© 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 Overview 1.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 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 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 Simulation Tool Protocols formally specified in SDL Y X SPEET Class Library ADTs - Random Generator - Statistical Evaluation - Simulation Parameter - other SDL2SPEETCL SPEET = SDL Performance Evaluation Environment and Tools

© Mesa-Workshop, 12th-13th September 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 TETRA: Simulation Results complementary distribution function RACH access delay [s] complementary distribution function Connection set up time [s] Connection set up times < 300 ms are hard to achieve

© Mesa-Workshop, 12th-13th September Overview 1.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 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 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 Traffic Models: Load arises with the transfer of messages performed by an SMTP user size is characterized by two log 2 -normal distributions plus an additional fixed quota (300 byte) 80% text-based s 20% mails with attached files

© Mesa-Workshop, 12th-13th September 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 Simulation Concept Models for Mobile Station Base Station Serving GPRS Support Node Gateway GPRS Support Node have been implemented

© Mesa-Workshop, 12th-13th September 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, 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 GPRS: Simulation Results (1) Application Response Time [s] Number of MS Pure WWW/ and WAP traffic Number of MS Mean DL IP Throughput per user [kbit/s] Pure WWW/ and WAP traffic 4PDCH WWW WAP, 1PDCH WAP

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

© Mesa-Workshop, 12th-13th September Overview 1.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 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 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 Packet-oriented vs. Channel-oriented The Distributed Coordination Function (DCF) of IEEE 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 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 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 W-CHAMB: E-signal Solving the hidden station problem completely through transmission of E-signals in minislots. VBR Packet dropping probabilityTraffic 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 W-CHAMB: Network Connectivity Connectivity=Mean number of neighbors, normalized by the maximum number Throughput [%] 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 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 Questions? Performance Analysis of TETRA and TAPS and Implications for Future Broadband Public Safety Communications Systems Chair of Communication Networks, Aachen University