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Downloaded from orbit.dtu.dk on: Oct 09, 2021 Performance Analysis and Evaluation of Advanced Designs for Radio Communication Systems for Communications-Based Train Control (CBTC) Farooq, Jahanzeb Publication date: 2017 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Farooq, J. (2017). Performance Analysis and Evaluation of Advanced Designs for Radio Communication Systems for Communications-Based Train Control (CBTC). DTU Fotonik. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Performance Analysis and Evaluation of Advanced Designs for Radio Communication Systems for Communications-Based Train Control (CBTC) Jahanzeb Farooq Ph.D. Thesis November 2017 PhD Thesis DRAFT Performance Analysis and Evaluation of Advanced Designs for Radio Communication Systems for Communications-Based Train Control (CBTC) Jahanzeb Farooq Technical University of Denmark Kgs. Lyngby, Denmark 2017 To my father, for his unprecedented determination and dedication in educating me during my early school-age years spent in Libya, where no international schools were accessible. Supervisors: Lars Dittmann José Soler Kasper Tipsmark Therkildsen Technical University of Denmark DTU Fotonik Department of Photonics Engineering Ørsteds Plads, Building 343, 2800 Kongens Lyngby, Denmark www.fotonik.dtu.dk Cover photo credits: Nils Meilvang (front) Rasmus Thystrup Karstensen (back) Abstract Communications-Based Train Control (CBTC) is a modern signalling system that uses radio communication to enable the exchange of high resolution and real-time train control information between the train and the wayside infrastructure. A vast majority of CBTC systems worldwide use IEEE 802.11 Wi-Fi as the radio technology particularly due to its cost-effectiveness. The trackside networks in these systems are mostly based on conventional infrastructure Wi-Fi. It means a train has to continuously associate (i.e. perform handshake) with the trackside Wi-Fi Access Points (AP) as it moves. This is a time-consuming process associated with a certain delay. Additionally, these APs are connected to the wayside infrastructure via optical fiber cables that incurs huge costs. To address these problems, a novel design of the CBTC trackside network was proposed at Siemens. In this design, trackside nodes function in ad-hoc Wi-Fi mode, which means no associations have to be performed with them prior to transmitting. A train simply broadcasts packets. A node upon receiving these packets forwards them to the next node and so on, forming a chain of nodes. Following this chain, packets arrive at the destination. To minimize the interference, transmissions are separated on multiple frequencies. Furthermore, redundancy is introduced in the design as a node forwards packets to not only one but two of its neighbors. The research work presented in this thesis investigates the performance of this new design using computer-based simulations. A large number of scenarios were investigated, in particular with the objective of studying the resiliency, redundancy and scalability supported by the design. The results from the first phase of the study show that due to the frequency separation and redundancy inherent in this design, significantly large numbers of packets can be successfully transferred across large networks. Nonetheless, the results expose two shortcomings of the design as well. They show that the train node undermines the frequency separation guaranteed by the chain nodes as it is required to transmit on all frequencies, and, the design under-estimates the interference produced by distant nodes in ideal propagation conditions despite the frequency separation. A large number of potential solutions to minimize these shortcomings were subse- quently investigated, including adjusting the transmission range of the train, employing a lower number of radios on the train, employing more robust modulation and coding schemes, among others. Additionally, two extensions to the design were proposed that iii iv involved extending the frequency separation distance by employing additional frequencies, and, introducing a separate frequency for train-to-trackside communication. The results show that substantial improvements can be achieved with these solutions. In the last phase of the study, scenarios to investigate the impact of parameters such as the number of trains, train speed, headway distance, train’s location on the track, train direction, and track layouts, were carried out. One of the objectives of this study was to investigate if high data rates can be supported by this design, to enable non-CBTC applications on top of the typical CBTC traffic. The results for these scenarios show that while the design can successfully support the data requirements of typical CBTC traffic, enabling higher data rates is challenging when the number of data traffic flows involved becomes large. Resumé Communications-Based Train Control (CBTC) er et moderne signaleringssystem, der anvender radiokommunikation til at muliggøre udveksling af højopløsnings- og realtids togkontrolinformation mellem toget og kommunikationsinfrastruktur på strækningen. Langt størstedelen af verdens CBTC systemer anvender IEEE 802.11 Wifi som radiokom- munikationsteknologi, hovedsageligt pga. dets omkostningseffektivitet. Disse systemers trackside-netværk anvender hovedsageligt konventionel infrastruktur Wifi. Dette betyder, at et tog hele tiden skal associere (dvs. udføre handshake) med trackside-Wifi Access Points (AP) mens det kører. Dette er en tidskrævende proces som er forbundet med forsinkelse. Desuden er disse AP forbundet med Trackside-infrastrukturen med optiske fibre, hvilket giver store udgifter. For at adressere disse problemer har Siemens lavet et nyt design af CBTC trackside- netværket. I dette design benyttes trackside-AP i ad-hoc Wifi mode, hvilket betyder, at man ikke behøver at associere med et AP inden der kan kommunikeres. Et tog kan simpelthen bare broadcaste pakker. Når et AP modtager en pakke, kan det bare videresende den til det næste AP og så fremdeles og på den måde skabe en kæde af AP. For enden af kæden ankommer pakkerne til deres destination. For at minimere interferens, transmitteres der på flere frekvenser. Endvidere sikres redundans ved at et AP ikke kun sender til sin nærmeste nabo men til sine nærmeste to naboer. Den forskning, der præsenteres i denne afhandling, undersøger performance af dette nye design ved hjælp af computersimulering. Et stort antal scenarier er blevet undersøgt med det specifikke formål at undersøge resiliens, redundans og skalerbarheden af de- signet. Resultater fra første del af studiet viser at anvendelsen af flere frekvenser og den indbyggede redundans i designet muliggør at et stort antal pakker kan sendes gennem netværket. Ikke desto mindre, viste simuleringerne også to svagheder ved designet. De viste, at transmissionerne fra toget havde en negativ effekt på den garanterede frekvenssep- aration, fordi det skal sende på alle frekvenser. Desuden underestimerer designet den interferens der kommer fra andre AP under ideelle transmissionsforhold, på trods af frekvensseparationen. Et stort antal potentielle løsninger til at minimere disse to mangelfuldheder er efter- følgende blevet undersøgt, inklusive blandt andet at justere rækkevidden af togets trans- missioner, brug af færre frekvenser på toget, brug af mere robust modulation og kodning. Desuden er to udvidelser til designet blevet foreslået, som involverer brug flere frekvenser og anvendelse af en separat frekvens til tog til trackside kommunikation. Resultaterne v vi viser, at disse to forslag forbedrer designet væsentligt. I undersøgelsens sidste del er der undersøgt scenarier, der undersøger indflydelsen af en række parametre såsom antallet af tog, toghastighed, headway distance, togets position, retning og sporlayout. Et af målene med dette studie, var at undersøge om højhastighedsdatakommunikation var mulig med dette design, for det ville kunne under- støtte ikke-CBTC applikationer oven på den sædvanlige CBTC trafik. Resultaterne viser, at selvom designet fint understøtter typisk CBTC trafik, så er højhastighedsdatakommu- nikation en udfordring hvis der er mange dataflows. Preface This dissertation is submitted to the Department of Photonics Engineering at the Technical University of Denmark (DTU) in partial fulfillment of the requirements for the degree of Doctor of Philosophy (PhD). This Industrial PhD project was financed by Siemens A/S, Denmark, and partly by the Ministry of Higher Education and Science of Denmark (Innovation Fund Denmark) within the framework of its Industrial PhD Programme. The project was carried out at the Networks Technologies and Service Platforms group at the Department of Photonics Engineering at DTU, Kgs. Lyngby, Denmark, and at Siemens A/S, Ballerup,

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