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• Macro Cellular Network* Ardis, RAM Mobitex

* CDPD

* ASM/CSD/SMS/GPRS/EDGE: 9.6~384Kbps; circuit or packet data.

* CDMA (IS-95): 9.6 and 14.4 Kbps circuit data.

* WCDMA/CDMA 2000: up to 2 Mbps~10Mbps for wireless multimedia services.

Multi-Tier Wireless Data Access

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• Micro Cellular Network

* Metricom: packet forwarding; ISM band at 902-928MHz; up to 128Kbps.

* PHS: circuit operation; 64/128Kbps.

* DECT

* PACS

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• Wireless LAN* Wave LAN: by NCR for banking services; 2Mbps at

900MHz ISM band.

* IEEE 802.11

* HIPERLAN: high-performance wireless LAN

* Wireless ATM

* Bluetooth: sub-wireless LAN.

* Home RF: relax PHY specs from 802.11

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• CMU Project Andrew has demonstrated multi-tier wireless packet data access using WaveLAN and CDPD equipment providing 2 Mbps within a campus and about 10 Kbps over wide areas.

• Dual-mode PHS-PDC

• Dual-mode GPRS-HiperLAN

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ISM (Industrial, Scientific, and Medical) band

• 902-928MHz, 2400-2483.5 MHz, and 5725-5850 MHz

• Must be shared with other users (neighboring wireless LAN) and devices (microwave ovens)

• Required to use spread spectrum transmission techniques.

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Two Classes of Wireless LANs

• Infrastructure Wireless LAN: an infrastructure of wireless access points that the portable devices can communicate with to access a backbone network.

• Ad hoc wireless LAN: a set of portable devices communicate one with another to form, on demand, a self-contained LAN.

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IEEE 802.11

• 2 Mbps DS and FH modes at 900 MHz and 2.4 GHz

• 11 Mbps DS mode at 2.4 GHz (802.11b)

• 20 Mbps HIPERLAN at 5 GHz.

• 30 Mbps OFDM mode at 5.7 GHz

• IrDA for high speed infrared system.

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9

802.11

Wireless Local Area Network

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Architecture

AccessPoint

AccessPoint

station

station

stationstation

station

Distribution System

serverExtendedService Set

Basic ServiceSet

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IEEE 802.11 Architecture

• BSS consists of some number of stations executing the same MAC protocol and competing for access to the same shared medium.* The smallest building block

* Can be isolated or connected by a distribution system.

• ESS consists of two or more BSS’s interconnected by a distribution system.* Appeared as a single logical LAN to LLC level

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Three Types of Stations ( based on mobility )

• No-transition* Stationary station or stations that move within a BSS.

• BSS-transition* stations that move between BSS in the same ESS

• ESS-transition* Stations that move across ESS boundary.

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14

Physical Medium

• Infrared at 1 Mbps and 2 Mbps at a wavelength between 850 and 950 nm.

• Direct-sequence spread spectrum in the 2.4 GHz ISM band.

• Frequency-hopping spread spectrum in the 2.4 GHz ISM band.

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Medium Access Control

• DFWMAC (distributed foundation wireless MAC): * provides a distributed access-control mechanism with an

optional centralized control built on top of that.

• DCF (distributed coordination function) uses a contention algorithm to provide access to all traffic.

• PCF (point coordination function) uses a centralized algorithm over DCF to provide contention-free service.

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17

Distributed Coordination Function (DCF)

• Use CSMA with prioritized fair control.

• A set of delays called interframe space (IFS) is used for priority control. * A station transmits data if the medium is sensed idle for IFS.

* If the medium is busy, defer transmission and continue to monitor the medium until the current transmission is over.

* Once the transmission is over, the station delay another IFS. If the medium remains idle for this period, then the station backs off using a binary exponential backoff scheme and again sense the medium. If the medium is still idle, the station may transmit.

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Prioritized Access Control

• SIFS (short IFS). * The shortest IFS, used for all immediate response

actions.

• PIFS (point coordination function IFS). * A mid-length IFS, used by the centralized controller

in the PCF scheme when issuing polls to take precedence over normal-contention traffic.

• DIFS (distributed coordination function IFS).* The longest IFS, used as a minimum delay for

asynchronous frames contending for access.

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Prioritized Access Control (cont’)

• Any station using SIFS to determine transmission priority has the highest priority. The SIFS is used when* Acknowledgment (ACK): to speed up multi-frame LLC

PDU transmission.

* Clear to Send (CTS): A station can ensure that its data frame will get through by first issuing a small Request to Send (RTS) frame. All other stations defer using the medium until they see a corresponding CTS, or until a timeout occurs.

* Poll response.

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Point Coordination Function (PCF)

• A centralized polling master ( Point Coordinator ( PC ) ) polls in a round-robin fashion to all stations configured for polling.

• Once a polling cycle is started, the medium is seized by the PC and asynchronous traffic is locked out.

• A superframe is defined in which the PC may optionally seize control and issue polls for a given period of time. The interval is varied. The remainder of the superframe is available for contention-based access.

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Future Wideband OFDM for WLAN

• Multicarrier modulation techniques

• Multigate the effect of frequency selective fading

• Peak power reduction techniques

• Dynamic packet assignment techniques can provide very high spectral efficiency.

• Asymmetrical access

• The use of diversity/interference suppression/smart antenna with OFDM

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Wireless Networking for the Connected Home

• PC/Internet lacks mobility and convenience of location ( last 150 feet ).

• Major opportunity in home networking is to extend PC/Internet throughout yard and home.

• Resource sharing in multi-PC home.

• Home RF working group in 1997* Enable interoperable wireless voice and data networking

within the home.

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Home RFTechnical Summary

• Hybrid TDMA/CSMA frame

• Beacon from Connection Point (CP) sets frame structure

• Frequency hopping, 50 hops/sec

• 2 or 4 FSK yields 1 or 2 Mb/s

• Also supports TCP/IP voice

• Range up to 50 meters

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Home RF Technical Summary--Data

• Relaxed PHY specs from 802.11* Lowers radio cost significantly

* Same hop sequences

+ Localized for France, Spain, Japan, US, EC

+ Different BW for Japan, France, Spain

• Comparable backoff, packet structure, ad-hoc capabilities

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Home RF Technical Summary--Voice

• DECT with retransmission

• Uses DECT calling stack

• Uses DECT A/B fields

• 32kb/s ADPCM

• 20ms frames—retransmit in beginning, outbound at end

• Up and down link packets interleaved

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Home RFNetwork Architecture

• Isochronous* Used for cordless tele/vi

deophones* Can make calls with no

PC* PC connected gives enh

anced services

• Asynchronous* Peer-peer* For resource sharing (fil

e, modem, printer)

• Mixed I and A• Power Management

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SWAP

• Shared Wireless Access Protocol (SWAP) * TCP/IP networking

* Internet access

* Voice telephony via PSTN (VoIP)

* Revision 1.2 specification is available.

• Support both isochronous clients and an asynchronous network of peer devices.

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Applications

• PC-enhanced cordless telephone.

• Mobile viewer appliance.

• Resource sharing among multiple PCs in the same home.

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SWAP Architecture

• Support isochronous services and ad hoc peer-to-peer network that provides traditional data networking.

• Three kinds of devices:* A connection point (CP): a gateway between PC, PSTN, and SWA

P-compatiable devices.* Voice devices ( I node )* Asynchronous data devices ( A-nodes )

• TDMA for client/server interactive voice and CSMA for data services.

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MAC Overview

• Interoperate with PSTN using a subset of Digital Enhanced Cordless Telecom (DECT) standard.

• Use frequency-hoping radio and TDMA for isochronous data

• Use CSMA/CA to support delivery of asynchronous data.

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Feature of SWAP MAC

• Good support for voice and data by using both TDMA and CSMA/CA access mechanisms.

• Support four high-quality voice connection with 32 kb/s ADPCM

• High data throughput of 1.6 Mb/s

• Data security

• Power management for both I and A nodes

• 24-bit network ID

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Frame StructureFrequency Hopping

TDMSynchronization &Retransmission signal

20 msec

Connection requect

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Superframe Structure

• Two Contention-Free Periods ( CFPs) and a contention period.

• A frame is 20 msec long.

• A beacon is transmitted immediately after the hop for* maintain network synchronization* control the format of the superframe* manage when each node should transmit and receive data

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Superframe Structure (cont.)

• CFP2 is used for the initial transmission of the voice data.

• CFP1 is used for optional up to four retransmission of any data which was not received or incorrectly received in the previous dwell.

• Each voice channel contain 640 bit ADPCM data and 56 bits of control data.

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Superframe Structure (cont.)

• CFP2 and CFP1 are separated by frequency hop, giving freq. And time diversity.

• Piggy back ack in each uplink packet for acknowledgement.

• A service slot after CFP1 for connection request by voice devices.

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CSMA/CA

• Use a contention window and backoff counter.

• Algorithm:Select a backoff counter and start listenwhile backoff counter \=0 {

if medium is free up to DIFS

while the medium is free and backoff counter \= 0

decrease backoff counter by one for each free contention slot;if backoff counter = 0 and the medium is free {

transmit data immediately;if success, break;else { enlarge collision window from 8 exponentially to 64

select a new backoff counter }}

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Countdown

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Power Management

• I-node with an Active connection, * wake CPB ( CP Beacon ) & receive assignment

* wake when assigned slots are due

• I-node without active connection* wake every N dwell times

* N is system configuration

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Power-Saving Asynchronous nodes ( PS-nodes )

• CP maintains a countdown to the next dwell when PS-nodes should wake up, which is broadcast in CPB

• PS-nodes receives the countdown from CPB and goes back to sleep.

• Countdown is a system parameter depending on the buffer size and latency.

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Broadcast for PS-nodes

1

2 3

4

5

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Unicast for PS-nodes

Wake up flag

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Bluetooth Radio System

• Piconet based networking with dynamically formed master and slave nodes.

• At most 8 nodes in a pico net.

• Master node ID is used to identify each pico net.

• (FH)-CDMA is used for bandwidth sharing.

• Frequency 2.45 MHz in ISM band.

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FH/TDD Channel

Dwell time

FrequencyHoping

TDD

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FH-CDMA

• 79 hop carriers are defined at 1 MHz spacing

• minimum well time is 625 micro sec.

• A large number of pseudo-random hopping sequence are defined

• master determines the hop sequence used.

• The native clock of master also defines the phase in the hopping sequence.

• Slave selects sequence and tune clock to master

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MAC Protocol

• A pico net is dynamically generated and identified by master’s identity and clock.

• Peer communication. Master/slave is applied only when pico net is formed.

• Master controls the traffic and access control of the pico net.

• Master implements centralized control in alternately manner ( M ==> S & S ==>M)

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MAC ( cont. )

• Master uses a polling technique:* for each slave-to-master slot, the master decides which slave is

allowed to transmit.

* Per-slot basis

* Master-to-slave data transmission is implicitly polling

* No data, master must explicitly polls slaves.

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Packet-Based Communications

• Information stream is fragmented into packets.

• In each slot, only a packet can be sent.

• All packets have the same format* access code

* packet header

* user payload

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Packet Format

• Access code includes the identity of the piconet master.

• Packet header contains link control information.

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Packet Header Format

• 3-bit slave address

• 1 bit ACK/NACK for ARQ

• 4 bit packet types

• 8 bit header error check (HEC).

• 1/3 rate forward error correction ( FEC ) coding.

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Four Control Packets

• ID packet:* only consist of the access code; for signaling

• NULL packet* only contain access code and packet header for link control

• POLL packet* Similar to NULL, used by master to force slaves to return a

response.

• FHS packet* An FH-synchronization packet.

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Multi-slot Packets

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Multi-slot packets

• 16 different payload types: 4 control packets and 12 other types.

• 12 types are divided into 3 segments:* Segment 1: specify packets that fit into a single slot.* Segment 2: specify packets that fit into a 3-slot* Segment 3: specify packets that fit into a 5-slot

• During multislot packet transmission, the hop carrier which is valid in the first slot is ued for the remainder of the packet.

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Multislot packets

• No frequency switch in the middle of the packet.

• After the packet has been sent, the hop carrier as specified by the current master clock value is used.

• Only an odd number of multislot packets have been defined to guarantees that the TX/RX timing is maintained.

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Bandwidth

• The maximum user rate over asynchronous link is 723.2 kb/s and the return link of 57.6 kb/s.

• Synchronous link is 64 kb/s in both direction.

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Synchronous and Async. links

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Link types

• Synchronous connection-oriented (SCO) link:* A point-to-point link between master and slave* reservation of duplex slots at regular intervals

• Asychrnous connectionless (ACL) link* point-to-multipoint link between master and all the slaves on

the pico net

* can use all of the remaining slots on the channel not used for SCO links.

* Scheduled by master

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Power Saving & Connection

• A unit in idle mode sleep most of the time to save power.

• No control channel is used in a true Ad-hoc network.

• How does a unit know a connection request?

• A unit periodically wakes up to listen for its identity ( the access code derived from its identity ).

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Wake Up Sequence

• A unit wakes up to scan for its identity at a different hop carrier ( 10 msec ).

• Wake up hop sequence is only 32 hops in length and is cyclic.

• The sequence is pseudo-random and unique for each Bluetooth device and is derived from the unit’s identity.

• The phase in the sequence is determined by the free-running native clock in the unit.

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Paging

• Solve the frequency-time uncertainty.

• Once the receiver’s identity is known, the paging unit knows its identity and hence wake up sequence.

• The paging unit transmits the access code repeatedly at different frequencies: every 1.25 msec.

• The paging unit transmits two access codes and listens twice for a response.

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Paging at two hop carriers

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Paging

• Consecutive access codes are transmitted on different hops selected from the wake-up sequence.

• In a 10 msec period 16 different hop carriers are visited.* Transmit cyclically during sleep period

* if no response is heard after a sleep time, transmit the remaining 16 hop carriers.

* Maximum access delay is twice the sleep time

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Synchronization

PagingUnit Y

Idle Unit X

Paging ( access code x )

( Access Code X )

FHS ( access code & clock y )

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Speed Up Access Time

• The paging unit stores the offset between their free running native clocks at recent connection.

• The paging can use the offset to estimate the phase of the idle unit.

• F(m) at time m, and assume the idle unit will wake up in f(k’), transmit access codes in f(k’-8), f(k’-7),…., f(k’), f(k’+1),..,f(k+7)

• Offset is useful at least 5 hours at 250 ppm.

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Inquiry

• if partner’s code is unknown, it uses a 32-hop inquiry broadcast to get the id and clock information.

• Inquiry uses a reserved identity ( the inquiry address ).

• Units that receive the inquiry message return an FHS packet.

• Transmission of FHS packets follow a random backoff mechanism.

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Bluetooth Protocol Stacks

• RF layer: specify the radio parameters.

• Baseband layer: lower-level operations at the bit and packet levels. ( FEC operations, CRC calculation, ARQ protocol )

• Link manager (LM) layer: connection establishment and release, authentication, connection and release of SCO and ACL channels, traffic scheduling, power management.

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Bluetooth Protocol Stacks

• Logical Link Control and Adaptation Protocol (L2CAP): interface between standard protocol and bluetooth protocol.

* Functions: multiplexing, segmentation/reassembly of large packets.

• Control between application and LM:* configuration of the Bluetooth transceiver for the considered appli

cation.

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Bluetooth Profiles

• Profiles guarantee that two units speak the same language.

• Profiles are associated with application.

• Profile specifies:* Which protocol elements are mandatory in certain application.

• Profile encourages strongly reduced protocol stack.

• Profile are dynamic.

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Recent Advances

• BRAN (Broadband Radio Access Network)

• UWB (Ultra-Wideband Technology) (802.15.3a)

• Broad WLAN (802.11n, >=100M)

• Wireless MAN(802.16)

• 4G(802.20)

• Software-Defined Radio(SDR)