The Electromagnetic Spectrum The electromagnetic spectrum and its uses for communication.

ISM Unlicensed Frequency Bands Extremely Low Very Low MediumHighVery High Ultra High Super High InfraredVisible Light Ultra- violet X-Rays Audio AM Broadcast Short Wave RadioFM Broadcast Television Infrared wireless LAN Cellular (840MHz) NPCS (1.9GHz) MHz 26 MHz 5 GHz (IEEE ) HyperLAN HyperLAN2 2.4 – GHz 83.5 MHz (IEEE )

900 MHz vs. 2.4 GHz vs. 5GHz 900 MHz2.4 GHz PROs CONs Greater Range than 2.4 GHz ( For in- Building LANs) Maximum Data Rate 1 Mbps Limited Bandwidth Crowded Band Global Market IEEE b/g Higher Data Rates (10+ Mbps) Less Range than 900 MHz (For In- Building LANs) 5 GHz Global Market IEEE a Higher Data Rates (20+ Mbps, up to 50M) Much Less Range than 900 or 2.4GHz Higher Cost RF Components Large Antenna required

The Standard –2 Mbps 2.4G Mbps 5G Orthogonal FDM Mbps 2.4G Mbps 2.4G Power Management (awake, doze) Timing Management (beacon, sync within 4usec)

Frequency Hopping 79 Channels, 1 MHz Each Maximum time on any one freq is.4 sec in any 30 sec period Changes frequency (Hops) at least every 0.4 seconds (dwell time – adjustable), Lost packets are re-transmitted on next hop Synchronized hopping sequences required by same random number generators in every station 26 hopping patterns in three different sets with minimum interference with each other – called orthogonal patterns GHz2.483 GHz Time

Direct Sequence Similar to CDMA 22 MHz wide stationary channels (11 chips) Each data bit becomes a string of chips (Barker sequence) transmitted in parallel across a wide frequency range, data may be decoded from redundant bits 3 non-overlapping channels, c an move to an alternate channel to avoid interference 3 Access Points can occupy same area b DSSS 1 M baud data rate with 1 bit (1Mbps), 2 bit (2 Mbps) HR-DSSS M baud, 4 bit (5.5M), 8 bit (11 Mbps)

IEEE Architecture Ad-Hoc Mode Infrastructure Mode

Ad-Hoc Mode Computers are brought together to form a network. There is no structure to the network; there are no fixed points; and usually every node is able to communicate with every other node. No administration and pre configuration IETF MANET (Mobile Ad hoc Networks) working group Ad-Hoc Mode

Infrastructure Mode It uses fixed network access points (AP) with which mobile nodes can communicate. These network APs are connected to wired network to widen the LAN's capability by bridging wireless nodes to other wired nodes. All communications between mobiles and wired network clients go through the AP. Mobiles can roam between APs and seamless wide area coverage is possible. Infrastructure Mode

Wireless LANs Issues (CSMA) The range of a single radio may not cover the entire system Hidden station problem (A->B, C->B since C does not hear A, collision) Exposed station problem (B->A, C hears B, C won’t send to D, reduced efficiency)

Multiple Access with Collision Avoidance IDEA: having a short frame transmitted from both sender and receiver before the actual transfer A sending a short RTS (30 bytes) to B with length of L B responding with a CTS to A, whoever hears CTS shall remain silent for the duration of L A sends data (length L) to B Further optimization as MACAW (MACA for Wireless) RTS, not CTS Tx ok CTS, not RTS Keep silent CTS,RTS

Medium Access Control Distributed Coordination Function Distributed Control, Ethernet-like CSMA CSMA/CA (collision avoidance) Physical channel sensing Sense channel, transmit entire frame, retry if necessary Virtual channel sensing (MACAW) Add ACK frame Network Allocation Vector (quiet time) Short frame (30B) Contains data length data length copied from RTS

Fragmentation for Throughput fragment burst Unreliable ISM bands Error rate p = 10 -4, success rate for full Ethernet frame (12,144 bit) <30%, (1-p)**n Error rate p = 10 -6, 1% will be damaged.

Medium Access Control Point Coordination Function (PCF) Central Control Base polls other stations Broadcast a beacon frame periodically (10ms to 100ms) with system parameters (hopping sequence, dwell time, clock synchronization) Base determines the transmission priority QoS guarantee Can Coexist with DCF Short InterFrame Spacing RTS/CTS/ACK Fragment burst

The Data Frame Structure WEP More Frames Ordered frames Data Control Mgmt To AP RTS CTS ACK Intercell traffic addresses Sleep / Awake Frame length plus ack (used for NAV) Intercell traffic addresses Fragment sequence

AP Services Distribution Services Association station reports identity, data rate, power Disassociation Reassociation handover Distribution routing Integration format conversion IntraCell Services Authentication conducted after association Deauthentication Privacy Wired-Equivalent Privacy WEP RC4 Data Deliver

Steps to Association: Client evaluates AP response, selects best AP. AP sends Probe Response Access Point A Access Point B Initial connection to an Access Point Client sends probe Client sends authentication request to selected AP (A). AP A confirms authentication and registers client. Client sends association request to selected AP (A). AP A confirms association and registers client. Association Process -- Passive Scanning

Steps to Re-association: Adapter listens for beacons from APs. Adapter evaluates AP beacons, selects best AP. Adapter sends association request to selected AP (B). AP B confirms association and registers adapter. Access Point A Access Point B Roaming from Access Point A to Access Point B AP B informs AP A of re-association with AP B. AP A forwards buffered packets to AP B and de-registers adapter. Re-association Process

Cellular and b Cellular True mobility Secure Roaming & Handoff Integration with SP Voice networks Data to 384Kbps with 2.5G Max at 2Mbps with 3GPP Higher network costs/user Licensed spectrum b 11Mbps today Integration with Enterprise data network Unlicensed spectrum Higher client costs/user Limited mobility/roaming QoS and Security, voice in development Many Enterprises see the need for both solutions in the medium-term

Bluetooth Frequency: 2.4 GHz ISM Band - FHSS G, 79Mhz = 79x1Mhz, 1600 hops per sec Range: 10m (100m), Omni-directional, save power Low Power: 1mW (100mW with amplifier) Speed: 1Mbps gross Network: 8 devices (1master+7slave) in a piconet 3 Simultaneous voice plus data Data -- or 10 piconet can form a scatternet Low Cost Ericsson, IBM, Nokia, Intel, Toshiba, etc. Founded Feb 98,