Allocation of Walsh codes and quasi-orthogonal functions in cdma2000 forward link

Tsai, Shang-Chun; Khaleghi, F.; Oh, Seong-Jun; Vanghi, V.

doi:10.1109/vtc.2001.956870

Cited by 16 publications

(5 citation statements)

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“…A direct-sequence code division multiple-access (CDMA) third generation wireless network (see [1]) employs the orthogonal variable spreading factor (OVSF) Walsh codes [2][3][4][5][6][7]. In OVSF systems, the mobile stations (MSs or users) that require higher transmission rate in the current frame of the forward channel (from the base station (BS) to the MS) should use shorter length codes.…”

Section: Introductionmentioning

confidence: 99%

On Walsh code assignment

Tsybakov¹,

Tsybakov

2012

Probl Inf Transm

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The paper considers the problem of orthogonal variable spreading Walsh-code assignments. The aim of the paper is to provide assignments that can avoid both complicated signaling from the BS to the users and blind rate and code detection amongst a great number of possible codes. The assignments considered here use a partition of all users into several pools. Each pool can use its own codes that are different for different pools. Each user has only a few codes assigned to it within the pool. We state the problem as a combinatorial one expressed in terms of a binary n × k matrix M where is the number n of users, and k is the number of Walsh codes in the pool. A solution to the problem is given as a construction of M, which has the assignment property defined in the paper. Two constructions of such M are presented under different conditions on n and k. The first construction is optimal in the sense that it gives the minimal number of Walsh codes l assigned to each user for given n and k. The optimality follows from a proved necessary condition for the existence of M with the assignment property. In addition, we propose a simple algorithm of optimal assignment for the first construction.

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Section: Introductionmentioning

confidence: 99%

On Walsh code assignment

Tsybakov¹,

Tsybakov

2012

Probl Inf Transm

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“…It is well known that the performance of a CDMA system is always interference-limited due to the presence of multiple access interference (MAI) and multipath property is that the capacity of all currently available CDMA-based 2-3G wireless systems [1][2][3][4][5] can offer a capacity equal to merely about one-third to a half of its processing gain, even using so called orthogonal codes (such as Walsh-Hadamard sequences [12], OVSF codes [3][4][5], etc.). As the core technologies of 2G and 3G CDMA systems are very similar, we would like to refer them as to the first generation CDMA (1G-CDMA) technologies, all of which make use of traditional unitary spreading codes for channelization and need a great deal of auxiliary sub-systems, such as the power control and RAKE, etc., to mitigate the problems associated with the spreading codes, such as near-far effect and MI, etc.…”

Section: Introductionmentioning

confidence: 99%

An algebraic approach to generate super‐set of perfect complementary codes for interference‐free CDMA

Chen

Chu

Kuroyanagi

et al. 2006

Wireless Communications

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This paper introduces an algebraic approach to generate the super-set of perfect complementary (PC) codes suitable for new generation CDMA applications, characterized by isotropic multiple access interference (MAI) free and multipath interference (MI) free properties. The code design methodology proposed in this paper takes into account major impairing factors existing in real applications, such as MAI, MI, asynchronous transmissions, and random signs in consecutive symbols, such that a CDMA system using the generated codes can insure a truly interferencefree operation. Two important facts will be revealed by the analysis given in this paper. First, implementation of an interference-free CDMA will never be possible unless using complementary code sets, such as the PC code sets generated in this paper. In other words, all traditional spreading codes working on an one-code-per-user basis are not useful for implementation of an MAI-free and MI-free CDMA system. Second, to enable the interference-free CDMA operation, the flock size of the PC codes should be made equal to the set size of the codes, implying that a PC code set can support as many users as the flock size of the code set. A systematic search has been carried out to generate the super-set of various PC codes with the help of carefully selected seed codes belonging to distinct sub-sets. This paper will also propose an implementation scheme based on multi-carrier CDMA architecture and its performance is compared by simulations with the ones using traditional spreading codes.

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“…A direct consequence from such interference-limited property is that the capacity of all currently available CDMA-based 2-3G wireless systems [1][2][3][4][5] can offer a capacity equal to merely about one-third to a half of its processing gain, even using so called orthogonal codes (such as Walsh-Hadamard sequences [12], OVSF codes [3][4][5], etc.). As the core technologies of 2G and 3G CDMA systems are very similar, we would like to refer them as to the first generation CDMA (1G-CDMA) technologies, all of which make use of traditional unitary spreading codes for channelization and need a great deal of auxiliary sub-systems, such as the power control and RAKE, etc., to mitigate the problems associated with the spreading codes, such as near-far effect and multipath interference, etc.…”

Section: Introductionmentioning

confidence: 99%

“…The study on spreading codes for CDMA applications is a traditional research topic and many candidate codes have been found in the literature, such as Gold codes [6], GMW codes [7], No codes [8], Bent sequences [9], Kasami codes [11], m-sequence [10], Walsh-Hadamard sequence [12] and OVSF codes [3][4][5], to just name a few as examples, all of which are unitary codes, meaning that only one code should be assigned to each user. Some of them have already been integrated into 2-3G mobile cellular standards as an indispensable part of the systems.…”

Section: Introductionmentioning

confidence: 99%

The REAL Approach to Generate Orthogonal Complementary Codes for Next Generation CDMA Systems

Chen

2006

IIS

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This paper introduces a new approach to generate the orthogonal complementary (OC) codes suitable for new generation CDMA applications, characterized by isotropic multiple access interference (MAI) free and multipath interference (MI) free properties. The code design methodology proposed in this paper is named as ''Real Environment Adaptation Linearization'' (REAL) approach and it takes into account major impairing factors existing in real applications, such as MAI, MI, asynchronous transmissions and random signs in consecutive symbols. A CDMA system using the generated codes can ensure a truly interference-free operation. Two important facts will be revealed by the analysis given in this paper. First, implementation of an interference-free CDMA will never be possible unless using complementary code sets, such as the OC code sets. In other words, all traditional spreading codes working on an one-code-per-user basis are not useful for implementation of an MAI-free and MIfree CDMA system. Second, to enable the interference-free CDMA operation, the flock size of the OC codes should be made equal to the set size of the codes, implying that a OC code set can support as many users as the flock size of the code set. A systematic search has been carried out to generate the super-set of various OC codes with the help of carefully selected seed codes belonging to distinct sub-sets. This paper will also propose an implementation scheme based on multi-carrier CDMA architecture and its performance is compared by simulations with the ones using traditional spreading codes.

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Allocation of Walsh codes and quasi-orthogonal functions in cdma2000 forward link

Cited by 16 publications

References 0 publications

On Walsh code assignment

On Walsh code assignment

An algebraic approach to generate super‐set of perfect complementary codes for interference‐free CDMA

The REAL Approach to Generate Orthogonal Complementary Codes for Next Generation CDMA Systems

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