Chih-Chuan Cheng The Network Simulation NS-2 NIST add-on IEEE model (MAC+PHY)‏

2 Outline Background  Fixed WMAN+Mobile WMAN  Deployment  Inside WiMax: Coverage  Transmission Parameters in MAC Messages Contention Resolution NIST: IEEE model (MAC+PHY)‏  MAC module structure  MAC PDU format  Bandwidth Allocation and Request Mechanisms  Parameters  Statistics

3 Fixed WMAN+Mobile WMAN Rural industrial SOHO PTP backhaul BS First/Last Mile Civic& Business Building e Point to Multipoint Global Network

Deployment

5 ~15%~18%~39%~28% 64QAM 16QAM QPSK BPSK Effective channel capacity at maximum range =3.8Mbps 2.0km3.0km4.4km5.2km Inside WiMax: Coverage

6 Transmission Parameters in MAC Messages

7 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)‏

8 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

9 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

10 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)‏

11 Contention Resolution

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

13 MAC PDU format ~ns2/wimax/mac802_16pkt.h

14 Bandwidth Allocation and Request Mechanisms ~ns2/wimax/scheduling/contentionslot.h

15 Bandwidth Allocation and Request Mechanisms ~ns2/wimax/scheduling/contentionrequest.h

16 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

17 Statistic Some statistics are collected at the MAC sublayer. The following command is used to display their values during the simulation. -Mac/ set print_stats_ true

18 Bandwidth Request (SstoBS and BstoSS)‏ WimaxTimer start()‏ stop()‏ pause()‏ resume()‏ WimaxBackoffTimer handle()‏ pause()‏ resume()‏ ContentionRequest expire()‏ starttimeout()‏ pause()‏ resume()‏ BwRequest expire()‏ getCID()‏ ContentionSlot getBackoff_start()‏ getBackoff_stop()‏ getSize()‏ setBackoff_start()‏ setBackoff_stop()‏ setSize()‏ resumeTimer()‏ pauseTimer()‏ BwContentionSlot addRequest()‏ removeRequest()‏ removeRequests()‏ getRequest()‏ resumeTimer()‏ pauseTimer()‏