You can freely build on How Early Cell Phones Handled Calls Across Different Towers

What this patent covers

This patent describes a "portable radio telephone system" (Claim 1) designed for mobile communication. It uses multiple base stations, each with a "predetermined coverage area," that transmit on "outgoing signalling channels" and "outgoing communications channels." Smaller "receiver sites" are strategically placed around these base stations to pick up signals from portable units. When a portable unit (Claim 2) needs to communicate, its "portable receiver" scans various "outgoing signalling channels" from different base stations. A "signal strength detector" then identifies the strongest signal, and "logic means" automatically tunes the "portable transmitter" to the correct "incoming signalling channel" associated with that strongest signal. For example, if you were making a call while moving between city blocks, your phone would continuously monitor which cell tower offered the best connection and seamlessly switch to it, ensuring your call remained uninterrupted.

What is now free to use

All 1 claims of US 3906166 are in the public domain. Specifically:

The 1 dependent claim add narrowing limitations and are also free.

What is NOT covered

Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.

• Does not cover systems where the portable unit cannot automatically adjust its transmitting frequency based on the strongest received signal (Claim 2).

• Does not cover systems without multiple, smaller "receiver sites" distributed within a larger base station coverage area (Claim 1).

• Does not cover systems that lack a "scanning means" in the portable receiver to sequentially check different outgoing signalling channels (Claim 2).

• Does not cover systems where the base station does not compare signal strengths from its various receiver sites to determine the strongest signal from a portable unit (Claim 1).

• Does not cover portable units with a transmission range equal to or greater than the base station transmitter range (Claim 2).

Who is building on this today

Major telecommunications companies like Ericsson, Nokia, and Huawei continue to build on and refine cellular network technologies. Mobile device manufacturers such as Apple and Samsung also implement sophisticated signal management and power optimization within their smartphones, relying on the principles of efficient handoff and resource allocation described here.

Products built on expired version of this technology

How to cite this patent in your documentation

Motorola Inc. US Patent 3906166. Radio telephone system. Granted 1975, expired 1993. Now in the public domain.

Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.

PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.