Information Technology Wireless Network Technologies

Information Technology I Wireless Communications � Wireless telephony � Wireless LANs � Location-based services The Technology: Radio Spectrum � Radio Spectrum: from 30 KHz to 3 GHz � � � � � AM radio: 540KHz – 1800 KHz FM radio: 88 MHz – 108 MHz Cellular (e.g. AMPS): 824 – 849, 869 – 894 MHz Cellular (e.g. GSM): 890 – 915, 935 – 960 MHz PCS frequencies: 1800 – 2200 MHz � Microwaves: from 3 GHz to 300 GHz � Infrared Spectrum: from 300 GHz to 300 THz Information Technology I The electromagnetic spectrum Issue: Spectrum is a scarce resource! Possible Solutions: � Frequency reuse (cells) � Multiplexing Information Technology I How a cell phone works Cellular Phone Networks � Frequency reuse � Handoff Information Technology I Cellular Phone Networks � Frequency reuse � Handoff Cellular Phone Networks � Frequency reuse � Handoff Information Technology I Problem: Reuse not good enough! � Radio waves attenuate at a rate proportional to the square of distance (1/r2) � This means that faraway cells are irrelevant but we still can have interference from adjacent cells � Therefore, a cell cannot reuse the same channels as its 6 immediate neighbors � This means that each cell can only use 1/7th of the spectrum allocation… � Example: AMPS system � Each operator was given 416 2-way channels but could only use about 416/7 ~ 60 channels at any given cell Multiple Access Technologies � FDMA: Frequency Division Multiple Access � � TDMA: Time Division Multiple Access � � Each call occupies a different frequency and has an exclusive use of that frequency during the call Several calls can share the same frequency by alternating in time CDMA: Code Division Multiple Access � Multiple calls mixed together; each call spread over the entire available spectrum; calls can be reconstructed by using call-specific keys. Information Technology I TDMA: Time Division Multiple Access TDMA - Time Division Multiple Access Cellular phone 1 Cellular phone 1 e3 Message 1 Message 2 Message 3 Time Slot 1 Time Slot 2 Time Slot 3 M Cellular phone 3 Cellular phone 2 Cellular phone 3 Cellular phone 2 TDMA � Dual-Mode Capability � 3x the capacity of analog networks � 6 time slots per channel � 30 kHz Channel Spacing � 2 time slots per mobile � uplink Tx � 832 Channels � downlink Rx � 8 kbps (Full Rate Mobiles) � 3 calls per channel 30 kHz Channel Time Slot 1 Time Slot 2 Time Slot 3 Time Slot 4 Time Slot 5 Time Slot 6 lot 2 Time Slot 1 Time Slot 3 Time Slot 2 Time Slot 5 Time Slot 4 Time Slot 6 Information Technology I TDMA � 4 Kbps (Half Rate Mobiles) � 6 time slots per channel � 1 time slots per mobile – handles both uplink Tx/ downlink Rx � 6 calls per channel 30 kHz Channel Time Slot 1 Time Slot 2 Time Slot 3 Time Slot 4 Time Slot 5 Time Slot 6 CDMA: Code Division Multiple Access CDMA - Code Division Multiple Access Code 1 Cellular phone 1 Message Code 3 Code 2 Message Message Cellular phone 3 Cellular phone 2 Code 3 Voice Packets Message Code 1 Code 2 Message Message Information Technology I Frequency Hopping Spread Spectrum Short duration hops between radio frequencies � Sender and receiver know sequence Frequency Slots � 80 60 40 20 0 0 1 2 3 4 5 6 7 8 Time Random number generators � � Simplest approach is to use the following recurrence sequence: x 0 x n+1 =P1xn +P2 (mod N) n = 0,1,2,... For example: P � = given, 1 = 16807, P 2 = 0, and N= 2 31 -1 = 2147483647 Basic property: � If P1, P2 known, then different choices of the initial seed x0 result in completely distinct sequences � Therefore, the seed x0 can act as the code, to be exchanged between sender and receiver Information Technology I History of CDMA � Co-invented by actress Hedy Lamarr during World War II as a technique against interference of submarine communications � She was inspired by the musical notes encoded on the scrolls of a player piano Summary of multiplexing methods Information Technology I Advantages of CDMA � Spread Spectrum Analysis � 1.23 MHz channel vs. 30 kHz � Each call is distinguished by a unique digital code different from others users transmitting at the same frequency band � >= 10 times the capacity of analog networks � Lower Power Terminals/Longer Battery Life Generations of mobile phone technologies � 1G � 2G � 2.5G � 3G Information Technology I History � First Generation: Analog � � � Second Generation: Digital � � � GSM (1st Europe, then world-wide) Digital AMPS (IS-54) 2.5: PCS � � � � AMPS (USA) NMT (Europe) DCS-1800 (world-wide except USA) DCS-1900 (USA) CDMA (IS-95, USA) Third Generation: Personal Communication Systems � UMTS Migration of Digital Cellular Systems Circuit-Switched Voice Circuit-Switched Packet-Switched Data Packet-Switched GSM Circuit-Switched Voice Packet Data GPRS EDGE IS-136 Circuit-Switched Voice Packet Voice & Data over EDGE IS-136+ EDGE GPRS: General Packet Radio Service (17.6 kbps x 8) EDGE: Enhanced Data for GSM Evolution (59.2 kbps x 8) UMTS: Universal Mobile Telecomm Systems UMTS CDMA2000 Packet Voice & Data over UMTS (WCDMA) Information Technology I General Packet Radio Service (GPRS) � Extension to GSM to support packet transmission � Transmission rates: 57.6 and 115.2Kbps initial rates will be lower: 20-30 Kbps � Good integration with the TCP/IP protocol � Cingular Wireless deploys GPRS network in San Francisco/San Jose in March 2001; uses Ericsson’s 520 handsets Summary Information Technology I Wireless LANs and PANs Major developments: � IEEE 802.11 standard for wireless LANs � Home Radio Frequency Spec (HomeRF) � Bluetooth Wireless LAN industry will grow from $300M in 1998 to $1.6B in 2005 (Frost & Sullivan) IEEE 802.11 Standard � Operates in 2.4-2.4835GHz frequency band � � 2 standards: � � � unlicensed band for industrial/scientific/medical apps original 802.11: transmission rates 1-2Mbps 802.11b (High Rate): transmission rates up to 11Mbps (actual data transmission rate is about 7Mbps) Transmission distances: � � � top transmission rates achieved within 150 ft; 1Mbps rates can be achieved within 1000 ft; signals can be transmitted through walls Information Technology I Advantages of 802.11b � network access freedom for mobile workers � cost-effective network setup for hard-to-wire locations (e.g., old buildings) � reduced cost of ownership especially when frequent network changes required Total economic benefits can add up to $16K per user (“WLANs : ROI/Cost-Benefit Study,” WLANA, Oct 1998) Wireless LAN Applications � Earlier applications: mostly vertical � � manufacturing facilities, warehouses, retail stores, car rentals More recent applications: � � � healthcare facilities (bedside access to patient info by doctors), educational institutions (e.g., Stern - study group meetings, research links) corporate offices (on-site consultants, database access for roving supervisors, customer info) Information Technology I Bluetooth � A PAN – has a set of wireless protocols; enables devices to communicate within 10m distance. � Transmission rates: 432.5Kbps (both ways for symmetric transmission) � 721/57.6 Kbps (asymmetric transmission) � 1300 companies support Bluetooth (12/1999) � Applications: cars, homes, wireless phones Bluetooth � Consortium: Ericsson, Intel, IBM, Nokia, Toshiba - many members � Scenarios � connection of peripheral devices � support of ad-hoc networking � bridging of networks - loudspeaker, joystick, headset - small devices, low-cost - e.g., GSM via mobile phone - Bluetooth - laptop � Simple, cheap (target < $5/device), replacement of cables and IrDA, low range, lower data rates � 2.4 GHz, FHSS, TDD, CDMA Information Technology I Piconets and Scatternets � Each piconet has one master and up to 7 slaves � Master determines hopping sequence, slaves have to synchronize � Participation in a piconet = synchronization to hopping sequence � Communication between piconets = devices jumping back and forth between the piconets piconets Bluetooth Applications � Wireless PDAs always connected to desktop via mobile phone � Wireless headphones connected to notebook � Office/Home device networks that automatically reconfigure by presence � … Information Technology I Bluetooth Success Factors � Low enough cost � � Existence of wideband, circuit-switched mobile networks � � Currently $25-50, will reach $5 at 2003-4 Depends on 3G mobile developments Standardized software protocols � … still mostly on paper! Summary Information Technology I Location-based Services: Definition “Location-based services (LBS) are any activity conducted over a cellular network where the accurate determination of a user’s position is fundamental to the enabling of that activity” (Yankee Group) Cell-ID • old technology • cell size varies from 100m radius to 35km radius • still: sufficient accuracy for many applications Information Technology I Time Difference of Arrival (TDOA) • calculates difference in arrival time at pairs of cell sites • requires two pairs, i.e. three different cell sites • clocks at cell sites need to be synchronized TDOA Implementation • Existing antennas can be used • Additional device (clock, measurement unit) installed in each base station Information Technology I Angle of Arrival (AOA) • only two base stations required • complex antenna array in precise pattern • cost and practical issues (zoning regulations) • accuracy degrades over distance • mainly used to supplement TDOA in areas where only two base stations are available Enhanced Observed Time Difference • Cursor EOTD by CPS in UK beta trial with Vodafone • Requires 3 Base station and Location Measurement Unit • Promises under 50m precision with 3G • Location circles by computing time delta between BTS and handset vs BTS and LMU. • Intersection of 3 circles gives location 42 Information Technology I Assisted GPS • Snaptrack (Qualcomm) • Increased sensitivity receiver allows for GPS tracking even when no line of sight • Cell location sends request for snapshot from relevant GPS satellite • Limitations within buildings • Combines precision of GPS with information given by cell ID to achieve rapid location A Classic Example of Standards War Precision Market stage Location fix Network Modifications Handset Modifications E911 complient Cell Id 100m to 30 km Proven 3 sec None None No TDOA/AOA E-OTD A-GPS 100 to 250m 50 to 125m 5 to 50m Beta Beta 2002 3-5 sec 10 sec 5 sec Clock Location None Measurement Measurement Units or Units Antennas None Software Hardware: installation GPS enabled units Yes Yes Yes Difficult to predict the emerging standard the real winner might be upstream in the value chain Information Technology I Location-Based Service Categories Information Yellow pages Navigation services Traffic information Trigger Services Tracking Fleet Management Asset Tracking People Tracking Location Services Safety Emergency Services Roadside Assistance Personal Security Event-Based Advertising/Promotions Location-Sensitive Billing Entertainment Gaming