Public Safety Advocate: Apple’s ProSe Patent, Useful or Useless?

Apple was recently issued a U.S. Patent that will be or won’t be useful to public safety professionals in the field. As always, it will be up to the public safety community to review this patent, look at what Apple claims, and perhaps test-drive devices that meet the requirements of the patent. 


The one “unfinished” portion of the 3GPP Mission-Critical Push-To-Talk (MCPTT) standard is that its off-network communications solution “Proximity Services” (ProSe) does not provide anywhere near what public safety needs. ProSe was designed to provide off-network communications between broadband devices.

When the 3GPP standards body was asked by the Public Safety Communications Research (PSCR) Division of NIST to develop a standard for Push-to-Talk over LTE, it developed Mission Critical Push-to-Talk or MCPTT, to be followed by Push-to-X, or pushing data, pictures, or video. In any event, because the 3GPP standard was modeled after existing Land Mobile Radio (LMR) Push-To-Talk (PTT), the 3GPP included what LMR users call “off-network” or simplex communications.

After Samsung delivered its 3GPP-compliant Push-To-Talk (PTT) client to FirstNet (Built with AT&T), there was some hope that since Samsung had embedded ProSe in the chipset it would work. However, it turned out not to be up to public safety standards. As you may know, I refer to ProSe as a technology where two people can yell to each other farther than ProSe can talk. Still, many companies continue to try to come up with a solution for off-network broadband communications services that are suitable for public safety. 

Apple’s Patent

I am not at all sure when this patent was approved since it is made up of existing technology and art, but it was. Basically, Apple’s patent states that it will be able to provide off-network communications using ProSe (see below) and configuring it as a mesh network. 

A  recent article about the Apple patent starts out basically saying this patent could have saved lives at the World Trade Center on 9/11. This was the first thing I took exception to. I am not sure if the next statement is the author’s assumption or if it came from Apple. “The approach is intended primarily for law enforcement and emergency services personnel, and it’s possible that the tech could have saved the lives of first responders inside the World Trade Center on 9/11.”

I also took exception to the statement that part of the patent is, “based on Intercept laws for law enforcement to enable them to listen to phone conversations.” Reading the patent and the article, I don’t have a clue why Apple thought this set of laws is related to what it is proposing. 

Land Mobile Radio Push-To-Talk

In the LMR world, off-network functions when in range of a network or when one unit is in range and another is not, and it provides one-to-one and one-to-many communications, which is the final fallback mode if all other forms of communications fail.

LMR handhelds have a number of advantages over smartphones when it comes to one-to-one simplex communications. First, they operate at much higher power levels (5, 4, 3, or 2 watts depending on the radio band) the radios all have external antennas to better radiate and receive radio signals, and the batteries that power LMR handhelds will power the devices over a full shift and are replaceable either with another rechargeable battery or by using standard off-the-shelf AA batteries.

Proximity Services (ProSe)

Taken from the Apple Patent

“Some techniques may allow devices to establish direct communication paths with one another (e.g., without going through a cellular base station or WiFi access point). For example, devices that are located in proximity to one another may discover one another and subsequently establish direct communication paths with one another. In specifications published by the 3.sup.rd Generation Partnership Project (3GPP), direct communication between wireless devices may be referred to as “proximity services” (ProSe). ProSe communications can have a number of advantages, such as improved spectrum utilization, improved overall throughput and performance, and improved energy consumption. In the context of public safety services, ProSe communications can provide an important fallback public safety network that may function when a cellular network (e.g., a 3GPP cellular network) has failed or is unavailable. […]

With ProSe communications, a relay device, e.g., a mobile device acting as a relay, may be used to couple another mobile device (such as one that is out of the coverage area of the cellular network) to the cellular network. However, implementing lawful intercept in this situation can be problematic, however, as the mobile device that is to be targeted for lawful intercept may not be visible to the cellular network.   

Apple’s approach is to add mesh networking to ProSe. The concept of mesh networks is not new, it has been used for Wi-Fi, the amateur radio community (hams) and other types of networks. A mesh network is usually designed to be self-healing. If one node disappears, another can fill in the gap.” 

Mesh Networks Have to be Smart

ProSe, as implemented by the 3GPP, starts out at a huge disadvantage: power for smartphones is limited to 0.25 watts while public safety Band 14 (only) permits up to 1.25 watts of power; smartphones are full duplex, (transmit and receive at the same time); and antenna system(s) are encased in the phone so signal loss to and from the smartphone is much greater than if the antenna was externally mounted; and batteries for most smartphones have a lot less capacity than LMR handheld batteries; and smartphone batteries usually cannot be changed out in the field.

Finally, smartphones are normally controlled by the network and each phone can be on a different segment of radio spectrum and still communicate. When you take smartphones off-network, they are still licensed in the area where they are being used. (Band 14 is a nationwide license but most other band segments are not). There are many questions and perhaps we will see some answers. 

When ProSe was first introduced as part of MCPTT, many of us said it was basically useless for public safety’s off-network communications needs. Still, some within the communications community believe if ProSe or some other type of LTE (and now 5G) off-network communications can be made to work on smartphones, land mobile radio will no longer be needed. Smartphones would be able to do everything LMR radios can do today and more. So far, nothing has even come close to matching the simplex range and capabilities of LMR handheld radios with broadband.

Now it appears that Apple thinks by extending ProSe to a Mesh network environment it may be able to accomplish what no one has been able to do before now. I will admit that I am skeptical of this this methodology. On the other hand, none of us had a clue that Apple would change broadband communications with the iPhone and continue to change how we all communicate with the introduction of the iWatch and more. 

Before any public safety agency simply accepts that ProSe or Apple ProSe devices will solve their off-network issues they need to measure their results against my “must pass” list that I published a few years ago.

Simplex Must 

Simplex communications must be usable both when in network coverage and when out of network coverage, and when one device is still in network coverage and another is not.

Simplex communications must be capable of one-to-one and one-to-many communications.

Distance and Range Tests

  • Unit-to-unit for at least ten city blocks with both units outdoors.
  • One unit on the street and one in a sub-basement.
  • One unit on the street and one in an underground parking garage.
  • One unit on the street and other units inside a multi-story building.
  • Provide safe two-way communications to those working a wildland fire
  • One unit at the top of a well or shaft into the ground and another unit being used by the rescuer in the shaft

There are probably other tests that need to be run but this is a good start. Again, show me even though I am not from Missouri. Communications is the lifeline of our first responders, and in many cases, it is also the lifeline for anyone being rescued by our first responders. 

Coming from the LMR world into cellular and broadband, I am accustomed to a single device that can be on or off the network, in and out of network coverage, and usually controlled by the user (at least for simplex operation). Smartphones are controlled by the network so you have to wonder how you tell, say, five first responders at an incident to turn their phones into part of a mesh network. Once that is accomplished, will it really provide the same off-network coverage as LMR does today? I have been in discussions with others who say this new Apple Patent might be a partial solution for off-network LTE but it might not fulfill all of the needs of the public safety community. My response is that we will need to add yet another level of complexity for our firsts responders to deal with while they are busy in the field trying to save lives and property. 

I am willing to be proven wrong about my first impressions of Apple’s patent. However, the first question I have to ask the good folks at Apple is if anyone involved in crafting this patent have been on one or more ride-alongs with public safety on a busy Friday or Saturday night. Or was this patent based only on some engineer’s idea of solving a problem without fully understanding the depth of the problem that needs to be solved if broadband is to be able to match what first responders can do today with land mobile radio devices. 

It will be interesting to see what actually comes of this patent and if it will be restricted to Apple devices. If so, the device will be a non-starter in the public safety community since every solution needs to work on both iOS and Android devices.

Winding Down

It is interesting that I commented only last week on inventions or technologies for the sake of the technology rather than developing technologies that solve problems. Yes, off-network communications (simplex) over LTE is a problem and cellular systems were not designed for off-network use. In fact, most network operators are not fans of their paying customers being able to leave the network and talk directly to other units without using network airtime or data, which is how network operators make money. 

I am hearing that at least one High Power User Equipment device (HPUE) is about to come onto the market in the form of a belt-worn smartphone with high-power capability. I am anxious to learn more about the unit and if it can be used for off-network LTE communications. If it can, I would like to see how it stacks up against existing LMR off-network communications. I remain skeptical that a smartphone can be turned into an off-network one-to-many device that will function both in and out of network coverage. 

I have to wonder if those looking for an answer to the LTE off-network issue are actually looking for a way to make LMR obsolete so broadband will be the only network public safety will need. I, for one, do not believe we should be trying to replace LMR at this point just to say we replaced it. I would rather the smart engineers in the industry work on combining the features and functions of both devices. Even then, some within the public safety community will feel more secure having both types of devices to choose from as appropriate. Time with tell, but I believe LMR will be around for a very long time to come.

Until next week…
Andrew M. Seybold©2022, Andrew Seybold, Inc.


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