Downloaded from www.jayaram.com.np I. History ♦ Wired Communications Wireless and Mobile Communications: 1834 − Gauss and Weber build telegraph system in Germany 1844 − Morse connects Baltimore and Washington by telegraph 1858 − First transatlantic telegraph cable laid Reference Book: Theodore S. Rappaport 1876 − Alexander Bell demonstrates telephone 1911 − New York can telephone Denver ♦ Wireless Communications → Not so “new” Lecture 1: Introduction had slow growth at first compared to other inventions. But now is growing very rapidly. Chapter 1 - Introduction to Wireless Communication Systems “The ability to communicate with people on move” -1st invented by Guglielmo Marconi in 1897 -Demonstrated radio’s ability to provide continuous contacts with ships sailing the English Channels. -Then rapid growth. -Digital and R.F fabrication improvements. -New large scale circuit integration & other miniaturization technologies -Smaller , cheaper and more reliable -Digital switching technology - Facilitated large scale deployment of affordable, easy to use radio communication - Driven by consumer demand. Downloaded from www.jayaram.com.np/1 Downloaded from www.jayaram.com.np 1935 − Edwin Armstrong demonstrates FM radio system, which became the primary modulation technique. 1940 − First microwave radar 1965 − First commercial communication satellite 1968 − AT&T proposes cellular phone system to Federal Communications Commission (FCC) 1983 − FCC allocates spectrum for analog cellular service (AMPS) 1990 − GSM digital cellular service introduced in Europe 1995 − FCC auctions new Personal Communication Service (PCS) licenses in U.S. for digital services 1998 − 40 million cellular phone users in U.S. 2000 − In some countries, mobile users outnumber conventional wireline customers. 2001 − 630 million subscribers worldwide (as compared to 1 billion wired phone lines. 2001 − Over 1% of worldwide wireless subscribers have abandoned wired telephone service for home use. 1899 − Marconi sends first radio message across Atlantic 2005 − Over 130 million cellular phone users in U.S. (out of 1905 − Hulsmeyer detects ships with radar population 1927 − US & Europe telephones linked by HF radio of 300 million including children). 1934 − AM mobile police radios for public safety widely used II. Frequencies Downloaded from www.jayaram.com.np/2 • general classification.np ♦ RF − Radio Frequency First microwave radar. better tuned oscillators. I Method: FM radio -Dial via paging system access number with a telephone I key pad or modem.com. Flow Graph of gradual growth: * Garage door opener. I stock quotations and faxes may AM mobile police radio for public safely be send. alpha numeric and voice. Paging system: I Telephone -Sends a brief message to another subscriber.jayaram. Radio message in ships (English Channel) Objective: I -To notify a subscriber of the need to call a particular Ship detection with radar telephone number. first commercial communication 1 MHz to 1 GHz Satellite. Telegraph 1. etc. not absolute I 100 MHz to 1 GHz 1G: Cellular phone (AMPS) • more widely used definition I ♦ Microwave 2G: GSM 1 GHz to 300 GHz − general I 1 GHz to 100 GHz − more widely used 2.np/3 .news headlines. Downloaded from www. I -Types of message: Numeric.jayaram.5G: GPRS ♦ Trends towards use of higher frequencies I greater signal bandwidth (BW) per channel 3G:WCDMA more users and/or higher data rates but more difficult to design! → more money. Or I -Travels to a known location to receive further instruction. US & Europe telephone link by HF radio -Modern paging system has facilities like. Home Appliances: * TV remote control. more engineering required for Examples of wireless communication systems: sharper filters. Downloaded from www.com. Portable unit communicates with dedicated base units. .A receiver.np -Issued message called page. Uses radio to connect a portable handset to dedicated BS.jayaram. . landline link paging terminal . Cordless Telephone system: Cellular Telephone Systems: Downloaded from www. nd 2 generation: city n paging terminal . paging control center city 2 . Full duplex communication system. paging control center city 1 . specific telephone number on PSTN.com. 2. . codeless handset • Wide area paging system : . .Transciever connected a subscriber line on the PSTN. . landline link paging terminal PSTN .Coverage upto few hundred meters.Many BS. Downloaded from www. then response to the page using codeless telephone. o Subscriber may first be paged.jayaram. .Network of telephones lines.Large powerful transmitter & 1st generation .Manufactured in 1980. fixed port -The paging system then transmit the page through out the PSTN (BS) service area using Base Station which broadcast the page on a radio carrier. . o Has limitation on mobility over a larger distance.np/4 .Allows subscriber to use their handset at many outdoor satellite link locations within urban centers.com. Range: • Simple – 2 to 5 km.Just an extension of wired telephone lines. Provides world wide coverage.Modern Fig. Which then connected to dedicated telephone line with .Primarily for home use.Only over short distance (few meters). o cordless combine with paging system. wide area paging system. Wide area paging system consist of: . With limited frequency spectrum. Consists of several Transmitter and receiver. . Generally have tower which support transmitting and o Uses frequency reuse concept. Each mobile communicates via radio with BS.Connects the entire cellular system to the PSTN. geographical area. .Channels used for voice channels are forward voice channel (FVC) and reverse voice channel (RVC). BS serves as a bridge between all mobile users in the cell and connects the simultaneous mobile calls via telephone lines or microwave links to MSC. Simultaneously handle full duplex communications. receiving antennas. Contains transceiver.Specifies four different channels. an antenna and control circuitry. Quality Of Service BS: o High as compared to landline. . various simultaneous conversations at a time. . . Fig.MSC handles multiple subscribers. . . .In large cities several MSCs are used by the single carrier. 2 for voice and 2 for o MSC(mobile switching center) OR mobile control. Provides wireless connection to the PSTN for any user . . unit.Communication between base station and mobile. location within the range of the system. . .jayaram. switching telephone office(MTSO).Accommodates all billing and system maintenance function.np .com. o Base station. o Achieved by BS transmitter is limited to small . Basic cellular system consist of: Common Air interface (CAI): o Mobile station. MSC: .jayaram. Downloaded from www. A cellular system. Mobile station: Downloaded from www. May be mounted in a vehicle or used a handheld portable geographical areas.It coordinates the activates of all the BS and . Accommodates large number of user over the large .np/5 . MSC PSTN . .com. . 16 .com. . . .call initiates request on the reverse control channel. Fig. .Scans for strongest FCC. signal. Again scan the control channel in search of strongest BS o MIN and ESN (electronic serial no). once found . Control channels occupies 5% of the total number of transmit power level for particular user. MIN (mobile identification number) is then broadcast as a . Using another data message instruct the mobile to ring then • Call initiated by landline subscriber. Done by MSC. BS relay acknowledgement sent by mobile and informs . then sends voice channel within the cell.sends acknowledgement. Cellular phones.np .jayaram. Downloaded from www. Scans the group of forward control channel for strongest signal.com. Here . . . MSC instructs BS to move the call to an unused voice stayed “captured” to particular FCC. Downloaded from www. .7. . Cellular phone turned on but not yet engaged in a call. MSC adjusts the transmitter power of the mobile unit and Fig. One the call is in progress. Often called setup dispatches the requests to all the BS. How the cellular call is made? . Control channel transmit and receives data message for paging message over all FCC. Channels used for initiating calls forward control channel . 1.Mobile unit transmit: . 1. pg. end users. usable levels.np/6 . Out of range . . pg. . channels available and 95% dedicated to voice and data for . When the telephone call is placed to a mobile user MSC (FCC) and reverse control channel. Mobile receives the paging message sent by the BS which . call initialization and service request.Makes connections to the called party PSTN. BS signals the mobile to change frequency to an unused VC and RVC. 17 BS to maintain call quality.BS receives this and sends to MSC. .6. instructing the user to answer the phone.MSC validates requests. channel. over it. . system. When the mobile originates a call: . Monitors the control channels until the signal drops below a . RCC. MSC of handshake.handoff.jayaram. o Also transmits station class indicates mark . FCC – broad cast all traffic requests for all mobiles in a monitors and responds by identifying itself over RCC. • Call initiated by mobile. . Instructs unused FVC and RVC for communication.• Several types of services and capabilities are offered .• PCS = Personal Communication Services .Receives inform from HLR.• prominent in non-industrialized nations .16 standard has been developed for WLL. Digital Cellular/PCS .( Service area different from home registered as a roamer) . keyboards. Radio Frequency Identification Tags (RFID’s) on merchandize in . etc. . Mobile computers/email .com. themselves to monitor environments using a variety of then one from which service is subscribed.jayaram. Wireless Device Connectivity between computer peripherals (printers.Emerging .jayaram.com. 4.monitors. Downloaded from www.) – Bluetooth .• new IEEE 802.• cheaper to install than wired lines . Wireless Local Loop (WLL) . . Wireless-enabled Personal Digital Assistants (PDAs) . Sensor networks – small devices wirelessly communicating among Roaming: Allows subscriber to operates in service areas other .np/7 .np .• Motorola/Iridium . sensors. WLAN: Wireless Local Area Networks .warehouses and stores. Satellite to mobile ground units → Land Mobile Satellite (LMS) . .• local phone service via wireless connection . Downloaded from www. . np/8 .com.Downloaded from www.np Downloaded from www.jayaram.jayaram.com. Use voice calls only.Has advanced feature like caller identify and text messaging . o Poor security. (GSM – Global system for mobile): returned from handset to BS. . Data rate upto 9. o Dropped calls at handoffs.Band 935-960 Mhz used for downlink form BS to MS. . . &.The band of 890 – 915 Mhz dedicated to uplink from MS channels each of which would be used by particular callers. . to BS. o 8 time slotted user for each 200 kHz radio channel. Direct sequence.Each band is divided into 124 carrier frequency. o CDMA/FDD o Different users use diff. not suitable for web browsing and . Downloaded from www.Examples . Mobile assisted handoff.These systems used analog ckt-switched technology.6kbps . o Unreliable handover. Spread spectrum.com. . and faximile 3.jayaram. freq bands. o Poor voice quality.These systems typically allocated one 25 Mhz frequency band for the signals to be sent for the cell BS to the hand set Four Popular Standard for 2G: and the second different 25 mhz band for signals being 1. .Two frequency bands of 25Mhz bandwidth are used. .Generations (wireless communication systems): .Popular in North American.com. dividing spectrum up into frequency bands. .np/9 . multimedia applications. .jayaram. Pacific Digital Cellular. . .Three time-Slotted users per 30k Hz channel.These bands were then split into a no of communication . o Uses 30khz voice channels. o AMPS (Advanced mobile phone systems users. Access technology – 1st Generation: o TDMA/FDD or CDMA/FDD. South America & Australia. Downloaded from www. Frequency hopped.With frequency Division Multiple Access (FDMA).The network had a low traffic capacity. o TDMA: . Interim Standard 136 (IS -136): o Avoid the risk of interference & . o Multiple users are provided access to systems by User occupies different time slots. 2. . Signal is digitized . o Therefore total no of possible channels = 124×8 2nd Generation: producing 992(max) simultaneous conversations.Also called North American Digital cellular (NADC).A mobile phone systems that used purely digital technology. .np Lecture 2. o Work mainly in the 800-900 Mhz bands. Has the concept of Base station controller. Application possible: .Same air interface. Japan: First county to have a successful widespread mobile Advantages of 2G: data service. 4. Wireless application protocol(WAP) that allocates standard .jayaram.np/10 .A 2. that limit data users to a single ckt switched voice channel.6 kbps.Upgrade to software. o Popular in Europe and Japan. Interim Standard 95 (IS-95) . . Mobile commerce. .com.CDMA webpages to be viewed in acompressed format. . o From NTT DOCOMO (company). . equipment.5 G allows existing 2G equipment to be modified for TDMA upgrades: higher data rate transmissions. (b) Trial mode: (CDMA in PCS band. Downloaded from www.com. Many phones are compatible with more then one technology.64 user in 1025 MHz channel orthogonally coded. o Can send short message to another subscribers . Similar to IS-136.Also known as CDMA one . o SMS in GSM. (a) Dual mode: ( CDMA in PCS band Analog ) o Emode.Limited internet browsing. .) Games Color graphics. CDMA in cellular Proprietary data service band analog. More advanced applications are possible. changes at the base stations. . Japanes standard.Short message. .2. . . .jayaram. o Do not want to require wholesale RF equipment . . . Location based services.3 upgrade paths for GSM.Throughput less. directions etc). Drawbacks of 2G: Interactive web page browsing at 9. (map. Migration path: . . Downloaded from www.2G technology used ckt switched data modems channel Surprisingly popular: 25 million subscriber.5 G technology must match an upgrade path for the 2G technology that is in place.np .Can be used in 800 Mhz & 1900 Mhz bands. Email . .Addition of more equipment to work with base station phones. o Web browsing. o Email . 1.Upto 57. . o Cannot achieve 171.Adaptive modulation that uses the best modulation for . Takes away form the 171. . the more 171.GPRS units tune into GPRS radio channels and are o Packets are sent with different amount of error “Always on” to send data at any time. o Additional new hardware and software at BS.com. o Support technology path to 3G. instantaneous conditions of the network. o All data is sent as packets. Enhanced data rates for GAM Evolution (EDGE) for . 2. Downloaded from www.2 kbps when others users are . also sending data. o Applications must provide their own error correction bits. capable the system is at receiving from bad o 8 times 21. .jayaram. .More advance upgrade to GSM than GPRS. . coding.4 kbps (rate with error coding) channel quality. routers and internet gateway. Generalized packet radio service (GPRS) for GSM and o No change to RF hardware.np/11 . Upgrade requirements: o Streaming voice or low quality video.Ideal for “Voice like” services.If all 8 times slots are taken by one users. can achieve The more error coding is used . Started for GSM but upgraded to also support IS-136.2kbps. web browsing. 2 are also upgrades for IS-136. IS-136: .Shares individual radio channels and time slots.com.np . o New software at BS. since user traffic is o Different modulation technology possible than usually bursty GSM. o Users transmits in short bursts and then are idle.2 kbps.Completely refined air interface to handle packet data .Good for data applications.Assumes users download much more than the upload. o Can support many more users. .Allows subscriber to use groups of times slots in TDMA.6kbps. o Four 1404 kbps channels.jayaram. 3. . . GSM and IS-136: o Slower data rate upload than download. able to detect errors. High speed ckt switched data (HSCD) for GSM: Add additional bits (like CRC codes) to be . Downloaded from www.Only requires a software change at GSM base station. o Connections of BS into data network through o Interactive web sessions. . faxes. o Since it still uses voice channel capability. o Bit level packing same as GSM. . o GSM/IS-136/PDC (by the 3G partnership project o Upgrade path for IS-95 A to IS-95 B.Receiving line music.Additional bandwidth and capacity.Voice communication over internet protocol. and lower data rate. Telecommunication systems (UMTS) • 14. maximum data rate. . .5G for Wideband CDMA-3GPP) versus IS-95/IS-95B CDMA . Third Generation(3G) wireless Networks: HSCSD. Downloaded from www. for 2. GPRS. multiple GSM channels.Backwards compatible with GSM.jayaram. 3GPP2).2 kbps. to downturns in the telecommunication industry.Evolved since 1996.np o Start sending with maximum error protection and .np/12 .com. o Equipment for the previous technology will work .Voice activated calls. Until match is found with network conditions. can actually be achieved. Wideband-CDMA (W-CDMA) or the Universal Mobile simultaneously. . New spectrum allocation are being considered for 3G. o Although specrum auctions have been delayed due o Practical raw data rates upto 384 kbps . Interactive video.“Always on” access. in UMTS. . Users can use upto 8 CDMA codes 1. (by the 3G partnership project for cdma2000 - Only one upgrade path for IS-95. Virtual home entertainment. .From GSM/IS -136/PDC • Practical throughput is 64kbps that .Multi megabit internet access .Unparallel new capabilities. Simultaneous voice and data.From European Telecommunication Standards Institutue(ETSI). . . Broadcasting Subsequent packets sent with less protection .com. .Two major competing camps. .4kbps*8 = 115. o Network structure same as GSM. Downloaded from www. PDC. Much higher data rates.jayaram. channel o Based on what 2G technology is used already by o Can achieve server megabits per seconds by using each camp. . . IS-136. . and EDGE. For single user taking a full 200 khz GSM . Downloaded from www.com. o Do not have to change out entire base stations. manner. Videoconferencing. each base station. o Commonly just referred to as cdma2000 1X. location. ¾ Needs a minimum spectrum allocation of 5 Mhz. o RTT = Radio Transmission Technology. o If user is stationary. o Instantaneous data rate of 307 kbps. o Instead of 200 khz for GSM. coverage using PDD and indoor cordless type ¾ Allows wireless carriers to introduce 3G in a gradual using TDD.2.048 Mbps per user. ¾ Up to 2.25 MHz. o Requires complete change of RF equipment at Depends on number of users. o 6 times more efficient use of spectrum that GSM. chipping rates. Depends on velocity of the user. ¾ Uses twice as many voice users as 2G CDMA standard. o Many types of high data rates services are o Do not have to use different spectrum. Games. CDMA 2000 additional hardware. offering a simple form of 3G at first.np o WCDMA focuses on 3GPP standard body ¾ From IS-95/IS-95B. o Need dual-mode and tri-mode phones in the o Uses rapidly adjusting baseband singling and meantime. o To switch between 2G. for longer lasting battery life. ¾ Installation will likely be slow and gradual because ev. o Can introduce 3G capabilities at each cell. o Examples: Sprint PC’s 3G. Typical rates upto 144 kbps. WCDMQ.np/13 .jayaram. o Uses CDMA. ¾ Works within original 2G CDMA channel bandwidth of o Developing both for wide area mobile cellular 1. possible. Broadcasting. o 1X = one times the original IS-95(cdmaOne) Interactive video. All changes make in software or with 2. channel bandwidth. Downloaded from www. ¾ First air interface: cdma2000 1xRTT.com. They can Gradually implement 3G while Virtual home entrertainment. o Up to 8 Mbps in the future.5G and 3G depending on o No additional RF equipment is needed. Depends on the propagation conditions.jayaram. ¾ Provides subscriber unit with upto 2 times standby time CDMA requires expensive BS equipment. All from a small portable wireless video. np ¾ CDMA2000 1xEV.com. o Uses high frequencies. o 144 kbps with twice as many voice channels as IS. Can use the same spectrum.np/14 . Time-invariant o Throughput of 2 Mbps. tec. ¾ 1xEV-DO Same RF equipment. Rapidly deployable. internet. IS-95. o Can use wireless connections where there is o Actual data rates usually much lower. New RF hardware is needed. o 3xRTT uses three adjacent 1.com. Inexpensive. more seamless and less expensive upgrade path o High data rate packet standard overlaid on existing compared to W-CDMA. o Advocates of cdma2000 3xRTT claim a much o EV = Evolutionary enhancement. Now used to mean a “last-mile” connection o Three channels can be operated simultaneously in to a home or office.25 Mhz channel strictly on data users. Old telephone term for a loop of copper to ¾ Ultimate 3G CDMA connect a telephone to a telephone central o Multicarrier 3x and beyond. No new RF hardware is needed.25MHz channels. cable. ¾ 1xEV-DV o One broadband Internet connection could handle o Data and voice channel all needs for a home or office.4 Mbps throughput per ♦ Rapid growth of demand for internet connectivity. o Three channels can be operated as a group. and velocity of mobile. Downloaded from www. . o Much more predicable wireless channel. Downloaded from www. IS-95B. Similar to W-CDMA. No mobility. Particularly in developing nations.jayaram. office. o Data only channel Same air interface framework. parallel. o Highly dependent on number of users. o Local loop. ♦ What summarizes the difference in 2G and 3G? o Supports greater than 2. 95B. Voice .jayaram. user. propagations. o Restricts a 1. inadequate telecommunication infrastructure. 28 Ghz and higher. ♦ Fixed wireless. o Typical: Several hundred kbps. and cdma2000 networks. data. Goal is to promote interoperability between Cannot have any obstructions in between Tx vendors (interoperability between one and Rx.S. still expensive. Antennas can be of small physical size.11i is addressing an important non-radio o But large potential market in developing countries. o 802. o Unproven. vendor’s wireless card and a different Can be affected by weather. discuss yet. to be used.np/15 .S.4 GHz band. of spectrum allocation at several frequency levels o Current standard: UP to 20 Mbps. Downloaded from www.com. 802.7Ghz. vendor’s wireless access point).11b – 11Mbps. shorter range (only about 1/3 the range of o New types of service.11 – 2Mbps in 2. Downloaded from www. o Also 802. o High performance radio Local Area Networks o Unlicensed use has been encouraged through lots o European standard. 2. 5.11x (security VII.5 Mbps. o Also 802. ♦ IEEE 802. in addition to 2 Tens or hundreds of megabits per second are Mbps in 2.jayaram. Named Wi-Fi by the Wireless Ethernet o Line-of-sight. (www. o 802.jayaram.).4 Ghz band .11a -54 Mbps in 5 Ghz band with much ♦ Little market in the U.4Ghz.11b). o So owner does not need a license to set up a ♦ HIPERLAN: WLAN. Compatability Alliance. Wireless Local Area Networks (WLAN’s) keys)! ♦ Local Area Networks on the order of 100 meters or less in o There are lots of technical details we will not diameter. 5.11 o Predominant standard in the U. o HIPERLAN/2: Up to 54 Mbps.com. o 802. (900 Mhz. issue – security.11g is being developed for a different o Dependent on millimeter wave equipment that is type of radio transmission approach.np Allows very high gain directional antennas o Uses CDMA.11f (roaming) and 802. possible without distortion.wi-fi. o And 802.com) Much like light. ♦ Use unlicensed spectrum. o Uses frequency hopping spread spectrum. VIII.4 Ghz ISM unlicensed band. Important in WLANs. o Embraced by over 1. applications.000 manufactures. cell phones. connections with other devices. Networks of devices that are all peers and Early mobile: talk to whoever is near enough. o No “base station” concept. Goal is to unify the connectivity chores of o Ability to move equipment throughout an office.System Design Fundamentals Ad hoc – Formed for or concerned with one specific purpose (usually also considered I. Mouse cables. In a personal area Network (PAN). Printer cables. The Cellular Concept . military applications. Downloaded from www. installation based on a building floor plan. o Within 10 meters ranges. smart cards. military devices all could be wireless.jayaram. • Design objective: Downloaded from www. o Bluethooth is named after King Harold Bluetooth . o Needs good placement of equipment. o Uses 2. they change their WLAN is installed. etc. o In “ad hoc networks” devices talk to whatever other devices they can talk to. applications. o Uses an Ad-hoc network approaches. ♦ Wearable computers.jayaram. Norway. position location • Seen in WLANs.np ♦ WLAN performance depends heavily on how well the As devices move. o New opportunities for computes that are worn. 10th century Viking who united Denmark and Headphone cables. o Open standard.np/16 . May have to send data through a sequence o Author discusses tools for easy and effective of neighbors to reach and end destination. o PDAs.com. ♦ Bluetooth. o Ability to replace cumbersome cords. Introduction temporary ).com. etc. Bluetooth and Personal Area Networks: (PAN’s) o Why would Bluethooth want to use an ad-hoc approach? ♦ Roaming the wire. and shorter towers High capacity Small coverage areas called “cells” Large coverage area Each cell allocated a % of the total number of available Efficient use of limited spectrum channels Nearby (adjacent) cells assigned different channel groups • to prevent interference between neighboring base stations and mobile users Downloaded from www.jayaram.interference) (Bell system in New York City had 12 simultaneous channels for 1000 square miles ) • Small # users • Poor spectrum utilization What are possible ways we could increase the number of channels available in a cellular system? Solution: Cells labeled with the same letter use the same group of channels. (Applied in Bell system in New York City had early mobile radio) • Low cost • Achieved good coverage but Impossible to reuse those same frequencies throughout the system (Result.jayaram.np To use a single. Downloaded from www.com.com. high powered transmitter Frequency reuse pattern − Figure with antenna wanted on a tall tower. Cellular concept: Cell Cluster: group of N cells using complete set of available channels Goals of a Cellular System Many base stations. lower power.np/17 . Downloaded from www.np Same frequency channels may be reused by cells a base station antennas are designed to cover a “reasonable” specific cell area distance away hexagonal cell shape assumed for planning • reused many times as long as interference between same • simple model for easy analysis → circles leave channel gaps (co-channel) cells is < acceptable level • actual cell “footprint” is amorphous (no specific As frequency reuse ↑ # possible simultaneous users ↑ shape) # subscribers ↑ but system cost ↑ (more towers) . reduce cell sizes (more base stations) # possible coverage) simultaneous users ↑ .jayaram. ♦ The design process involves selecting & allocating .com. cellular base stations ♦ Two competing/conflicting objectives: System Capacity 1) maximize frequency reuse in specified area 2) minimize interference between cells For finding out the capacity of the system let us consider a ♦ Cells system having Downloaded from www.com.np/18 .Note that what is defined as a “corner” is somewhat flexible → a sectored antenna covers 120° of a hexagonal Frequency Reuse/Planning cell. reusing channels in .not necessarily in the exact center (can be The cellular concept allows all mobiles to be manufactured up to R/4 from the to use the ideal location) same set of frequencies • cell corners → sectored or directional antennas on 3 corners with *** A fixed # of channels serves a large # of users by 120° coverage.jayaram.very common a coverage area *** .where Tx successfully serves mobile unit To increase number of users without increasing radio base station location frequency • cell center → omni-directional antenna (360° allocation.So one can define a cell as having three antennas in the groups of channels to center or antennas at 3 corners. must ↑ to o To connect without gaps between adjacent cells— cover the entire coverage area (more clusters needed). etc. j ≥ 1. where i. systems like GSM. Downloaded from www. ♦ N cells/cluster ♦ If cluster size (N) is reduced and the geographic area for each ♦ Due to the fact of hexagonal geometry cell is kept o has six equidistant neighbor and lines joining constant: centers of the any cell and each of its neighbors are The geographic area covered by each cluster is smaller. level of co-channel interference determined by: A mobile or base station can only tolerate so much amount of allocated spectrum interference from channel BW → modulation format and/or standard specs.. ♦ k : number of channels for each cell (k < S) large N → large D → low interference → but small M and ♦ N : cluster size → # of cells forming cluster low C ! ♦k=S/N Tradeoff in quality and cluster size. the ♦ M : # of times a cluster is replicated over a geographic poorer the coverage area quality.) distance between co-channel cells (D) ♦ S : total # of duplex channels available for use in a given area. N.np (Note: Most of this discussion relates to FDMA/TDMA based capacity. can only have values which So C ↑.4.np/19 .g.12. ♦S=kN The larger the capacity for a given geographic area. satisfies the following equation: The smallest possible value of N is desirable to maximize system N = i2+ij+j2 .7. ♦ Cluster size N determines: AMPS. Frequency reuse is different for CDMA systems.com. so M separated by multiples of 60o. C=MS=MkN ♦ Frequency reuse factor = 1 / N (assuming exactly MN cells will cover the area) each frequency is reused every N cells each cell assigned k ≈ S / N Here. ♦ System Capacity = Total # Duplex Channels = C N = Cluster size – can be 3.jayaram. AMPS) quality. of cells per cluster. Downloaded from www.jayaram.com. the geometry of hexagon is such that the number S remains constant (same number of channels per cluster). we can see that. other cells using the same frequency and maintain sufficient (e. np/20 . Move i cells along any chain of hexagon and E 2. Downloaded from www. Here.000/50 60 i =3 = 165 channels A (a) for N = 4. Assume 75 voice channels are used for each cell in a ♦ Goal is to minimize interference & maximize use of capacity cluster size of N = 7 with one additional voice channel used as a lower interference allows smaller N to be used → control channel per cell. j = 660/7 = 95 channels. Example: Given a Frequency Division Duplex cell system Channel Assignment Strategies using two 25 kHz channels for frequency division duplex operation. Assume omni-directional antennas (1 greater frequency antenna/cell). i = 3.com. A B=165. A (Notes: number of channels in A = 165.jayaram. reuse → larger C What amount of spectrum is needed for such a system? ♦ Two main strategies: Fixed or Dynamic ♦ Fixed Given . Turn 60o anticlockwise and move j cells. A Channel BW = 2 *25 kHz A = 50 kHz/duplex channels.com.jayaram. (c) For N = 12 660/12 = 55 channels.D=165) (b) For N =7 D To find the nearest co-channel neighbor one must do the A F C following: B G 1. N= 19. A A C B A D j =2 60 Total number of channels per cell = 660/4 = 165 channels.np Total BW = 33 MHz = 33000khz. Downloaded from www. =2.C=165. 60 Total available channels = (Total BW)/ (Channel BW) = 33. jayaram.jayaram. Disadvantage: increases storage & computational load @ MSC Co-Channel Interference and System Capacity: • requires real-time data from entire network related to: Using frequency Reuse concept: − channel occupancy Many cells in a given coverage area use the same set of − traffic distribution channel Downloaded from www. that o Has been recognized as the major bottle neck in are using the same frequency) increasing the capacity of the cellular system. it Two major types of system-generated interference: increases the 1) Co-Channel Interference (CCI) trunking capacity). cellular radio systems.com. and increases voice quality 2) Adjacent Channel Interference (ACI). − likelihood of future call blocking in the cell o Interference: − reuse distance (interference potential with other cells o More in urban areas. − channel frequency All frequencies in a market are available to be used Advantage: reduces call blocking (that is to say.np/21 .com. channels NOT allocated permanently ♦ Interference on the voice channels call request → goes to serving base station → goes to o Causes cross talks on the control channels & MSC On the control channels MSC allocates channel “on the fly” o Causes missed and blocked calls due to error in the • allocation strategy considers: digital signaling.np each cell allocated a pre-determined set of voice − radio signal strength indications (RSSI's) from all channels channels • calls within cell only served by unused cell channels Interference and System capacity: • all channels used → blocked call → no service ♦ Interference several variations o Major limiting factor in the performance of • MSC might allow a cell to borrow a VC (that is to say. Downloaded from www. band. a ♦ Source of interference FVC/RVC pair) from an adjacent cell o Another mobile in the same cell or • donor cell must have an available VC to give o Any non cellular system which leaks energy in the ♦ Dynamic cellular freq. jayaram. Increase base station Tx power to improve radio signal reception? This will also increase interference from co. and coverage patterns ≈ same & BS transmits same power. ♦ Fundamental tradeoff in cellular system design: Downloaded from www. increased co-channel ♦ How to overcome? interference (CCI) → reduced voice quality → not Possible Solutions: so great A.jayaram.np frequencies to increase system capacity (C) small Q → small cluster size → more frequency Co-channel cells → cells that share the same set of reuse → larger system frequencies capacity → great ♦ Interference between signals form these cells is called co. Co-channel interference depends on: • R : cell radius • D : distance to base station of nearest co-channel cell if D / R ↑ then spatial separation relative to cell Small value of Q → provides larger capacity since ‘N’ is small. Voice Quality channel cells by the same amount no net improvement B. coverage area ↑ Large value of Q→ improves transmission quality due to • improved isolation from co-channel RF energy smaller level of co-channel interference. Downloaded from www. Separate co-channel cells by some minimum distance to provide sufficient isolation from propagation of radio signals? if all cell sizes.com. Tradeoff: Capacity vs.np/22 . But also: small Q → small cell separation → channel interference. transmit powers. Q = D / R : co-channel reuse ratio S/I → signal to interference ratio for a mobile receiver that • hexagonal cells → Q = D / R = 3N monitors forward channel is expressed as.com. com. and n is the same throughout coverage area Propagation measurement show that average received single (not always strength at a point decays as a power law of the distance true) then the above equation can be used.np/23 . separation between a transmitter and receiver.if base stations have equal Tx power (same S/I ratio for forward link can be found by sign the above S everywhere) equation (1).jayaram.jayaram. radio propagation properties are roughly the io : # of co-channel interfering cells same everywhere If the signal levels of co-channel cells are known. d → Distance from transmitting antenna Pr= Po (d/do )-n R −n Po →power received at a close interference point in the far field S/I = io region of the antenna at a small distance do. • When transmitting power of each BS is equal & Pr → Average received power • Path loss exponent is same through out the coverage area.is equal to distant D between cell centers.assuming the same n throughout the Ii→interference power caused by ith interferencing co-channel coverage area means cells.com.free space or line of sight (LOS) (no • AMPS → S / I ≥ 18 dB (assumes path loss exponent n obstruction) → n = 2 = 4) Downloaded from www. S/I = = i0 io Note: • n ranges from 2 to 4 in the urban area What determines acceptable S / I ? • voice quality → subjective testing .urban cellular → n = 2 to 4.(1) . . ∑ (D ) i =1 i −n n→ path loss exponent Considering only 1st layer of interfering cells and all BS are at Di →distance of the ith interference from mobile received equidistant --. . Downloaded from www.np S = S ……. signal decays i0 I faster with ∑I i =1 i distance away from the base station S→ desired signal power. power at a given mobile due to the ith interfering cell will be ( D / R) n ( 3N ) n proportional to (Di)-n . np • Most reasonable assumption is io (# of co-channel interfering cells) = 6 • Many assumptions involved in the above equation : • same Tx power • hexagonal geometry • n same throughout area • Di ≈ D (all interfering cells are equidistant from the base station receiver) • optimistic result in many cases • propagation tools are used to calculate S / I when assumptions aren’t valid • S / I is usually the least when a mobile is at the cell edge . i. Downloaded from www.np/24 .jayaram.e.low signal power from its own base station & high interference power from other cells.com.com. N =7 and S / I ≈ 17 dB (S / I) for forward link only.jayaram. the cochannel base Tx interfering with desired base station transmission to mobile unit • so this considers interference @ the mobile unit What about reverse link co-channel interference? • less important because signals from mobile antennas (near the ground) don’t propagate as well as those from tall base station antennas Downloaded from www. – More accurate picture: Fig. 56 dB. stations First consider N = 7 can regulate transmit power of mobiles to be no larger than We know S/I = (4. all of Since this is greater than minimum required S/I.np/25 .583 ( 3N ) n Signal to interference ratio S/I = io ( 3N ) n Signal to interference ratio S/I = io The no of co-channel cells in the 1st tier is 6.3 = 18. necessary Since this is less than minimum required S/I (i.2 We need to use larger N. 18 dB) Example: 3. Use suitable used.04 = 12. Solution: (a) n = 4.com. approximations.com.jayaram. Therefore . what is the frequency reuse factor and cluster size that io should be used for maximum capacity? If the path loss S/I = 1/6 × (6)3 = 36 = 15.05dB. • also weaker because mobile Tx power is variable → base (b) n = 3. S/I = 1/6 (4. We know that Frequency reuse ratio Q = D/R = √(3N) = √(3×7) = √(21) = 4. consider N=12. Downloaded from www. Downloaded from www. exponent is (a) n = 4.np • obstructions near ground level significantly attenuate mobile Since this is greater than minimum required S/I. If the signal to interference ratio of 15dB is required for Now. satisfactory forward channel performance of the cellular ( 3N ) n S/I = =6. N = 12 is them at the same distance from the mobile. First consider 7 cell reuse pattern.0 system.66 dB.jayaram.583)4 = 75. N = 7 can be energy in direction of base station Rx used. (b) n = 3. Assume that there are six co-channel cells in the 1st tier.5830)3/6 = 16.e. jayaram.com.jayaram.np Downloaded from www.np/26 .com. Downloaded from www.