Advanced Modem Prototype for Interactive Satellite Terminals

Status

Ongoing
Status date

2014-06-10

Objectives

The project has designed and demonstrated a protocol for VSAT communication with significantly higher performance for the return link than achievable with DVB-RCS (ETSI EN 301 790). Also transmission modes for lower SNR have been included. Parts of the new design have been accepted in the current DVB-RCS2 (ETSI EN 301 545-2) specification and all of the design is included in a pending revision of the current DVB-RCS2 standard. Demonstrations with the implemented prototype confirms that the performance expected from the simulations can be achieved in an implementation, and that ACM can be effectuated to dynamically select the transmission mode that fits best with the instantaneous channel conditions, both with respect to maximizing the bandwidth efficiency and minimizing the packet loss. This has been demonstrated for different fading conditions. Different burst size combinations have been investigated and the final set of new transmission modes includes alternative transmission burst durations allowing a dynamic trade-off between QoS and bandwidth efficiency.
Additionally, methods for estimating signal compression due to insufficient OBO at the remote SSPA have been investigated, and methods for combining UPC, ACM and ACS (DRA) have been investigated.

Challenges

The key issue is the opportunity to do ACM on the return link for each VSAT, complementing ACM on the forward link. Further, the physical layer is new with customized burst constructions using less overhead, a state-of-the art 16-state Turbo FEC and support for different orders of modulation with 16QAM, 8PSK, QPSK and BPSK available. Work has been done on the physical layer framing and preamble/pilot design to maximize the burst demodulator performance. New FEC codes have been designed (derived from the former Turbo-Phi FEC through optimization for the new frame sizes). The ACM capabilities are integrated with ACS (DRA) to extend the operational range of the system. The burst constructions are designed to fit into a unified slot grid allowing the space to be utilized by different burst sizes at just-in-time decision. This flexibility is useful to sustain the burst payload size when changing transmission mode and also to adapt the burst payload size when the level of traffic vary and QoS requirements vary. An adaptive user packet encapsulation scheme has been developed to enhance the efficiency in the utilization of a varying burst payload size.

Benefits

A more power/bandwidth efficient return link physical layer

Opportunity to exploit ACM on the return link

Extended operational range of the return link

Improved design accepted for the revision of the DVB-RCS standard

Features

The project has contributed with the following;

Protocol design and receiver algorithm design for a very efficient broadband VSAT system return link
Reference performance benchmarks for the protocol and the receiver algorithms
A laboratory test-bed with a prototype modulator and a prototype demodulator implementing the protocol
Test procedures for verification of the performance of the modulator and demodulator
A test campaign verifying the protocol implementation in the prototype modulator and demodulator
28 burst transmission modes for user traffic, spanning a large dynamic range and with several alternatives for transmission burst duration (and thus burst payload size)
2 burst transmission modes to support acquisition at different operating points
2 burst transmission modes to support control signalling at different operating points
Insight into methods for estimating SSPA compression of the signal
Insight into methods for combining UPC, ACM and ACS (DRA)