J. Choi et al.: On the Calculation of the Maximal MOT Throughput in T-DMB Manuscript received July 14, 2007 0098 3063/07/$20.00 © 2007 IEEE 877 On the Calculation of the Maximal MOT Throughput in T-DMB Jihoon Choi, Student Member, IEEE, Donghwan Lee, Student Member, IEEE, Jieun Yu, Student Member, IEEE, Kyunghwi Kim, Student Member, IEEE, and Wonjun Lee, Senior Member, IEEE Abstract —Digital Multimedia Broadcasting (DMB) is one of burgeoning communication technologies, which can provide audio, video, and data services to mobile terminals using broadcasting infrastructures. Data services in Terrestrial- Digital Multimedia Broadcasting (T-DMB) inherently have the disadvantage of retransmitting a lot of data unnecessarily for reliability. This paper proposes a novel optimized transmission policy using segment size and repetition number variability, which maximizes the object- level throughput as well as improves reliability. The theoretical modeling and simulation results demonstrate that our policy provides a throughput gain over the conventional protocol 1 . Index Terms — T-DMB, MOT protocol, throughput optimization. I. INTRODUCTION Digital Multimedia Broadcasting (DMB) is the convergence technology of communication and broadcasting, which can provide digital radio, TV, and data services to mobile terminals via broadcasting station infrastructures. By adding video capability such as TV service in Korea, T-DMB has evolved from Digital Audio Broadcasting (DAB) which is the European standard. It allows mobile terminal users to enjoy high quality of broadcasting services. DMB can be classified into Satellite-DMB (S-DMB) and Terrestrial-DMB (T-DMB) according to transmission methods. For S-DMB, the broadcasting station sends data to the satellite and then the satellite forwards it so that the signal can reach everywhere in Korea. On the other hand, for T-DMB, several broadcasting stations send data directly to mobile terminals in their each region and each station has the limit of its transmission range. Recently, more users choose T-DMB than S-DMB because T- DMB service is offered free. We focus on only T-DMB in this paper. DMB data broadcasting service provides mobile users with various data such as web sites, picture files, and traffic reports through its data channels. The data service can be either related with TV/radio services or not. In the former case, users will be supplied with the prices of products shown on TV 1 This research was supported by ITRC project supervised by IITA, IITA- 2005-(C1090- 0501-0019). Wonjun Lee, Jihoon Choi, Donghwan Lee, Jieun Yu, and Kyunghwi Kim are with Division of Computer and Communication Engineering, College of Information and Communication, Korea University, Seoul, Korea. Wonjun Lee is a corresponding author (e-mail: wlee@kroea.ac.kr). programs, get the lyrics of the song on-air, and see the jackets of the music disks. In the latter case, independent data services called BWS (Broadcasting Web Site) can be provided. In BWS, a web page is provided by a unit of hyperlink, and a user can receive only necessary pages preferentially. Compared with unicast-based networks, broadcast-based infrastructure has the advantage of affording very large asynchronous channel to massive users. However, the data broadcasting service cannot detect receiver-side packet delivery errors because there is no return path to receive user’s feedback. Moreover, data service requires higher reliability than video and radio service. In order to provide some level of reliability, the current system is designed to often perform a number of unnecessary data retransmissions. Therefore, T- DMB needs a mechanism which allocates optimal network resource as well as guarantees a certain level of reliability. Tracing the history of the study on DMB, we found that most studies have focused only on minimizing user’s waiting time and there have been very few research efforts on the optimal transmission policy for reliability in T-DMB. For the reason stated above, we extend our previous work [1] and propose optimal transmission policies to reduce transmission overhead, maximize throughput, and guarantee the requested level of reliability. While TCP protocol makes the best use of users’ feedback and controls to send data, in broadcasting infra, it is impossible to change transmission policy dynamically according to the feedback. The alternative approach to the efficient transmission is controlling transmission policy according to the known error rate of specific environments. Hence, our basic idea is to optimally adjust the parameters of the transmission policy according to the error rate. For the data broadcasting environment, T-DMB uses Multimedia Object Transfer (MOT) protocol [2] instead of TCP. The MOT protocol is used for file transmission in T- DMB and provides various parameters. For reliability, we focus on two parameters, i.e., segment size and repetition number. If the segment size gets smaller, the error probability is reduced but the segment overhead is getting bigger and the total transmission time becomes longer. Similarly, if the repetition number increases, the error probability decreases but the total transmission time becomes longer. We need an appropriate mathematical model to find the optimal value of two parameters for guaranteeing reliability and maximizing throughput. We attempted to optimize the performance of data broadcasting by applying Non-Linear Programming (NLP) [3] to the above two parameters.