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

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 ,

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

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  1. 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 psi@comnets.rwth-aachen.de

  2. Overview • Performance Evaluation of TETRA • Performance Evaluation of TAPS • Traffic Models • 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. ADTs - Random Generator - Statistical Evaluation • Simulation Parameter • other Simulation Tool Protocols formally specified in SDL Y X SDL2SPEETCL SPEET = SDL Performance Evaluation Environment and Tools SPEET Class Library Mesa-Workshop, 12th-13th September 2002

  6. Simulation Concept • Protocol 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. complementary distribution function complementary distribution function RACH access delay [s] Connection set up time [s] TETRA: Simulation Results 800 800 400 400 Connection set up times < 300 ms are hard to achieve Mesa-Workshop, 12th-13th September 2002

  8. Overview • Performance Evaluation of TETRA • Performance Evaluation of TAPS • Traffic Models • 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 Concept • Models 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. Pure WWW/e-mail and WAP traffic Pure WWW/e-mail and WAP traffic Application Response Time [s] Mean DL IP Throughput per user [kbit/s] Number of MS Number of MS GPRS: Simulation Results (1) 4PDCH WWW 4PDCH e-mail e-mail WWW WAP, 1PDCH WAP WAP Mesa-Workshop, 12th-13th September 2002

  16. Traffic Mix Traffic Mix Application Response Time [s] Mean DL IP Throughput per user [kbit/s] Number of MS Number of MS GPRS: Simulation Results (2) E-mail WWW WAP WWW E-mail WAP Mesa-Workshop, 12th-13th September 2002

  17. Overview • Performance Evaluation of TETRA • Performance Evaluation of TAPS • Traffic Models • 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. VBR Packet dropping probability Traffic load W-CHAMB: E-signal • Solving the hidden station problem completely through transmission of E-signals in minislots. 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 No E-Signal With E-Signal Mesa-Workshop, 12th-13th September 2002

  24. C=0.93 C=0.60 Throughput [%] C=0.24 Traffic load W-CHAMB: Network Connectivity • Connectivity=Mean number of neighbors, normalized by the maximum number 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 Mesa-Workshop, 12th-13th September 2002

  26. Questions? Performance Analysis of TETRA and TAPS and Implications for Future Broadband Public Safety Communications Systems Chair of Communication Networks, Aachen University Mesa-Workshop, 12th-13th September 2002

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