Multimedia Environment for Mobiles (MEMO) - Interactive Multimedia Services to Portable and Mobile Terminals Thomas Lauterbach* and Matthias Unbehaun Robert Bosch Multimedia-Systems GmbH & Co. KG, P.O. Box 77 77 77, 31134 Hildesheim, Germany Thomas.Lauterbach@Fr.Bosch.De Matthias.Unbehaun@Fr.Bosch.De * after 1/9/97: Georg-Simon-Ohm Fachhochschule, FB AI, Keßlerplatz 12, D - 90486 Nürnberg Abstract: The objective of the MEMO project is to design, integrate and operate applications which utilise interactive mobile Multimedia services by integrating two subsystems: a high-speed broadcasting system, and a low speed bi-directional communications system. This is realised by combining the existing GSM mobile telecommunications network and the Digital Audio Broadcasting system. After a first successful trial with this platform for mobile Multimedia services [1], the project is now in a stage to consolidate the user requirements and to define and develop its second generation equipment, based on experience gained using first generation equipment. The principal objective of the second generation MEMO demonstrator is to integrate the technical components in order to provide the full functionality required by the services and to improve the performance of the overall system. Especially, the 2nd generation terminal design will provide a higher degree of portability and mobility by connecting a laptop PC through a wireless LAN to a DAB/GSM transceiver box which can be placed remotely. The paper will report on the basic principles of MEMO, the assumptions and findings of the requirements studies, and the state of implementation of the second generation equipment, as well as on trial design and example services. Introduction Data rate versus mobility in current wireless systems Currently existing systems for mobile telecommunications provide either considerably high data rates or a high grade of mobility. Wireless LAN networks achieve up to 20 Mbps, but the networks cover only a few hundred meters, whereas GSM allows roaming across Europe but just delivers 9.6 kbps (see figure 1). Since Multimedia services, such as Internet access or video applications, often involve a highly asymmetrical data traffic, the MEMO project combines the telecommunications infrastructure data rate 20 Mbit/s 2 Mbit/s 50 kbit/s 9.6 kbit/s wireless LAN local ~100 m mobile data networks limited mobility ~10 km MEMO system GSM mobility international ~100...1000 km Figure 1: Currently available systems for wireless data communication
with a digital broadcasting system. The Digital Audio Broadcasting system DAB DAB was originally developed for sound broadcasting to mobile and portable receivers, but can also carry any kind of digital data as well. The key features are its high data rate of up to 1.7 Mbps, the reliable transmission (convolutional coding and interleaving in both time and frequency domain) and the flexibility of the packet mode data transfer. Single frequency DAB networks allow to cover large areas. DAB-networks are already operated in several countries, e.g. in Norway, Sweden, Finland, UK, Belgium, France, Germany, Switzerland, Italy, Canada, Australia, China and India. The BBC for example is setting up a single frequency network of 27 transmitters, covering up to 60 percent of the British population until mid 1998. Beside the actual transmission network, service provider associating DAB and GSM, two further components are needed (see figure 2): the service provider, being an Internet/Intranet access node or producing the data service content; the gateway server, which links the DAB/GSM network to the service provider and provides the necessary DABspecific formatting and pre-processing of data. GSM gateway server DAB terminal terminal terminal Figure 2: MEMO system architecture Types of Multimedia applications which are suitable for the MEMO architecture The MEMO architecture allows to operate mobile Multimedia services in various fields: Intranet applications (video conferencing, access to data bases, etc.) Entertainment for buses and trains, Internet access for business travellers. But two different types should be distinguished: Highly interactive services The DAB/GSM system creates a closed loop and allows a bi-directional access to the service provider. Contrary to cable based networks some time constraints and limitations, particularly for the GSM-based up-link have to be considered. Following an example for Internet access: The user sends a request, usually a short string containing the URL he refers to (e.g. http://www.info.com/weather) via GSM to the gateway server and receives the DAB frequency and channel for the answer to follow. After retrieving the wanted information the gateway server applies the formatting and pre-processing and forwards the data to the user via DAB.
Broadcast type services and virtual interactive services The DAB down-link is used to mainly broadcast information of general interest. On the receiver side the information is filtered and stored in a local data base, consequently the interactivity is only virtual. In case the user needs additional, specific material, this information could be downloaded using the interactive method. Furthermore the user can reply to the received information via the GSM link (e.g. e-mail to the author or for public auctioning). The two service paradigms selected for the MEMO trials and results gained The first example MEMO application was derived from a former ISDN-based application for the building construction industry, representing the fully interactive approach. Architects and construction engineers can access the document repository in the companies headquarters with the browser shown in figure 5. It allows to view, download and update any printed matter, drawings, protocols and standards. These types of documents are usually rather large and GSM alone is not sufficient since download times could add up to several minutes (e.g. >15 min. to transfer 1 Mbyte at 9.6 kbps). Figure 4: The browser used for the building construction industry application The other application is a system in the publishing industry to broadcast up-to-date Multimedia journals. Daily issues of the newspaper, comprising text, pictures, audio and video clips, are broadcast to a large number of customers simultaneously. Technical background and findings during the first project phase A first set of tests were undertaken in Rennes/France with a 1st generation architecture shown in figure 5. It is mainly assembled from off-the-shelf equipment: gateway server with connection to the service provider infrastructure, modem for incoming calls and DAB transmitter network; portable Notebook PC with high speed optical data link to the DAB receiver and GSM phone; The main purpose of these tests was to verify the assumptions and the feasibility of the gateway server index article other pages client GSM up-link DAB down-link DAB information about the transmission structure Figure 5: Implementation of the MEMO system for the first Figure trials, 3: using Cyclic off-the-shelf transmission equipment of data in an object carousel...
combined DAB/GSM architecture. Evaluation of the system performance Data files of about 1 Mbyte were downloaded from a server in about 2 minutes in a realistic environment, i.e. the MEMO terminal was installed in a car and operated on a construction site in the city of Rennes. About 25% of the download time were needed for the request via GSM and the actual data rate for the DAB transmission was restricted to 128 kbps due to the limited data processing capabilities of the used Notebook PCs. Improved system architecture of the second trial phase and consequences for the implementation The overall system architecture was then revised on both server/transmitter and terminal side based on the results of the first trial. For seamless access to Internet-based applications a complete TCP/IP protocol stack was introduced. The partially implemented DSM-CC functionality (download and object carousel) allows to run electronic commerce-, video- and game-software in a mobile environment. A Virtual Server allows the user to run Internet programs unchanged, i.e. without being aware of the underlying MEMO architecture, as well as "off-line", i.e. without the GSM return channel continuously switched on. The implementation steps described in the following two sections are envisaged for the next project phase of MEMO and possible future projects. Network extensions A new service type is planned to be introduced in the near future. It is called Personal Services and requires both a cellular network structure and mobility management, i.e. hand-over, roaming. This approach provides a significantly higher data throughput and a more flexible use of the DAB air interface resource. Some additional functionalities in the server architecture regarding the TCP/IP protocol stack will allow to use Internet-push applications. Terminal modifications It was found to be advantageous to provide additional pre-processing and buffering, so that the Notebook PC can provide full resources to the actual application in use. Tasks particularly consuming processing power were identified as: managing the transfer protocols when decoding several incoming data streams in parallel; applying advanced algorithms for detecting and recovering transmission errors; resolving the multi-protocol encapsulation. Therefore the actual receiver and decoder is separated from the Notebook as an individual Mini-PC. Both components are connected by either wireless LAN or an infrared interface. In the future, this arrangement will allow to use also PDAs and Palmtop PCs as terminals, assuming that such interfaces will become a standard feature of these devices. The access to the MEMO system resources is provided by a generic low-level API, based on commonly used interface Winsock2. This simplifies the adaptation of Microsoft-compatible Windows applications on MEMO terminals.
Some remarks regarding transmission protocols used in MEMO The adaptation and implementation of the various telecommunication protocols is practically achieved by encapsulating the packets or datagrams in the DAB packet mode. Specific parameters, such as packet size, repetition rates or segmentation, can be adjusted according to the requirements of the embedded protocol. Data transmission will mainly rely on the following three transmission protocols: TCP/IP for Internet- and Intranet-based services; DSM-CC for video- and related applications; Multimedia Object Transfer protocol (MOT), which was specifically developed for file broadcasting in DAB networks. The MOT protocol is well suited for broadcasting Multimedia data via DAB and exploits various DAB specific functionalities for signaling, encryption and recovering of transmission errors. It is currently under standardisation within ETSI. The layered architecture of the 2nd generation terminal The software architecture of the MEMO terminal is separated into three layers (see figure 6), connected with two APIs: Layer above the High-level API, comprising the specific user software to access and display the Multimedia services; High-level API allowing to flexibly integrate and implement a variety of applications; MEMO-System-Layer, managing e.g. client sessions, security functions, event handling and caching; Transport-Layer below the Low-level API, providing real-time data processing and decoding. This layer hides specific hardware components and the operating system used on the receiver/decoder Mini-PC; Internet Virtual Server MOT DSM-CC Internet MEMO system layer MOT DSM-CC U-U DSM-CC U-N DAB Data Group Transport DAB Object carousel Data carousel Download PPP/UDP TCP/IP GSM High Level API Low Level API WinSock2 Figure 6: Layered architecture and APIs of the MEMO system The layered architecture provides a maximum grade of flexibility and interoperability. Further development in both service and technical domain Seamless integration of mobile Multimedia services In the future, the MEMO system will be part of a large and powerful communications infrastructure, rather than being a separate data carrier for specific use. Therefore the seamless integration into other
network topologies will be investigated and considered concerning the design of future generation equipment. One could for example assume a scenario, where access to a company's internal network is provided by an infrared link at the desktop, providing maximum performance for stationary use. As soon as the user starts to move around in the office building, the wireless LAN system takes over the network connection. But once the user leaves the building, the network connection is automatically re-routed to the MEMO network, re-connecting to the home office location. Performance reduces with an increasing grade of mobility, but the user will always stay connected and not even become aware of the automatic network hand-over. Further development of receiver and terminal equipment A 2nd generation terminal equipment combines DAB and GSM together with a Mini-PC in a single housing. Being connected to the user's Notebook via wireless LAN or infrared link and having a size of around 10x10x10 cm 3, the MEMO cube will be a simple-to-use and convenient travel companion. Further integration towards the size of a PCMCIA card could be envisaged for the future, but strongly depends on the progress of IC development for DAB. Software components are planned to be implemented as system independent code (e.g. JAVA), so that the different modules of both system specific layers and application programs can be dynamically configured and up-dated. Summary The MEMO system described above shows the potential of a point-to-point telecommunications system combined with Figure 7: Design study of the 2nd generation MEMO receiver a broadcasting system. It is based on the assumption that communication involved in interactive Multimedia services, such as Internet access, is highly asymmetrical, thus requiring only a narrow band data channel to up-link requests, but demanding a high capacity to carry the requested material, such as text, pictures, audio or video clips, to the user. Furthermore, a high percentage of the information is of general interest to many customers and thus can be continuously transmitted very efficiently using a broadcasting system. The advantages of the proposed system allow to carry Multimedia services to mobile users and to exploit the different characteristics of both broadcasting and telecommunications infrastructure in a very advantageous way. Acknowledgement The authors thank their colleagues of the ACTS project AC054 MEMO for their extraordinary support and collaboration, which helped to present the reported results and the European Commission for supporting this project. References [1] Th. Lauterbach et al., Using DAB and GSM to Provide Interactive Multimedia Services to Portable and Mobile Terminals, ECMAST '97, Milan, 1997