Application of frequency hopping spread spectrum

• Wireless local area networks (WLAN) standard for Wi-Fi
• Wireless personal area network (WPAN) standard for Bluetooth
• In a large facility especially with multiple floors
• It can be used multiple FSK
• In FHSS each station using I/M of bandwidth but allocation change at every hop
• Various military application
• Civilian application

What is spread spectrum

Overview :

Spread spectrum is a one types of techniques it can be used for transmitting radio or telecommunication signal. The increasing demand of wireless communication have faced problems because of limited spectrum capacity and multi-path propagation. These problems can be minimized by spread spectrum communication.

Feature of spread spectrum :

• Capability of multiple access
• Resistant to jamming
• It has the ability to resist multi path propagation 
• Because of multi-path propagation. It provide  immunity to distortion
• Higher channel capacity
• It can not be intercepted by any unauthorized person

Spread spectrum model :

Figure shows the general block diagram of a spread spectrum digital communication system. so not let us talk about one by one block in spread spectrum model in detail.

To shown in figure the input is given to a channel encoder that produces the analog signal with narrow bandwidth at the center frequency.

The the signal is modulated by a spreading code or sequence. The spreading code is generated by pseudo noise or pseudo random number generator. 

Modulation increases the bandwidth of the signal to be transmitted. At the receiver end the digit sequence is used to demodulate the spread signal. The signal is sent to the recover the data.

Spread spectrum model

Advantages of spread spectrum :

• Reduced cross talk interference
• Inherent security
• Hard to detect
• Longer operating distance
• Better voice quality 
• Harder to jam
• Interception of signal will be difficult
• Privacy due to pseudo-random code
• Co-existence
• Less multi path fading

Processing gain of spread spectrum :

The processing gain is defined as the factor by which the bandwidth of the message signal is increased.

Processing gain : N = Bss / B

Where, 
B = Message signal bandwidth
Bss = Spread spectrum signal bandwidth

Types of spread spectrum : 

• Direct sequence spread spectrum (DS/SS)
• Frequency hopping spread spectrum (FH/SS)

Application of Spread spectrum :

• Prevent signal jamming
• Cellular technology
• Cell phones
• Global positioning system
• Wireless local are network security
• Prevent Interference at specific frequency
• In obtaining the message signal

You may also check it out difference between DSSS and FHSS

Advantages and disadvantages of frequency hopping spread spectrum

There are some of the advantages of frequency hopping spread spectrum (FH-SS) given below :

• It has less distance effect.
• Provide the greatest amount of spreading.
• The bandwidth of these systems is large.
• It has a short acquisition time.
• Best discrimination against multi-path.
• Very large bandwidth.
• The synchronization is not greatly dependent on distance.
• This system can be programmed to avoid some part of the spectrum.

There are some of the disadvantages of Frequency hopping spread spectrum (FH-SS) given below :

• It needs complex and costly digital frequency synthesizers are required to be used.
• It needs error detection.
• The processing gain is higher than that of a direct sequence spread spectrum.
• This system is not useful for the range and range rate measurement.
• The modulation scheme has become obsolete.

Some more advantages of FH/SS compared to DS/SS is given below :

• FS/SS is less susceptible to be near-far problems than DS/SS.
• The processing gain is higher than that of system DS/SS.
• FH/SS can produce signals of wider bandwidth than DS/SS.
• In FS/SS the problem of a relative power level of co-channel signals is not critical as than DS/SS.

Explore more information:

1. Advantages and disadvantages of DSSS
2. What are the difference between DSSS and FHSS

What is frequency hopping spread spectrum

Frequency hopping spread spectrum is a method of transmitting radio signals by rapidly switching a carrier.  

In FHSS among many frequency channels using pseudorandom sequence known to both transmitter and receiver. 

Overview :

In FHSS the data bits that are transmitted in the different frequency slots are changed by the PN sequence.

FHSS is often used as a method to allow multiple transmitter and receiver pairs, it can operate in the same space on he same broad channel at the same time.

In FHSS the data sequence is spread over small frequency slots of the spread spectrum signal.

FHSS is a wireless technology that spreads its signal over rapidly changing frequencies. 

Advantages and disadvantages :

The advantages of Frequency hopping spread spectrum given below :

• It has less distance effect.
• Provide greatest amount of spreading.
• The bandwidth of these system is large.
• It has a short acquisition time.
• Best discrimination against multi-path.
• Very large bandwidth.
• The synchronization is not greatly dependent on distance.
• It can be programmed to avoid some part of the spectrum.

Disadvantages of Frequency hopping spread spectrum given below :

• It needs complex and costly digital frequency synthesizers are required to be used.
• It need error detection.
• The processing gain is higher than that of direct sequence spread spectrum.
• It is not useful for range and range rate measurement.

Application :

• Wireless local area network standard for Wi-Fi.
• Military communication equipment.
• Wireless personal area network standard for bluetooth.

Application of direct spread spectrum sequence

• Cordless phones operating in the 900 MHz, 2.4 GHz and 5.8 GHz bands. 
• United status GPS technology, European Galileo and Russian GLONASS satellite navigation systems used DS/SS system with a single PN code in conjunction with FDMA and later it is used to achieve CDMA with multiple PN code.  
• Used in the low probability of intercept signal.
• It obtain message privacy.
• Used military and many commercial application.
• The unique spreading codes support code division multiple access.
• Support various decision making level.
• To reject unintentional  interference.
• To minimize self interference due to the multi-path propagation.
• It is used in automatic meter reading. 
• Used in IEEE 802 11b and Zigbee network. 
• Radio controlled model automotive vehicles. 

Advantages and disadvantages of direct sequence spread spectrum

Advantages of DS/SS :

• It has best noise and anti-jam performance.
• Simple hard ware implementation.
• It support high coverage range due to low SNR requirement at receiver.
• Do no require high speed fast setting frequency synthesizer.
• It has best discrimination against multi-path signals.
• The unidentified receivers find it difficult to detect the direct sequence signals.
• It can be employed in point to point application at the rate of 11 Mbps.
• Determination of relative timing between transmitter and receiver. 

Disadvantages of DS/SS :

• DS/SS has a longer acquisition time.
• It require wideband channel with small phase distortion.
• The pseudo noise generator must generate sequence at high rates.
• Near-far problem.
• Fast code generator needed.
• The system is prone to error at lower than frequency hoping spread spectrum.

Explore more information:

1. Advantages and disadvantages of FHSS 

What is direct sequence spread spectrum

Direct sequence spread spectrum (DSSS) is spread spectrum modulation technique used in telecommunication to reduce overall signal interface. 

Direct sequence spread spectrum (DSSS) is one type of channel access method is better known as direct sequence CDMA. This is mainly used in IEEE 802.11b and also used  Zigbee technology. 

Overview : 

• The term DS/SS stands for direct sequence spread spectrum
• In this method, the pseudo-random code is used when the signal can be detected at the receiver end. If avoid unauthorized signal access.
• The DS/SS is affected by the near-far problem. This problem occurs because of the unequal power that is received by the user.
• It is a very sensitive technology.
• Many users can be used in the same band with a better signal to noise ratio. 
• DS/SS is used point to point scenario.
• The DS/SS signal spectrum is spread over a wide band while the PSD is small, Hence, it is simple to hide the signal within the noise floor.
• DS/SS delivers capacity of about 11 Mbps.

Advantages of  DS/SS :

• It has the best noise and antijam performance.
• Simple hardware implementation.
• It supports high coverage range due to low SNR requirement at receiver.
• Do not require high-speed fast setting frequency synthesizer.
• It has the best discrimination against multi-path signals.
• The unidentified receivers find it difficult to detect the direct sequence type of signals.
• It can be employed in point to point the application at the rate of 11 Mbps.

Disadvantages of DS/SS :

• DS/SS has a longer acquisition time.
• It requires a wideband channel with small phase distortion.
• The pseudo noise generator must generate a sequence at high rates.
• Near-far problem.
• Fast code generator needed.
• The system is prone to error at lower compared to FH/SS.

Application of DSSS :

The application of direct spread spectrum analysis is listed below.

• DSSS is used in the low probability of intercept signal.
• It obtains message privacy.
• It is used military and much commercial application.
• It can support the unique spreading codes support code division multiple access.
• Support various decision-making level.
• To reject unintentional interference.
• To minimize self-interference due to the multi-path propagation.

Explore more information:

1. Difference between FHSS and DSSS