© 2002 chair of communication networks, aachen university performance analysis of tetra and taps...
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© 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
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
Mesa-Workshop, 12th-13th September 2002 3©
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
Mesa-Workshop, 12th-13th September 2002 4©
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
Mesa-Workshop, 12th-13th September 2002 5©
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
Mesa-Workshop, 12th-13th September 2002 6©
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
Mesa-Workshop, 12th-13th September 2002 7©
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
Mesa-Workshop, 12th-13th September 2002 8©
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
Mesa-Workshop, 12th-13th September 2002 9©
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
Mesa-Workshop, 12th-13th September 2002 10©
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
Mesa-Workshop, 12th-13th September 2002 11©
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
Mesa-Workshop, 12th-13th September 2002 12©
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.)
Mesa-Workshop, 12th-13th September 2002 13©
Simulation ConceptModels for
•Mobile Station
•Base Station
•Serving GPRS Support Node
•Gateway GPRS Support Node
have been implemented
Mesa-Workshop, 12th-13th September 2002 14©
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
Mesa-Workshop, 12th-13th September 2002 15©
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
WAP, 1PDCH WAP
WAP
Mesa-Workshop, 12th-13th September 2002 16©
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
Mesa-Workshop, 12th-13th September 2002 17©
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
Mesa-Workshop, 12th-13th September 2002 18©
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
Mesa-Workshop, 12th-13th September 2002 19©
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
Mesa-Workshop, 12th-13th September 2002 20©
Packet-oriented vs. Channel-oriented
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.
Mesa-Workshop, 12th-13th September 2002 21©
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
Mesa-Workshop, 12th-13th September 2002 22©
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.
Mesa-Workshop, 12th-13th September 2002 23©
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
Mesa-Workshop, 12th-13th September 2002 24©
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
Mesa-Workshop, 12th-13th September 2002 25©
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