Wireless LANs and PANs - 高速通訊與計算實驗室hscc.cs.nthu.edu.tw/~sheujp/lecture_note/11wn/Chapter 15.pdf · Wireless LANs and PANs Chapter 15 1. ... It is the standard

Copyright © 2011, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved

Wireless LANs and PANs

Chapter 15

1


Outline

Introduction Wireless Local Area Networks (WLANs) Enhancement for IEEE 802.11 WLANs Wireless Metropolitan Area Networks (WMANs) using WiMAX and Mesh Networks Mesh Networks Wireless Personal Area Networks (WPANs) ZigBee Summary

2


Data rate

Scope of Various WLAN and WPAN Standards

802.11n*

Power consumption Complexity

802.15.I

Bluetooth

802.11a

HiperLAN

802.11g*

802.11

WPAN

802.11b

WLAN

* Standard in progress

WMAN

802.16

WiMAX

WMN

802.16*

802.15.4

3


Wireless Local Area Networks (WLANs)

IEEE group published a standard for WLANs named as IEEE 802.11 (now known as IEEE 802.11a) Higher bit rates at 2.4GHz ISM band resulted in high-speed standard called the IEEE 802.11b (popularly known as Wi-Fi) Can be used to have an ad hoc network using peer-to-peer mode, Or, as a client/server wireless configuration

Ad hoc Client/server

4


IEEE 802.11

It is the standard for wireless LANs.

It specifies MAC procedures and operate in 2.4 GHz range with data rate of 1Mbps or optionally 2Mbps.

User demand for higher bit rates and international availability of 2.4 GHz band has resulted in development of a high speed standard in the same carrier frequency range.

This standard called 802.11b, specifies a PHY layer providing a basic data rate of 11 Mbps and a fall-back rate of 5.5 Mbps.

5


IEEE 802.11

In the ad hoc network mode, as there is no central

controller, the wireless access cards use the CSMA/CA

protocol to resolve shared access of the channel.

In the client/server configuration, many PCs and

laptops, physically close to each other (20 to 500 meters),

can be linked to a central hub [AP]

A larger area can be covered by installing several APs

The access points track movement of users and make

decisions on whether to allow users to communicate

WLAN cards could be operated in continuous aware

mode (radio always on) and power saving polling mode

(radio in sleep state to extend battery life) 6


Distributed Wireless Network

Station

Access

point

Wired network

Access

point

Distributed

system

Access

point

Station

Station Station

7


IEEE 802.11 and variants

IEEE 802.11a With a throughput up to 54Mbps IEEE 802.11a operates on 5GHz It has less interference as compared to IEEE 802.11b/g since 2.4GHz band is heavily used Uses orthogonal frequency-division multiplexing (OFDM) with 52 subcarriers spanning over a 20MHz spectrum

IEEE 802.11b (WiFi) Operates on 2.4GHz band with throughput of up to 11Mbps Direct-sequence spread spectrum DSSS on PHY layer

IEEE 802.11g Operates on 2.4G using either DSSS or OFDM Can achieve higher throughput of up to 54Mbps

IEEE 802.11n Multiple-input multiple-output (MIMO) technology Bandwidth can be 40MHz in 2.4GHz and 5GHz

8


Enhancement for IEEE 802.11 WLANs

The keys behind all the above networks are the wireless cards and wireless LAN access points

In an ad hoc network mode, there is no central controller, the wireless access cards use CSMA/CA protocol to resolve shared access

MAC layer access uses one of following methods:

distributed coordination function (DCF), point

coordination function (PCF), and hybrid coordination

function (HCF)

DCF is carrier sense multiple access with collision

avoidance (CSMA/CA) and senses the medium before

sending frame 9


Enhancement for IEEE 802.11 WLANs

IEEE 802.11e working group has developed enhanced

DCF (EDCF) so that the differentiated service could

be provided

MSs with shorter AIFS have a higher priority to

access channel than stations with longer AIFS

Two EDCF priority schemes: interframe space (IFS)

priority scheme and contention window (CW) priority

scheme

IFS priority scheme works better when the number of

competing stations is large and can improve up to

50% for the real-time packets

10


Issues in MAC Protocol

Challenges security related and support of multicast and location management

Many mobile applications require support for group communication

Location-based services include providing listings of local restaurants or movie theaters, emergency services, and vehicle tracking

Scalability is a major concern to WLANs

In client server model, many PC’s or laptops physically close to each other (20-500m) can be linked to a central hub (access point) which acts as a bridge between the wireless and wired network

A large area can be covered by installing several access points in the building

11


Roofnet and HyperLAN

Roofnet is an experimental multi-hop IEEE 802.11b consists of about 50 nodes in apartments of Cambridge

Few nodes act as gateways to wired Internet

Requires no pre-configuration and users can connect on the fly

HiperLAN stands for high-performance LAN

Employs 5.15GHz and 17.1GHz frequency bands and has a data rate of 23.5Mbps with a coverage of 50m and mobility < 10 m/s

Supports 25 audio connections at 32 kbps with a maximum latency of 10 ms, 1 video connection of 2Mbps with 100ms latency, and data rate of 13.4 Mbps

12


Features of Hiper LAN/2

HiperLAN type 2 has been specifically developed to

have a wired infrastructure

Type 1 has a distributed MAC with QoS provisions,

whereas type 2 has a centralized scheduled MAC

Type 1 is based on Gaussian minimum shift keying

(GMSK), whereas type 2 is based on OFDM

HiperLAN/2 automatically performs handoff to the

nearest AP which is basically a radio BS that covers an

area of about 30 to 150 meters

13


Features of Hiper LAN/2

The goals of HiperLAN are:

QoS (to build multiservice networks)

Strong security

Handoff when moving between local area and wide areas

Increased throughput

Ease of use, deployment, and maintenance

Affordability

Scalability

The connection oriented approach makes support for

QoS easy

It supports automatic frequency allocation, eliminating

the need for manual frequency planning as in cellular

networks 14


HyperLAN/2 Features

Fixed network

AP

AP AP

AP

MS MS

A simple HyperLAN/2 system

15


HyperLAN/2 Features MS may at any time request the AP and enter a low-power state for a sleep period Control is centralized at AP Channel spacing is 20MHz allowing high bit rates per channel Selective repeat ARQ is an error control mechanism used Radio link control (RLC) protocol provides following services:

Association control with feature negotiation Encryption algorithms and convergence layers, authentication, key negotiation, and convergence layer negotiation Radio resource control to support handoff capability, to perform radio measurements in assisting the APs in selecting an appropriate radio channel, and to run the power-saving algorithm Connection control for the establishment and release of user connections

16


HomeRF

Two kind of networks: HomeRF (for home), Hiper LAN (for business workspace).

43 million US homes now contain more than one PC.

A home network typically consists of one high speed internet access port providing data to multiple networked nodes.

Home networking allows all computers in a home to simultaneously utilize the same high speed ISP (Internet Service Provider) account.

Home networking allows two options: wired solution and wireless solution.

17


HomeRF (cont’d)

Wired Solutions such as Ethernet, phone

line offers a fast reliable secure connections,

but the cost of wiring and installation is

high.

Wireless networks such as PC-Centric Data

offer more mobility to the users of the

network.

18


Figure 14.6 Architecture of HomeRF system

Baby

monitor

Phone connection

Cell phone

Main PC

Clock

Palmtop

Wireless

headset

Satellite dish

Fridge data pad

Television Handheld

communicator

Lapt

op

2nd PC Cable

modem

19


Advantages of Wireless HomeRF

Mobility

Flexibility: Simultaneous internet access while sharing

a single internet connection with other PCs.

Simple: Installation time is small.

Economical: Less than $100 for each networked PC.

Secure

Based on industry Standards: Enables interoperability

between many different manufacturers.

20


HomeRF Technology

In HomeRF all the devices can share the same

connections for voice and data

Provides the foundation for a broad range of

interoperable consumer devices

A specification for wireless communications in the

home called Shared Wireless Access Protocol

(SWAP) has been developed

21


Home RF Network

A network consists of Resource providers, which are gateways to different resources like cordless phones, printers, fileservers and TV.

The goal of Home RF is to integrate all of them in to a single Network suitable for all applications and also remove all wires and utilize RF links in the network.

This will support the mobility of devices.

With Home RF, cordless phone can connect to PSTN ordinarily, but can also connect through a PC for enhanced services.

22


Comparison of WLAN Standards

Technology Wireless LAN

IEEE 802.11b

(WiFi)

HomeRF HiperLAN

Operational

spectrum

2.4 GHz 2.4 GHz 5.GHz

Physical layer DSSS FHSS with FSK OFDM with QAM

Channel access CSMA/CA CSMA–CA and

TDMA

Central resource

control/TDMA/TDD

Nominal data

rate

2 Mbps 10 Mbps 32–54Mbps

Coverage 100 m >50m 30–150m

Power level issues <350mA current

drain

<300mA peak

current

Uses low power states

like

sleep

Interference Present Present Minimal

Price/complexity Medium (<$100) Medium High (>$100)

Security Low High High

23


Wireless Metropolitan Area Networks (WMANs)

IEEE 802.16 based WiMAX

Offers less expensive opportunity

Supports point-to-multipoint broadband wireless access

Very high bit rates in the range of 3.5 MHz

Support a variety of backhaul requirements, including both

ATM and packet-based protocols

Convergence sublayers are used to map the transport-layer–

specific traffic to a MAC and offers features such as payload

header suppression, packing, and fragmentation

Supports 99.999 percent link availability

MAC supports automatic repeat request (ARQ)

24


Wireless Metropolitan Area Networks (WMANs)

Data to the subscriber stations are multiplexed in TDM fashion. The uplink (UL) is shared between SSs in TDMA fashion SS has a standard 48-bit MAC address MAC PDU consists of a fixed-length MAC header, a variable-

length payload, and an optional cyclic redundancy check (CRC) MAC supports various higher-layer protocols such as ATM or IP

CID lsb (8) HCS (8)

LEN lsb (8) CID msb (8)

Type (6) LEN Msb(3)

HT=

0 (

1)

Rsv

(1)

EC(1

)

Rsv

(1)

CI(

1)

EKS (2)

25


IEEE 802.16 MAC

MAC supports both TDD and FDD

10–66GHz: line-of-sight (LOS) needed

Burst design allows coexistence of both TDD and FDD forms

2–11GHz: three air interfaces are defined

Air Interface Specification

WMAN–SC2 A single-carrier modulation is used

WMAN–

OFDM

License-exempt bands necessarily use this TDMA access

interface. OFDM is present with a 256-point transform

WMAN–

OFDMA

Each receiver is assigned a set of multiple carriers to

enable multiple access. OFDM is present with a 2048-

point transform

Three 2–11GHz Air Interface of the IEEE 802.16a Draft 3 Specifications

26


IEEE 802.16 MAC Physical Layer

Channel bandwidths are 20, 25MHz (typical U.S. allocation) or 28MHz (typical European allocation) Frame size can be 0.5, 1, or 2 ms Negotiated burst profile is used to provide synchronization with the Down Link

P

MAC PDU which has started in previous TC PDU

First MAC PDU, this TC PDU

Second MAC PDU, this TC PDU

TC sublayer PDU

27


Wireless Mesh Network

Figure 15.9 Illustration of a Wireless Mesh Network (WMN)

Internet

IGW 1

IGW 2

MR1

MR2 MR3

MR4

MR5

MR6

Backbone

Mesh Clients

28


Wireless Mesh Network

Comprise of:

Internet Gateways (IGWs)

Mesh Routers (MRs)

Mesh Clients (MCs)

Multi-hop WMN, traffic is predominantly oriented towards

IGWs from MRs

Traditional routing solutions of MANETs are not adequate

for WMNs

TCP could result in excessive packet delays

Vulnerable to variety of security attacks

29


Ricochet

A mobile data access service that is always on,

provides high speed, secure mobile access to the

desktop from outside the office.

It allows to link to the internet or the corporate

network without needing phone lines or cable

connections.

The Ricochet service is provided by Metricom.

30


Ricochet Mobile Communication Network

Network interconnection facility Microcell radios on

street lights, utility poles

Wireless access point

Name server

Router

Gateway

Gateway to Internet, Intranets,

LANS, Compuserve, AOL and

other on-line services Computer device

Modem radio

31


Ricochet

The Ricochet service is a wide area wireless system using

spread spectrum packet switching data.

The network operates within 902-928 MHz portion of RF

spectrum.

The Ricochet wireless Micro Cellular Data Network

(MCDN), consists of shoebox sized radio receivers, called

Micro cell radios (Fig 14.5)

Micro cells are typically mounted to street poles.

Micro cells require a small power from the street lights.

Each Micro cell radio employs 162 frequency hopping

channels.

32


The Ricochet Wireless Modem

It weighs 13 ounces.

Has the general dimensions of a small paperback

book, plugs directly into a desktop.

When a Ricochet modem is configured to operate

in bridge mode, it translates signals from other

Ricochet modems into signals that a wired modem

can receive.

V.34, 28,800 bps access

Good Availability

Unlimited access

Flexible pricing

33


Services Provided by Ricochet

Provides immediate, dependable and secure

connections without the cost and

complexities of land based phone lines.

Sending E-mails, access to documents in

home networks.

Many real estate agents use this to search

for property listings while on road.

34


Comparison of WMAN Standards

Technology Wireless MAN

IEEE 802.16 Ricochet

Operational spectrum 10–66GHz, LOS required,

20/25/28MHz channels

900MHz

Physical layer TDMA-based uplink, QPSK, 16-QAM,

64-QAM

FHSS

Channel access TDD and FDD variants CSMA

Minimum data rate possible 120/134.4Mbps for 25/28MHz channel 176 kbps

Coverage Typically a large city As of September, 2002 only Denver, CO

Power level issues Complicated power control algorithms

for different burst profiles

Low power modem compatible with

laptops and hand-held

Interference Present but limited Present

Price complexity Not available Medium

Security High. Defines an extra privacy sublayer

for authentication

High (Patented security system)

35


Wireless Personal Area Network

Bluetooth initially conceived to replace RS232

cables, is the only WPAN technology to be

commercially available

Since 2002, its presence has become visible in

devices ranging from laptops to wireless mouse to

cameras, to headsets, to printers and cell phones

IEEE 802.15.x protocols to address needs of

WPANs with varied data rates

Bluetooth has adopted as IEEE 802.15.1 (medium

rate) while the IEEE 802.15.3 (high rate) and

802.15.4 (low rate) are also available 36


IEEE 802.15 Task Groups IEEE 802.15 WPAN/Bluetooth TG1

IEEE 802.15 Coexistence TG2: TG2 (the IEEE 802.15.2) is

developing recommended practices to facilitate coexistence of

WPANs (the IEEE 802.15) and WLANs (the IEEE 802.11).

IEEE 802.15 WPAN/High Rate TG3: The TG3 for WPANs is

chartered to draft a new standard for high-rate (20Mbps or greater)

WPANs

IEEE 802.15 WPAN/Low Rate TG4: The goal is to provide a

standard for ultra-low complexity, cost, and power for low-data-rate

(200 kbps or less) wireless connectivity among inexpensive fixed,

portable, and moving devices

37


Bluetooth

It is named after the King of Denmark that unified

different factions in Christianity through the country.

It is a short range RF communication.

Low cost, low power, radio based wireless link

eliminates the need for short cable.

Bluetooth radio technology built into both the cellular

telephone and the laptop would replace the cable used

today to connect a laptop to cellular phone.

Printers, desktops can all be wireless.

It also provides a universal bridge to existing data

networks (Fig 14.11). 38


Bluetooth

Cellular

Link

Figure 14.9 Use of Bluetooth to connect notebook

Base Station

39


Figure 14.10 Bluetooth connecting printers, PDA’s, desktops, fax

machines, keyboards, joysticks and virtually any other digital device

40


Fixed Line

Figure 14.11 Bluetooth providing a universal bridge to

existing data networks

41


Bluetooth: A mechanism to form ad hoc networks of connected

devices away from fixed network infrastructures

Bluetooth

Personal

Ad hoc

Network

42


Bluetooth

The ultimate goal is to make small products

(PC/Laptops) have only one wire attached to

power cord.

In case of PDA, the power cord is also eliminated.

A simple application of Bluetooth is updating the

phone directory of the PC from a mobile telephone.

A typical Bluetooth has a range of 10 m.

43


Features

Fast frequency hopping to reduce interference.

Adaptive output power to minimize interference.

Short data packets to maximize capacity.

Fast acks allowing for low coding overhead for links.

Flexible packet types that support a wide application range.

CVSD (Continuous Variable Slope Delta Modulation)

voice coding that can withstand high bit error rates.

Transmission/reception interface tailored to minimize

power consumption

44


Architecture of Bluetooth System and Scatternet

Piconet 1

Piconet 4

Piconet 3

Piconet 2

M2

M1

M3

M4

S2,1

S2,2

S2,3

S3,1 S3,2

S3,3

S2,4 /S3,4

S1,2 /S2,5

S 1,3 /S 4,4

S1,1

S1,4

S1,5

S4,1

S4,2 S4,3

45


Bluetooth Technological Characteristics

Frequency band 2.4 GHz (unlicensed ISM band)

Technology Spread spectrum

Transmission method Hybrid direct sequence and frequency hopping

Transmission power 1 milli-watt (0 dBm)

Range 10 meters (40 feet)

Number of devices 8 per piconet, 10 piconets per coverage area

Data speed Asymmetric link: 721+57.6 kbps

Symmetric link: 432.6 kbps

Maximum voice channels 3 per piconet

Maximum data channels 7 perpiconet

Security Link layer w/s fast frequency hopping (1600 /sec)

Power consumption 30 μA sleep, 60 μA hold, 300 μA standby, 800 μA max transmit

Module size 3 square cm (0.5 square inches)

Price Expected to fall to $5 in the next few years

C/I co-channel 11 dB (0.1% BER)

C/I 1 MHz -8 dB (0.1% BER)

C/I 2 MHz -40 dB (0.1% BER)

Channel switching time 220 μs

46


Architecture

Bluetooth radio typically hops faster and uses shorter packets as compared to other systems operating in the same frequency band.

Use of FEC (Forward Error Correction) limits the impact of random noise.

As the interference increases, the performance decreases.

47


Architecture (cont’d)

Bluetooth devices can interact with other Bluetooth devices.

One of the devices acts as a master and others as slaves.

This network is called “Piconet”.

A single channel is shared among all devices in Piconet.

There can be up to seven active slaves in the Piconet.

Each of the active slaves has an assigned 3 bit Active Member

address.

A lot of other slaves can remain synchronized to the Master

through remaining inactive slaves, referred to as parked nodes.

A parked device remains synchronized to the master clock and

can become active and start communicating in the Piconet

anytime.

48


Architecture (cont’d)

If Piconets are close to each other, they have overlapping

areas

The scenario where the nodes of two or more Piconets

mingle is called Scatternet

Before any connections in the Piconet are created all

devices are in STDBY mode

In this mode an unconnected unit periodically “listens” for

message every 1.28 seconds

Each times a device wakes up, it tunes on the set of 32 hop

frequencies defined for that unit

49


Upper Layer

Baseband

SDP

LMP Audio L2CAPE

Low Radio Layer

SDP – Service Discovery

Protocol

L2CAP – Logical Link

Control and Adaptation

Layer Protocol

LMP – Link Manager

Protocol

Bluetooth Core Protocol

SDP: Provides a mean for applications to discover which services are provided by or available through a Bluetooth device

L2CAP: Supports higher level protocol multiplexing, packet segmentation and reassembly and conveying of QoS information

LMP: Used by Link managers for link set up and control

Baseband: Enables the physical RF link between Bluetooth units forming a Piconet

50


625sec 1-slot packet

3-slot packet

5-slot packet

Core Protocols

Type User Payload (bytes)

FEC

Symmetric (kbps)

Asymmetric (kbps)

DM1 0–17 Yes 108.0 108.8 108.8

DH1 0–27 No 172.8 172.8 172.8

DM3 0–121 Yes 256.0 384.0 54.4

DH3 0–183 No 384.0 576.0 86.4

DM5 0–224 Yes 286.7 477.8 36.3

DH5 0–339 No 432.6 721.0 57.6

HV1 0–10 Yes 64.0

HV2 0–20 Yes 128.0

HV3 0–30 No 192

51


Bea

con

Contention

access

period

(CAP)

Bea

con

Guaranteed time slot

(GTS)

Superframe

WPAN parameters

Non-QoS data frames:

• Short bursty data

• Channel access requests

CAP/GTS boundary

dynamically adjustable Data frames with QoS provisions:

• Image Files

• MP3 music files (multimedia files)

• Standard definition MPEG2, 4.5 Mb/s

• High-definition MPEG2, 19.2 Mb/s

• MPEG1, 1.5 Mb/s

• DVD, up to 9.8 Mb/s

• CD audio, !.5 Mb/s

• AC3 Dolby digital, 448 Kb/s

• MP3 streaming audio, 128 Kb/s

IEEE 802.15.3 MAC and PHY Layer Details

52


IEEE 802.15.4

Some applications that require high data rates such as shared Internet

access, distributed home entertainment, and networked gaming

However, there is an even bigger market for home automation,

security, and energy conservation applications

IEEE 802.15.4 defines specification for low-rate, low-power

WPANs

Application areas include industrial control; agricultural, vehicular,

and medical sensors; and actuators

53


Upper layers

Network layer

Data link layer

IEEE

802.15.4

868/915

MHz

PHY

IEEE

802.15.4

2400 MHz

PHY

IEEE 802.2

LLC, type 1

SSCS

Other

LLC

IEEE 802.15.4 MAC

IEEE 802.15.4 Data Link Layer (DLL) Details

54


Bytes:

PHY

Layer

General MAC frame format

PHY protocol data unit (PPDU)

MAC protocol data unit (MPDU)

Synchronization

header

Physical

header PHY service data unit (PSDU)

Payload Frame check

sequence

Address

Info

Sequence

number

Frame

control

MAC header (MHR) MAC service data

unit (MSDU)

MAC footer

(MFR)

2 2 Variable 0-20 1

MAC

Layer

55


Preamble

Start of

packet

delimiter

PHY

header

PHY service data unit (PSDU)

6 bytes 127 bytes

PHY protocol data unit (PPDU)

PHY packet fields:

Preamble (32 bits) – synchronization

Start of packet delimiter (8 bits) – signify end of preamble

PHY header (8 bits) – specify length of PSDU

PSDU ( 127 bytes) – PHY layer payload

802.15.4 PHY layer Packet Structure

56


Comparison of WPAN Systems

Technology Bluetooth (802.15.1) 802.15.3 802.15.4

Bluetooth 3.0 HS

Operational

spectrum

2.4GHz ISM band 2.402–2.480GHz ISM

band

2.4GHz and

868/915MHz

2.4–2.4835GHz or

6–9GHz

Physical layer

details

FHSS, 1600 hops

per

second

Uncoded QPSK trellis

coded QPSK or

16/32/64-QAM

scheme

DSSS with BPSK or

MSK (O–QPSK)

UWB

Channel

access

Master slave

polling,

time division

duplex

(TDD)

CSMA–CA, and

guaranteed time slots

(GTS) in a superframe

structure

CSMA–CA, and

guaranteed

time slots (GTS)

in a superframe

structure

802.11 radio

protocol

Maximum

data rate

Up to 1Mbps 11–55Mbps 868MHz–20,

915MHz–40,

2.4GHz–250 kbps

480 Mbps

Coverage <10m <10m <20m ?

Power level

issues

1mA–60mA

<80mA Very low current drain

(20–50 mA)

ultra-low power

Interference Present Present Present Minimum

Price Low (<$10) Medium Very low ?

57


ZigBee ZigBee is pertinent in various sensor applications

ZigBee is designed to respond quickly, while Bluetooth takes

much longer

ZigBee is a control technology on wireless standard Data rate of

250 Kbps in 2.4 GHz ISM band, 20 kbps in the 868 MHz band in

Europe, and 40 kbps in 915MHz band used in North America

and Australia

ZigBee can choose up to 16 different 5 MHz channels within 2.4

GHz band, several do not overlap with 802.11 and WiFi

ZigBee has active and sleep modes

All devices must have a short 16-bit IEEE addressing

Application layer maintains table of binding for matching

two or more devices

58

Documents

Wireless LANs and PANs - 高速通訊與計算實驗室hscc.cs.nthu.edu.tw/~sheujp/lecture_note/11wn/Chapter 15.pdf · Wireless LANs and PANs Chapter 15 1. ... It is the standard