Errorless Codes for Over-Loaded CDMA with Active User Detection

Pad, Pedram; Soltanolkotabi, Mahdi; Hadikhanlou, S.; Enayati, Arash; Marvasti, Farokh

doi:10.1109/icc.2009.5199003

Cited by 12 publications

(25 citation statements)

References 18 publications

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“…In [23], the authors have shown a new class of overloaded codes that not only detects the active users but also provides errorless transmission in a noiseless channel. These codes are called Codes for Overloaded Wireless CDMA with Detection of Active Users (COWDA).…”

Section: Overloaded Cdma With Active User Detection (Cowda)mentioning

confidence: 99%

“…For developing these kinds of codes, the authors of [23] have used the same geometric interpretation as in the COW/COO case. The only difference is that in this case the vertices of the hypercube are taken from the set {0, ±1}…”

Section: Overloaded Cdma With Active User Detection (Cowda)mentioning

confidence: 99%

“…Thus, to find such COWDA matrices, KerC should be compared with 5 n vectors. But in [23], a method was shown in which the number of comparisons is reduced to 5…”

Section: Overloaded Cdma With Active User Detection (Cowda)mentioning

confidence: 99%

“…None of the above codes guarantee errorless transmission in the absence of channel noise for overloaded CDMA systems. There are also some codes that are not designed upon cross-correlation and are designed such that they can provide one-to-one transformation such as codes for overloaded wireless (COW) and codes for overloaded optical (COO) codes [20][21][22][23]. By using these codes, we can achieve errorless transmission in the absence of channel noise for highly overloaded systems.…”

Section: Introductionmentioning

confidence: 99%

“…In this case, the signature entries and input alphabets are completely arbitrary (real or complex) [20,21]. But in real communication systems, we deal with more practical applications, and therefore, some special cases such as the binary input and binary signature CDMA systems [22] and the codes being able to detect the active users in a CDMA system [23] are considered. We will also take a brief look at CDMA systems with WBE (Welsh Bound Equality) codes that are optimum for analog inputs [11].…”

Section: Introduction To Optimum Codes For Cdma Transmissionmentioning

confidence: 99%

See 4 more Smart Citations

A review on synchronous CDMA systems: optimum overloaded codes, channel capacity, and power control

Hosseini

Javidbakht

Pad

et al. 2011

J Wireless Com Network

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This paper is a tutorial review on important issues related to code-division multiple-access (CDMA) systems such as channel capacity, power control, and optimum codes; specifically, we consider optimum overloaded codes that achieve errorless transmission in the absence of noise for the binary and nonbinary cases. A survey of lower and upper bounds for the sum channel capacity of such systems is given in the presence and absence of channel noise. The asymptotic results for the channel capacity are also investigated. The channel capacity, errorless transmission codes, and power estimation for near-far effects are also explored. The emphasis of this tutorial review is on the overloaded CDMA systems.Keywords: Code Division Multiple Access (CDMA), Optimum codes, channel capacity bounds, near-far effects, power control I Introductioncode-division multiple access (CDMA) has been the most important multiple access technology for the 3rd generation GSM and American Cellular systems [1]. Optical CDMA systems have become an alternative multiple access for fiber optics and optical wireless systems [2][3][4].In CDMA systems, each user is assigned a unique code signature that consists of a number of chips. The signature length (also called chip rate) is defined as the number of chips in each signature code. Each user signature is multiplied by the respective data, and the transmitted vectors are added up in the common channel. The resultant vector is then observed at the received user end. In order to decode the received signal, the detector of the received user should know its own unique signature. These codes should be designed such that the cross-correlations between the code of the desired user and the codes of the other users are minimal.For the wireless case, the most well-known binary (Endnote a) code for the synchronous case is Hadamard orthogonal code that is appropriate for fully and underloaded CDMA systems. (Endnote b) But because of bandwidth limitation in the communication systems, we are interested in finding codes that can support more users than the chip rate (overloaded case). In the overloaded case, we cannot use Hadamard codes; Even random codes create interference that cannot be eliminated completely [5][6][7]. Optical orthogonal codes (OOC) [3,8] are not really orthogonal; however, using interference cancelation, we can remove interference completely. Most of the research in the overloaded case is related to code design and multi-access interference (MAI) cancelation in order to decrease the probability of error. Examples of these types of codes are pseudo random spreading [9,10], Welsh Bound Equality (WBE) codes with minimal total square correlation (TSC) [11][12][13][14], OCDMA [15][16][17], Multiple-OCDMA [18], and PN/ OCDMA [19] signature sets. None of the above codes guarantee errorless transmission in the absence of channel noise for overloaded CDMA systems. There are also some codes that are not designed upon cross-correlation and are designed such that they can provide one-to-one transfor...

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Section: Overloaded Cdma With Active User Detection (Cowda)mentioning

confidence: 99%

Section: Overloaded Cdma With Active User Detection (Cowda)mentioning

confidence: 99%

“…Thus, to find such COWDA matrices, KerC should be compared with 5 n vectors. But in [23], a method was shown in which the number of comparisons is reduced to 5…”

Section: Overloaded Cdma With Active User Detection (Cowda)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introduction To Optimum Codes For Cdma Transmissionmentioning

confidence: 99%

See 3 more Smart Citations

A review on synchronous CDMA systems: optimum overloaded codes, channel capacity, and power control

Hosseini

Javidbakht

Pad

et al. 2011

J Wireless Com Network

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Generalisation of code division multiple access systems and derivation of new bounds for the sum capacity

Dashmiz¹,

Takapoui

Moazeni

et al. 2014

IET Communications

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In this study, the authors explore a generalised scheme for the synchronous code division multiple access (CDMA). In this scheme, unlike the standard CDMA systems, each user has different codewords for communicating different messages. Two main problems are investigated. The first problem concerns whether uniquely detectable overloaded matrices (an injective matrix, i.e. the inputs and outputs are in one-to-one correspondence depending on the input alphabets) exist in the absence of additive noise, and if so, whether there are any practical optimum detectors for such input codewords. The second problem is about finding tight bounds for the sum channel capacity. In response to the first problem, the authors have constructed uniquely detectable matrices for the generalised scheme and the authors have developed practical maximum likelihood detection algorithms for such codes. In response to the second problem, lower bounds and conjectured upper bounds are derived. The results of this study are superior to other standard overloaded CDMA codes since the generalisation can support more users than the previous schemes.

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A new decoding scheme for errorless codes for overloaded CDMA with active user detection

Mousavi

Pad

Delgosha

et al. 2011

2011 18th International Conference on Telecommunications

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Recently, a new class of binary codes for overloaded CDMA systems are proposed that not only has the ability of errorless communication but also suitable for detecting active users. These codes are called COWDA [1]. In [1], a Maximum Likelihood (ML) decoder is proposed for this class of codes. Although the proposed scheme of coding/decoding show impressive performance, the decoder can be improved. In this paper by assuming more practical conditions for the traffic in the system, we suggest an algorithm that increases the performance of the decoder several orders of magnitude (the Bit-Error-Rate (BER) is divided by a factor of about in some ⁄ 's). The algorithm supposes the Poison distribution for the time of activation/deactivation of the users.

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Errorless Codes for Over-Loaded CDMA with Active User Detection

Cited by 12 publications

References 18 publications

A review on synchronous CDMA systems: optimum overloaded codes, channel capacity, and power control

A review on synchronous CDMA systems: optimum overloaded codes, channel capacity, and power control

Generalisation of code division multiple access systems and derivation of new bounds for the sum capacity

A new decoding scheme for errorless codes for overloaded CDMA with active user detection

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