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Reply To: 3G Carrier Freqs

Wallis Dudhnath

Frequency hopping is linked to CDMA (IS-95) 3G/WCDMA, 4G/LTE(OFDMA), etc..

First of all when compared to TDMA / FDMA, Wideband CDMA (WCDMA) is a power based system that uses the full spectrum bandwidth. WCDMA is based on spread spectrum. With previous modulation schemes the signal was prone to errors, e.g. multipath fading, interference,
co-channel issues, etc..

Frequency Hopping is seen as a way to reduce on the radio errors and to ensure that a level of signal quality is maintained. The way how Frequency Hopping works is that the signal to be
transmitted is mixed with a Pseudo Randam Binary Sequence (PRBS) that is known to the TX and RX. This allows each of the transmitted signals to be spread throughout the defined bandwidth.

The receiver can then extract the signals and create the intelligence. For more information and the mathematics that goes with this area you can look at Direct Sequence Spread Spectrum and Fast Fourier Transformation (FFT).

Note that a good example of CDMA / WCDMA is the “cocktail party”. You are in a noisy party and the background noise is like a Gaussian Bell shaped curve. Despite the noise when somebody mentions
your name you will instantly home in on the discussion even though you are several meters aways and surrounded by noise.

VBR/ Wallis Dudhnath