Thanks to everyone for helping to divine the mysteries of CDMA. Loved the parking lots, freeways, cocktail parties, and especially comforted to know that the good guys are in the cement trucks with the nasties in the geos. Unless I miss my guess, engineer has probably already resigned from this thread and will disavow any knowledge when IEEE membership rolls around. Michael (or techy-Mike to avoid confusion) made the not unreasonable request that I be specific in my thirst for knowledge--here goes. One thing I'd like to know is the path of the communication signal. When I yak into a mighty Q handset, how in God's name does the conversation get to where it's supposed to go? Does the handset have the circuity to take my string of pearls and convert them to a series of 1's and 0's? If so, and it is now ready to launch this bit stream, I take it that said stream is flung into the air where it is picked up by a nearby base station (bs). Does the bs then read the bit stream and say, ha, ha, this is intended for Ramsey and then initiate a signal to Ramsey's phone which then rings and a connection is established and then maintained so that I can then continue the economic education of a basket weaver? But how does the bs know where Ramsey is? He could be on the beach, in a bar, modesty prevents me from going further but you get the idea. These phones are after all mobile which I think is the whole idea. Second and related point is how can something so little "throw" the bit stream from San Francisco to San Diego? I know it must get help from a series of bs's from SF to SD each playing some amazing relay game but it still seems so hard to grasp. I can "see" electromagnetic impulses/bit streams whatever riding the rail of a wire but air born base station hopping is kind of wild. (Note: I also have difficulty believing a 747 gets airborne even after I have just ridden the damn thing--so my visual imagery strength may be wanting.) Anyway, if you guys will just take a shot at this signal path thing, it would be great.
George Gilder used two other analogies in attempting to describe why/how CDMA can pack the freeways and parking lots with more cars than tdma. He described tdma as pointing at a continuous moving belt of railroad cars--as each car goes by in a precisely timed sequence, data is deposited into the box car IF there is data to be deposited at that instant. If not the car goes on empty and the data gets deposited in the next car. Thus TDMA inevitably wastes capacity cause there will indisputably be some empty cars and ergo it has not made the best available use of available spectrum. I'm cool with that. His second point to describe how you could really pack signals together was to think of flashlights each emitting a different color of light. All the beams can co-exist without bumping into each other cause they each retain their own unique identity (color=code). Actually, this stuff is just a whole lot more fun than world wide financial collapse. Somebody tell me the markets are closed. Regards, Mike Doyle |
