The GEMMA project concerns the design, development and demonstration of innovative gateway and user terminal prototypes able to support and provide M2M services in either geostationary or non-geostationary scenarios characterized by user mobility and high Doppler and exploiting the aid of an ad-hoc Forward Link designed in the frame of the project.
The main objectives of the activity are:
- Based on the relevant state-of-art, to design a new forward link air interface enabling solutions that minimize the M2M terminals’ cost, power consumption and computational complexity.
- Envisage innovative solutions in a gateway prototype able to establish synchronization and detection with M2M terminals characterized by low cost oscillators and operating in systems targeting M2M application with user mobility as main target operation scenario.
- To demonstrate the developed solutions in a representative laboratory environment.
The main challenge of the project is to support bi-directional M2M services via low-cost user terminals (i.e. with low EIRP, low quality oscillators and low complexity) in a difficult environment like the satellite communications one, characterized by huge distances and huge Doppler (for LEO scenarios).
Due to the preciousness of the satellite resources, the dedicated bandwidth must be exploited in a very efficient manner, allowing to serve the maximum possible number of user terminals.
A further challenge is coming from the mobile nature of the main target applications. Mobility, in fact, brings with itself potentially strong fading.
Airbus Italia and MBI are strategic partners and have a strong heritage in the development of ground solutions for M2M applications based on E-SSA (Enhanced Spread Spectrum Aloha) random access, being among the inventors of the technology. Such know-how was gained from both ESA studies (including the precursor Artes 5.1 AO6830) and commercial projects.
E-SSA technology proved to be the most suitable to manage a large and uncoordinated population of inexpensive terminals and ESA has largely supported the development of E-SSA in the past.
The main advantages of the proposed solution are its efficiency and the high flexibility in terms of supported system scenarios, channelization and terminal characteristics.
Furthermore, the following benefits apply:
- Output maturity level higher than a typical Artes AT thanks to the availability of pre-existing building blocks;
- Synergy with other activities in both Artes AT (e.g. AO8871/MASSIVE) and commercial projects, potentially leading to the development of a complete state-of-art solution;
- Strong complementarity of Airbus Italia and MBI (the companies are strongly committed to make E-SSA the foundation of one of their product strategic roadmaps);
- Satellite Operators directly interested in exploiting the outcome of the project.
The proposed solution is bi-directional and can support a variety of services also exploiting the ad-hoc forward link designed for the scope. The E-SSA-based return link is completely asynchronous and can operate in different environments and with different bandwidth constraints (e.g. from 50KHz to several MHz). It supports operation with terminals having very low EIRP (e.g. -15 dBW). Bitrates per terminal in the order of hundreds of bits per second can be provided on the return link, with an aggregated spectral efficiency in the order of 1 bit/s/Hz. The great versatility of the E-SSA technology makes it suitable for implementation with extremely simple terminals, asynchronous and low-power without any limitation of band and satellite system.
The forward link allows on one side to enable applications based on outbound communication and on the other side to efficiently support the inbound communication, enhancing the return link management and helping in minimizing the terminals’ cost.
The system designed, developed and demonstrated in the project is a testbed consisting in three main components:
- User terminal prototype
- Traffic generator
The gateway implements both a E-SSA-based demodulator (return link) in charge of receiving messages from a population of terminals and a transmitter able to send data to terminals through the ad-hoc forward link air interface.
The traffic generator produces aggregated traffic, allowing tests in realistic conditions, emulating packets coming from a huge population of terminals. It is also able to modify the generated traffic according to the signaling received (via TCP) from the gateway.
The user terminal prototype implements a simple tx chain for asynchronous transmission and a rx chain allowing to demonstrate the forward link air interface performance.
The testbed is based on SDR technology, allowing SW implementation of all the relevant modules. The architecture is provided below.
The following figure shows the testbed HW aspect. It is noted that the testbed can be used in conjunction with the MASSIVE (AO8871) testbed return link demodulator to enhance the performance of the return link.
During the first phase of the project (ending with the SRR milestone) the applicable scenarios and requirements were defined. Furthermore, a state-of-art analysis was carried out to derive the design guidelines.
The second phase (ending with the CDR milestone) dealt with system design and has produced the system air interface and the related reference performance.
During the third phase (ending with the TRR milestone), SW implementation was carried out and the testbed has been set up.
The last project phase is the validation and demonstration of the implemented testbed (ending with the FR milestone).
The project has been completed. Tests have been successfully executed and the testbed features have been demonstrated to ESA.