The data delivery performance of current GNSS signals is generally assessed in terms of the C/N0 value required to achieve a certain error probability when decoding the information blocks. The navigation messages transmitted on the Galileo and modernized GPS signals are protected by the combination of convolutional codes and block interleavers. Although the required C/N0 values obtained by analyzing the performance of these signals in the AWGN seem to have enough margin with respect to the minimum signal levels received on ground, in real environments like in the urban and suburban scenarios, the performance of these codes can be highly degraded by the presence of multipath and shadowing effects [RD 1]. In this work we investigate various channel coding techniques that are widely used in current satellite communication standards in order to assess their suitability to protect the GNSS messages. After a wide range literature survey including a complexity evaluation, we focus on two special classes of Turbo codes and on LDPC codes. The performance is assessed considering values for the bit rates, block lengths and block durations that are typical of GNSS signals. Furthermore a new hypothetical pure communication channel to be combined together with a pilot ranging channel is considered. In this way the wellknown limitation of using low symbol rates in order not to limit the coherent integration time can be overcome. The simulations are performed in the AWGN channel as well as modeling the Land Mobile Satellite (LMS) channel. The results show that if minimum information blocks lengths of some hundreds of bits are considered, the use of Turbo codes and SOTC would allow to improve the GNSS data delivery performance in terms of lower thresholds and in terms of higher bit rates to be used either to increase the data throughput or to reduce the Time-To-First-Fix.
A Fresh Look into Designing Channel Error Protection Codes for Satellite Navigation Messages
A Tarable;
2011
Abstract
The data delivery performance of current GNSS signals is generally assessed in terms of the C/N0 value required to achieve a certain error probability when decoding the information blocks. The navigation messages transmitted on the Galileo and modernized GPS signals are protected by the combination of convolutional codes and block interleavers. Although the required C/N0 values obtained by analyzing the performance of these signals in the AWGN seem to have enough margin with respect to the minimum signal levels received on ground, in real environments like in the urban and suburban scenarios, the performance of these codes can be highly degraded by the presence of multipath and shadowing effects [RD 1]. In this work we investigate various channel coding techniques that are widely used in current satellite communication standards in order to assess their suitability to protect the GNSS messages. After a wide range literature survey including a complexity evaluation, we focus on two special classes of Turbo codes and on LDPC codes. The performance is assessed considering values for the bit rates, block lengths and block durations that are typical of GNSS signals. Furthermore a new hypothetical pure communication channel to be combined together with a pilot ranging channel is considered. In this way the wellknown limitation of using low symbol rates in order not to limit the coherent integration time can be overcome. The simulations are performed in the AWGN channel as well as modeling the Land Mobile Satellite (LMS) channel. The results show that if minimum information blocks lengths of some hundreds of bits are considered, the use of Turbo codes and SOTC would allow to improve the GNSS data delivery performance in terms of lower thresholds and in terms of higher bit rates to be used either to increase the data throughput or to reduce the Time-To-First-Fix.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
