Definitoin of DSSS and FHSS

In telecommunications, Direct-Sequence Spread Spectrum (DSSS) is a spread-spectrum modulation technique primarily used to reduce overall signal interference. The direct-sequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth. 

Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly changing the carrier frequency among many frequencies occupying a large spectral band. The changes are controlled by a code known to both transmitter and receiver. FHSS is used to avoid interference, to prevent eavesdropping, and to enable code-division multiple access (CDMA) communications.

Advantages of FHSS

Robust Transission Path: FHSS provides a very robust transmission path even in the presence of interferences such as multipath, noise, and other wireless transmissions. This robustness is due to its support of wide bandwidth.

Point-to-Multipoint Applications: FHSS can be effectively employed in point-to-multipoint scenarios, allowing multiple devices to communicate with a central hub or access point.

Minimal Interference: It supports about ten nearby WLAN-compliant Access Points (APs) without significant interference issues.

Security: FHSS ensures security against intrusion since only the transmitter and receiver are aware of the pseudo noise codes used for frequency hopping.

Disadvantages of FHSS

Bursty Errors: As FHSS relies on carrier frequencies to transmit information bits, it can lead to strong bursty errors due to frequency-selective fading.

Lower Data Rate: FHSS supports a lower data rate (around 3 Mbps) compared to the 11 Mbps supported by Direct-Sequence Spread Spectrum (DSSS).

Coverage Range: It has a lower coverage range due to the high Signal-to-Noise Ratio (SNR) requirement at the receiver.

Obsolete Modulation Scheme: FHSS has become less common due to the emergence of newer wireless technologies in consumer products.

Advantages of DSSS

Interference Minimization: DSSS uses both time and frequency planes to transmit information bits. This minimizes the impact of interference and fading, making it robust in challenging environments.

Point-to-Point Applications: DSSS can be effectively employed in point-to-point scenarios, achieving a data rate of about 11 Mbps.

Coverage Range: It supports a higher coverage range due to its low Signal-to-Noise Ratio (SNR) requirement at the receiver.

Disadvantages of DSSS

Sensitivity to Harsh Environments: DSSS is sensitive to harsh conditions such as collocated cells, larger coverage areas, and multiphase interference. Its narrow bandwidth operation makes it vulnerable.

Error Sensitivity: DSSS is more prone to errors at lower levels compared to Frequency-Hopping Spread Spectrum (FHSS).

Bandwidth: The channel bandwidth required is very large.

In short, Frequency-hopping spread spectrum (FHSS) and Direct sequence spread spectrum (DSSS) are both types of spread spectrum techniques that are used in a variety of applications, including wireless communication, radar, and GPS. FHSS involves rapid frequency switching of the transmitted signal among a set of specific frequencies, while DSSS involves spreading the spectrum of the original signal over a wider bandwidth by multiplying it with a pseudo-random sequence of bits.