Scheduling in Wireless Systems

2

CDMA2000: Overall Architecture

Mobile Station

3

Mobile Station

• Reference Points (Interfaces)

TE2 MT2 RANRm Um

Mobile Station • 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)

Interface Entities Applicable standard

Rm TE2 – MT2 IS-707

Um RAN - MS IS-2000/IS-707

4

Radio Access Network (RAN)

MS

A7Base Station

BSC

BTS

Abis

PCF PDSN

MSC

Base Station

BSC

BTS

Abis

Um

Signaling

A3

User Traffic, Signaling

A9

A8

Signaling

User Traffic

A1 (Signaling)

A2 (Voice)

A5 (CS data traffic)

A11

A10

Signaling

User Traffic

• 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