Evdo Notes

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Video Delivery over CDMA EV-DO

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Evolution of Mobile Telephone

First mobile telephone call, St. Louis, MO, June 17, 1946

(Primitive) Features

A single transmitter on a central tower

A few channels for an entire metropolitan area

At most 3 subscribers could make calls at one time (party line)

$15 per month, 30 to 40 cents per local call

80 pound equipment

Press a button to talk, release to listen

Team

Alton Dickieson

D. Mitchell

H. I. Romnes

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Evolution of Mobile Telephone

4G LTE, A 3GPP Technology

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Evolution Path

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EVDO: Evolution Data Optimized

CDMA Cell Sectoring

Red hexagon is the cell

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EVDO: Evolution Data Optimized

Broadband access radio technology

standardized by 3GPP2

Rev 0: 2.4 Mbps DL, 153 Kbps UL

Rev A: 3.1 Mbps DL, 1.8 Mbps UL

Rev B: 14.7 Mbps DL, 5.4 Mbps UL

Rev C: …

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EVDO Rev 0 Reverse Link

Reverse Traffic Channel: AT (Access Terminal) to AN

(Access Network)

Pilot channel: Channel estimation and coherent detection

RRI (Reverse Rate Indicator) channel: Indicates rate on data channel

DRC (Data Rate Control) channel: AT indicates the AN of the selected

serving sector & requested forward data rate

ACK (Acknowledgement) channel: AT informs the AN of successful

packet reception on forward channel

Data channel: Variable length packet fed into turbo encoder & then

BPSK modulated

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EVDO Rev 0 Overview

Stochastic Distributed Rate Control

Each AN computes

Sector loading by measuring RoT (total received power over thermal

noise)

Each AN broadcasts

Binary RAB (Reverse Activity Bit): congested or not based on RoT

threshold

Two rate transition probability vectors

Each AT receives all RABs and probability vectors from its active

set computes effective RAB (logical OR)

Each AT adjusts rate

Doubles, halves, or keeps the same based on available data, power

amplifier, probability vectors

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6 old channels modified, 2 new channels added

EVDO Rev A Reverse Link

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EVDO Rev A Reverse Link MAC

Comprehensive Centralized Control

Flow-oriented QoS approach

Two sided control philosophy

AN determines long-term resource for each flow (centralized)

AT determines time-critical allocation each PHY packet (distributed)

Rise-over-Thermal (RoT) control

Stability of CDMA RL is strongly related to total sector received power

Traffic-to-Pilot (T2P) power as sector resource

Adaptive token bucket access control

Unified approach to intra-AT QoS (multiple MAC flows within an

AT) and inter-AT QoS

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Traffic-to-Pilot (T2P) Power as Sector Resource

MAC-layer variable T2PInflow for each flow

Measure of RoT consumption (average transmission resource available)

T2PInflow is determined by

A single control bit (measured in each slot): Filtered RAB (FRAB)

Two load adaptive ramping functions: T2Pup(), T2Pdn()

Each AT receives all RABs from active sectors and computes Quick

RAB (QRAB) by computing logical OR

If QRAB is busy, decreases T2PInflow by T2Pdn(); else increases by

T2Pup()

Tradeoff in ramping function design

Faster ramping leads to quicker reaction to changes in sector loading,

but less RoT stability

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Adaptive Token Bucket Access Control

Converts average flow-level resource (T2PInflow) into PHY packet-

level resource (TxT2P)

One bucket for each AT flow, representing stored T2P resource

Token bucket filled every subframe with T2PInflow, and emptied

by actual TxT2P for a PHY packet transmission

RAB=0: More packets and

larger payloads can be sent

as bucket level increases at

a fast pace

RAB=1: Fewer packets and

smaller payloads can be

sent as bucket level

increases at a slower pace

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Adaptive Token Bucket Access Control

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Courtesy Qualcomm

RL MAC Algorithm

AN sends to each AT

Ramping functions: T2Pup(), T2Pdn()

T2Pmin, T2Pmax

BucketFactor() function

BurstDurationFactor

TxT2P profiles

TerminationTarget

At every slot, AT computes

QRAB (indication of instantaneous sector loading)

FRAB (indication of long-term sector loading)

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RL MAC Algorithm

Update

Update T2PInflow

Determine payload

and TxT2P profile

Update bucket level

QRAB=1 (busy)

QRAB=0 (not busy)

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Intra-AT QoS

Supports 4 different kinds of flows

Delay-sensitive low-rate (VoIP)

Delay-sensitive high-rate (fixed

rate video telephony)

Delay-sensitive elastic (video)

Delay-tolerant best effort (FTP)

MAC parameters control allocation

for each data flow in each AT

Performance of delay-sensitive

flows is unaffected by delay-

tolerant flows

AT resource allocation is the sum

of its MAC flow allocations

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Hybrid-ARQ (Automatic Repeat Request)

Packet transmissions are staggered in time

Allows the AN to demodulate and send ACK/NACK

Early termination of PHY layer packet

Each packet is transmitted using up to 4 subpackets, each subpacket

spans 4 slots (1 slot = 1.66 ms)

Capacity-Latency Tradeoff

Higher data rates through larger payload for delay-tolerant app

Lower latencies through smaller payload for delay-sensitive app

Documents

Evdo Notes