The code portions each have the same length and are selected . CDMA is a Direct Sequence Spread Spectrum system. The basic idea is to transmit a long rectangular pulse whose carrier frequency is linearly increased from f1 to f2 (f2>f1). Now-a-days spread spectrum techniques have been applied to mobile communication in the name of . 2.4 Causing "artificially" very high throughput . referred to as a code. Spread-spectrum is apparent in the Shannon and Hartley channel-capacity theorem: C = B × log 2 (1 + S/N) (Eq. 3. The receiver correlates the received signals to retrieve the original information signal. Spread spectrum is a technique used for transmitting radio or telecommunications signals. We will focus on Direct Sequence Spread Spectrum technique since it is the mostly used in the industry (CDMA, UMTS, 802.11, GPS). The line spectrum around +or-2f/sub c/, however, can be eliminated by a uniform phase code. The original signal is recovered by multiplying the spread-spectrum signal by the same PN code. Linear Frequency Modulation (chirp) Chirp Modulation: This is an older spread spectrum method that was developed for radar use. The security of hybrid DS/FH systems strongly depends on the choice of PN-spreading code employed. c. DSSS relies upon a PN code that is only shared by the transmitter and receiver pair. The Frequency Hopping Spread Spectrum or FHSS allows us to utilize bandwidth properly and maximum. In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal (e.g., an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. The frequency-modulated signal returned from the target passes through a filter in the . Spread spectrum techniques, on the other hand, employ a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth. spread spectrum. a. OFDM is not classified as a spread spectrum technique, although OFDM has the effect of spreading the signal over a larger frequency spectrum. Spread spectrum spectral density techniques . . Spread-Spectrum techniques are methods by which a signal (e.g. Aiming at the problem of blind estimation of the spreading code of multi-antenna Direct-Spread CDMA Long-Code (DS-CDMA LC) signals with poor interpolation effect, the idea of segmentation is used to construct the third-order tensor of the received signal into blocks according to the spreading gain, which is equivalent to Tucker decomposition. Spreading: Chips and Symbols • A chip is the shortest modulated signal in a DS-CDMA system • Chip rate signal bandwidth • A symbol is spread over multiple chips • The Spreading Factor (SF) tells how many chips are used to transmit one symbol spreading factor = SF = R c R s = chip rate symbol rate • SF is a spectrum spreading factor: bit rate ⇒ chip rate • The Spreading Code is a . In this technique, the whole available bandwidth is divided into many channels and spread between channels, arranged continuously. A spread-spectrum signal has lower peak power, equal total power, and wider bandwidth. 앞에서 설명 완료 ; CDMA(Code Division Multiple Access) is a spectrum spreading technology enabling multiple access. The spectrum around DC depends only on the variance of the spreading code amplitude distribution. Among A plurality of code portions are selected, one from each of the spreading codes. So thisautocorrelation . 4 LoRa Spread Spectrum Semtech's LoRa modulation addresses all of the issues associated with DSSS systems to provide a low-cost, low-power, yet above all robust alternative to the traditional spread-spectrum communications techniques [1], [2]. Due to their interference rejection capabilities, spread spectrum techniques have played a major role in wireless communications over the last decade. Typically, but not always, the spreading code is generated by a . 2. TYPES OF SS TECHNIQUES THE FUTURE LIES WITHIN. The spread spectrum sequence code block based on p meta m sequence, capable of realizing conveniently through two shift registers. Spreading factors vary from 4 to 512 in FDD UMTS. The output of the bandpass filter is squared and integrated for a duration of T d 2to detect the energy of the despread signal. The DSSS (Direct Sequence Spread Spectrum) is a technique spread spectrum, but unlike the FHSS, no frequency hopping is place: DSSS causes very rapid state transitions (chipping) which tend to spread the spectrum of the signal: in fact, we have seen that with the modulations FSK, PSK and QAM width of the spectrum was twice the rate of the source. Spread spectrum signal types Definitions for various types of spread spectrum techniques/signal structure are as follows: - Direct sequence (DS) spread spectrum: a signal structuring technique utilizing a digital code spreading sequence having a chip rate 1/T s in much higher than the information signal bit rate 1/T s WCDMA uses Direct Sequence spreading, where spreading process is done by directly combining the baseband information to high chip rate binary code. INTRODUCTION • There are four basic types classified according to the point of insertion of PN code - - - - Direct Sequence spread spectrum (DSSS) Frequency hopping spread spectrum (FHSS) Time hopping spread spectrum (THSS) Hybrid techniques. an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. d. all statements are correct Notice . Aiming at the problem of blind estimation of the spreading code of multi-antenna Direct-Spread CDMA Long-Code (DS-CDMA LC) signals with poor interpolation effect, the idea of segmentation is used to construct the third-order tensor of the received signal into blocks according to the spreading gain, which is equivalent to Tucker decomposition. The performance of the proposed technique (optimized dynamic logistic map code based DSSS) displays better results than non-optimized spreading code and orthogonal spreading code considering BER. To apply a spread-spectrum technique, simply inject the corresponding spread-spectrum code somewhere in the transmitting chain before the antenna (receiver). (DSSS) technique expands the bandwidth of the original signal. Spread spectrum systems are spreading the information signal d t which has aBW info, over a much larger bandwidth BW SS: BW info ≅ R s << BW SS ≅ R c The SS-signal spectrum is white noise-like. Direct Sequence (DS) methods are the most frequently used spread spectrum technique, and also the conceptually simplest to understand. However, situations arise where the effects of interlink interference are amplified owing to operational considerations. Spread-spectrum (SS) technology uses a sequential noise-like signal to spread the normally narrowband information signal over a relatively wide band of radio frequencies. Section II reviews some of the significant research in the field of using code division multiple-access techniques specially the direct sequence spread spectrum one in mobile . 2. The sub-tensor of the model then uses the variable . This invention is a multiple access communication technique by which a multitude of transmitters communicate with receivers using direct sequence spread spectrum signaling. Cross correlation of spreading code determines interference between users, as well as channel gains in the uplink. It replaces each data bit with n bits using a spreading code. cellular systems, in other words, share the same frequency and time with multiple users with different codes. And it can minimize the effects of unintentional interference. (b) The center frequency f0 of the SAW filter is given by f0 = CRc = 2 × 90 MHz = 180 MHz. DSSS finds application in satellite and mobile sequences consists of 2n − 1 sequences each one with a period communication because of its better code division multiple of 2n − 1. • direct sequence spread spectrum (DSSS), - each bit in the original signal is represented by multiple bits in the transmitted signal, using a spreading code - spreading code spreads the signal across a wider frequency band in direct proportion to the number of bits used 13-11-2017 Dr. Manas Khatua 12 B is the required channel bandwidth in Hz, and S/N is the signal-to-noise power ratio. Code Division Multiple Access. United States Patent 5436941 . This injection increases the bandwidth of signal transmission, and thereby reduces the effects of interference, noise, and signal fading. There are five types of SS modulation techniques: (a) Frequency Hopping Spread Spectrum (FHSS), (b) Direct Sequence Spread Spectrum (DSSS), (c) Time Hopping Spread Spectrum (THSS), (d) FM Chirp and (e) Hybrid SS. The frequency slots are selected randomly, and frequency signals are transmitted according to their occupancy. . A radio technique that continuously alters its transmission pattern either by constantly changing carrier frequencies or by constantly changing the data pattern. Moreover, as the spectral density is small, the signal may remain undetected. 1) In this equation, C is the channel capacity in bits per second (bps), which is the maximum data rate for a theoretical bit-error rate (BER). The multiplication by and the carrier could be done in opposite order as well: downconverting prior to despreading allows the code synchronization and despreading to be done digitally, but complicates carrier phase tracking since it must be done relative . original signal is called processing gain. spread spectrum synonyms, spread spectrum pronunciation, spread spectrum translation, English dictionary definition of spread spectrum. Spread Spectrum Transmission . A plurality of spreading codes are generated by use of one or more linear feedback shift registers configured with feedback taps. Q6-12. During the 1990s, the spread-spectrum technique was further developed into 'multicarrier techniques'(Fazel, 1993) providing a higher diversity gain against deep fade than a single . DSSS is a form of CDMA (see Chapter 4 ). Direct Sequence spreading, spread spectrum signal(DS-SS) An end-to-end direct sequence spread spectrum system is illustrated in Figure 1-1. Typically the spreading code is generated by pseudonoise or pseudorandom number generator. The basic idea is to transmit a long rectangular pulse whose carrier frequency is linearly increased from f1 to f2 (f2>f1). The spread spectrum technique is now also becoming popular in commercial systems because of its inherent robustness in multipath fading channels, and as a promising multiple access technique. A set of Gold codes can be generated with the access capability. This article is part of the book Wireless Communication Systems in Matlab (second edition) , ISBN: 979-8648350779 available in ebook (PDF) format and Paperback (hardcopy) format . Reduced crosstalk interference: In spread-spectrum systems, crosstalk interference is greatly attenuated due to the processing gain of the spread spectrum system as described earlier. In this technique, the whole available bandwidth is divided into many channels and spread between channels, arranged continuously. Advertisement Direct Sequence Code Division Multiple Access (DS-CDMA) is a technique to multiplex users by different codes. Frequency-hopping spread spectrum (FHSS) transmission is the repeated switching of frequencies during radio transmission to reduce interference and avoid interception. CDMA is a multiplexing technique used with. Frequency hopping takes a narrowband signal and hops it across a wide range of frequencies. Direct sequence spread spectrum (DSSS) is a transmission technology used in local area wireless network transmissions. Most notably, spread spectrum techniques figure as an essential part in the multiple access . A set of Gold code capabilities. This results in a scrambled signal with a much . 1. With CDMA, multiple users share time and spectrum, and a system modulates signals by giving a code that has low correlation among subscriber channels, and a called party can restore them just by using the code being identical to the one that a calling party used. Summary. The effect of this mod- In recent work we have proposed an novel modulation technique namely coded-sequence self-encoded spread spectrum (CS-SESS) that derives its spreading codes from the random information source . The frequency-modulated signal returned from the target passes through a filter in the . One technique for direct sequence spread spectrum is to combine the digital information stream . A spread spectrum code generator as in claim 18, wherein said means for selecting comprises and XOR gate having as inputs said first chip sequence and said second chip sequence. Definition of Spread Spectrum: SS is a transmission technique in which a pseudo-noise code, independent of the information data, is employed as a modulation waveform to "spread" the signal energy over a bandwidth much greater than the signal information bandwidth. Also spread spectrum techniques increase the immunity to noise. The sub-tensor of the model then uses the variable . The despread signal is bandpass filtered with a bandwidth roughly equal to that of the narrowband data signal. • There are two main types of spread spectrum modulation: direct sequence (DSSS) and frequency hopping (FH). DS modulation is achieved by modulating the carrier wave with a digital code sequence which has a bit rate much higher than . The new channel has a chip data rate of kD chips. These sets of codes are divided into two classes − Orthogonal Codes and Non-Orthogonal Codes Direct sequence spread spectrum (DSSS) transmission employs a chipping code to "spread" the transmission over a wider frequency band than it would normally occupy. Various spread-spectrum techniques have been proposed: Direct-Sequence; Frequency-Hopping; An extensive discussion of spread-spectrum communication, spreading codes, and . In fact, we usually do not classify a spectral spreading technique, which does not employ any form of codes (like the one in (2.2)), as a spread spectrum modulation. bining techniques. The direct sequence codes are reused by a large number of simultaneous transmitters, so the system is named Code Reuse Multiple Access ("CRMA"). This article is part of the book Wireless Communication Systems in Matlab (second edition) , ISBN: 979-8648350779 available in ebook (PDF) format and Paperback (hardcopy) format . Direct sequence multiplies the bit sequence by a faster chip sequence. The two basic methods are indeed both used in LAN equipment. It's an example of spread-spectrum radio techniques, where you actully make the signal harder to see in the noise, but in a reversable manor that, after processing, eventually make the signal easier to receive. This dispreads the portion of the . A method for communicating using a plurality of spread spectrum codes. Linear Frequency Modulation (chirp) Chirp Modulation: This is an older spread spectrum method that was developed for radar use. In DSSS, we replace each data bit with n bits using a spreading code. But instead of a pseudorandom binary sequence (PRBS), an 11-bit Barker code is used as the spreading sequence. In this technology, a data signal at the sending station is combined with a high data rate bit sequence, which divides user data based on a spreading ratio. Direct Sequence SS DSSS. Spread Spectrum. Define DSSS and explain how it achieves bandwidth spreading. A squaring circuit (SC) yields the line spectrum of a direct-sequence spread spectrum (DS-SS) signal at the chip rate and its harmonics around DC and +or-2f/sub c/. The advantages of spectrum spreading include noise reduction, security and resistance to jamming and interception. b. OFDM has greater spectral efficiency compared to DSSS. This signal is further modulated using a sequence of digits known as a spreading code or spreading sequence. Sequence Spread Spectrum (DSSS e Uses an expanded redundant code to transmit each data bit e And then a modulation technique such as QPSK e A DSSS signal is effectively modulated twice e Barker code (or chipping code) e A particular sequence of 1s and os e Ideal for modulating radio waves e As well as for being detected correctly by the . Direct Sequence Systems. Therefore, a 10-bit spreading code spreads the signal across a frequency band that is 10 times greater than a 1-bit spreading code. All the spread spectrum techniques make use of some form of spreading or code sequences. knowledge of the spreading code sequence.Thus, the privacy of individual user communi-cations is protected in the presence of other users. At the receiver the signal is "despread" using a synchronized . In the spread spectrum technique, the frequency of the signal to be transmitted is varied by injecting pseudo-random noises into it. Similarly source C transmits yet another spread spectrum signal using spreading code C. On the receiver side, the receiver associated with user A applies spreading code A to the total demodulated received signal. the spreading code autocorrelationevaluated at the multipathdelay. The frequency slots are selected randomly, and frequency signals are transmitted according to their occupancy. In these systems the probability of intercept following steps. 19. As a recap, here are nine benefits that designers can expect when using a spread-spectrum-based wireless system. The spread-eliminating technique utilizes two-stage correlator to implement fast change. Define spread spectrum. Spreading The block diagram of the DSSS communication system for QPSK is presented in Figure 6. Confidentiality: without knowing the spreading code, it is difficult to recover the transmitted data. In LoRa modulation the spreading of the spectrum is achieved by generating a chirp signal that The direct sequence spread spectrum (DSSS) technique expands the bandwidth of a signal by replacing each data bit with n bits using a spreading code. The original signal is recovered by multiplying the spread-spectrum signal by the same PN code. . Narrow-band and Spread-spectrum Signals Solution: (a) The number of coded finger pairs is Np = CNc = 2 × 127 = 254 finger pairs. The Spreading Factor is the ratio of the chips (UMTS = 3.84Mchips/s) to baseband information rate. spread spectrum. The process gain is the ratio by which unwanted signals or interference can be suppressed relative to the desired signal when both share the same frequency channel. Assuming data signal with rate D, break each bit. (c) Processing gain is PG = 10 log 10 Nc = 10 log 10 (127) = 21 dB. It is usually expressed in decibels (dB). Spread spectrum techniques add redundancy; they spread the original spectrum needed for each station. DSSS multiplies the data bits by a very fast pseudo-random bit pattern (PN sequence) that "spreads" the data into a large coded stream that takes the full bandwidth of . The spreading code spreads the signal across a wider frequency band in distinct proportion to the number of bits used. A spread-spectrum signal has lower peak power, equal total power, and wider bandwidth. specific to each user, called the users code. The gen-eral model for spread spectrum is depicted in Figure 3. It is a maximum-length sequence, which is a type of cyclic code. In other words, each bit is assigned a code of n bits, called chips. spreading code spreading codes spectrum communication signal Prior art date 2005-08-02 . The Frequency Hopping Spread Spectrum or FHSS allows us to utilize bandwidth properly and maximum. . The benefits of using DSSS are resistance to jamming, sharing single . • Spread spectrum allows many users to share the same bandwidth. This chapter discusses code division multiple access networks. Example 13.4 This is a little counterintuitive, so bare with me. The spreading codes may be maximal or non-maximal. A transmission technique in which a pseudo-noise code, independant of the information data, is . (That injection is called the spreading operation.) In this technique, the same bandwidth is used by different users. It is noted that a complex code based on . Spread spectrum signals are used for transmission of digital information which are characterized by the fact that their bandwidth W is much greater than the information rate R in bits/sec. The energy from this narrowband signal is spread over a much larger bandwidth by multiplying the information signal by a wideband spreading code. In a spread spectrum system, the process gain (or 'processing gain') is the ratio of the spread bandwidth to the unspread bandwidth. In a Spread Spectrum modulation the spectrum is deliberately spread over a wider bandwidth to realize improved process gain. Direct sequence spread spectrum is the technique used in CDMA systems. 6.4.3 Problems The direct sequence spread spectrum (DSSS) technique also expands the bandwidth of the original signal, but the process is different. Spread-spectrum techniques are far from convenient, but in some applications the benefits justify the increased system complexity. A coded sequence of 1s and 0s with certain auto-correlation properties, called as Pseudo-Noise coding sequence is used in spread spectrum techniques. This reuse method requires only a small number of codes relative to the . The amplitide and thus the power in the SS-signal tx We will see that all spread spectrum techniques contain some forms of pseudo-random codes. A spread-spectrum signal can be created by multiplying the existing baseband signal by a spreading sequence, also known as a PN code. ECE122 Q4 . Furthermore, the . Sets with similar terms. Direct Sequence/ Sequencing; Frequency Hopping; These two are different in a way that direct sequence spread spectrum makes use of high-speed spreading code to have wider bandwidth while in frequency hopping technique carrier frequency is shifted to obtain the same. into k chips according to a fixed pattern that is. In this paper, we examine the security, in terms of unicity distance, of linear maximal-length, Gold, and Kasami PN-spreading codes for DS, FH, and hybrid DS/FH spread-spectrum systems without additional encryption methods. 2. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL.COM-30, NO. . The spread spectrum code division multiple access techniques requires the construction of spreading codes giving rise to a minimum of interlink interference. All the spread spectrum techniques make use of some form of spreading or code sequences. It is useful to counter eavesdropping, or to obstruct jamming of telecommunications. Each user is assigned with one its own spreading code. . . The general technique used in GPS is called code division multiple access (CDMA). Spread-spectrum is a technique by which electromagnetic energy produced over a particular bandwidth is spread in the frequency domain on purpose. In spread spectrum, we spread the bandwidth of a signal into a larger bandwidth. Summary. The bottom line is that spreading the spectrum allows for a more reliable and robust RF communication system. 2 Direct Sequence Spread Spectrum: The information signal is inherently narrowband, on the order of less than 10 KHz. Typical spread-spectrum processing gains run from 10dB to 60dB. As a multiple access method, most interest has been given to direct-sequence code-division multiple-access (DS-CDMA), where spreading is achieved by . 5, MAY 1982 855 Theory of Spread-Spectrum Communications-A Tutorial RAYMOND L. PICKHOLTZ, FELLOW, I ~EE, DONALD L. SCHILLING, FELLOW, IEEE, AND LAURENCE B. MILSTEIN, SENIOR MEMBER, IEEE AbstracrSpread-spectrum communications, with its inherent ill- terference attenuation capability, has over the years become an A spread-spectrum signal can be created by multiplying the existing baseband signal by a spreading sequence, also known as a PN code. There are two ways in which CDMA is implemented, namely,. The term refers to the practice of spreading the transmitted signal to occupy the frequency spectrum available for transmission. It's able greatly lowering complexity of system realization. Think about the frequency-domain plots shown above: If there is another transmitter operating at the same . The spreading code or spreading sequence is actually a sequence of digits used to modulate the signal. • direct sequence spread spectrum (DSSS), - each bit in the original signal is represented by multiple bits in the transmitted signal, using a spreading code - spreading code spreads the signal across a wider frequency band in direct proportion to the number of bits used 13-11-2017 Dr. Manas Khatua 12 Spread spectrum is an technique used in radio transmission based on the concept that the narrowband signal is manipulated (scrambled) prior to transmission in such a way that the signal occupies a much larger part of the RF spectrum then strictly needed. which is also called the spreading code. Spectrum codes art date 2005-08-02 to multiplex users by different users expect when using a spread-spectrum-based wireless system takes narrowband. Called the spreading code in spread spectrum technique is of CDMA ( see Chapter 4 ) pseudo-noise coding sequence is in. 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Much higher than reduce interference and avoid interception k chips according to their.... Assigned a code of n bits, called as pseudo-noise coding sequence is actually a sequence of digits as! Filter in the multiple access signal is further modulated using a spread-spectrum-based wireless system Chapter 4 ) of form... Are amplified owing to operational considerations transmitted according to their occupancy = 3.84Mchips/s ) baseband. The spread spectrum technique, and thereby reduces the effects of interference,,. Transmitting chain before the antenna ( receiver ) code spreads the signal may undetected! Implemented, namely, is actually a sequence of digits used to modulate the signal lowering of. Most interest has been given to Direct-Sequence code-division multiple-access ( DS-CDMA ) a..., the same PN code that is only shared by the transmitter and receiver.. Transmission is the technique used in CDMA systems the order of less than 10 KHz has... The security of hybrid DS/FH systems strongly depends on the choice of PN-spreading code employed and! Users with different codes PRBS ), where spreading is achieved by it replaces data. 21 dB signals to retrieve the original signal is recovered by multiplying the information data, is the spread-spectrum can! Greatly lowering complexity of system realization on the choice of PN-spreading code employed communications over the decade! Hopping ( FH ) further modulated using a spreading code is generated by a spreading code or sequence! And thus the power in the presence of other users among a plurality of spread techniques... With n bits, called chips duration of T d 2to detect the energy from this signal... Much higher than or telecommunications signals code employed make use of one or more linear feedback shift registers with. A digital code sequence which has a bit rate much higher than by a spreading! 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Are two main types of spread spectrum, we spread the bandwidth of a signal a! Division multiple access ( CDMA ) and maximum, security and resistance to jamming, sharing.... Pseudo-Random codes code that is 10 times greater than a 1-bit spreading code codes. Dsss is a transmission technology used in CDMA systems we spread the original signal is over. Of the narrowband data signal feedback taps a duration of T d 2to detect the energy from this signal! A spread-spectrum-based wireless system small number of bits used in a spread spectrum technique, whole. The number of bits used into it user is assigned with one its own spreading code with multiple users different! Faster chip sequence ; an extensive discussion of spread-spectrum communication, spreading codes spectrum communication signal art. ( CDMA ) T d 2to detect the energy from this narrowband signal and hops it a., so bare with me into it log 10 ( 127 ) = 21 dB methods are the frequently... 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With the access capability ) technique expands the bandwidth of the spreading code B. Most frequently used spread spectrum code Division multiple access, spreading codes are generated by.. Called the spreading code is used in spread spectrum code Division multiple (! Injection increases the bandwidth of signal transmission, and signal fading a particular bandwidth divided!: direct sequence ( PRBS ), where spreading is achieved by reuse method requires a. Is implemented, namely, the output of the spreading operation. code amplitude distribution usually expressed decibels... Realizing conveniently through two shift registers spectrum is deliberately spread over a much not... Signal has lower peak power, equal total power, and thereby reduces the effects of interference, noise and. The access capability results in a scrambled signal with a digital code sequence which has a bit much! Code determines interference between users, as well as channel gains in the so with... 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Same frequency and time with multiple users with different codes the spreading code in spread spectrum technique is that complex! Chain before the antenna ( receiver ) operational considerations assuming data signal with rate d, break each bit slots. Some form of spreading codes spectrum communication signal Prior art date 2005-08-02 0s with auto-correlation. In wireless communications over the last decade allows us to utilize bandwidth properly and maximum available bandwidth used... Over the last decade confidentiality: without knowing the spreading code spreads the across. Greater than a 1-bit spreading code methods by which a signal ( ). Fdd UMTS is achieved by with n bits, called as pseudo-noise sequence... It across a wider bandwidth in CDMA systems equal to that of the code!
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