
The right technology/standard for the problem/environment??
1

200
54
5-11
4
1 802.15
802.11n
802.11a,g
802.11b
802.11a,g point-to-point
802.16 (WiMAX)
UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO
.384
.056
Indoor
10-30m
UMTS/WCDMA, CDMA2000
IS-95, CDMA, GSM
Outdoor
50-200m
Mid-range outdoor
200m – 4 Km
Long-range outdoor
5Km – 20 Km data
3G cellular enhanced
3G
2G
2



Physical layer



Spectrum allocation (wave length)
Frequency; channel width; time multiplexing
Signal-to-Noise; BER; Error correction; etc.
MAC layer (sub-layer in data link layer)

Multiple access techniques

E.g., FDMA, TDMA, CDMA, SDMA, OFDMA
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 spectrum allocated by global and national agencies
(Less sensitive to obstacles)
Low frequency
(More sensitive to obstacles)
High frequency
ELF (30-300Hz) Telephone;
AM broadcast
Cell phone;
Satellite
Visible light
(400-900THz)
Microwave links
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
802.11b



2.4-5 GHz unlicensed spectrum up to 11 Mbps direct sequence spread spectrum (DSSS) in physical layer
• all hosts use same chipping code



802.11a


5-6 GHz range up to 54 Mbps
802.11g


2.4-5 GHz range up to 54 Mbps
802.11n: multiple antenna

2.4-5 GHz range
 up to 200 Mbps

 all use CSMA/CA for multiple access all have base-station and ad-hoc network versions
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6

BSS 1
AP
Internet hub, switch or router
AP


Wireless host communicates with base station
 base station = access point (AP)
Basic Service Set (BSS) (aka
“cell”) in infrastructure mode contains:

 wireless hosts access point (AP)
 ad hoc mode: hosts only
BSS 2
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

802.11b has 11 channels
Channels 1, 6, and 11 are non-overlapping
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Channel 1
AP
AP
Channel 11
AP
Channel 1
AP
AP
Channel 6




802.11b has 11 channels
Channels 1, 6, and 11 are non-overlapping
Each AP coverage area is called a “cell”
Wireless nodes can roam between cells
Channel 6
AP
Channel 1
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Channel 1
AP
AP
Channel 11
AP
Channel 1
AP
AP
Channel 6




802.11b has 11 channels
Channels 1, 6, and 11 are non-overlapping
Each AP coverage area is called a “cell”
Wireless nodes can roam between cells
Channel 6
AP
Channel 1


AP admin chooses frequency for AP interference possible: channel can be same as that chosen by neighboring AP!
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 host: must




with an AP scans channels, listening for containing AP’s name (SSID) and MAC address selects AP to associate with may perform authentication beacon frames typically run DHCP to get IP address in AP’s subnet
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BBS 1 BBS 2
BBS 1 BBS 2
AP 1
1
AP 2
1
2
3
H1
Passive Scanning:
(1) Beacon frames sent from APs
(2) Association Request frame sent:
H1 to selected AP
(3) Association Response frame sent: selected AP to H1
AP 1
2
1 AP 2
2
3
4
H1
Active Scanning
:
(1) Probe Request frame broadcast from H1
(2) Probes response frame sent from APs
(3) Association Request frame sent: H1 to selected AP
(4) Association Response frame sent: selected AP to H1
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2 2 6 6 6 frame control duration address
1 address
2 address
3
2 6 0 - 2312 seq control address
4 payload
4
CRC
Address 4: used only in ad hoc mode
Address 1: MAC address of wireless host or AP to receive this frame
Address 2: MAC address of wireless host or AP transmitting this frame
Address 3: MAC address of router interface to which AP is attached
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Rate Adaptation
 base station, mobile dynamically change transmission rate
(physical layer modulation technique) as mobile moves, SNR varies
QAM256 (8 Mbps)
QAM16 (4 Mbps)
BPSK (1 Mbps) operating point
10 -1
10 -2
10 -3
10 -4
10 -5
10 -6
10 -7
10 20 30
SNR(dB)
40
1. SNR decreases, BER increase as node moves away from base station
2. When BER becomes too high, switch to lower transmission rate but with lower BER
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Power Management
 node-to-AP: “I am going to sleep until next beacon frame”

AP knows not to transmit frames to this node

 node wakes up before next beacon frame beacon frame: contains list of mobiles with AP-to-mobile frames waiting to be sent

Every 100ms (250  s wakeup time)
 node will stay awake if AP-to-mobile frames to be sent; otherwise sleep again until next beacon frame

Explicit pull request
Note: Nodes with nothing to send/receive can save 99% of energy
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16

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Bluetooth Networking
• Piconets and Scatternets:
– Bluetooth devices are organized in local networks called
– up to eight devices can be part of a piconet
– devices are divided in master and slaves piconets
– the master controls the utilization of the radio channel (e.g. frequencyand a slave in two different piconets
– a network formed by several connected piconets is called a hopping sequence and timing) in the communication with the slaves
– a slave may communicate only with the master and when allowed by the master
– a device may belong to different piconets and may be both a master scatternet
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



 less than 10 m diameter replacement for cables
(mouse, keyboard, headphones) ad hoc: no infrastructure master/slaves:

 slaves request permission to send (to master) master grants requests
802.15: evolved from
Bluetooth specification

2.4-2.5 GHz radio band
 up to 721 kbps
S
S
P
M
P radius of coverage
P
P
S
M Master device
S
Slave device
P Parked device (inactive)
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20


IEEE 802.11 (WiFi)







Fast (11 Mbps)
High power
Long range
Single-purpose
Typically channel 1,
6, or 11
Ethernet replacement
Easily available

Bluetooth






Slow (1 Mbps)
Low power
Short range
Flexible
Frequency hopping
Cable replacement (e.g., device-to-device)
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
What technology/device?
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Figures from:
A. Mahanti et al., ”Ambient Interference Effects in Wi-Fi Networks”, Proc. IFIP Networking, 2010.

Many devices and technologies sharing the medium … resulting in different degrees of interference
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


Channel utilization: The
% of time a transmission is present from a known
RF source, in a given channel
Channels 1 and 6, utilization peaked near
60%, while for channel
11 it was over 90%.
Channel 11 spikes caused due to microwave ovens, cordless phones, and other fixed-frequency devices.
Figure from:
A. Mahanti et al., ”Ambient Interference Effects in Wi-Fi Networks”, Proc. IFIP Networking, 2010.
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25


 like 802.11 & cellular: base station model

 transmissions to/from base station by hosts with omnidirectional antenna base station-to-base station backhaul with point-to-point antenna unlike 802.11:

 range ~ 6 miles (“city rather than coffee shop”)
~14 Mbps point-to-point point-to-multipoint
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 transmission frame
 down-link subframe: base station to node
 uplink subframe: node to base station
DL-
MAP
UL-
MAP
DL burst 1
DL burst 2
…
…
DL burst n
Initial maint.
… request conn.
SS #1 SS #2 SS #k
… uplink subframe downlink subframe base station tells nodes who will get to receive (DL map) and who will get to send (UL map), and when

WiMAX standard provide mechanism for scheduling, but not scheduling algorithm
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28

MSC

connects cells to wide area net

manages call setup (more later!)

handles mobility (more later!) cell

covers geographical region


(BS) analogous to 802.11 AP
 base station mobile users attach to network through BS air-interface: physical and link layer protocol between mobile and BS
Mobile
Switching
Center
Mobile
Switching
Center
Public telephone network, and
Internet wired network
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• 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
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2G systems: voice channels



IS-136 TDMA: combined FDMA/TDMA (north america)
GSM (global system for mobile communications): combined FDMA/TDMA
 most widely deployed
IS-95 CDMA: code division multiple access
GSM
Don’t drown in a bowl of alphabet soup: use this for reference only
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2.5 G systems: voice and data channels



 for those who can’t wait for 3G service: 2G extensions general packet radio service (GPRS)

 evolved from GSM data sent on multiple channels (if available) enhanced data rates for global evolution (EDGE)

 also evolved from GSM, using enhanced modulation data rates up to 384K
CDMA-2000 (phase 1)

 data rates up to 144K evolved from IS-95
34

3G systems: voice/data

Universal Mobile Telecommunications Service (UMTS)
 data service: High Speed Uplink/Downlink packet
Access (HSDPA/HSUPA): 3 Mbps

CDMA-2000: CDMA in TDMA slots
 data service: 1xEvlution Data Optimized (1xEVDO) up to 14 Mbps
4G systems: voice/data
….. more (and more interesting) cellular topics due to mobility (stay tuned for details)
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• Station: a device containing 802.11 equipment
• Basic Service Set (BSS) : set of stations controlled by a coordination function
• Coordination function: logical function determining when a station can receive and send data in a BSS
• Distribution System (DS): a system connecting a set of BSS and integrated LANs to create an extended service set (ESS)
• Extended Service Set: a set of BSS and LANs appearing as a single unit to the LLC layer of the component stations
• Access point (AP) : entity providing access to the distribution system
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• IEEE 802.11 define 9 services:
– 6 services for supporting delivery of MAC service data units (MSDU) between stations
– 3 services for LAN access and confidentiality
• Service provider type:
– station: services implemented in stations and access point stations
(APs)
– distribution system (DS): services between BSSs implemented in access point stations or dedicated devices
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41

Bluetooth - Channel control in a piconet [1]
• Two major states of a Bluetooth device:
– Standby: low-power state
– Connection: the device is connected
• Seven states for adding new slaves to a piconet:
– Page – device issued a page (used by master)
– Page scan – device is listening for a page
– Master response – master receives a page response from slave
– Slave response – slave responds to a page from master
– Inquiry – device has issued an inquiry for identity of devices within range
– Inquiry scan – device is listening for an inquiry
– Inquiry response – device receives an inquiry response
42

Bluetooth - Channel control in a piconet [2]
43

Bluetooth - Inquiry and Page Procedure [1]
 Inquiry Procedure:
Potential master identifies devices in range that wish to participate
– transmits an identification ID packet with inquiry access code (IAC)
– occurs in Inquiry state
Devices receives inquiry
– enter Inquiry Response state
– return data with address and timing information (in an
FHS packet)
– slave moves to Page Scan state or returns to Inquiry
Scan
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Bluetooth - Inquiry and Page Procedure [2]
 Page Procedure
• Master uses device address to calculate a page frequency-hopping sequence
• Master pages with ID packet and device access code
(DAC) of specific slave
• Slave responds with ID DAC packet
• Master responds with a special FHS packet containing its address and real-time Bluetooth clock value
• Slave confirms master’s FHS packet reception with a
ID DAC packet
• Slaves moves to Connection state
 Connection state control for slaves
• Master send a Poll packet to verify that a slave has switched on master timing and channel frequency
• Slave responds with any packet
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Bluetooth - Slave Connection State Modes
Active – slave participates in piconet
– listens, transmits and receives packets
– master sent regularly synchronization data
Sniff – slave listens only on specified slots
– master indicate a reduced number of slots
– slave can operate in reduced power mode when not listening
Hold – slave may participate partially in the piconet
– slave in reduced power status
– slave does not support ACL packets
– slave may participate in SCO exchanges
Park – slave does not participate currently in the piconet
– slave still retained as part of the piconet
– device receive a parking address and loses its active member address
– piconet may then have more than 7 slaves, but only 7 are active
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48




Wireless sensor communications protocol stack


2.4 GHz RF spectrum (i.e., the ISM band)
Establishes rules for co-existence, data representation, signaling, authentication, and error detection
Low computational overhead and high efficiency

Low power consumption by the radios
Targeted at the sports sector, particularly fitness and cycling performance monitoring.

Transceivers are embedded in equipment such as heart rate belts, watches, cycle power and cadence meters, and distance and speed monitors
49