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Cellular Networks

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Electroenthusiast

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Refer this Link, you see that the area of coverage increases as the frequency of the network decreases. How does this happen so?

Am i alloted a certain predifined frequency or does the frequency keep changing when i move around(handover)? How will the calls made to me only reach me(secure)?
 
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Refer this Link, you see that the area of coverage increases as the frequency of the network decreases. How does this happen so?

Low frequencies have more energy than high frequencies (per cycle). Have you noticed that when somebody has a party and plays music very loud.. all you hear at distance is the low frequency bass. High frequencies attenuate more quickly.
 
oh yeah... i keep forgetting this, thanks for reminding. BTW, i only hear vocal sounds when far away, considering an example of a music concert.
 
hi Nigel, i was asking it for a particular network and in a particular place. Now, i have a phone that which uses a GSM technology. Am i allocated a dedicated frequency?

Also, GSM and CDMA are alloted a same band of frequency, wont that interfere?
 
To the question on frequency and distance:
High frequency is more straight line, line of sight, does not bend, much like light.
Low frequencies tend to bend with the earth.
When I worked broadcast, our AM transmitter of only 1kw reached over the horizon and many times the distance of the horizon.
Our 100kw FM station reached to the horizon very well. At 2x the horizon it was gone.
By horizon I am talking about sitting on top of the tower horizon.

Ham radio is a good example. They use frequencies from very low to very high.
I have talked 1/2 way around the world using low and very low frequencies. On the high end the 2m band is only good for 30 miles here.
 
When FM waves wont reach so long, then whats the requirement of such a huge power(100x). 2x the horizon? thats too far away i guess.

That's interesting, what do i need to do to have an ham radio? And how private will i be, if i be an ham?
 
When FM waves wont reach so long, then whats the requirement of such a huge power(100x). 2x the horizon? thats too far away i guess.
FM is in the range of 100mhz. It only bends a little. To get beyond "line of sight" you just have to power over the horizon. Many FM radio stations that I know of have 800 feet antennas to get more distance.

That's interesting, what do i need to do to have an ham radio? And how private will i be, if i be an ham?
That depends on country. There are tests to pass. It is not private!
 
Google these words and bring back a report on what you learned.
From what i learn through google, GSM uses FDMA and TDMA together, some sources quote either FDMA or TDMA is used. Still not sure about the encryption or modulation technique used by the GSM. They do say that GSM uses frequency hopping.

TDMA is a multiple access technique, so is the FDMA. In TDMA, a single channel is divided, in FDMA the various frequency is used to provide multiple connectivety. So, this acc. to me is similar to TDM and FDM.

CDMA uses DSSS technique as modulation, but still here the same channel is shared. So, this confuses me with FDMA. Also, if CDMA uses DSSS, then why is it names as CDMA instead of DSSS.
 
It has been a while back, I did work for a phone IC maker. Now there are new frequencies for cell traffic, that came from old TV channels. (US) Back before that: The CDMA network operates in the frequency spectrum of CDMA 850 MHz and 1900 MHz while the GSM network operates in the frequency spectrum of GSM 850 MHz and 1900 MHz.

I never worked with cell RF but I did work cell audio.
TDMA provides multiuser access by chopping up the channel into different time slices and FDMA provides multiuser access by separating the used frequencies. TDMA is like having 128 phones connected to a 128 position switch that is spinning very fast. Each phone gets a time slot. FDMA each phone has a different frequency with in a carrier.

The CDMA is based on spread spectrum technology. It allows each user to transmit over the entire frequency spectrum all the time.
GSM operates on the wedge spectrum called a carrier. This carrier is divided into a number of time slots and each user is assigned a different time slot. GSM uses both Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA).

I find this complicated, in part because, I come from broadcast where we talk frequency not time. I transmit on 98.6mhz. The RF cell engineers I know talk in time not frequency. If you think time, cell is easier to understand. I am the wrong person to explain this because I have a hard understand "37.5nS later we transmit this then 37.5nS we to that". It hearts my head to think in time.
 
Thanks for the reply ronsimpson, that kept the thread alive. I'm a little confused with CDMA.

I had never heard of anyone speaking this in terms of time! Wow! I would like to hear more experiences from others.
 
CDMA is what GPS uses. All the satellites use the same frequency but are separated in the receiver by a correlator using different coding sequences that each satellite uses. It's complicated.

On a few other points raised...low frequencies propagate better by bouncing between the ionasphere (I thinks thats the one) and the ground thus allowing it to propagate globally. Higher frequencies will pass through the ionasphere.

As for low frequencies having more power than high frequencies....Max Plank would disagree. 1Watt of close proximity HF signal could give you cateracts. 1Watt of Gamma rays would peel your skin off you. The reason you can only hear bass audio frequencies at a distance is they are less attenuated by buildings and other clutter. That's a different argument.

https://en.wikipedia.org/wiki/Planck_constant
 
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