Comment by mdasen | Hacker News Reader

Comment by mdasen | Hacker News Reader

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Pardon my ignorance, but I guess I have a few questions. Wouldn't the hand-held nature be more dependent on batteries and technology than on the network technology? NiMH batteries weren't really commercial until 1989 and NiCd batteries have disadvantages. Likewise, advances in chips mean less space usage for many things.

I'm kinda surprised that AMPS uses so much less spectrum. From Wikipedia, it seems to indicate 0.5-1MHz (compared to 30kHz for AMPS). Was it just that radio equipment wasn't as good back then so you needed a lot of spacing in addition to the 30kHz voice signal? Something else?

It also seems like a big part of it would be making the tower spacing closer. The 0.6-3W AMPS signals at 800MHz wouldn't travel as far as the 25 watts for IMTS operating at 35-460MHz, yes? It seems like part of AMPS was betting on a large investment in infrastructure that would allow lower-power devices which would allow for smaller devices because of smaller batteries, yes?

Sorry to bombard you with questions, but I'm just curious about what things might have been trade-offs (like investing in more towers to allow smaller batteries) and what things might have been technology advances (like radios that could discriminate signals better requiring less spacing or new battery types).

I think the channel spacing with IMTS and AMPS was the same, there was just a lot more spectrum available at higher frequencies. AMPS was allocated 50MHz shared between two competing providers. IMTS I believe only used about 1.5MHz, although the specific frequencies it used were different in different areas.

I think that you're right that it's sort of a cascade of things that made AMPS possible.

1. You get the capacity from having a lot of towers with a wide bandwdith, but you have to pay for all of them, so you have to use the capacity, so you need demand.

2. You get the demand because with the higher capacity, the price can come down.

3. You also get the demand because you can have a truly mobile device, not just a car phone.

4. To have enough demand though, the price of the handset also needs to be low enough. The prices of the integrated circuits to make a handset came down dramatically between 1970 and 1985 or so when AMPS started to be widely deployed.

The electronics necessary to make an AMPS handset are also more sophisticated because (again to keep the service cost down) you need automated dialing (no operator), and you need to be able to hand the call off to the next cell if the user is moving. This means you need a microcontroller to be able to handle the pretty big state machine of the overall system.

Yeah, pretty much none of that is what mattered really. Making a phone small enough to fit in a pocket or purse meant all digital even for voice. that came with 3G but the brick showed the way.

Just getting back here. There were a number of things that made the hand-held possible and yes, not related to the network really except that, the cellular approach meant that you needed a microprocessor in the phone to handle the channel hopping and you of course needed cheap processors at the cell site to manage the radios and control channels. All of that was stuff that came after IMTS was developed. If you disassemble a brick phone, most of it is battery and heat sink. The thing that made thin phones possible came later, that was digital technology which mean the radio could be switched on and off as packets got sent and received a technology called DRX, discontinuous reception, that came with 3G later on. The exact frequencies used is sort of irrelevant TBH, that all just has to do with propagation and path loss which just changes the various engineering parameters like cell spacing and so forth. The thing that got people hooked on cell phones was that you could carry it around. That was the game changer. I have a slide deck where I do on cellular latencies, I show a picture of a brick phone and say, this was the wireless device with the lowest latency in history. Meaning, it was on all the time when connect. Something that changed with digital. But being able to shut things down in between bursts of packets is what made the dainty phones possible :)

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