Wireless Networks In this paper we present a communication platform dedicated to support a vehicular communication model developed by the authors for the exchange of safety-related data between traffic participants. Wireless networks

Wireless Networks Background Overview of Cellular Networks Lecture Outline Wireless Networks Background Overview of Cellular Networks Overview of Satellite Networks Overview of Wireless Local Area Networks Other Wireless Networks In this paper we present a communication platform dedicated to support a vehicular communication model developed by the authors for the exchange of safety-related data between traffic participants. Based on the book: “Wireless communication and networks” by © William Stallings, 2002 Prentice Hall

Communication Frequency Spectrum Electromagnetic spectrum and applications (Tanenbaum 2003)

Wireless Networks Background Aspects of Wireless Networks mobility and convenient deployment scarce frequency spectrum wireless implications such as transmission problems (e.g. interference, path loss, fading), security, battery, installation, health Wireless networks Cellular: GSM, PCS, IMT 2000 Satellite: IRIDIUM, Globalstar WLAN: IEEE 802.11, HiperLAN Ad-Hoc, PAN, HAN - 9000 injuries each day in E.U. in 1999 - interest in developing ITS service for traffic safety and convenience - vehicular communication can offer extensive support to ITS safety services - nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

Wireless Cellular Networks Extensive evolution and fast deployment First-Generation Mobile Phones: analog voice (e.g. AMPS, NMT) Second-Generation Mobile Phones: digital voice and some data (e.g. GSM, IS-95) Third-Generation Mobile Phones: digital voice and data (e.g. 3G) - 9000 injuries each day in E.U. in 1999 - interest in developing ITS service for traffic safety and convenience - vehicular communication can offer extensive support to ITS safety services - nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

Principles of cellular networks [1] Mobile Terminals and Base Stations Communication area divided in hexagonal cells Cell dimensions from hundreds of meters till tens of kilometers (e.g. GSM: 100m to 35 Km) Each cell served by a base station formed by a transceiver and a control unit Each cell allocated a frequency band for communication Communication from MS to BS -> reverse link Communication from BS to MS -> forward link - 9000 injuries each day in E.U. in 1999 - interest in developing ITS service for traffic safety and convenience - vehicular communication can offer extensive support to ITS safety services - nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

Principles of cellular networks [2] Frequency reuse: use the same frequency spectrum in different set of cells Cells that reuse the same frequency must be distant enough for avoiding interference Transmission power control Migration of a mobile station from one cell to another with continuance of communication -> handoff - 9000 injuries each day in E.U. in 1999 - interest in developing ITS service for traffic safety and convenience - vehicular communication can offer extensive support to ITS safety services - nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

Methods for increase capacity in cellular networks Adding new channels Frequency borrowing: congested cells use frequencies taken from adjacent cells Cell splitting: due to initial network design high-used cells are divided in smaller cells and frequencies are reallocated Cell sectoring: cells divided in sectors (e.g. 3, 6 sectors) each sector has allocated its own set of channels base stations use directional antennas for covering sectors Microcells and picocells: very small cells - 9000 injuries each day in E.U. in 1999 - interest in developing ITS service for traffic safety and convenience - vehicular communication can offer extensive support to ITS safety services - nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

Cellular systems - general architecture General cellular system: Mobile Station (MS) Base Station (BS) Mobile telecommunication switching office (MTSO) Communication between mobile station and base station use: Control channels: exchange control data for calls management Traffic channels: data or voice connections between users Dominant switching mode: circuit-switch MS BS

Cellular systems operation example [1] (a) Mobile station initialization (b) Mobile-originated call (c) Paging (d) Call accepted - 9000 injuries each day in E.U. in 1999 - interest in developing ITS service for traffic safety and convenience - vehicular communication can offer extensive support to ITS safety services - nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

Cellular systems operation example [2] (e) Ongoing call (f) Handoff Other operations: call blocking call termination call drop calls to/from fixed and remote mobile subscriber - 9000 injuries each day in E.U. in 1999 - interest in developing ITS service for traffic safety and convenience - vehicular communication can offer extensive support to ITS safety services - nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

Aspects of Cellular Networks [1] Radiowave propagation: signal strength fading diverse propagation patterns Handoff: assigning a MS to a BS other than the current one when MS move from one cell toward other cell Different handoff parameters: cell blocking probability, call dropping, call completion, handoff success, handoff blocking, ... Handoff strategies: relative signal strength relative signal strength with threshold relative signal strength with hysteresis relative signal strength with hysteresis and threshold prediction techniques - 9000 injuries each day in E.U. in 1999 - interest in developing ITS service for traffic safety and convenience - vehicular communication can offer extensive support to ITS safety services - nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

Aspects of Cellular Networks [2] Power control requirements: reduce interference increase battery life overcome transmission conditions equalize received power (SS) other... Open-loop power control (a) depends on mobile station Closed-loop power control (b) depends on base station (b) Closed-loop power control (a) Open-loop power control

Aspects of Cellular Networks [3] - Access Methods Frequency Division Multiple Access ->FDMA two (frequency) channels assigned per user, one for forward and one for reverse used in first generation cellular (e.g. AMPS) Time Division Multiple Access ->TDMA each physical channel divided in logical subchannels two logical channels assigned for user, for forward and reverse links transmission in repetitive sequence of frames divided in time slots each time slot position forms a logical channel that is assigned to the user used in second generation cellular (e.g. GSM) Code Division Multiple Access -> CDMA direct-sequence spread spectrum transmission -> use a chipping code for data two logical channels per user used in second and third generation cellular

Second Generation Cellular Networks - Example

GSM Cellular Network - 9000 injuries each day in E.U. in 1999 - interest in developing ITS service for traffic safety and convenience - vehicular communication can offer extensive support to ITS safety services - nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

First, Second, Third Generation Cellular Networks More in 2G than 1G: 2G have digital traffic channels, 1G pure analog encryption error detection and correction dynamic channel access -> users share dynamically channels 3G capabilities: voice quality comparable with switched telephone network up to 384 kbps data rate outdoor support for up to 2.048 Mbps indoor symmetrical/asymmetrical data transmission rates support for circuit switched and packet switched data services support for wide variety of equipment efficient spectrum usage Internet interface flexibility

Satellite Communication Communication between earth stations and satellites Uplink-> earth station to satellite Downlink-> satellite to earth station Satellite categorization: Coverage area: global, regional, national Service type: fixed service satellite (FSS), broadcast service satellite (BSS), mobile service satellite (MSS) General usage: commercial, military, amateur, experimental

Satellite Networks Configurations Point-to-point link Broadcast link

Satellite Communication and Wireless Terrestrial Communication Advantages of satellite communication: extensive area of coverage relative slowly variant conditions for communication between satellites transmission cost independent of distance support for broadcast, multicast and point-to-point communication high bandwidth and high data rates high quality of transmission Drawbacks of satellite communication : expensive installation transmission delay needed terminals power needed number of satellites for global coverage

Satellite and Orbits GEO - geostationary orbit satellites LEO - low earth orbit satellites MEO - medium earth orbit satellites

GEO and LEO GEO characteristics: LEO characteristics: no problems with the frequency change due to satellite movement simplified tracking of satellite very large area coverage (e.g. 3 satellite for almost whole Earth) weak signal and extensive delay (e.g. 0.5 s) due to long distance polar region poorly served LEO characteristics: small coverage area-> big number of satellites satellite visibility cca. 20 minutes frequency changes due to satellite movement significant atmospheric drag small latency high data rates, up to few Mbps for Big LEOs

Frequency Bands for Satellite Communication

Issues in Satellite Communication Problems: Distance between earth station antenna and satellite antenna Downlink: terrestrial distance between earth antenna and the “aim point” of the satellite Atmospheric attenuation: oxygen, water, higher frequencies Capacity Allocation Strategies: frequency division multiple access (FDMA) time division multiple access (TDMA) code division multiple access (CDMA)

Satellite Communication Examples IRIDIUM LEO Satellite System TDMA Satellite Transmission

Wireless Local Area Networks (WLAN) General considerations: limited utilization till last decade but extensive development lately usually in spaces where wired networks were difficult or not appropriate to deploy may increase reliability cost effective different standards different transmission medium used Some WLAN implications: transmission problems: connection, multipath propagation, path loss and radio signal interference network security system interoperability installation issues and health risks

WLAN Applications [1] LAN Extension: Cross-Building Interconnect: wireless extensions to fixed LANs stations in large open areas single or multiple cells Cross-Building Interconnect: connect nearby building usually point-to-point communication connected devices: usually routers and bridges

WLAN Applications [2] Nomadic Access: connect mobile terminals with a LAN hub Ad-hoc Networking: spontaneous established temporary networks

WLAN Requirements [1] Throughput: efficient use of the transmission medium Number of nodes: large number of nodes may be needed Connection to backbone LAN: usually a connection with a wired networks is needed Service area: typical 100 to 300 m Battery life time: efficient management of mobile station battery Transmission robustness and security: WLAN may be interference prone and may be eavesdropped

WLAN Requirements [2] Collocated network operations: more than one WLAN in the same area License free operation: user oriented approach Handoff and roaming: moving between cells and even networks may be needed Dynamic configuration: addition, deletion and reallocation of end systems without affecting the network functionality

WLAN Technologies [1] Categorized according with the used transmission technology: Infrared (IR) LAN : IR does not penetrate walls limited to a single room Spread Spectrum LAN: use spread spectrum usually operate in ISM band Narrowband microwave LAN: operate at microwave frequency (e.g. above 1 GHz) can use ISM or licentiate frequency spectrum do not use spread spectrum

WLAN Technologies [2]

Infrared (IR) WLAN Directed Beam IR (a) point-to-point links range depend on power and wave focus (a) Omnidirectional IR (b) single base station in LOS of all stations the base station acts as a repeater (b) Diffused (c) all transmitter focus at a point on ceiling IR radiation is retransmitted (reradiate) reradiated IR waves are received by all stations in the area (c)

Infrared (IR) WLAN vs. Microwave WLAN Strengths virtual unlimited spectrum unregulated spectrum simple equipment needed -> inexpensive reflected by light-colored objects does not penetrate walls: more secure against eavesdropping and does not introduce interference Drawbacks: sunlight, indoor lighting and other ambient radiation perceived as noise high-power transmitter required -> may introduce health problem (i.e. eye safety) and power consumption problems limited range

Spread Spectrum and Narrowband WLAN Spread Spectrum WLAN usually multi-cell with different frequencies hub or peer-to-peer topology in a cell hub topology: the hub may provide access control and repeater operations and is usually connected to a backbone network peer-to-peer topology: use ad-hoc connectivity without any hub usually unlicensed spectrum interference prone Narrowband WLAN usually use narrow microwave band for transmission unlicensed as well as licensed frequency spectrum does not use spread spectrum licensed -> interference-free

Other Wireless Networks - Cordless Systems Characteristics Residential: single base station with support for voice and data Office: single base station for small offices, multiple base stations deployed using a cellular configuration for larger offices Telepoint: a base station set up in a public place (e.g. an airport) Small range for hand set -> low power Inexpensive base station and hand set -> simple technical approaches Limited frequency flexibility -> must work in different places Cordless Systems Example: DECT Band: 1.88 - 1.9 GHz; Bandwidth: 20 MHz; Number of channels 120 Access Method : TDMA/FDMA Data rate: 1.152 Mbps; Speech rate: 32 kbps Mean power: 10 mW Maximum cell radius: 30 to 100 m Provide handoff

Other Wireless Networks - Wireless Local Loops (WLL) Narrowband WLL - replacement for telephony services Broadband WLL - high-speed voice and data services Usually use milimetric waves (e.g. above 10 GHz) Advantages: cost, installation time, selective installation Propagation problems: free space loss, rainfall attenuation, atmospheric and gaseous absorption, mutipath losses, vegetation effects Multichannel Multipoint Distribution Service: MMDS (ex. 2.67-2.68 GHz) Local Multipoint Distribution Service: LMDS, standardized as IEEE 802.16 (ex. 27.5-28.3 GHz)

Other Wireless Networks - Personal Area Networks (PAN) and Home Area Networks (HAN) Network serving a single person or a small group Usually accommodate diverse mobile devices Provide support for virtual docking station, peripheral sharing Examples: Bluetooth, Infrared Data Association (IrDA), HomeRF HAN Broadband smart house with intelligent appliances HANs over phone lines, powerline and wireless HANs: diverse combination possible Examples: HomeRF, Home Audio Video interoperability HAVi Control Networks: low-speed powerline networks specify protocols that are used via the power line examples: LonWorks, X10, CEBus

Lecture Summary Overview of wireless networks and frequency spectrum for wireless communication Cellular networks, cellular principles, channel access, different generations of cellular networks Satellite communication, GEO, LEO, MEO WLAN, infrared, spread spectrum, microwave Other wireless networks: WLL, HAN, PAN, ad-hoc