wman, part 1 contents
TRANSCRIPT
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Contents
IEEE 802.16 family of standards
Protocol layering
TDD frame structure
MAC PDU structure
Part 1:
Part 2: Dynamic QoS management
OFDM PHY layer
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IEEE 802.16
The standard IEEE 802.16 defines the air interface, includingthe MAC layer and multiple PHY layer options, for fixedBroadband Wireless Access (BWA) systems to be used in a
Wireless Metropolitan Area Network (WMAN) for residentialand enterprise use. IEEE 802.16 is also often referred to asWiMax. The WiMax Forum strives to ensure interoperabilitybetween different 802.16 implementations - a difficult taskdue to the large number of options in the standard.
IEEE 802.16 cannot be used in a mobile environment. For thispurpose, IEEE 802.16e is being developed. This standard willcompete with the IEEE 802.20 standard (still in early phase).
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IEEE 802.16 standardization
The first version of the IEEE 802.16 standard was completedin 2001. It defined a single carrier (SC) physical layer for line-of-sight (LOS) transmission in the 10-66 GHz range.
IEEE 802.16a defined three physical layer options (SC, OFDM,and OFDMA) for the 2-11 GHz range.
IEEE 802.16c contained upgrades for the 10-66 GHz range.
IEEE 802.16d contained upgrades for the 2-11 GHz range.
In 2004, the original 802.16 standard, 16a, 16c and 16d werecombined into the massive IEEE 802.16-2004 standard.
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Uplink / downlink separation
IEEE 802.16 offers both TDD (Time Division Duplexing) andFDD (Frequency Division Duplexing) alternatives.
Wireless devices should avoid transmitting and receiving atthe same time, since duplex filters increase the cost:
TDD: this problem is automatically avoided
FDD: IEEE 802.16 offers semi-duplex operation as anoption in Subscriber Stations.
(Note that expensive duplex filters are also the reason whyIEEE 802.11 WLAN technology is based on CSMA/CA insteadof CSMA/CD.)
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Uplink / downlink separation
TDD
FDD
Semi-duplexFDD
Downlink
Uplink
Adaptive
Frequency 1
Frequency 2
Frame n-1 Frame n Frame n+1
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IEEE 802.16 PHY
IEEE 802.16-2004 specifies three PHY options for the 2-11 GHzband, all supporting both TDD and FDD:
WirelessMAN-SCa(single carrier option), intended for a line-of-sight (LOS) radio environment where multipathpropagation is not a problem
WirelessMAN-OFDM with 256 subcarriers (mandatory forlicense-exempt bands) will be the most popular option inthe near future
WirelessMAN-OFDMA with 2048 subcarriers separates usersin the uplink in frequency domain (complex technology).
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IEEE 802.16 basic architecture
BS SS
SS
SS
Point-to-multipointtransmission
AP
AP
802.11WLAN
BS = Base StationSS = Subscriber Station
Fixednetwork
Subscriber line
replacement
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ATMtransport
IPtransport
Service Specific ConvergenceSublayer (CS)
IEEE 802.16 protocol layering
MAC Common Part Sublayer(MAC CPS)
Privacy sublayer
Physical Layer (PHY)
MA
C
Like IEEE 802.11, IEEE802.16 specifies the
Medium Access Control(MAC) and PHY layers ofthe wireless transmissionsystem.
The IEEE 802.16 MAClayer consists of three
sublayers.
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ATMtransport
IPtransport
Service Specific ConvergenceSublayer (CS)
IEEE 802.16 protocol layering
MAC Common Part Sublayer(MAC CPS)
Privacy sublayer
Physical Layer (PHY)
MA
C
CS maps data (ATM cellsor IP packets) to acertain unidirectionalconnection identified bythe Connection Identifier(CID) and associated
with a certain QoS.
CS adapts higher layerprotocols to MAC CPS.
May also offer payloadheader suppression.
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ATMtransport
IPtransport
Service Specific ConvergenceSublayer (CS)
IEEE 802.16 protocol layering
MAC Common Part Sublayer(MAC CPS)
Privacy sublayer
Physical Layer (PHY)
MA
C
MAC CPS provides thecore MAC functionality:
System access
Bandwidth allocation
Connection control
Note: QoS control is
applied dynamically toevery connectionindividually.
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ATMtransport
IPtransport
Service Specific ConvergenceSublayer (CS)
IEEE 802.16 protocol layering
MAC Common Part Sublayer(MAC CPS)
Privacy sublayer
Physical Layer (PHY)
MA
C
The privacy sublayer
provides authentication,key management andencryption.
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ATMtransport
IPtransport
Service Specific ConvergenceSublayer (CS)
IEEE 802.16 protocol layering
MAC Common Part Sublayer(MAC CPS)
Privacy sublayer
Physical Layer (PHY)
MA
C IEEE 802.16 offers threePHY options for the 2-11GHz band:
WirelessMAN-SCa
WirelessMAN-OFDM
WirelessMAN-OFDMA
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WiMAX
The WiMax (WorldwideInteroperability for MicrowaveAccess) certification program of
the WiMax Forum addressescompatibility of IEEE 802.16equipment
=>
WiMax ensures interoperability
of equipment from differentvendors.
ATMtransport
IPtransport
Service Specific Convergence
Sublayer (CS)
MAC Common Part Sublayer(MAC CPS)
Privacy sublayer
Physical Layer (PHY)
WiMax
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Overall TDD frame structure (1)
Frame n-1 Frame n Frame n+1 Frame n+2
Frame length 0.5, 1 or 2 ms
The following slides present the overall IEEE 802.16 framestructure for TDD.
It is assumed that the PHY option is WirelessMAN-OFDM, sincethis presumably will be the most popular PHY option (in thenear future). The general frame structure is applicable also toother PHY options, but the details may be different.
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Overall TDD frame structure (2)
Frame n-1 Frame n Frame n+1 Frame n+2
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
UL PHYburst k
DL subframe UL subframe
TDMA bursts from
different subscriberstations (each withits own preamble)
TDM signal
in downlink
For initial
ranging
For BW
requests
Adaptive
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UL PHYburst k
DL subframe structure (1)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
Preamble FCH DL burst 1 DL burst n
The DL subframe starts with a preamble (necessary for framesynchronization and equalization) and the Frame ControlHeader (FCH) that contains the location and burst profile ofthe first DL burst following the FCH. The FCH is one OFDMsymbol long and is transmitted using BPSK modulation.
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UL PHYburst k
DL subframe structure (2)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
Preamble FCH DL burst 1 DL burst n
The first burst in downlink contains the downlink and uplinkmaps (DL MAP & UL MAP) and downlink and uplink channel
descriptors (DCD & UCD). These are all contained in the firstMAC PDU of this burst. The burst may contain additional MACPDUs.
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UL PHYburst k
DL subframe structure (3)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
Preamble FCH DL burst 1 DL burst n
DL MAP
UL MAP
DCD
UCD
DL MAP
UL MAP
DCD
UCD
The downlink map (DL MAP) indicates thestarting times of the downlink bursts.
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UL PHYburst k
DL subframe structure (4)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
Preamble FCH DL burst 1 DL burst n
DL MAP
UL MAP
DCD
UCD
DL MAP
UL MAP
DCD
UCD
The uplink map (UL MAP) indicates thestarting times of the uplink bursts.
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UL PHYburst k
DL subframe structure (6)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
Preamble FCH DL burst 1 DL burst n
DL MAP
UL MAP
DCD
UCD
DL MAP
UL MAP
DCD
UCD
The uplink channel descriptor (UCD)
describes the uplink burst profile (i.e.,modulation and coding combination)and preamble length for each UL burst.
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Modulation and coding combinations
Modulation
BPSKQPSK
QPSK
16-QAM
16-QAM
64-QAM
64-QAM
Info bits /subcarrier
0.51
1.5
2
3
4
4.5
Info bits /symbol
88184
280
376
568
760
856
Peak datarate (Mbit/s)
1.893.95
6.00
8.06
12.18
16.30
18.36
Codingrate
1/21/2
3/4
1/2
3/4
2/3
3/4
Depends on chosen bandwidth (here 5 MHz is assumed)
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UL PHYburst k
DL subframe structure (7)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
Preamble FCH DL burst 1 DL burst n
Downlink bursts are transmitted in order of decreasing
robustness. For example, with the use of a single FEC typewith fixed parameters, data begins with BPSK modulation,followed by QPSK, 16-QAM, and 64-QAM.
BPSK 64 QAM
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UL PHYburst k
DL subframe structure (8)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
Preamble FCH DL burst 1 DL burst n
A subscriber station (SS) listens to all bursts it is capable of
receiving (this includes bursts with profiles ofequal orgreater robustness than has been negotiated with the basestation at connection setup time).
BPSK 64 QAM
Sorry, Icannotdecode
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UL PHYburst k
DL subframe structure (9)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
Preamble FCH DL burst 1 DL burst n
A subscriber station (SS) does not know which DL burst(s)
contain(s) information sended to it, since the Connection ID(CID) is located in the MAC header, not in the DL PHY PDUheader.
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UL PHYburst k
DL subframe structure (10)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
Preamble FCH DL burst 1 DL burst n
MAC PDU 1 MAC PDU k pad
IEEE 802.16 offers concatenation of severalMAC PDUs within a single transmission burst.
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UL PHYburst k
UL subframe structure (1)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
The uplink subframe starts with a contention slot that offerssubscriber stations the opportunity for sending initial rangingmessages to the base station (corresponding to RACHoperation in GSM).
A second contention slot offers subscriber stations theopportunity for sending bandwidth request messages to thebase station.
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UL PHYburst k
UL subframe structure (2)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
The usage ofbandwidth request messages in this contentionslot (and response messages in downlink bursts) offers amechanism for achieving extremely flexible and dynamicaloperation of IEEE 802.16 systems.
Bandwidth (corresponding to a certain modulation andcoding combination) can be adaptively adjusted for eachburst to/from each subscriber station on a per-frame basis.
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Example: Efficiency vs. robustness trade-off
Large distance => high attenuation => low bit rate
BS64 QAM
16 QAM
QPSK
SS
SS
SS
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UL PHYburst k
UL subframe structure (3)
DL PHYPDU
Contentionslot A
Contentionslot B
UL PHYburst 1
MAC PDU k pad
IEEE 802.16 offers concatenation of severalMAC PDUs within a single transmission burstalso in uplink.
Preamble MAC PDU 1
Preamble ineach uplinkburst.
UL PHY burst = UL PHY PDU
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MAC PDU structure
MAC Header MAC Payload CRC-32
6 bytes 0 - 2041 bytes 4 bytes
MAC payload containsmanagement messageor user data
For errorcontrol
Two MAC headerformats:
1. Generic MACheader (HT=0)
2. Bandwidthrequest header(HT=1)
No MAC payload, no CRC
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Generic MAC header (1)
Length of MACPDU in bytes
(incl. header)
Connection ID(CID) is in MAC
header!
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Generic MAC header (2)
CRC indicator
Encryption keysequence
Encryptioncontrol
Header checksequence
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Bandwidth request header
Type (3) BR msb (11)The bandwidth
request (BR) field
indicates thenumber of uplinkbytes requested
000 - incremental001 - aggregate
bandwith request
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Significance of Type field
MAC Header MAC PDU CRC-32
This field indicates if (and what kind of)MAC subheader(s) is (are) inserted inthe PDU payload after the MAC header.
MAC subheaders are used for: a) Fragmentationb) Packingc) Grant management
Subheader
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Fragmentation
Fragmentation is the process by which a MAC SDU is dividedinto one or more MAC PDUs. This process allows efficient useof available bandwidth relative to the QoS requirements of aconnections service flow.
H
MAC SDU
Fragmentation subheaders
T H T H T
MAC PDUs
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Fragmentation subheader (1 byte) format
FragmentationSequence Number(modulo 8)
Fragmentation Control
00 no fragmentation
01 last fragment10 first fragment11 middle fragment
Number values my be outdated
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Packing
Packing means that several MAC SDUs are carried in a singleMAC PDU. When packing variable-length MAC SDUs, a packingsubheader is inserted before each MAC SDU.
Header
MAC SDUs
2-byte packing subheaders
CRC
MAC PDU
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Packing subheader (2 byte) format
Length (in bytes) of the MAC SDU or SDU fragment,including the two byte packing subheader
This enablessimultaneousfragmentationand packing
Number values my be outdated
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Difference between concatenation & packing
Packing = within MAC PDU
MAC PDUMAC PDU MAC PDUMAC PDU MAC PDUMAC PDU
MACSDU
MAC
SDUMACSDU
MAC
SDU
PreamblePreamble DL or UL burst (PHY layer)DL or UL burst (PHY layer)
Concatenation = within burst
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Fragmentation & packing
If fragmentation or packing is enabled for a connection, it isalways the transmitting entity (base station in downlink orsubscriber station in uplink) that decides whether or not to
fragment/pack.Fragmentation and packing can be done at the same time(see packing subheader structure). In this way the channelutilisation can be optimised.