Scheduling in umts


Published on

Published in: Technology, Business
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Scheduling in umts

  1. 1. Scheduling in the UMTS enhanced uplink Camilo Orejuela Mesa & Geert Heijenk University of Twente Neill Whillans, Frank Brouwer & Sonia Heemstra de Groot Twente Institute for Wireless and Mobile Communications (WMC) Cost 290, TD(06)052 September 29, 200629-09-2006 Geert Heijenk 1
  2. 2. Problem Statement An important new technique for the UMTS enhanced uplink, as defined in 3GPP Release 6 , is fast packet scheduling. • How do different schedulers for the enhanced uplink compare? • What is the suitability of our current ns2- based simulator, for evaluating these schedulers?29-09-2006 Geert Heijenk 2
  3. 3. Outline • UMTS Enhanced Uplink • Enhanced Uplink Schedulers • Simulation • Conclusions & Future Work29-09-2006 Geert Heijenk 3
  4. 4. UMTS Architecture29-09-2006 Geert Heijenk 4
  5. 5. Enhanced Uplink High Speed Uplink Packet Access (HSUPA) – Defined for 3GPP R6 (HSDPA already in R5) • Main features – increases throughput (→5.76 Mbps) – reduces latency • Main new tecniques used: – Hybrid Automatic Retransmission Request (HARQ) – Fast Packet Scheduling (No higher order modulation)29-09-2006 Geert Heijenk 5
  6. 6. Fast Packet Scheduling • Based at the NodeB – reduces the delay – allows faster reaction than when residing at the RNC – controls the received power which is distributed among all the users in the cell.29-09-2006 Geert Heijenk 6
  7. 7. Scheduling Signalling Uplink: Downlink: – Happy bit: – Relative Grants: A single bit field indicates “up”, “down” or “hold”, whether the UE could indicating the UE to step use more resources or up, step down or hold the not. index of its allowed TFC – Total E-DCH buffer – Absolute Grants: status allows the NodeB – Highest priority logical scheduler to directly channel ID adjust the resources of – UE power headroom UEs under its control in one single command – Used transmit power?29-09-2006 Geert Heijenk 7
  8. 8. 2 extreme scheduling schemes – Users perform uplink – Only one or a set of UEs transmissions in parallel, are allowed to transmit at with a low rate, so that a given time so that the the noise rise level at the noise rise level at the NodeB does not exceed NodeB does not exceed the established the established threshold. threshold.29-09-2006 Geert Heijenk 8
  9. 9. Scheduling Procedure • UE requests resources (bit rate) • NodeB determines allowed rates for UEs, based on scheduling scheme (see next slides) Condition: – UEs must meet their required BLER – total received power below threshold (noise rise target) • NodeB sends grant (allowed rate) to UE • UE sends at granted rate – Or at lower rate if max power reached, lower grant from other nodeB, or not enough data – Delay from request to sending typically a few TTI (we assume 7, i.e. 14 ms)29-09-2006 Geert Heijenk 9
  10. 10. Schedulers (1/2) UE 4 – Rate Scheduling: UE 3 Try to grant to all UE 2 active UEs, assigning them UE 1 Rate low rates. UE 4 P – Round Robin P Scheduling: UE 3 Try to grant to a UE 2 P few UEs with the UE 1 P Rate maximum rate. TTI Time29-09-2006 Geert Heijenk 10
  11. 11. Schedulers (2/2) UE 4 UE 3 P P P P – Uplink CQI: Always selects the UE 2 UE with best UCQI UE 1 Rate and grants it with the maximum rate. UE 4 P – Rate Estimation: UE 3 P Estimate the rate UE 2 capabilities of the UEs to assign a rate. UE 1 P P Rate TTI time29-09-2006 Geert Heijenk 11
  12. 12. Simulator • Ns2-based • Detailed implementation of HARQ and fast scheduling • Single cell (fixed other-to-own cell interference ratio) • Link-level included by means of AVI: (Actual Value Interface: look-up tables for Eb/N0 BLER) • Path loss and shadowing based on position • Multi-path fading precalculated29-09-2006 Geert Heijenk 12
  13. 13. Simulation Parameters BLER 0.1 Noise Rise Ta rget 6dB TTI dura tion 2m s - 10m s Ma x UE tra nsm ission power 26dBm (-4dB) UE speed 3Km ph Cell ra dius 1.5Km Num ber of UEs 24 Tra ffic ra te per burst 250Kbps Burst period 5 sec Idle period 5 sec29-09-2006 Geert Heijenk 13
  14. 14. Total Transmitted Average Cell Power (dB) Throughput (kbps) 1800 Mean Std 1600 Rate scheduling -3.59 2.5 1400 Round Robin -5.46 3.05 Throug p ut (Kb p s) Rate Estimation -5.36 3.04 1200 Rate scheduling UCQI -9.58 7.1 1000 RoudRobin Rate Estim Sch 800 UCQI 600 400 200 029-09-2006 Geert Heijenk 14
  15. 15. Delay (sec) UE NodeB Mean Std Rate scheduling 0.36 0.22 RLC RLC Round Robin 0.22 0.16 t1 t2 Rate Estimation 0.21 0.14 MAC MAC UCQUI 0.16 1.72 PHY PHY delay=t2-t129-09-2006 Geert Heijenk 15
  16. 16. Conclusions & Future Work • Fast packet scheduling for the UMTS enhanced uplink can benefit from: – Scheduling few users at the same time with high bit rates. – Using the channel condition as a scheduling parameter to take advantage of the rapid reaction to channel variations. – Estimating the maximum rate that the UEs are able to support • To reliably compare and quantify the performance of schedulers, a multi-cell simulator is a necessity29-09-2006 Geert Heijenk 16
  17. 17. More info: – – Geert Heijenk 17