Direct sequence cdma device and method for using the same. 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. 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. In this technique, the same bandwidth is used by different users. The digital data is directly coded at a much higher frequency. 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. How does it support more than one group in the same channel. In this paper, several techniques for multiuser interference suppression from powercontrolled directsequence cdma systems are proposed and the emphasis is on the oneshot structure. 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. The digital matched filter dmf is a most powerful device that maximizes the synchronization systems performance. For browsing the web, to watch videos and to download music, cdma is better choice as compared to gsm.
The duration of an element in the code is called the chip time. Multiple access methods, spread spectrum methods, frequency hopping, direct sequence, multicarrier cdma an d ultrawideband pulse radio. 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. Pdf direct sequence cdma technology and its application. The ratio of pn sequence bit rate to data bit rate is called the. Apparatus and method for synchronization of direct sequence cdma signals us08596,037 expired lifetime us5764691a en 19950525. When allslices are occupied in the system no additional wireless terminal can be accommodated.
A simple approach for adaptive interference suppression for the downlink basetomobile link of a direct sequence ds based cellular communication system is presented. An evaluation of direct sequence cdma for future mobile. Direct sequence spread spectrum for resistance to jamming and multipath shengli zhou, student member, ieee, georgios b. From the beginning it was designed to be resistant to noise, interference, jamming, and unauthorized detection. So cdma is known to cover more area with fewer towers. 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. The goal of this project was the hardwaresoftware implementation of a direct sequence spread spectrum cdma demonstrator in the 2. Baum 3 in direct sequence code division multiple access dscdma systems, signal acquisition is nec essary before communication can commence. When you have completed this manual, you will be familiar with directsequence and frequencyhopping spread spectrum dsss and fhss. Direct sequence cdma technology and its application to future portable multimedia communication systems. The method employed in cdma is known as direct sequence spread spectrum. Understanding spread spectrum for communications national. This spread spectrum communication can be illustrated by using these key elements.
Figure 1 a binary information signal to modulate this signal, we would multiply this sequence with a. 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. There are two main types of codes used in cdma, pn sequence codes and walsh codes. The sequence produced by this implementation is shown in table 1. The technicality of cdma technology has given significant advantages over other parallel technologies in terms of spectrum efficiency and overall performance. 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.
Multiple access capability is also provided by code division multiple access cdma. The basics of code division multiple access jeanpaul m. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Citeseerx statistical modeling of biterrorrates in. Cdma is the only realizable nyquist rate transmission system. Direct sequence spread spectrum an overview sciencedirect. Transmitter 10 transmits a training bit sequence 31 coded with a spreading chip sequence. Cdma attracts much attention for its compact spectrum and the ability to suppress inter.
It is the technique by which same frequency and time interval is used by mobile subscribers base stations by way of unique digital codes. 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. This increases the data rate while adding redundancy to the system. Pdf an evaluation of direct sequence cdma for future mobile. Statistical modeling of biterrorrates in asynchronous. Finally, the maximum number of users in this directsequence code division multiple access dscdma rfid system is calculated under the condition of successfully acquired. This is the preferred method for implementing an m sequence in hardware. Cdma is the short form of code division multiple access. Each bit of the pn sequence is a chip, and the higher rate is known as the chip rate.
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. 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. May 17, 2016 in the nested direct sequence method, the security is maintained, and the cross. 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. 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. May 05, 2010 code division multiple access introduction cont. Basics of code division multiple access cdma spie digital library. 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. Direct sequence code division multiple access ds cdma technology is deployed in the air interface as the backbone of third generation 3g wireless systems. Pdf time hopping directsequence cdma for asynchronous. Direct sequence spread spectrum cdma is a direct sequence spread spectrum system. Global reach gsm is in use over 80% of the worlds mobile networks in over 210 countries as compared to cdma. Dscdma directsequence code division multiple access is a multiple access scheme based on dsss, by spreading the signals fromto different users with different codes.
Dsss direct sequence spread spectrum i xor of the signal with pseudorandom number code sequence many chips per bit e. 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. Here the word detect is used in the sense of to discover the presence of. This is the preferred method for implementing an msequence in hardware. Multiplying the input data by a pn sequence, the bit rate of which is much higher than the data bit rate, is called spreading. In this thesis, the design of a direct sequence code division multiple accessbinary phaseshift keying dscdmabpsk modem is examined. Code division multiple access or cdma has its roots in wwii era spread spectrum technology. Direct sequence spread spectrum is the technique used in todays most powerful cellular communications technology, code division multiple access. May 04, 20 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. Directsequence code division multiple access dscdma technology is deployed in the air interface as the backbone of third generation 3g wireless systems. Code division multiple access cdma has proven to be a viable enabling technique. In this prototype modem design, a short maximal length sequence of 31 chips is used to spread the information data. The receiver, knowing the code sequence of the user, decodes the received signal and recovers the original data.
Us5872808a apparatus and method for synchronization of. Note that the output sequence shown here is the reverse of the one in table 1. In direct sequence, the digital data is modulated by a much higher rate sequence of pn data. Nested and interleaved direct sequence spread spectrum to. Spreading codes for direct sequence cdma and wideband cdma. This article presents an overview of the spreading techniques for use in direct sequence cdma cellular networks. The design of flexible and efficient future mobile communication systems is a major challenge. In the nested direct sequence method, the security is maintained, and the cross. The cdma system works directly on 64 kbitsec digital. Each user is assigned with one its own spreading code.
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. A direct sequence ds cdma modulation technique using a pn code is shown in fig. Baum 3 in direct sequence code division multiple access ds cdma systems, signal acquisition is nec essary before communication can commence. Contribute to ammarelectricaldsss cdma development by creating an account on github. Pdf chip interleaving in direct sequence cdma systems. It allows multiple groups to share the same channel at the same time by assigning each group to different code. We will focus on direct sequence spread spectrum technique since it is the mostly used in the industry cdma, umts, 802. 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. The mostcommon techniques of cdma are frequencyhopped cdma or directsequence cdma. Spreading sequence design and theoretical limits for. In direct sequence spread spectrum transmission, the user data signal is multiplied by a code sequence. In 1985, the fcc allocated three frequency bands to spread spectrum communications. Adaptive interference suppression for the downlink of a.
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. Types of channels control channel forward downlink control channel. Direct sequence ds direct sequence code division multiple access ds cdma is a technique to multiplex users by different codes. Hybrid acquisition of direct sequence cdma signals 1 venugopal v. Digital multicarrier spread spectrum versus direct sequence. This text, aimed at the reader with a basic background in electrical or optical engineering, covers cdma fundamentals. Cdma is a form of direct sequence spread spectrum 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. The direct sequence process ds is probably the most well known and the most applied spread spectrum technology. International journal of information technology volume 4. Contribute to ammarelectricaldssscdma development by creating an account on github. 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.
There are several methods to perform frequency spreading. The demand for improved adaptive antenna array dscdma system performance is increasing because of its advantageous implementation and security related applications. The demand for improved adaptive antenna array ds cdma system performance is increasing because of its advantageous implementation and security related applications. The proposed schemes arise from the optimum detector that takes into account the existence of powercontrolled chipsynchronous multiuser interference and white. Direct sequence code division multiple access ds cdma is a technique to multiplex users by different codes. Dsss systems as proposed for the unlicensed ism band use a form of ds that. The most important aspect in the cdma receiver is pn sequence synchronization. Intelligent power management for a programmable matched filter us08821,003 expired fee related us5802102a en 19950525.
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. Cdma for our purposes in this chapter, we shall assume that the receiver is perfectly capable of regenerating the. In some situations it is required that a communication signal be difficult to detect, and difficult to demodulate even when detected. The ratio between the user symbol time and the chip time is called the spread factor. Signal broadcast over seemingly random series of frequencies.
906 1232 1562 1476 777 898 950 101 481 1056 657 487 1312 818 1193 761 955 517 501 1415 761 608 158 163 59 1302 1224 1242 77 1480 1087 528 891 861 647 1290 483 689 737 1402 619 1074 1295 958 1225 1424