Slow frequency hopping vs fast frequency hopping GSM | Difference between slow frequency hopping and fast frequency hopping

This page compares GSM slow frequency hopping vs fast frequency hopping and mentions difference between slow frequency hopping and fast frequency hopping used in GSM.

In the frequency hopping, RF carrier frequency used for transmission hops between available channels. This will generate frequency hopped spread spectrum signal. The successive carrier frequencies in the FH sequence are chosen based on PN (Pseudo Random) sequence. The aim of frequency hopping is to provide secured communication between GSM Mobile Station and Base Station. Depending upon relation between hopping rate and symbol rate there are two types viz. slow and fast.

GSM Slow frequency hopping

In slow frequency hopping type, more than one symbols are transmitted during the time between two frequency hops.

In slow frequency hopping, time duration between two hops (Th or Tc as shown) > data bit duration (Tb). This is depicted in the figure-1.
There are two types of slow hopping viz. synthesized and baseband hopping >>.

GSM Fast frequency hopping

In fast frequency hopping type, one complete or fraction of data symbol is transmitted during the time between two frequency hops. Due to this, frequency hopping rate may exceed often compare to data bit rate in a binary sequence.

In fast frequency hopping, time duration between two hops (Th or Tc as shown) <= data bit duration (Tb).
This is depicted in the figure-2.

➨The fast frequency hopping provides frequency diversity at symbol level. This will benefit the transmitted signal against fading as well as narrowband jamming.
➨The slow frequency hopping can achieve above benefits with the use of error correction coding.

GSM Channels

GSM RELATED LINKS

What is Difference between

RF and Wireless Terminologies