4. ASRao
Wireless Characteristics
– Communication without wires
– Wires are replaced by electromagnetic waves
– electromagnetic waves carry a signal through
atmospheric space
– use radio frequency RF waves, which ranges from
3 kHz to 300 GHz
– or infrared IR, which ranges from 3 THz to 430 THz
6. ASRao
What is Mobility?
Two types of mobility:
i)Device portability
ii)User Mobility
no mobility
mobile wireless user,
using same access
point
high mobility
mobile user,
connecting/
disconnecting from
network
Mobility Spectrum
mobile user, passing
through multiple
access point while
maintaining ongoing
connections
7. Degrees of Mobility
ASRao
• Walking Users
• Low speed
• Small roaming area
• Usually uses high-bandwidth
• Vehicles
•
•
•
•
High speeds
Large roaming area
Usually uses low-bandwidth
Uses sophisticated terminal equipment (cell phones)
8. ASRao
ORIGIN of Wireless Communication
1864
James
1886
Maxwell
Rudolph
Predicts existence of radio waves.
Hertz
Demonstrates radio waves.
J C Bose
In 1895 Bose gave his first public demonstration
of electromagnetic waves, using them to ring a
bell remotely (more than a mile) and to explode
some gunpowder
1895-1901
Guglielmo
Marconi
Demonstrates wireless communications over increasing distances at 13 May 1897
10. ASRao
First Generation
• Early Wireless communications
– Signal fires
– Morse Code
– Radio
Radio Transmitter 1928 Dorchester
11. ASRao
1G
• Advanced Mobile Phone Services (AMPS)
– Deployed in US , Japan : 1983
• Nordic Mobile Telephony (NMT)
– Sweden, Denmark, Norway, Finland : 1981
• Total Access Communication System (TACS)
– British System, similar to AMPS : 1985
15. ASRao
The Second Mobile Generation 2G
• The second generation (2G) of the
wireless mobile network was based on
low-band digital data signaling.
• The most popular 2G wireless technology
is known as Global Systems for Mobile
Communications (GSM).
• The first GSM systems used a 25MHz
frequency spectrum in the 900MHz band.
16. ASRao
2G Technologies
• Global System Mobile (GSM)
• Interim-Standard 136 (IS-136) or
North America Digital Cellular (NADC) or
US Digital Cellular (USDC)
• Pacific Digital Cellular (PDC)
• Interim-Standard 95 Code Division Multiple
Access (CDMA) (IS-95 or cdmaOne)
17. ASRao
2G – GSM
• Global system for Mobile
– Based on TDMA ; Europe
– 900 Mhz, 1800 Mhz.
– Later 850 Mhz and 1900 Mhz in America
– World Phones
18. ASRao
GSM Architecture
• The available 25MHz of bandwidth into 124 carrier
frequencies of 200 kHz each.
• Each frequency is then divided using a TDMA
scheme into 8 timeslots and allows eight
simultaneous calls on the same frequency.
• TDMA breaks down data transmission, such as a
phone conversation, into fragments and transmits
each fragment in a short burst, assigning each
fragment a time slot.
• Today, GSM systems operate in the 900MHz and
1.8 GHz bands throughout the world with the
exception of the Americas where they operate in the
1.9 GHz band.
19. GSM Architecture
ASRao
•Home location register (HLR) database – stores information about each subscriber that
belongs to it.
•Visitor location register (VLR) database – maintains information about subscribers
physically in the region currently
•Authentication center database (AuC) – used for authentication activities and holds
encryption keys
•Equipment identity register database (EIR) – keeps track of the type of equipment that
exists at the mobile station
20. ASRao
Interim Standard-136 (IS-136)
• Started in 1991
• Also known as North American Digital Cellular
(NADC) or US Digital Cellular (USDC)
• Uses p/4-DQPSK, speech coding
• Uses TDMA with 3 time slotted users for each
30 kHz radio channel.
• Capacity improvement is 3 times that of AMPS
and later 6 times due to advancement in DSP
21. ASRao
Interim Standard-95 (IS-95)
[cdma One (or) 2G-CDMA]
• It is a popular 2G CDMA standard.
• The main advantage of CDMA is that many more users
(up to 10 times more) can be supported as compared to
TDMA.
• Convolutional Channel coding used
•
Modulation technique used is BPSK
• Supports up to 64 users that are orthogonally coded and
simultaneously transmitted on each 1228 KHz channel.
• Major success in Korea, Used by Verizon and Sprint
• Easy Migration to 3G
22. ASRao
The IS-95 cellular system has different structures for its
forward (base station to mobile station) and backward links.
Forward Channel
Reverse Channel
The forward link consists of up to 64 logical CDMA channels,
each occupying the same 1228 kHz bandwidth. The forward
channel supports different types of channels:
•Traffic channels (channels 8 to 31 and 33 to 63) – these 55
channels are used to carry the user traffic (originally at 9.6 Kbps,
revised at 14.4 Kbps).
•Pilot (Channel 0) – used for signal strength comparison, among
other things, to determine handoffs
•Synchronization (Channel 32) – a 1200 bps channel used to
identify the cellular system (system time, protocol revision, etc.).
•Paging (channels 1 to 7) – messages for mobile stations
23. ASRao
• All these channels use the same frequency band – the chipping
code (a 64-bit code) is used to distinguish between users.
• Thus 64 users can theoretically use the same band by using
different codes. This is in contrast to TDMA where the band has to
be divided into slots – one slot per user.
• The voice and data traffic is encoded, assigned a chipping code,
modulated and sent to its destination.
• The data in the reverse travels on the IS-95 reverse links. The
reverse links consist of up to 94 logical CDMA channels, each
occupying the 1228 kHz bandwidth.
• The reverse link supports up to 32 access channels and up to 62
traffic channels.
• The reverse links support many mobile unit-specific features to
initiate calls, and to update location during handoffs.
24. ASRao
2G CDMA (IS-95) Network Architecture
•The overall architecture of 2G CDMA-based systems are similar to the TDMAbased GSM systems.
•The main difference is that the radio communication between the Base Station
Subsystem and Mobile System uses CDMA instead of TDMA.
26. ASRao
Why 2.5G ?
• The Second Generation (2G) wireless networks are
mostly based on circuit-switched technology which limit
the data user to a single circuit switched voice channel
• 2G are thus, limited to data throughput rate of an
individual user (approx on the order of 10kbps)
• In 2G, original GSM, CDMA, and IS-136 standards
which originally supported 9.6 kilobits per second
transmission rates for data messages.
• 2G wireless technologies can handle some data
capabilities such as fax and short message service
(SMS) at the data rate of up to 9.6 kbps, but it is not
suitable for web browsing, rapid email, and multimedia
applications.
27. ASRao
2.5G Standards
• So-called „2.5G‟ systems are introduced to
enhance the data capacity of GSM and mitigate
some of its limitations.
• These systems add packet data capability to GSM
networks.
• 2.5G standards are IS-95B, HSCSD, GPRS,
EDGE technologies.
• IS-95B (CDMAOne is upgraded which uses higher
data rate than IS-95 and more efficient Handoff
techniques)
28. ASRao
Features of 2.5G
• It allow existing 2G equipment to be modified and
supplemented with new infrastructure to support
high data rate transmission for
–
–
–
–
–
Web browsing
Email
Mobile-Commerce (m-commerce)
Location based mobile services
Support Wireless Application Protocol (WAP)
• WAP is web browsing format language that allows
standard web pages to be viewed in a compressed
format
29. ASRao
2.5G - GPRS
• General Packet Radio Service - An Overlay technology
on top of the existing GSM systems.
• GPRS (General Packet Radio Services) is a packet based
data network.
– Unlike HSCSD, which dedicates circuit switched
channels to specific users, GPRS supports circuit
switching for multi-user network sharing of individual
radio channels and time slots.
• GPRS can theoretically provide IP-based packet data
speeds up to a maximum of 160 Kbps.
• Typical GPRS networks operate at lower data rates. One
proposed configuration is 80 Kbps maximum (56 Kbps
typical) for the downlink and 20 Kbps maximum (14.4 Kbps
typical) for the uplink.
30. ASRao
•GPRS can be added to GSM infrastructures quite readily.
•It takes advantage of existing 200 kHz radio channels and does not
require new radio spectrum.
•GPRS basically overlays a packet switching network on the
existing circuit switched GSM network. This gives the user an
option to use a packet-based data service.
•The main component of a GPRS network is the GSN (GPRS
Support Node) that receives the packet data and transfers it to the
Internet or other GPRS networks.
•To provide GPRS services on top of GSM, the network operators
need to add a few GSNs and make a software upgrade to BSCs and
few other network elements. This quick upgrade capability has
fueled the popularity of GPRS.
• Efficient – as resources not tied up all the time.
32. ASRao
Comparison of GSM & GPRS
Data Rates
Modulation
Technique
Billing
Type of
Connection
GSM
9.6 Kbps
GPRS
14.4 to 115.2 Kbps
GMSK
GMSK
Duration of
connection
Circuit – Switched
Technology
Amount of data
transferred
Packet - Switched
Technology
33. ASRao
HSCSD
• High-Speed Circuit-Switched Data.
• An enhancement to CSD – Multiple timeslots used.
• Data rates up to 38.4 Kbps (4 times CSD).
– In reality supports 14.4Kbps.
• Expensive than CSD.
• HSCSD (High Speed Circuit Switched Data) use a circuit
switched technique in GSM network. Uses consecutive time
slots instead of one which increases the data rate from
9,600 bps to 14,400 bps. By using 4 consecutive time slots
it increases to 57.6 kbps.
• Inefficient – as resources ties up all the time, even when
nothing sent.
34. ASRao
• HSCSD is ideal for dedicated streaming Internet access or
real-time interactive web sessions
• HSCSD is a specification for data transfer over GSM
networks. HSCSD utilizes up to four 9.6Kb or 14.4Kb time
slots, for a total bandwidth of 38.4Kb or 57.6Kb.
• 14.4Kb time slots are only available on GSM networks that
operate at 1,800Mhz.
• 900Mhz GSM networks are limited to 9.6Kb time slots.
• Therefore, HSCSD is limited to 38.4Kbps on 900Mhz GSM
networks.
• HSCSD can only achieve 57.6Kbps on 1,800Mhz GSM
networks.
35. HSCSD vs. GPRS
ASRao
• HSCSD has an advantage over GPRS in that HSCSD
supports guaranteed quality of service because of the
dedicated circuit-switched communications channel. This
makes HSCSD a better protocol for timing-sensitive
applications such as image or video transfer.
• GPRS has the advantage over HSCSD for most data
transfer because HSCSD, which is circuit-switched, is less
bandwidth efficient with expensive wireless links than
GPRS, which is packet-switched.
• For an application such as downloading, HSCSD may be
preferred, since circuit-switched data is usually given priority
over packet-switched data on a mobile network, and there
are few seconds when no data is being transferred.
37. ASRao
EDGE
• EDGE (Enhanced Data rate for GSM)
• Superset of GPRS.
• Data rate = 4 times GPRS.
• EDGE (Enhanced Data rate for GSM Evolution)
introduces 8-PSK in addition to GSM‟s standard
GMSK modulation.
– EDGE allows for 9 different air interface formats known
as multiple modulation and coding schems (MCS) with
varying degree of error control protection.
38. ASRao
EDGE (Enhanced Data Rates for Global Evolution)
–
–
–
–
–
–
–
–
–
–
EDGE is add-on to GPRS
Uses 8-PSK modulation in good conditions
Increase throughput by 3x (8-PSK – 3 bits/symbol vs GMSK 1 bit/symbol)
Offer data rates of 384kbps, theoretically up to 473.6kbps
Uses 9 Modulation coding schemes (MCS1-9)
MCS(1-4) uses GMSK, while MCS(5-9) uses 8PSK modulation.
Modulation Bit rate – 810kbps
Radio data rate per time slot – 69.2kbps
User data rate per time slot – 59.2kbps (MCS9)
User data rate (8 time slots) – 473.6kbps
•
New handsets / terminal equipment; additional hardware in the BTS, Core
network and the rest remains the same
•
EDGE access develops to connect to 3G core
40. ASRao
Evolved EDGE
• Data rate = 1Mbps
• Encoding technique – 32QAM and 16QAM.
• Requires simple network enhancements with
software update.
41. IS-95B
ASRao
IS-95B is the evolved version of IS-95A and is designated as 2.5G.
IS-95B is capable of providing for higher speed data services.
The following are the key aspects of the standard:
• Theoretical data rates of upto 115 kbps, with generally experienced
rates of 64 kbps
• Additional Walsh codes and PN sequence masks, which enable a
mobile user to be assigned up to eight forward or reverse code
channels simultaneously, thus enabling a higher data rate
• Code channels, which are transmitted at full data rates during a
data burst
• Convolution Channel coding
• Binary Phase Shift Keying (BPSK) as the Modulation technique
used
42. CDMA 1xRTT
ASRao
•
1x is an abbreviation of 1xRTT (1x Radio Transmission
Technology).1x refers to the no. of duplex radio channels.
•
Supports 33-35 simultaneous voice calls per 1.25MHz.
•
Encoding technique:
– BPSK for forward and reverse link.
•
Supports theoretical data rates of upto 307 kbps, with generally
experienced rates of 144 kbps
•
Quality and Erasure indicator bits (QIB and EIB) on the reverse power
control sub channel. These help in indicating to the BS about bad
frames or lost frames received at the mobile station, so that they can be
retransmitted.
•
Convolutional and Turbo coding techniques used
•
Modulation technique used is QPSK
•
Software and minimum hardware update.
48. 3G Wireless Networks
ASRao
• 3G uses a technique called CDMA, in which multiple users
use the same frequency and time.
• For more efficient use of resources, one wishes to allow more
users to transmit simultaneously.
•It has very high data transfer rate.
•Works equally well with both mobile and PC.
•Works at higher frequency than 1G and 2G.
•Multimedia services add high speed data transfer to mobile
devices, allowing new video, audio and other applications
(including Internet Services) through mobile phones.
• Improved voice quality.
• symmetrical and asymmetrical data transmission.
• Global roaming across networks.
• Improved security.
49. ASRao
Applications of 3G
• Mobile Television
• Video Calling
• wireless Internet
• Audio/Video On Demand
• e-Post Cards
• Secure Mobile Communications
• Video Conferencing
• Traffic & Travelling Information
50. ASRao
3 G W-CDMA (UMTS)
• UMTS - Universal Mobile Telecommunications System.
Also known as W-CDMA.
• W-CDMA uses the DS-CDMA and TDD channel access
method with a pair of 5 MHz channels.
• Requires new cell towers & frequency allocations.
• Frequency bands:
– Uplink 1885-2025 MHz (mobile-to-base )
– Downlink 2110-2200 MHz (base-to-mobile).
51. ASRao
• UMTS, or W-CDMA, assures backward compatibility with the 2G GSM, IS136, and PDC TDMA technologies, as well as all 2.5G TDMA technologies
Although W-CDMA is designed to provide backward compatibility and
interoperability for all GSM, IS-136/PDC, GPRS, and EDGE switching
equipment and applications, it is clear that the wider air interface bandwidth
of W-CDMA requires a complete change out of the RF equipment at each
base station.
•W-CDMA is for both wide area mobile cellular coverage (using FDD) as
well as indoor cordless type applications (using TDD).
• Designed for “Always-ON” packet-based wireless service so that
computers, mobiles and laptops etc. may all share the same wireless
network to be connected to the Internet anytime, anywhere.
• W-CDMA supports data rates upto 2.408 Mbps per user to allow high
quality data, multimedia and streaming video broadcasting services.
• Requires a minimum spectrum allocation of 5 MHz where a channel (5
MHz) will be able to support 100 to 350 simultaneous voice calls at once.
52. ASRao
•
UMTS, in the terrestrial component has 3 types of cells:
- macro cell
- micro cell
- pico cell (with a min. of 5MHz of BW by cell)
The macro cell has radius from 1Km to 35Km and they are destined to
offer rural cover and highways for vehicles or other objects that move at
high speed (114kbps-data transmission).
The micro cell has radius from 50m to 1Km. this offers services to fixed
users or who and they move slowly with high density of traffic (urban)
with 384 kbps speeds.
The pico cells has radius until 50m. Offer located cover and interior
cover(stationary), with speeds of the order of the 2Mbps.
53. ASRao
3G CDMA2000
• EVDO Rel 0 (Evolution-Data Optimized or
Evolution-Data only Release 0)
• Data rates:
– Forward link - 2.4Mbps.
– Reverse link - 153kbps.
• Encoding technique:
– Forward link – 16QAM.
– Reverse link - BPSK.
54. ASRao
• Channel
bandwidth of 1.25 MHz per radio channel
• The first CDMA interface cdma2000 1xRTT means that a single
1.25 MHz radio channel is used.
• cdma2000 1X supports an instantaneous data rate upto 307 kbps
with typical throughput rate of 144kbps.
• cdma2000 1xEV : Evolutionary advancement for CDMA
• cdma2000 1xEV-DO: CDMA carriers with the option of Data
Only radio channels
• cdma2000 1xEV-DV: carriers with Data and Voice and can offer
usable data rates up to 144 kbps with about twice as many voice
channels as IS-95B.
55. ASRao
The cdma2000 3xRTT standard uses three adjacent 1.25 MHz radio channels that
are used together to provide instantaneous packet data throughput speeds in
excess of 2 Mbps per user, although actual throughput depends upon cell loading,
vehicle speed, and propagation conditions.
56. ASRao
3G TD-SCDMA
The China Academy of Telecommunications Technology (CATT) and Siemens
Corporation jointly submitted an IMT-2000 3G standard proposal in 1998, based on
Time Division-Synchronous Code Division Multiple Access (TD-SCDMA).
TD-SCDMA relies on the existing core GSM infrastructure and allows a 3G network to
evolve through the addition of high data rate equipment at each GSM base station.
Up to 384 kbps of packet data is provided to data users in TD-SCDMA
A 5 millisecond frame is used in TD-SCDMA, and this frame is subdivided into seven
time slots which are flexibly assigned to either a single high data rate user or several
slower users.
By using TDD, different time slots within a single frame on a single carrier frequency
are used to provide both forward channel and reverse channel transmissions.
For the case of asynchronous traffic demand, such as when a user downloads a file,
the forward link will require more bandwidth than the reverse link, and thus more time
slots will be dedicated to providing forward link traffic than for providing reverse link
traffic.
57. ASRao
Frequency-division duplexing (FDD) is a method for establishing a full-duplex
communications link that uses two different radio frequencies for transmitter
and receiver operation. The transmit direction and receive direction
frequencies are separated by a defined frequency offset.
In the microwave realm, the primary advantages of this approach are:
•The full data capacity is always available in each direction because the send and
receive functions are separated;
•It offers very low latency since transmit and receive functions operate
simultaneously and continuously;
•It can be used in licensed and license-exempt bands;
•Most licensed bands worldwide are based on FDD; and
•Due to regulatory restrictions, FDD radios used in licensed bands are coordinated
and protected from interference, though not immune to it.
Disadvantages of the FDD approach to microwave communication are:
•Complex to install. Any given path requires the availability of a pair of frequencies; if
either frequency in the pair is unavailable, then it may not be possible to deploy the
system in that band;
•Radios require pre-configured channel pairs, making sparing complex;
•Any traffic allocation other than a 50:50 split between transmit and receive yields
inefficient use of one of the two paired frequencies, lowering spectral efficiency; and
•Collocation of multiple radios is difficult.
58. ASRao
Time-division duplexing (TDD) is a method for emulating full-duplex
communication over a half-duplex communication link. The transmitter and
receiver both use the same frequency but transmit and receive traffic is switched
in time.
Advantages of this approach as it applies to microwave communication are:
•It is more spectrum friendly, allowing the use of only a single frequency for operation
and dramatically increasing spectrum utilization, especially in license-exempt or
narrow-bandwidth frequency bands ;
•It allows for the variable allocation of throughput between the transmit and receive
directions, making it well suited to applications with asymmetric traffic requirements,
such as video surveillance, broadcast and Internet browsing;
•Radios can be tuned for operation anywhere in a band and can be used at either end
of the link. As a consequence, only a single spare is required to serve both ends of a
link.
Disadvantages of traditional TDD approach to microwave communications are:
•The switch from transmit to receive incurs a delay that causes traditional TDD systems
to have greater inherent latency than FDD systems;
•Traditional TDD approaches yield poor TDM performance due to latency;
•For symmetric traffic (50:50), TDD is less spectrally efficient than FDD, due to the
switching time between transmit and receive; and
•Multiple co-located radios may interfere with one another unless they are
synchronized.
60. ASRao
HSPA
• High Speed Packet Access is a collection of two
mobile telephony protocols HSDPA and HSUPA.
• High Speed Downlink Packet Access (HSDPA)
– Data rates for Forward link - 14.4Mbps.
– Encoding technique – QPSK and 16QAM
• High Speed Uplink Packet Access (HSUPA) or
EUL(Enhanced Uplink)
– Data rates for Reverse link - 5.76Mbps.
• Just a software update for most WCDMA networks.
61. ASRao
HSPA+
• Evolved High Speed Packet Access (HSPA+)
• Data rates:
– Forward link - 42Mbps.
– Reverse link - 22Mbps.
• Encoding technique 64QAM.
62. ASRao
EVDO Rev A
• EVDO Rev A (Revision A)
• Also called as EV-DV (Evolution Data/Voice)
• Data rates:
– Forward link - 3.1Mbps.
– Reverse link - 1.8Mbps.
• Encoding technique:
– Forward link – 16QAM.
– Reverse link - QPSK and 8PSK.
63. ASRao
EVDO Rev B
• Combine up to fifteen 1.25MHz carriers (20MHz) in
forward and/or reverse link. Carriers not physically
combined and not adjacent to each other.
• Data rate:
– Forward link = 3.1Mbps*15channels = 47Mbps.
– Reverse link = 1.8Mbps*15channels = 27Mbps.
• Encoding technique 64QAM. Uplink data rate
increases from 3.1Mbps to 4.9Mbps per channel.
Thus, Data rate:
– Forward link = 4.9Mbps*15channels = 74Mbps.
• Only software updation required.
64. Wireless Local Loop (WLL) and LMDs
ASRao
What is WLL?
- WLL is a system that connects subscribers to the local telephone
station wirelessly.
•Unlike mobile cellular telephone systems, fixed wireless communication systems
are able to take advantage of the very well-defined, time-invariant nature of the
propagation channel between the fixed transmitter and fixed receiver.
•Furthermore, modern fixed wireless systems are usually assigned microwave or
millimeter radio frequencies in the 28 GHz band and higher, which is greater than
ten times the carrier frequency of 3G terrestrial cellular telephone networks.
•At these higher frequencies, the wavelengths are extremely small, which in turn
allows very high gain directional antennas to be fabricated in small physical form
factors.
•At higher frequencies, too, more bandwidth can be easily used.
•Fixed wireless networks at very high microwave frequencies are only viable where
there are no obstructions, such as in a relatively flat suburban or rural setting.
65. ASRao
Connection Setup
UWLL
WANU
PSTN
Trunk
Switch
function
Transceiver
WLL
Controller
Wireless Access Network Unit(WANU)
– Interface between underlying
telephone network and wireless link
– consists of
• Base Station Transceivers (BTS)
• Radio Controller(RPCU)
• Access Manager(AM)
• Home Location Register(HLR)
WASU
Air
AM Interface
HLR
TWLL
Wireless Access Subscriber
Unit(WASU)
– located at the subscriber
– translates wireless link into a
traditional telephone
connection
67. ASRao
•These services include the concept of Local Multipoint Distribution
Service (LMDS), which provides broadband telecommunications access in
the local exchange.
•In 1998, 1300 MHz of unused spectrum in the 27 - 31 GHz band was
auctioned by the US government to support LMDS.
•The US LMDS band is 27.5 - 28.35 GHz, 29.1- 29.25 GHz, and 31.075 31.225 GHz.
•One of the most promising applications for LMDS is in a local exchange
carrier (LEC) network.
•Unfortunately, finding a line-of-sight path is not the only requirement for
maintaining a suitable fixed wireless connection for millimeter wave fixed
wireless links.
•Rain, snow, and hail can create large changes in the channel gain
between transmitter and receiver.
68. ASRao
Wireless LAN
• In 1997 the FCC allocated 300 MHz of unlicensed spectrum in the
Industrial Scientific and Medical (ISM) bands of 5.150 - 5.350 GHz and
5.725 - 5.825 GHz for the express purpose of supporting low-power
license-free spread spectrum data communication.
• This allocation is called
Infrastructure (UNII) band.
the
Unlicensed
National
Information
• By providing a license-free spectrum allocation, the FCC hoped to
encourage competitive development of spread spectrum knowledge,
spread spectrum equipment, and ownership of individual WLANs and other
low power short range devices that could facilitate private computer
communications in the workplace
• Popularity of the Internet combined with wide scale acceptance of
portable, laptop computers caused WLAN to become an important and
rapidly growing segment.
69. ASRao
• IEEE 802.11 was finally standardized in 1997 and provided interoperability
standards for WLAN manufactures using 11 Mcps DS-SS spreading and 2
Mbps user data rates (with fallback to 1 Mbps in noisy conditions).
• In 1999, the 802.11 High Rate standard (called IEEE 802.11b) was
approved, thereby providing new user data rate capabilities of 11 Mbps, 5.5
Mbps in addition to the original 2 Mbps and 1 Mbps user rates of IEEE
802.11, which were retained.
70. ASRao
• Both frequency hopping and direct sequence approaches were used in
the original IEEE 802.11 standard ( 2 Mbps user throughput), but as of late
2001 only direct sequence spread spectrum (DS-SS) modems had thus far
been standardized for high rate (11 Mbps) user data rates within IEEE
802.11.
• The IEEE 802.11a standard provides up to 54 Mbps throughput in the 5
GHz band.
• The DS-SS IEEE 802.11b standard has been named Wi-Fi
• IEEE 802.11g is developing Complimentary Code Keying Orthogonal
Frequency Division Multiplexing (CCK-OFDM) standards in both the
2.4 GHz (802.11b) and 5 GHz (802.11a) bands, and will support roaming
capabilities and dual-band use for public WLAN networks, while supporting
backward compatibility with 802.11b technology.
• The frequency-hopping spread spectrum (FH-SS) proponents of IEEE
802.11 have formed the HomeRF standard that supports frequency hopping
equipment.
71. ASRao
• In 2001, HomeRF developed a 10 Mbps FH-SS standard called HomeRF
2.0.
• It is worth nothing that both DS and FH types of WLANs must operate in
the same unlicensed bands that contain cordless phones, baby monitors,
Bluetooth devices, and other WLAN users.
• The channelization scheme used by the network installer becomes very
important for a high density WLAN installation, since neighboring access
points must be separated from one another in frequency to avoid
interference and significantly degraded performance.
• User throughput performance changes radically when access points or
clients are located near an interfering transmitter or when frequency
planning is not carefully conducted.
72. ASRao
• In mid 1990s, the High Performance Radio Local Area Network
(HIPER-LAN) standard was developed to provide a similar capability to
IEEE 802.11.
• HIPERLAN was intended to provide individual wireless LANs for
computer communications and used the 5.2 GHz and the 17.1 GHz
frequency bands.
• HIPERLAN provides asynchronous user data rates of between 1 to 20
Mbps, as well as time bounded messaging at rates of 64 kbps to 2.048
Mbps. HIPERLAN was designed to operate up to vehicle speeds of 35
km/hr, and typically provided 20 Mbps throughput at 50 m range.
• In 1997, Europe‟s ETSI established a standardization committee for
Broadband Radio Access Networks (BRANs).
• The goal of BRAN is to develop a family of broadband WLAN-type
protocols that allow user interoperability, covering both short range (e.g.,
WLAN) and long range (e.g., fixed wireless) networking.
73. ASRao
• HIPERLAN/2 has emerged as the next generation European WLAN
standard and will provide up to 54 Mbps of user data to a variety of networks,
including the ATM backbone, IP based networks, and the UMTS core.
• HIPERLAN/2 is anticipated to operate in the 5 GHz band.
• Meanwhile, IEEE 802.11a is emerging as North America‟s next generation
WLAN.
• Like HIPERLAN/2, IEEE 802.11a supports up to 54 Mbps user data rate for
integration into backbone ATM, UMTS, and IP networks and will operate in
the 5.15 - 5.35 GHz ISM band.
• Meanwhile, Japan‟s Multimedia Mobile Access Communication System
(MMAC) has been developing high data rate ( 25Mbps) WLAN standards for
use in the 5.15 5.35 GHz band.
74. ASRao
Pros & Cons of 802.11
Pros..
•Mobility
•Compatible with IP networks
•High speed data connectivity
•Unlicensed frequencies
•Highly secure
•Easy and fast installation
•Simplicity
•Scalability
•Very low cost
Cons..
•Shared-medium technology –
bandwidth limited by RF spectrum
•Limited number of non overlapping
channels
•Multipath effects indoor
•Interference in the 2.4 GHz and 5 GHz
bands
•Limited QoS
•Power control
•High overhead MAC protocol
76. ASRao
•802.11a was the first wireless networking standard, but 802.11b was the
first widely accepted one, followed by 802.11g and 802.11n.
•802.11b and 802.11g use the 2.4GHz ISM band, because of this choice of
frequency band, 802.11b and g equipment may occasionally suffer
interference from microwave ovens and cordless phones.
•Bluetooth devices, while operating in the same band, in theory do not
interfere with 802.11 b/g because they use a frequency hopping spread
spectrum signaling method (FHSS) while 802.11 b/g uses a DSSS.
•802.11 a uses the 5GHz UNII band, which offers 8 non-overlapping
channels rather than the 3 offered in the 2.4GHz ISM frequency band.
•802.11 a (5GHz) , this high carrier frequency brings a slight disadvantage:
the effective overall range of 802.11a is slightly less than that of 802.11 b/g;
802.11 a signals cannot penetrate as far as those for 802.11 b because
they absorbed more readily by walls and other solid objects in their path.
•802.11 b devices suffer interference from other products operating in the
2.4GHz band. Devices operating in the 2.4GHz range include: microwave
ovens, Bluetooth devices, baby monitors and cordless telephones.
•802.11g hardware is fully backwards compatible with 802.11 b hardware.
77. ASRao
•802.11 d is enhancement to 802.11 a and b that allows for global roaming.
•802.11 e enhancement to 802.11 that includes QoS.
•802.11 h enhancement to 802.11 a that resolves interference issues.
•802.11 i enhancement to 802.11 that offers additional security for WLAN
applications, which defines more robust encryption and authentication.
78. ASRao
Personal Area Network (PAN)
• RFID
- Very short range (10 meters) sensor technology used
to supplement bar-code reader type applications
• Infrared
- Short range, usually line-of-sight, non-RF technology,
- used mostly for wireless remote control, or wire
replacement applications
• Zig bee
-Very low power (and low speed) short distance (10m)
transmission standard
-Operates in 868-918 KHz, and 2.4GHz bands using
802.15.4 PAN standards
80. ASRao
Bluetooth @ Home
NO WIRES
Digital Camera
Computer
Scanner
Inkjet
Printer
xDSL
Access Point
Home Audio System
MP3
Player
PDA
Cell Phone
Cordless Phone
Base Station
81. ASRao
•Bluetooth operates in the 2.4 GHz ISM Band ( 2400 2483.5 MHz) and uses a
frequency hopping TDD scheme for each radio channel.
•Each Bluetooth radio channel has a 1 MHz bandwidth and hops at a rate of
approximately 1600 hops per second.
•Transmissions are performed in 625 microsecond slots with a single packet
transmitted over a single slot.
•For long data transmissions, particular users may occupy multiple slots using the
same transmission frequency, thus slowing the instantaneous hopping rate to below
1600 hops/second.
•The frequency hopping scheme of each Bluetooth user is determined from a cyclic
code of length 227 - 1, and each user has a channel symbol rate of 1 Mbps using
GFSK modulation.
•The standard has been designed to support operation in very high interference
levels and relies on a number of forward error control (FEC) coding and automatic
repeat request (ARQ) schemes to support a raw channel bit error rate (BER) of
about 10-3 .
•Different countries have allocated various channels for Bluetooth operation.
82. ASRao
•Audio, text, data, and even video is contemplated in the Bluetooth standard.
•The IEEE 802.15 standards committee has been formed to provide an international
forum for developing Bluetooth and other PANs that interconnect pocket PCs,
personal digital assistants (PDAs), cell phones, light projectors, and other appliances
Fig: Example of a Personal Area Network (PAN) as provided by the Bluetooth standard.
83. ASRao
Bluetooth system is based on a low cost, short range radio-link
which enables devices to communicate wirelessly via short range
radio link.
The Bluetooth is a universal radio interface on the Globally 2.4 GHz
frequency band facilitating wireless
communication of data and voice in stationary and mobile
environments.
This chip is tiny, low-power consuming and can be easily imbedded
in existing electronic devices.
These devices can form a quick ad-hoc
secure “piconet” and start communication.
Connections in the “piconets” can occur
even when mobile.
84. Strength of Bluetooth
Cheap Initial costs $ 20
ASRao
Future target $ 5
Tiny It is only 10.2 *14* 1.6 mm. Easy implementation.
low-power consumption - Bluetooth radio consumes less than 3% of the
power compared to that of modern mobile phone.
It works all over the world - Operates on ISM radio band, Unlicensed band.
Supports point-to-point & point-to-multi-point communication.
High Security
interference.
- It allows authentication & encryption - Protection against
High speed - Current speed up to 1 Mbps (723.2 Kbps)
85. ASRao
A collection of devices connected via Bluetooth technology in an
ad hoc fashion.
•
A piconet starts with two connected devices, and may grow to
eight connected devices.
•
All Bluetooth devices are peer units and have identical
implementations. However, when establishing a piconet, one
unit will act as a Master and the other(s) as slave(s) for the
duration of the piconet connection.
•
Spread-Spectrum frequency hopping
•
•
•
•
A device will use 79 individual randomly chosen frequencies within a
designated range, changing from one to another on a regular basis.
The designated range is from 2.402GHz to 2.480GHz, in steps of
1MHz.
The frequency hopping is done at a rate of 1600 times a second.
This allows more devices to use the limited time slice and secondly
reduces the chance of two transmitters being on the same frequency at
the same time.
86. ASRao
• Ad hoc client/server topology, 8 active & up to 256 parked devices
per piconet.
• 1 master per piconet “speaking” to slaves via TDM.
• Multiple piconets up to 13 per scatternet.
