on the use of cellular technology for digital tv bi-directional return channel services guilherme d....

2COPPE/UFRJCETUC/PUC-RIO

Summary

Motivation & GoalsCdma2000 1xEV-DO: OverviewTraffic Model EV-DO Model: Layers 1 e 2Experiments, Results and DiscussionConclusions


Motivation & Goals

Evaluate EV-DO rev.0 as a alternative for the return channel of the Digital TV: Throughput Delay User population Fairness

Could we do better?


Cdma2000 1xEV-DO: Overview

Reverse Link

Rates from 9.6 to 153.6Kbps per user

BPSK modulation 53.30ms packets

Besides the data channel Control Channel

Power controlled: - open loop - closed loop

CDMA

Phase reference for demod.; Channel timing

Forward link rate sent to the BS

Reverse RateIndicator

Pilot DRC RRI ACK

Forward channel data packets acknowledgment



Always at max. power

1.67ms TDM slots

Forward Link

Rates from 38.4kbps to 2.4Mbps through adaptive coding/modulationDepends on the state of the forward linkHigher bit rates: lower robustness to channel impairments

PFS recommended for slot allocation

Main goal: throughput



Forward Link (more...) Four Packet Interlacing

Avoids temporary monopolization of slots

Early Termination Gradual redundancy

Besides the data channel Control Channel

Pilot RPC RA Bit

open loop power control

closed-loop power control

congestion control

Always at max. power

1.67ms TDM slots


Tangram-II Simulation Model Overview Simulation Tool:

Tangram-II (Federal University of Rio de Janeiro – Brazil)

Why Tangram-II instead of NS? Modeling is done through a high level interface: simplicity Includes additional high-level constructs to facilitate the modeling task

COPPE/UFRJCETUC/PUC-RIO


Proposed model

Detailed (Physical and Link layers) EV-DO model Related work typically:

Physical layer modeling Lack of detailed traffic model

Few works modeling higher layers: No open-source model presenting system capacity results

as a function of user population No detailed fairness analysis

• Almost no clues on what could be done about fairness


Traffic Model

Assumptions There is no users entering or leaving the

system

No mobility – predominant scenario in the BDTvS


Traffic Model (more...)

Web users, on-off source

COPPE/UFRJCETUC/PUC-RIO


EV-DO Model

Assumptions:

A single EV-DO cell, no setorization: Thus, no soft-handoff

Early Termination not implemented Static users: low channel diversity


EV-DO Model: Physical layer

Propagation Total power loss Ltotal[dB]

dBDdBLdBLdBL penetraçãopropagaçãototal propagation penetration

Propagation loss penetration loss (10dB)

shadowing fading (log-normal dist. de mean=0 and σ =8dB dense urban scenario)



Propagation (more...) Okumura-Hata’s Propagation model for dense

urban scenario dhhahfdBL ERBTAERBcurbano loglog55.69.44log82.13log16.2655.69

97.475.11log2.3 2 TATA hdBhaCarrier frequency

(450MHz)

BS antenna height (40m)

AT height (1.5m)

dense urban correction factor :


Power Control: Open Loop

Step 1: Pilot channel sensing

Step 2: Choose the lowest power such that:• After power losses it still reaches the receiver with

enough strength to achieve the desired PER (1%)



Power Control (more…): Closed loop

Step 1: BS calculates for each user

Step 2: • Matches the received power with d

• Commands the AT to increase or decrease its power


pilot channel received energy

total perceived interfering power

thermal noise channel bandwidth (1.25MHz)


DRC Estimation: Geometric Method

Step 1: Measure the received power from the BS: X Step 2: Calculate SINR: Relation between X and the

interference from rings 1 and 2


First interferingring

Second interferingring


DRC Estimation : Step 3: Find the higher DRC that matches the

calculated SINR value, send it to the BS


PER = 1%

DRC

Rate(kbps)

SINR(dB)


Scheduling Algorithm – PFS Choose user j

Updating average rate for user i

EV-DO Model: Link layer

)(

)(maxarg

tR

tDRC

ij

i

i

ji tCRTi

ji DRCitCRTitCRTitRitRi

se 0)(

se )()()()1()1(

Last DRC value Received from user i

User i average transmission rate

PFS “fairness” parameter

User i current transmission rate


Congestion Control Noise rise – δR

δR =Nt/N0

δR = 5 as a threshold for the RA bit activation

• If the base station activates the RA Bit, ATs decreases its reverse date rate transmissions

EV-DO Model: Link layer

total interfering power

thermal noise power


Experiments: Considerations Dense urban scenario

Web user population: from 10 to 80

Interest Metrics: Throughput; Delay;

Fairness Description0 Value Unit

AT Maximum Power 23 dBm

Antenna Maximum Power 55.8 dBm

Penetration Loss 10 dB

Thermal Noise -165 dB

PFS α 0.001

Cable loss 3 dB

Antenna Gain 17 dB

AT Sensibility -119 dB


Results: User Throughput vs. Pop. and zone

Zone

Population

Th

rou

gh

pu

t (K

bp

s)

Decreasing Throughput with increasing population and distance


Results: User Delay vs. Pop. and zone

Zone

Population

De

lay

(s

)

Increasing delay with increasing population and distance


Results: User Throughput vs. PFS α

PFS α - Extreme values: no significant fairness variation α = 1 – Round Robin α = 0.001 – PFS: Strong Throughput priority

Zone

thro

ug

hp

ut

(K

bp

s)

alpha = 1.0 alpha = 0.001 Round Robin

PFS


Discussion: Fairness issue

Throughput, delay quite worse for the most distant users

PFS α parameter adjustment

Same fairness issue

Worst overall throughput


Proposed Solution: Directional Antenas

Experiment 1: Experiment 2: Experiment 3:

Distance Zone

1 2 3 … 8 9 10

… … … … … …

…

…

…

no-users (no directional antennas)2-zones

1-zone

1-user

Former experiments:


Results: User Thoughput - fairness through directional antennas

Zone

t

hro

ug

hp

ut

(

Kb

ps

)

No user 1-user 1-zone

2-zones

From white to black bars: Increasing Fairness (thoughput)

Population of 60 users


Results: User Delay - fairness through directional antennas

Zone

D

ela

y

(s

)

No user 1-user 1-zone

2-zones

From white to black bars: Increasing Fairness (delay)

Population of 60 users


Results: User throughput - directional antennas for two zones

Zone

t

hro

ug

hp

ut

(

Kb

ps

)

60 users 80 users

Increased population: No significant fairness difference The are no direction antennas in zones 1 to 8

directional antennas

on the use of cellular technology for digital tv bi-directional return channel services guilherme d....

Documents

fairness slide

throughput slide

reverse channel

bdtvs slide

low channel diversity

overview traffic model

federal university of

traffic model assumptions