Uderstanding Wimax Model With OPNET

Understanding WiMAX Model Internals and Interfaces

Network R&D

Session 1579

CONFIDENTIAL ─ RESTRICTED ACCESS: This information may not be disclosed, copied, or transmitted in any format without the prior written consent of OPNET Technologies, Inc.

© 2008 OPNET Technologies, Inc.

CONFIDENTIAL ─ RESTRICTED ACCESS: This information may not be disclosed, copied, or transmitted in any format without the prior written consent of OPNET Technologies, Inc. © 2008 OPNET Technologies, Inc. 2

1579 Understanding WiMAX Model Internals and Interfaces

Session Abstract



Agenda

IntroductionWiMAX Model OverviewLab 1: Adaptive Subframe AllocationData Plane Design• Data Packet Processing• Bandwidth Request System• Interface with Control Plane

Control Plane Design• Admission Control• Scheduler• Ranging• Measurement Module• Mobility

Lab 1: Forced Handover Initiated by the Network • ARQ• HARQ• Adaptive Modulation and Coding• MIMO

Conclusion



Agenda




Conclusion



WiMAX Specifications

IEEE 802.16-2004• Air Interface for Fixed Broadband Wireless Access Systems

IEEE 802.16e-2005• Air Interface for Fixed and Mobile Broadband Wireless Access Systems

WiMAX Forum• WiMAX System Evaluation Methodology (AATG/AWG)• Network architecture and reference points (WiMAX Forum NWG)

WiMAX End-to-End Network Systems Architecture

Flexibility• Multiple alternatives• Many optional features



OPNET's Model Development Consortia

WiMAX Model Development Consortium• Prominent network equipment manufacturers, service providers, defense

organizations• Benefits to consortium members

Early access to WiMAX modelOpportunity to influence design requirements

• Phased release schedule• Current members: 53• Founding member: Motorola• Successful past consortia

MPLS, UMTS, DOCSIS, MANET• Guidelines from WiMAX Forum AATG/AWG

Upcoming model development consortium: 3GPP LTE



WiMAX Model Features

MAC• Bandwidth allocation and request mechanisms

BS scheduler for uplink and downlinkScheduling service for UGS, ertPS, rtPS, nrtPS, BE• Multi-level ertPS allocations (15.0)

MSDU packing and fragmentationCDMA based bandwidth requests (aggregated)Piggyback bandwidth requests (incremental)

• FramingGrant consolidation per Basic CIDBurst rectangulationMAP generationIP convergence sub-layerService flow configuration and mapping of traffic to service flowsFrame reservation – implicitly modeled frame usageFrame overloading factor (15.0)




MAC• Initial and periodic ranging • ARQ

In-order SDU deliveryCumulative and selective (bitmap and block sequence) ACKsFragmentation and Packing

• Hybrid ARQ (chase combining)• Mobility

Scanning-based BS selectionHandoverAccess service network (ASN) Assisted Handover (L3)Multi-target BS

• Adaptive Modulation and Coding• Uplink open-loop power control (15.0)• Power saving (15.0)




PHY• TDD• OFDMA, SOFDMA

Preset values for SOFDMA (FFT 128, 512, 1024, 2048)• Co-channel Interference

Subcarrier to subchannel mappingPre-computed tables for subcarrier overlapPermbase

• Multi-path fadingITU models (Pedestrian A, Pedestrian B, Vehicular A, Vehicular B)Finite State Markov Channel models

• Pathloss modelingITU (Pedestrian, Vehicular)Erceg (terrains A, B, C)

• MIMO STC 2x1 (downlink only)

Network features• Multi-cell• Multi-sector (3-sector BS available)• IP Connectivity



Agenda




Conclusion



WiMAX Model Entities

Nodes• WiMAX Configuration Utility

• Subscriber Station NodeFixed or mobile (MS)Full stack

• Base Station NodeFixed (BS)IP-stack (router)



WiMAX Model Statistics

MS-node only• Per service flow statistics• Ranging and mobility• ARQ• HARQ



WiMAX Model Statistics

BS-node onlyFrame occupancyNeighbor advertisements

Both MS and BS• Per node traffic statistics• PHY statistics

MAC drops(overflow)

WiMAX MAC

Load (no MAC overhead)

WiMAX MAC

Traffic Sent (MAC overhead)

Throughput (no MAC overhead)

Traffic Received (MAC overhead)



WiMAX Reports

Admission control reports• Collected on each BS (without explicit user intervention)



One WiMAX cell

Multiple WiMAX cells/sectors

WiMAX Topologies

WiMAXWiMAXWiMAXWiMAX

WLAN Hotspot

WLAN HotspotWLAN

Hotspot

WLAN Hotspot

WiMAXWiMAX

WiMAXWiMAX

WiMAXWiMAX

WiMAXWiMAX



WiMAX Topologies (cont.)

Mobile subscriber nodes• Layer 2 Handover: WiMAX• Layer 3 Handover: Mobile IP or Access Service Network

WiMAXWiMAX

WiMAXWiMAX

WiMAXWiMAX

WiMAXWiMAX



WiMAX Model Abstractions

Four abstraction levels• Incremental accuracy, backward compatibility• Set via “Efficiency Mode” attribute of WiMAX Config node

Efficiency Enabled: Abstracted MAC without physical layer

• Most common use case: capacity planning

Framing Module Enabled: MAC (frame-by-frame) + abstracted PHY

• Most common use case: QoS and application deployment planning

• Delays more accurate than in “Efficiency Enabled”

Physical Layer Enabled: MAC (frame-by-frame) + PHY• Most common use case: PHY transmission and channel effects• Co-channel interference, multipath fading and pathloss effects• Broadcast connections

Mobility and Ranging Enabled: Previous + mobility and ranging capabilities

• Most common use case: Mobility modeling• Scanning and handover delays• Initial and periodic ranging (delays, MS power levels)



Model Architecture – Node Level

MAC and physical layerFull stack (support for TCP, UDP, IP, routing, application, etc)

wimax_ss_wkstn wimax_bs_router

WiMAX MAC module

WiMAX PHY support



wimax3_bs_atm2_ethernet2_slip4_wlan_router_adv

wimax_3sector_bs_atm2_ethernet2_slip4_wlan_router_adv

Model Architecture – Node Level (cont.)

3 sector base stations• ASN support: IP interface with 3

WiMAX portsAll WiMAX MACs connect to the same IP subnet

• Mobile IP support: 3 IP/WiMAX interfaces

Each WiMAX MAC connects to a different IP subnet

mac_interface module• oms_mux_demux_user_position_update()• oms_mux_demux_user_position_remove()



Model Architecture – Process Level

wimax_mac_module• Root process: wimax_mac.pr.m

Main data plane functions• Child processes:

wimax_bs_control.pr.m• Control plane operation for BS

wimax_ss_control.pr.m• Control plane operation for SS

wimax_bs_control

wimax_ss_control

wimax_mac



MS Control Characteristics

MS control contains mobility-related transient states

Entry & Initial Ranging

Scanning & Handover

Operational Steady StateWhen mobility mode is not used the

“idle_alt” is the operational state



Antenna Modeling Enhancements in 15.0

Enhancements for defining antenna patterns• A second axis and target point, namely

rotation handle, to prevent ambiguity with asymmetrical patterns

• Improved antenna pattern editor GUI• Formula based gain computation:

external libraries



Antenna Modeling Enhancements in 15.0 (cont.)

Multiple antennas can have separate locations on the node• Specify the position of the antenna with respect to the center of the node

Support for “bolted” antennas• Alternative to “targeted” antennas• Coverage area turns with the node when the node changes direction while

moving

x-y plane view

x-z plane view

primary and secondary targets – click and drag to set

antenna location –click and drag to set



Antenna Modeling Enhancements in 15.0 (cont.)

For all details on antenna modeling and visualization, and these new features: session 1577



Agenda




Conclusion



DL Subframe UL Subframe

Lab 1: Adaptive Subframe Allocation

Lab1: Implement a vendor-specific component• Dynamically change the resource allocated to the uplink and downlink subframes• Define an mechanism that evaluates utilization conditions and perform re-allocation of

resources

Lab1: Summary• Performing adaptive subframe allocation

Allow a more flexible balance of the system capacity between uplink and downlink segmentsVendor specific algorithms requires simulation to characterize their behavior and how they affect the system

• OPNET’s open source code facilitates vendor-specific customizations of WiMAX models

DL Subframe UL SubframeInitial partition

UL “grows”

DL Subframe UL SubframeReset



Agenda




Conclusion



WimaxT_Multiplexer

MAC Data Plane: Higher Layer Packet

Data packet arrives from higher layer

1 Classify the packet2 Enqueue packet into connection

(update BW requirements)

CID

wimax_support.h (detail)

Classifier SDUSDU Data Queue

BW requirements

Per CID data connection: WimaxT_Shaper_Queue_Elem

wimax_mac (detail)

MPDU



MAC Data Plane: Classifier

Packet is classified• Into a service class (according to classifier attributes)• (service class, destination MAC) => actual connection (CID)

Packets not matchingAssigned to “System Default” connection (Best Effort)



MAC Data Plane: Lower Layer Packet

Data packet arrives from lower layerwimax_mac (detail)

1 Associate packet with connection

WimaxT_Demultiplexer

CID SDUMPDU Reassembly

service flow

Per CID Rx data connection: WimaxT_Receiver Conn_Element

SDUs To higher layer



Bandwidth Request System

Interface with Data Plane

Aggregated request size = total_bw_required_bytes

Incremental request size = total_bw_required_bytes – last_bw_requsted_bytes



Incremental

Aggregated

As integer

As a BW request message

BW Request Type

Aggregated• CDMA based BW request (BE)• BW request for polling services• Requested size = current BW requirements• Overrides total BW requirements for the

connection at the BS


wimax_support.ex.c (detail) Query BW requirements (aggregated or incremental)

BE

nrtPS, rtPS

Examples

A

B

AA

B BE, nrtPS, rtPS

Incremental• Piggyback BW request• Difference between the size

of the last aggregated BW request sent and the current BW requirements

• Increases the BW requirements at the BS by the indicated amount

• Disable/enable via attribute



Send the MPDU

Update BW requirements

Dequeue from SDU queue (create a MAC PDU)Fragmentation and packing are performed

Grant Arrival

Grant for data packet transmission arrives from control planewimax_mac (detail) Use the grant to send a data packet

Unframed MAC efficiency mode

Framed MAC efficiency mode

1

OR2

3

4

a

b



MAC Data Exchange Chart (rtPS)

Example of uplink (SS » BS) transmission



MAC Data/Control Plane Interface

Shared memory• Parent-to-child memory: WimaxT_Data_Plane_Config

wimax_support.h

Data plane modules

Control plane modules



MAC Data/Control Plane Interface

Immediate invocations• From data plane (root process) to control (child

process) on arrival of a control message

Scheduled interrupts• From control (child process) after MAP-decoding

the list of grants is passed to the data plane (root process)

wimax_mac (detail)

wimax_ss_control

wimax_mac

wimax_support_grant_to_data_plane_give( )wimax_support.ex.c (details)



Agenda




Conclusion



Base Station Admission Control

Admission control context• Triggered by the arrival of DSA-REQ at the BS

wimax_bs_control_dsa_req_process()

Set of admitted flows stored• List admission_control_flow_lptr• Inside the WimaxT_Data_Plane_Config• Used in admission control report

wimax_bs_control_dsa_req_process()

Extract the service flow from DSA

Estimate symbols per frame (x) needed to satisfy service flow

If x < C (capacity available for admission), admit the flow

Is flow DL ?

Set up connection in data mux

yesno

Send DSA-RSP back to SS; set up state in demux

END

1

2

wimax_bs_control_is_svc_flow_admitted()

wimax_bs_control_admission_rate_check()



Base Station Admission Control (cont.)

Admission control state• Structure WimaxT_Admission_State_Info• Preserved as state variable in wimax_bs_control (one per BS)• Contains:

Available UL, DL subframe space (in modulation symbols)

Admission control functions• Defined in Function Block of wimax_bs_control• wimax_bs_control_admission_rate_check()

UGS, ertPS: guaranteed Max Sustained Traffic RatertPS: guaranteed Min Reserved Traffic Rate + polling for Max SustainednrtPS: guaranteed Min Reserved Traffic Rate + polling for Min ReservedBE: no guarantee (admitted without checks!)



Agenda




Conclusion



Scheduling for Best Effort and Polling ServicesBW request queues for Polling Services

Determine the order of grants to rtPS, nrtPS, BE connections

UGS grants bypass the scheduler order (most time sensitive)

Feed the MAP generation module with an ordered list of grants

Base Station Scheduler

rtPS, CID

8

rtPS, CID

6

nrtPS, CID

5

nrtPS, CID

1

MDRR

Modified Deficit Round Robin

BW request queues for Best Effort Service

BE, C

ID8

BE, C

ID6

BE, C

ID5

BE, C

ID1

WRR

Weighted Round Robin

PQPriority Queuing

BE is serviced only if PS queues are empty

To MAP generation



BS Scheduler and MAP Generation

Two schedulers: one for UL-MAP, one for DL-MAPAs long as there is space in the frame• Dequeue grants from the scheduler• Place grants in the frame; make MAP IE accordingly• UGS and polls are “injected” periodically, bypassing scheduler



BS Scheduler and MAP Generation



BS Scheduler Interfaces

When setting up state within the scheduler for a new flow• wimax_bs_control_sched_new_flow_notify()• Called from wimax_bs_control_dsa_req_process() if the flow is admitted

When feeding a bandwidth request in• wimax_bs_control_sched_bw_req_notify()

Called for two types of bandwidth requests• Local (from BS data plane), going into DL scheduler• Remote (from SS data plane), going into UL scheduler

When drawing a grant out• wimax_bs_control_sched_bw_req_dequeue()

Called from map generation functions (SC, OFDMA)Called as many times as needed to fill the subframe

To replace scheduler functionality• Polling services: wimax_bs_control_sched_mdrr_q_select()• Best Effort: wimax_bs_control_sched_rr_q_select



Agenda




Conclusion



Ranging Data Exchange Chart



Ranging Implementation

Transmission power control algorithm• First Initial Ranging CDMA code → ½ Maximum Transmission Power

• BS issues per-subchannel power density correction in RNG-RSPδ = (Minimum Power Density + Maximum Power Density)/2 – Rx PowerMinimum/Maximum Power Density are in dBm/subchannelCode reference: wimax_bs_control_cdma_process()

• MS adjusts the transmitted power by δ dBm/subchannelIf the resulting total power is higher than Maximum Transmission Power, MS sets total power to Maximum Transmission Power• The MS sends new CDMA code with Maximum Transmission Power• If RNG-RSP status is again Continue, the MS abandons ranging with the BS

Code reference: wimax_ss_control_rng_rsp_process()



Ranging Implementation

Enforcing a maximum number of MS per BS• BS responds to any ranging CDMA code with RNG-RSP (Abort) if

The number of MS per BS equals “Maximum Number of SS Nodes”

The MS always sends CDMA codes for the purpose of ranging• Except a one-time sending of RNG-REQ during Initial Ranging

The exception is required by the assignment of Basic CID



Agenda




Conclusion



Used for: UL/DL, RSSI and CINROne measurement module per receiver

Measurements Module

Measurement Entity

Measurement Entity

Measurement State

Notification State

Actual measurements Moving average

(of weight α)

E[X]

time

E[X^2]

time

Var[X] = E[X]^2 – E[X^2]

- Threshold → notification trigger condition: average < threshold

- Threshold evaluated after each measurement

- Client state (installed as interrupt state)

- Interrupt event handle

- Client module where remote interrupt is sent


RSSI

CINR

α

Hash

Hash

key

key

Measurement Module



Measurements Module

Measurement module APIs• To register measurement by key: wimax_support_measurement_register()

Key in BS: ss_mac_objidKey in SS: group_id (BS_ID of the serving BS)

• To set the trigger for notification when average falls below threshold: wimax_support_measurement_by_type_notification_threshold_set()

• To retrieve current average: wimax_support_measurement_by_type_read()

• To collect a new measurement from packet: wimax_phy_support_measurements_collect()



Agenda




Conclusion



Scanning Data Exchange Chart



Scanning Implementation

Initiated by the MS or BSMS scans only advertised BS neighbors (MOB_NBR-ADV)Scanning mode – synchronized between MS and BS

• Scanning – tune to different target BS (in neighbor list) and measure• Serving BS blocks all traffic to MS, as long as MS scans• BS maintains scanning state for each attached MS

• Interleaving – tune back toserving BS (normal operation)



BS Neighborhoods Formation

Based on attribute Neighborhood Membership• List of Neighborhood IDs• Each BS may belong to multiple

neighborhoods (multiple IDs)Each BS advertises all BS nodes included in the unionof all neighborhoods it belongs toMS can only performhandover with BS nodeswithin the advertisedlist



Handover and ASN Anchor Mobility



Scanning Thresholds

Scanning trigger: Multiple scanning thresholds



Scanning/Handover Integration

Handover trigger: uses HO threshold hysteresisTarget list : uses HO multi-target hysteresis



Handover Implementation

MS-initiatedHO decision taken based on scanning of neighbor BS nodes• Neighborhood of any BS is specified via attribute “Neighborhood

Membership” in lieu of backbone discovery of neighborsRetain Timer• MS can return to old BSif network entry fails withtarget

To Initial Ranging



Scanning/Handover Integration (cont.)

Transitions across mobility procedures (wimax_ss_control)



Agenda




Conclusion



Lab 2: Network Initiated Handover

Lab2: WiMAX Protocol R&D• Implement a non-standard component

Network-initiated handover based on sector capacityMS load is balanced among capacity-constrained set of BSs

Lab2: Summary• The non-standard network-initiated handover

Improves overall throughput over the WiMAX networkCan be fine-tuned for performance under a large variety of scenarios

• OPNET’s open source code facilitates vendor-specific customizations of WiMAX models



Agenda




Conclusion



ARQ

ARQ is enabled optionally on a per service flow basisCumulative, Selective Bitmap and Selective Block Sequence ACKs are supportedAPIs in wimax_arq_support.ex.c



Agenda




Conclusion



HARQ Support and Model Entities

The HARQ support package defines physical-layer functionality for HARQ operationOPNET Models support Chase Combining variant of HARQThe following are the HARQ entities explained in brief

• HARQ handler Abstraction of a “data flow pipe” between a wireless Tx-Rx pair

• HARQ channelLogical entity that lets you transfer packets over an HARQ handler Each channel has a buffer with limited configurable size associated

BS

SS

DL HARQ handler

UL HARQ handler

DL HARQ channels

UL HARQ channels



Basic HARQ Operations

Transmissions• Occur on “Open HARQ channels”• Multiple channels in a handler allow parallel transmissions• An HARQ packet can hold a MAC PDU from only one connection (CID).

Acknowledgements (ACKs)• Support for implicit (UL) and explicit ACK (DL)• Absence of ACK represents a NACK

Retransmissions• The allocation requests for HARQ retransmissions are serviced with highest priority

compared to other allocation requests in a given scheduling class

Chase combining • Signal-to-noise ratio (SNR) of the retransmitted packets is added to the SNR of the original

transmitted packet ∑=

i

k iSINRSINR )(



HARQ Functions

HARQ support code : harq_support.ex.c Location: <rel_dir>/models/std/wireless

Function definitions : harq_support.hLocation: <rel_dir>/models/std/include

Important data type• HarqT_Handle• HarqT_Transmission_State• HarqT_Receiver_State

Important functions • harq_support_transmission_channel_find()

Finds an “open HARQ channel” in the given HARQ handler for a new HARQ transmission

• harq_support_packet_transmission_prepare Prepare a MAC PDU for new HARQ transmission Prepare a MAC PDU for a retransmission

• harq_support_packet_coding_gain_calculate Computes the coding gain achieved from Chase combining



Agenda




Conclusion



AMC Implementation

CINR measurements are used to determine MCS changes• For DL, measurements are collected from MAP (collected at SS)• For UL, measurements are collected from data bursts (collected at BS)

CQICH period is provided to the SS during the network entry procedure.All the service flows with adaptive modulation use the same MCS for a given direction (UL or DL) in a SS. MCS change happens as per the AMC table.

• UL and DL have a separate AMC table for each other



AMC Implementation



AMC Functions and Files

All the functions related to AMC are available in the external file wimax_amc_support.ex.c

The MCS change algorithm is given in the function wimax_amc_modulation_coding_adapt() which is available in the file wimax_amc_support.ex.c



Agenda




Conclusion



wimax_phy_mpath_support.h

STC 2x1 MIMO Implementation

STC 2x1 MIMO is only available in DL and with multipath enabled

The STC 2x1 MIMO implementation is a part of the multipath framework of OPNET’s WiMAX models

There is an FSMC associated for every channel model and a system configuration pair

The DL system configuration is decided by this attribute in the base station:

wimax_phy_mpath_support.ex.c

The system configurations are internally handled in a data structure given on the left

Insert new system configurations

Decides the initialization of the

channel models



STC 2x1 MIMO Implementation (cont.)

The FSMC data structure consists of 3 parts • Transition Probability Matrix• A rule to convert average SNR to effective SNR based on the current channel state

Coefficients of a polynomial• Antenna power normalization factor

0 dB for single transmitter and 3 dB for 2 transmitters

wimax_phy_mpath_support.h



STC 2x1 MIMO Implementation (cont.)

The tpm and eesm_poly_coeff in an FSMC are initialized with the values obtained from offline simulations.

Initializations



Agenda




Conclusion



References

IEEE Standards• IEEE 802.16-2004• IEEE 802.16e-2005

WiMAX Forum (www.wimaxforum.org/technology/documents)• “WiMAX Forum Mobile System Profile, Version 1.0”• “WiMAX Forum Network Architecture, Version 1.2”• WiMAX Forum whitepapers (may require membership to access)

“WiMAX System Evaluation Methodology Version 2.01”“Mobile WiMAX – Part I: A Technical Overview and Performance Evaluation”, 2006“Mobile WiMAX – Part II: A Comparative Analysis”, 2006



Related Sessions

WiMAX-specific:• 1571 “Introduction to WiMAX Modeling for Network R&D and Planning”• 1827 “Introduction to WiMAX”• 1566 “Case Studies: WiMAX Networks”

Other related sessions: • 1577 “Modeling and Visualizing Antennas”• 1502 “Debugging Simulation Models - Introduction”• 1503 “Debugging Simulation Models - Advanced”• 1530 “Modeling Custom Wireless Effects”• 1538 “Case Studies: Specialized Wireless Network Modeling”• 1540 “Case Studies: Wireless Protocol Modeling”• 1550 “Accelerating Simulations Using Efficient Modeling Techniques”



Take-Away Points

OPNET’s WiMAX model suite supports a rich set of features of 802.16e standard, also following WiMAX forum recommendations

Various modeling techniques and optional abstraction approaches are implemented to significantly improve the simulation execution performance of the models

Subframe partition size is a critical system parameter that should be carefully estimated according to the application traffic expected in the WiMAX network

Implementation of 802.16e protocol requires many vendor specificalgorithms and procedures• Open source code of OPNET’s WiMAX models can be customized to help you

design and analyze any vendor specific feature implementation



Appendix

WiMAX OFDMA PHY DesignMAP GenerationAcronyms



WiMAX-Specific Modeling

Pipeline stages modified for WiMAX

Pathloss models (ITU and IEEE); log-normal shadow fading

Co-channel interference model used to compute per-subcarrier interference noise

Multipath-fading correction, based on Raleigh-varying channel model

AWGN-based BLER curves

A transmitter communicates with receivers that share same PHY profile, communication direction (UL/DL)

If packet originates in the same sector as the receiver, it is valid; otherwise, it is interference

Propagation delay = 0 within same sector (to model sync to BS clock)



Co-channel Interference Assumptions

Assumptions about the two interfering sectors• Interference only between same PHY profiles• Permutation zones boundaries overlap perfectly

One zone per UL, one zone per DL (current limitation)• Subframe boundaries overlap perfectly

Frames synchronized in timeUL-DL boundaries fixed in same location (within frames)

DL Zone1 UL Zone1

DL Zone2 UL Zone2

Frequency

TimeDL subframe UL subframe

WiMAX Sector 1

WiMAX Sector 2

(co-channel interferer of 1)

Same permutation zone (e.g. UL

PUSC), but possibly different PermBases

Freq. width



Co-channel Interference Model

CoCh interference computed at the receiver, given two packets• Valid packet (signal locked to receiver)• Interference packet

Each packet carries• Subchannel range

Count overlapping subcarriers• For every pair of subchannels• Given subcarrier-to-subchannel maps

Permutation, PermBase

I = #overlapping subcarriers

#subcarriers in interfering pk. * Pinterfering pk.



Co-channel Interference Implementation

Inoise pipeline stage• Receiver pipeline stage• Invoked once for every packet

Whose reception overlaps in time with the current packetCurrent packet is the packet to which receiver is signal-locked

May be called several times for a given time interval.

Interference cumulates with

every call.



Multipath Fading

Applicable to OFDMA (SC assumed equalization in receiver)

Multiplicative correction to per-tone SNR• The multiplicative correction factor h[i] for a given tone i evolves in time• The evolution of h[i] is time correlated

EESM (per-tone SNR for all tones in subchannel) = effective SNR• EESM yields the effective SNR “equivalent” to the set of per-tone SNRs• “Equivalent” SNR = SNR for AWGN channel that produces same error rates

Feed effective SNR into BLER vs. SNR curve for AWGN channel

Retrieve BLER



Multipath Fading Implementation

Conceptual schematic

Delay portfolio(multipath

channel model)

τ1 τ2

σ1

σ2

SNR

BLER

Rx Power

(0-average multipath fading)

Noise

Interference

Avg SNR

BLER

BLER of the packet (accounting for all channel impairments, and all the coding + modulation at the tx/rx)

Modulation Coding

Instantaneous fading state

FSMC

FSMC is selected based

on the multipath channel model

EffectiveSNR



Multipath Fading Implementation

Signal to Noise Ratio pipelineForm the average SNR first (multipath fading is a zero-mean process)Add the current correction for multipath fading• The correction factor changes over time (as given by FSMC)

Called once for every interval of constant average SNR during the packet reception



Appendix




MAP Generation Interfaces

One function call per sub-frame: UL, DL• wimax_bs_control_map_generate()• First call for UL, second call for DL

Order is imposed by need to know UL-MAP overhead on DL

Two stages• Choose a set of grants to cover the current sub-frame• Generates bursts containing the grants

Amalgamate the grants into bursts: by CID, by MS (Basic CID)Map the coordinates of each burst in the frame

The two stages (choose grants, generate bursts) differ for UL, DL• UL: overhead is independent of burst order

Amalgamation can be done after mapping, by permuting bursts• DL: overhead is dependent on burst order

Amalgamation must happen in tandem with mapping



MAP Generation

Four IE Dimension TypesBurst Type1 (SC)

start symbol duration symbols

Burst Type2 (OFDMA)

start symbolduration symbolsstart subchannel

duration subchannels

start symbol

start subchannel

duration symbolsBurst Type3 (OFDMA)

OPNET interference modeled on rectangular bursts



MAP Generation Flowchart

UL-MAP generation



MAP Generation

MAP overhead minimization strategy• Amalgamate all bursts dedicated to same CID in one burst

Many IEs → one IEMAC PDU overhead saving via fragmentation and packing

Burst amalgamation differs between UL and DL• UL

Step1: decide the duration of each dim type3 UL burstStep2: permute the bursts so that same CID bursts are adjacentStep2 is done after Step1 is repeated once for each burst• wimax_bs_control_ul_ofdma_map_shuffle()

• DLStep1: amalgamate same-CID grants into one burstStep2: decide the dim type 2 coordinates of each burst• Both steps taken in wimax_bs_control_one_ofdma_map_generate()



MAP Generation

UL burst amalgamation

DL burst amalgamation



Appendix




Acronyms

AMC Adaptive Modulation And CodingARQ Automatic Repeat-RequestASN Access Service Network BE Best EffortBER Bit Error RateBLER Block Error RateBS Base StationBW BandwidthCDMA Code division multiple accessDL Downlink DOCSIS Data Over Cable Service Interface SpecificationEESM Exponential Effective SINR MappingertPS Extended Real Time Polling ServiceFSMC Finite State Markov ChainGPC Grant Per ConnectionGPSS Grant Per Subscriber StationHARQ Hybrid Automatic Repeat-RequestHO HandoverIE Information Element (in the MAP)IEEE Institute of Electrical and Electronics EngineersITU International Telecommunication UnionMANET Mobile Ad-hoc Networks



Acronyms (cont.)

MDRR Modified Deficit Round RobinMIMO Multiple Input Multiple Output MPLS Multi Protocol Label SwitchingMS Mobile StationNWG Network Working GroupnrtPS Non-Real Time Polling ServiceOFDMA Orthogonal Frequency Division Multiple AccessPQ Priority QueuingPS Polling ServiceQoS Quality Of ServicertPS Real Time Polling ServiceRSSI Received Signal Strength IndicationSOFDMA Scalable Orthogonal Frequency Division Multiple AccessSINR Signal To Interference And Noise Ratio (referred to as SNR in some slides)SNR Signal To Noise RatioSS Subscriber StationSTC Space Time CodingUGS Unsolicited Grant ServiceUL UplinkUMTS Universal Mobile Telecommunications System WiMAX Worldwide Interoperability for Microwave AccessWRR Weighted Round Robin

Documents

Uderstanding Wimax Model With OPNET