This project represents the first step in a roadmap which aims at the development of a MESH communications product to be potentially used both in civil and operational applications. The next step will be to follow a HW implementation for all functions developed in SW in the frame of this project in order to eliminate the data rate limitation imposed by the software implementation.
The first Test-Bed, implemented by Space Engineering, is summarized in the block diagram of the following figure, it includes three terminals, a Hub emulator, three emulators of satellite links, a Network Control Centre and a Traffic emulator.
This Test-Bed is designed to be able to:
- establish three peer-to-peer connections between 3 different Modem Terminals;
- provide unicast and multicast services;
- support the multicarrier reception
The implementation is based on a real-time fully software emulation platform supported by an appropriate hardware.
An additional unit (not displayed in the block diagram) was included in the Test-Bed to control and monitor all the units. This unit was implemented as a web-based application and permits to define and execute the scenarios used to validate the system with data, video and VoIP flows (both real-time and not real-time video and VoIP flows are supported).
Each MESH terminal is summarized in the block diagram of the following figure. It is implemented as SW application, except for the digital to analogue and analogue to digital conversions, running on commercial PCs.
The second Test-Bed, implemented by Mavigex, is designed to be able to establish three peer-to-peer connections between 3 different CPM Modem Terminals with the aim to emulate MESH connectivity between different nodes. The implementation is based on a real-time fully software emulation platform supported by an appropriate hardware. Each CPM Terminal modem is implemented using a hybrid platform composed of a high performance GPU from NVIDIA able to process CPM algorithms in real-time installed in a Workstation needed to manage also the interfaces between the CPM Modem, the CPM Front-End, and the Traffic generator; a USRP N210 from Ettus Research able to convert data from analog to digital and from digital to analog, able to manage the NCR signal for a synchronous transmission between terminals and able to filter and resample data. Moreover, an additional workstation is dedicated to Traffic Generator and Control & Monitoring functions, and a NCR-like signal generator is used to synchronize the three terminals. The next figure shows the high-level architecture of the CPM Test-Bed where the distinction between hardware, software and firmware elements is highlighted using the colour scheme described in the legend of the Figure.
The CPM Terminal Modem is composed of two main parts: the CPM Modem, which is in charge of the digital transmission and reception of CPM operational modes (Base-Band section), implemented in a PC-like Workstation with a GPU, and the CPM Front-End implemented in an USRP N210 from Ettus which performs both AD and DA conversions, IF to BB and BB to IF conversion and the adaptions required for the multiple access functionality. The implemented CPM scheme is based on a partial response continuous phase modulated signal, serially concatenated with a convolutional code (CC-CPM). The CPM Terminal Modem block scheme is shown in the following figure.