How Early Cell Phones Handled Calls Across Different Towers
This patent describes a system for early portable phones to automatically find the strongest signal from a base station and switch channels as the user moves, reducing battery drain and interference.
Original patent title: “Radio telephone system”
This patent describes a system for early portable phones to automatically find the strongest signal from a base station and switch channels as the user moves, reducing battery drain and interference. Granted to Motorola Inc in 1975 with 35 claims and 206 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
This patent describes a "portable radio telephone system" (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 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.
The gap
What does this patent NOT cover?
- Does not cover systems where the portable unit cannot automatically adjust its transmitting frequency based on the strongest received signal (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 2).
- Does not cover systems without multiple, smaller "receiver sites" distributed within a larger base station coverage area (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1).
- Does not cover systems that lack a "scanning means" in the portable receiver to sequentially check different outgoing signalling channels (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 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 (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1).
- Does not cover portable units with a transmission range equal to or greater than the base station transmitter range (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 2).
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The noveltynoveltyThe requirement that an invention be different from anything publicly known before its priority date.Read more → lies in the system's ability to automatically hand off a portable unit between different base station coverage areas by continuously monitoring signal strength and retuning both the portable unit and the base station connection. This also includes dynamically reducing the portable unit's power to save battery and minimize interference.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Early analog cellular networks (1G)
Modern cellular networks (2G, 3G, 4G, 5G)
Mobile phone handovers between cell towers
Dynamic power control in mobile devices
Why it matters
The bigger picture
This patent, assigned to Motorola, describes foundational technology for cellular communication. Martin Cooper, one of the inventors, is widely recognized for making the first public handheld cellular phone call in 1973. The system's ability to manage calls across different base stations and optimize portable unit power was crucial for making mobile phones practical and user-friendly, laying the groundwork for modern cellular networks.
Filed
October 17, 1973
Granted
September 16, 1975
Market context
Who's building on this
Companies in this space
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.
Market impact
This patent laid fundamental groundwork for the cellular phone industry. By enabling portable phones to seamlessly move between coverage areas and efficiently manage power, it made mobile communication practical and reliable. This capability was essential for the eventual widespread adoption of cell phones, creating a multi-trillion-dollar global industry and transforming personal and business communication.
Claim 1 — Plain English
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.
The clever bit
The novelty lies in the system's ability to automatically hand off a portable unit between different base station coverage areas by continuously monitoring signal strength and retuning both the portable unit and the base station connection. This also includes dynamically reducing the portable unit's power to save battery and minimize interference.
What it does not cover
- 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).
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
High impact
Citation count
40/40
Highly cited
Claim breadth
20/20
Very broad protection
Recency
0/20
Older than 20 years
Assignee scale
20/20
Major company or institution
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$84K – $269K
Midpoint $168K · expired or expiring · industry ×1.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
35 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Mikulski, J. J., Sangster, J. H., Mitchell, J. F., Leitich, A. J., Dronsuth, R. W., Cooper, M., Richardson, R. A., & Lynk, J. C. N. (1975). How Early Cell Phones Handled Calls Across Different Towers (U.S. Patent No. 3,906,166). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/3906166/cellular-mobile-phone-radio-telephone
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How Early Cell Phones Handled Calls Across Different Towers cover?
This patent describes a system for early portable phones to automatically find the strongest signal from a base station and switch channels as the user moves, reducing battery drain and interference.
Who owns patent US 3906166?
Motorola Inc owns this patent, granted in 1975.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 3906166 cited by?
This patent has been cited by 206 later patents that build on its ideas.
What problem does this patent solve?
This patent, assigned to Motorola, describes foundational technology for cellular communication. Martin Cooper, one of the inventors, is widely recognized for making the first public handheld cellular phone call in 1973. The system's ability to manage calls across different base stations and optimize portable unit power was crucial for making mobile phones practical and user-friendly, laying the groundwork for modern cellular networks.
What does this patent NOT cover?
Does not cover systems where the portable unit cannot automatically adjust its transmitting frequency based on the strongest received signal (Claim 2).
Patent monitoring