Whereas most GPS repeater based indoor navigation systems apply time switching between the different repeaters, the proposed system uses different frequencies among the repeaters. Rather than cycling through the different repeaters, the repeaters all transmit simultaneously in time. However, prior to retransmission, each repeater translates the signal onto a different frequency location within the ISM band at 2.4 GHz. Such a system has a couple of significant advantages: First, precision accuracies reported in [2] and [5] are preserved since the fundamental arrangement (e.g., geometry, signal structure etc.) remains. Second, no time synchronization between the repeaters/translators is necessary. The receiver does not need to synchronize its time to the repeaters (apart from the usual GPS range/time reception and computation). Third, there is no danger of GPS interference. Other standard GPS equipment will either work undisturbed indoors if it has weak-signal capability or will not be interfered outdoors close to buildings containing the translator system. Fourth, the RF front-end of such a repeater/translator might potentially be combined with WLAN access points, since 802.11b/g use the same band. Coexistence of WLAN and GPS translator technology is provided through the spread-spectrum approach of either of the systems. Different navigation solutions are shortly discussed and convergence regions for a couple of setups of translator geometries are given based on Matlab simulations. Complying with FCC and other regulations as far as radiation in ISM bands are considered, the current approach is believed to gain more acceptance than other systems, where interference to the L1 band is a potential hazard.
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