# Cellular Networks Lecture 6 Paul Flynn.

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Cellular Networks Lecture 6 Paul Flynn

Cellular Telephony - Architecture

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

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

Access Methods FDMA TDMA CDMA Frequency Frequency Time Time Frequency

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

Example - Frequency Spectrum Allocation in U.S. Cellular Radio Service
Reverse Channel Forward Channel 991 992 1023 1 2 799 991 992 1023 1 2 799 MHz MHz Channel Number Center Frequency (MHz) Reverse Channel 1 <=N <= 799 991 <= N <= 1023 0.030N 0.030(N-1023) Forward Channel 1 <=N <= 799 991 <= N <= 1023 0.030N 0.030(N-1023) (Channels are unused) Channel bandwidth is 45 MHz

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

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

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

Frequency Reuse using 7 frequencies allocations
Each cell is generally 4 to 8 miles in diameter with a lower limit around 2 miles.

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

Cellular Concept with Sectors
frequency re-use base station

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

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

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

Type Year Intro Multiple Access Frequency Band (MHz) Modulation Channel BW (KHz) AMPS Cellular 1983 FDMA FM 30 USDC 1991 TDMA DQPSK CDPD 1993 FH/Packet GMSK IS-95 Cellular/PCS CDMA QPSK/BPSK 1250 FLEX Paging Simplex Several 4-FSK 15 DCS-1900 (GSM) PCS 1994 200 PACS Cordless/PCS TDMA/FDMA 300

Major Mobile Radio Standards - Europe
Type Year Intro Multiple Access Frequency Band (MHz) Modulation Channel BW (KHz) ETACS Cellular 1985 FDMA 900 FM 25 NMT-900 1986 12.5 GSM Cellular/PCS 1990 TDMA GMSK 200KHz C-450 20-10 ERMES Paging 1993 FDMA4 Several 4-FSK CT2 Cordless 1989 GFSK 100 DECT 1728 DCS-1800 Cordless/PCS 200

Example - Frequency Spectrum Allocation in U.S. Cellular Radio Service
Reverse Channel Forward Channel 991 992 1023 1 2 799 991 992 1023 1 2 799 MHz MHz Channel Number Center Frequency (MHz) Reverse Channel 1 <=N <= 799 991 <= N <= 1023 0.030N 0.030(N-1023) Forward Channel 1 <=N <= 799 991 <= N <= 1023 0.030N 0.030(N-1023) (Channels are unused) Channel bandwidth is 45 MHz

2G Technologies cdmaOne (IS-95) GSM, DCS-1900 IS-54/IS-136 PDC
Uplink Frequencies (MHz) (Cellular) (US PCS) MHz (Eurpe) (US PCS) 800 MHz, 1500 Mhz (Japan) Downlink Frequencies MHz (US Cellular) MHz (US PCS) (Europa) (US PCS) MHz (Cellular) (US PCS) 800 MHz, 1500 MHz (Japan) Deplexing FDD Multiple Access CDMA TDMA Modulation BPSK with Quadrature Spreading GMSK with BT=0.3 p/4 DQPSK Carrier Seperation 1.25 MHz 200 KHz 30 KHz (IS-136) (25 KHz PDC) Channel Data Rate Mchips/sec Kbps 48.6 Kbps (IS-136) 42 Kbps (PDC) Voice Channels per carrier 64 8 3 Speech Coding CELP at 13Kbps EVRC at 8Kbps RPE-LTP at 13 Kbps VSELP at 7.95 Kbps

GSM Speech Signal Processing

GSM and CDMA Coverage Map Worldwide

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

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

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:

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

WiMax Deployment