SAMBA Project: A test bed for PLC application as a digital inclusion tool

Moacyr Martucci Junior*, Andre Riyuiti Hirakawa*, Pedro Luiz de Oliveira Jatoba**

*Departamento de Engenharia de Computação e Sistemas Digitais Escola Politécnica da Universidade de São Paulo, São Paulo, Brazil

**Eletrobras, Rio de Janeiro, Brazil mmartucc@usp .br, andre.hirakawa@poli.usp.br, pedro.jatoba@eletrobras.com

Abstract — This paper aims to present an overview of the project conducted inside of the framework of the SAMBA Project funded by the European Commission and the architectural solution for the Return Channel (RC), based on PLC, needed to implement the interactivity in the services delivered by digital television. The PLC technology was adopted due to its easy implementation and capillarity, especially for regions with low-income people and not covered by ADSL, cable or other communication infrastructure. Services implemented in the SAMBA include e-health, e-government and e-learning. As contribution, the paper presents the architecture proposal for PLC-RC and the requirements and constraints considered.

Keywords - PLC, Interactive Digital TV, Return Channel, Interactive Services

I. INTRODUCTION One of the objectives of the SAMBA (System for

Advanced interactive digital television and Mobile services in BrAzil) Project [1] is the proof of concept of a return channel for implementing the interactive services related to e-health and e-learning applications, applied to low-income regions. This means that the cost for the end user must be very low, in other words, it is needed a low cost Digital TV set top box and a very low cost return channel solution, for example, a return channel with very high capillarity whose infrastructure could be shared by a wide number of costumers.

The TV broadcasting in Brazil has a very deep penetration in the population and it is a strong tool for mass education and public information. The possibility to use the potential interactivity facilities of the Digital TV is a very attractive goal for the authorities in order to leverage this potential and transform the new television set in a real tool for digital inclusion. Complementary efforts have been doing by the Brazilian government in order to reach 100% of the homes with the electric grid until 2008. [2] Called “Light For All”, the program has a budged of $ 4 billion and aims to connect more than 2 million new costumers. The lack of traditional telecommunication infrastructure (the fixed telephony network reach just 55% of the homes and the cable TV hardly serve 20% of the these) associated with the deep penetration of the electric grid made the Brazilian case a big opportunity to use the PLC channel as an effective tool for digital inclusion.

The Brazilian government adopted as its Digital-TV system the SBTVD based on the ISDB-T Japanese standard, and as objectives, SBTVD includes promoting social inclusion by Digital TV and its interactive e-services. [5]

In this scenario, the cost of the Set-Top-Boxes (STBs) for Digital TV is an issue to reach such objectives. However, considering the interactivity requirement, the RC is a key issue for SBTVD. Around the world there is a number of communication technology that can be used as RC, like ADSL, GSM or, in the near future, WiMAX. But those technologies are not suitable for implementing the RC, mainly because of the prices of the services and the new infrastructure and business models required. The idea to reach in a sustainable solution is to use an existing infrastructure and to have in mind the shared use of this infrastructure. The electric power grid is in the middle of a technological change towards the SMART GRID concept and the use of Power Line Communication – PLC technology could be the infrastructure needed, considering specially that the PLC networks have been used by the electric power operators to implement some services needed by them to measure the costumer consumption, the quality of energy and to communicate with their costumers, and in experimental way for controlling the electrical power grid. This infrastructure can be shared with the local government or social institutions, and, why not, with private service providers, focused on some target people, aiming to dilute the prices for the end users. [10]

Considering that every home is connected to the electric power grid, every home could be connected to a data communication network through PLC technology, so that can be used to implement the RC for iDTV (interactive Digital TV), with low cost for the end user, with high capillarity for the service providers, and using a existing infrastructure, allowing of several payers provide services sharing the resources, and contributing for decreasing the prices and collaborating for the sustainability of the solution. This is the main idea of SAMBA Project, whose architecture is shown in the figure 1.

II. SAMBA PROJECT SYSTEM ARCHITECTURE The general view of the SAMBA Project system

architecture, and specially the information flow are shown in the figure 1. In the figure, it is shown that the architecture has three domains: Content Domain, SAMBA Platform Domain and User Domain [1].

The Content Domain is responsible for interfacing the Internet content and all external information of SAMBA environment content sources with the Content Creation Factory of the SAMBA Platform Domain and for managing the Community content production to be used by SAMBA as well. In other words, the Content Domain enables the creation of the content to be delivered by SAMBA.

Inside of the SAMBA Platform Domain, the services will be produced by Content Creation Factory, using the content provided by the Content Domain, and delivered to the final users by the Community Access iDTV Channels. The Content Creation Factory is implemented by a Portal to allow the access from the Web in other to collect the content created by local communities. This portal is based on CMS (Content Management System) and Open Source technologies, such as Linux.

In addition, to implement the interactivity in the SAMBA Platform Domain, the RC is managed by the Return Channel Server, which sends the information collected by the PLC network for home users and by GPRS/UMTS service providers for mobile users to Content Creation Factory.

The User Domain is responsible for the management of the final user interfacing with SAMBA System, and consists of Set Top Boxes, Interactive Digital Television Sets and PLC MODEMS for home users, and DVB-H Receivers and GPRS/UMTS Devices for mobile users.

Considering the flexibility, as shown in the figure 1, the User Domain allows the user to be connected to a PLC network or GPRS/UMTS channel to implement the RC, depending on the availability and the prices of each technology for each application. In the same way, it is provided a DVB-H infrastructure for mobile services (in this case only GPRS/UMTS can be used as RC). This means that the Portal (Services) can be accessed in multiple ways, such as: PC browsers, Digital TV Set-Top-Boxes or, in the new future, mobile DVB-H devices.

III. PLC SYSTEM AS RETURN CHANNEL (RC) As already stated, there is a lot of customers (95%)

connected to electrical power network that can access the communication network by Power Line Communication - PLC. So, PLC seems a good medium for implementing Interactive Digital TV Return Channel, as proposed in the SAMBA project. However, the restricted capacity of the PLC networks calls for an adequate topology, organization of MAC (Medium Access Control) layer, including a multiple access of numerous stations/subscribers to the PLC transmission medium. Also, following topics must be considered: [3]

- Analysis and characterization of the PLC network infrastructure to be able to integrate the various backbones involved (IP Public Backbone, Village Metro PLC Backbone, etc.) and to allow the implementation of PLC based iDTV interaction channel;

- Identification of the necessary mechanisms for user interactivity using PLC network as iDTV return channel, and maintain the synchronism between the source of the content or application and the end user;

- Return Channel throughput for achieve all interactive services and for transmitting additional data such as network management information from the terminals; data related to the interaction between service and consumer; and feedback information about services.

SAMBA project considers two test bed sites for implementing iDTV Return Channel (RC) by PLC. One of them is the Barreirinhas City located at Maranhão State – Brazil. The second one is the Natz city at Bolzano County – Italy.

The requirements and constraints for the RC were defined in the previous activity at SAMBA project and considers he services defined and user needs. [4] As results, the RC should support full duplex transmission of the text files, xml files and photos files. In a common sense, the biggest files may be the images ones, but taking in account the Standard Definition (SD) of the TV display end device, the average size of the file should be less than 100 KB. Considering a typical data, composed by some presentation program language and images,

500 kbps of bandwidth for each user may be enough to achieve full interactive RC.

Despite of topology definition, several factors can interfere on PLC network performance:

• User/customer type: residential, industrial, business, etc.

• User/customer density: number of users in a PLC network;

• Network length: short – middle – long.

There could be different numbers of connected users in different networks and, of course, in different network section. The users can be more concentrated or not and they can be distributed in a symmetric or in an asymmetric way. However, considering a PLC standard that allows up to 200Mbps of bandwidth, the following characteristic values were established or measured to identify the network and setup performance tests:

• Number of users in the network: 150 ~ 450;

• Number of network sections: ~ 3;

• Number of users in a network section: 50 ~ 150;

• Network section length: ~ 500 m.

As results of performance analysis and the requirements for RC, typical PLC topology, composed by Head End (HE), Repeater (REP) and Customer Premises Equipment (CPE) was chosen as presented in following section.

A. PLC-RC Architecture In the Figure 2, the connection between the three HE is

mainly over Medium Voltage Power Line. However, in other scenario it is possible to make the connections through Low Voltage Line. The distance between HE is up to 500m., which is the actual distance between users site at the low voltage segments. In the same way, REP may be used if the distance of CPEs is bigger or if the channel quality must be improved, reducing BER and improving performance. Also in the figure, gray balloon CPEs represents the Secondary User (User that input information, such as content and several Medias, and receives large amount of messages and connections) Interfaces, which requires higher bandwidth and better network service qualities. The yellow balloon CPEs represents the Primary User interface, which comprises all other kind of SAMBA users. Primary Users will use the communication channel mainly for interactive services. The PLC RC for Natz is similar to Barreirinhas and is shown in Figure 3.

B. Set Top Box Solution The solution for the set top boxes to be use in the proof of

the concept of SAMBA Project is based on the branch of DVB-T, which integrates an existing DVB-T conventional box with a PLC MODEM using the Ethernet interface. The figure 4 shows the integration of DVB Set Top Box with a PLC return channel, called as SAMBOX for now on.

The same solution can be used for Brazilian ISBT Set Top Boxes, when available.

III. CONCLUSIONS This paper presented an overview of the SAMBA Project

conducted by the partners as an EU research project, which the main objective is to provide new interactive Digital TV services using a PLC-RC. At the moment, some services and user interfaces were defined considering the user needs. Also, user requirements analysis, system specification, project and test of PLC system have been accomplished. The PLC-RC is suitable for implementing interactivity services for low income customers. New business models that foster the introduction of sustainable application and to allow the local governments deliver social services, sharing the network infrastructure, will be useful for the community development.

Next steps include the implementation of the SAMBOX and related interfaces and software, configuration of actual PLC devices and the installation of PLC equipments at the Power Line and at user sides.

ACKNOWLEDGMENT This paper is based on the work of the team of the Open

System Laboratory of the Computing and Digital Systems Engineering Department of Escola Politécnica of Universidade de São Paulo and is partially funded by European Commission under SAMBA Project, contract number 045403.

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