Multicarrier codedivision multiple access wikipedia. This spreading code has a higher chip rate this the bitrate of the code, which results in a wideband time continiuous scrambled signal. Code acquisition in direct sequence spread spectrum. The concept of cdma is based around the fact that a data sequence is multiplied by a spreading code or sequence which increases the bandwidth of the signal. Apparatus and method for synchronization of direct sequence cdma signals us08596,037 expired lifetime us5764691a en 19950525. The walkstation project involves researchers from different areas in order to find a solution via a global system approach. Topics based on electronics, communication and computer are given emphasis. In direct sequence, the digital data is modulated by a much higher rate sequence of pn data. On receiving end, digit sequence is used to demodulate the spread. Cdma, mmse, equalization, adaptive, multiuser detection 1.
Spectral plots illustrate directsequence spreadspectrum dsss and frequencyhopping spreadspectrum fhss methods. The results indicate a superior performance for this system over a pn sequence based cdma system when a set of dsequences with zero or nearzero crosscorrelation is employed. Generate a local pseudorandom code with a higher rate than the data to. This is a gain factor and the actual data propagation rate. The are then independent, with a gaussian distribution such that. Here multi carrierdirect sequence code division multipleaccess mcdscdma system is used as the modulation technique to support multimedia services in mobilewireless communication. International journal of recent technology and engineering. Traditionally, a pseudo random pn sequence is used for dscdma systems, but it lacks security due to fact that there is limited number of. Direct sequence spread spectrum cdma is a direct sequence spread spectrum system. Ds cdma direct sequence code division multiple access is a multiple access scheme based on dsss, by spreading the signals fromto different users with different codes. Code division multiple access or cdma has its roots in wwii era spread spectrum technology. 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. The digital data is directly coded at a much higher frequency. Pdf direct sequence cdma technology and its application.
Adaptive interference suppression for the downlink of a. The spreading architecture used in the direct sequence physical layer is not to be confused with cdma. The duration of an element in the code is called the chip time. The code is generated pseudorandomly, the receiver knows how to generate the same code, and correlates the received signal with that code to extract the data. An introduction to directsequence spreadspectrum communications a tutorial overview of spread spectrum principles. The design of flexible and efficient future mobile communication systems is a major challenge. Direct sequence cdma technology and its application to future portable multimedia communication systems conference paper pdf available august 1994 with 66. This modulation technique is basically a combination of ds cdma and orthogonal frequency division multiplexing. The ratio between the user symbol time and the chip time is called the spread factor. Spectral plots illustrate direct sequence spreadspectrum dsss and frequencyhopping spreadspectrum fhss methods. An introduction to direct sequence spreadspectrum communications a tutorial overview of spread spectrum principles. May 04, 20 when allslices are occupied in the system no additional wireless terminal can be accommodated.
Pdf time hopping directsequence cdma for asynchronous. Direct sequence code division multiple access ds cdma is an attractive allocation technique that allows users to be simultaneously active over the total available bandwidth. Direct sequence code division multiple access cdma systems are considered, in a multipath environment. Drm d macleod ma phd mieee, in telecommunications engineers reference book, 1993. Transmitter 10 transmits a training bit sequence 31 coded with a spreading chip sequence.
Direct sequence spreadspectrum the information bearing signal is multiplied directly by a high chip rate code signal. Covers both direct sequence and fast hopping methods. Then within the receiver the same spreading code or sequence is used to extract the required data. Short pn sequences for direct sequence spread spectrum. Design and implementation of dssscdma transmitter and. Here the word detect is used in the sense of to discover the presence of. Direct sequence code division multiple access dscdma. Direct sequence spread spectrum dsss is a spread spectrum technique whereby the original data signal is multiplied with a pseudo random noise spreading code. Direct sequence spread spectrum, also known as direct sequence code division multiple access ds cdma, is one of two approaches to spread spectrum modulation for digital signal transmission over the airwaves. There are several methods to perform frequency spreading. In this technique, the same bandwidth is used by different users. Understanding spread spectrum for communications national.
Introduction is95, the second generation us digital cellular standard, is based on direct sequence ds code division. The method employed in cdma is known as direct sequence spread spectrum. Direct sequence cdma technology and its application to future portable multimedia communication systems conference paper pdf available august 1994 with 66 reads how we measure reads. This sequence provides 10db of processing gain that meets the minimum requirements for the rules set forth by the fcc. Pdf chip interleaving in direct sequence cdma systems. Introduction direct sequence spread spectrum is one of the spread spectrum techniques. Modulation of forward link cdma signals the data transmitted on the forward link channel in cellular cdma systems i. Pdf this paper investigates transmission schemes for asynchronous transmitter only wireless sensor nodes. The bandwidth of the coded data signal is chosen to be much larger than the bandwidth of the original data signal, that is, the encoding process enlarges spreads the spectrum of the data signal. Multiple access methods, spread spectrum methods, frequency hopping, direct sequence, multicarrier cdma an d ultrawideband pulse radio. This article presents an overview of the spreading techniques for use in direct sequence cdma cellular networks.
In 1985, the fcc allocated three frequency bands to spread spectrum communications. In a cdma communication system 100 capable of communicating between a receiver 10 and a transmitter 20 direct sequence spread spectrum communication signals 30, a system and method for synchronizing receiver chip timing and transmitter chip timing. Direct sequence spread spectrum, dsss is a form of radio transmission used in a variety of radio transmissions. Additionally, the transmission security afforded by long pn sequences in the waveform is important as is the ability to do code division multiple access cdma.
How does it support more than one group in the same channel. Multi tone direct sequence code division multiple access mtds cdma. Theoretical equations are given to allow performance estimates. In the transmitter, the input data stream is xored with the pn signal before. Multicarrier codedivision multiple access mccdma is a multiple access scheme used in ofdmbased telecommunication systems, allowing the system to support multiple users at the same time over same frequency band mccdma spreads each user symbol in the frequency domain. Nov 11, 2016 direct sequence spread spectrum dsss is a transmission technology used in local area wireless network transmissions.
This is the preferred method for implementing an msequence in hardware. In some situations it is required that a communication signal be difficult to detect, and difficult to demodulate even when detected. Cdma, dsss, bpsk, pn code, states started in octoddfs. In direct sequence spread spectrum transmission, the user data signal is multiplied by a code sequence.
Multicarrier codedivision multiple access mc cdma is a multiple access scheme used in ofdmbased telecommunication systems, allowing the system to support multiple users at the same time over same frequency band. Mmse interference suppression for timing acquisition and. Cdma can be implemented in several ways, two of which are frequency hopping and direct sequencing. In a cdma communication system 100 capable of communicating between a receiver 10 and a transmitter 20direct sequence spread spectrum communication signals 30, a system and method for synchronizing receiver chip timing and transmitter chip timing.
Note that the output sequence shown here is the reverse of the one in table 1. The design and implementation of a semicustom transmitter for a cdma direct sequence spreadspectrum transceiver. An introduction to spreadspectrum communications tutorial. Introduction in communication systems an attractive approach for economical, spectral efficient, and high quality digital cellular and personal communication services is the use of direct sequence code division multiple access dscdma technique 1.
Dsss systems as proposed for the unlicensed ism band use a form of ds that. Apr 03, 2017 notes for engineering in electronics, communications and computer science subjects are added. Mc cdma spreads each user symbol in the frequency domain. Spreading codes for direct sequence cdma and wideband cdma. Code division multiple access cdma the concept of signal spreading and its uses in communications lets take a stright forward binary signal of symbol rate 2. Direct sequence code division multiple access dscdma is an attractive allocation technique that allows users to be simultaneously active over the total available bandwidth. Each user is assigned with one its own spreading code.
The direct sequence process ds is probably the most well known and the most applied spread spectrum technology. Carrier direct sequence cdma with fading rayleigh and rician thesis 1. In direct sequence spread spectrum dsss, the transmitter and receiver contain identical psuedorandom sequence generators producing a pseudonoise pn signal. Direct sequence code division multiple access dscdma is a technique to multiplex users by different codes. Intelligent power management for a programmable matched filter us08821,003 expired fee related us5802102a en 19950525. 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. Intelligent power management for a programmable matched filter us08821,003 expired fee related us5802102a en 199505. Direct sequence spread spectrum dsss is a transmission technology used in local area wireless network transmissions. When allslices are occupied in the system no additional wireless terminal can be accommodated. Us5872808a apparatus and method for synchronization of. Direct sequence spread spectrum an overview sciencedirect. Short pn sequences for direct sequence spread spectrum radios.
Introduction in communication systems an attractive approach for economical, spectral efficient, and high quality digital cellular and personal communication services is the use of direct sequence code division multiple access ds cdma technique 1. The performance of a dsequence based direct sequence cdma system over an additive white gaussian noise awgn channel is analyzed. The recently developed is95 standard for commercial codedivision multiple access cdma communications involves a stagedirect sequencespreading process, first with a walsh function and then with a longer pseudonoise pn sequence. Abstract direct sequence spread spectrum dsss, is also called as direct sequence code division multiplexing dscdma. The goal of this project was the hardwaresoftware implementation of a direct sequence spread spectrum cdma demonstrator in the 2. Then within the receiver the same spreading code or. Blind adaptation algorithms for direct sequence spreadspectrum cdma singleuser detection nevena zeeevic and jeffrey h. Mar 05, 2019 2 direct sequence ds which introduces rapid phase transition to the data to make it larger in bandwidth. Reed mobile and portable radio research group mprg virginia polytechnic institute and state university abstract singleuser detection techniques mitigate multiple ac cess interference and the nearfar problem in direct. Multiple access capability is also provided by code division multiple access cdma. Performance analysis of multicarrier direct sequence. Hybrid acquisition of direct sequence cdma signals 1 venugopal v. The mostcommon techniques of cdma are frequencyhopped cdma or directsequence cdma.
The basics of code division multiple access jeanpaul m. The receiver, knowing the code sequence of the user, decodes the received signal and recovers the original data. Part of this work was presented at the 36th annual allerton conference on communication, control and computing, monticello, illinois, september 1998. Direct sequence spread spectrum, also known as direct sequence code division multiple access dscdma, is one of two approaches to spread spectrum modulation for digital signal transmission over the airwaves.
It allows multiple groups to share the same channel at the same time by assigning each group to different code. Notes for engineering in electronics, communications and computer science subjects are added. Pdf of the signal coming into the comparator, as in rappaport 1969. Baum 3 in direct sequence code division multiple access ds cdma systems, signal acquisition is nec essary before communication can commence. Figure 1 a binary information signal to modulate this signal, we would multiply this sequence with a sinusoid and its spectrum would look like as in figure 2. Multiple accesses is a technique where many subscribers or local stations can share the use of the use of a communication channel at the same time or nearly so despite the fact originate from.
Here multi carrier direct sequence code division multipleaccess mcds cdma system is used as the modulation technique to support multimedia services in mobilewireless communication. Baum 3 in direct sequence code division multiple access dscdma systems, signal acquisition is nec essary before communication can commence. That is, each user symbol is carried over multiple parallel subcarriers, but it is phase. Here, the data signal is multiplied by a pseudo random code pn code pseudo noise code, which has similar characteristics as noise does. Akansu, senior member, ieee, and radha poluri abstractwalsh codes are perfectly orthogonal binary antipodal block codes that found their use in many popular applications over several decades including synchronous multiuser communications.
What is direct sequence spread spectrum dsss or direct. Direct sequence code division multiple access ds cdma. Blind adaptation algorithms for directsequence spreadspectrum cdma singleuser detection nevena zeeevic and jeffrey h. Pdf direct sequence cdma technology and its application to. The sequence produced by this implementation is shown in table 1. Asynchronous cdma consider an asynchronous directsequence cdma system with simultaneous antipodal users over an additive white gaussian noise awgn baseband channel. We will focus on direct sequence spread spectrum technique since it is the mostly used in the industry cdma, umts, 802. Direct sequence spreading page 7 of 16 2 the shift around method is shown in figure 5.
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