Since our focus is on synchronized cases, orthogonal spreading codes are of most interest. Citeseerx performance of orthogonal cdma codes for quasi. Multicarrier code division 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 mc cdma spreads each user symbol in the frequency domain. When the transmitter is equipped with four antennas, super quasi orthogonal spacetime trellis codes sqosttcs are used. For example, if the code c 41 in the tree is assigned to a user, the codes c 10, c 20, c 82, c 83, and so on, cannot be assigned to any other user in the same cell.
Home browse by title proceedings icdcn 09 performance comparison of orthogonal gold and walsh hadamard codes for quasi synchronous cdma communication. The method comprises generating an msequence, and specific left and right sequences having a good full correlation property with the m. An orthogonal design separates different concerns of the system data access, security, business logic in a way that enables changes to be made in isolated areas of the code. For the mixed allocation strategy, in turn a walsh code followed by a quasiorthogonal code are assigned. Sum capacity optimal signatures in synchronous codedivision multipleaccess cdma systems are functions of the codebook length as well as the number of active users. A new code design method for quasisynchronous cdma is proposed. Presented is an ideal communication system that is most e ective. In this section, a chirprate based dsss cdma system is proposed by assigning mutually orthogonal pn sequences to different users and then using quasi orthogonal chirp signals for modulation. These codes correspond to lines of a special square matrix called the hadamard matrix. A method of generalized orthogonal complementary codes applying in. Many papers have applied fixedlength orthogonal walsh codes in cdma systems. A method for generating a complex quasi orthogonal code for channel spreading in a cdma communication system is disclosed. Code division multiple access cdma linkedin slideshare. Alternative code assignment policies for the forward link of a multicarrier ds cdma system employing the recently proposed quasi orthogonal sequences are put forth in this paper.
The orthogonal pn codes modulate multiple data streams together with a nonorthogonal pn code having desirable autocorrelation properties. The orthogonal itu uses a set of four pn sequences chosen such that they possess good crosscorrelation properties with respect to each other and to each of the original 4 pn generator the 4 pn. On the use of quasiorthogonal spacetimefrequency codes. Channelization codes are orthogonal codes, based on orthogonal variable spreading factor ovsf technique can separate the transmission to multiple users from a single source downlink limited orthogonal codes must be reused in every cell.
Walshcode mit vier chips, wie er beim synchronen cdma. Performance comparison of orthogonal gold and walsh hadamard codes for quasi synchronous cdma communication. The method comprises generating an msequence and then generating specific sequences having a good full correlation property with the msequence. Two quasi orthogonal spacetime block codes with better. A method of generating a waveform with a plurality of orthogonal pn codes for use in a communications network utilizing quasisynchronous code division multiple access. Pdf ber analysis of quasiorthogonal codes in quasi. Woo, orthogonal code design for quasisynchronous cdma. Let n be the number of stations establishing multiple access over a common channel. Mary qam orthogonal expanded walsh codes for cdma networks. Quasi orthogonal spreading codes are often used in real systems because they yield performance comparable to that of orthogonal codes. In cdma 2000 standard, 256 walsh codes are used to handle maximum 256 unique users under a base. Walsh codes are the most common orthogonal codes used in cdma applications.
Data transmission and pn ranging for 2 ghz cdma link. The conventional channelization code, walsh code does not have enough available bits to cope with maximal use. Consideration is given to code divisionmultipleaccess systems which use binary codes of nonorthogonal address and codes which involve mutual interference between the various links. A method for generating a quaternary complex quasi orthogonal code in a cdma communication system is disclosed. Elsewhere kerdock codes have appeared with application to cdma but in different contexts, e.
Qcom, pioneer and world leader of code division multiple access digital technology, today announced the introduction of the worlds first semiconductor and software solution for the thirdgeneration 3g air interface standard that has been submitted by the u. The transmitter mixes the packets constituting a message into the digital signal stream in an order determined by a pseudorandom number sequence that is also known to the. This method enhances the orthogonality between users, further suppresses mai, and improves the reliability of multinode communication in the underwater. Note on the utilization of quasi orthogonal codes in random multipleaccess systems borgonovo, f. Comparing to orthogonal frequency division multiplexing ofdm, qotdm is less sensitive to carrier frequency offset and power.
Multiple level orthogonal codes and their application in mc. Codedivision multipleaccess cdma systems use pseudonoise binary sequences as signature. Walsh codes are most commonly used in the orthogonal codes of cdma applications. They also typically have a large family size, and are easy to generate. Orthogonal codes for cdmabased asynchronous medical. Two codes are said to be orthogonal if when they are multiplied together the result is added over a period of time they sum to zero. When using the cyclic orthogonal walshhadamard codes cowhc as spreading codes in the cdma based wban, the cyclic orthogonality property helps mitigate mai amongst the onbody sensors. This paper proposes an efficient transmission scheme, quasi orthogonal time division multiplexing qotdm, which employs the shift orthogonal property of the pulse function with raisedcosine spectral shape, and the signal waveforms are quasi orthogonal in time domain. Quasiorthogonal time division multiplexing and its. Quasisynchronous cdma using properly scrambled walsh codes. Multiple users occupying the same band by having different codes is known as cdma code division multiple access system let w spread bandwidth in hz r 1tb date rate s received power of the desired signal in w j received power for undesired signals like multiple access users, multipath. In this paper, we propose a novel class of space frequency and spacetimefrequency block codes based on quasi orthogonal designs, over a frequency selective rayleigh fading channel. To see how cdma works, we have to understand orthogonal sequences also known as chips.
In this paper, we attempt to compare orthogonal and quasi. Performance comparison of orthogonal and quasiorthogonal. Quasiorthogonal function how is quasiorthogonal function. Whether the wrong code is mistakenly used by the target user or other users attempting to decode the received signal, the resulting correlation is always zero because of the orthogonal property of codes. In manz02, several code allocation policies for the downlink of an mccdma system are discussed. It is demonstrated how different allocation strategies of quasi orthogonal codes alter the interference level suffered by active units.
In concept this is attractive, but the known orthogonal codes have. Cdma code division multiple access also called spreadspectrum and code division multiplexing, one of the competing transmission technologies for digital mobile phones. Capacity improvement in cdma downlink with orthogonal. Quasiorthogonal sequences are employed and the variable spreading factor technique is applied to support different user data rates. Direct sequence code division multiple access dscdma is a technique to multiplex users by different codes. Code division multiple access cdma is the most important multiple access scheme for 3g mobile communication systems. The system is implemented by complex wavelet filters which are able to lower computational complexity and increase flexibility. The proposed spacefrequency code is able to achieve rateone and full space and multipath diversity gains available in the mimoofdm channel. Since codes assigned to different users in the same cell must be orthogonal, this restricts the number of available codes for a given cell.
Quasiorthogonal spacefrequency and spacetimefrequency. The key finding of this paper is to explore the performance improvement technologies for mc. Cdma 3g and 4g packet services, more ocs may be needed. In this technique, the same bandwidth is used by different users. We can categorize some of codes into two groups, those with orthogonal and those with quasi orthogonal structures. Ber analysis of quasi orthogonal codes in quasi synchronous cdma communication. Large set orthogonal kasami codes for cdma system 35 fig 2 ber vs snr performance for 10 users users, the proposed large set orthogonal fig 3 ber vs snr performance for 12 users the ber vs snr of walsh hadamard code, small set orthogonal kasami, and the proposed large set orthogonal kasami codes are shown above. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Performance analysis of optimal orthogonal spreading codes.
Code division multiple access cdma schemes and combination of cdma with ofdm have been considered as attractive. Twodimensional quasi orthogonal complete complementary codes. Orthogonal codes for cdmabased asynchronous medical wireless. In this paper, we studied the performance of dscdma signals with walshhadamard orthogonal codes, orthogonal gold codes and quadraticresidue qr orthogonal codes in a quasisynchronous transmission. Complete complementary codes use of direct sequence orthogonal complete complementary codes the orthogonal complete complementary code is based on a flock of element codes jointly instead of a single code as in traditional cdma. Therefore software was written to test all possible codes meeting system requirements. The proposed scheme, based on the theory of finite projective planes, has the following advantages. The walsh based orthogonal codes are used for data transmission in onchip. Hence the selection of an appropriate spreading code for cdma system is important. Generate orthogonal variable spreading factor ovsf code. In qostbcs, the orthogonality between columns or rows is partially relaxed, allowing for more symbols to be transmitted in the code blocks. Ber analysis of quasiorthogonal codes in quasisynchronous. In our paper, we simply use ofdm to swap time for frequency and thus largely reuse our proven methods 11, 12, 14 for narrowband communication systems in order to transmit 4 and 5.
This same property can be applied to specific binary codes. The receiver first acquires the channel state information csi and then decodes each ofdm frame using the viterbi algorithm. Quasi orthogonal sequences are employed and the variable spreading factor technique is applied to support different user data rates. Quasiorthogonal spacetime block codes with full diversity. Us6324159b1 method and apparatus for code division multiple. These systems follow the worldwide standard international mobile telecommunications2000 imt2000, part of which is the european standard umts, adopted in january 1998. This allows several users to share a band of frequencies see bandwidth. New quasiorthogonal bchderived sequences for cdma applications. Quasisynchronous cdma using properly scrambled walsh codes as user spreading sequences. For the mixed allocation strategy, in turn a walsh code followed by a quasi orthogonal code are assigned. Quasiorthogonal functions qof the forward link of a 3g code division multiple access cdma system may become a limiting factor when the number of users increases maximal capacity. The codes used in cdma spread spectrum are orthogonal codes in a specific sense. Cdma code division multiple access is a communication technique that allows multiple users to communicate simultaneously over one frequency. We propose a gaussian pulse shaping for multicarrier cdma systems to utilize the time and frequency resources effectively.
It is well known that co stbcs for more than two tx antennas cannot provide the full rate. That is, each user symbol is carried over multiple parallel subcarriers, but it is phaseshifted typically 0 or 180. The method comprises generating an msequences having a length n and a specific sequence having a good full correlation property with the msequence. A device and method for generating a binary quasi orthogonal code in a cdma communication system.
A multiscrambling code for wideband code division multiple access w cdma 2 and a quasi orthogonal function for cdma2000 3 were proposed to alleviate this code shortage. This enables to create 64 separate channels per base stations i. Multicarrier codedivision multiple access wikipedia. Jan 09, 2007 applied to software design, orthogonality is the ability to change a conceptual part of the software system while minimizing impact to other parts of the software system. Improvement of code utilization cdma for onchip communication. Based on two methods recently proposedthe ranging criterion rc and the generators ranging criterion grcnew quasi. Qualcomm cdma technologies announces worlds first third. The codes at depth r in the tree are the rows of the matrix c n, where n 2 r note that two ovsf codes are orthogonal if and only if neither code lies on the path from the other code to the root. Applications of complete complementary codes and propositions. Hassanpour introduced super quasi orthogonal spacetime trellis codes sqosttcs for four transmit antennas in. The term orthogonal is analogous to the property of orthogonal vectors.
In manz02, several code allocation policies for the downlink of an mc cdma system are discussed. Error free despreading of orthogonal codes in quasi. Quasiorthogonal spacetimefrequency codes in mbofdm uwb. We search for sets of sequences that minimize the probability of bit detection error, given that there is imperfect synchronization among the signals. For any sequence x x n, and any shift l, self correlation is. Lecture notes of the institute for computer sciences, social informatics and telecommunications engineering, vol 6. For a set of walsh codes of length n, it consists of n lines to form a square matrix of n. Quasiorthogonal multicarrier cdma kyushu university. When the wrong code is used for dispreading, the resulting correlation yields an average of zero. Codedivision multiplexing synchronous cdma edit the digital modulation method is analogous to those used in simple radio transceivers.
Code division multiple access cdma schemes and combination of cdma with. A set of walsh codes of length n consists of the n rows of an n. Abstractthis paper examines the application of quasi orthogonal spacetimefrequency codes qostfcs to ad. Chirprate quasiorthogonality based dssscdma system for. Telecommunications industry association tia to the international telecommunications union itu. Orthogonal code generation in cdma using walsh matrix in.
In this paper, orthogonal gold codes are presented as a possible option for spreading sequences in quasi synchronous cdma qs cdma. Tight synchronization is required to use orthogonal codes, which then break in a multipath channel anyway quasiorthogonal codes cause selfinterference, which dominates the performance in most cdma systems nearfar problem is a serious hindrance, requiring fast and. Application of quasiorthogonal spacetimefrequency codes. The multiple access techniques based on chaotic signals suffer from high cochannel interference due to pseudoorthogonal nature of chaotic. Java cdma code division multiple access geeksforgeeks. To overcome this disadvantage, in 21, the author proposed quasi orthogonal stbcs qostbcs for four and eight tx. Walshlike nonlinear phase orthogonal codes for direct.
Cdma is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. Performance of an improved mccdma system based on dtocwdm. Code division multiple access cdma is a channel access method used by various radio communication technologies. On quasiorthogonal signatures for cdma systems abstract. Walsh codes are most commonly used in cdma applications orthogonal codes.
Jun 17, 2019 cdma used another type of code called walsh hadamard code. Today, many stbcs with various characteristics designed for open loop multiinput multioutput mimo systems are in existence. Each user is assigned with one its own spreading code. Quasiorthogonal spacetimefrequency codes in mbofdm. These codes are compared with walsh hadamard codes in terms of individual user performances and average ber performance. Quasi orthogonal functions qof the forward link of a 3g code division multipleaccess cdma system may become a limiting factor when the number of users increases maximal capacity. Cellular communication networks andreas mitschelethiel, jens. Performance comparison of orthogonal gold and walsh. In this paper, we propose a new improved mc cdma system which combines spreading codes from quasi orthogonal matrix with orthogonal complex wavelet division multiplexing ocwdm. In this case, the performance of each user is the same. Ber analysis of quasiorthogonal codes in quasisynchronous cdma communication. Orthogonal codes are integral part of any broadband cellular systems.
A feature of pn codes is that if the same versions of the pn code are time shifted, then they become almost orthogonal, and can be used as virtually orthogonal codes within a cdma system. The matrix is defined recursively as in example 1 b, where n is the dimension of the matrix and the overscore denotes the logical not of the bits in the matrix. Patents by inventor jaeyoel kim jaeyoel kim has filed for patents to protect the following inventions. Application of quasiorthogonal spacetimefrequency codes in mbofdm uwb l. In is95 cdma, 64 walsh codes are used per base station. Quasi orthogonal function set how is quasi orthogonal. Wo2000042711a1 method for generating complex quasi. This is a clear demonstration of the advantage of the orthogonal property of the codes. Note on the utilization of quasiorthogonal codes in. Cdma code division multiple access cowhc cyclic orthogonal walshhadamard codes dbpsk di erential binary phase shift keying dqpsk di erential quadrature phase shift keying dsss direct sequence spread spectrum ecg electrocardiogram eeg electroencephalogram fcc federal communication commission fdma frequency division multiple access ffd full. Orthogonal codes are ideal for use in perfectly synchronous scenario like downlink cellular communication. Performance of a multicarrier cdma system with multiple classes of users employing walsh and quasi orthogonal codes.
In this paper, the performance of quasi synchronous directsequence cdma communication systems based on different sets of orthogonal codes is investigated. Quasi orthogonal codes are preferred over orthogonal codes in the uplink communication where perfect synchronization cannot be achieved. Then the properties of orthogonal sequences can be stated as follows. Communications theory workshop ausctw, 2011 australian 2011. Abstractwalsh codes are perfectly orthogonal binary an tipodal block. For each pair of sequence x x n and y y n, and any shift l, the cross correlation is less. Based on two methods recently proposed the ranging criterion rc and the generators ranging criterion grc new quasiorthogonal even bchderived sequences are generated which are very attractive for synchronous or quasisynchronous code division multipleaccess cdma systems. However, these techniques result in a loss of perfect orthogonality between codewords. Synchronous orthogonal codes asynchronouspseudorandom codes in cdma system, a number of spreading codes are used as signature codes for the users, which are one of the responsible factors to influence the system performance. An orthogonal sequence can be thought of as a 1xn matrix. The synchronization error considered is smaller than the chip duration. Whether the wrong code is mistakenly used by the target user or other users attempting to decode the. Orthogonal and quasiorthogonal codes are integral part of any ds cdma based cellular systems.
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