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With the 20:20 vision of hindsight, some of these ideas look ridiculous, but please bear with the author, because there are some interesting concepts here, such as SYNSOL, which as far as I am aware have yet to be utilised. If mobile telephones could be made to form their own synthetic networks, doing away with cells and repeaters, then one of the major problems facing their development (public resentment about cell phone masts) would go away. Also they would require no central management and therefore would become just consumer products with no need for a monthly fee and or call costs. SYNSOL and SYNSPEC developed using an open architecture system such as developed LINUX could have a major effect on the electronic industry.
However readers of the Appendices will note that these ideas were not originally intended to be world wide, just for a particular area to feed into an optical cable network.
This lecture depicts the likely developments in telecommunications during the next half century. The main overland and submarine information highways will consist of wideband optical quadratic-law fibres with laser-type repeaters spaced just overt km apart. Local-area distribution will be based on narrower band glass fibres with a fibre information rate of the order of 300 megabits/sec as opposed to the 10 to 20 gigabits/sec per fibre on the main highway, Switching will use both time and space switches employing advanced optical techniques. The whole network will use digital techniques and lasers throughout. Holographic crystal stores using lasers for writing and reading will be located at strategic points. Standard subscriber's equipment will include video cameras and receivers, crystal stores, play-back devices, and terminals for communicating with computers, banks, shopping centres, etc. Mobile telephone services will be universal and will employ revolutionary techniques. Free space radio will be restricted almost entirely to mobile services. Pocket telephones and global personal telephone numbers will be commonplace. Information retrieval centres will replace central libraries. Aircraft and ships will employ earth satellites for communication and navigation on an extensive scale, while similar services to space vehicles in the solar system will be highly developed.
In the title of this talk, by the word `future' I mean `future', - for I shall be speaking tonight almost entirely about the end of this century,
and the beginning of the 21st. Why? Am I indulging in merely an academic exercise of no value to this rightly very practical Institute, or
have I an aim that makes hard-headed sense? If my main predictions that follow are right, there is indeed a practical aim: to help prevent
the big waste of capital investment that will certainly occur in about twenty years from now, in urgent communication expansions, if the
networks are then allowed to develop on the present lines, instead of by new methods, much more efficient for wide bandwidths, that are
now being studied in the world's laboratories. I refer chiefly to laser-beams carried by very small optical waveguides; but also to quite new
radio frequency bands essential in my view for the greatly increased mobile traffic in builtup areas by about AD 2000. These coming
changes will amount to a complete technological revolution, to be ignored by any truly developed nation or region only at the expense of a then rapid fall in its standard of living -
for many competing areas will be prepared for it.
The economic benefits from the new methods, and the
coming demands that will make them necessary, are
unlikely to be obvious to cautious planners in less than
fifteen years from now - which will make a taking of the
wrong fork in the road not only easy but apparently
quite sensible. There have been several costly planning
mistakes in the past, e.g. in relying much too long on
do methods of telephone signalling. Let us be far-sighted
enough now to avoid repeating such costly errors.
The new technologies will not come easily. They will
involve a lot of money, spread over several decades. But
eventually they will save far more than they cost. Their
fruition will be a real challenge, worthy of the steel of the
best brains in their fields that the world can supply. But
surely that is a thing, not an objection; life would
not be worth living, at least to me and I'm sure to you,
if every rock face climbed failed to show a still more
difficult pitch ahead! A good start has been made already
on all fronts. I shall outline very briefly, first the main
reasons for vastly increased traffic demands, and then
my own best guesses now as to the future technical ways
of meeting them - admittedly a very personal approach,
but unless I speak with conviction, right or wrong, I
know I shall be wasting your time.
If we could wave a magic wand to give us at once the
know-how and the assured flow of money to make it
sensible to start planning and producing now a really
ideal global communication network, what should we
ask for as its final goal? One view is that communication
should always be deliberately restricted - for both
between humans and machines the intercouplings can be
too tight as well as too loose, thus restricting harmfully
a vital ability that in either case can be described as
`individual initiative'. Within each social, business, or
professional group we can see the danger already; it is
much easier to `follow the herd' than to think for oneself, an essential to true human progress. In leading
staff it is easier to direct than to educate and encourage;
and in science we see far more often a conformist than
a Galileo. People must learn to control their
couplings, often cutting them off in order to think,
while using their outside contacts to the full when these
are really needed. It is only mentally or emotionally
sub-normal or immature persons, a now large but
eventually decreasing proportion, we hope, who need
temporary help in the process by artificial limits to their
links with others.
The resulting self-restriction to communications,
though, leads to an interesting result: for the wiser the
individual, or the better the design of an inter-connected
network element, the more urgent will be the need for an
outside contact when it is desired, for otherwise it would
not be searched for. Our ideal communications network,
then, must to this extent be
efficient because of its
self-restricted customer demands, for even maximum
peak loads must be catered for without appreciable
waiting times, or serious loss of efficiency or at least
unnecessary frustrations could often result.
How much would the next generation in a region be
willing to pay as its share in a nearly ideal
global communications network, one that would virtually
eliminate the effects of mere distance altogether -
assuming that it is technologically available to it, as I
firmly believe that it can and will be? That will depend,
of course, on its expected over-all value, particularly on
its cost savings in other ways. Clearly a really excellent
network would be worth a great deal; for in modernised
areas the communication network is like the nerve
systems of a complex animal, without which the creature
cannot live at all, let alone survive against odds. But in
rather more detail, let us take as an example this nation
of yours, the Republic of South Africa. As yet I know
little of your precise problems; but this I do know, that
you have set yourselves to be right in the forefront in
technical progress, and the benefits it will bring. Your
aim is a balanced economy, that only a suitable spreading in the range of your production can achieve. Already
your manufactured goods, no longer your mining or
agriculture, provide the largest single factor in your
revenue.
In view of increasing world-wide competition you will
streamline to their limits your manufacturing methods.
On this point it is becoming increasingly obvious that
knowledge is power; competitively, it is the
speed
of
acquiring knowledge, in the form of practical know-how,
that really counts. So you will undoubtedly streamline
your ways of access to the very best sources of relevant
information. For this you will need telecommunication
access not only to the new information processing
centres, largely computerised, that will emerge in your
own country, gradually replacing technical and other
libraries, but immediate access as well to similar information centres abroad.
To keep in close touch with your customers, to save
costs I think you will take quick advantage of the highquality video-phone circuits and video teleconference
facilities of the era, as they will be life-like enough to
reduce a great deal the need for the much more expensive
human transport - alternatives available first on land
routes, and later on a global basis. With the vastly better
communications, but increasing road congestion, more
and more of your people will want and be able to work
from their homes, checking what they do by individual
television channels. Increasing numbers will continue
their studies in their homes, largely by educational
television films of their own choice. Increased leisure
time will bring a rising demand, too, for good videophone channelsforindividualand group social purposes,
increasing to more distant places. I predict a greatly
increased demand, as well, for mobile radio-telephone
equipment connected with the fixed networks, both
vehicle mounted and by pocket-phones alone. Mail,
even newspapers or pre-selected news reports, will be
sent largely by the telecommunication networks, to
cheap facsimile receivers in the homes and offices, because it will prove less costly as well as much quicker.
Machine-to-machine data links will be a salient feature,
vital to the economy.
All these demands combined will produce peak loads
on the networks that will soon use a fair proportion of
even the vastly greater bandwidths that the optical
transmission methods will cheaply provide. Even on
purely economic grounds the total extra profits, resulting from savings in human transport costs, important
reductions in cycle times in meeting customer requirements, and in marketing methods, will easily justify
more than three times the present average fixed annual
operating expense per subscriber line, in present value
for money, which will eventually be about all that will be
needed.
2 Technical strategy
The currently used free-space radio-frequency bands
are already overcrowded, even in the microwave region.
On the eastern sea-board of the USA, for example,
mutual interference is being experienced between the
various microwave highways. I am sure therefore that by
the end of this century international agreements on the
lines indicated below will have to be made and enforced.
That with only a few agreed exceptions, all free-space
routes be reserved for mobiles, which must have them.
These exceptions will include:
(a) The rarely authorised use for short-section freespace fixed communications of the range between
about 55 and 65 GHz. A broad oxygen-absorption
band in the earth's atmosphere gives an extra and
exponential attenuation factor that reaches a
peak of about 15 dB per km at 60 GHz at sea
level, thus making impossible any serious interference with other services even at fairly short
distances.
(b) Free-space fixed laser-beam links, usually restricted physically to below-horizon ranges, to
avoid risk of interfering with inter-spacecraft
communication and control that will also use
optical bands.
(c) An agreed small section of the 0.9 to 10 GHz
band for fixed communications and satellite
broadcasting in difficult terrain and in underdeveloped regions.
(d) Agreed small sections of the band under about
0.4 GHz for direct broadcasting to homes in such
under-developed areas, and to mobiles.
That for all frequency-shared mobile services otherwise reasonably capable of causing interference outside
national or locally agreed super-national boundaries, the
radio frequencies be restricted to those bands physically
incapable of causing inadmissible field strengths in
unwanted places at the powers transmitted, even when
water-vapour inversion and other atmospheric conditions give abnormally long ranges. Where the
boundaries lie in congested areas, suitable parts of the
oxygen-absorption region will again be needed.
3 Basic new techniques and their costs
I shall now try to sketch with a broad brush the main
new techniques that we can expect the next twenty to
fifty years to bring. Some of the predictions that follow
may seem startling. But science and technology have
already begun to meet the coming challenge; an almost
perfect communication system is not an idle dream! As I
have based these predictions merely on what I consider
to be reasonable extrapolations from present-day theory
and experiments, I believe that far from proving rash,
some of them will seem to the generation of 2020 to be as
amusingly conservative as Lord Kelvin's prophecy that
`no heavier-than-air vehicle could fly' - a correct
calculation with the power-to-weight ratios of the prime
movers of his day. In the next fifty years there will
undoubtedly be important and very relevant discoveries
in physics, and breakthroughs in technologies, but of a
nature that at the moment would be pure speculation,
suitable only for science fiction. So for our present
purpose we must neglect such dreams until fiction has at
least started to become fact.
The chief of our new techniques, one now firmly based,
will be the use of optical carrier frequencies, by laser
beams conveyed mainly by very small, flexible waveguides. Having studied competitive, partial solutions,
it is my firm opinion that at most by about AD 2000 it
will have started to become, for all fixed routes including the local areas, the outstandingly key tool in the
whole of our art, to meet the vastly greater bandwidths that will then be needed. The bandwidth in the
visual octave plus the next one lower, in the near
infra-red, if it could all be used would be enough for
seven-thousand million good-quality speech circuits per
waveguide, or one-and-a-half million high-quality individual television (TV) channels in colour - all by a
digital method, such as pulse code modulation (PCM),
to avoid noise accumulation with many repeaters.
Even one three-thousandth of this bandwidth per
optical conductor, at the future acceptable prices that I
shall give reasons to predict, would put all lower-frequency methods right out of the running, except for
earth-bound mobiles-which in my view is precisely
what will happen in about twenty-five years time.
Cheap, reliable mass production of the waveguides at
the needed tolerances will be quite a challenge, but
almost certainly feasible within the next twenty years.
They will be available in at least two forms, providing
information rates per fibre of first, about 300 megabits/
sec, enough for one excellent future individual TV
channel by PCM, or the equivalent; and secondly, a
wideband version suitable for about 10 to 20 gigabits/sec.
The first type will be used mainly to provide individual
circuits in the local areas. Both versions will be flexible
enough, mechanically and in guiding characteristics, to
bend round radii of at most 50 cm, even when in suitable
multi-core forms, with attenuations not exceeding
20 dB/km. See Appendices 11.1 and 11.2.
Repeaters will be based on a new form of semiconductor laser, probably of gallium arsenide, operating
very largely in time division multiplex (TDM) networks.
These modified lasers will present the second stimulating but almost certainly surmountable challenge,
both to further basic semiconductor research and in production know-how, especially towards the elimination
of cooling. For telecommunication applications the laser
must usually be small, reasonably power efficient, in the
right frequency range for the transmission medium, have
a long useful life, be able to be modulated into pulses of
at most 10 picoseconds (for the high-capacity TDM
routes of the future); and (often) have a fairly high
non-linear optical amplitude coefficient, with a very
low time-constant, at radiances that are not unpracticably high. The gallium arsenide laser meets this bill very well - but as now made only at temperatures not
higher than about 80°K. Recent work in the USA,
though,' foreseen by Dr G. H. B. Thompson of STL,2
has brought us a big step forward towards roomtemperature versions. It is probable, too, that the new heterojunction technique and its further improvements
will increase the useful lives of the lasers - though this
point has not yet been proved.
In about two years we can now expect that lasers will
begin to be available, of peak optical powers sufficient
to give repeater spacings of about 3 km for the 300
megabits/sec type, and of about 2.25 km for 10 gigabits/
sec operation. There is now firmly based evidence of
recent major breakthroughs in gallium arsenide laser
design which should shorten the time scale by about
ten years.', 2,28The power consumption will be about 1.2
watts per laser in about seven years, with about 2.4
watts per complete repeater per fibre - with further
economies later on. See Appendix 11.3. 1 think it
reasonable to predict an average useful life for each
repeater of at least five years in about ten years time,
sufficient for the easily accessible land routes.
In the much more difficult case of the sub-ocean
routes, it may take up to about twenty years to produce
repeaters with long enough average lives to give complete cables 5 000 km long that will operate without
maintenance for an average period of twenty years -
but it can be and certainly will be done. See Appendix
11.4.
At least 80 per cent of the total operating expense of a
mainly optical global network will be in the local and
extended-local areas, just as with existing systems. The
chief single expense item at a home subscriber's terminal,
the future good but cheap picture-type solid-state TV
screen and associated information processor, will be
there in any case in nearly all developed areas, for
entertainment. Neglecting this, and also extra but
optional subscriber equipment, some of it used only
for business purposes, Appendix 11.5 describes the main
cost factors in these future local areas. It also outlines
the reasons for believing that their annual total fixed
charge need not exceed three times the present typical
figure per subscriber line, when the research and development costs, together with the needed additional
capital investment, have been absorbed. The latter
factor will have less relative importance in a rapidly
expanding and developing country such as the South
African Republic, for large capital investments in the
communication network would be needed even if the
techniques used remained as they are. When compared
with present analogue transmission systems, in terms of
megahertz-miles available, Me cost will be reduced by a
factor of about 1 000. For information that originates as
digital data, this cost reduction factor rises in some cases
to over 16 000.
It is worth while to guess the total future cost of the
other extreme units in a future global network, the
optical sub-ocean cables. At present value for money,
the figure for each deep-water submarine repeater may
amount to about R35 000 (but not more). Its main
factor, of course, will be the price of its necessary waterpressure protection, and the need for extreme pre-
testing of all components, as at present. The total
repeater cost on a 5 000 km transatlantic cable, for
example, would then be about R70 million. The complete installed cable may cost about 8250 million - not
a small sum, but cheap for the then needed 400 gigabits/
sec digital service that it will provide - no more, in
fact, than the cost of 150 miles of an average motorway.
When we learn to realise that the transport of intelligence
and information is often much more sensible than the
much slower and more expensive moving about of human
bodies, it will be accepted without hesitation. The cost
of at least one suitable stand-by cable (perhaps bidireetional), preventing entire disruption in case of
complete, almost certainly mechanical failure of the
main link, will of course have to be added. This will be
relatively expensive while there is only one main cable;
but less so according to the number of main links that
have been installed.
The optional terminal equipment for home and office
use will of course involve the subscriber in an extra
charge, typically amounting in AD 2010 to the extra
rental on apparatus costing perhaps 8150. A pocketphone containing the subscriber's personal attachment
is included in his normal equipment. When produced at a
rate of several millions per year the cost should be about
R35. Also included in his normal equipment is a miniaturised, integrated-circuit, PCM coder/decoder and
transducer to and from his optical fibre - costing
eventually about R20. The optional equipment will then
usually comprise:
Approximate cost in Rand | |
Fascimite receiver (probably by photographing by much cheaper methods the TV frames) | 25 |
T V camera, for transmitting diagrams, etc., to called facsimile receivers, and pictures of himself for video-telephone calls | 35 |
Desk control panel for push-button access to internal files | 10 |
Crystal store and play-back apparatus into his TV screen | 50 |
Individually-tailored control panel, for doing his work from his home (cost will vary) | 30 |
Total cost of optional equipment | 8150 |
New switching methods will be available, both electrooptical and purely optical. They will be needed for the
much higher bandwidths and digital bit rates. See
Appendix 11.6. By AD 2000, though, they are unlikely
to be more expensive than present types, in some circumstances being in fact cheaper; so we can neglect this
factor in the economics of our global planning. Some
further features of future optical networks have been
described recently.3 To facilitate the switching methods,
and also information retrieval by subscribers from the
future information processing centres, much more
compact digital stores will be available, having capacities
of up to at least 1012 bits per cm3 of storage material.
One of the best versions is likely to arise from extensions
to present work on holographic storage by the movement of small electric charges from one `trap' to another in electro-optic crystals such as lithium niobate, using
laser beams for writing in and reading out, as a parallel
operation, both in not more than 1 nanosecond eventually, per group of at least 1 000 bits. See Appendix 11.7.
4.1 General concepts
We shall now take a look at the world's future
mobile speech equipment - the available new devices, and its
network planning and operation. I say `speech' equipment not because mobile videophones are by any means impossible, but because their much greater loading on the
non-optical frequency bands they will usually need, will
rarely justify mobile TV equipment on an individualchannel basis. Every subscriber is often a `mobile'; the problem of wandering subscribers is a vital factor in the
whole network plan. It is my experience in Britain today,
even during normal working hours at each end, that
when I call someone therein about a 40 per cent chance
that the person I wands not there. If it is urgent he has
to be searched for, usually a lengthy and often an almost
impossible process, a frustrating and mainly unnecessary obstacle that our next generation will not tolerate.
Because of much better telecommunication their future
wanderings will be far more often for leisure and pleasure than for their work, but faster and cheaper air
travel will take many of them into almost any part of
the earth. The problem of immediate access to subscribers, therefore cannot be truly solved without the
use of completely mobile world-wide personal telephone
numbers. We shall now explain how the vastly cheaper
and smaller, fast data storage-and-retrieval devices that
are on the way, together with the much wider-band,
cheap transmission channels, can at last bring to reality
this planners' dream.
4.2 Global personal telephone numbers
Assume that in AD 2020 the world population is about
16 x 109. Even if a quarter of this number became
subscribers, 32 binary digits would be enough to identify
each. We may decide to reduce to about one-thousandth
the chance of getting and disturbing a wrong number
due to a single false digit, by adding ten more. Each
personal number would then contain 42 digits, recorded
in permanent and very compact form within an attachment to a miniature pocket-phone that the subscriber would always carry with him, be supplied by his local
telephone administration, and be used automatically for
call-costing and all other identification purposes.
The attachment could be as in Fig 1, and contain 42
printed-circuit connections about 0.1 mm apart, the
code group being made by now-standard laser-beam
cutting techniques.' A `cut' could be a `0' digit, with a
`no-cut' as a `1'. When power is supplied each connector that is uncut could change the bias and the bistable state of one of 42 integrated-circuitry flipflops,
all monitored in sequence at a convenient rate by conventional techniques. The code group would then go into a temporary store in the sub-set or pocket-phone for
automatic transmission when required at a second
convenient rate. The attachment would also contain a
variation on now-available devices - a narrow magnetic
tape up to about 10 cm long, on which up to about 90
other global telephone numbers could be erasably
stored, each in the lateral direction. This number would
be the maximum that most people would need to record
in advance, pre-call selection being by moving two small
wheels each in decimal steps. For both write-in and
read-out the magnetic head could be quickly moved
laterally across the desired code group by a small spring
released electrically at the right moments, again to or
from a temporary store in the pocket-phone, or directly
into the sub-set when a pocket-phone is plugged in.
In the subscribers' nominal homes and offices they
would plug in the pocket-phone to their fixed sub-sets on
arrival. When in any vehicle, they could plug their
pocket-phones into a sub-set socket in that vehicle,
connected to an appropriate mobile radio network. When
just walking they could use and be called by their
pocket-phones alone. When a pocket-phone is plugged
into a fixed sub-set or into a vehicle, its do power supply
would be automatically transferred from its miniature
storage cells to the central battery system of the network or vehicle, the pocket-phone cells being then on
charge instead of discharge, thus ensuring that these
cells are almost never allowed to run down. When the
pocket-phone is plugged in to a fixed (optically operated)
sub-set, the operation would also cause its stored data to
be written-in to an optical-type store in the sub-set
having the much faster read-out time appropriate to the
optical network. At all times except when a subscriber
has his pocket-phone plugged into a fixed sub-set at his
nominal home or office, this pocket-phone, either via the
fixed networks or by free-space paths, will cause his
location to be automatically recorded at suitable fixed
points, at intervals appropriate to his network, unless he
deliberately presses a bistable button to cut this operation off. When plugged into someone else's fixed sub-set,
the record will show the personal number of its nominal
user. At other times it will show the wanderer's areanumber, channel group and channel number in the
mobile network he is in - but usually only in terms of
changes in this information.
In spite of much better telecommunication, some
firms will prefer to go on using some large office blocks
even after AD 2020. In these cases most of the movement
of staff in working hours will be within these buildings.
Within each, all that will be needed is a fairly conventional audible calling system, picked up by an additional miniaturised part of his pocket-phone, by which
any one of up to about 1 000 people in the building can
be called to the nearest fixed sub-set, only a few feet
away when he is a guest in someone else's office. Appendix 11.8 illustrates a simple way of minimising mutual
interference, both within any one and between adjacent
such buildings. It is based on the use of a fairly large
number of low-power calling transmitters, together with
an inverse-cube law with distance from each. For this
application the wandering subscriber's nearest sub-set
or small group of sub-sets will be constantly recorded on a
channel of a temporary store entirely in the building,
together with his global telephone number, only these
sub-sets being used if he receives a call. When he leaves
the building, as long as he remains in his nominal local
area his new location will be stored, in terms of only the
appropriate last few digits in his global location code,
entirely at new fixed points associated with fixed or
mobile sub-networks within that local area. When he
leaves his nominal local area all his digits associated
with that area will usually change, to conform also with
his then new sub-area, channel group, and channel
number coding. As he moves further away a similar
process takes place, all his digits relative to these larger
areas and his location within them being changed, but
still recorded in stages as before.
When he has moved more than an average of about
100 km away, however, the process changes; it will
then usually be found more economic to up-date automatically his entire personal global code, in world capacity stores (see Appendix 11.9), in developed areas
about 400 km apart, except for ocean spacings. After
this has happened the world-wide store concerned, by a
similar process in stages back to its own location, keeps
track of the wanderer's further movements in every
relevant detail, until he moves into the next 400 km
square which then takes over. When the man is called
on his nominal number, then via this particular worldwide store, a switching centre associated with it completes the call's establishment by the quickest free routes,
just as if it were the original caller, and at the same time
automatically up-dates the called person's then location
code in the calling subscriber's pocket-phone store.
By the then high-speed optical methods, the total
delay in ringing the called subscriber, due to the opticalswitch delays alone in a tandem chain of up to about 20,
should not exceed about 50 nanoseconds. On a transglobal call between fixed subsets of route length of say
20 000 km, an additional and more important cause of
delay, will be the propagation time (about 150 milliseconds) after the call button on the pocket-phone has
been pressed. A third delay, the time for automatic
dialling of the 42-digit code, may amount to 5 milliseconds. These figures assume no waiting for free channels all the way, which will usually be true, even via
ocean routes, as in future optical sub-ocean paths a
total of at least a 10 gigabits/sec rate through each
fibre of a 30-fibre bundle will become common practice -
sufficient for 100 000 improved-quality PCM speech
circuits in both directions, if a pair of fibres in the cable
were reserved for such non-TV demands.
The world-capacity, global personal-number stores,
400 km apart, will also be used as the telephone directories of the future, having the added advantage that they can be constantly up-dated. Their needed access rates, though, will depend on the type of subscriber to be called, the main division being between private, and business or professional people having direct access to the public. The need for private numbers will be quite rare. For any information a man receives that leads him to need a new individual private number will practically always contain this telephone number as well, being
added automatically, at least for a time, to his own small
store in a free place within it. An average of only on such need per year per subscriber is probably a fair estimate. He may well need indiscriminate access to
business or listed professional numbers, though, in a
given category about three times as often, on account
of the advertising he electronically receives. Particularly
when he is in an area strange to him, the event leading
to his need will not usually give him automatic access
as well to the corresponding listed numbers. So these
requirements must be catered for by additional means,
leading to a total average directory demand per subscriber of about four per year.
Much the quickest and most practical way for the
average subscriber to get the telephone number of a
particular name and address, or of any one at random in a
listed business or professional group, will be to say what
he wants through his microphone, especially when he ie
using his pocket-phone alone. Speech recognition
machines present many challenging problems, and do
not yet exist in really satisfactory forms. But the
present state of this art is such that I believe we can
confidently predict their arrival, for directory-enquiry
purposes and for stylised general information retrieval,
within twenty years from now, and at economic prices.
So an access point in such a machine in his local area
would receive his demand; it would then transmit it to
the nearest world-capacity store at a rate of 10 gigabits/
sec. In a local area containing 50 000 subscribers the
average total directory demand would thus amount to
about one every three minutes, handled by about
6 machine access points, with a normal maximum
waiting time that would be acceptable for this very
occasional service. When a subscriber is at a fixed subset the directory-enquiry service will be improved if
suitable parts of the automatic information feedback to
the caller are in visual rather than audible forms, displayed on his TV screen. Confirmation that the computer
has interpreted correctly the spoken name and address
of the person demanded, for example, will then take
appreciably less time, and be always unambiguous.
At the world-capacity storage centres, we have seen
already that if the recording is in hologram form in,
say, a lithium niobate crystal, both the write-in and
read-out times per number could probably be not more
than 1 nanosecond; and that at least 1012 information
bits could be stored in 1 cm3 of crystal material. It is
interesting and important to estimate how the needed
access arrangements for up-dating the global numbers
among the mobiles could be provided. We can see from
Appendix 11.9 that all that is needed at the crystal is a
single 10 gigabits/sec optical fibre.
The access arrangements at world-capacity stores for
directory enquiries could possibly be as follows:
The subscriber capacity of each, by a previous assumption, will be about 4 X 109, leading to a bit-capacity
need of about 1.6 x 1011.Even assuming that the average
rate of changing a nominal global personal telephone
number is as high as 1 per year, this leads to an average
up-dating rate of only 120 per second - many orders
smaller than could be dealt with quite easily by a
single movable laser beam on to a crystal of 1 cm3 in
volume, allowing 10 per cent extra space for the listed
business and professional people. The read-out access
would be to its own area containing not more than 50
million subscribers, at the total average demand rate
we have already assumed of 4 per year per subscriber,
thus totalling only 6 per second. This is still more easily
obtainable - it is in fact so much below the limiting
speed that it is almost inelegant to use it! But it will
almost certainly prove in on economics. In practice, of
course, we shall at least triplicate each type of largearea store in case of occasional breakdowns, in separate locations not too near together.
4.3 Devices and principles in future mobile networks
We shall now look briefly at the extreme limits of the
mobile density that could be handled. It is clear that
this possible number of mobiles per km2, by new methods,
could be many times greater than has so far been accepted, well above any easily foreseeable demands, and by means quite within cheap and sound engineering
tolerances.
The internal calling networks within a building has
already been dealt with. Next, what about cars on
motorways and ordinary roads; walkers on golf courses,
hills, beaches; and inland and near-shore boats? To
make interference impossible between mobile areas,
the oxygen absorption band centred on 60 GHz will
have to be used more-and-more frequently. Fig 2 shows
that there is a central band about 6 GHz wide where the
extra (exponential) attenuation is nowhere less than
12 dB/km at seal level. With digital systems, receivers
will usually be immune at 3 km away as they will
have low-level threshold clippers, and any normal type
of receiver will be immune at 6 km.
Miniature solid-state oscillators suitable to fit into
the pocket-phones, for both transmitting and receiving,
will almost certainly be available within less than 10
years, drawing up to about 1 watt do mean power at
10 to 15 volts, and radiating up to about the needed
0.15 watts on the peaks. It looks now as if these will be
based on Gunn-effect diodes, probably within the LSA
sub-group (Limited Space-change Accumulation).16 In a
c.w. oscillator of the LSA type in gallium arsenide, the
theoretical power efficiency is limited to about 30 per
cent, on account of the rather small peak-to-valley
current ratios available in their N-shaped current-tovoltage characteristics. I believe that most future mobile applications will use a pulse modulation on the
carriers, normally lasting about 1 nanosecond per pulse,
produced internally within the oscillator in the wellknown `squegging' mode. To prevent further waste of power during the non-oscillating periods, a suitable highfrequency transistor can be used to cut off the drive
current during these parts of the modulation cycles. A
resulting over-all pulsed-oscillator power efficiency of
about 15 per cent is likely to be achievable, giving
about 150 milliwatt RF output from 1 watt input -
quite adequate for most applications, as the normal
maximum path length will be only 1 km. For higher
efficiencies, it may well be necessary to find or make, if
possible, a semiconductor material otherwise as suitable
as gallium arsenide at 60 GHz but that has a larger peakto-valley current ratio.
No quartz crystals will be used in the mobiles for local
frequency control. All accurate timings for channel
selection will be derived from the ground stations,
tolerances on resonant-circuit tunings being as wide as
about ± 0.3 per cent. This will eliminate the much more
accurate quartz crystals that otherwise our future
mobile networks would need.
Mobile networks by FDM
With FDM(Frequency-Division-Multiplex) systems,
in the 6 GHz-wide oxygen-absorption band there is
room, of course, for about 40 000 PCM channels all in
use at once, each 100 kHz wide, (to cater for the higher
quality speech circuits of the future). On double sideband, probably essential in practice, there could be
20 000 channels. To ensure that all parts of the signal
band are always at least 36 dB down in adjacent areas,
these 20 000 mobile channels would have to be spread
out over 25 kmz, giving a maximum mobile density of
800 per km2, having an average linear spacing of about
28 metres. This would be quite adequate for most
purposes, allowing for, say, a 30 per cent simultaneous
usage from all cars in two 8-lane motorways in any one
area, with a 40 per cent reserve space for other mobiles,
even if the cars have an average longitudinal spacing of
only 10 metres. This shows that the useful, limitedrange frequency band in the 60 GHz region could deal with most mobile-traffic densities by conventional
FDM methods alone. But though equipments exist
already called 'synthesisers', for handling the frequent
wavelength changes at any one user point that such an
FDM-PCM mobile network would need, it is very doubtful if even by future miniature integrated circuits, terminating in the 60 GHz band, the apparatus could
be either small or cheap enough to fit into a pocketphone, for adequate protection against cross-modulation among signals of widely different field strengths. By
using instead a rather revolutionary new principle,
though, we can handle if need be still higher mobile
densities, and do it more cheaply.
This different method, that I have named `SYNSOL'
(the SYNthetic SOLid-state principle)8 is a very recent
concept. Both more rigorous analysis and a fair amount
of computer simulation will be needed before all its
difficulties and limitations are apparent. It is a new and
powerful non-linear network-planning concept. It is
obvious that not only its possible snags but also its full
latent advantages, together with applications in other
fields, can be appredated only after a great deal more
thought.
I shall now describe some of the aspects of
what it can do, not how it does it.
Without contravening orthodox information theory, it
can handle a theoretically vastly greater number of
users without mutual interference, all in the same
frequency band and in a given area or volume. It is
self-adaptive to the number of users, and to wide
variation in their location densities. The needed channel
changes, too, as a mobile progresses through a network
can be automatic by simple means. The required equipment, even for an output in the 60 MHz band, can be
cheap, have wide tolerances, and by integrated circuit
methods be small enough for pocket-phones; and where
the mobiles and ground stations have the same designs,
reception reliability of the signals can be satisfactory and
nearly constant up to a predetermined distance, e.g. the
point where the channel concerned is transduced into
the land network, and then fall substantially to zero
quite abruptly.
It is unusual to publish an idea while it is still in an
initial, rather `woolly' stage. In speaking about the
future, though, I believe it is sometimes necessary, as
otherwise the picture painted could have a vital feature
left out. The main idea behind the method is easy to
grasp. First, a line of mobiles between the calling unit
and the ground station, A and B in Fig 3, form a chain,
normally in single file. Each link gives a 2-way speech
channel between the mobiles or ground station at its
ends, becoming when established immune to everything
else. The result is something like a solid-state longchain molecule, if its cross-section were monatomic.
Similar chains then form successively among the remaining, non-aligned mobiles. In this way we produce
separate paths between the mobiles and the ground
stations feeding the land network, each becoming immune to signals from other paths just as if insulated
copper conductors had been grown between the desired
points. Each link in the chain is bistable, in the sense
that once broken it remains so unless specifically reestablished - as a broken soldered connection has to be
soldered again.
Each mobile in a given chain, as well as being able
itself to have 2-way conversation with the ground
station that temporarily terminates it, can also act as a
repeater towards a ground station for all other mobiles
in that chain. Thus the limit to the mobile density is set
almost entirely by the ground stations; but in the same
way they themselves can use the same frequency bands,
or by pulse methods the same time-slots within them,
so if there are enough of them the true limit can be put
almost indefinitely further away. If while a new chain is
being formed it finds no unaligned mobiles immediately
round it, these are automatically by-passed until free,
alignable units are found. The same thing happens if it
finds any mobile in its normal chain to have a radio that
is out of action.
To use an analogy, in the solid state, the adhesive
forces between atoms and molecules - due to the
interactions between the nuclear and electronic electric
fields, the magnetic fields due to the electron spins and
orbital movements, and the quantum 'exchange forces'have very short ranges of action, the electron clouds
becoming predominant and causing only repulsion
between atoms when two metal surfaces (say) are pressed
together after a mechanical break. It is by analogous
processes that in SYNSOL the mobiles in a chain adhere
together firmly as a signal-carrying group up to a certain
value of tension, while repelling away the causes of
forces from other chains. It is still another fascinating
example of the multitude of useful things that can be
done by delving into the so-far largely untapped storehouse that non-linear methods provide. I find that such
more sophisticated non-linear circuits are often liable to
frighten away the average electronics designers. But I
assure you that the reason is merely that they are not
yet sufficiently familiar with them. When correctly made
they can be just as reliable as a good watch, which
already uses such circuits, in mechanical form. By an
AGC (automatic gain control) at each receiver, in combination with an APC (automatic power control) at each
transmitter, after a link in the chain has been established
the receivable range of the chain-locking signals at each
end of that link is made to be nearly linearly proportional
to the link length. In this way the same frequency band
can be used by every mobile, even when some of them
are only a few metres apart, still maintaining negligible
mutual interference between different-chain members.
In the preferred form, the chain-locking signals will be
pulses of about I nanosecond duration, 100 per centmodulating the 60 GHz carriers. It is after a link has
been established that it can start to convey speech
information to and from the appropriate ground station
on a multi-channel basis, connecting all the mobiles
within it. Some further details of the SYNSOL method
are given in Appendix 11.10. Any approach to a complete description or explanation though, even on some
of its more basic features, must wait for later publications.
An alternative has been called by me the SYNSPEC
scheme (the SYNthetic SPECular reflection method).9
Instead of relying on a grouping of the mobiles into long
chains, it operates by the formation of temporary holograms, within larger groups of mobile users. Study of this
alternative has hardly yet been started. It is of course
impossible to predict now which of the two will prove
the better, and in what circumstances.
To cope with long links in the SYNSOL chains under
heavy rain conditions, a reserve carrier frequency of, say,
1 GHz will automatically be brought into action, as at
60 GHz the rain attenuation itself can occasionally
amount to about 90 dB/km, while being less than 1 dB at
1 GHz. The circuit plan to achieve this is particularly
simple if the chain links when at 1 GHz consist of
dipulses (Fig 4) containing mostly 1 GHz components.
See Appendix 11.11. The 1 GHz carrier will also come
into use sometimes without rain, when a link needs a
degree of diffraction round an obstacle that is impossible
at 60 GHz but obtainable at I GHz.
5 Information retrieval centres
We shall now examine briefly the design and operation
of the future equipments that will replace the central
libraries that we now have. If such an IRC in AD 2020
contained all the information then considered worth
recording for immediate access, at least at one place
and at one time, how many information bits would it
need to store? There are several reasonable bases on
which to form an estimate. Consider an extreme estimate
of the storage capacity needed for immediate access,
assuming that in AD 2020 the man-made written
information considered worth storing by the IRCs,
assessed by the economics of the probable demands to
extract it or in any other way, has been generated by
109 people, with an average of 10 000 words, i.e. about
300 000 bits, from each. Assume we also want to store in
PCM form, at any one time and place, 500 films each
running for an average of one hour. Suppose we decide
we need to store, in addition, 20 per cent of the above
total number of bits for machine-made information,
e.g. computer results, photographs, etc. The total
capacity then needed is about 1015 bits.
This number of bits will almost certainly be storable,
in hologram form, by trapped charges in not more than
about 1 000 CM3 of suitable electro-optical material.
If we multiply this volume by 3 000 to allow for laserbeam access to each crystal, and for the needed optical
switch-gear to and from the user wideband optical
channels in the local areas that each IRC serves, we get
3 cubic metres. The main space requirement, though,
would be for the man-machine interface; for though
both fault-finding and fault correction will become
more and more automatic, some manual monitoring and
servicing will still be required. To this extent the relatively enormous size of the human body, and particularly of its arms and fingers, will be the over-riding
factor. However, the whole future IRC should go into a
building smaller than many present telephone exchanges.
The storage could be for at least 100 years, without
regeneration where the number of read-outs per year is
low, and at ordinary temperatures. To achieve our aim
we must learn how to dope the material to ensure that
almost all the traps are of a fairly uniform depth of, say,
1 electron-volt in energy level. The resulting bit capacity
of about 1012 per cm3 is enough for one good-quality
film in PCM form running for one hour. The write-in
can be slow and use a variety of methods. The direct
read-out, though, causes all the bits in one frame to
arrive in parallel. To feed into the user's lines, a parallel to-serial converter is needed.
One means of access to future crystal stores, suitable
for the film-storing types, and using future optically
pumped integrated circuit lasers instead of the nowusual junction types, is described in Appendix 11.12. If
the user requires not a film but only a digital word
contained in a fraction of a film frame, the same technique can be used, the required bits being extracted by
the then-normal TDM pulse-selection methods. The
stores for global telephone numbers, perhaps about
400 km apart will usually be sections of the more general
information retrieval centres. The needed much faster
write-in, though, will require the different crystal-store
lay-out that is discussed in a section of Appendix 11.7.
Each general-purpose IRC will rarely need an information store of truly world capacity, but be partly
selective and be to some extent complementary to
others. The best access method at the subscriber end is
a very thought-provoking problem. On balance I think
that a necessity for a subscriber to look up the nearest
information sub-group title in a very large and complicated list, even when displayable quite quickly when he
is at his desk, will not be accepted by the general public.
I believe that his demand for general information will
eventually have to be dealt with via an access point in a
multichannel speech-recognition computer, these units
being in each local area. They will have to be more
sophisticated than the speech recognisers for directory
enquiries. Research to date has already shown us the
main lines on which they can be made to be quickly
self-adaptive to individual voices, e.g. as to accent and
speech formant frequencies.1° Each machine will need,
too, audible feedback from itself to each user, via a
channel in a stored-voice mechanism, sent in PCM form.
Here again we already know fairly well how to do it.
The subscribers will have to learn to use a stylised, nonredundant syntax. Multi-lingual machines will present
added difficulties, at least quantitatively. But I think
that eventual success is assured - but only by people
clear-sighted enough not to be appalled at the apparent
magnitude of the task!
It is necessary to say a few words about rapid access.
Suppose the local area serves 50
X 103 subscribers and
that, except for films, we choose the extreme aim of
never allowing any appreciable waiting time even when
all the subscribers are using their speech-recognition
machine at once. The total rate then needed from each
local area to its IRC is 5 gigabits/sec (half the capacity of
a single wideband fibre). Access time to longer and
shorter films, and to words or word-groups occupying
fractions of one frame, is discussed in the following
paragraph. There seems to be no difficulty in making the
waiting times quite acceptable.
Suppose that at any one IRC there are 250 64-minute
films stored at any one time, and an equal number of
32-minute, 16-minute, and 8-minute films. The 64minute films would occupy 250 cm slices of crystal, one
for each; the remainder could be stored in the form of
2, 4, and 8 per similar crystal slice respectively. If we
cater for groups of simultaneous users for all these
films, each kind having the same spacing between
optional starting times of 2 minutes, the number of
simultaneous user groups needed is 32, I6, 8, and 4
respectively, and the read-out techniques already
described can apply. When the demand is for a bit
group occupying one frame, (5 X 105 bits) or less, stored
in other crystals at one or more per frame with as rapid
as possible a random access in these cases, the waiting
period would in general be limited merely by the time
needed to transmit and process the binary-coded
address. In the case of a demand for a 1 000-bit word,
the address would need 27 bits, if there were (say) 108 of
them stored. This would take 2.7 nanoseconds to
transmit from the local-area processor, using a single
wideband fibre - and about another 5 nanoseconds to
complete the total access to the IRC crystal.
6 Isolated mobiles
We have not yet dealt with the communication needs
of aircraft and ships when out of range of the future
land-based stations, nor of land mobiles in areas so
sparsely populated or undeveloped that they do not
justify such networks. Our future ocean-going aircraft,
public or private, when out of visual-distance range of
land stations, will certainly get their communications by
Cosmat-type satellites, with HIP equipment in reserve
for emergencies only. While they are taking off or landing
they can use the land stations, probably at the lowerfrequency end of the 10-to-0.9 GHz band. Before they are too far away to continue on this band they will
almost always be above cloud; they will then use a
stationary satellite, on an optical or 10 GHz radio band,
the satellite completing the call to ground at 10-to-0.9
GHz. In the gallium arsenide optical band, the mobile
would in practice have to produce a 0.004° wide beam,
e.g. by using a paraboloid 1.5 em in diameter at each
end, to produce enough photons to give an adequate
signal-to-noise ratio from a mean transmitted power of
300 milliwatts. This is likely to become feasible, and
also the corresponding auto angular lock-follow, but not
at or too near the earth's surface, on account of
directional shimmering due to air turbulence. Above
40 000 ft altitude, with certain types of airframe, it
might conceivably be possible.
Existing optical techniques, when combined, could
achieve this by an ititial rough manual locking, with a
defocussed beam and a narrow received band-width,
followed by an automatic electro-mechanical finer
adjustment, and a final non-mechanical, precise adjustment from a miniature controller that changes the
positions of virtual images of the lasers by electro-optic
crystals. In addition, the time-constant and the angular
range of the final process could easily be made fast and
large enough to compensate against aircraft vibration.
Beam-splitting methods have been devised by which a
single satellite could serve a number of aircraft at the
same time, with auto lock-follow to each. As to the
ocean-going larger ships, they will use satellites via
radio, preferably near the 10 GHz end of the cloudpenetrating band so as to minimise antenna size. Beams 0.1° wide with auto lock-follow will be possible, as will
beam-splitting at a given satellite, if justified; but
3-metre-diameter dishes at each end, or the equivalent
in total antenna gain, would then be needed. A 2-metre
dish at the satellite, with a 1-metre version on the ship
would usually be more practical, 0.2 watts transmitted
power then being used at each end. At the 10 GHz end
6.5 per cent of the frequency band could cater for at
least 2 500 PCM audio channels per satellite, with a
total radiated power of 0.5 kW from the satellite.
Currently planned satellite solar cells, with solid-state
transmitters of 20 per cent efficiency, could thus cater
for double this number per satellite. Satellite nuclear
power packs, too, are now being considered. Air turbulence would in general prohibit the use of sufficiently
narrow laser beams. Lone yachtsmen, etc., who sail the
oceans in small boats, will in general still use the 2-12
MHz radio band.
We are left now with the cars in undeveloped areas,
out of range of the future visual-distance land networks.
They too will be unable to contact a satellite efficiently
by laser beams. So they will have to make their calls,
rather expensively, by using part of the 10-to-1 GHz
band. They will get into trouble if they switch on their
HF equipments except in a real emergency! To do so
they can use a 1-metre dish, with auto lock-on and lockfollow to a I°-wide beam-splitting satellite, with 0.2
watts transmitted from each end, like the ships in
similar circumstances.
7 Space communication
There will again be the problem of getting through
the earth's cloud. In the cloud-penetrating band of
10-to-1 GHz, though, it will probably never be reasonably possible to achieve enough field strength at the
earth's surface on really long-distance paths, since for
good audio channels the paraboloids would have to be
about 100 metres in diameter at each end (or the equivalent), from a space vehicle about 2 000 X 106 km away, if the spacecraft's transmitted power is limited to 100
watts. But there is a feasible answer: to transmit by
laser beam between the vehicle and a satellite, and then
to change frequency to the 10 GHz band for thesatelliteearth path. The limiting factors would then be the sizes and tolerances at the laser paraboloid. If the spacecraft
had a 1-metre-diameter paraboloid and the satellite
(then probably a space platform - or the moon) had
a 2-metre paraboloid good 2-way audio contact up to
about 6 000 X 106 km would be possible, with a delay, of
course, of over five hours in each direction. This would
cater for manned spacecraft at the distance of the
planet Pluto.
The speed problems in the orientation of both dishes
by automatic lock-follow are basically no worse as the
spacecraft gets further away. The maximum speed of the
feedback-loop controller to achieve it is reduced linearly
with distance; but for given values of the unpredictable
changes in the vehicle's position, so are the parallax
changes that these unpredictables cause. The lock-on
orientations of both dishes, of course, would need
precisions varying linearly with distance, as the reciprocal of this distance determines the needed beam widths. But this is not a
basic problem, and in practice it would
be quite soluble at 6 000 X 106 km. For intercommunicating entirely outside planet atmospheres that absorb in the useful laser-beam band, suitable laser-beam
methods alone will of course suffice.
8 Conclusion
We have taken a brief look at many aspects of the
communication revolution that is undoubtedly coming.
We have seen that mere distance
can be virtually
eliminated, and by means that even now have outlines
that at least to my mind are clear. I suggest that those
in the communication field who believe the picture I
have painted, at least in the main, should first decide if
they like it and if they want it. If they do want it they
should take all the necessary steps, to ensure that the
countries and areas that concern them do not leave it too
late to reap their shares of the fruits it will bring. The
goal may not be the single most vital thing that the
world now needs, but a world-wide `nerve system' of an
altogether new order, streamlining the way to all other
aims, will be no mean achievement. The effort will be
hard and long enough to bring creative fun and pleasure
to some of the very best minds that we have!
9 Acknowledgements
So many of my STL colleagues have helped me in the
preparation of this lecture that it is impossible to
mention them all individually. I ask them to accept my
sincere thanks. Though all of them would have put in an
equal effort if I had asked them, the following have in
fact contributed most. They are: C. F. Drake, C. C.
Eaglesfield, V. G. Herrington, K. C. Kao, S. F. Laurence,
A. E. Mounter, M. M. Ramsay, J. C. de Rivaz, I. F.
Scanlan, P. R. Selway, G. B. H. Thompson, and R. J.
Whelan. I hold none of them responsible for any predictions or opinions that I have expressed! I am indebted as well to the University of Strathclyde,
Glasgow, for their permission to reproduce certain
extracts from their 1969 `John Logic Baird Memorial'
Lecture, which is published by them. I am similarly
indebted to the Elsevier Publishing Company, London
and Amsterdam, concerning Fig 5.
10 References