Cellular Networks 1

Overview 1G Analog Cellular 2G TDMA - GSM 2G CDMA - IS G 3G 4G and Beyond Cellular Engineering Issues 2

1G (<1Kbps) 1 Kbps 10 Kbps 100 Kbps 2 Mbps 1 Mbps Data Rates G (9.6Kbps) 2.5G (10-150Kbps) 3G (144Kbps to 2Mbps) Years Overview 3

Cellular networks: From 1G to 3G 1G: First generation wireless cellular: Early 1980s –Analog transmission, primarily speech: AMPS (Advanced Mobile Phone Systems) and others 2G: Second generation wireless cellular: Late 1980s –Digital transmission –Primarily speech and low bit-rate data (9.6 Kbps) –High-tier: GSM, IS-95 (CDMA), etc –Low-tier (PCS): Low-cost, low-power, low-mobility e.g. PACS 2.5G: 2G evolved to medium rate (< 100kbps) data 3G: future Broadband multimedia –144 kbps kbps for high-mobility, high coverage –2 Mbps for low-mobility and low coverage Beyond 3G: research in 4G 4

A Cellular Network Public Switched Telephone Network (PSTN) Mobile Telephone Switching Center (MTSC) Base Transceiver Station (BTS) Mobile User Cell 1 Cell 2 Cordless connection Wired connection HLRVLR HLR = Home Location Register VLR = Visitor Location Register 5

Mobile telecommunications switching office (MTSO) Essentially an end office to connect calls between mobile units Several base stations connected to an MTSO In a large system, many MTSOs may be connected to a second level MTSO and so on MTSO connected to BSs, PSTN and each other through packet switching (ATM) Two types of channels available between mobile unit and BS –Control channels – used to exchange information having to do with setting up and maintaining calls –Traffic channels – carry voice or data connection between users 6

Cellular System Handoffs (typically 30 mseconds): 1. At any time, mobile station (MS) is in one cell and under the control of a BS 2. When a MS leaves a cell, BS notices weak signal 3. BS asks surrounding BSs if they are getting a stronger signal 4. BS transfers ownership to one with strongest signal 5. MTSO assigns new channel to the MS and notifies MS of new boss Public Switched Telephone Network (PSTN) Mobile Telephone Switching Center (MTSC) Cell 1 Cell 2 HLRVLR 7

Cellular Network Organization Cell design (around 10 mile radius) –Served by base station consisting of transmitter, receiver, and control unit –Base station (BS) antenna is placed in high places (churches, high rise buildings) - Operators pay around $500 per month for BS –10 to 50 frequencies assigned to each cell –Cells set up such that antennas of all neighbors are equidistant (hexagonal pattern) In North America, two 25-MHz bands allocated to AMPS –One for transmission from base to mobile unit –One for transmission from mobile unit to base 8

AMPS Operation Each phone has a 32 bit serial no and 10 digit phone no in its PROM When a phone is turned on, it scans for control signals from BSs It sends this info to BS with strongest control signal - passed to MTSO Subscriber initiates call by keying in phone number and presses send key MTSO verifies number and authorizes user MTSO issues message to user’s cell phone indicating send and receive traffic channels MTSO sends ringing signal to called party Party answers; MTSO establishes circuit and initiates billing information Either party hangs up; MTSO releases circuit, frees channels, completes billing 9

Mobile Station and Base Station Subsystem (BSS) Mobile station Mobile station communicates across Um interface (air interface) with base station transceiver in same cell as mobile unit Mobile equipment (ME) – physical terminal, such as a telephone or PCS –ME includes radio transceiver, digital signal processors and subscriber identity module (SIM) GSM subscriber units are generic until SIM is inserted –SIMs roam, not necessarily the subscriber devices BSS BSS consists of base station controller and one or more base transceiver stations (BTS) BSC reserves radio frequencies, manages handoff of mobile unit from one cell to another within BSS, and controls paging 10

Network Subsystem Center Mobile Switching Center (MSC) is at core; consists of several databases Home location register (HLR) database – stores information about each subscriber that belongs to it Visitor location register (VLR) database – maintains information about subscribers currently physically in the region Authentication center database (AuC) – used for authentication activities, holds encryption keys Equipment identity register database (EIR) – keeps track of the type of equipment that exists at the mobile station 11

4G Systems Wireless networks with cellular data rates of 20 Mbits/second and beyond. AT&T has began a two-phase upgrade of its wireless network on the way to 4G Access. Nortel developing developing features for Internet protocol-based 4G networks Alcatel, Ericsson, Nokia and Siemens found a new Wireless World Research Forum (WWRF) for research on wireless communications beyond 3G. Many new technologies and techniques (multiplexing, intelligent antennas, digital signal processing) Industry response is mixed (some very critical) 12