Therefore, a 10-bit spreading code spreads the signal across a frequency band that is 10 times greater than a 1-bit spreading code. Furthermore, the . 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 Each user is assigned with one its own spreading code. A set of Gold code capabilities. (That injection is called the spreading operation.) At the receiver the signal is "despread" using a synchronized . A method for communicating using a plurality of spread spectrum codes. 1. To apply a spread-spectrum technique, simply inject the corresponding spread-spectrum code somewhere in the transmitting chain before the antenna (receiver). The despread signal is bandpass filtered with a bandwidth roughly equal to that of the narrowband data signal. Most notably, spread spectrum techniques figure as an essential part in the multiple access . CDMA is a Direct Sequence Spread Spectrum system. Spread-spectrum is apparent in the Shannon and Hartley channel-capacity theorem: C = B × log 2 (1 + S/N) (Eq. This reuse method requires only a small number of codes relative to the . 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 spreading code or spreading sequence is actually a sequence of digits used to modulate the signal. spread spectrum. Advertisement The Frequency Hopping Spread Spectrum or FHSS allows us to utilize bandwidth properly and maximum. . The frequency slots are selected randomly, and frequency signals are transmitted according to their occupancy. As a multiple access method, most interest has been given to direct-sequence code-division multiple-access (DS-CDMA), where spreading is achieved by . . 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 . It is usually expressed in decibels (dB). 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. Narrow-band and Spread-spectrum Signals Spread-spectrum techniques are far from convenient, but in some applications the benefits justify the increased system complexity. Direct sequence multiplies the bit sequence by a faster chip sequence. A radio technique that continuously alters its transmission pattern either by constantly changing carrier frequencies or by constantly changing the data pattern. The frequency-modulated signal returned from the target passes through a filter in the . In a Spread Spectrum modulation the spectrum is deliberately spread over a wider bandwidth to realize improved process gain. spread spectrum. The output of the bandpass filter is squared and integrated for a duration of T d 2to detect the energy of the despread signal. 2.4 Spreading factors vary from 4 to 512 in FDD UMTS. spreading code spreading codes spectrum communication signal Prior art date 2005-08-02 . DSSS is a form of CDMA (see Chapter 4 ). referred to as a code. • 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 And it can minimize the effects of unintentional interference. This is a little counterintuitive, so bare with me. In this technique, the whole available bandwidth is divided into many channels and spread between channels, arranged continuously. An extensive discussion of spread-spectrum communication, spreading codes, and . d. all statements are correct 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/. There are two ways in which CDMA is implemented, namely,. United States Patent 5436941 . knowledge of the spreading code sequence.Thus, the privacy of individual user communi-cations is protected in the presence of other users. 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 . This invention is a multiple access communication technique by which a multitude of transmitters communicate with receivers using direct sequence spread spectrum signaling. Among specific to each user, called the users code. 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 advantages of spectrum spreading include noise reduction, security and resistance to jamming and interception. 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 . Moreover, as the spectral density is small, the signal may remain undetected. The energy from this narrowband signal is spread over a much larger bandwidth by multiplying the information signal by a wideband spreading code. . which is also called the spreading code. All the spread spectrum techniques make use of some form of spreading or code sequences. This signal is further modulated using a sequence of digits known as a spreading code or spreading sequence. The basic idea is to transmit a long rectangular pulse whose carrier frequency is linearly increased from f1 to f2 (f2>f1). 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. In the spread spectrum technique, the frequency of the signal to be transmitted is varied by injecting pseudo-random noises into it. The sub-tensor of the model then uses the variable . Also spread spectrum techniques increase the immunity to noise. In LoRa modulation the spreading of the spectrum is achieved by generating a chirp signal that 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. 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. Direct Sequence spreading, spread spectrum signal(DS-SS) An end-to-end direct sequence spread spectrum system is illustrated in Figure 1-1. original signal is called processing gain. spread spectrum synonyms, spread spectrum pronunciation, spread spectrum translation, English dictionary definition of spread spectrum. The original signal is recovered by multiplying the spread-spectrum signal by the same PN code. The Frequency Hopping Spread Spectrum or FHSS allows us to utilize bandwidth properly and maximum. Notice . Spread-spectrum is a technique by which electromagnetic energy produced over a particular bandwidth is spread in the frequency domain on purpose. Spread spectrum techniques, on the other hand, employ a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth. Define spread spectrum. Q6-12. (c) Processing gain is PG = 10 log 10 Nc = 10 log 10 (127) = 21 dB. The direct sequence codes are reused by a large number of simultaneous transmitters, so the system is named Code Reuse Multiple Access ("CRMA"). c. DSSS relies upon a PN code that is only shared by the transmitter and receiver pair. It replaces each data bit with n bits using a spreading code. Due to their interference rejection capabilities, spread spectrum techniques have played a major role in wireless communications over the last decade. A spread-spectrum signal has lower peak power, equal total power, and wider bandwidth. The term refers to the practice of spreading the transmitted signal to occupy the frequency spectrum available for transmission. (DSSS) technique expands the bandwidth of the original signal. Spreading The block diagram of the DSSS communication system for QPSK is presented in Figure 6. Various spread-spectrum techniques have been proposed: Direct-Sequence; Frequency-Hopping; 2. Direct sequence spread spectrum (DSSS) transmission employs a chipping code to "spread" the transmission over a wider frequency band than it would normally occupy. The spectrum around DC depends only on the variance of the spreading code amplitude distribution. 3. Direct Sequence Code Division Multiple Access (DS-CDMA) is a technique to multiplex users by different codes. 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 . The line spectrum around +or-2f/sub c/, however, can be eliminated by a uniform phase code. Spread spectrum techniques add redundancy; they spread the original spectrum needed for each station. 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]. In these systems the probability of intercept following steps. 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. Sets with similar terms. 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 . These sets of codes are divided into two classes − Orthogonal Codes and Non-Orthogonal Codes In other words, each bit is assigned a code of n bits, called chips. It is noted that a complex code based on . It is a maximum-length sequence, which is a type of cyclic code. However, situations arise where the effects of interlink interference are amplified owing to operational considerations. . the spreading code autocorrelationevaluated at the multipathdelay. 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 . Typical spread-spectrum processing gains run from 10dB to 60dB. The frequency-modulated signal returned from the target passes through a filter in the . Assuming data signal with rate D, break each bit. . • 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 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. bining techniques. A set of Gold codes can be generated with the access capability. The general technique used in GPS is called code division multiple access (CDMA). The spreading codes may be maximal or non-maximal. • Spread spectrum allows many users to share the same bandwidth. 19. Linear Frequency Modulation (chirp) Chirp Modulation: This is an older spread spectrum method that was developed for radar use. into k chips according to a fixed pattern that is. Confidentiality: without knowing the spreading code, it is difficult to recover the transmitted data. In this technique, the same bandwidth is used by different users. Now-a-days spread spectrum techniques have been applied to mobile communication in the name of . IEEE TRANSACTIONS ON COMMUNICATIONS, VOL.COM-30, NO. This injection increases the bandwidth of signal transmission, and thereby reduces the effects of interference, noise, and signal fading. A spread-spectrum signal can be created by multiplying the existing baseband signal by a spreading sequence, also known as a PN code. 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. Direct Sequence SS DSSS. 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. It is useful to counter eavesdropping, or to obstruct jamming of telecommunications. The spread-eliminating technique utilizes two-stage correlator to implement fast change. The Spreading Factor is the ratio of the chips (UMTS = 3.84Mchips/s) to baseband information rate. A spread-spectrum signal can be created by multiplying the existing baseband signal by a spreading sequence, also known as a PN code. A coded sequence of 1s and 0s with certain auto-correlation properties, called as Pseudo-Noise coding sequence is used in spread spectrum techniques. One technique for direct sequence spread spectrum is to combine the digital information stream . The receiver correlates the received signals to retrieve the original information signal. 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. 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). 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. . TYPES OF SS TECHNIQUES THE FUTURE LIES WITHIN. 2. CDMA is a multiplexing technique used with. 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. The code portions each have the same length and are selected . 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 . 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 Spread spectrum is a technique used for transmitting radio or telecommunications signals. Define DSSS and explain how it achieves bandwidth spreading. . In spread spectrum, we spread the bandwidth of a signal into a larger bandwidth. Direct sequence spread spectrum is the technique used in CDMA systems. Spread spectrum spectral density techniques .
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