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894415005 Chih-Chuan Cheng

The Network Simulation NS-2 NIST add-on

IEEE 802.16 model (MAC+PHY)

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Outline Background

Fixed WMAN+Mobile WMAN 802.16 Deployment Inside WiMax: Coverage Transmission Parameters in MAC Messages

Contention Resolution NIST: IEEE 802.16 model (MAC+PHY)

MAC module structure MAC PDU format Bandwidth Allocation and Request

Mechanisms Parameters Statistics

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Fixed WMAN+Mobile WMAN

Rural

industrial

SOHO

PTP backhaul

BS

BS

First/Last Mile

Civic& Business Building802.16-2004

802.16e

Point to Multipoint

Global Network

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802.16 Deployment

5~15% ~18% ~39% ~28%

64QAM

16QAM

QPSK

BPSK

Effective channel

capacity at

maximum range

=3.8Mbps

2.0km 3.0km 4.4km 5.2km

Inside WiMax: Coverage

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Transmission Parameters in MAC Messages

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Contention Resolution Collisions may occur during Initial

Ranging and Request intervals defined by their respective IEs

The BS controls assignments on the uplink channel through the UL-MAP messages and determines collisions

An SS can have multiple uplink service flows (each with its own CID), contention resolution is done on a per CID basis.

In the UCD message: Request Backoff Start / End (for BW Request) Ranging Backoff Start / End (for Initial

Ranging)

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Contention Resolution Algorithm

Contention resolution is based on a truncated binary exponential backoff The initial backoff window and maximum backoff

window controlled by the BS These values are as part of the UCD message

and power-of-two. E.g. 4 for (0,15) window; 10 for (0,1023)

The SS shall randomly select a number of contention within its backoff window

The random value is the number of contention transmission opportunities that the SS shall defer before transmitting

After a contention transmission, the SS waits for a Data Grant Burst Type IE in a subsequent map (or waits for a RNG-RSP message for initial ranging).

Once received, the contention resolution is complete

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Contention Resolution Algorithm

The SS shall consider the contention transmission lost if no data grant has been given within T16 ( or T3 for initial ranging). T16:10ms(min), QoS(max);T3:200ms The SS shall increase its backoff window by a

factor of two, as long as it is less than the maximum backoff window.

Retry limits: Request Retries for BWR; Contention Ranging Retries for initial ranging.

Retry limit is independent of initial and maximum backoff windows that defined by the BS

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Example of Contention Resolution

Assume that Three SS (SS1,SS2 and SS3) compete to send BW Request The Broadcast Request IE = 2 transmission opportunities

(the Broadcast Request IE is part of UL-MAP determined by BS)

The initial backoff window is 0 to 15 The random values for each SS are: 2 (SS1), 3 (SS2) and 5

(SS3)

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Contention Resolution

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MAC module structure~ns2/wimax/mac802_16(/BS/SS).h

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MAC PDU format

~ns2/wimax/mac802_16pkt.h

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Bandwidth Allocation and Request Mechanisms

~ns2/wimax/scheduling/contentionslot.h

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Bandwidth Allocation and Request Mechanisms

~ns2/wimax/scheduling/contentionrequest.h

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Parameters

/ns2.31/tcl/lib/ns-wimax.tcl Mac/802_16 set rng_backoff_start_ 2

Mac/802_16 set rng_backoff_stop_ 6 Mac/802_16 set bw_backoff_start_ 2 Mac/802_16 set bw_backoff_stop_ 6

Mac/802_16 set contention_rng_retry_ 16 Mac/802_16 set request_retry_ 2 ;#16

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Statistic

Some statistics are collected at the MAC sublayer. The following command is used to display their values during the simulation.

-Mac/802.16 set print_stats_ true

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Bandwidth Request (SstoBS and BstoSS)WimaxTimer

start()stop()pause()resume()

WimaxBackoffTimerhandle()pause()resume()

ContentionRequestexpire()starttimeout()pause()resume()

BwRequestexpire()getCID()

ContentionSlotgetBackoff_start()getBackoff_stop()getSize()setBackoff_start()setBackoff_stop()setSize()resumeTimer()pauseTimer()

BwContentionSlotaddRequest()removeRequest()removeRequests()getRequest()resumeTimer()pauseTimer()