Frequently Asked Questions (FAQ)

How to calculate the attenuation of free space?

The Free Space Attenuation (FSA) corresponds to the weakening suffered by a radio signal during its transmission power in the air.

It is calculated as follows:

  • FSA = 32,44 + 20*log(F) + 20*log(d)
  • FSA is expressed in dB, F in MHz & d in km

Difference between dBm & dB?

DBm is the unit of absolute power (0dBm = 1mW), while dB expresses a relationship between two powers: for example we can say that the power amplifier is 47dBm (ie 50W), which is an absolute value, whereas if we speak of its gain which is 20 dB for example, this corresponds to a ratio between input power and output power of 100.


Difference between base station & repeater?

A base station generates a signal to the mobile, while a repeater only repeats the signal from the base station.

A base station is an autonomous element that allows itself to dispose of traffic and to have a high output power.

A repeater is directly dependent on its home base station (for example regarding the capacity of traffic).


Difference between UMTS & 3G?

There is no difference: UMTS means « Universal Mobile Transmission System » and corresponds to the third generation mobile phone standard, known as 3G. This third generation can carry information at a rate of up to 2Mbit.


What is the difference between GSM, GPRS &EDGE?

GSM is the second-generation mobile telephony, limited to relatively low flow rates (9.6 Kbps). This technology has evolved to increase the flow, and two solutions can be implemented to increase this flow:


GPRS is a technology that realizes a group within the GSM frame by merging time-slots and thus allows better matching of data to GSM. GPRS allows introducing an Internet Protocol (IP) within the GSM system, and allows a transmission speed of 115 Kbit/s.

EDGE is a technology that represents an improvement in base stations by increasing the spectral efficiency (from a 4-state modulation type GMSK to 8PSK), a timeslot on the capacity from 9.6 Kbit/s to 48Kbit/s or 60Kbit/s in good radio conditions. The baseband filtering is linearized, which means that the 8PSK "fit" in the mask of GSM spectrum.

By combining these two technologies, one can in theory reach speeds of 500Kbits/s, but in practice, 3G networks are there to ensure the highest flow rates.

GPRS and EDGE with higher data rates than GSM and less than UMTS are sometimes called 2G ½.


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