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Patent

Spreading codes for a satellite navigation system (concerning memory codes)

One embodiment of the present invention provides a method of creating a set of spreading codes for use in a satellite navigation system comprising a constellation of satellites. Each satellite in the constellation is to be allocated a spreading code.

Details

Identification
2966
Publication date
31 May 2016

Description

Satellite navigation systems are becoming increasingly important in a wide range of applications, including handheld devices for position determination, in-car navigation support, and so on. A satellite navigation system comprises a constellation of satellites that each broadcasts one or more signals to earth.

The invention allows an entire spreading code to be stored in a memory device, such as a register, rather than using a linear feedback shift register (LFSR) for code generation. Such a memory device is present in both the satellite payload, for code transmission, and also in receivers, for code receipt. The code is read out from the memory device bit for bit, in contrast to being generated in accordance with some mathematical algorithm. This allows any form of code to be utilised. The codes can actively be optimised for desired properties, such as minimal side-lobes in the auto-correlation function (ACF) and minimum cross-correlation with other codes. The approach also allows a decision on the final form of the spreading codes to be delayed until a very late stage of system development, since the hardware (e.g. a memory device) will not normally be specific to a given code (unlike a particular LFSR). Furthermore, the memory can accommodate a new spreading code to be broadcast from a satellite in orbit by loading the new code into the memory.

THE MAIN APPLICATION AREAS

The present invention relates to the generation and use of a set of spreading codes for a satellite navigation system in which each satellite is allocated one or more spreading codes.

THE MAIN INNOVATIVE ASPECTS AND ADVANTAGES

The revision of codes may also be useful for commercial purposes, if perhaps a license payment is required to obtain the new codes, or for security reasons, to limit access to positioning services to those in possession of the new codes.

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Spreading codes for a satellite navigation system (concerning memory codes)
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