Each bit in original signal is represented by multiple bits in the transmitted signal. In this prototype modem design, a short maximal length sequence of 31 chips is used to spread the information data. Introduction code division multiple access cdma is a very popular multiple access technique for which directsequence cdma dscdma has been one of the prominent multiple access schemes for the air interface for 3rd generation cellular systems normalization wcdma, umts, cdma2000 1. Generate a local pseudorandom code with a higher rate than the data to. Then the sequence is called a maximal length shift register mlsr or. Dscdma directsequence code division multiple access is a multiple access scheme based on dsss, by spreading the signals fromto different users with different codes. The direct sequence process ds is probably the most well known and the most applied spread spectrum technology. Cdma is the only realizable nyquist rate transmission system. The technicality of cdma technology has given significant advantages over other parallel technologies in terms of spectrum efficiency and overall performance. The most important aspect in the cdma receiver is pn sequence synchronization.
Frequency hopping, direct sequence, multicarrier cdma an d ultrawideband pulse radio. Code division multiple access or cdma has its roots in wwii era spread spectrum technology. Apparatus and method for synchronization of direct sequence cdma signals us08596,037 expired lifetime us5764691a en 19950525. Baum 3 in direct sequence code division multiple access dscdma systems, signal acquisition is nec essary before communication can commence. Transmitter 10 transmits a training bit sequence 31 coded with a spreading chip sequence. This spread spectrum communication can be illustrated by using these key elements. There are several methods to perform frequency spreading. In direct sequence, the digital data is modulated by a much higher rate sequence of pn data. May 04, 20 when allslices are occupied in the system no additional wireless terminal can be accommodated. The ratio between the user symbol time and the chip time is called the spread factor. When the channel uses the me coding combined with a dsss code and ook without fm0 encoding as is disclosed in the epcc1g2iso 180006 type c standard. It allows multiple groups to share the same channel at the same time by assigning each group to different code. Direct sequence, codedivision multiple access cdma schemes offer an attractive alternative for sharing a transmission medium among many users, while requiring minimal cooperation among them. The method employed in cdma is known as direct sequence spread spectrum.
Cdma i about the tutorial code division multiple access cdma is a channel access method normally used by 3g radio communication technology as well as in some other technologies. Nested and interleaved direct sequence spread spectrum to. Direct sequence cdma device and method for using the same. Direct sequence code division multiple access ds cdma is a technique to multiplex users by different codes. Citeseerx statistical modeling of biterrorrates in.
The demand for improved adaptive antenna array dscdma system performance is increasing because of its advantageous implementation and security related applications. 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. Direct sequence spread spectrum for resistance to jamming and multipath shengli zhou, student member, ieee, georgios b. The use of spreading codes which is independent for each user along with synchronous reception will allow multiple users to access the same channel simultaneously. The sequence produced by this implementation is shown in table 1. This article presents an overview of the spreading techniques for use in direct sequence cdma cellular networks. This text, aimed at the reader with a basic background in electrical or optical engineering, covers cdma fundamentals. Direct sequence code division multiple access ds cdma technology is deployed in the air interface as the backbone of third generation 3g wireless systems.
Direct sequence spread spectrum techniques spread spectrum technology was first introduced about 50 years ago by the military as a way of sending secure communications. Introduction code division multiple access cdma is a very popular multiple access technique for which direct sequence cdma ds cdma has been one of the prominent multiple access schemes for the air interface for 3rd generation cellular systems normalization w cdma, umts, cdma2000 1. 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. In this paper, several techniques for multiuser interference suppression from powercontrolled directsequence cdma systems are proposed and the emphasis is on the oneshot structure. Pdf an evaluation of direct sequence cdma for future mobile. Statistical modeling of biterrorrates in asynchronous. Spreading codes for direct sequence cdma and wideband cdma. So cdma is known to cover more area with fewer towers. The ratio of pn sequence bit rate to data bit rate is called the. System study on direct sequence spectrum of radiofrequency. Directsequence code division multiple access dscdma technology is deployed in the air interface as the backbone of third generation 3g wireless systems. Multiplying the input data by a pn sequence, the bit rate of which is much higher than the data bit rate, is called spreading. This increases the data rate while adding redundancy to the system. For browsing the web, to watch videos and to download music, cdma is better choice as compared to gsm.
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. This is the preferred method for implementing an msequence in hardware. 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. Short pn sequences for direct sequence spread spectrum. The goal of this project was the hardwaresoftware implementation of a direct sequence spread spectrum cdma demonstrator in the 2.
Multiple access methods, spread spectrum methods, frequency hopping, direct sequence, multicarrier cdma an d ultrawideband pulse radio. The design of flexible and efficient future mobile communication systems is a major challenge. The duration of an element in the code is called the chip time. In some situations it is required that a communication signal be difficult to detect, and difficult to demodulate even when detected. Direct sequence spread spectrum is the technique used in todays most powerful cellular communications technology, code division multiple access. Us5872808a apparatus and method for synchronization of. Spreading sequence design and theoretical limits for. Dsss direct sequence spread spectrum i xor of the signal with pseudorandom number code sequence many chips per bit e. Is95 cdma is95 cdmaone 2g digital cellular standard motivation intended as a new system greenfield or replacement for amps not an upgrade increase system capacity add new featuresservices history. The proposed schemes arise from the optimum detector that takes into account the existence of powercontrolled chipsynchronous multiuser interference and white.
An evaluation of direct sequence cdma for future mobile. Intelligent power management for a programmable matched filter us08821,003 expired fee related us5802102a en 19950525. 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. Adaptive interference suppression for the downlink of a. When allslices are occupied in the system no additional wireless terminal can be accommodated. Cdma can be implemented in several ways, two of which are frequency hopping and direct sequencing. The receiver, knowing the code sequence of the user, decodes the received signal and recovers the original data. Here the word detect is used in the sense of to discover the presence of.
The basics of code division multiple access jeanpaul m. Contribute to ammarelectricaldsss cdma development by creating an account on github. There are two main types of codes used in cdma, pn sequence codes and walsh codes. Cdma attracts much attention for its compact spectrum and the ability to suppress inter. In the nested direct sequence method, the security is maintained, and the cross. The cdma system works directly on 64 kbitsec digital. Pdf chip interleaving in direct sequence cdma systems. The digital data is directly coded at a much higher frequency. An evaluation of direct sequence cdma for future mobile communication networks by a bateman, ma beach, a hammer, sa allpress and jp mcgeehan download pdf 583 kb.
Note that the output sequence shown here is the reverse of the one in table 1. Hybrid acquisition of direct sequence cdma signals 1 venugopal v. This paper presents a method for modeling the biterrorrate ber probability density functions pdf of asynchronous multicarrier code division multiple access mccdma and directsequence code division multiple access dscdma systems. Basics of code division multiple access cdma spie digital library. 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. Basics idea about cdma technology and its applications. International journal of information technology volume 4. Each bit of the pn sequence is a chip, and the higher rate is known as the chip rate.
A direct sequence ds cdma modulation technique using a pn code is shown in fig. In this paper, several techniques for multiuser interference suppression from powercontrolled direct sequence cdma systems are proposed and the emphasis is on the oneshot structure. May 17, 2016 in the nested direct sequence method, the security is maintained, and the cross. Signal broadcast over seemingly random series of frequencies. This is the preferred method for implementing an m sequence in hardware.
Cdma for our purposes in this chapter, we shall assume that the receiver is perfectly capable of regenerating the. We will focus on direct sequence spread spectrum technique since it is the mostly used in the industry cdma, umts, 802. The digital matched filter dmf is a most powerful device that maximizes the synchronization systems performance. Digital multicarrier spread spectrum versus direct sequence. From the beginning it was designed to be resistant to noise, interference, jamming, and unauthorized detection. In this thesis, the design of a direct sequence code division multiple accessbinary phaseshift keying dscdmabpsk modem is examined.
Here, the data signal is multiplied by a pseudo random code pn code pseudo noise code, which has similar characteristics as noise does. Cdma is a form of direct sequence spread spectrum communications. Code division multiple access cdma has proven to be a viable enabling technique. Dsss systems as proposed for the unlicensed ism band use a form of ds that. Pdf direct sequence cdma technology and its application. Finally, the maximum number of users in this directsequence code division multiple access dscdma rfid system is calculated under the condition of successfully acquired. The mostcommon techniques of cdma are frequencyhopped cdma or directsequence cdma. Multiple access capability is also provided by code division multiple access cdma. It is the technique by which same frequency and time interval is used by mobile subscribers base stations by way of unique digital codes.
Contribute to ammarelectricaldssscdma development by creating an account on github. In digital communications, a chip is a pulse of a directsequence spread spectrum dsss code, such as a pseudorandom noise pn code sequence used in directsequence code division multiple access cdma channel access techniques. A simple approach for adaptive interference suppression for the downlink basetomobile link of a direct sequence ds based cellular communication system is presented. In this technique, the same bandwidth is used by different users. The walkstation project involves researchers from different areas in order to find a solution via a global system approach. Baum 3 in direct sequence code division multiple access ds cdma systems, signal acquisition is nec essary before communication can commence. Global reach gsm is in use over 80% of the worlds mobile networks in over 210 countries as compared to cdma. Direct sequence cdma technology and its application to future portable multimedia communication systems.
In direct sequence spread spectrum transmission, the user data signal is multiplied by a code sequence. Code division multiple access cdma user 1 time frequency users share bandwidth by using code sequences that are orthogonal to each other some second generation systems use cdma most of third generation systems use cdma user 2 user n code. Direct sequence ds direct sequence code division multiple access ds cdma is a technique to multiplex users by different codes. Giannakis, fellow, ieee, and ananthram swami, senior member, ieee abstract we compare single user digital multicarrier spread spectrum mcss modulation with direct sequence ds ss. Types of channels control channel forward downlink control channel. Direct sequence spread spectrum an overview sciencedirect. The base station transmits the sum of the signals destined for the different mobiles, typically attempting to avoid intracell interference by employing orthogonal spreading sequences for different mobiles. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Download fulltext pdf an evaluation of direct sequence cdma for future mobile communication networks conference paper pdf available in vehicular technology conference, 1988, ieee 38th june. Pdf time hopping directsequence cdma for asynchronous. Understanding spread spectrum for communications national. Each user is assigned with one its own spreading code. When you have completed this manual, you will be familiar with directsequence and frequencyhopping spread spectrum dsss and fhss. Direct sequence spread spectrum cdma is a direct sequence spread spectrum system.
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