- Modularity and expansibility of the offered services: the modular and scalable architecture allows the construction of value added applications/services based on the requirements of the system users;
- Dual mode mobile communications (satellite and ground wireless networks – GSM/GPRS/UMTS);
- Integration with Satellite Navigation services (GPS, EGNOS, in prospect GALILEO).
The integration of different communication and navigation systems will guarantee a global coverage and service with uninterrupted duration in every operative scenario, reducing as much as possible the information degradation.
In the following paragraphs the architecture and the principal services will be described and the status of the demonstrations will be shown in detail.
II. SWATHE ARCHITECTURE
The main elements of the SWATHE service center are:
- The Framework;
- The Communication and Navigation Gateways;
- The User Terminal.
A. Framework
The framework is the core part representing a unique, scalable and centralized backbone over which the services are built and relayed to the users.
Being based on CORBA the framework is totally distributed and intrinsically scalable to cope with increasing number of service subscribers.
Computational intensive operations like cartographic rendering can be distributed over different nodes and assigned to nodes that have the lowest current computational load or possibly made in parallel in different nodes.
In the framework, reside all the common functionalities related to the management of the service customers (e.g. creation of customer service profiles), the management of the security aspects (e.g. authentications, authorizations), and the management of the different components by configuring, deploying and monitoring the distributed components of the service center.
The business logic module has many functions, all implemented as a set of CORBA components, which implement the supported applications. It is related to the concept of policy. A policy is a business rule that applies to some business object within the system. For example:
- Event policies are rules that are executed when some event occurs, for example every time a new message arrives from a terminal;
- Request policies are rules that are executed when some external actor accesses the Service Center, like when a Customer Operation Center requires the position update for some terminals.
In the framework, developing a specific application means assembling and applying event or request policies in a specified order.
B. Communication gateway
The purpose of the communication gateway (Figure 1) is to interface the framework to the wireless networks. Satellite or terrestrial network can be used depending on the particular application requirements.
The communication gateway has been developed taking into account the requirements of supporting a number of different terminals (black box, PDA etc.) and a number of different networks (GSM, GPRS/UMTS, ORBCOMM etc.).
C. Navigation gateway
The purpose of the Navigation gateway is computing the position of users when availability, integrity and continuity of the positioning service are required.
Different techniques are implemented in the Gateway:
- Assisted GPS;
- WiFi positioning;
- EGNOS positioning.
When the continuity of the positioning service is required also in indoor applications (i.e. an intermodal node etc.), the A-GPS basic technique or a COTS WiFi based location system is used, allowing better availability of the position especially in indoor environments.
The EGNOS corrections and integrity data can be used when particular certification issues are required (i.e. dangerous goods applications). A simple but efficient technique to broadcast EGNOS corrections when GEO satellites are not visible, is to use the EGNOS to RTCM transformation. The flow of SBAS data is converted into a set of RTCM type 1 corrections, taking into account the position of the user.
Another technique that is implemented by the Navigation Gateway, is the direct computation of position and protection level on demand; the receiver has only to acquire raw data and to send them to the Navigation Gateway that is in charge of all the position processing. By this second operation mode the data connection is required only for the raw data sending, while in the first mode a continuous data stream is required for obtaining a corrected position.
These techniques allows the availability of EGNOS integrity even in urban and difficult environments.
The communication front end has to implement the proper communication protocol with the user terminal, in particular the http 1.1.
Fig. 1 Navigation gateway : EGNOS to RTCM operation mode
D. User terminal
As said before different types of terminals are implemented depending on the particular application.
They are based on two basic types of terminals:
The two terminals can be connected allowing the provision of the full set of applications.
III. SERVICES
The definition of SWATHE products is based on a hierarchical structure:
- the “Module” that is the function or basic application; for example the Fleet manager, the Auth-Autentication, POI (poit of interest) management etc.
- the “Service” that is a composition of different modules (different services can have common modules)
- the “Product” that is a composition of different services.
For example the base distribution Product is based on two different services:
- Efleet Management
- Base Pathfinding