{"id":132,"date":"2018-07-13T07:01:46","date_gmt":"2018-07-13T07:01:46","guid":{"rendered":"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/?post_type=chapter&#038;p=132"},"modified":"2019-05-15T09:33:02","modified_gmt":"2019-05-15T09:33:02","slug":"spread-spectrum-technology-frequency-hopped-spread-spectrum","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/chapter\/spread-spectrum-technology-frequency-hopped-spread-spectrum\/","title":{"rendered":"Spread Spectrum Technology: Frequency Hopped Spread Spectrum"},"content":{"raw":"<div><span style=\"float: right;\"><a href=\"https:\/\/youtu.be\/FfuDTqA__pU\" target=\"_blank\" rel=\"noopener\"><img src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"epgp books\" width=\"75px\" height=\"75px;\" \/><\/a>\r\n<\/span><\/div>\r\n<div>\r\n\r\n<strong>Learning Objectives<\/strong>\r\n<ul>\r\n \t<li style=\"text-align: justify;\">History of spread spectrum technology<\/li>\r\n \t<li style=\"text-align: justify;\">Difference between Narrow band and Spread Spectrum Signal<\/li>\r\n \t<li style=\"text-align: justify;\">Understand the advantage of Spread Spectrum Technology over narrow band<\/li>\r\n \t<li style=\"text-align: justify;\">Discuss types of Spreading techniques<\/li>\r\n \t<li style=\"text-align: justify;\">Introduction to Frequency Hopped Spread Spectrum and its working<\/li>\r\n \t<li style=\"text-align: justify;\">Understand the variants of Frequency Hopped Spread Spectrum<\/li>\r\n<\/ul>\r\n<strong>Introduction<\/strong>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify;\">A famous Hollywood actress, Hedy Lamaar along with film music composer George Antheil, patented \u201cSecret Communication System\u201d in 1942 which received U.S. Patent #2.292.387. The Spread Spectrum communication technology was introduced. The invention was believed to be quite ahead of time and was not taken seriously until 1980\u2019s when U.S. military declassified it and since then it is foundation of today\u2019s wireless technologies like CDMA, Wireless LAN, IMT- 2000, Bluetooth, 3G and Global Positioning Systems(GPS). Narrow band signals transmit at a very constant frequency for eg. FM radio will always transmit at the frequency allocated to it say 98.3. The receiver has to tune onto this frequency to get the broadcast. Since the narrow band transmission always uses the same and predefined frequency, it is very easy to intercept, interfere and jam. It also requires high power to transmit. Spread Spectrum technology offers a solution to these problems. Spread spectrum devices transmit at varied frequencies occupying greater bandwidth but less power. Transmission on different frequencies makes the transmission hard to intercept and interfere. Spread Spectrum technology is a technique that spreads the narrow band signal to a broad range of frequencies. This is done by using different spreading techniques mainly Frequency Hopped Spread Spectrum and Direct Sequence Spread Spectrum. This module explains the Spread Spectrum technology, various spreading techniques and the technologies implementing it.<\/p>\r\n\r\n<\/div>\r\n<strong>History of Spread Spectrum Technology<\/strong>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify;\">Spread spectrum use is on the verge of potentially explosive commercial development, especially in relation to the internet. what's is surprising is that the inventor behind this amazing process is an incredibly beautiful and talented actress of the 1940's! .Her name is Hedy Lamarr, known as \"The Most Beautiful Girl in The World\"<\/p>\r\n&nbsp;\r\n<p class=\"hanging-indent\"><img class=\"aligncenter wp-image-133 size-medium\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic1-240x300.jpg\" alt=\"\" width=\"240\" height=\"300\" \/><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\"><span style=\"font-size: 1em; text-align: initial; text-indent: -1em;\">She with American composer George Antheil, came up with was an idea for a sophisticated anti-jamming device for use in radio-controlled torpedos during world war II. Lamarr and Antheil realized that radio-controlled torpedoes, which could be important in the naval war, could easily be jammed, thereby causing the torpedo to go off course. If pianos could be synchronized to hop from one note to another, why couldn't radio signals - steering a torpedo - hop as well? Their inventive partnership was born. Hedy's idea was if you could make both the transmitter and the receiver simultaneously jump from frequency to frequency, then someone trying to jam the signal wouldn't know where it was. They designed a frequency-hopping system that would continually change the radio signals sent to the torpedo.<\/span><\/p>\r\n&nbsp;\r\n\r\n<em>They were awarded U.S. Patent Number 2,292,387 on August 11, 1942, under the name \"Hedy Keisler Markey\" and George Antheil for a \"Secret Communications System.\"<\/em>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify;\">Who would have known that a glamorous female movie star of the 1940's would defy all stereotypes and create a communications system that was decades ahead of its time and is only now coming into widespread use. The invention could not be implemented during World War II and only came into use 20 years later during the 1962 Cuban Missile Crisis their patent catalyzed the use of Spread Spectrum, which is a highly efficient way of using radio frequencies at the same time, without interfering with each other. This is the basis for the cellular phones, faxes, and other wireless communications systems in widespread use today and is foundation of today\u2019s wireless technologies like CDMA, Wireless LAN, IMT-2000, Bluetooth, 3G and Global Positioning Systems (GPS).<\/p>\r\n&nbsp;\r\n<p class=\"hanging-indent\"><strong>Narrow band Signal<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">In a transmission system, the information is modulated with a carrier signal and then transmitted. When transmitted, all\u00a0 the power transmitted is\u00a0 centered around a particular frequency. This frequency represents a specific channel and has a narrow band. This narrow band signal has certain disadvantages like:<\/p>\r\n\r\n<ol>\r\n \t<li style=\"text-align: justify;\">Since the transmission is always on a constant frequency, it is easy to intercept<\/li>\r\n \t<li style=\"text-align: justify;\">It requires more power to overcome the noise<\/li>\r\n \t<li style=\"text-align: justify;\">Suffers from interference<\/li>\r\n \t<li style=\"text-align: justify;\">Prone to jamming and tapping<\/li>\r\n<\/ol>\r\n<p style=\"text-align: center;\"><img class=\"aligncenter wp-image-134 size-full\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic2.jpg\" alt=\"\" width=\"640\" height=\"350\" \/><b>Figure 1: Narrow band vs Spreader\u00a0signal<\/b><\/p>\r\n\r\n<div>\r\n\r\n<strong>Spread Spectrum signal<\/strong>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify;\">Spread Spectrum technology is a technique that spreads the narrow band signal to a broad range of frequencies. Spread spectrum devices transmit at varied frequencies occupying greater bandwidth but less power. Transmission on different frequencies makes the transmission hard to intercept and interfere. Spread spectrum modulation spreads out the\u00a0 modulated signal bandwidth so it is much greater than the message bandwidth.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\"><span style=\"font-size: 1em;\">A signal that occupies a bandwidth of B, is spread out to occupy a bandwidth of Bss (Fig 2). Spread spectrum increases BW of message signal by a factor N, known as Processing Gain<\/span><\/p>\r\n\r\n<\/div>\r\n&nbsp;\r\n\r\n<img class=\"aligncenter wp-image-135 size-full\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic3.jpg\" alt=\"\" width=\"1206\" height=\"470\" \/>\r\n\r\n&nbsp;\r\n<p style=\"text-align: center;\"><strong>Figure 2: Signal Spreading<\/strong><\/p>\r\n\r\n<div>\r\n\r\n<img class=\"aligncenter size-full wp-image-136\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic4.jpg\" alt=\"\" width=\"337\" height=\"83\" \/>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<strong>Advantages of Spreaded Signal<\/strong>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify;\">There are several advantages of the scheme which prima face appears as wastage of bandwidth they are:<\/p>\r\n\r\n<ol>\r\n \t<li style=\"text-align: justify;\"><strong>Hard to Intercept: <\/strong>Figure 1 shows narrow band signal as well as the spreaded signal. It can be seen that power level of spreaded signal is much less than the original narrow signal. It can also be lower than background noise and thus hard to detect.<\/li>\r\n \t<li style=\"text-align: justify;\"><strong>Power requirement is low: <\/strong>During transmission it is always possible that some atmospheric noise will creep into the transmission which can be misinterpreted as radio signals. To overpower this noise, the narrow band signals need to be transmitted with high power than noise. Spreading the signal over frequency can lower the power requirements. For instance if narrow band signal requires 10 watts to transmit 1 MHz, a spread spectrum signal may require only 100 miliwatts to transmit 20 MHz signal.<\/li>\r\n \t<li style=\"text-align: justify;\">Used for hiding and encrypting signals because only a recipient who knows the spreading code can recover the coded information<\/li>\r\n \t<li style=\"text-align: justify;\">Reduces narrow band interference<\/li>\r\n \t<li style=\"text-align: justify;\">Since the transmission is on varied frequencies, it is difficult to jam the signal, the inherent property for which it was used in military applications<\/li>\r\n \t<li style=\"text-align: justify;\">Several users can independently use the same Bandwidth with very little interference<\/li>\r\n \t<li style=\"text-align: justify;\">Has built-in security<\/li>\r\n<\/ol>\r\n<strong style=\"text-align: initial; font-size: 1em;\">Spread Spectrum techniques<\/strong>\r\n\r\n&nbsp;\r\n\r\n<span style=\"text-align: initial; font-size: 1em;\">The spread spectrum system is a two-step process:<\/span>\r\n\r\n<\/div>\r\n<ol>\r\n \t<li style=\"text-align: justify;\">Data is modulated<\/li>\r\n \t<li style=\"text-align: justify;\">Carrier is modulated causing it spread over a large bandwidth<\/li>\r\n<\/ol>\r\nThe signal can be spreaded in many ways. Some of the spreading techniques are mentioned below\r\n<ol>\r\n \t<li style=\"text-align: justify;\"><strong>DSSS<\/strong>: Used for digital information transmission. The information is spreaded by the means of a code. The information is transmitted along with a pseudo random code known as chipping sequence.<\/li>\r\n \t<li style=\"text-align: justify;\"><strong>Frequency Hopping<\/strong>: The Frequency of carrier is changed many times within a fixed time period. Hence instead of transmitting on a single frequency, varied frequencies are used<\/li>\r\n \t<li style=\"text-align: justify;\"><strong>Chirp<\/strong>: The Carrier is swept over a range of frequencies known as chirp spread spectrum. It is mainly used in radar systems and ranging devices.<\/li>\r\n \t<li style=\"text-align: justify;\"><strong>Time Hopping<\/strong>: The carrier is ON-OFF keyed in a pseudo noise sequence.<\/li>\r\n \t<li style=\"text-align: justify;\"><strong>Hybrid<\/strong>: Takes best points of 2 or more spread spectrum systems<\/li>\r\n<\/ol>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">Only FHSS and DSSS are available for commercial and amateur use. Rest are reserved for military and space sciences. In this module we will discuss FHSS in detail<\/p>\r\n&nbsp;\r\n<p class=\"hanging-indent\"><strong>Frequency hopped Spread Spectrum<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">In this spread spectrum technique, the total available bandwidth is divided into many channels of smaller bandwidth with guard spaces between them. Transmitter transmits by changing or hopping from one frequency to another in a\u00a0 pseudo random but predictable manner. The technique spreads the original signal as well as provide immunity to interference. The receiver as to synchronize itself to the pseudo random sequence in order to despread the signal.<\/p>\r\n&nbsp;\r\n\r\n<img class=\"aligncenter size-full wp-image-137\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic5.jpg\" alt=\"\" width=\"802\" height=\"377\" \/>\r\n<p style=\"text-align: center;\"><strong>Figure 3 Frequency hopped Spread Spectrum<\/strong><\/p>\r\n&nbsp;\r\n<p class=\"hanging-indent\"><strong>Advantages of FHSS over standard FDMA<\/strong><\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify;\">Resistant to narrowband interference.<\/li>\r\n \t<li style=\"text-align: justify;\">Difficult to intercept. An eavesdropper would only be able to intercept the transmission if they knew the pseudo random sequence.<\/li>\r\n \t<li style=\"text-align: justify;\">If the hop sequence of two transmitters are different and never transmit the same frequency at the same time, then there will be no interference among them hence allowing multiple access (Fig 5).<\/li>\r\n<\/ul>\r\n<img class=\"aligncenter size-full wp-image-138\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic6.jpg\" alt=\"\" width=\"825\" height=\"431\" \/>\r\n\r\n&nbsp;\r\n<p style=\"text-align: center;\"><strong>Figure 4 Multiple access via FHSS<\/strong><\/p>\r\n&nbsp;\r\n<p class=\"hanging-indent\"><strong>Technologies using FHSS<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">The original standard for IEEE 802.11 popularly known as Wi-Fi\u00a0\u00a0\u00a0 defines 13 hopping channels for North America and Europe and 23 hopping channels for Japan each with band of 1 MHz in 2.4 GHz ISM band.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">For IEEE 802.11b<\/p>\r\n\r\n<ul>\r\n \t<li>U.S. allows the use of channels 1 thru. 11<\/li>\r\n \t<li>U.K. can use channels 1 through 13<\/li>\r\n \t<li>Japan allows the use of all 14 channels<\/li>\r\n<\/ul>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">Bluetooth uses 79 channels for frequency hopping in the unlicensed ISM band at 2.4 -2.4835 GHz. Each device performs frequency hopping with 1600 hops\/sec. Collection of devices with same hopping sequence forms a piconet. Master of piconet determines the hopping pattern and the slaves have to synchronized to this pattern.<\/p>\r\n&nbsp;\r\n\r\n<img class=\"aligncenter size-full wp-image-139\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic7.jpg\" alt=\"\" width=\"416\" height=\"197\" \/>\r\n<p style=\"text-align: center;\"><strong>Figure 5 Bluetooth Technology<\/strong><\/p>\r\n&nbsp;\r\n<div>\r\n\r\n<strong>Components of FHSS<\/strong>\r\n\r\n<\/div>\r\n<ul>\r\n \t<li style=\"text-align: justify;\"><strong>Hopset: <\/strong>Set of different frequencies over which the hopping occurs. The bandwidth of channel used in hopset is called instantaneous bandwidth. Total bandwidth over which hopping occurs is called total hopping bandwidth. In the Fig 4 Frequencies f1 to f8 forms the hopset.<\/li>\r\n \t<li style=\"text-align: justify;\"><strong>Hopping Sequence: <\/strong>Sequence of channels used is dictated by a spreading code. Both transmitter and receiver should use the same code to tune into sequence of channels for synchronization. Fig 7 shows the hopping sequence<\/li>\r\n \t<li style=\"text-align: justify;\"><strong>Hop Time: <\/strong>Small amount of time during a frequency change in which no transmission takes place<\/li>\r\n \t<li style=\"text-align: justify;\"><strong style=\"text-align: initial; font-size: 1em;\">Dwell Time: <\/strong><span style=\"text-align: initial; font-size: 1em;\">Time spent on a particular channel with a carrier frequency.<\/span><\/li>\r\n<\/ul>\r\n<img class=\"aligncenter size-full wp-image-140\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic8.jpg\" alt=\"\" width=\"992\" height=\"586\" \/>\r\n\r\n&nbsp;\r\n<p style=\"text-align: center;\"><strong>Figure 6 Hop set and hopping sequence<\/strong><\/p>\r\n<p class=\"hanging-indent\"><strong>Variants of FHSS<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">According to the dwell time, there are two variants of Frequency Hopped Spread Spectrum namely:<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\"><strong>Slow Hopping: <\/strong>The transmitter remains on one frequency channel during transmission of many bits. Like the dwell time for GSM is 4.2 ms. Features of this scheme are:<\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify;\">Cheaper to implement<\/li>\r\n \t<li style=\"text-align: justify;\">Too much of synchronization among sender and receiver is not required<\/li>\r\n \t<li style=\"text-align: justify;\">Low immunity to narrow band interference.<\/li>\r\n \t<li style=\"text-align: justify;\">Very slow hopping is as good as FDMA<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify;\"><strong>Fast Hopping: <\/strong>The transmitter hops to many frequency channels during the transmission of a single bit. Eg Bluetooth. Features of this scheme are:<\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify;\">Complex Implementation<\/li>\r\n \t<li style=\"text-align: justify;\">Precise Synchronization required<\/li>\r\n \t<li style=\"text-align: justify;\">Low narrow band interference.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify;\">The two variants are illustrated in the diagram given below<\/p>\r\n&nbsp;\r\n\r\n<img class=\"aligncenter size-full wp-image-141\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic9.jpg\" alt=\"\" width=\"663\" height=\"470\" \/>\r\n<p style=\"text-align: center;\"><strong>Figure 7 slow and fast hopping<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">The above figure demonstrates slow and fast frequency hopping. To understand the figure let us understand the following terms:<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">Tb= bit period = time required to transmit 1 bit Td = dwell time<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">The figure shows transmission of user data bits 0 1 0 1 1 0. The available bandwidth is divided into 4 parts f1, f2, f3 and f4.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">In the slow hopping part we can see that the transmission remains on frequency channel f2 for transmission of three bits. The dwell time td = 3* tb<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">Similarly we can see in second case that during transmission of a single bit, the transmission has changed 4 times in a sequence f1 f4 f3 f2.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\">The dwell time td = tb\/4<\/p>\r\n&nbsp;\r\n\r\n<img class=\"aligncenter size-full wp-image-142\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic10.jpg\" alt=\"\" width=\"662\" height=\"167\" \/>\r\n\r\n&nbsp;\r\n<p class=\"hanging-indent\" style=\"text-align: center;\"><strong>Figure 8 Block diagram of frequency hopped spread spectrum sender<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify;\"><strong>Step 1<\/strong>: Modulation according to digital-to-analog modulation technique. It results in a narrow band signal<\/p>\r\n<p style=\"text-align: justify;\"><strong>Step 2<\/strong>: Modulation according to digital-to-analog modulation technique. It results in a narrow band signal<\/p>\r\n<p style=\"text-align: justify;\"><strong>Step 3<\/strong>: Frequency hopping is performed based on hopping sequence<\/p>\r\n<p style=\"text-align: justify;\"><strong>Step 4<\/strong>: \u00a0The \u00a0hopping \u00a0sequence \u00a0is \u00a0fed \u00a0into \u00a0frequency \u00a0synthesizer \u00a0to \u00a0generate \u00a0the \u00a0carrier frequencies and the narrow band signal is spreaded. The spreaded signal is transmitted<\/p>\r\n&nbsp;\r\n\r\n<img class=\"aligncenter size-full wp-image-143\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic11.jpg\" alt=\"\" width=\"594\" height=\"184\" \/>\r\n<p style=\"text-align: center;\"><strong>Figure 9 Block diagram of Frequency hopped spread Spectrum Sender<\/strong><\/p>\r\n&nbsp;\r\n\r\n<strong>Step 1<\/strong>: The receiver knows the hopping sequence via frequency synthesizer\r\n\r\n<strong>Step 2<\/strong>: It dispreads the spreaded signal using the hoping sequence. Narrow band signal is achieved\r\n\r\n<strong>Step 3<\/strong>: Narrow band signal is demodulated again to obtain the user data\r\n\r\n&nbsp;\r\n<p class=\"hanging-indent\"><strong>Summary<\/strong><\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify;\">Spread Spectrum technology was conceived by Hady Lamaar<\/li>\r\n \t<li style=\"text-align: justify;\">It spreads the required bandwidth via different techniques to reduce interference and to provide protection against jamming and tapping<\/li>\r\n \t<li style=\"text-align: justify;\">FHSS is a spread the total available bandwidth is divided into many channels of smaller bandwidth with guard spaces between them. Transmitter transmits by changing or hopping from one frequency to another in a pseudorandom but predictable manner. The technique spreads the original signal as well as provide immunity to interference<\/li>\r\n \t<li style=\"text-align: justify;\">Two variants of FHSS are slow hopping and fast hopping<\/li>\r\n<\/ul>\r\n<table>\r\n<tbody>\r\n<tr>\r\n<td><strong>you can view video on Spread Spectrum Technology: Frequency Hopped Spread Spectrum<\/strong><\/td>\r\n<td><a href=\"https:\/\/youtu.be\/FfuDTqA__pU\" target=\"_blank\" rel=\"noopener\"><img class=\"alignnone wp-image-120\" src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"\" width=\"36\" height=\"36\" \/><\/a><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n\r\n\r\n<strong>Suggested Reading:<\/strong>\r\n<ol>\r\n \t<li style=\"text-align: justify;\">Mobile Communication 2nd edition by Jochen Schiller, Pearson education<\/li>\r\n \t<li style=\"text-align: justify;\">Mobile Computing by Asoke Talukder, Roopa Yavagal (Tata McGraw Hill)<\/li>\r\n \t<li style=\"text-align: justify;\">\"Wireless communication and networking\" by William Stallings<\/li>\r\n \t<li style=\"text-align: justify;\">Mobile Cellular Telecommunications \u2014 W.C.Y. Lee, Mc Graw Hill<\/li>\r\n \t<li style=\"text-align: justify;\">Wireless Communications \u2013 Theodore. S. Rapport, Pearson Education<\/li>\r\n \t<li style=\"text-align: justify;\">Reza B'Far (Ed), \"Mobile Computing Principles\", Cambridge University Press.<\/li>\r\n<\/ol>","rendered":"<div><span style=\"float: right;\"><a href=\"https:\/\/youtu.be\/FfuDTqA__pU\" target=\"_blank\" rel=\"noopener\"><img decoding=\"async\" src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"epgp books\" width=\"75px\" height=\"75px;\" \/><\/a><br \/>\n<\/span><\/div>\n<div>\n<p><strong>Learning Objectives<\/strong><\/p>\n<ul>\n<li style=\"text-align: justify;\">History of spread spectrum technology<\/li>\n<li style=\"text-align: justify;\">Difference between Narrow band and Spread Spectrum Signal<\/li>\n<li style=\"text-align: justify;\">Understand the advantage of Spread Spectrum Technology over narrow band<\/li>\n<li style=\"text-align: justify;\">Discuss types of Spreading techniques<\/li>\n<li style=\"text-align: justify;\">Introduction to Frequency Hopped Spread Spectrum and its working<\/li>\n<li style=\"text-align: justify;\">Understand the variants of Frequency Hopped Spread Spectrum<\/li>\n<\/ul>\n<p><strong>Introduction<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">A famous Hollywood actress, Hedy Lamaar along with film music composer George Antheil, patented \u201cSecret Communication System\u201d in 1942 which received U.S. Patent #2.292.387. The Spread Spectrum communication technology was introduced. The invention was believed to be quite ahead of time and was not taken seriously until 1980\u2019s when U.S. military declassified it and since then it is foundation of today\u2019s wireless technologies like CDMA, Wireless LAN, IMT- 2000, Bluetooth, 3G and Global Positioning Systems(GPS). Narrow band signals transmit at a very constant frequency for eg. FM radio will always transmit at the frequency allocated to it say 98.3. The receiver has to tune onto this frequency to get the broadcast. Since the narrow band transmission always uses the same and predefined frequency, it is very easy to intercept, interfere and jam. It also requires high power to transmit. Spread Spectrum technology offers a solution to these problems. Spread spectrum devices transmit at varied frequencies occupying greater bandwidth but less power. Transmission on different frequencies makes the transmission hard to intercept and interfere. Spread Spectrum technology is a technique that spreads the narrow band signal to a broad range of frequencies. This is done by using different spreading techniques mainly Frequency Hopped Spread Spectrum and Direct Sequence Spread Spectrum. This module explains the Spread Spectrum technology, various spreading techniques and the technologies implementing it.<\/p>\n<\/div>\n<p><strong>History of Spread Spectrum Technology<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">Spread spectrum use is on the verge of potentially explosive commercial development, especially in relation to the internet. what&#8217;s is surprising is that the inventor behind this amazing process is an incredibly beautiful and talented actress of the 1940&#8217;s! .Her name is Hedy Lamarr, known as &#8220;The Most Beautiful Girl in The World&#8221;<\/p>\n<p>&nbsp;<\/p>\n<p class=\"hanging-indent\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-133 size-medium\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic1-240x300.jpg\" alt=\"\" width=\"240\" height=\"300\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic1-240x300.jpg 240w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic1-65x81.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic1-225x282.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic1-350x438.jpg 350w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic1.jpg 503w\" sizes=\"auto, (max-width: 240px) 100vw, 240px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\"><span style=\"font-size: 1em; text-align: initial; text-indent: -1em;\">She with American composer George Antheil, came up with was an idea for a sophisticated anti-jamming device for use in radio-controlled torpedos during world war II. Lamarr and Antheil realized that radio-controlled torpedoes, which could be important in the naval war, could easily be jammed, thereby causing the torpedo to go off course. If pianos could be synchronized to hop from one note to another, why couldn&#8217;t radio signals &#8211; steering a torpedo &#8211; hop as well? Their inventive partnership was born. Hedy&#8217;s idea was if you could make both the transmitter and the receiver simultaneously jump from frequency to frequency, then someone trying to jam the signal wouldn&#8217;t know where it was. They designed a frequency-hopping system that would continually change the radio signals sent to the torpedo.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p><em>They were awarded U.S. Patent Number 2,292,387 on August 11, 1942, under the name &#8220;Hedy Keisler Markey&#8221; and George Antheil for a &#8220;Secret Communications System.&#8221;<\/em><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">Who would have known that a glamorous female movie star of the 1940&#8217;s would defy all stereotypes and create a communications system that was decades ahead of its time and is only now coming into widespread use. The invention could not be implemented during World War II and only came into use 20 years later during the 1962 Cuban Missile Crisis their patent catalyzed the use of Spread Spectrum, which is a highly efficient way of using radio frequencies at the same time, without interfering with each other. This is the basis for the cellular phones, faxes, and other wireless communications systems in widespread use today and is foundation of today\u2019s wireless technologies like CDMA, Wireless LAN, IMT-2000, Bluetooth, 3G and Global Positioning Systems (GPS).<\/p>\n<p>&nbsp;<\/p>\n<p class=\"hanging-indent\"><strong>Narrow band Signal<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">In a transmission system, the information is modulated with a carrier signal and then transmitted. When transmitted, all\u00a0 the power transmitted is\u00a0 centered around a particular frequency. This frequency represents a specific channel and has a narrow band. This narrow band signal has certain disadvantages like:<\/p>\n<ol>\n<li style=\"text-align: justify;\">Since the transmission is always on a constant frequency, it is easy to intercept<\/li>\n<li style=\"text-align: justify;\">It requires more power to overcome the noise<\/li>\n<li style=\"text-align: justify;\">Suffers from interference<\/li>\n<li style=\"text-align: justify;\">Prone to jamming and tapping<\/li>\n<\/ol>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-134 size-full\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic2.jpg\" alt=\"\" width=\"640\" height=\"350\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic2.jpg 640w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic2-300x164.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic2-65x36.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic2-225x123.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic2-350x191.jpg 350w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><b>Figure 1: Narrow band vs Spreader\u00a0signal<\/b><\/p>\n<div>\n<p><strong>Spread Spectrum signal<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">Spread Spectrum technology is a technique that spreads the narrow band signal to a broad range of frequencies. Spread spectrum devices transmit at varied frequencies occupying greater bandwidth but less power. Transmission on different frequencies makes the transmission hard to intercept and interfere. Spread spectrum modulation spreads out the\u00a0 modulated signal bandwidth so it is much greater than the message bandwidth.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\"><span style=\"font-size: 1em;\">A signal that occupies a bandwidth of B, is spread out to occupy a bandwidth of Bss (Fig 2). Spread spectrum increases BW of message signal by a factor N, known as Processing Gain<\/span><\/p>\n<\/div>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-135 size-full\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic3.jpg\" alt=\"\" width=\"1206\" height=\"470\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic3.jpg 1206w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic3-300x117.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic3-768x299.jpg 768w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic3-1024x399.jpg 1024w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic3-65x25.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic3-225x88.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic3-350x136.jpg 350w\" sizes=\"auto, (max-width: 1206px) 100vw, 1206px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: center;\"><strong>Figure 2: Signal Spreading<\/strong><\/p>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-136\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic4.jpg\" alt=\"\" width=\"337\" height=\"83\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic4.jpg 337w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic4-300x74.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic4-65x16.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic4-225x55.jpg 225w\" sizes=\"auto, (max-width: 337px) 100vw, 337px\" \/><\/p>\n<\/div>\n<div>\n<p><strong>Advantages of Spreaded Signal<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">There are several advantages of the scheme which prima face appears as wastage of bandwidth they are:<\/p>\n<ol>\n<li style=\"text-align: justify;\"><strong>Hard to Intercept: <\/strong>Figure 1 shows narrow band signal as well as the spreaded signal. It can be seen that power level of spreaded signal is much less than the original narrow signal. It can also be lower than background noise and thus hard to detect.<\/li>\n<li style=\"text-align: justify;\"><strong>Power requirement is low: <\/strong>During transmission it is always possible that some atmospheric noise will creep into the transmission which can be misinterpreted as radio signals. To overpower this noise, the narrow band signals need to be transmitted with high power than noise. Spreading the signal over frequency can lower the power requirements. For instance if narrow band signal requires 10 watts to transmit 1 MHz, a spread spectrum signal may require only 100 miliwatts to transmit 20 MHz signal.<\/li>\n<li style=\"text-align: justify;\">Used for hiding and encrypting signals because only a recipient who knows the spreading code can recover the coded information<\/li>\n<li style=\"text-align: justify;\">Reduces narrow band interference<\/li>\n<li style=\"text-align: justify;\">Since the transmission is on varied frequencies, it is difficult to jam the signal, the inherent property for which it was used in military applications<\/li>\n<li style=\"text-align: justify;\">Several users can independently use the same Bandwidth with very little interference<\/li>\n<li style=\"text-align: justify;\">Has built-in security<\/li>\n<\/ol>\n<p><strong style=\"text-align: initial; font-size: 1em;\">Spread Spectrum techniques<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p><span style=\"text-align: initial; font-size: 1em;\">The spread spectrum system is a two-step process:<\/span><\/p>\n<\/div>\n<ol>\n<li style=\"text-align: justify;\">Data is modulated<\/li>\n<li style=\"text-align: justify;\">Carrier is modulated causing it spread over a large bandwidth<\/li>\n<\/ol>\n<p>The signal can be spreaded in many ways. Some of the spreading techniques are mentioned below<\/p>\n<ol>\n<li style=\"text-align: justify;\"><strong>DSSS<\/strong>: Used for digital information transmission. The information is spreaded by the means of a code. The information is transmitted along with a pseudo random code known as chipping sequence.<\/li>\n<li style=\"text-align: justify;\"><strong>Frequency Hopping<\/strong>: The Frequency of carrier is changed many times within a fixed time period. Hence instead of transmitting on a single frequency, varied frequencies are used<\/li>\n<li style=\"text-align: justify;\"><strong>Chirp<\/strong>: The Carrier is swept over a range of frequencies known as chirp spread spectrum. It is mainly used in radar systems and ranging devices.<\/li>\n<li style=\"text-align: justify;\"><strong>Time Hopping<\/strong>: The carrier is ON-OFF keyed in a pseudo noise sequence.<\/li>\n<li style=\"text-align: justify;\"><strong>Hybrid<\/strong>: Takes best points of 2 or more spread spectrum systems<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">Only FHSS and DSSS are available for commercial and amateur use. Rest are reserved for military and space sciences. In this module we will discuss FHSS in detail<\/p>\n<p>&nbsp;<\/p>\n<p class=\"hanging-indent\"><strong>Frequency hopped Spread Spectrum<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">In this spread spectrum technique, the total available bandwidth is divided into many channels of smaller bandwidth with guard spaces between them. Transmitter transmits by changing or hopping from one frequency to another in a\u00a0 pseudo random but predictable manner. The technique spreads the original signal as well as provide immunity to interference. The receiver as to synchronize itself to the pseudo random sequence in order to despread the signal.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-137\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic5.jpg\" alt=\"\" width=\"802\" height=\"377\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic5.jpg 802w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic5-300x141.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic5-768x361.jpg 768w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic5-65x31.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic5-225x106.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic5-350x165.jpg 350w\" sizes=\"auto, (max-width: 802px) 100vw, 802px\" \/><\/p>\n<p style=\"text-align: center;\"><strong>Figure 3 Frequency hopped Spread Spectrum<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p class=\"hanging-indent\"><strong>Advantages of FHSS over standard FDMA<\/strong><\/p>\n<ul>\n<li style=\"text-align: justify;\">Resistant to narrowband interference.<\/li>\n<li style=\"text-align: justify;\">Difficult to intercept. An eavesdropper would only be able to intercept the transmission if they knew the pseudo random sequence.<\/li>\n<li style=\"text-align: justify;\">If the hop sequence of two transmitters are different and never transmit the same frequency at the same time, then there will be no interference among them hence allowing multiple access (Fig 5).<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-138\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic6.jpg\" alt=\"\" width=\"825\" height=\"431\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic6.jpg 825w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic6-300x157.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic6-768x401.jpg 768w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic6-65x34.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic6-225x118.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic6-350x183.jpg 350w\" sizes=\"auto, (max-width: 825px) 100vw, 825px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: center;\"><strong>Figure 4 Multiple access via FHSS<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p class=\"hanging-indent\"><strong>Technologies using FHSS<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">The original standard for IEEE 802.11 popularly known as Wi-Fi\u00a0\u00a0\u00a0 defines 13 hopping channels for North America and Europe and 23 hopping channels for Japan each with band of 1 MHz in 2.4 GHz ISM band.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">For IEEE 802.11b<\/p>\n<ul>\n<li>U.S. allows the use of channels 1 thru. 11<\/li>\n<li>U.K. can use channels 1 through 13<\/li>\n<li>Japan allows the use of all 14 channels<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">Bluetooth uses 79 channels for frequency hopping in the unlicensed ISM band at 2.4 -2.4835 GHz. Each device performs frequency hopping with 1600 hops\/sec. Collection of devices with same hopping sequence forms a piconet. Master of piconet determines the hopping pattern and the slaves have to synchronized to this pattern.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-139\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic7.jpg\" alt=\"\" width=\"416\" height=\"197\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic7.jpg 416w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic7-300x142.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic7-65x31.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic7-225x107.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic7-350x166.jpg 350w\" sizes=\"auto, (max-width: 416px) 100vw, 416px\" \/><\/p>\n<p style=\"text-align: center;\"><strong>Figure 5 Bluetooth Technology<\/strong><\/p>\n<p>&nbsp;<\/p>\n<div>\n<p><strong>Components of FHSS<\/strong><\/p>\n<\/div>\n<ul>\n<li style=\"text-align: justify;\"><strong>Hopset: <\/strong>Set of different frequencies over which the hopping occurs. The bandwidth of channel used in hopset is called instantaneous bandwidth. Total bandwidth over which hopping occurs is called total hopping bandwidth. In the Fig 4 Frequencies f1 to f8 forms the hopset.<\/li>\n<li style=\"text-align: justify;\"><strong>Hopping Sequence: <\/strong>Sequence of channels used is dictated by a spreading code. Both transmitter and receiver should use the same code to tune into sequence of channels for synchronization. Fig 7 shows the hopping sequence<\/li>\n<li style=\"text-align: justify;\"><strong>Hop Time: <\/strong>Small amount of time during a frequency change in which no transmission takes place<\/li>\n<li style=\"text-align: justify;\"><strong style=\"text-align: initial; font-size: 1em;\">Dwell Time: <\/strong><span style=\"text-align: initial; font-size: 1em;\">Time spent on a particular channel with a carrier frequency.<\/span><\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-140\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic8.jpg\" alt=\"\" width=\"992\" height=\"586\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic8.jpg 992w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic8-300x177.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic8-768x454.jpg 768w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic8-65x38.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic8-225x133.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic8-350x207.jpg 350w\" sizes=\"auto, (max-width: 992px) 100vw, 992px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: center;\"><strong>Figure 6 Hop set and hopping sequence<\/strong><\/p>\n<p class=\"hanging-indent\"><strong>Variants of FHSS<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">According to the dwell time, there are two variants of Frequency Hopped Spread Spectrum namely:<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\"><strong>Slow Hopping: <\/strong>The transmitter remains on one frequency channel during transmission of many bits. Like the dwell time for GSM is 4.2 ms. Features of this scheme are:<\/p>\n<ul>\n<li style=\"text-align: justify;\">Cheaper to implement<\/li>\n<li style=\"text-align: justify;\">Too much of synchronization among sender and receiver is not required<\/li>\n<li style=\"text-align: justify;\">Low immunity to narrow band interference.<\/li>\n<li style=\"text-align: justify;\">Very slow hopping is as good as FDMA<\/li>\n<\/ul>\n<p style=\"text-align: justify;\"><strong>Fast Hopping: <\/strong>The transmitter hops to many frequency channels during the transmission of a single bit. Eg Bluetooth. Features of this scheme are:<\/p>\n<ul>\n<li style=\"text-align: justify;\">Complex Implementation<\/li>\n<li style=\"text-align: justify;\">Precise Synchronization required<\/li>\n<li style=\"text-align: justify;\">Low narrow band interference.<\/li>\n<\/ul>\n<p style=\"text-align: justify;\">The two variants are illustrated in the diagram given below<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-141\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic9.jpg\" alt=\"\" width=\"663\" height=\"470\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic9.jpg 663w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic9-300x213.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic9-65x46.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic9-225x160.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic9-350x248.jpg 350w\" sizes=\"auto, (max-width: 663px) 100vw, 663px\" \/><\/p>\n<p style=\"text-align: center;\"><strong>Figure 7 slow and fast hopping<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">The above figure demonstrates slow and fast frequency hopping. To understand the figure let us understand the following terms:<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">Tb= bit period = time required to transmit 1 bit Td = dwell time<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">The figure shows transmission of user data bits 0 1 0 1 1 0. The available bandwidth is divided into 4 parts f1, f2, f3 and f4.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">In the slow hopping part we can see that the transmission remains on frequency channel f2 for transmission of three bits. The dwell time td = 3* tb<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">Similarly we can see in second case that during transmission of a single bit, the transmission has changed 4 times in a sequence f1 f4 f3 f2.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\">The dwell time td = tb\/4<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-142\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic10.jpg\" alt=\"\" width=\"662\" height=\"167\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic10.jpg 662w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic10-300x76.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic10-65x16.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic10-225x57.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic10-350x88.jpg 350w\" sizes=\"auto, (max-width: 662px) 100vw, 662px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p class=\"hanging-indent\" style=\"text-align: center;\"><strong>Figure 8 Block diagram of frequency hopped spread spectrum sender<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify;\"><strong>Step 1<\/strong>: Modulation according to digital-to-analog modulation technique. It results in a narrow band signal<\/p>\n<p style=\"text-align: justify;\"><strong>Step 2<\/strong>: Modulation according to digital-to-analog modulation technique. It results in a narrow band signal<\/p>\n<p style=\"text-align: justify;\"><strong>Step 3<\/strong>: Frequency hopping is performed based on hopping sequence<\/p>\n<p style=\"text-align: justify;\"><strong>Step 4<\/strong>: \u00a0The \u00a0hopping \u00a0sequence \u00a0is \u00a0fed \u00a0into \u00a0frequency \u00a0synthesizer \u00a0to \u00a0generate \u00a0the \u00a0carrier frequencies and the narrow band signal is spreaded. The spreaded signal is transmitted<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-143\" src=\"http:\/\/itp12.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic11.jpg\" alt=\"\" width=\"594\" height=\"184\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic11.jpg 594w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic11-300x93.jpg 300w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic11-65x20.jpg 65w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic11-225x70.jpg 225w, https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-content\/uploads\/sites\/27\/2018\/07\/M08Pic11-350x108.jpg 350w\" sizes=\"auto, (max-width: 594px) 100vw, 594px\" \/><\/p>\n<p style=\"text-align: center;\"><strong>Figure 9 Block diagram of Frequency hopped spread Spectrum Sender<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p><strong>Step 1<\/strong>: The receiver knows the hopping sequence via frequency synthesizer<\/p>\n<p><strong>Step 2<\/strong>: It dispreads the spreaded signal using the hoping sequence. Narrow band signal is achieved<\/p>\n<p><strong>Step 3<\/strong>: Narrow band signal is demodulated again to obtain the user data<\/p>\n<p>&nbsp;<\/p>\n<p class=\"hanging-indent\"><strong>Summary<\/strong><\/p>\n<ul>\n<li style=\"text-align: justify;\">Spread Spectrum technology was conceived by Hady Lamaar<\/li>\n<li style=\"text-align: justify;\">It spreads the required bandwidth via different techniques to reduce interference and to provide protection against jamming and tapping<\/li>\n<li style=\"text-align: justify;\">FHSS is a spread the total available bandwidth is divided into many channels of smaller bandwidth with guard spaces between them. Transmitter transmits by changing or hopping from one frequency to another in a pseudorandom but predictable manner. The technique spreads the original signal as well as provide immunity to interference<\/li>\n<li style=\"text-align: justify;\">Two variants of FHSS are slow hopping and fast hopping<\/li>\n<\/ul>\n<table>\n<tbody>\n<tr>\n<td><strong>you can view video on Spread Spectrum Technology: Frequency Hopped Spread Spectrum<\/strong><\/td>\n<td><a href=\"https:\/\/youtu.be\/FfuDTqA__pU\" target=\"_blank\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-120\" src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"\" width=\"36\" height=\"36\" \/><\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong>Suggested Reading:<\/strong><\/p>\n<ol>\n<li style=\"text-align: justify;\">Mobile Communication 2nd edition by Jochen Schiller, Pearson education<\/li>\n<li style=\"text-align: justify;\">Mobile Computing by Asoke Talukder, Roopa Yavagal (Tata McGraw Hill)<\/li>\n<li style=\"text-align: justify;\">&#8220;Wireless communication and networking&#8221; by William Stallings<\/li>\n<li style=\"text-align: justify;\">Mobile Cellular Telecommunications \u2014 W.C.Y. Lee, Mc Graw Hill<\/li>\n<li style=\"text-align: justify;\">Wireless Communications \u2013 Theodore. S. Rapport, Pearson Education<\/li>\n<li style=\"text-align: justify;\">Reza B&#8217;Far (Ed), &#8220;Mobile Computing Principles&#8221;, Cambridge University Press.<\/li>\n<\/ol>\n","protected":false},"author":4,"menu_order":8,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["miss-suchit-purohit"],"pb_section_license":""},"chapter-type":[],"contributor":[59],"license":[],"class_list":["post-132","chapter","type-chapter","status-publish","hentry","contributor-miss-suchit-purohit"],"part":3,"_links":{"self":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/pressbooks\/v2\/chapters\/132","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/wp\/v2\/users\/4"}],"version-history":[{"count":10,"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/pressbooks\/v2\/chapters\/132\/revisions"}],"predecessor-version":[{"id":634,"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/pressbooks\/v2\/chapters\/132\/revisions\/634"}],"part":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/pressbooks\/v2\/parts\/3"}],"metadata":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/pressbooks\/v2\/chapters\/132\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/wp\/v2\/media?parent=132"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/pressbooks\/v2\/chapter-type?post=132"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/wp\/v2\/contributor?post=132"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/itp12\/wp-json\/wp\/v2\/license?post=132"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}