Mariano Vergara

Spreading code design for a MC-CDMA based GNSS pilot signal

Multicarrier CDMA (MC-CDMA) can represent an alternative to classical DS-CDMA for the design of GNSS ranging signals. A first requirement MC-CDMA signals must fulfill is that their generation on a satellite payload be feasible. It is well known, indeed, that multicarrier signals have a high Peak-to-Average Power-Ratio (PAPR) and GNSS signals, as well as other signals used in satellite communications, must have PAPR values much lower than values usually considered acceptable in other applications. Therefore, maintaining the PAPR of a MC-CDMA ranging signal within acceptable limits is a fundamental issue in any signal GNSS signal design using a multicarrier technique. The main contribution of this work is to propose a way of designing a MC-CDMA pilot signal based on Huffman codes. Such approach allows to shape the autocorrelation (or equivalently the power spectrum) of the pilot signal according to the specific needs of a GNSS service, guaranteeing arbitrary small PAPR values in all cases.

Multi-service data dissemination for space-based augmentation systems

New SBAS (Satellite Based Augmentation System) signals could include the provision of new additional services alongside the defined SBAS L1/L5 aeronautical service [1], if additional power becomes available. In this paper we present a solution that efficiently makes use of the additional available power in order to increase the overall data rate of a new multi-service SBAS signal. These new SBAS signals will be backward compatible. The high power efficiency of the proposed scheme is guaranteed by a variation of the interplex scheme that is characterized by a variable envelope signal constellation. A coding scheme based on generalized low density parity check (LDPC) codes ensures that service requirements can be met with a lower SNR (Signal-to-Noise Ratio).

Two-dimensionally spread multicarrier CDMA ranging signals with PAPR lower than 3dB

In this work we propose a methodology to design two-dimensional spreading codes for a multicarrier CDMA (code division multiple access) system with minimal multiple access interference (MAI) and minimal peak-to-average-power-ratio (PAPR). In particular, we minimise the cross-correlation peak between two two-dimensionally spread CDMA signals, with the side-constraints that both multicarrier signals must have a PAPR lower than 3 dB, and autocorrelation side-peaks lower than a certain value. The underlying principle of this work is that the users of a CDMA system need not be allocated exactly the same pulse shape, and that by assigning different pulse shapes, it is possible to increase the decorrelation among interfering signals. The resulting multi-dimensional non-linear optimization problem is solved by inspection of all possible solutions, as we show that the feasible region is a discrete countable set, whose size is reasonably small. The mathematical tool used in the solution of this paper consists of some radar pulse compression codes called Huffman codes.