, co-channel cell must be separated by a minimum distance. When the size of the each cell is approximately the same & theBS txmit the same power then CCI ratio is independent on Transmitted power Radius of cell R distance betn center of the nearest co-channel cell D Increasing the ratio Q=D/R,the interference is reduced. Q is called the co-channel reuse ratio Frequency reuse distance Dept of E& TC, SCOE,Pune 4187 For a hexagonal geometry A small value of Q provides large capacity A large value of Q improves the transmission quality - smaller level of co-channel interference A tradeoff must be made between these two objectives NRDQ 3 = = Let io be the number of co-channel interfering cells. The signal-to-interference ratio (SIR) for a mobile receiver can be expressed as S: the desired signal power : interference power caused by the ith interfering co-channel cell base station The average received power at a distance d from the transmitting antenna is approximated by or n is the path loss exponent which ranges between 2 and 4. ==01iiiISISiInrddP P||.|

\|=00||.|

\| =00log 10 ) dBm ( ) dBm (ddn P Prclose-in reference point When the transmission power of each base station is equal, SIR for a mobile can be approximated as Consider only the first layer of interfering cells ( )==01iininDRIS( )0 03 ) / (iNi R DISnn= = Example: AMPS requires that SIR be greater than 18dB N should be at least 6.49 for n=4. Minimum cluster size is 7 60 = i For hexagonal geometry with 7-cell cluster, with the mobile unit being at the cell boundary, the signal-to-interference ratio for the worst case can be approximated as4 4 4 4 44) ( ) 2 / ( ) 2 / ( ) ( 2 + + + + + + =D R D R D R D R DRISAdjacent Channel Interference Adjacent channel interference: interference from adjacent in frequency to the desired signal. Imperfect receiver filters allow nearby frequencies to leak into the passband Performance degrade seriously due to near-far effect. desired signalreceiving filter responsedesired signalinterferenceinterferencesignal on adjacent channelsignal on adjacent channelFILTER Adjacent channel interference can be minimized through careful filtering and channel assignment. Keep the frequency separation between each channel in a given cell as large as possible A channel separation greater than six is needed to bring the adjacent channel interference to an acceptable level. Improving Capacity in Cellular Systems Methods for improving capacity in cellular systems Cell Splitting: subdividing a congested cell into smaller cells. Sectoring: directional antennas to control the interference and frequency reuse. Coverage zone : Distributing the coverage of a cell and extends the cell boundary to hard-to-reach place. Cell Splitting Split congested cell into smaller cells. Preserve frequency reuse plan. Reduce transmission power. microcell Reduce R to R/2 Illustration of cell splitting within a 3 km by 3 km square Transmission power reduction from to Examining the receiving power at the new and old cell boundary If we take n = 4 and set the received power equal to each other The transmit power must be reduced by 12 dB in order to fill in the original coverage area. Problem: if only part of the cells are splited Different cell sizes will exist simultaneously Handoff issues - high speed and low speed traffic can be simultaneously accommodated 1 tP2 tPnt rR P P1] boundary cell old at[nt rR P P ) 2 / ( ] boundary cell newat[21612ttPP =Sectoring Decrease the co-channel interference and keep the cell radius R unchanged Replacing single omni-directional antenna by several directional antennas Radiating within a specified sector Interference Reduction position of the mobile interference cells Microcell Zone Concept Antennas are placed at the outer edges of the cell Any channel may be assigned to any zone by the base station Mobile is served by the zone with the strongest signal. Handoff within a cell No channel re-assignment Switch the channel to a different zone site Reduce interference Low power transmitters are employed