© 2002 Chair of Communication Networks, Aachen University Performance Analysis of TETRA and TAPS...

© 2002 Chair of Communication Networks, Aachen University

Performance Analysis of TETRA and TAPS and Implications for Future

Broadband Public Safety Communication Systems

Workshop on Broadband Wireless Ad-Hoc Networks and Services, 12th-13th September 2002,

ETSI, Sophia Antipolis, France

Christian Hoymann, Dirk Kuypers, Peter Sievering, Peter Stuckmann, Bernhard Walke, Bangnan Xu

[email protected]

Mesa-Workshop, 12th-13th September 2002 2©

Overview1. Performance Evaluation of TETRA

2. Performance Evaluation of TAPS

Traffic Models

3. Implications for Broadband Public Safety Communication Systems

Centralized vs. Decentralized

Packet-oriented vs. Channel-oriented

Performance


Performance Evaluation of TETRA

TETRA Release 1 offers circuit switched speech services and connectionless or connection oriented data services with data rates at about 4.8 kbit/s

ETSI defined 10 scenarios for the comparison of TETRA systems

Scenario 10 (public or private network for airlines ground services, airport security, fire brigades) defined highest amount of offered traffic per terminal


Scenario 10: Parameters and Assumptions 2500 users Speech:

3.6 calls/h per user (PP and PMP) Mean duration 20 s

Data: Short data (100 byte): 20 h-1

Medium data (2 kbyte): 0.5 h-1

4 TETRA cells Configurations with

400, 500, 600, 700 and 800 users per cells 6 carrier frequencies, 1 control channel


Simulation ToolProtocolsformallyspecified in SDL

C++ CodeGenerator C++SDL - GR SDL - PR

PerformanceSimulation

Y

X

SDL TraceSimulator

State

Signal

Task

Start

Graphical Traceand Debug

MSC

Compile+ Link

SPEET Class Library

ADTs- Random Generator- Statistical Evaluation- Simulation Parameter- other

SDL2SPEETCL

SPEET = SDL Performance Evaluation Environment and Tools


Simulation ConceptProtocol stack for TETRA implemented in SDL

Traffic load generators for speech, FTP, HTTP, SMTP...

Propagation models: error pattern files (here: error free transmission)

->Evaluation of multi-cellular scenarios under consideration of co-channel interference


TETRA: Simulation Resultsco

mp

lem

enta

ry d

istr

ibu

tion f

unct

ion

RACH access delay [s]co

mp

lem

enta

ry d

istr

ibu

tion

funct

ion

Connection set up time [s]

Connection set up times < 300 ms are hard to achieve

400 400

800 800




Traffic Models




Performance


TETRA Advanced Packet Service IP driven requirement for higher-speed

packet data TAPS is an overlay system and heavily

based on GPRS and EDGE standards for GSM

Changes introduced are mainly concerned with the matching of frequency bands

Net bit rates up to 384 kbit/s Needs new infrastructure and terminals


Traffic Models: WWW HTTP organizes the transfer of HTML

documents WWW sessions consist of requests for a

number of objects with a certain object size

Reading time describes user‘s behavior Parameters for thin clients:

2.5 objects per page 3700 byte mean object size


Traffic Models: E-mail Load arises with the transfer of

messages performed by an SMTP user

E-mail size is characterized by two log2-normal distributions plus an additional fixed quota (300 byte) 80% text-based e-mails 20% mails with attached files


Traffic Models: WAP WAP is a suite of specifications that defines an

architecture framework containing Optimized protocols (WDP, WTP, WSP) Compact XML-based content representation (WML,

WBXML) Other mobile-specific features

A WAP session consists of several requests for a deck

Parameters used: 20 decks per session (geometric distribution) 511 byte mean CONTENT packet size (log2-normal

distribution) 14.1 s mean interval between decks (neg.-exp.)


Simulation ConceptModels for

•Mobile Station

•Base Station

•Serving GPRS Support Node

•Gateway GPRS Support Node

have been implemented


Simulation Parameters and Assumptions 1, 4, 6 and 8 fixed PDCHs C/I = 12 dB (13.5% BLEP) Coding Scheme 2 (CS-2) LLC and RLC/MAC in acknowledged mode for

WWW, e-mail and WAP Multislot capability is 1 uplink and 4 downlink

slots TCP/IP header compression in SNDCP 1500 byte maximum IP datagram size for WAP,

552 byte for TCP-based applications


GPRS: Simulation Results (1)A

pplic

ati

on R

esp

on

se T

ime [

s]

Number of MS

Pure WWW/e-mail and WAP traffic

Number of MS

Mean D

L IP

Thro

ug

hput

per

use

r [k

bit

/s] Pure WWW/e-mail and WAP traffic

4PDCH

4PDCHWWW

WWW

e-mail

e-mail

WAP, 1PDCH WAP

WAP


GPRS: Simulation Results (2)A

pplic

ati

on R

esp

on

se T

ime [

s]

Number of MS

Traffic Mix

Number of MS

Traffic Mix

Mean D

L IP

Thro

ug

hput

per

use

r [k

bit

/s]

WAP

E-mailWWW

WWWE-mail

WAP




Traffic Models




Performance


Implications for Broadband Public Safety Communication Systems

Self-organizing networks can work without infrastructure and can be rapidly deployed. Especially beneficial for temporary application scenarios extension of radio coverage of fixed

infrastructure radio networks disaster relief

Robust network as departure and failure of nodes will not cause a failure of the whole network


Centralized vs. Decentralized Self-organizing seems to mean that no central

control will be needed. Provision of Quality of Service (QoS)

requirements may be easily realized by a central controller.

Centralized solutions suffer from Increased hardware requirements for central controller

in a broadband wireless network Temporary chaos caused by failure or departure of the

selected central controller Direct Mode and multihop communication can not be

realized efficiently Neighboring central controllers must use different

frequencies => Dynamic channel allocation not easy



The Distributed Coordination Function (DCF) of IEEE 802.11 is fully decentralized and self-organizing, but can not guarantee QoS.

Provision of QoS requirements of high performance multimedia applications in a packet-oriented self-organizing wireless networks appears to be impossible.


Wireless Channel-oriented Ad-hoc Multihop Broadband Network

Inspired from GPRS and DECT concepts: From GPRS: statistical multiplexing From DECT: dynamic channel selection

Ability to operate in a fully distributed and efficient manner

Meets QoS demands for different services Transmission of packets is channel-

oriented


The Hidden Station Problem Hidden Station: can not sense transmission of sending

WT, but causes interference to the receiving WT, if it transmits.

Hidden Stations may degrade the network performance substantially.

Solutions Busy Tone: sent by the receiving WT to make hidden station

aware of ongoing transmission and prevent it from interfering. A separate narrow band channel and additional hardware is needed.

RTS/CTS: RTS sent by sending WT. Receiving WT answers with CTS. WTs that receive RTS and/or CTS deffer their access according to transmission duration information in RTS/CTS packets. Some cases remain where due to interference hidden stations can not receive the CTS packet.


W-CHAMB: E-signal Solving the hidden station problem completely

through transmission of E-signals in minislots.

VB

R P

ack

et

dro

ppin

g p

robabili

ty

Traffic load

Scenario: 20 WTs

Mix of 50% ABR and 50% VBR traffic

PER=3%

Connectivity=0.58

No E-signal: RTS/CTS mechanism

Minislot length: 10% of normal slot length

With E-Signal

No E-Signal


W-CHAMB: Network Connectivity Connectivity=Mean number of neighbors,

normalized by the maximum number

Thro

ugh

put

[%]

Traffic load

C=0.24

C=0.60

C=0.93

Throughput increases linearly with traffic load until saturation

Packet dropped, if maximum delay of 300 ms is exceeded

Smaller connectivity reduces system throughput

Length of connections (hop count) is reduced


Conclusions Traffic performance of existing TETRA and

(E)GPRS systems give lower bounds for achievable delays and throughput in broadband communication systems

Channel oriented packet transmission is appropriate to control QoS in a self-organizing wireless network

A network with decentralized control is best suited for the operation of a self-organizing wireless network

Performance analysis by simulation gives input in early stages of standardization


Questions?

Performance Analysis of TETRA and TAPS and Implications for Future Broadband Public Safety Communications Systems

Chair of Communication Networks, Aachen University

© 2002 Chair of Communication Networks, Aachen University Performance Analysis of TETRA and TAPS...

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