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Cellular Networks Lecture 6 Paul Flynn. Cellular Telephony - Architecture.

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Presentation on theme: "Cellular Networks Lecture 6 Paul Flynn. Cellular Telephony - Architecture."— Presentation transcript:

1 Cellular Networks Lecture 6 Paul Flynn

2 Cellular Telephony - Architecture

3 Very Basic Cellular/PCS Architecture Base Station (BS) Mobile Station Base Station Controller Mobility Database Mobile Switching Center (MSC) Radio Network Public Switched Telephone Network

4 Duplex Communication - FDD FDD: Frequency Division Duplex Base Station B Mobile Terminal M Forward Channel Reverse Channel Forward Channel and Reverse Channel use different frequency bands

5 Access Methods Frequency Time Frequency Time Frequency Time FDMA TDMA CDMA

6 Clusters A cluster is a group of cells –No channels are reused within a cluster A seven Cell Cluster

7 Example - Frequency Spectrum Allocation in U.S. Cellular Radio Service … … … … MHz MHz Reverse ChannelForward Channel Channel NumberCenter Frequency (MHz) Reverse Channel 1 <=N <= <= N <= 1023 Forward Channel 1 <=N <= <= N <= N (N-1023) N (N-1023) (Channels are unused) Channel bandwidth is 45 MHz

8 Frequency Reuse Only a small number of radio channel frequencies were available for mobile systems –Therefore engineers had to find a way to reuse radio channels to carry more than one conversation at a time –The solution the industry adopted was called frequency reuse. Implemented by restructuring the mobile telephone system architecture into the cellular concept

9 Frequency Reuse The concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area –Cells are assigned a group of channels that is completely different from neighbouring cells –The coverage area of cells is called the footprint and is limited by a boundary so that the same group of channels can be used in cells that are far enough apart

10 Frequency Reuse Cells with the same number have the same set of frequencies Frequency Reuse

11 Frequency Reuse using 7 frequencies allocations f4 f3 f2 f1 f6 f7 f5 f4 f3 f2 f1 f6 f7 f5 f4 f3 f2 f1 f6 f7 f5 f4 f3 f2 f1 f6 f7 f5 f4 f3 f2 f1 f6 f7 f5 Each cell is generally 4 to 8 miles in diameter with a lower limit around 2 miles.

12 Cell Splitting Allows urban centres to be split into as many areas as necessary for acceptable service levels in heavy-traffic regions, while larger, less expensive cells can be used to cover remote rural regions

13 Cellular Concept with Sectors base station frequency re-use

14 Hand-off The final obstacle in the development of the cellular network involved the problem created when a mobile subscriber moved from one cell to another during a call

15 Internet PSTN (Telephone Network) Looking to PCS from different Angles Mobile Users -Cell phone users -Cordless phone users Mobile Users -Laptop users -Pocket PC users -Mobile IP, DHCP enabled computers Wireless Access Telecom People View Data Networking People View

16 Telecom and Data Networking -Radio Propagation -Link Characteristics -Error Models -Wireless Medium Access (MAC) - Error Control -Data Transmission -Mobile IP (integrating mobile hosts to internet) -Ad-hoc Networks -TCP over Wireless -Service Discovery - Voice Transmission - Frequency Reuse - Handoff Management -Location Tracking -Roaming -QoS -GSM, CDMA, Cordless Phones, -GPRS, EDGE Telecom InterestData Networking Interest

17 Major Mobile Radio Standards USA StandardTypeYear Intro Multiple Access Frequency Band (MHz) ModulationChanne l BW (KHz) AMPS Cellular1983FDMA FM30 USDC Cellular1991TDMA DQPSK30 CDPD Cellular1993FH/Packet GMSK30 IS-95 Cellular/PCS1993CDMA QPSK/BPSK1250 FLEX Paging1993SimplexSeveral4-FSK15 DCS-1900 (GSM) PCS1994TDMA GMSK200 PACS Cordless/PC S 1994TDMA/FDMA DQPSK300

18 Major Mobile Radio Standards - Europe StandardTypeYear Intro Multiple Access Frequency Band (MHz) ModulationChanne l BW (KHz) ETACS Cellular1985FDMA900FM25 NMT-900 Cellular1986FDMA FM12.5 GSM Cellular/PCS1990TDMA GMSK200KHz C-450 Cellular1985FDMA FM20-10 ERMES Paging1993FDMA4Several4-FSK25 CT2 Cordless1989FDMA GFSK100 DECT Cordless1993TDMA GFSK1728 DCS-1800 Cordless/PC S 1993TDMA GMSK200

19 Example - Frequency Spectrum Allocation in U.S. Cellular Radio Service … … … … MHz MHz Reverse ChannelForward Channel Channel NumberCenter Frequency (MHz) Reverse Channel 1 <=N <= <= N <= 1023 Forward Channel 1 <=N <= <= N <= N (N-1023) N (N-1023) (Channels are unused) Channel bandwidth is 45 MHz

20 2G Technologies cdmaOne (IS-95)GSM, DCS-1900IS-54/IS-136 PDC Uplink Frequencies (MHz) (Cellular) (US PCS) MHz (Eurpe) (US PCS) 800 MHz, 1500 Mhz (Japan) (US PCS) Downlink Frequencies MHz (US Cellular) MHz (US PCS) (Europa) (US PCS) MHz (Cellular) (US PCS) 800 MHz, 1500 MHz (Japan) DeplexingFDD Multiple AccessCDMATDMA ModulationBPSK with Quadrature Spreading GMSK with BT=0.3  DQPSK Carrier Seperation1.25 MHz200 KHz30 KHz (IS-136) (25 KHz PDC) Channel Data Rate Mchips/sec Kbps48.6 Kbps (IS-136) 42 Kbps (PDC) Voice Channels per carrier 6483 Speech CodingCELP at 13Kbps EVRC at 8Kbps RPE-LTP at 13 KbpsVSELP at 7.95 Kbps

21 GSM Speech Signal Processing

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23 GSM and CDMA Coverage Map Worldwide

24 What is WiMax? Worldwide Interoperability for Microwave Access Last mile wireless broadband access Alternative to cable and DSL Deliver data, voice, video Support hundreds to thousands of homes/business

25 Defined by IEEE as Typical target environment: Targets fixed, portable, and mobile stations Environments with and without line of sight Cell radius of 3-10 kilometers Capacities of up to 40 Mbps per channel Mobile network deployments of up to 15 Mbps, 3 km radius

26 Builds on and Extends WiFi Technology Advantages of WiFi are: Easy to deploy, unlicensed spectrum, low cost Supports (limited) mobility But WiMax needs to address the following:

27 WiFi limitations Susceptible to interference targets short-range indoor operation (mostly) Security is a concern Limited level of mobility WiMax is intended to complement WiFi WiMax Forum: promotes WiMax and looks after interoperability

28 WiMax Deployment


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