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PHY Layer

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Multiple Access and Duplexing

• Time-Division Duplex (TDD) – DL & UL time-share the same RF channel – Dynamic asymmetry (also named as Demand Assigned Multiple

Access : DAMA) – Half-duplex – SS does not transmit/receive simultaneously (low cost)

• Frequency-Division Duplex (FDD)

– DL & UL on separate RF channels – Static asymmetry – Full-duplex SSs supported – Half-duplex SSs supported (low cost)

» SS does not transmit/receive simultaneously » Need resynchronization

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TDD Frame • Frame duration: 0.5/1/2 ms (SC), 2.5/4/5/8/10/12.5/20 ms

(OFDM), 2/2.5/5/8/10/12.5/20ms (OFDMA) • Physical Slot (PS) = 4 symbols (SC/a) , 4/sampling_freq(Fs)

(OFDM/A) • Minislot : A unit of uplink bandwidth allocation equivalent to n

physical slots (PSs), where n = 2m and m is an integer ranging from 0 through 7.

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Adaptive Burst Profiles

• Burst profile – Modulations and FEC

• AMC : Advanced Modulation and Coding • Dynamically assigned according to link conditions • Burst by burst, per subscriber station • Trade-off capacity vs. robustness in real time • Roughly doubled capacity for the same cell • Burst profile for downlink channel (broadcast) is well-

known and robust – Other burst profiles can be configured “on the fly” – SS capabilities recognized at registration

» SBC-REQ/RSP

SS Basic Capability Request

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System Parameters

QPSK, 16-QAM and 64-QAM

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Radio Link control (RLC)

• RLC control – transition of burst profile – power level – ranging

• RLC begins with periodic BS broadcast of the burst

profiles that have been chosen for the uplink and downlink

– according to rain region and equipment capabilities.

• Burst profiles for the downlink/uplink are each tagged with a Downlink/Uplink Interval Usage Code (DIUC/UIUC).

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Burst Profile

• Burst profile is a basic tool for MAC to do link adaptation – �Containing a set of PHY-related parameters which changes

dynamically and possibly very fast

• Set of parameters that describe the uplink or downlink transmission properties associated with an interval usage code (IUC). – The burst profile to use for any uplink transmission is

defined by the Uplink Interval Usage Code (UIUC). – Each UIUC is mapped to a burst profile in the UCD message

• Each profile contains parameters such as a) modulation type b) forward error correction (FEC) type c) preamble length d) guard times

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Burst Profile

• If the received CINR (Carrier to Interference-plus-Noise Ratio) goes outside of the allowed operating region, the SS requests a change to a new burst profile using one of two methods

1. If the SS has been granted uplink bandwidth, it shall send

a DBPC-REQ message in that allocation. The BS responds with a DBPC-RSP message.

2. If grant is not available and the SS requires a more robust burst profile on the downlink, it shall send a RNG-REQ message in an Initial Ranging interval.

– Note : using the Basic CID of the SS

Downlink Burst Profile Change Request (DBPC-REQ)

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Uplink Channel Descriptor (UCD) message • Configuration Change Count

– Incremented by one (modulo 256) by the BS whenever any of the values of this channel descriptor change.

– This value is also referenced from the UL-MAP messages.

• UCD Count

– Matches the value of the Configuration Change Count of the UCD, which describes the uplink burst profiles that apply to this map.

• The Uplink_Burst_Profile is a compound TLV

encoding that associates with a UIUC,

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Burst Profile Transition

Transition to a more robust operational burst profile.

As SS receives unclear signals!

Ranging request (RNG-REQ) or downlink burst profile change request (DBPC-REQ)

(page 8)

C/(N+I) :carrier to noise and interference ratio

DL-MAP

DL Data more or equally robust as DIUC k

RNG-RSP or DBPC-RSP (at DIUC k)

Continue monitor DL data on DIUC more or equally

robust as DIUC n

Continue monitor DL Data on DIUC more or

equally robust as DIUC k

DL Data more or equally robust as DIUC k

RNG-REQ or DBPC-REQ change to DIUC k

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Burst Profile Transition

Transition to a less robust operational burst profile.

As SS receives strong signals!

C/(N+I) :carrier to noise and interference ratio

DL Data more or equally Robust as DIUC n

DBPC-REQ change tp DIUC m

DBPC-RSP (at DIUC m )

DL Data more or equally Robust as DIUC m

Start monitor DL data on DIUC more or

equally robust as DIUC m

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Burst Profile Threshold

• C/(N+I) :carrier to noise and interference ratio

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Map Relevance and Synchronization (TDD) ATDD : adaptive time division duplexing

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Map Relevance and Synchronization (FDD)

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Map Relevance • WirelessMAN-SC PHY & WirelessMAN-OFDM PHY

– Allocation Start Time (AST) is subject to the following limitations:

» FDD : • minimum AST value = round trip delay + Tproc , • maximum AST value = Tf (i.e., the beginning of the next frame).

» TDD : the AST value is either the ATDD split or the ATDD split + Tf.

• The allocation shall be within a single frame.

• WirelessMAN-SCa PHY & WirelessMAN-OFDMA PHY

– Allocation Start Time shall be subject to the following limitations:

» Minimum value: Allocation Start Time Tf » Maximum value: Allocation Start Time < 2 × Tf

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Adaptive Antenna System

• A system adaptively exploiting more than one antenna to improve the coverage and the system capacity

• Adapt the antenna pattern and concentrating its radiation to each individual subscriber

• The spectral efficiency can be increased linearly with the number of antenna elements

– steering beams to multiple users simultaneously so as to realize an inter-cell frequency reuse

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Adaptive PHY • Adaptive modulation

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Optional MAC AAS Support Support in WirelessMAN-SCa, OFDM, and OFDMA

• signal-to-noise ratio (SNR) gain realized by

coherently combining multiple signals, and the ability to direct this gain to particular users.

• Reduce interference

• MIMO/SIMO/MISO.

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Optional MAC AAS Support

• Provides a mechanism to migrate from a non-AAS system to an AAS enabled system

– dedicating part of the frame to non-AAS traffic and part to AAS traffic

time

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Optional MAC AAS Support • Alerting the BS about presence of a new SS in an AAS

system – AAS BS may reserve a fixed, pre-defined part of the frame as

initial-ranging contention slots (called AAS-alert-slots) for this alert procedure

• FDD/TDD support – use channel state information of both downlink and uplink – Two ways :

» (reciprocity) using the uplink channel state estimation as the downlink channel state (TDD)

» (feedback) transmitting the estimated channel state from the SS to BS. (FDD or TDD)

– using two MAC control messages: » AAS-FBCK-REQ and AAS-FBCK-RSP » The BS shall provide an uplink allocation to enable the SS to transmit

this response. » Using FDD, the BS shall issue AAS-FBCK-REQ messages. » Using TDD, the BS may issue AAS-FBCK messages. (pp. 165)

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Scheduling Flexibility

Allows scheduling flexibility

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Uplink TDD/FDD Subframe

UIUC: Uplink Interval Usage Code

(ranging) (band. req)

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TDD Downlink Subframe

DIUC: Downlink Interval Usage Code

Well known

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Receive/transmit Transition Gap (RTG) in TDD

• A gap between the uplink burst and the subsequent downlink burst in a TDD transceiver.

– Not applicable for FDD systems – transmit/receive transition gap (TTG) : similar

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FDD Downlink Subframe

• TDMA portion: transmits data to some half-duplex SSs (the ones scheduled to transmit earlier in the frame than they receive)

– Need preamble to re-sync (carrier phase)

Well known

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Nine Data Rates in 802.16

• Modulation Schemes : QPSK, 16-QAM and 64-QAM • 20 MHz/channel (4M PSs/frame/ms = 16Msymols/ms)

– 32Mbps / 64Mbps / 96Mbps • 25 MHz/channel (5M PSs/frame/ms = 20Msymbols/ms)

– 40Mbps / 80Mbps / 120Mbps • 28 MHz/channel (5.6M PSs/frame/ms = 22.4Msymbols/ms)

– 44.8Mbps / 89.6Mbps / 134.4Mbps

US

European 0.5, 1 or 2 ms

Uplink mandatory

downlink mandatory

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Data Rate in 802.16e OFDMA

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10-66 GHz PHY parameters

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Uplink PHY

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Downlink PHY

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Shortened FEC blocks—TDMA/TDM case • Reed-Solomon over Galois field GF(256)

TDMA w/ TDM w/o

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IEEE 802.16a

Medium Access Control Modifications and Additional Physical Layer Specifications for 2-11 GHz

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802.16a PHY Alternatives

• Different Applications, Bandplans, and Regulatory

• OFDM (WirelessMAN-OFDM Air Interface) – 256-point FFT with OFDM (TDD/FDD)

• OFDMA (WirelessMAN-OFDMA Air Interface)

– 2048-point FFT with OFDMA (TDD/FDD) – CDMA ranging code

• Single-Carrier (WirelessMAN-SCa Air Interface)

– TDMA (TDD/FDD) – BPSK, QPSK, 4-QAM, 16-QAM, 64-QAM – Most vendors will use Frequency-Domain Equalization for solving

delay spread issue

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Key 802.16a MAC/PHY Features

• 2-11GHz • License-exempt band 5-6 GHz • OFDM/OFDMA support • ARQ • Space-Time Coding (STC)

– There are two transmit antennas on the BS side and one reception antenna on the SS side.

• Dynamic Frequency Selection (DFS) – license-exempt

• Adaptive Antenna System (AAS) support • Mesh Mode

– Optional topology for license-exempt operation only (TDD only) – Subscriber-to-Subscriber communications (Mesh mode) – Complex topology and messaging

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Features • OFDM (WirelessMAN-OFDM Air Interface)

– Two contention based BW request mechanisms 1. Bandwidth Request Header 2. Focused Contention Transmission with Contention Code over

Contention Channel consisting of 4 carriers

• OFDMA (WirelessMAN-OFDMA Air Interface) – Two contention based BW request mechanisms

1. Bandwidth Request Header 2. Specifies a Ranging Subchannel and a subset of Ranging Codes

that are used for contention-based BW requests (CDMA mechanism)

• The WirelessHUMAN system provides optional support for Mesh topology.

– Unlike the point-2-multipoint (PMP) mode, there are no clearly separate downlink and uplink subframes in the Mesh mode.

HUMAN : High-Speed Unlicensed Metropolitan Area Network

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Mesh-based WirelessMAN

Source: Nokia Networks

Roofnet ??

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WirelessHUMAN Mesh deployment model

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Mesh Networks • Mesh systems typically use omnidirectional or 360°

steerable antennas, but can also be co-located using sector antennas.

• Directed Mesh (DM) : The realization of a physical mesh using substantially directional antennas.

• Nodes : systems in Mesh networks – Mesh BS : a system that has a direct connection to backhaul

services outside the Mesh network. – Mesh SS : all the other systems of a Mesh network

• Neighbor : The nodes with which a node has direct links • Neighborhood :Neighbors of a node form a neighborhood

(one-hop) • Extended neighborhood : all the neighbors of the

neighborhood (two-hops)

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Mesh Networks

• Using distributed scheduling, all the nodes including the Mesh BS shall coordinate their transmissions in their two-hop neighborhood and shall broadcast their schedules (available resources, requests and grants) to all their neighbors.

• The schedule may also be established by directed uncoordinated requests and grants between two nodes. (Optionally)

– Nodes shall ensure that the transmissions do not collide with the traffic scheduled by any other node in two-hop neighborhood.

• Both the coordinated and uncoordinated scheduling employ a three-way handshake

– Request/Grant/Confirm

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Mesh Networks • Using centralized scheduling, the Mesh BS shall gather

resource requests from all the Mesh SSs within a certain hop range.

• Ensure collision-free scheduling over the links in the routing tree

• Determine the amount of granted resources for each link – each node shall compute it by using the predetermined

algorithm with given parameters. • QoS is provisioned over links on a message-by-message

basis.

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Mesh Networks • 48-bit universal MAC address • When authorized to the network the node receives a 16-bit

node identifier (Node ID) upon a request to the Mesh BS – Node ID is transferred in the Mesh subheader, which follows

the generic MAC header, in both unicast and broadcast messages.

• For addressing nodes in the local neighborhood, 8-bit link identifiers (Link IDs) shall be used.

• The Link ID is transmitted as part of the CID in the generic MAC header in unicast messages.

• The Link IDs shall be used in distributed scheduling to identify resource requests and grants.

• Since these messages are broadcast, the receiver nodes can determine the schedule using the transmitter’s Node ID in the Mesh subheader, and the Link ID in the payload of the MSH-DSCH (Mesh Mode Schedule with Distributed Scheduling) message.

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Mesh Networks

8 bits

Messages with larger Drop Precedence shall have higher dropping likelihood during congestion.

Link ID

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Mesh Networks Frame Structure

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IEEE 802.16 , 16a and 16e

Mesh topology * 5-6GHz

5MHz/channel ; 200 channels

Mesh topology *

HUMAN : High-Speed Unlicensed Metropolitan Area Network

mobile

mobile

mobile HARQ

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Spectrum

GHz 1 3

2 4

UNII ISM

5

International Licensed

US Licensed

Japan Licensed

International Licensed

• 802.16a has both licensed and license-exempt options • License

• 2.3(Korea), 2.5(U.S.), 3.5(various countries), 4.8 GHz(Japan)

• License-exempt • 2.4, 5.8 GHz (ISM)

6

Unlicensed National Information Infrastructure (U-NII) industrial, scientific and medical (ISM)

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Licensed Band

• Licensed Band: 2.5 GHz and 3.5 GHz

– License band has a more generous power budget

– Federal Communication Commission (FCC) has create the Broadband Radio Service (BRS) for wireless broadband access

» 2.495 GHz ~ 2.690 GHz bands (US) » Question : what will happen if we design a gateway box

with 2.4GHz 802.11b/g and 2.5GHz 802.16x NICs ?

– European Telecommunications Standards Institute (ETSI) has allocated the 3.5 GHz band

» Originally used for Wireless Local Loop (WLL)

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Licensed-Exempt Band

• Licensed-Exempt Band: 5 GHz

– The majority usage around world is 5.15-5.35 GHz and 5.725-5.825 GHz

– Some governments and service providers concern the usage of the band could affect critical public and government communication networks

» UK is currently introducing restriction on certain 5 GHz channels and enforcing the use of DFS function

» Mexican government is moving toward licensing at least one of the 5 GHz “to benefit the people”

Dynamic Frequency Selection

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Spectrum

• Band and frequencies available for WiMAX

Band Frequencies License Required Availability

2.5 GHz 2.5~2.69 GHz Yes Allocated in Brazil, Mexico, some Southeast Asian countries and U.S. Ownership varies by country

3.5 GHz 3.3~3.8 GHz (primary 3.4~3.6 GHz)

Yes, in some countries

In most countries, the 3.4 GHz to 3.6 GHz band is allocated for broadband wireless

5 GHz 5.25~5.85 GHz No In the 5.725 GHz to 5.85 GHz portion, many countries allow higher power output (4W), which can improve coverage

Source : Intel White Paper

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Dynamic Frequency Selection

• DFS is mandatory for license-exempt operation • A channel selection algorithm is required for uniform channel

spreading across a minimum number of channels

• DFS procedures – Testing channels for primary users

» A BS or SS cannot use a channel which contains primary users – Discontinuing operations after detecting primary users

» If a BS or SS is operating in a channel and detects primary users – Detecting primary users

» Each BS and SS shall use a method to detect primary users in a channel

– Scheduling for channel testing » A BS may measure one or more channel itself and request SSs to

measurement – Requesting and reporting of measurements – Selecting and advertising a new channel

» A BS may decide to stop operating in a channel at any time

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Mobility-WMAN Requirement

Adopted from : 802.16e requirements from an operator’s perspective, Mar. 2003.

(0.5w) (50mw)

ant: antenna

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Technical Glossary • AAA – Authentication Authorization Accounting • BS – Base Station • BTC – Block Turbo Code • CMAC – Cipher based Message Authentication Code • CTC – Convolutional Turbo Code • DL – Down Link Transmission (BS to MS) • EAP – Extensible Authentication Protocol • FEC – Forward Error Correction scheme • FFT – Fast Fourier Transform • HMAC – Hash based Message Authentication Code • LE – License Exempt • LOS – Line of Sight • MAC – Media Access Control (Logical Link Layer) • MBS – Multicast Broadcast Services

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Technical Glossary

• MIB – Management Information Base • MIMO – Multiple Input Mulitple Output (Multi Antenna

transmissions) • MS – Mobile Station or Terminal • N-LOS – Non Line of Sight • OFDM – Orthogonal Frequency Division Multiplex • OFDMA – Orthogonal Frequency Division Multiple Access • PKM – Privacy Key Management Protocol • PMK –Pairwise Master Key • QoS – Quality of Service • STC – Space Time Coding • TEK – Traffic Encryption Key • UL – Up Link Transmission (MS to BS)

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THANK YOU !

Questions