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When I was first asked to participate in a panel discussion at Wireless World ’96 on the topic of “New Analog Features vs. Digital Capabilities,” my thoughts turned to the network. For most features, it makes no difference whether they are being used from an analog or digital phone, but for roamers, network support sure makes a difference. Short Message Service, for example, is available on both newer digital and analog phones. But this feature will not work for subscribers away from home unless the entire cellular network is upgraded to support short message capabilities.
The standard that supports seamless capabilities on the network is TIA’s IS-41 (which, by the way, will soon be changing its name to TIA/EIA-689). While IS-41 Revisions 0, A and B supported bread and butter capabilities such as inter-system handoff and automatic call delivery, IS-41 Rev. C went wild with new features. If implemented by all vendors and installed by all carriers, this revision could provide not only short message service, but also message waiting notification, calling number presentation, multi-party conference calls and even, for international roamers, announcements and operator services in their own language! Unfortunately, there are so many features in IS-41 Rev. C, that not all vendors and carriers will make the same decision about which to implement. So, some features may be available only for a subscriber in their home system for a long time to come.
Getting back to the intended topic of the panel (and not my warped interpretation), everyone knows that digital is better than analog ... except it ain’t necessarily so. Many of you may remember the transition from analog to digital watches, with pundits predicting the end of the analog watch face. One of the digital watch face technologies that has long since been forgotten is the LED watch. While it was highly accurate, very cheap and easily seen in the dark, the time could not be read on a sunny day and they required two hands to view the time by pressing the button that saved the battery because the LED display consumed too much power. Although, the LCD watch has survived, the analog watch face has clearly won the style battle, with an LCD watch being as appropriate on someone with a nice suit as sneakers. On the inside however, digital won the day, with all watch mechanisms using digital logic. One might summarize this as “digital ticks and tocks with analog looks.”
The digital versus analog battle in cellular has lasted much longer because, although digital will eventually win, analog has had more staying power than anyone predicted. Analog cellular actually still has some significant advantages over digital. Voice quality is still rated higher in real analog systems than in digital, although perhaps the new CDMA 13 kbps voice coder or the new IS-136 TDMA voice coder will finally overcome the perception that speaking in a digital phone in a noisy environment is like talking in a toilet while it is being flushed. Another less known advantage of analog is, surprisingly, that it is better for sending data. Since most transmission of data is still analog-modem oriented, analog cellular phones can simply be hooked up to a landline modem, although special modem protocols, such as ETC and MNP-10 significantly improve performance. Digital cellular phones, however, cannot be used with a modem because the digital voice coders corrupt the modem tones. In order to utilize digital cellular to send data, a whole new infrastructure has to be developed with some unique problems. Calling a digital cellular phone in order to transmit data is especially problematical because the radio interface has to be adjusted to remove the voice coders, yet there is generally no indication that the incoming call is going to be transmitting data.
These advantages of analog cellular will fade with time, as digital voice coders continue to improve and as data transmission moves away from modems and towards digital connections to the internet. The increasing trend towards the internet will also lessen the problem of terminating data calls, because of the asymmetric nature of internet calls: All calls are from a terminal to a host, as people dial in to pick up email and surf the web.
This discussion of modems and analog cellular reminds me of one of my pet peeves, the assumption that everything that is a little bit analog is entirely analog. A modem does transmit bits as electrical analogs of tones of a particular frequency and duration on the ‘analog’ side. However, the modem transmits bits on both sides and is therefore digital on both sides. This misconception appears to be based on the mistaken idea that everything electronic is digital (i.e. the voltage used to represent a 1 bit on the digital side of a modem) and everything based on tones is analog (i.e. the frequency used to represent a 1 bit on the analog side of a modem). However, if a modem was truly digital on one side and analog on the other side, an attempt to transmit the number 1,000 would come in precisely as a series of bits on one side and out as only an approximation on the other side, perhaps 999.5.
This black and white view of analog also infects analog cellular, where the original control channel is often called the “analog control channel,” and the new control channels associated with CDMA and TDMA digital voice transmission, the “digital control channel.” Although there is no question that voice is transmitted as analog information in analog cellular, signaling information, whether in a cellular system or a landline phone system, has to be digital. I hope that if someone dials my phone number (1-403-289-6609) from a phone on the other side of the world, that it will arrive at my telephone exchange as 1-403-289-6609 and not 1-403-289-6608.4. The “analog” control channel allows for the communication of messages composed of a well-defined sequence of bits between the base station and the mobile, exactly what the “digital” control channel does. This brings me back to my original point: analog can do most of what digital can do, and many features can be handled entirely by the network using capabilities present in all mobiles (e.g. message waiting notification or multi-party conference calls). The only advantage of the newer “digital” control channels is higher capacity, and that is mainly because they are newer, not because they are somehow more digital. There is no reason that a higher-performance digital control channel for mobiles using analog voice transmission could not be designed if there was a demand for it.
As of today, analog cellular phones still dominate the market. And this will probably continue until digital mobiles can be made more cheaply than analog. The current situation has ended up as a reverse of the watch scenario: For cellular phones, it is “analog talks with digital looks.”
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