- telephones are for places, not people
- "Some people, some places, some of the time"
- telephones are for people, in the right places
- "all people, some places, some of the time"
- telephones are for people, not places
- "all people, all places, all the time"
First let's look at the way in which telecommunications networks have evolved. POTS fixes
'phones to places - you may find the person you want at the place you call, but you can't be
sure. This has led us to develop "add on" features to enhance network such as call
forwarding and transfer. But phones still essentially fixed to places
CELLULAR NETWORKS broke the "fixed place" link. We carry our 'phones in our
pockets and they are linked to us and (except when we forget and leave them at home!) not to
places. BUT they don't work everywhere and are dependent on infrastructure... indoors...
remote areas... overseas... won't always find us.
PERSONAL COMMUNICATIONS aims to break the final "infrastructure" link. The phone
is truly linked to the person and not the place or the time and the link to Captain Kirk is
So, what is "Personal communications"?
- Affordability and capacity
-"Universal Service Concept"
Traditional telecommunications networks are just that... "network oriented".
Features and services defined by the network and not the user but.. PCN's are more user
Mobility - service independent of user location.
Location - network identifies user location and addresses services there
Tailoring - service parameters under user control.
Affordability/Capacity - both critical because of widespread nature of service and expected
Security - the same or enhanced beyond the fixed networks Universal Service - "anyone,
anyplace, anytime" Leads us to Satellite-PCN.
Concept (3): S-PCN
-Satellite based (enhanced) network
-Hand held terminal / direct access
- Low Earth Orbit
- Medium Earth Orbit
- Geostationary Earth Orbit
Look at the definition of PCN and it soon becomes clear that delivery by satellite is a key
way of achieving the service objectives. By basing a network entirely on satellite or by
adding satellite as an overlay to a terrestrial based network we can achieve the universal
service requirement. Some of the areas I'll try and explore... Hand-held terminal... impact
on system design Orbit - does the choice matter? Network... how configured?
Concept (4) - Hand Held Terminal
-Main limitation on network design
- Maintain battery life
- User safety (< 0.5 W average RF power)
- Defines link and satellite design
-Multi-mode for better network integration
The whole network design is terminal driven... (slide) Because of low power availability
from terminal defines absolutely the parameters of the satellite receiving system... antenna
gain -> size -> link margin (coping with fades and blockage) Multimode important
too... ability to route calls through terrestrial network (cheaper) if it is available.
Concept (5) - Choice of Orbit
-Does the orbit really matter?
-Clearly pros and cons for different orbits
-No consensus amongst designers!
- LEO - Iridium / Globalstar
- MEO - ICO
- GEO - ACES / APMT / THURAYA
Much has been written about which orbit is "best" for S-PCN. I have a personal
preference, but we'll come to that later. Test is probably that there is no consensus
amongst the system designers. But we've introduced some terms that probably need to be