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S-72.1130 Telecommunication Systems

S-72.1130 Telecommunication Systems. Wireless Local Area Networks. Outline. LAN basics Structure/properties of LANs WLANs Link layer services Media access layer frames and headers CSMA/CA Physical layer frames modulation Direct sequence Frequency hopping Infrared Installation

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S-72.1130 Telecommunication Systems

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  1. S-72.1130 TelecommunicationSystems Wireless Local Area Networks

  2. Outline • LAN basics • Structure/properties of LANs • WLANs • Link layer services • Media access layer • frames and headers • CSMA/CA • Physical layer • frames • modulation • Direct sequence • Frequency hopping • Infrared • Installation • Security

  3. LAN Basics LAN Basics WLAN Basics 802 LANs 802.11 Service Sets 802.11 LLC 802.11 MAC 802.11 PHY

  4. RAM RAM Typical Wired LAN • Transmission Medium • Network Interface Card (NIC) • Unique MAC “physical” address Serial format Ethernet Processor ROM NIC implements MAC protocol & physical port. Parallel interface to PC Reference: A. Leon-Garcia, I. Widjaja, Communication Networks , Instructor's Slide Set

  5. A A A A Example: How Ring Networks Work • A node functions as a repeater • Only destination station copies the frame, all other nodes discard the frame • Unidirectional link • Signal propagatesencoded by line codes • Example: 802.5 • Reliability: link failure (FDDI appliesdouble ring) A A C B C B B transmits frame addressed to A C ignores the frame A A C B C B A copies the frame at the reception B absorbs the returning frame

  6. Token Ring • A ring consists of a single or dual (FDDI) cable in the shape of a loop. Ring reservation supervised by rotating token. • Each station is physically connected to each of its two nearest neighbors. Data in the form of packets passes around the ring from one station to another in uni-directional way. • Advantages : • (1) Access method supports heavy load without statistical multiplexing degradation of performance because the medium is shared for pair-wise stations • (2) In practice several packets can simultaneous circulate between different pairs of stations. • Disadvantages: • (1) Complex management - especially for several rings • (2) Re-initialization of the ring whenever a failure occurs

  7. C D A B D term term - Line coded, serial data - Twisted pair or coaxial cable Example: Bus Network • In a bus network, one node’s transmission traverses the entire network and is received and examined by every node. The access method can be : • (1) Contention scheme : multiple nodes attempt to access bus; only one node succeeds at a time (e.g. CSMA/CD in Ethernet 802.3) • (2) Round robin scheme : a token is passed between nodes; node holding the token can use the bus (e.g.Token bus 802.4) • Advantages: • (1) Simple access method • (2) Easy to add or remove stations • Disadvantages: • (1) Poor efficiency with high network load in contention schemes • (2) Security taken care by upper network levels term: terminator impedance

  8. Wireless Local Area networks (WLANs) - basics LAN Basics WLAN Basics 802 LANs 802.11 Service Sets 802.11 LLC 802.11 MAC 802.11 PHY

  9. Wireless LANs (WLANs) - features • High date rates • IEEE 802.11b supports rates up to 11 MBps (in practice 6 Mb/s), and 802.11g reaches up to 54 Mb/s, need to have the bandwidth • No new wiring and installation on difficult-to-wire areas • Offices, public places, and homes • Factories, vehicles, roads, and railroads • Mobility • Increases working efficiency and productivity • Roaming support: extended on-line times -> universal access & seamless services • Reduced installation time • No cabling time • Easy setup • Standard enables interoperability between different vendors • Roaming with GSM and UMTS is a research issue

  10. WLAN Technology Challenges • Flexible error control: in physical, MAC and/or in upper levels • Physical level takes care of physical transmission of packets over a medium (modulation, line coding, channel coding) • Interference & noise • Working in ISM band means sharing the frequency bands with microwave oven, cordless telephones, Bluetooth etc. -> Modulation and MAC design challenge: • Pros: Freedom from spectral regulatory constraints at ISM Band (Industrial, Science and Medical) • Multi-path propagation • Remedies: channel coding / rake-reception • Dynamic network management • Stations movable and may be operated while moved • addressing and association procedures • interconnections (roaming)

  11. Challenges … • MAC protocol takes care of optimizing throughput for the expected services • Wireless channel is also the reason why access method for 802.11 is CSMA/CA and not CSMA/CD • Difficult to detect collisions in wireless environment-> Hidden terminal problem (see PSTN lecture) • Security • Traditional WEP (Wired Equivalent Privacy) now replaced by WPA (Wi-Fi Protected Access) and 802.11i (WPA2) • AAA (Authentication, Authorization, Accounting) can be taken care by separate server as RADIUS (Remote Authentication Dial In User Service ) CSMA/CA: Carrier Sense Multiple Access/Collision Avoidance CSMA/CD: Carrier Sense Multiple Access/Collision Detection

  12. IEEE 802 LAN Standards LAN Basics WLAN Basics 802 LANs 802.11 Service Sets 802.11 LLC 802.11 MAC 802.11 PHY

  13. hub stations hub stations hub stations hub router server IEEE 802-series of LAN Standards • 802 standards free to download from http://standards.ieee.org/getieee802 WiMAX Demand priority: A round-robin (see token rings-later) method to provide LAN access based on message priority level DQDB: Distributed queue dual buss, see PSTN lecture

  14. The IEEE 802 LAN Standards (http://www.ieee802.org/) OSI Layer 3 Network IEEE 802.2 Logical Link Control (LLC) LLC OSI Layer 2 (data link) IEEE 802.11 Wireless IEEE 802.3 Carrier Sense IEEE 802.4 Token Bus IEEE 802.5 Token Ring b: Wi-Fi MAC a b g Ethernet Physical Layers - options: twisted pair, coaxial, optical, radio paths; (not for all MACs above!) OSI Layer 1 (physical) Bus (802.3…) Star (802.3u…) Ring (802.5…)

  15. IEEE 802.11 Wireless Local Area Networks (WLANs): Service Sets LAN Basics WLAN Basics 802 LANs 802.11 Service Sets 802.11 LLC 802.11 MAC 802.11 PHY

  16. IEEE 802.11 Architecture • 802.11 networks can work in • Basic service set (BSS) • Extended service set (ESS) • BSS can also be used in ad-hocnetworking Network LLC 802.xx MAC FHSS PHY DSSS IR Propagation boundary Internet Distribution system Station B LLC: Logical Link Control Layer MAC: Medium Access Control Layer PHY: Physical Layer FHSS: Frequency hopping SS DSSS: Direct sequence SS SS: Spread spectrum IR: Infrared light BSS: Basic Service Set ESS: Extended Service Set Station A BSS 1 BSS 2 Basic (independent) service set (BSS) Extended service set (ESS) (infrastructure-mode) Access Point Portal: gateway access to other networks/Internet

  17. Basic and Extended Service Sets • Basic Service Set (BSS) – tens of meters • Operates in Basic Service Area (BSA) that is much like the are of a cell in mobile communications • BSSs may geographically overlap, be physically disjoint, or they may be collocated (one BSS may use several antennas) • Ad-hoc or Infrastructure (nomadic) mode: Access coordinated by the given instance of MAC • Extended Service Set (ESS) • Multiple BSSs interconnected by a Distribution System (DS) • Each BSS is like a cell and stations in BSS communicate with an Access Point (AP). • Portals attached to DS provide gateways as access to Internet or other ESS

  18. Distribution system (DS) services • DS provides distribution services: • Transfer MAC SDUs between APs in ESS (I) • Transfer MSDUs between portals & BSSs in ESS (II) • Transfer MSDUs between stations in same BSS (III) • Multicast, broadcast, or stations’s preference • ESS looks like a single BSS to LLC layer Propagation boundary Internet II III III SDU: Service Data Unit (inter-layer data) LLC: Logical Link Control Layer MAC: Medium Access Control Layer MSDU: MAC Service Data Unit PHY: Physical Layer FHSS: Frequency hopping SS DSSS: Direct sequence SS SS: Spread spectrum IR: Infrared light BSS: Basic Service Set ESS: Extended Service Set AP: Access Point Distribution system Station B IIIb Station A I BSS 1 BSS 2 Basic (independent) service set (BSS) Extended service set (ESS) Access Point Portal: gateway access to other networks/Internet

  19. IEEE 802.11 Mobility (b/g) • Standard defines the following mobility types: • No-transition: no movement or moving within a local BSS • BSS-transition: station movies from one BSS in one ESS to another BSS within the same ESS • ESS-transition: station moves from a BSS in one ESS to a BSS in a different ESS (continuos roaming not supported) • Especially: 802.11 don’t support roaming with GSM! - Address to destination mapping - seamless integration of multiple BSS ESS 1 ESS 2

  20. IEEE 802 LAN Standard: Logical Link Layer (LLC) LAN Basics WLAN Basics 802 LANs 802.11 Service Sets 802.11 LLC 802.11 MAC 802.11 PHY

  21. 802.11 WLAN ArchitectureLogical Link Control (LLC) • LLC provides addressing and data link control – common to all 802 LANs • Utilizes services of HDLC* (High-level Data Link Control) • Therefore, LLC SAPs separate upper layer data exchanges => NIC applies different buffer segments for each SAP (port) • LLC provides means to exchange frames between LANs using different MACs IEEE 802.2 Logical Link Control (LLC) LLC b: Wi-Fi IEEE 802.11 Wireless IEEE 802.3 Carrier Sense IEEE 802.4 Token Bus IEEE 802.5 Token Ring MAC Ethernet a b g Physical layer: DSSS, FHSS, IR PHY CSMA/CA: Carrier Sense Multiple Accesswith Collision Avoidance LLC: Logical Link Control Layer MAC: Medium Access Control Layer SS: Spread Spectrum FHSS: Frequency hopping SS DSSS: Direct sequence SS IR: Infrared light NAV: Network Allocation Vector SAP: Service Access Point DCF: Distributed Coordination Function PCF: Point Coordination FunctionNIC: Network Interface Card *Overview of HDLC also in supplementary…

  22. Logical Link Control Layer (LLC) • Specified by ISO/IEC 8802-2 (ANSI/IEEE 802.2) • Objective: exchange data between users across LAN using 802-based MAC controlled link • Provides addressing and data link control (routing) • Independent of topology, medium, and chosen MAC access method Data to higher level protocols Info: carries user data Supervisory: carries flow/error control Unnumbered: carries protocol control data Source SAP LLC’s Protocol Data Unit (PDU) (SAP: Service Access Point)

  23. SAP Addressing IEE802.11 (CSMA/CA)... ATM... IEE802.11 (CDMA)... Reference: W. Stallings: Data and Computer Communications, 7th ed

  24. A TCP/IP PacketEncapsulation TCP makes logical connection to deliver the packet Control header LLC constructs PDU* by adding a control header SAP (service access point) MAC lines up packets using by using a MAC protocol MAC frame withnew control fields PHY layer transmits packet using a modulation method (DSSS, OFDM, IR, FHSS) Traffic to the target BSS / ESS *Protocol data unit

  25. Encapsulation … Reference: W. Stallings: Data and Computer Communications, 7th ed

  26. LLC Services • A Unacknowledged connectionless service • Point-to-point, multicast (assigned users), broadcast (group of users) addressing • no error or flow control - no ack-signal • higher levels take care or reliability - thus fast • Often referred as ‘Unnumbered frame mode of HDLC*’ • B Connection oriented service • connection phases: Connection setup, data exchange, and release • supports unicast only • error/flow control (cyclic redundancy check (CRC)), sequencing • ‘Asynchronous mode of HDLC’ • C Acknowledged connectionless service • Can handle several logical connections, distinguished by their SAPs • ack-signal used • error and flow control by stop-and-wait ARQ • faster setup than for B *High-Level Data Link Control

  27. IEEE 802.11 Wireless Local Area Networks (WLANs): Media Access Protocol LAN Basics WLAN Basics 802 LANs 802.11 Service Sets 802.11 LLC 802.11 MAC 802.11 PHY

  28. Selecting a Medium Access Control • Environment: Wired / Wireless? • Applications: • What type of traffic? • Voice streams? Steady traffic, low delay/jitter • Data? Short messages? Web page downloads? • Enterprise or consumer market? Reliability, cost • Scale: • How much traffic can be carried? • How many users can be supported? • Examples: • Design MAC to provide wireless DSL-equivalent access for rural communities • Design MAC to provide Wireless-LAN-equivalent access to mobile users (user in a car travelling at 130 km/h)

  29. MAC techniques - examples • Contention • Medium is free for all, packet collisions do happen • A node senses the free medium and occupies it as long as data packet requires it • Example: Ethernet (IEEE 802.3 CSMA/CD) • Reservation (short term statistical access) • Gives everybody a turn • Reservation time depends on token holding time (set by network operator) • For heavy loaded networks • Example: Token Ring/IEEE 802.5, Token Bus/IEEE 802.4, FDDI • Reservation(long term) • Link reservation for multiple packets (whole session) • Example: scheduling a time slot: GSM using TDMA. FDMA applied for uplink/dowlink separation. • Hybrid… (example: contention+reservation) • Flexible compromise: 802.11 WLANs

  30. Media Access Control (MAC): Ways to Share a Medium • Medium sharing required for multiple users to access the channel • Communications by • unicasting • multicasting • broadcasting Medium sharing techniques Static channelization Dynamic medium access control • FDMA,TDMA, CDMA • Uses partition medium • Dedicated allocation to users • Examples: • Satellite transmission • Cellular Telephone Scheduling Random access (contention) • Polling (take turns): Token ring 802.5 • Reservation systems: Request for slot in transmission schedule 802.4 • Loose coordination • Send, wait, retry if necessary • Aloha • CSMA/CD (Ethernet) • CSMA/CA (802.11 WLAN)

  31. Example 802.3: MAC of Ethernet (CSMA/CD*) • CSMA/CD: 1. If the medium is idle, transmit; otherwise, go to step 2 2. If the medium is busy, continue listening (CS: carriersensing) until the channel is idle, then transmit immediately 3. If a collision is detected (CD) during transmission, transmit brief jamming signal to assure all stations know about collision and then cease transmission 4. After transmitting the jamming signal, wait a random time (back-off time), then attempt to transmit again *Carrier sense multiple access/collision avoidance

  32. Throughput Performance of CSMA/CD r (Load) We can see that in Ethernet transfer delays grow very fast as the load increases for the given value of delay-bw product a. Note: Large value of parameter a scales results for propagation delay and/or signaling rate – if their product becomes larger, throughput (in terms of transfer delay) gets smaller. tprop: one-way delay, R: signaling rate, L: frame length Reference: A. Leon-Garcia, I. Widjaja, Communication Networks, 2nd ed

  33. 802.11 WLAN ArchitectureMedium Access Control (MAC) - Summary • 802.11 MAC • Services • Station service: Authentication, privacy, MSDU* delivery • Distributed system: Association**, participates to data distribution • Transmits frames based on MAC addresses (in NIC) • Connectionless/Connection oriented frame transfer service • Coordinates access to medium • Joining the network (NAV, addressing) • MAC scheme CSMA/CA: • Contention-free access (PCF) • Contention access (DCF) IEEE 802.2 Logical Link Control (LLC) LLC b: Wi-Fi IEEE 802.11 Wireless IEEE 802.3 Carrier Sense IEEE 802.4 Token Bus IEEE 802.5 Token Ring MAC Ethernet a b g Physical layer: DSSS, FHSS, IR PHY CSMA/CA: Carrier Sense Multiple Accesswith Collision Avoidance LLC: Logical Link Control Layer MAC: Medium Access Control Layer SS: Spread Spectrum FHSS: Frequency hopping SS DSSS: Direct sequence SS IR: Infrared light NAV: Network Allocation Vector SAP: Service Access Point DCF: Distributed Coordination Function PCF: Point Coordination FunctionNIC: Network Interface Card * MSDU: MAC service data unit ** with an access point in extended or basic service set (ESS,BSS)

  34. IEEE 802.11 Coordination Functions Reference: W. Stallings: Data and Computer Communications, 7th ed

  35. Media Access Control in 802.11 WLANs • Distributed Wireless Foundation MAC (DWFMAC): • Distributed access control mechanism (CSMA/CA) • Optional centralized control on top (PCF) • MAC flavours provided by coordination functions: • Distributed coordination function (DCF) – CSMA/CA • Contention algorithm to provide access to all traffic • Asynchronous, best effort-type traffic • Application: bursty traffic, add-hoc networks • Point coordination function (PCF) – polling principle(rarely applied in practical devices) • Centralized MAC algorithm • Connection oriented • Contention free • Built on top of DCF • Application: timing sensitive, high-priority data

  36. IEEE 802.11 MAC (DWFMAC): Timing in Basic Access duration depends on MAC load type duration depends on network condition MAC frame: Control, management , data + headers(size depends on frame load and type) PCF: Point Coordination Function (asynchronous, connectionless access) DCF: Distributed Coordination Function (connection oriented access) DIFS: DCF Inter Frame Space (minimum delay for asynchronous frame access) PIFS: PCF Inter Frame Space (minimum poll timing interval) SIFS: Short IFS (minimum timing for high priority frame access as ACK, CTS, MSDU…) MSDU: MAC Service Data Unit Reference: W. Stallings: Data and Computer Communications, 7th ed

  37. IEEE 802.11 MAC Logic(DWFMAC) duration depends on MAC load type IFS: Inter Frame Space (= DIFS, SIFS, or PIFS) DWFMAC: Distributed Wireless Foundation MAC Reference: W. Stallings: Data and Computer Communications, 7th ed

  38. DWFMAC summarized • Collision Avoidance • When station senses channel busy, it waits until channel becomes idle for DIFS period & then begins random backoff time (in units of idle slots) • Station transmits frame when backoff timer expires • If collision occurs, recompute backoff over interval • Receiving stations of error-free frames send ACK • Sending station interprets non-arrival of ACK as loss • Executes backoff and then retransmits • Receiving stations use sequence numbers to identify duplicate frames

  39. Carrier Sensing in 802.11 MAC - Summary • Physical Carrier Sensing • Analyze all detected frames for errors • Monitor relative signal strength from other sources • Virtual Carrier Sensing at MAC sublayer • Source stations inform other stations of transmission time (in msec) for an MPDU (MAC Protocol Data Unit) • Carried in Duration field of RTS (Request to send) & CTS (Clear to send) • Stations adjust their Network Allocation Vector (NAV) to indicate when the channel will become idle • Channel busy if either sensing is busy Reference: A. Leon-Garcia, I. Widjaja, Communication Networks , Instructor's Slide Set

  40. Transmission of MPDU without RTS/CTS DIFS NAV: Network allocation vector DIFS: DCF Inter Frame Space (async) SIFS: SIFS: Short IFS (ack, CTS…) RTS: Request to send CTS: Clear to send MPDU: MAC Protocol Data Unit DCF: Distributed Coordination Function PCF: Point Coordination Function Data Source SIFS ACK Destination DIFS NAV Other Wait for Reattempt Time Defer Access Reference: A. Leon-Garcia, I. Widjaja, Communication Networks , Instructor's Slide Set

  41. Transmission of MPDU with RTS/CTS (DCF) NAV: Network allocation vector DIFS: DCF Inter Frame Space (async) SIFS: SIFS: Short IFS (ack, CTS…) RTS: Request to send CTS: Clear to send MPDU: MAC Protocol Data Unit DCF: Distributed Coordination Function PCF: Point Coordination Function Hidden terminal solution DIFS RTS Data Source SIFS SIFS SIFS CTS Ack Destination DIFS NAV (RTS) NAV (CTS) Other NAV (Data) RTS: Request to Send CTS: Clear to Send Reference: A. Leon-Garcia, I. Widjaja, Communication Networks , Instructor's Slide Set Defer access

  42. D2+Ack+Poll D1 + Poll U 2 + ACK U 1 + ACK PCF Frame Transfer TBTT Fixed super-frame interval Contention-free repetition interval (PCF) SIFS SIFS SIFS SIFS SIFS Contention period (DCF) CF End B PIFS Reset NAV NAV NAV: Network allocation vector PIFS: PCF Inter Frame Space DIFS: DCF Inter Frame Space (async) SIFS: SIFS: Short IFS (ack, CTS…) RTS: Request to send CTS: Clear to send MPDU: MAC Protocol Data Unit DCF: Distributed Coordination Function PCF: Point Coordination Function CF_Max_duration D1, D2 = frame sent by point coordinator U1, U2 = frame sent by polled station TBTT = target beacon transmission time B = beacon frame (initiation)

  43. Point Coordination Function • PCF provides connection-oriented, contention-free service through polling • Point coordinator (PC) in AP performs PCF • Polling table up to implementer • Contention free period (CFP) repetition interval • Determines frequency with which contention free period occurs • Initiated by beacon frame transmitted by Point Coordinator (PC) in AP • During CFP stations may only transmit to respond to a poll from PC or to send ACK • All stations adjust Network Allocation Vector (NAV) to indicate when channel will becomes idle Reference: A. Leon-Garcia, I. Widjaja, Communication Networks , Instructor's Slide Set

  44. MAC Frame Types • Management frames • Station association & disassociation with AP (this establishes formally BSS) • Timing & synchronization • Authentication & de-authentication (option for identifying other stations) • Control frames • Handshaking • ACKs during data transfer • Data frames • Data transfer Reference: A. Leon-Garcia, I. Widjaja, Communication Networks , Instructor's Slide Set

  45. MAC Frame • NOTE: This frame structure is common for all data send by a 802.11 station control info (WEP, data type as management, control, data ...) frame orderinginfo for RX next frame duration frame specific,variable length -Basic service identification BSSID*-source/destination address-transmitting station-receiving station frame check sequence (CRC) *BSSID: a six-byte address typical for a particular access point (network administrator sets) CRC: Cyclic Redundancy Check WEP: Wired Equivalent Privacy

  46. IEEE 802.11 Wireless Local Area Networks (WLANs): Physical Level LAN Basics WLAN Basics 802 LANs 802.11 Service Sets 802.11 LLC 802.11 MAC 802.11 PHY

  47. 802.11 WLAN bands and technologies - summary • IEEE 802.11 standards and rates • IEEE 802.11 (1997) 1 Mbps and 2 Mbps (2.4 GHz band ) [FH, DS] • IEEE 802.11b (1999) 11 Mbps (2.4 GHz band) = Wi-Fi [QPSK] • IEEE 802.11a (1999) 6, 9, 12, 18, 24, 36, 48, 54 Mbps (5 GHz band) [OFDM] • IEEE 802.11g (2001 ... 2003) up to 54 Mbps (2.4 GHz) backward compatible to 802.11b [OFDM] • IEEE 802.11 networks work on license free Industrial, Science, Medicine (ISM) bands: 26 MHz 83.5 MHz 200 MHz 255 MHz 902 928 2400 2484 5150 5350 5470 5725 f/MHz 200 mW indoors only EIRP power in Finland 1 W 100 mW EIRP: Effective Isotropically Radiated Power - radiated power measured immediately after antenna Equipment technical requirements for radio frequency usage defined in ETS 300 328

  48. 802.11 WLAN ArchitecturePhysical Level (PHY) • 802 Physical level specifies • Star, bus or ring topology • Cabling and electrical interfaces: Twisted pair, coaxial, fiber… • Line coding (wired LANs) or modulation (WLANs) • Three physical layers for 802.11 • FHSS: Frequency Hopping Spread Spectrum (SS) • DSSS: Direct Sequence SS • IR: Infrared transmission IEEE 802.2 Logical Link Control (LLC) LLC b: Wi-Fi IEEE 802.11 Wireless IEEE 802.3 Carrier Sense IEEE 802.4 Token Bus IEEE 802.5 Token Ring MAC Ethernet a b g Physical layers PHY CSMA/CA: Carrier Sense Multiple Accesswith Collision Avoidance LLC: Logical Link Control Layer MAC: Medium Access Control Layer SS: Spread Spectrum FHSS: Frequency hopping SS DSSS: Direct sequence SS IR: Infrared light NAV: Network Allocation Vector SAP: Service Access Point DCF: Distributed Coordination Function PCF: Point Coordination FunctionNIC: Network Interface Card

  49. Physical Levelof 802.11: DSSS • 802.11 supports 1 and 2 Mbps data transmission, uses BPSK and QPSK modulation (802.11b,a,g apply higher rates) • 802.11 applies 11 chips Barker code for spreading - 10.4 dB processing gain • Defines 14 overlapping channels, each having 22 MHz channel bandwidth, from 2.401 to 2.483 GHz • Power limits 1000mW in US, 100mW in EU, 200mW in Japan • Immune to narrow-band interference, cheaper hardware DSSS-transmitter PPDU:Baseband Data Frame Unit, BPSK: Binary Phase Shift Keying, QPSK: Quadrature PSK DSSS: Direct Sequence Spread Spectrum, PN:Pseudo Noise

  50. Physical Level of 802.11: FHSS • Supports 1 and 2 Mbps data transport and applies two level - GFSK modulation* (Gaussian Frequency Shift Keying) • 79 channels from 2.402 to 2.480 GHz ( in U.S. and most of EU countries) with 1 MHz channel space • 78 hopping sequences with minimum 6 MHz hopping space, each sequence uses every 79 frequency elements once • Minimum hopping rate 2.5 hops/second • Tolerance to multi-path, narrow band interference, security • Low speed, small range due to FCC TX power regulation (10mW)

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