Frequency Shifting Repeaters for PMR Coverage and ISI Reduction

The patent introduces frequency shifting as an intermediary mechanism between the received signal and the retransmitted signal. The repeater receives signals on a first frequency, shifts them to a second frequency for processing, and then retransmits on the first frequency. This frequency translation acts as a mediator that allows the signal to pass through the repeater circuitry without causing direct feedback oscillation between transmit and receive paths.

The patent changes the frequency parameter of the signal during processing at the repeater. By converting the signal from one frequency to another and then back, the system modifies the signal's frequency characteristic temporarily during transmission through the repeater. This parameter change prevents the receive antenna from directly picking up the transmit signal, thereby avoiding oscillation while maintaining coverage extension.

The patent uses repeater stations as simplified copies or replicas of the main BTS functionality. Instead of deploying multiple full BTS equipment units, the system deploys lighter-weight repeater stations that copy the essential signal reception and retransmission functions. These repeaters receive signals from the main BTS, process them with frequency shifting, and retransmit to extend coverage, providing a cost-effective alternative to full BTS deployment.

The patent segments the coverage extension function from the main BTS equipment. Rather than requiring complete BTS systems at every coverage location, the system divides the functionality into a central BTS and distributed repeater units. This segmentation allows coverage expansion using simpler, less expensive repeater equipment while maintaining system coordination through the central BTS.

The patent applies preliminary frequency shifting at the repeater before signal retransmission. The signal is shifted to a different frequency, processed, and then shifted back before being transmitted to mobile stations. This preliminary frequency transformation prevents oscillation issues from occurring in the first place, eliminating the need for later corrective actions that might compromise signal integrity.

The patent maintains continuous frequency shifting throughout the signal path at the repeater, ensuring that the signal never exists at the original frequency while passing through the repeater circuitry. This continuous frequency translation ensures both oscillation prevention and signal integrity by maintaining a consistent frequency separation between transmit and receive paths throughout the entire signal processing duration.