The current SBAS (satellite-based augmentation system), one of GPS augmentation systems, is defined to use L1 single frequency to broadcast augmentation information. The introduction of the second frequency on L5 is being investigated in order to support multi-constellation and multi-frequency GNSS environment. While the data rate of SBAS message on L5 will likely be specified as 250 bps which is identical with L1 signal, the reduction of the length of preamble header from 8 bits to 4 bits is proposed. The preamble header shall be used by SBAS receivers for the initial acquisition, so it is necessary to investigate the effects on the performance of the initial acquisition. This paper reports the effects by reduction of the length of the peramble header.

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