578 IEEE TRANSACTIONS ON BROADCASTING, VOL. 54, NO. 3, SEPTEMBER 2008 User Level Fairness of a Multirate 3G Technology (EVDO) With Application to Digital TV Return Channel Technology Guilherme Dutra Gonzaga Jaime, Rosa M. M. Leão, Edmundo de Souza e Silva, and J. Roberto Boisson de Marca Abstract—In this work we investigate the end-to-end perfor- mance of individual users when a particular multi-rate 3G wireless air-interface is adopted. This technology, similarly to most modern wireless communications systems, adopt an adaptive modulation and coding procedure and a schedule algorithm that favors users that enjoy better channel/interference conditions aiming at op- timizing the overall system throughput. The motivation for this effort was the choice of a radio technology to implement a return channel for a countrywide Digital TV system. In this application it is essential that the quality of service offered to users does not differ substantially due to their geographical location that, in most instances, will be fixed. In order to evaluate user performance we implemented a simulation model for the EVDO technology, including detailed physical and link layer characteristics. Using this tool for a very general scenario that mixes a majority of fixed users with some mobile terminals it was observed that the average user performance is very adequate for the intended application. However, there are severe differences in performance depending on the positioning of the terminals. We discuss different ways of overcoming the user-level unfairness of this technology that do not depend on modifications to the scheduling algorithm because we feel that these would be ineffective to cope with the tradeoff between user fairness and system throughput. It is then shown that a simple solution can greatly improve the fairness characteristics without sacrificing the overall throughput. Index Terms—EVDO, fairness, mobility, modeling, wireless, 3G. I. INTRODUCTION T HIS WORK was motivated by the desire of the Brazilian government to include a bi-directional return channel to the Digital TV system soon to be deployed in the country. The reference architecture, as defined by ITU, for a digital TV system can be found in [1]. The availability of the return (or interactive) channel is considered key to allow a significant part of the country’s population to cross the digital gap by having access to modern life information services (e-mail, Manuscript received September 30, 2007; revised April 4, 2008. Published August 20, 2008 (projected). This work was supported in part by grants from CNPq, Faperj and FINEP. G.D.G. Jaime has a fellowship from CNPq. G. D. G. Jaime, R. M. M. Leão, and E. de Souza e Silva are with the COPPE/PESC - Federal University of Rio de Janeiro, Rio de Janeiro RJ 21941-972, Brazil (e-mail: gdjaime@land.ufrj.br; rosam@land.ufrj.br; edmundo@land.ufrj.br). J. R. B. de Marca is with the CETUC/PUC - Pontif. Catholic University of Rio de Janeiro, Rio de Janeiro RJ 22453-900, Brazil (e-mail: jrbm@cetuc.puc- rio.br). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TBC.2008.2002100 banking, e-government, medical related services, etc.) through the Internet. The access terminals, will be mostly set-top boxes with limited processing and memory capabilities placing some constraints on which services can be offered and how they can be accessed. The target is to offer bit rates to the users at least comparable to those obtained today through dial up services, leading to a requirement of a minimum average rate of 50 Kbps. There is also a willingness that higher peak bit rates be available for part of the time and that these be higher than 100 Kbps. Because of the limitations on the cost and complexity of the set-top boxes it is envisioned that most services will be web based which also simplifies the human interface. This assump- tion influenced the choice of traffic model used to obtain the performance results reported in this paper. Another assumption that was made is that a vast majority of the users will be sta- tionary, at least for the first years of system deployment. Mobile users will be a minority and most will be moving at pedestrian speeds, i.e., at about 3 Km/h. This second assumption did in- fluence the choice of parameter values and features to be con- sidered in the analysis of the technology addressed in this study which is the CDMA20001x EVDO (Evolution Data Optimized) Rev.0 (IS-856). Although the initial motivation of this work was a part of the Brazilian Digital TV System project, which considered only static users, the assessed observations and results may be used by another EVDO applications because in this paper we have also considered mobile users. This mix of static and mobile users is expected to be a very common scenario in EVDO net- works. The EVDO [2], [3] is a third generation cellular technology conceived to serve an increasing demand for wireless packet data communications. In the transmission from terminal to base station direction (reverse channel) this technology operates as the CDMA20001x with all normal features of this technology such as soft hand-off. In the other direction (forward channel) the EVDO is a time division multiplexing system designed to provide a high total sector throughput allowing a maximum bit rate of 2.4 Mbps in its revision 0 (3.1 Mbps in Rev.A). An important consideration in designing a return channel that will be used as a main Internet access tool for a large population is that the system should provide comparable (or at least good quality) services to all its subscribers. It is not desirable that a user, due to its geographical location, be in a permanent disad- vantage with respect to other users which are paying the same price for the subscription. Note that in a highly mobile environ- ment this is very hard to occur because users are changing their 0018-9316/$25.00 © 2008 IEEE Authorized licensed use limited to: JILIN UNIVERSITY. Downloaded on January 6, 2010 at 22:36 from IEEE Xplore. Restrictions apply.