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Scheduling in Wireless Systems

Scheduling in Wireless Systems

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Scheduling in Wireless Systems

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  1. Scheduling in Wireless Systems

  2. CDMA2000: Overall Architecture Mobile Station

  3. Mobile Station Rm Um RAN TE2 MT2 Mobile Station • Reference Points (Interfaces) • TE2 : Terminating Equipment 2 • MT2 : Mobile Terminal 2 • RAN : Radio Access Network • Connectivity to the network • External device (Laptop) • Data processing device • Phone service (voice)

  4. Base Station Base Station A11 A9 A7 PCF PDSN Signaling Signaling BSC BSC Signaling A8 A10 Um User Traffic User Traffic Abis Abis A1 (Signaling) MS A3 BTS BTS A2 (Voice) MSC User Traffic, Signaling A5 (CS data traffic) Radio Access Network (RAN) • BSC : Base Station Controller • BTS : Base Transceiver Station • PCF : Packet Control Function • PDSN : Packet Data Serving Node • MSC : Mobile Switching Center • CS : Circuit-Switched

  5. Base Transceiver Station (BTS) • Terminating the radio links with the mobile station • RF resources such as frequency assignments, sector separation, transmit power control • BTS connects to BSC through un-channelized T1 facilities or direct cables in co-located equipment (Abis) • The protocols are proprietary and are based on High-level data link control (HDLC) • Typically terminates the IS-2000 LAC/MAC protocols for common channels, although in some implementations such protocols are terminated at the BSC • In case of dedicated channels, the BTS exchanges physical layer frames with the BSC over Abis interface • Typically equated to the physical site of the wireless network where antennas are located • 3-cell BTS configuration is most common (max. up to 6 cell BTS)

  6. Base Station Controller (BSC) • Call processing • Radio resource management • Mobility management • Transmission facilities management • SDU (Selection/distribution unit) : when soft handoff, this selects the best incoming air interface data frame from the receivers • Vocoder • BSC-BTS : Abis a set of trunks : backhaul • BSC-MSC : A1/A2/A5  a set of trunks : fronthaul

  7. Packet Control Function (PCF) • Maintains the status of the radio resources associated with a packet data call  bursty traffic • Main functionality is to direct PPP connection requests from TE to the appropriate PDSN that should handle the TE (or from BS to PDSN) • Control between active period and inactive period • Can be a standalone device serving multiple BSCs, or it can be implemented within one BSC

  8. CDMA 1xEv-DO • Evolution of CDMA2000 3G • Data only • Some radio resource management (RRM) functions moved from BSC to BTS • Packet scheduling in BTS • AMC • HARQ • Downlink data rate • 2.4Mbps in Rev. 0 • 3.1Mbps in Rev. A • 4.9Mbps in Rev. B • Single user per time slot • No power control • Rate control important • Slot size 1.67ms

  9. Scheduling algorithms • Round robin • Max C/I • Proportional Fair • Moving average of throughput • User selected • Policy-based QoS-aware Scheduling

  10. Example: Policy Rules • Gold and Silver Classes • Gold user’s min. throughput: 128kbps • Silver user’s min. throughput: 64kbps • Rule 1 • All gold users have higher priority and should achieve 128kbps. • Rule 2 • Silver users should have higher priority than any gold user whose throughput is higher than 128kbps. • Rule 3 • Once all gold and silver users have received their minimum throughput, the remaining should be distributed such that the ratio of the th(gold)/th(silver)=2.

  11. BTS Function Architecture

  12. Marginal Utility Function

  13. Fixed MSs

  14. Overloaded

  15. Mobility

  16. Fairness