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4G MO W SS WMAX4G MOBILE WIRELESS WIMAX
Aditya K. JagannathamIndian Institute of Technology KanpurIndian Institute of Technology KanpurCommonwealth of Learning Vancouver
MOOC on M4D 2013
WSSUS Channel Variables DelayWSSUS Channel Variables ‐ Delay
• Typical wireless channel delay spreads are of the order of 3 μs.
~ Km~ Km~ Km
MOOC on M4D 2013
WSSUS Channel Variables DelayWSSUS Channel Variables ‐ Delay
• Therefore, to avoid ISI, T > Td = 3 μs.• It is immediately clear the maximum symbol rate in outdoor channels is,
1 Kbps 3331031
6max
R
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Coherence bandwidthCoherence bandwidth
• Coherence bandwidth of the channel is defined in terms of delay spread as,
c TB 1
d
c T
• For outdoor channels, Td ~ 3 s as seen earlier.– Hence, the coherence bandwidth Bc is given as,, c g ,
KHz3331B
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KHz333103 6
cB
Single Carrier SchematicSingle Carrier Schematic
B
B/20B/2 B/2Carrier
0‐B/2
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B = 10 – 20 MHz
Single Carrier Vs Multi CarrierSingle Carrier Vs. Multi Carrier
• Consider instead a multi‐carrier modulation (MCM) with N sub‐bands of bandwidth B/N.( )
E h b d f b d id h B/N h b i• Each band of bandwidth B/N has a subcarrier.
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Multi Carrier SchematicMulti Carrier Schematic
B
B/N 2B/N B/2‐B/N‐2B/N‐(N/2‐1)B/N
B/NSubcarriers
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B = 10 MHz, N = 1000, B/N = 10 KHz
Multi Carrier CommunicationMulti‐Carrier Communication
• The N subcarriers are at frequencies
NBN
NB
NB
NBN
NBN
2,,,0,,,2
2,1
2
• The ith SC is at if where f = B/N is the
The i SC is at ifo, where fo = B/N is the fundamental frequency of the multi‐carrier
tsystem.
21
2 , NiN
NBiiff oi
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22
,N
ff oi
MCM – Overall RateMCM – Overall Rate• In an MCM system one is transmitting NIn an MCM system, one is transmitting Nparallel symbols over time N/B.
bols
rriers
lel sym
subcar
Nparal
Over N
N O
MOOC on M4D 20139
Symbol Time = N/B
Orthogonal Frequency Division Multiplexing (OFDM)
• By converting a wideband channel intoBy converting a wideband channel into multiple orthogonal narrowband channels, one can tremendously simplify the receiveone can tremendously simplify the receive processing.
If the subcarrier bandwidth is less than the– If the subcarrier bandwidth is less than the coherent bandwidth, then each narrowband carrier experiences flat‐fading.carrier experiences flat fading.
• It can be processed with much lower complexity compared to frequency selectivecomplexity compared to frequency‐selective fading.
MOOC on M4D 201310
Orthogonal Frequency Division Multiplexing
• Orthogonal subcarriersOrthogonal Subcarriers in OFDM for WiMAX • Orthogonal subcarriers in a WiMAX system 0.8
g
with a carrier spacing of 15.625 KHz.0.4
0.6
er A
mpl
itude
• Observer, there is NO guard band0
0.2Sub
carri
e
guard band– Hence, efficient use of -60 -40 -20 0 20 40 60
-0.2
0
Frequency (KHz)
spectrumq y ( )
MOOC on M4D 201311
Orthogonal Frequency Division MultiplexingMultiplexing
• An OFDM schematic employing a bank of modulators (BoM) is given below.
S/PDemux
Bank Of
ModulatorsSummer
nnel
k
Cha
Bank of
Correlators
P/SMux Repeater
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WIMAXW IWORLDWIDE INTEROPERABILITY FORMICROWAVE ACCESS
MOOC on M4D 2013
WiMAX Timeline BeginningsWiMAX Timeline ‐ Beginnings• IEEE 802 16 group was formed in 1998IEEE 802.16 group was formed in 1998
– To develop an air‐interface standard for wireless b db dbroadband.
• Initially focused at development of an LOS‐based point‐to‐multipoint WBS.– Slated for operation in the 10GHz–66GHzSlated for operation in the 10GHz 66GHz millimeter wave band.
MOOC on M4D 201314
WiMAX Timeline BeginningsWiMAX Timeline ‐ Beginnings
• The resulting standard—the original 802.16 was completed in December 2001.p
• Salient features of this standard includedSi l i h i l (PHY) l– Single‐carrier physical (PHY) layer.
– Burst time division multiplexed (TDM) MAC layer.
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WiMAX Timeline PrecursorWiMAX Timeline ‐ Precursor • The IEEE 802.16 group subsequently produced 802.16a, an amendment to the 802.16 standard.– Included NLOS applications in the 2GHz–11GHz band (Multipath Propagation).
– Employed an Orthogonal Frequency Division Multiplexing (OFDM) based physical layer.
– Additions to the MAC (Medium Access Control) layer, such as support for Orthogonal Frequency Division Multiple Access (OFDMA), were also included.
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WiMAX Timeline PrecursorWiMAX Timeline ‐ Precursor
• Further revisions resulted in a new standard in 2004, called IEEE 802.16‐2004.– This formed the basis for the first WiMAXsolution.solution.
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WiMAX Timeline InceptionWiMAX Timeline ‐ Inception• Early solutions based on the IEEE 802.16‐y2004 targeted fixed applications.– Referred to as fixed WiMAX.Referred to as fixed WiMAX.
• In December 2005, the IEEE 802.16 group completed and approved IEEE 802 16ecompleted and approved IEEE 802.16e‐2005.
A d d th li fi d WiMAX IEEE 802 16– Amended the earlier fixed WiMAX IEEE 802.16‐2004 standard to add mobility support. Thi f th b i f th WiMAX l ti f– This forms the basis for the WiMAX solution for mobile applications.Oft f d t bil WiMAX
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– Often referred to as mobile WiMAX.
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PHY (Physical) LayerPHY (Physical) Layer• PHY is responsible for transmission andPHY is responsible for transmission and reception of radio signals
• The WiMAX physical layer (PHY) is based on Orthogonal Frequency Division Multiplexing.g q y p g– This offers simplified reception in multipath and allows WiMAX to operate in NLOS conditions.allows WiMAX to operate in NLOS conditions.
– OFDM is now widely recognized as the PHY of choice for mitigating multipath in Broadbandchoice for mitigating multipath in Broadband Wireless Access (BWA) – WLAN, LTE, Bluetooth
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WiMAX OFDM ParametersParameter Fixed Mobile WiMAXParameter Fixed
WiMAXMobile WiMAX
Number of Subcarriers 256 128 512 1024 2048
Used data subcarriers 192 72 360 720 1440
Pilot subcarriers 8 12 60 120 240
/ 368Number of null/guardbandsubcarriers
56 44 92 184 368
Cyclic Prefix 1/32, 1/16, 1/8, 1/4
Oversampling Rate (Fs/BW)Depends on BW. 7/6 for 256 OFDM, 8/7 for multiples of 1.75 MHz and 28/25 for multiples of 1.25 MHz, 1.5 MHz, 2
MHz or 2 75 MHzMHz or 2.75 MHz.
Channel BW (MHz) 3.5 1.25 5 10 20
Subcarrier spacing 15.625 10.94p g
MOOC on M4D 2013
WiMAX FeaturesWiMAX Features• WiMAX Supports Several Advanced Features• WiMAX Supports Several Advanced Features
– Scalable Data rate and number of subcarriers (128 – 2048)
– Adaptive Modulation and Coding (Number of bits per symbol and Error Control)
– High Peak Data Rates ~ 75‐100 Mbpsg p– Advanced Antenna Techniques
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WiMAX FeaturesWiMAX Features
AlamoutiSpace‐Time CodeSpace‐Time Code
BeamformingBeamformingDirectional Transmission
Spatial MultiplexingTransmission of Multiple Streams
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WiMAX FeaturesWiMAX Features• Support for TDD and FDDSupport for TDD and FDD
– Fixed‐WiMAX and mobile‐WiMAX support both TDD d FDDTDD and FDD.
– This allows for a low‐cost system implementation.
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Flexible & Dynamic Resource AllocFlexible & Dynamic Resource Alloc.• Both UL and DL resource allocation are controlled by a scheduler in the BS.
• Capacity is shared among multiple users on a p y g pdemand basis, using a burst TDM scheme.
• Further, using the OFDMA‐PHY mode, multiplexing is additionally done in the frequency dimension.
B ll i diff b f OFDM b i– By allocating different subsets of OFDM subcarriers to different users.
• Resources may be allocated in the spatial domain• Resources may be allocated in the spatial domain employing Advanced Antenna Systems (AAS).
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OFDMA Resource AllocationFrequency
Timee
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WiMAX Frame StructureWiMAX Frame StructureGuard Time
FCH
MAP
DL B #2
Burst 1
FAP
UL‐M DL Burst #2
Burst 3
Burst 2
Preamble
DL‐M
A DL Burst #1
DL Burst #4
DL Burst #3DL B t CK
‐CH
Burst 4
Burst 3
P
MAP
DL Burst #5DL Burst #6
AC
Burst 5
UL‐
DL Burst 7 RangingFast Feedback
MOOC on M4D 2013DL Subframe UL Subframe
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WiMAX Scheduling ServicesWiMAX Scheduling Services
• MAC uses a scheduling service to deliver and handle services with different QoS reqs.q
• Determines the mechanism the network uses to allocate UL and DL resources for theto allocate UL and DL resources for the services.
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WiMAX Scheduling ServicesScheduler type Services
Unsolicited grant services Support for fixed‐size data packets at a constant bitUnsolicited grant services (UGS):
Support for fixed size data packets at a constant bitrate (CBR). ‐ Voice
Real‐time polling services Designed to support real‐time service flows, such asp g(rtPS):
g pp ,MPEG video, that generate variable‐size data packetson a periodic basis. ‐ Video
Non‐real‐time polling service (nrtPS):
Designed to support delay‐tolerant data streams, suchas an FTP, that require variable‐size data grants at aminimum guaranteed rate.g
Best‐effort (BE) service: Supports data streams, such as Web browsing, that donot require a minimum service‐level guarantee. –q gInternet, e‐mail
Extended real‐time variable t (ERT VR) i
For real‐time applications, such as VoIP with silencei th t h i bl d t t b t i
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rate (ERT‐VR) service suppression, that have variable data rates but requireguaranteed data rate and delay.
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Mobility Supporty pp• WiMAX supports the following types of mobilitmobility
Type Features
Nomadic. The user is allowed to take a fixed subscriber station and reconnect from a different point of attachment.
Portable. Nomadic access is provided to a portable device, such as a PC card with expectation of a best‐effort handoveras a PC card, with expectation of a best effort handover.
Simple mobility. The subscriber may move at speeds up to 60 kmph with brief interruptions (less than 1 sec) during handoff.
Full mobility: Up to 120 kmph mobility and seamless handoff (less
MOOC on M4D 2013
Full mobility: Up to 120 kmph mobility and seamless handoff (less than 50 ms latency and <1% packet loss) is supported.
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AAA Authentication, Authorization, AccountingReference Network Architecture
ASN‐GW Access Service Network Gateway
ASP Application Service Provider
MIP HA Mobile IP Home AgentMIP‐HA Mobile IP Home Agent
MS Mobile Station
OSS Operational Support Systems
BSS Business Support Systems
BSAAA
Internet
ASP
MSBS
IP
MIP‐HA
IPNetwork
MS BSAccessNetwork
ASNGW
IPNetwork
OSS/ PSTN
MS
BS
BSS
Gateway
MOOC on M4D 2013
3GPP/3GPP2
ASN CSN31