EC8004WIRELESS NETWORKS
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
TEXT BOOKS:
1. Jochen Schiller, ”Mobile Communications”, Second Edition, Pearson Education 2012.(Unit I,II,III)
2. Vijay Garg, “Wireless Communications and networking”, First Edition, Elsevier 2007.(Unit IV,V)
REFERENCES:
1. Erik Dahlman, Stefan Parkvall, Johan Skold and Per Beming, "3G Evolution HSPA and LTE for Mobile
Broadband”, Second Edition, Academic Press, 2008.
2. Anurag Kumar, D.Manjunath, Joy kuri, “Wireless Networking”, First Edition, Elsevier 2011.
3. Simon Haykin , Michael Moher, David Koilpillai, “Modern Wireless Communications”,
First Edition, Pearson Education 2013
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
UNIT I WIRELESS LAN
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
INTRODUCTIONWireless means transmitting signals using radio waves as the medium instead of wires.
Wireless technologies are used for tasks as simple as switching off the television or as complex as supplying the sales force with information from an automated enterprise application while in the field.
Now cordless keyboards, mice and cellular phones have become part of our daily life.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Some of the inherent characteristics of wireless communications systems which
make it attractive for users, are given below −
Mobility − A wireless communications system allows users to access information
beyond their desk and conduct business from anywhere without having a wire
connectivity.
Reachability − Wireless communication systems enable people to be stay
connected and be reachable, regardless of the location they are operating from.
Simplicity − Wireless communication system are easy and fast to deploy in
comparison of cabled network. Initial setup cost could be a bit high but other
advantages overcome that high cost.EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Maintainability − In a wireless system, you do not have to spend too much cost
and time to maintain the network setup.
Roaming Services − Using a wireless network system, you can provide service any
where any time including train, buses, aero planes etc.
New Services − Wireless communication systems provide various smart services
like SMS and MMS.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WIRELESS NETWORK TOPOLOGIESThere are basically three ways to set up a wireless network
POINT-TO-POINT BRIDGEAs you know, a bridge is used to connect two networks. A point-to-pointbridge interconnects two buildings having different networks. For example, a wirelessLAN bridge can interface with an Ethernet network directly to a particular accesspoint.
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POINT-TO-MULTIPOINT BRIDGEThis topology is used to connect three or more LANs that may be located on different floors in abuilding or across buildings
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MESH OR AD HOC NETWORKThis network is an independent local area network that is not connected to a wired infrastructureand in which all stations are connected directly to one another
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WIRELESS TECHNOLOGIES
Wireless technologies can be classified in different ways depending on their range. Each wireless
technology is designed to serve a specific usage segment. The requirements for each usage segment
are based on a variety of variables, including Bandwidth needs, Distance needs and Power.
Wireless Wide Area Network (WWAN)
This network enables you to access the Internet via a wireless wide area network (WWAN) access
card and a PDA or laptop. These networks provide a very fast data speed compared with the data
rates of mobile telecommunications technology, and their range is also extensive. Cellular and mobile
networks based on CDMA and GSM are good examples of WWAN.
Wireless Personal Area Network (WPAN)
These networks are very similar to WWAN except their range is very limited.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WIRELESS LOCAL AREA NETWORK (WLAN)
This network enables you to access the Internet in localized hotspots via a wireless local area
network (WLAN) access card and a PDA or laptop.
It is a type of local area network that uses high-frequency radio waves rather than wires to
communicate between nodes.
These networks provide a very fast data speed compared with the data rates of mobile
telecommunications technology, and their range is very limited. Wi-Fi is the most widespread
and popular example of WLAN technology.
WIRELESS METROPOLITAN AREA NETWORK (WMAN)
This network enables you to access the Internet and multimedia streaming services via a
wireless region area network (WRAN).
These networks provide a very fast data speed compared with the data rates of mobile
telecommunication technology as well as other wireless network, and their range is also
extensive.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
ISSUES WITH WIRELESS NETWORKS
There are following three major issues with Wireless Networks.
Quality of Service (QoS): One of the primary concerns about wireless data delivery is that, unlike the
Internet through wired services, QoS is inadequate. Lost packets and atmospheric interference are recurring
problems of the wireless protocols.
WLANs typically offer lower quality than their wired counterparts. The main reasons for this are the
lower bandwidth due to limitations in radio transmission (e.g., only 1–10 Mbit/s user data rate instead of 100–
1,000 Mbit/s)
Security Risk: This is another major issue with a data transfer over a wireless network. Basic network
security mechanisms like the service set identifier (SSID) and Wireless Equivalency Privacy (WEP); these
measures may be adequate for residences and small businesses, but they are inadequate for the entities
that require stronger security.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Reachable Range: Normally, wireless network offers a range of about 100 meters or less. Range is
a function of antenna design and power. Now a days the range of wireless is extended to tens of
miles so this should not be an issue any more.
Proprietary solutions: Due to slow standardization procedures, many companies have come up
with proprietary solutions offering standardized functionality plus many enhanced features. At least
most components today adhere to the basic standards IEEE 802.11b or (newer) 802.11a
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Design goals have to be taken into account for WLANs to ensure their commercial success
Global operation: WLAN products should sell in all countries so, national and international frequency
regulations have to be considered.
Low power: Devices communicating via a WLAN are typically also wireless devices running on
battery power. The LAN design should take this into account and implement special power-saving
modes and power management functions.
License-free operation: LAN operators do not want to apply for a special license to be able to use the
product. The equipment must operate in a license-free band, such as the 2.4 GHz ISM band.
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Robust transmission technology: Compared to their wired counterparts, WLANs operate under difficult
conditions. If they use radio transmission, many other electrical devices can interfere with them (vacuum
cleaners, hairdryers, train engines etc.).
Easy to use: In contrast to huge and complex wireless WANs, wireless LANs are made for simple use. They
should not require complex management, but rather work on a plug-and-play basis.
Protection of investment: A lot of money has already been invested into wired LANs. The new WLANs should
protect this investment by being interoperable with the existing networks. This means that simple bridging
between the different LANs should be enough to interoperate, i.e., the wireless LANs should support the same
data types and services that standard LANs support.
Transparency for applications: Existing applications should continue to run over WLANs
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
IN FR A S T R UC T UR E A N D A D - H O C
N E T W O R KS
M a n y W L A N s of t o d a y n e e d a n i n fr a s tru c t u r e n et w ork . I nfr a str u ct ur e
n e t w ork s n ot o n l y pr o v i d e a c c e s s t o ot h er n e t w ork s , b ut a l s o i n c l u d e f or w ar d i n g
fu n c tio n s , m e d iu m a c c e s s c o n tro l e tc .
I n t h e s e i nfr a str u ct ure - b a s e d w ir e l e s s n etw ork s , c o m m u n i c ati o n ty p i c a l ly t a k e s
p l a c e o n l y b et w e e n th e w ir e l e s s n o d e s a n d t h e a c c e s s p o i nt , b u t n ot d ir e ctly
b e tw e e n th e wire le s s n o d e s .
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In fra s tru c tu re - b a s e d wire le s s n e tw o rks
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T h e a c c e s s p o in t d o e s n o t ju s t c o n tro l m e d iu m a c c e s s , b u t a ls o a c ts a s a b rid g e to o th e r w ire le s s o r w ire d
n e tw o rk s .
S e v e ra l w ire le s s n e tw o rk s m a y fo rm o n e lo g ic a l w ire le s s n e tw o rk , s o th e a c c e s s p o in ts to g e th e r w ith th e fixe d
n e tw o rk in b e tw e e n c a n c o n n e c t s e v e ra l w ire le s s n e tw o rk s to fo rm a la rg e r n e tw o rk b e y o n d a c tu a l ra d io
c o v e ra g e . D e s ig n o f in fra s tru c tu re - b a s e d w ire le s s n e tw o rk s is s im p le r.
T h is s tru c tu re is re m in is c e n t o f s w itc h e d E th e rn e t o r o th e r s ta r- b a s e d n e tw o rk s , w h e re a c e n tra l e le m e n t (e . g . ,
a s w itc h ) c o n tro ls n e tw o rk flo w.
T y p ic a l c e llu la r p h o n e n e tw o rks a re in fra s tru c tu re - b a s e d n e tw o rk s fo r a w id e a re a . A ls o s a te llite - b a s e d c e llu la r
p h o n e s h a v e a n in fra s tru c tu re – th e s a te llite s
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Ad-h o c w ire le s s n e tw o rk s , h o w e v e r, d o n o t n e e d a n y in fra s tru c tu re to w o rk . E a c h n o d e c a n c o m m u n ic a te
d ire c tly w ith o th e r n o d e s , s o n o a c c e s s p o in t c o n tro llin g m e d iu m a c c e s s is n e c e s s a ry.
N o d e s w ith in a n a d - h o c n e tw o rk c a n o n ly c o m m u n ic a te if th e y c a n re a c h e a c h o th e r p h y s ic a lly, i . e . , if th e y a re
w ith in e a c h o th e rs ra d io ra n g e o r if o th e r n o d e s c a n fo rw a rd th e m e s s a g e .
I n a d - h o c n e tw o rk s , th e c o m p le x ity o f e a c h n o d e is h ig h e r b e c a u s e e v e ry n o d e h a s to im p le m e n t m e d iu m
a c c e s s m e c h a n is m s
ad-hoc wireless networks
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E XA M PL E :
I E E E 8 0 2 . 1 1 a n d H ip e rL A N 2 a re ty p ic a lly in fra s tru c tu re - b a s e d n e tw o rk s , w h ic h a d d itio n a lly s u p p o rt
a d - h o c n e tw o rk in g . B lu e to o th is a typ ic a l w ire le s s a d - h o c n e tw o rk .
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
W L A N T E C H N O L O G I E S :
INFRARED
UHF(Narrow band)
SPREAD SPECTRUM
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1. Infrared Technology:
Infrared is an invisible band of radiation that exists at lower end of visible electromagnetic
spectrum.
There are two types of infrared WLAN solutions:
• Direct beam (or line-of-sight)
• Diffused beam (uses reflected rays)
Direct beam WLANs offer faster data rates while diffused beam technology achieves lower data
rates in 1-2 Mbps range.
The advantage of using this technology is that there are no government regulations on its use and
also it is immune to EM and RF interference.
The disadvantage is that it is a short range technology (30-50 ft radius under ideal conditions).Also,
it requires line-of-sight. The signal gets affected by solid objects like doors, walls, etc. The signal is
also affected by fog, dirt, ice, snow.
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2. UHF Narrowband technology:
The frequency range is 430 to 470 MHZ and rarely segments in 800 MHZ range.
The portion 430-450 MHZ is unlicensed while 450-470 MHZ band is licensed.
The term narrow band is used because RF signal is sent in a very narrow band width,
typically 12.5 KHz or 25 KHz.
There are two systems: Synthesized and Un-synthesized system uses crystal controlled
frequency operation. There can be frequency drift problem in crystal.
The synthesized uses single, standard crystal. Multiple frequencies are achieved using
dividing the crystal frequency and then multiplying it to desired channel frequency.
The advantage of this technology is that it has longest range and its low cost for large
sites.
The disadvantages of this include the need of license, no multivendor inter operability
and interference potential.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
3.Spread Spectrum Technology:
In this technique, the entire allotted bandwidth is shared instead of dividing itinto discrete private parts.
The spread spectrum spreads the transmission power over entire usable spectrum.Thus, though bandwidth efficiency decreases; reliability, integrity and securityincrease.
In commercial applications, spread spectrum techniques currently offer data ratesup to 2Mbps.
Two modulation schemes are used to encode spread spectrum signals : frequencyhopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS)
FHSS uses a narrowband carrier that changes frequency in a pattern known to bothtransmitter and receiver. To some other receiver, FHSS appears to be a short-duration impulse noise. Thus, the data security increases.
Similarly, DSSS generates redundant bit pattern for every bit to be transmitted,known as spreading code, known only to transmitter and receiver. To some otherreceiver, DSSS appears as low-power, wideband noise and is rejected.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
802.11 Wi-Fi Wireless LAN Media Access Control and Physical Layer specification. 802.11a,b,g,etc.are amendments to the original 802.11 standard. Products that implement 802.11standards must pass tests and are referred to as "Wi-Fi certified."
IEEE 802.11
Additional features of the WLAN should include the support of power
management to save battery power, the handling of hidden nodes, and the
ability to operate worldwide.
The 2.4 GHz ISM band, which is available in most countries around the world,
was chosen for the original standard.
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IEEE 802.11:
• System architecture
• Protocol architecture
• Physical layer
• MAC layer
• 802.11b
• 802.11a
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Station (STA)
• terminal with access mechanisms to the wireless medium and radio contact to the access point
Basic Service Set (BSS)
• group of stations using the same radio frequency
Access Point
• station integrated into the wireless LAN and the distribution system
Portal
• bridge to other (wired) networks
Distribution System
• interconnection network to form one logical network (EES: Extended Service Set) based on several BSS
Distribution System
Portal
802.x LAN
Access
Point
802.11 LAN
BSS2
802.11 LAN
BSS1
Access
Point
STA1
STA2 STA3
ESS
System architectureWireless networks can exhibit two different basic system architectures infrastructure-based or ad-hoc.
Infrastructure-based
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Extended Service Set (ESS) and has its own identifier, the ESSID. The ESSID is the ‘name’ of a network and
is used to separate different networks. Without knowing the ESSID (and assuming no hacking) it should not be
possible to participate in the WLAN.
Stations can select an AP and associate with it. The APs support roaming (i.e., changing access points), the
distribution system handles data transfer between the different APs. APs provide synchronization within a BSS.
In addition to infrastructure-based networks, IEEE 802.11 allows the building of ad-hoc networks
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802.11 LAN
IBSS2
802.11 LAN
IBSS1
STA4
STA5
STA2
STA3
STA1
ARCHITECTURE OF AN AD-HOC NETWORK
Direct communication within a limited range• Station (STA): terminal with access mechanisms to the
wireless medium
• Independent Basic Service Set (IBSS): group of stationsusing the same radio frequency
In this case, an IBSS comprises a group of stations using the same radio frequency.
This means for example that STA3 can communicate directly with STA2 but not with STA5.
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PROTOCOL ARCHITECTUREApplications should not notice any difference apart from the lower bandwidth
and perhaps higher access time from the wireless LAN. The WLAN behaves like a slow wired LAN.The higher layers (application, TCP, IP) look the same for wireless nodes as for wirednodes.
An IEEE 802.11 wireless LAN
connected to a switched IEEE 802.3
ethernet via a bridge.
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The IEEE 802.11 standard only covers the physical layer PHY and medium access layer MAC like the other
802.x LANs do.
The physical layer is subdivided into the physical layer convergence protocol (PLCP) and the
physical medium dependent sublayer PMD
The basic tasks of the MAC layer comprise medium access, fragmentation of user data, and encryption.
PLCP sublayer provides a carrier sense signal, called clear channel assessment (CCA), and provides a
common PHY service access point (SAP) independent of the transmission technology. Finally, the PMD
sublayer handles modulation and encoding/decoding of signals.
The main tasks of the PHY management include channel
tuning and PHY MIB maintenance.
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PHYSICAL LAYER:
IEEE 802.11 supports three different physical layers: One layer based on infra redTwo layers based on radio transmission
The PHY layer offers a service access point (SAP) with 1 or 2 Mbit/s transfer rate to the MAC layer.
THREE VERSIONS OF PHY LAYER:
1. Frequency Hopping Spread Spectrum
2. Direct Sequence Spread Spectrum
3. Infra Red
} Radio Transmission
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Frequency Hopping Spread Spectrum
Frequency hopping spread spectrum (FHSS) is a spread spectrum technique which allows for the
coexistence of multiple networks in the same area by separating different networks using different
hopping sequences.
The original standard defines 79 hopping channels for North America and Europe, and 23 hopping
channels for Japan.
The selection of a particular channel is achieved by using a pseudo-random hopping pattern.
The standard specifies Gaussian shaped FSK (frequency shift keying), GFSK, as modulation for the FHSS
PHY. For 1 Mbit/s a 2 level GFSK is used (i.e., 1 bit is mapped to one frequency), a 4 level GFSK for 2 Mbit/s
(i.e., 2 bits are mapped to one frequency).
While sending and receiving at 1 Mbit/s is mandatory for all devices, operation at 2 Mbit/s is optional.
This facilitated the production of low-cost devices for the lower rate only and more powerful devices for
both transmission rates in the early days of 802.11.
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Format of an IEEE 802.11 PHY frame using FHSS
Synchronization: This pattern is used for synchronization of potential receivers and signal detection by the CCA.
Start frame delimiter (SFD): The following 16 bits indicate the start of the frame and provide frame synchronization.
PLCP_PDU length word (PLW): This first field of the PLCP header indicates the length of the payload in bytes
PLCP signalling field (PSF): This 4 bit field indicates the data rate of the payload following.
Header error check (HEC): Finally, the PLCP header is protected by a 16 bit checksum
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Direct sequence spread spectrum
Direct sequence spread spectrum (DSSS) is the alternative spread spectrum method separating
by code and not by frequency.
In the case of IEEE 802.11 DSSS, spreading is achieved using the 11-chip Barker sequence (+1, –1,
+1, +1, –1, +1, +1, +1, –1, –1, –1). The key characteristics of this method are its robustness against
interference and its insensitivity to multipath propagation.
However, the implementation is more complex compared to FHSS.
The system uses differential binary phase shift keying (DBPSK) for 1 Mbit/s transmission and
differential quadrature phase shift keying (DQPSK) for 2 Mbit/s as modulation schemes.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Format of an IEEE 802.11 PHY frame using DSSS
Synchronization: The first 128 bits are not only used for synchronization, but also gain setting, energy detection
(for the CCA), and frequency offset compensation.
Start frame delimiter (SFD): This 16 bit field is used for synchronization at the beginning of a frame
Signal: Only two values have been defined for this field to indicate the data rate of the payload. The value 0x0A
indicates 1 Mbit/s (and thus DBPSK), 0x14 indicates 2 Mbit/s (and thus DQPSK).
Service: This field is reserved for future use
Length: 16 bits are used in this case for length indication of the payload in microseconds.
Header error check (HEC): Signal, service, and length fields are protected by this checksum.EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Infra Red
The PHY layer, which is based on infra red (IR) transmission, uses near visible light at 850–950 nm.
The standard does not require a line-of-sight between sender and receiver, but should also work with
diffuse light. This allows for point-to-multipoint communication.
The maximum range is about 10 m if no sunlight or heat sources interfere with the transmission.
Typically, such a network will only work in buildings, e.g., classrooms, meeting rooms etc.
Today, no products are available that offer infra red communication based on 802.11.
Proprietary products offer, e.g., up to 4 Mbit/s using diffuse infra red light. Alternatively, directed infra red
communication based on IrDA can be used (IrDA, 2002).
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Medium access control layer
It has to control medium access, but it can also offer support for roaming, authentication, and power
conservation.
The basic services provided by the MAC layer are the mandatory asynchronous data service and an optional
time-bounded service.
While 802.11 only offers the asynchronous service in ad-hoc network mode, both service types can be
offered using an infrastructure-based network together with the access point coordinating medium access.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
The following three basic access mechanisms have been defined for IEEE 802.11:
1. The mandatory basic method based on a version of CSMA/CA
2. An optional method avoiding the hidden terminal problem
3. A contention-free polling method for time-bounded service.
DCF only offers asynchronous service, while PCF offers both asynchronous and time-bounded.
The MAC mechanisms are also called distributed foundation wireless medium access control
(DFWMAC).
} distributed coordination function (DCF)
point coordination function (PCF).
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Medium access and inter-frame spacing
Short inter-frame spacing (SIFS): The shortest waiting time for medium access (so the highest priority)
is defined for short control messages, such as acknowledgements of data packets or polling responses.
PCF inter-frame spacing (PIFS): A waiting time between DIFS and SIFS (and thus a medium priority) is
used for a time-bounded service.
DCF inter-frame spacing (DIFS): This parameter denotes the longest waiting time and has the lowest
priority for medium access. This waiting time is used for asynchronous data service within a contention
periodEC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
1.Basic DFWMAC-DCF using CSMA/CA
• Station ready to send starts sensing the medium (carrier sense based on CCA, clear channelassessment)
• If the medium is free for the duration of an inter-frame space (IFS), the station can startsending (IFS depends on service type)
• If the medium is busy, the station has to wait for a free IFS, then the station mustadditionally wait a random back-off time (collision avoidance, multiple of slot-time) CW = 7,15, 31, 63, 127
• If another station occupies the medium during the back-off time of the station, the back-offtimer stops (fairness)
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802.11 - competing stations - simple version (no RTS/CTS)
t
busy
boe
station1
station2
station3
station4
station5
packet arrival at MAC
DIFS
boe
boe
boe
busy
elapsed backoff time
borresidual backoff time
busy medium not idle (frame, ack etc.)
bor
bor
DIFS
boe
boe
boe bor
DIFS
busy
busy
DIFS
boe busy
boe
boe
bor
bor
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802.11 - CSMA/CA access method IISending unicast packets
Station has to wait for DIFS before sending data
Receivers acknowledge at once (after waiting for SIFS) if the packet was received correctly (CRC)
Automatic retransmission of data packets in case of transmission errors
t
SIFS
DIFS
data
ACK
waiting time
other
stations
receiver
senderdata
DIFS
contention
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2. 802.11 – DFWMAC (Distributed Foundation Wireless MAC)
Sending unicast packets• Station can send RTS with reservation parameter after waiting for DIFS (reservation determines
amount of time the data packet needs the medium) • Acknowledgement via CTS after SIFS by receiver (if ready to receive)• Sender can now send data at once, acknowledgement via ACK• Other stations store medium reservations distributed via RTS and CTS
t
SIFS
DIFS
data
ACK
defer access
other
stations
receiver
senderdata
DIFS
contention
RTS
CTSSIFS SIFS
NAV (RTS)NAV (CTS)
NAV – Network Allocation Vector
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
The RTS packet includes the receiver of the data transmission to come and the duration of the whole
data transmission.
This duration specifies the time interval necessary to transmit the whole data frame and the
acknowledgement related to it.
Every node receiving this RTS now has to set its net allocation vector (NAV) in accordance with the duration
field.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Fragmentation
t
SIFS
DIFS
data
ACK1
other
stations
receiver
senderfrag1
DIFS
contention
RTS
CTSSIFS SIFS
NAV (RTS)NAV (CTS)
NAV (frag1)NAV (ACK1)
SIFSACK2
frag2
SIFS
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3. DFWMAC-PCF with polling
The two access mechanisms presented so far cannot guarantee a maximum access delay or minimum
transmission bandwidth.
To provide a time-bounded service, the standard specifies a point coordination function (PCF) on top of
the standard DCF mechanisms.
Using PCF requires an access point that controls medium access and polls the single nodes. Ad-hoc
networks cannot use this function.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
DFWMAC-PCF
PIFS
stations‘
NAV
wireless
stations
point
coordinator
D1
U1
SIFS
NAV
SIFS
D2
U2
SIFS
SIFS
SuperFramet0
medium busy
t1
contention free period
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DFWMAC-PCF II (cont.)
t
stations‘
NAV
wireless
stations
point
coordinator
D3
NAV
PIFSD4
U4
SIFS
SIFSCFend
contention
period
contention free period
t2 t3 t4
CFend - contention free period end
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
MAC frames
Frame control: The first 2 bytes serve several purposes. They contain several sub-fields as explained after the
MAC frame.
Duration/ID: The duration field contains the value indicating the period of time in which the medium is occupied
(in μs).
Address 1 to 4: The four address fields contain standard IEEE 802 MAC addresses (48 bit each), as they are
known from other 802.x LANs.
Sequence control: Due to the acknowledgement mechanism frames may be duplicated. Therefore a sequence
number is used to filter duplicates.
Data: The MAC frame may contain arbitrary data (max. 2,312 byte), which is transferred transparently from a
sender to the receiver(s).EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Checksum (CRC): Finally, a 32 bit checksum is used to protect the frame as it is common practice in all 802.x
networks.
Protocol version: This 2 bit field indicates the current protocol version and is fixed to 0 by now.
Type: The type field determines the function of a frame: management (=00), control (=01), or data (=10). The
value 11 is reserved
Subtype: Example subtypes for management frames are: 0000 for association request, 1000 for beacon.
More fragments: This field is set to 1 in all data or management frames that have another fragment of the
current.
Retry: If the current frame is a retransmission of an earlier frame, this bit is set to 1. With the help of this bit it may
be simpler for receivers to eliminate duplicate frames.
Power management: This field indicates the mode of a station after successful transmission of a frame. Set to 1
the field indicates that the station goes into power-save mode. If the field is set to 0, the station stays active.
More data: In general, this field is used to indicate a receiver that a sender has more data to send than the
current frame.
Wired equivalent privacy (WEP): This field indicates that the standard security mechanism of 802.11 is applied.
Order: If this bit is set to 1 the received frames must be processed in strict order.EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
802.11 - MAC management• Synchronization
• try to find a WLAN, try to stay within a WLAN• timer etc.
• Power management• sleep-mode without missing a message• periodic sleep, frame buffering, traffic measurements
• Association/Reassociation• integration into a LAN• roaming, i.e. change networks by changing access points • scanning, i.e. active search for a network
• MIB - Management Information Base• managing, read, write (SNMP)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Synchronization using a Beacon (infrastructure)
beacon interval
tmedium
access
point
busy
B
busy busy busy
B B B
value of the timestamp B beacon frame (BSSID, Timestamp)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Synchronization using a Beacon (ad-hoc)
tmedium
station1
busy
B1
beacon interval
busy busy busy
B1
value of the timestamp B beacon frame
station2
B2 B2
random delay
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Power management• Idea: switch the transceiver off if not needed
• States of a station: sleep and awake• Timing Synchronization Function (TSF)
• stations wake up at the same time
• Infrastructure• Traffic Indication Map (TIM)
• list of unicast receivers transmitted by AP• Delivery Traffic Indication Map (DTIM)
• list of broadcast/multicast receivers transmitted by AP
• Ad-hoc• Ad-hoc Traffic Indication Map (ATIM)
• announcement of receivers by stations buffering frames• more complicated - no central AP• collision of ATIMs possible (scalability?)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Power saving with wake-up patterns (infrastructure)
TIM interval
t
medium
access
pointbusy
D
busy busy busy
T T D
T TIM D DTIM
DTIM interval
BB
B broadcast/multicast
station
awake
p PS poll
p
d
d
ddata transmission
to/from the station
PS – Power SavingTraffic Indication Map (TIM)
Delivery Traffic Indication Map (DTIM)-for multicast data transmission
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Power saving with wake-up patterns (ad-hoc)
awake
A transmit ATIM D transmit data
t
station1
B1 B1
B beacon frame
station2
B2 B2
random delay
A
a
D
d
ATIM
window beacon interval
a acknowledge ATIM d acknowledge data
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Scanning• Scanning involves the active search for a BSS. IEEE 802.11 differentiates
between passive and active scanning.
• Passive scanning - listening into the medium to find other networks, i.e.,receiving the beacon of another network issued by access point.
• Active scanning - sending a probe on each channel and waiting for aresponse. Beacon and probe responses contain the information necessaryto join the new BSS.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Active Scanning
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
802.11b
Some companies offered proprietary solutions with 11 Mbit/s.
This standard describes a new PHY layer and is by far the most successful version of IEEE 802.11 available
today.
All the MAC schemes, management procedures etc. are still same.
Depending on the current interference and the distance between sender and receiver 802.11b systems offer
11, 5.5, 2, or 1 Mbit/s. Maximum user data rate is approx. 6 Mbit/s. The lower data rates 1 and 2 Mbit/s use
the 11-chip Barker sequence
The standard defines several packet formats for the physical layer. The mandatory format interoperates with
the original versions of 802.11. The optional versions provide a more efficient data transfer
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
long PLCP PPDU:
One difference is the rate encoded in the signal field this is encoded in multiples of 100 kbit/s.
0x0A represents 1 Mbit/s
0x14 is used for 2 Mbit/s
0x37 for 5.5 Mbit/s
0x6E for 11 Mbit/s.
Short PLCP PPDU:
The short synchronization field consists of 56 scrambled zeros instead of scrambled ones.
The length of the overhead is only half for the short frames (96 μs instead of 192 μs).
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Channel plan for IEEE 802.11b
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
IEEE 802.11b non-overlapping channel selection
The spacing between the center frequencies should be at least 25 MHz
This results in the channels 1, 6, and 11 for the US/Canada or 1, 7, 13 for Europe, respectively.
It may be the case that, e.g., travellers from the US cannot use the additional channels (12 and 13) in
Europe as their hardware is limited to 11 channels.EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
802.11a
• Initially aimed at the US 5 GHz U-NII (Unlicensed National Information Infrastructure) bands IEEE 802.11a
offers up to 54 Mbit/s using OFDM.
• ETSI (Europe) defines different frequency bands for Europe: 5.15–5.35 GHz and 5.47–5.725 GHz
• It requires two additional mechanisms for operation: dynamic frequency selection (DFS) and transmit power
control (TPC)
• Japan allows operation in the frequency range 5.15–5.25 GHz and requires carrier sensing every 4 ms to
minimize interference.
• To be able to offer data rates up to 54 Mbit/s IEEE 802.11a uses many different technologies.
• The system uses 52 subcarriers (48 data + 4 pilot) that are modulated using BPSK, QPSK, 16-QAM, or 64-
QAM. To mitigate transmission errors, FEC is applied using coding rates of 1/2, 2/3, or 3/4.
• To offer a data rate of 12 Mbit/s, 96 bits are coded into one OFDM symbol. These 96 bits are distributed
over 48 subcarriers and 2 bits are modulated per sub-carrier using QPSK
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WLAN: IEEE 802.11 – developments
• 802.11c: Bridge Support
• Definition of MAC procedures to support bridges as extension to 802.1D
• 802.11d: Regulatory Domain Update
• Support of additional regulations related to channel selection, hopping sequences
• 802.11e: MAC Enhancements – QoS
• Enhance the current 802.11 MAC to expand support for applications with Quality of Servicerequirements, and in the capabilities and efficiency of the protocol
• Definition of a data flow (“connection”) with parameters like rate, burst, period…
• Additional energy saving mechanisms and more efficient retransmission
• 802.11f: Inter-Access Point Protocol
• Establish an Inter-Access Point Protocol for data exchange via the distribution system
• 802.11g: Data Rates > 20 Mbit/s at 2.4 GHz; 54 Mbit/s, OFDM
• Successful successor of 802.11b, performance loss during mixed operation with 11b
• 802.11h: Spectrum Managed 802.11a
• Extension for operation of 802.11a in Europe by mechanisms like channel measurement for dynamicchannel selection (DFS, Dynamic Frequency Selection) and power control (TPC, Transmit Power Control)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WLAN: IEEE 802.11– developments• 802.11i: Enhanced Security Mechanisms
• Enhance the current 802.11 MAC to provide improvements in security.
• TKIP enhances the insecure WEP, but remains compatible to older WEP systems
• AES provides a secure encryption method and is based on new hardware
• 802.11j: Extensions for operations in Japan• Changes of 802.11a for operation at 5GHz in Japan using only half the channel width at larger range
• 802.11k: Methods for channel measurements• Devices and access points should be able to estimate channel quality in order to be able to choose a better access
point of channel
• 802.11m: Updates of the 802.11 standards
• 802.11n: Higher data rates above 100Mbit/s• Changes of PHY and MAC with the goal of 100Mbit/s at MAC SAP
• MIMO antennas (Multiple Input Multiple Output), up to 600Mbit/s are currently feasible
• However, still a large overhead due to protocol headers and inefficient mechanisms
• 802.11p: Inter car communications• Communication between cars/road side and cars/cars
• Planned for relative speeds of min. 200km/h and ranges over 1000m
• Usage of 5.850-5.925GHz band in North America
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WLAN: IEEE 802.11– future developments
• 802.11r: Faster Handover between BSS
• Secure, fast handover of a station from one AP to another within an ESS
• Current mechanisms (even newer standards like 802.11i) plus incompatible devices from different vendors are massive problems for the use of, e.g., VoIP in WLANs
• Handover should be feasible within 50ms in order to support multimedia applications efficiently
• 802.11s: Mesh Networking
• Design of a self-configuring Wireless Distribution System (WDS) based on 802.11
• Support of point-to-point and broadcast communication across several hops
• 802.11t: Performance evaluation of 802.11 networks
• Standardization of performance measurement schemes
• 802.11u: Interworking with additional external networks
• 802.11v: Network management
• Extensions of current management functions, channel measurements
• Definition of a unified interface
• 802.11w: Securing of network control
• Classical standards like 802.11, but also 802.11i protect only data frames, not the control frames. Thus, this standard should extend 802.11i in a way that, e.g., no control frames can be forged.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
HIPERLAN(High Performance Local Area Network)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WLAN allowing for node mobility and supporting ad-hoc and infrastructure-based topologies
Names have changed and the former HIPERLANs 2, 3, and 4 are now called HiperLAN2, HIPERACCESS,
and HIPERLINK.
The current focus is on HiperLAN2, a standard that comprises many elements from ETSI’s BRAN
(broadband radio access networks) and wireless ATM activities.
Neither wireless ATM nor HIPERLAN 1 were a commercial success.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Historical: HIPERLAN 1
Wireless LAN supporting priorities and packet life time for data transfer at 23.5 Mbit/s, including forwarding
mechanisms, topology discovery, user data encryption, network identification and power conservation
mechanisms. HIPERLAN 1 should operate at 5.1–5.3 GHz with a range of 50 m in buildings at 1 W transmit
power.
The service offered by a HIPERLAN 1 is compatible with the standard MAC services known from IEEE 802.x
LANs.
For power conservation, a node may set up a specific wake-up pattern. This pattern determines at what time
the node is ready to receive, so that at other times, the node can turn off its receiver and save energy. These
nodes are called p-savers and need so-called p-supporters that contain information about the wake-up
patterns of all the p-savers they are responsible for. A p-supporter only forwards data to a p-saver at the
moment the p-saver is awake.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Elimination-yield non-preemptive priority multiple access (EY-NPMA)
It is a heart of the channel access providing priorities and different access schemes. EY-NPMA divides
the medium access of different competing nodes into three phases:
Prioritization: Determine the highest priority of a data packet ready to be sent by competing nodes.
Contention: Eliminate all but one of the contenders, if more than one sender has the highest current priority.
Transmission: Finally, transmit the packet of the remaining node.
prioritization contention transmissiontransmission
synchro
niz
atio
n
prio
rity
dete
ctio
n
prio
rity
assert
ion
t
user
data
elim
ina
tio
n b
urs
t
elim
ina
tio
n s
urv
iva
l
ve
rifica
tio
n
yie
ld lis
tenin
g
IYSIPS IPA IES IESV
The contention phase
is further subdivided
into an elimination
phase and a yield
phase.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
EY-NPMA (Elimination Yield Non-preemptive Priority Multiple Access)
3 phases: priority resolution, contention resolution, transmission
Finding the highest priority
• Every priority corresponds to a time-slot to send in the first phase, the higher the priority the earlier the
time-slot to send
• Higher priorities can not be preempted
• If an earlier time-slot for a higher priority remains empty, stations with the next lower priority might send
• After this first phase the highest current priority has been determined
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Several terminals can now have the same priority and wish to send
CONTENTION PHASE
Elimination Burst: all remaining terminals send a burst to eliminate contenders
(11111010100010011100000110010110, high bit- rate)
Elimination Survival Verification: contenders now sense the channel, if the channel is free they can continue,
otherwise they have been eliminated
Yield Listening: contenders again listen in slots with a nonzero probability, if the terminal senses its slot idle it is free to
transmit at the end of the contention
DATA TRANSMISSION
The winner can now send its data (however, a small chance of collision remains).if the channel was idle for a longer
time a terminal can send at once without using EY-NPMA
synchronization using the last data transmission
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Wireless ATM
(Wireless Asynchronous Transfer Mode)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WATM: sometimes also called wireless, mobile ATM, wmATM
IEEE WLANs originate from the data communication community, many WATM aspects come
from the telecommunication industry
Motivation for WATM:
1. The need for seamless integration of wireless terminals into an ATM network.
2. ATM networks scale well from LANs to WANs – and mobility is needed in local and wide area
applications.
3. For ATM to be successful, it must offer a wireless extension.
4. WATM could offer QoS for adequate support of multi-media data streams.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Wireless ATM working group:
ATM Forum formed the Wireless ATM Working Group in 1996, which aimed to develop a set of specifications that
extends the use of ATM technology to wireless networks.
The following more general extensions of the ATM system also need to be considered for a mobile ATM:
Location management: Similar to other cellular networks, WATM networks must be able to locate a wireless terminal
or a mobile user.
Mobile routing: Even if the location of a terminal is known to the system, it still has to route the traffic through the
network to the access point currently responsible for the wireless terminal. Each time a user moves to a new access
point, the system must reroute traffic.
Handover signalling: The network must provide mechanisms which search for new access points
QoS and traffic control: In contrast to wireless networks offering only best effort traffic, and to cellular networks
offering only a few different types of traffic, WATM should be able to offer many QoS parameters. To maintain these
parameters, all actions such as rerouting, handover etc. have to be controlled.
Network management: All extensions of protocols or other mechanisms also require an extension of the
management functions to control the networkEC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WATM services:
1. Office environments
2. Universities, schools, training centre
3. Industry
4. Hospitals
5. Home
6. Networked vehicles
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Generic reference model
WATM
terminal
adapter
MATM
termi-
nal
RASEMAS
-E
EMAS
-N
ATM-
Switch
fixed
end
system
radio segment fixed network segment
A mobile ATM (MATM) terminal uses a WATM terminal adapter to gain wireless access to a WATM RAS
(Radio Access System).
MATM terminals could be represented by, e.g., laptops using an ATM adapter for wired access plus
software for mobility.
The WATM terminal adapter enables wireless access, i.e., it includes the transceiver etc., but it does not
support mobility.
The RAS with the radio transceivers is connected to a mobility enhanced ATM switch (EMAS-E), which in
turn connects to the ATM network with mobility aware switches (EMAS-N)
Finally, a wired, non-mobility aware ATM end system may be the communication partner in this example.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
HANDOVER:
The main problem for WATM during the handover is rerouting all connections and maintaining connection quality.
Different requirements have been set up for handover
Handover of multiple connections:
Handover in WATM must support more than one connection.
This results in the rerouting of every connection after handover.
However, resource availability may not allow rerouting of all connections or forces QoS degradation.
The terminal may then decide to accept a lower quality or to drop single connections.
Handover of point-to-multi-point connections:
WATM handover should also support these types of connection.
However, due to the complexity of the scheme, some restrictions might be necessary.
QoS support:
Handover should aim to preserve the QoS of all connections during handover.
However, due to limited resources, this is not always possible.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
LOCATION MANAGEMENT
As for all networks supporting mobility, special functions are required for looking up the current position of a mobile
terminal, for providing the moving terminal with a permanent address, and for ensuring security features such as
privacy, authentication, or authorization.
MOBILE QUALITY OF SERVICE
Wired QoS: The infrastructure network needed for WATM has the same QoS properties as any wired ATM network.
Wireless QoS: The QoS properties of the wireless part of a WATM network differ from those of the wired part.
Channel reservation and multiplexing mechanisms at the air interface strongly influence cell delay variation.
Handover QoS: A new set of QoS parameters are introduced by handover. For example, handover blocking due to limited
resources at target access points, cell loss during handover
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Hard handover QoS: While the QoS with the current RAS may be guaranteed due to the current
availability of resources, no QoS guarantees are given after the handover.
Soft handover QoS: Even for the current wireless segment, only statistical QoS guarantees can be
given, and the applications also have to adapt after the handover.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
BRANBroadband Radio Access Networks
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
The main motivation behind BRAN is the deregulation and privatization of the telecommunication
sector in Europe.
Many new providers experience problems getting access to customers because the telephone
infrastructure belongs to a few big companies.
One possible technology to provide network access for customers is radio. The advantages of radio
access are high flexibility and quick installation.
BRAN standardization has a rather large scope including indoor and campus mobility, transfer
rates of 25–155 Mbit/s, and a transmission range of 50 m–5 km.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
BROADBAND NETWORK TYPES
HIPERLAN/2• short range (< 200 m), indoor/campus, 25 Mbit/s user data rate
• access to telecommunication systems, multimedia applications, mobility (<10 m/s)
HIPERACCESS• wider range (< 5 km), outdoor, 25 Mbit/s user data rate
• fixed radio links to customers (“last mile”), alternative to xDSL or cable modem, quick installation
• Several (proprietary) products exist with 155 Mbit/s plus QoS
HIPERLINK – currently no activities• intermediate link, 155 Mbit/s
• connection of HIPERLAN access points or connection between HIPERACCESS nodes
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
HiperLAN2
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
This wireless network works at 5 GHz and offers data rates of up to 54 Mbit/s including QoS support and
enhanced security features.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Reference model and configurations
2
3
1
AP
APT APC Core
Network
(Ethernet,
Firewire,
ATM,
UMTS)APT
APT
APC
AP
MT4
MT3
MT2
MT1
Sector handover (Inter sector): If sector antennas are used for an AP, which is optional in the standard, the AP
shall support sector handover. This type of handover is handled inside the DLC layer so is not visible outside the
AP
Radio handover (Inter-APT/Intra-AP): As this handover type, too, is handled within the AP, no external interaction
is needed. In the example of Figure the terminal MT3, moves from one APT to another of the same AP. All context
data for the connections are already in the AP
Network handover (Inter-AP/Intra-network): This is the most complex situation: MT2 moves from one AP to
another. In this case, the core network and higher layers are also involved. This handover might be supported by
the core network
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Centralized vs. direct mode
MT1
AP/CCAP
MT2
data
control control
MT1 MT2data
control
Centralized Direct
MT1 MT2 +CCdata
control
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
HiperLAN2 protocol stackHigher layers
Convergence layer
Data link control -
basic data
transport functionScope of
HiperLAN2
standards
DLC control
SAP
DLC user
SAP
Radio link control sublayer
Physical layer
Radio
resource
control
Assoc.
control
DLC
conn.
control
Error
controlRadio link control
Medium access control
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Physical layer reference configuration
scrambling FEC coding interleaving
mapping OFDMPHY bursts
(PPDU)
PDU train from DLC
(PSDU)
radio
transmitter
1. Scrambling of all data bits with the generator polynomial for DC blocking and whitening of the
spectrum.
2. FEC coding for error protection
3. For mitigation of frequency selective fading interleaving is applied.
4. mapping process first divides the bit sequence in groups of 1,2, 4, or 6 bits depending on the modulationscheme (BPSK, QPSK, 16-QAM, or 64-QAM).
5. The OFDM modulation step converts these symbols into a baseband signal with the help of the inverse FFT.
6. Creation of PHY bursts Each burst consists of a preamble and a payload.
7. radio transmission shifts the baseband signal to a carrier frequency depending on the channel numberEC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Operating channels of HiperLAN2 in Europe
5150 [MHz]5180 53505200
36 44
16.6 MHz
center frequency =
5000 + 5*channel number [MHz]
channel40 48 52 56 60 64
5220 5240 5260 5280 5300 5320
5470
[MHz]
5500 57255520
100 108
16.6 MHz
channel104 112 116 120 124 128
5540 5560 5580 5600 5620 5640
132 136 140
5660 5680 5700
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Basic structure of HiperLAN2 MAC frames
MAC frame MAC frame MAC frame MAC frame
2 ms 2 ms 2 ms 2 ms
broadcast phase downlink phase uplink phaserandom
access phase
. . .
TDD,
500 OFDM
symbols
per frame
variable variable variable
LCH PDU typesequence
numberpayload CRC
UDCH transfer syntax
(long PDU)
54 byte
2 10 396 24 bit
LCH PDU type payload CRC
2 406 24
LCH transfer syntax
bit
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Valid configurations of HiperLAN2 MAC frames
MAC frame MAC frame MAC frame MAC frame
2 ms 2 ms 2 ms 2 ms
BCH FCH ACH DL phase DiL phase UL phase RCHs
. . .
BCH FCH ACH DiL phase UL phase RCHs
BCH FCH ACH DL phase UL phase RCHs
BCH FCH ACH UL phase RCHs
BCH FCH ACH DL phase DiL phase RCHs
BCH FCH ACH DiL phase RCHs
BCH FCH ACH DL phase RCHs
BCH FCH ACH RCHs
Valid
combinations
of MAC frames
for a single
sector AP
broadcast downlink uplink
random
access
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Mapping of logical and transport channelsBCCH FCCH RFCH LCCH RBCH DCCH UDCH UBCH UMCH
BCH FCH ACH SCH LCH
downlink
UDCH DCCH LCCH ASCH
SCHLCH RCH
uplink
UDCH UBCH UMCH
LCH
DCCH RBCH
SCH
LCCH
direct link
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
BluetoothIdea
• Universal radio interface for ad-hoc wireless connectivity
• Interconnecting computer and peripherals, handheld devices, PDAs, cell phones –replacement of IrDA
• Embedded in other devices, goal: 5€/device (2005: 40€/USB bluetooth)
• Short range (10 m), low power consumption, license-free 2.45 GHz ISM
• Voice and data transmission, approx. 1 Mbit/s gross data rate
One of the first modules (Ericsson).
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Bluetooth• History
• 1994: Ericsson (Mattison/Haartsen), “MC-link” project• Renaming of the project: Bluetooth according to Harald “Blåtand” Gormsen [son of Gorm],
King of Denmark in the 10th century• 1998: foundation of Bluetooth SIG, www.bluetooth.org• 1999: erection of a rune stone at Ercisson/Lund ;-)• 2001: first consumer products for mass market, spec. version 1.1 released• 2005: 5 million chips/week
• Special Interest Group• Original founding members: Ericsson, Intel, IBM, Nokia, Toshiba• Added promoters: 3Com, Agere (was: Lucent), Microsoft, Motorola• > 2500 members• Common specification and certification of products
(was: )
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
History and hi-tech…
1999:
Ericsson mobile
communications AB
reste denna sten till
minne av Harald
Blåtand, som fick ge
sitt namn åt en ny
teknologi för trådlös,
mobil kommunikation.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
…and the real rune stoneLocated in Jelling, Denmark,
erected by King Harald “Blåtand”
in memory of his parents.
The stone has three sides – one side
showing a picture of Christ.
This could be the “original” colors
of the stone.
Inscription:
“auk tani karthi kristna” (and
made the Danes Christians)
Inscription:
"Harald king executes these sepulchral
monuments after Gorm, his father and
Thyra, his mother. The Harald who won the
whole of Denmark and Norway and turned
the Danes to Christianity."
Btw: Blåtand means “of dark complexion”
(not having a blue tooth…)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Characteristics
2.4 GHz ISM band, 79 (23) RF channels, 1 MHz carrier spacing• Channel 0: 2402 MHz … channel 78: 2480 MHz• G-FSK modulation, 1-100 mW transmit power
FHSS and TDD• Frequency hopping with 1600 hops/s• Hopping sequence in a pseudo random fashion, determined by a master• Time division duplex for send/receive separation
Voice link – SCO (Synchronous Connection Oriented)• FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-to-point, circuit switched
Data link – ACL (Asynchronous ConnectionLess)• Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s symmetric or 723.2/57.6
kbit/s asymmetric, packet switched
Topology• Overlapping piconets (stars) forming a scatternet
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Piconet
• Collection of devices connected in an ad hoc fashion
• One unit acts as master and the others as slaves for the lifetime of the piconet
• Master determines hopping pattern, slaves have to synchronize
• Each piconet has a unique hopping pattern
• Participation in a piconet = synchronization to hopping sequence
• Each piconet has one master and up to 7 simultaneous slaves (> 200 could be parked)
• 3 bit address is used by Bluetooth device. M=Master
S=Slave
P=Parked
SB=Standby
M
S
P
SB
S
S
P
P
SB
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Forming a piconetAll devices in a piconet hop together
• Master gives slaves its clock and device ID• Hopping pattern: determined by device ID (48 bit, unique worldwide)
• Phase in hopping pattern determined by clock
Addressing• Active Member Address (AMA, 3 bit)
• Parked Member Address (PMA, 8 bit)
SB
SB
SB
SB
SB
SB
SB
SB
SB
M
S
P
SB
S
S
P
P
SB
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
ScatternetLinking of multiple co-located piconets through the sharing of common master or slave devices
• Devices can be slave in one piconet and master of another
Communication between piconets• Devices jumping back and forth between the piconets
M=Master
S=Slave
P=Parked
SB=Standby
M
S
P
SB
S
S
P
P
SB
M
S
S
P
SB
Piconets
(each with a
capacity of
720 kbit/s)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Bluetooth protocol stack
Radio
Baseband
Link Manager
Control
Host
Controller
Interface
Logical Link Control and Adaptation Protocol (L2CAP)Audio
TCS BIN SDP
OBEX
vCal/vCard
IP
NW apps.
TCP/UDP
BNEP
RFCOMM (serial line interface)
AT modem
commands
telephony apps.audio apps. mgmnt. apps.
AT: attention sequence
OBEX: object exchange
TCS BIN: telephony control protocol specification – binary
BNEP: Bluetooth network encapsulation protocol
SDP: service discovery protocol
RFCOMM: radio frequency comm.
PPP
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Radio layer
Power class 1: Maximum power is 100 mW and minimum is 1 mW (typ. 100 m range without obstacles). Power control is mandatory.
Power class 2: Maximum power is 2.5 mW, nominal power is 1 mW, and minimum power is 0.25 mW (typ. 10 m range without obstacles). Power control is optional.
Power class 3: Maximum power is 1 mW.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
BasebandPiconet/channel definition
Low-level packet definition• Access code
• Channel, device access, e.g., derived from master address (48-bit)
• Packet header• 1/3-FEC, active member address (broadcast + 7 slaves), link type, alternating bit
ARQ/SEQ, checksum
access code packet header payload
68(72) 54 0-2745 bits
AM address type flow ARQN SEQN HEC
3 4 1 1 1 8 bits
preamble sync. (trailer)
4 64 (4)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
S
Frequency selection during data transmission
fk
625 µs
fk+1 fk+2 fk+3 fk+4
fk+3 fk+4fk
fk
fk+5
fk+5
fk+1 fk+6
fk+6
fk+6
MM M M
M
M M
M M
t
t
t
S S
S S
S
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
SCO payload typespayload (30)
audio (30)
audio (10)
audio (10)
HV3
HV2
HV1
DV
FEC (20)
audio (20) FEC (10)
header (1) payload (0-9) 2/3 FEC CRC (2)
(bytes)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
ACL Payload typespayload (0-343)
header (1/2) payload (0-339) CRC (2)
header (1) payload (0-17) 2/3 FEC
header (1) payload (0-27)
header (2) payload (0-121) 2/3 FEC
header (2) payload (0-183)
header (2) payload (0-224) 2/3 FEC
header (2) payload (0-339)DH5
DM5
DH3
DM3
DH1
DM1
header (1) payload (0-29)AUX1
CRC (2)
CRC (2)
CRC (2)
CRC (2)
CRC (2)
CRC (2)
(bytes)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Baseband link types• Polling-based TDD packet transmission
• 625µs slots, master polls slaves
• SCO (Synchronous Connection Oriented) – Voice • Periodic single slot packet assignment, 64 kbit/s full-duplex, point-to-point
• ACL (Asynchronous ConnectionLess) – Data • Variable packet size (1,3,5 slots), asymmetric bandwidth, point-to-multipoint
MASTER
SLAVE 1
SLAVE 2
f6f0
f1 f7
f12
f13 f19
f18
SCO SCO SCO SCOACL
f5 f21
f4 f20
ACLACL
f8
f9
f17
f14
ACL
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Robustness• Slow frequency hopping with hopping patterns determined by a master
• Protection from interference on certain frequencies
• Separation from other piconets (FH-CDMA)
• Retransmission• ACL only, very fast
• Forward Error Correction• SCO and ACL
MASTER
SLAVE 1
SLAVE 2
A C C HF
G G
B D E
NAK ACK
Error in payload
(not header!)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Baseband states of a Bluetooth devicestandby
inquiry page
connected
AMA
transmit
AMA
park
PMA
hold
AMA
sniff
AMA
unconnected
connecting
active
low power
Standby: do nothing
Inquire: search for other devices
Page: connect to a specific device
Connected: participate in a piconet
detach
Park: release AMA, get PMA
Sniff: listen periodically, not each slot
Hold: stop ACL, SCO still possible, possibly
participate in another piconet
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Example: Bluetooth/USB adapter (2002: 50€)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
L2CAP - Logical Link Control and Adaptation Protocol• Simple data link protocol on top of baseband
• Connection oriented, connectionless, and signalling channels
• Protocol multiplexing• RFCOMM, SDP, telephony control
• Segmentation & reassembly• Up to 64kbyte user data, 16 bit CRC used from baseband
• QoS flow specification per channel• Follows RFC 1363, specifies delay, jitter, bursts, bandwidth
• Group abstraction• Create/close group, add/remove member
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
L2CAP logical channels
baseband
L2CAP
baseband
L2CAP
baseband
L2CAP
Slave SlaveMaster
ACL
2 d 1 d d 1 1 d 21
signalling connectionless connection-oriented
d d d
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
L2CAP packet formats
length
2 bytes
CID=2
2
PSM
2
payload
0-65533
length
2 bytes
CID
2
payload
0-65535
length
2 bytes
CID=1
2
One or more commands
Connectionless PDU
Connection-oriented PDU
Signalling command PDU
code ID length data
1 1 2 0
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Security
E3
E2
link key (128 bit)
encryption key (128 bit)
payload key
Keystream generator
Data Data
Cipher data
Authentication key generation
(possibly permanent storage)
Encryption key generation
(temporary storage)
PIN (1-16 byte)
User input (initialization)
Pairing
Authentication
Encryption
Ciphering
E3
E2
link key (128 bit)
encryption key (128 bit)
payload key
Keystream generator
PIN (1-16 byte)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
SDP – Service Discovery Protocol
• Inquiry/response protocol for discovering services• Searching for and browsing services in radio proximity• Adapted to the highly dynamic environment• Can be complemented by others like SLP, Jini, Salutation, …• Defines discovery only, not the usage of services• Caching of discovered services• Gradual discovery
• Service record format• Information about services provided by attributes• Attributes are composed of an 16 bit ID (name) and a value• values may be derived from 128 bit Universally Unique Identifiers (UUID)
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Additional protocols to support legacy protocols/apps.• RFCOMM
• Emulation of a serial port (supports a large base of legacy applications)• Allows multiple ports over a single physical channel
• Telephony Control Protocol Specification (TCS)• Call control (setup, release)• Group management
• OBEX• Exchange of objects, IrDA replacement
• WAP• Interacting with applications on cellular phones
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WPAN: IEEE 802.15-1 – Bluetooth•Data rate
• Synchronous, connection-oriented: 64 kbit/s
• Asynchronous, connectionless• 433.9 kbit/s symmetric
• 723.2 / 57.6 kbit/s asymmetric
•Transmission range• POS (Personal Operating Space) up to
10 m
• with special transceivers up to 100 m
•Frequency• Free 2.4 GHz ISM-band
•Security• Challenge/response (SAFER+), hopping
sequence
•Availability• Integrated into many products, several
vendors
•Connection set-up time
• Depends on power-mode
• Max. 2.56s, avg. 0.64s
•Quality of Service
• Guarantees, ARQ/FEC
•Manageability
• Public/private keys needed, key management not specified, simple system integration
•Special Advantages/Disadvantages
• Advantage: already integrated into several products, available worldwide, free ISM-band, several vendors, simple system, simple ad-hoc networking, peer to peer, scatternets
• Disadvantage: interference on ISM-band, limited range, max. 8 devices/network&master, high set-up latency
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WPAN: IEEE 802.15
• 802.15-2: Coexistance• Coexistence of Wireless Personal Area Networks (802.15) and Wireless Local Area
Networks (802.11), quantify the mutual interference
• 802.15-3: High-Rate• Standard for high-rate (20Mbit/s or greater) WPANs, while still low-power/low-cost • Data Rates: 11, 22, 33, 44, 55 Mbit/s • Quality of Service isochronous protocol • Ad hoc peer-to-peer networking • Security • Low power consumption • Low cost • Designed to meet the demanding requirements of portable consumer imaging and
multimedia applications
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WPAN: IEEE 802.15 – future developments 2
Several working groups extend the 802.15.3 standard
802.15.3a:• Alternative PHY with higher data rate as extension to 802.15.3
• Applications: multimedia, picture transmission
802.15.3b:• Enhanced interoperability of MAC
• Correction of errors and ambiguities in the standard
802.15.3c:• Alternative PHY at 57-64 GHz
• Goal: data rates above 2 Gbit/s
• Not all these working groups really create a standard, not all standards will be found in products later …
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WPAN: IEEE 802.15 – future developments 3
• 802.15-4: Low-Rate, Very Low-Power• Low data rate solution with multi-month to multi-year battery life and very low complexity• Potential applications are sensors, interactive toys, smart badges, remote controls, and home
automation• Data rates of 20-250 kbit/s, latency down to 15 ms• Master-Slave or Peer-to-Peer operation• Up to 254 devices or 64516 simpler nodes• Support for critical latency devices, such as joysticks• CSMA/CA channel access (data centric), slotted (beacon) or unslotted• Automatic network establishment by the PAN coordinator• Dynamic device addressing, flexible addressing format• Fully handshaked protocol for transfer reliability• Power management to ensure low power consumption• 16 channels in the 2.4 GHz ISM band, 10 channels in the 915 MHz US ISM band and one channel in
the European 868 MHz band
• Basis of the ZigBee technology – www.zigbee.org
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Emerging Technologies
WiMAX
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Current ScenarioThink about how you access the Internet today. There are basically three different options:
Broadband access - In your home, you have either a DSL or cable modem. At the office,your company may be using a T1 or a T3 line.
WiFi access - In your home, you may have set up a WiFi router that lets you surf the Webwhile you lounge with your laptop. On the road, you can find WiFi hot spots in restaurants,hotels, coffee shops and libraries.
Dial-up access - If you are still using dial-up, chances are that either broadband access isnot available, or you think that broadband access is too expensive.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Current Scenario The main problems with broadband access are that it is pretty expensive and it doesn't
reach all areas. The main problem with WiFi access is that hot spots are very small, socoverage is sparse.
What if there were a new technology that solved all of these problems? This newtechnology would provide:
The high speed of broadband service.
Wireless rather than wired access, so it would be a lot less expensive than cable or DSL
and much easier to extend to suburban and rural areas.
Broad coverage like the cell phone network instead of small WiFi hotspots.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Wireless Broadband
This system is actually coming into being right now, and it is called WiMAX. WiMAX is short for
Worldwide Interoperability for Microwave Access, and it also goes by the IEEE name 802.16.
Also known as Wireless Metropolitan Area Network (Wireless MAN).
Offers an alternative to high bandwidth wired access networks like fiber optic, cable modems and
DSL.
Provides network access to buildings through exterior antennas communicating with radio base
stations.
Networks can be created in just weeks by deploying a small number of base stations on buildings or
poles to create high capacity wireless access systems.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WiMax Vs. WiFi WiMAX operates on the same general principles as WiFi - it sends data from one computer to another via
Radio signals.
A computer (either a desktop or a laptop) equipped with WiMAX would receive data from the WiMAX
transmitting station, probably using encrypted data keys to prevent unauthorized users from stealing access.
The fastest WiFi connection can transmit up to 54 megabits per second under optimal conditions.
WiMAX should be able to handle up to 70 megabits per second.
Even once that 70 megabits is split up between several dozen businesses or a few hundred home users, it
will provide at least the equivalent of cable-modem transfer rates to each user.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WiMax Vs. WiFi
The biggest difference isn't speed; it's distance. WiMAX outdistances WiFi by miles. WiFi's range is about
100 feet (30 m). WiMAX will blanket a radius of 30 miles (50 km) with wireless access.
The increased range is due to the frequencies used and the power of the transmitter.
Of course, at that distance, terrain, weather and large buildings will act to reduce the maximum range in
some circumstances, but the potential is there to cover huge tracts of land.
WiMax is not designed to clash with WiFi, but to coexist with it.
WiMax specifications also provides much better facilities than WiFi, providing higher bandwidth and high
data security by the use of enhanced encryption schemes.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
WiMAX is not Wi-Fi
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Overview of IEEE 802.16
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Sub-standards of IEEE 802.16
IEEE 802.16.1 - Air interface for 10 to 66 GHz
IEEE 802.16.2 - Coexistence of broadband wireless access systems
IEEE 802.16.3 - Air interface for licensed frequencies, 2 to 11 GHz
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Basics of IEEE 802.16
IEEE 802.16 standards are concerned with the air interface between a subscriber’s transceiver station and a base transceiver station
The Physical Layer
MAC Layer
Convergence Layer
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
IEEE 802.16 Protocol Architecture
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Physical Layer
Specifies the frequency band, the modulation scheme, error-correction techniques,synchronization between transmitter and receiver, data rate and the multiplexing structure
Both TDD and FDD alternatives support adaptive burst profiles in which modulation andcoding options may be dynamically assigned on a burst-by-burst basis
Three physical layer for services: Wireless MAN-SC2, Wireless MAN-OFDM and WirelessMAN-OFDMA
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Medium Access Control Layer
Designed for point-to-multipoint broadband wireless access
Addresses the need for very high bit rates, both uplink (to the base station) anddownlink (from the base station)
Services like multimedia and voice can run as 802.16 MAC is equipped to accommodateboth continuous and bursty traffic
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Convergence Layer
Provides functions specific to the service being provided
Bearer services include digital audio/video multicast, digital telephony, ATM, Internetaccess, wireless trunks in telephone networks and frame relay
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Reference Network Model
• The IEEE 802.16e-2005 standard provides the air interface for WiMAX but does not define the full end-to-
end WiMAX network. The WiMAX Forum's Network Working Group (NWG), is responsible for
developing the end-to-end network requirements, architecture, and protocols for WiMAX, using IEEE
802.16e-2005 as the air interface.
• The WiMAX NWG has developed a network reference model to serve as an architecture framework for
WiMAX deployments and to ensure interoperability among various WiMAX equipment and operators.
• The network reference model envisions a unified network architecture for supporting fixed, nomadic, and
mobile deployments and is based on an IP service model.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Reference Network Model
• The overall network may be logically divided into three parts:
1. Mobile Stations (MS) used by the end user to access the network.
2. The access service network (ASN), which comprises one or more base stations and oneor more ASN gateways that form the radio access network at the edge.
3. Connectivity service network (CSN), which provides IP connectivity and all the IP corenetwork functions.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Reference Network Model
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Reference Network Model
• The network reference model developed by the WiMAX Forum NWG defines a number of functional
entities and interfaces between those entities. Fig below shows some of the more important functional
entities.
1) Base station (BS): The BS is responsible for providing the air interface to the MS. Additional functions that
may be part of the BS are micromobility management functions, such as handoff triggering and tunnel
establishment, radio resource management, QoS policy enforcement, traffic classification, DHCP (Dynamic
Host Control Protocol) proxy, key management, session management, and multicast group management.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Reference Network Model
2) Access service network gateway (ASN-GW): The ASN gateway typically acts as a
layer 2 traffic aggregation point within an ASN. Additional functions that may be part of
the ASN gateway include intra-ASN location management and paging, radio resource
management and admission control, caching of subscriber profiles and encryption keys,
establishment and management of mobility tunnel with base stations, QoS and policy
enforcement, foreign agent functionality for mobile IP, and routing to the selected CSN.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Reference Network Model
3) Connectivity service network (CSN): The CSN provides connectivity to the Internet, ASP, other public
networks, and corporate networks.
The CSN is owned by the NSP and includes AAA servers that support authentication for the devices, users,
and specific services. The CSN also provides per user policy management of QoS and security.
The CSN is also responsible for IP address management, support for roaming between different NSPs, location
management between ASNs, and mobility and roaming between ASNs.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Advanced Features of WiMAX
An important and very challenging function of the WiMAX system is the support of various advanced
antenna techniques, which are essential to provide high spectral efficiency, capacity, system performance, and
reliability.
Two Type of Services:
WiMAX can provide two forms of wireless service:
1) Non-line-of-sight: service is a WiFi sort of service. Here a small antenna on your computer connects to the
WiMAX tower. In this mode, WiMAX uses a lower frequency range -- 2 GHz to 11 GHz (similar to WiFi).
2) Line-of-sight: service, where a fixed dish antenna points straight at the WiMAX tower from a rooftop or
pole. The line-of-sight connection is stronger and more stable, so it's able to send a lot of data with fewer
errors. Line-of-sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Advanced Features of WiMAX
• Very high peak data rates:
WiMAX is capable of supporting very high peak data rates. In fact, the peak PHY data rate can be as high as
74Mbps when operating using a 20MHz wide spectrum.
More typically, using a 10MHz spectrum operating using TDD scheme with a 3:1 downlink-to-uplink ratio,
the peak PHY data rate is about 25Mbps and 6.7Mbps for the downlink and the uplink, respectively.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Advanced Features of WiMAX
• Scalable bandwidth and data rate support:
WiMAX has a scalable physical-layer architecture that allows for the data rate to scale easily with available
channel bandwidth.
For example, a WiMAX system may use 128, 512, or 1,048-bit FFTs (fast fourier transforms) based on
whether the channel bandwidth is 1.25MHz, 5MHz, or 10MHz, respectively.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Advanced Features of WiMAX
• Quality-of-service support:
The WiMAX MAC layer has a connection-oriented architecture that is designed to support a variety of
applications, including voice and multimedia services.
WiMAX system offers support for constant bit rate, variable bit rate, real-time, and non-real-time traffic
flows, in addition to best-effort data traffic.
WiMAX MAC is designed to support a large number of users, with multiple connections per terminal, each
with its own QoS requirement.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K
Advanced Features of WiMAX
• Robust security:
WiMAX supports strong encryption, using Advanced Encryption Standard (AES), and has a robust privacy and
key-management protocol.
The system also offers a very flexible authentication architecture based on Extensible Authentication Protocol
(EAP), which allows for a variety of user credentials, including username/password, digital certificates, and
smart cards.
• Support for mobility:
The mobile WiMAX variant of the system has mechanisms to support secure seamless handovers for delay-
tolerant full-mobility applications, such as VoIP.
EC8004/WIRELESS NETWORKS/RAJKUMAR.K.K