What I want out of Personal Communications

While I had a Unix account at school (1988-1994), my .project file explained what I wanted to be able to do with personal (portable) communications:

I still desire the same feature set, but now that I see how small normal cell phones are getting, I'd probably add to my list the ability to do some voice communication. (I'd probably pass on voice over a satellite link - these phones are still too heavy and expensive for me.) However, the rest of this document, which I wrote quite a while ago, still considers the data only case.

Introduction

With the first Low Earth Orbit (LEO) satellite systems getting ready to come on line, the types of markets for Universal Personal Communications are becoming clearer. One such market includes the user who wants a small light device to communicate occasional small amounts of information, such as letting someone know they will be late or setting up a meeting. Sometimes the small amount of information has an incredible amount of significance such as a request for a rescue in the wilderness or a service truck on a dangerous stretch of highway. Very often voice is not required for these short transmissions and advantages of email such as privacy, cost and flexible answering speed are significant. If a small, light, rugged, and relatively inexpensive communications transceiver was available that offered to satisfy the above need, I believe it is capable of capturing a significant fraction of the market. I will refer to this device as a Personal Email Transceiver (PET).

My first claim is that many users can achieve most of their communications needs with email (equivalently referred to as paging, messaging or data) as opposed to voice. This will allow the unit to be considerably smaller while still having enough battery power to allow monitoring of incoming pages for several weeks, or with accompanying transmissions, two-way operation for several days. Email has some other inherent advantages that users may prefer. There is no requirement to answer the phone. Messages can be sent privately with no one to over-hear them (or no need to worry about bothering anyone by talking). It is a reduction of freedom to have a cellular phone which one is expected to answer immediately without knowing the purpose of the incoming call. In fact, many users of email wish that all communication begin at the paging level moving up to the level of voice (or in the future video) only when both parties agree to do so on the lower level.

There are five functions that I view as being useful for a PET. Depending on costs, consumer preferences, and application, several combinations of functionality might be possible as final products.

1] Communication using a satellite channel from one of the planned LEO constellations. As constellations are in the early stages of filling, the delay may be fairly long before a satellite comes into view but this may be the only link available and is thus still useful regardless of the delay. When constellations are finished, delays should be on the order of 10 seconds to a minute.

2] GPS location positioning. Current devices sold for general GPS use start at around $300. They offer advanced navigational features such as the ability to store a set of locations and guide the user back to these locations on the return path. These types of features may not be necessary for a PET and reduced functionality or different designs may be necessary in order to keep the cost of the entire unit down.

3] Communication directly between two PET's when they are close enough. This single-hop communication could be done (if FCC rules allow) through some Public Band such as Citizen's Band or the ISM band. When satellites are always available with low delay, this feature does not improve coverage, but it will dramatically reduce the cost of certain applications. It will almost certainly cost at least 25 cents to a dollar to send even a very short message over a satellite net. When two PET's are close to each other and communicating often, this expense can be avoided. An example of such a use is a pair of climbers that are separated by a 50 meter rope and might exchange 25 messages over the day. Another example of communication between close PET's is given in item [4]. The same method to communicate between close PET's could also be used to send a notification signal from a PET (which could be in a purse or briefcase) to a wristwatch.

4] Differential GPS (DGPS) location positioning. This function takes advantage of the communication described in [3] and computes the relative change in position between two PET's. Depending on the precision, several applications arise. Position as precise as 10 centimeters would be useful in some applications such as avalanche rescue. More precise differences would be useful for various measurement applications.

5] Communication using land based cellular base stations. Although this would be a very useful feature when the satellite is not desirable for reasons of cost or delay, this functionality may add too much complexity to the device to be marketable. Issues relate to the large number of frequencies currently in use for land based paging.

Possible Theoretical Problems

There are some interesting network control issues when many users are trying to communicate point to point in a small area. This might occur in a rescue situation for example. There are other network issues related to how to choose when to attempt point to point and when to use the satellite channel. This is sometimes referred to as multimedia network control, but as this term is currently too connected with the information content of the message itself, I prefer the term multi-link network control. Consider two channels, a bandpass AWGN channel for direct PET to PET communication and a different channel describing the satellite behavior, what is the best way to utilize both of these networks in terms of approaching capacity? It is also possible to assign costs to the to types of transmissions and set up a cost minimization problem. Some assumptions about user's positions and messaging activity need to be made and these might be deterministic or statistical.

Within the GPS area, there may be opportunities for new problems. Most of these relate to low cost implementation of regular GPS and DGPS.

Appendix: More thoughts

More thoughts on Differential GPS

Although Differential GPS is currently more expensive, there are good reasons for wanting to incorporate this feature into the device. Consider the problem with 911 service and current cellular phones. Ambulances can not locate the device to within a floor of a building. This could potentially cause expensive litigation problems. Of course it might not be the case that GPS signals can even be received inside most buildings, in which case perhaps there is the potential to use multiple devices (that do receive GPS signals) to perform triangulation to find a PET with disabled GPS. (One circumstance where GPS might be disabled is when a user is buried under the snow in an avalanche).

Thoughts on keyboard design

Since most communications products are handheld, the keyboard design should optimize the ease of data entry given this hand position. Also since users are sometimes left handed, the keyboard should be symmetric from right to left with the capability of re-mapping the keys (in a similar manner as some desktop computers). The advantage to having keys set up to allow the possibility of mimicking a QWERTY layout is that most users who are comfortable with email are familiar with this order of keys from use on a larger keyboard.

Other interfaces

Voice: The ideal interface for a user carrying an actual phone since hardware is already present to digitize voice. The number pad could be used for select menu functions that might be misinterpreted as part of the message (e.g. editing commands, send). Since voice recognition is fallible, the displayed word should show up on a screen and a spelling checker should offer options of new words.

Pen: Possibly the next most ideal interface. More appropriate for a large screen (i.e. not a phone). This interface could be coupled with voice input to possibly improve speed on systems that aren't that reliable in terms of recognition. Pens are the fastest way to navigate through several menu windows also, but they have the disadvantage that they are easy to lose.