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I understand that GSM regulations establish that transmissions power for two bands must be as follows,

-Class 4 (2 W @ 850/900 MHz) -Class 1 (1 W @ 1800/1900MHz)

But I also know that lower the frequency higher the range for equal transmission power. In that case, does it mean 1800/1900 MHz band has lesser range than the first? And also essentially result "better" than Class 1?

Denis
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2 Answers2

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My short answer is that there is no better or worse, it is a generic answer "that depends"

It is true that you will have a larger coverage with the lower frequency (assuming, the TX power is fixed). GSM is a cellular network which means that it consists of multiple small networks (cells) formed by BTSs (base transceiver station) which has an ability to serve maximum number of users. More dense areas (city centre, shopping malls, etc.) it is desired to have smaller cells (means smaller coverage) to be able to serve more users to provide a better performance (higher frequency, lower TX power of BTS). If it is a rural area, GSM operators may want to have a larger coverage to decrease their costs. Therefore, larger coverage does not mean that it is better or worse, it depends on where and why it is applied.

GSM900 has 4 power classes (39dBM to 29dBM) and GSM1800 has 3 power classes (30dBM to 36dBM). Transmit power of the mobile platforms are adaptive, closer to the BTS, lower TX power. If you have noticed it, the uplink of mobile devices are designated on lower frequency than the downlink in order to lower the power consumption on the mobile devices.

Higher frequency allows higher data-rate and most of all, it allows smaller antenna size which is important for the mobile platforms and easier to hide BTS's antennas in the public domains.

Angs
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    I think it is dangerous to say that higher frequencies "allow" higher data-rate. What is correct to say is that wider frequency bands allow higher data-rate. The fact we are migrating for higher frequencies does not mean we are searching more data rate, just that we are taking what is available. – gstorto Feb 17 '15 at 14:11
  • according to this answer : http://electronics.stackexchange.com/questions/154527/wifi-channel-vs-a-sub-1-ghz-channel-of-same-width I believe faster frequency does not mean faster data rate. Could you kindly elaborate on that? Im a little confused. I mean how could higher frequencies provide more users higher performance? – Denis Feb 17 '15 at 14:14
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    900 and 1800 MHz are the carrier frequencies. The bandwidth can't be larger than the transmit frequency. In that sense, I meant high frequency allows higher data rate. You may see that (opposite examples as well) higher bandwidth is allocated for the higher frequencies (this does not mean that it will carry more data), GSM1800 has a larger bandwidth than GSM900, but GSM operators allocates more user to that bandwidth, enduser-wise you get the same performance – Angs Feb 17 '15 at 14:44
  • under the circumstance that all base stations of all career frequencies offering similar range, a mobile phone working on 900MHz career will transmit less power than a mobile phone switched to a 1800MHz. Is this statement correct? – Denis Feb 18 '15 at 01:22
  • If we purely consider the RF signal, by referring to the free space path loss formula, the statement is correct. If all the conditions are the same, then the higher frequency signals needs to be transmitted with a higher powerto have the same coverage of lower frequency signal. If we take it as a mobile phone as a whole, t0hen you need to check it with a link budget. That depends on multiple factors, such as how well antenna of the phone is implemented & antenna gain, and how well the RF part of the phone is implemented (RF coupling, EMI/EMC), receive sensitivity of the BTS, RF chipsets,... – Angs Feb 18 '15 at 11:48
  • In order not to sound wrong, link budget does not consider implementation part, just antenna gains, receive sensitivity, SNR, path loss, etc. But the implementation is another consideration of a device's performance and used component's or chipsets – Angs Feb 18 '15 at 12:06
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Well I certainly do not agree with that. As the penetration (building, steel, concrete) of the signal may depend on its frequency, the range you may successfully transmit and receive depends on many other factors.

Considering an ideal scenario, where you have no obstacles, no background noise. For equal transmission power, the other factors are: the frequency band you have available and of course, the data rate you are intending to transmit/receive.

If you are going to transmit one bit per hour, I guarantee you could have an extremely narrow frequency band with low power transmission. Unfortunately, it is not sufficient for many applications.

gstorto
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