Complex Orthogonal Variable Spreading Factor Codes Based on Polyphase Sequences

Tomoko K. MATSUSHIMA; Shoichiro YAMASAKI

doi:10.1587/transfun.2019DMP0007

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Complex Orthogonal Variable Spreading Factor Codes Based on Polyphase Sequences

Tomoko K. MATSUSHIMA, Shoichiro YAMASAKI

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Summary :

The direct sequence code division multiple access (DS-CDMA) technique is widely used in various communication systems. When adopting orthogonal variable spreading factor (OVSF) codes, DS-CDMA is particularly suitable for supporting multi-user/multi-rate data transmission services. A useful property of OVSF codes is that no two code sequences assigned to different users will ever interfere with each other, even if their spreading factors are different. Conventional OVSF codes are constructed based on binary orthogonal codes, called Walsh codes, and OVSF code sequences are binary sequences. In this paper, we propose new OVSF codes that are constructed based on polyphase orthogonal codes and consist of complex sequences in which each symbol is represented as a complex number. Construction of the proposed codes is based on a tree structure that is similar to conventional OVSF codes. Since the proposed codes are generalized versions of conventional OVSF codes, any conventional OVSF code can be presented as a special case of the proposed codes. Herein, we show the method used to construct the proposed OVSF codes, after which the orthogonality of the codes, including conventional OVSF codes, is investigated. Among the advantages of our proposed OVSF codes is that the spreading factor can be designed more flexibly in each layer than is possible with conventional OVSF codes. Furthermore, combination of the proposed code and a non-binary phase modulation is well suited to DS-CDMA systems where the level fluctuation of signal envelope is required to be suppressed.

Publication: IEICE TRANSACTIONS on Fundamentals Vol.E103-A No.10 pp.1218-1226

Publication Date: 2020/10/01

Publicized

Online ISSN: 1745-1337

DOI: 10.1587/transfun.2019DMP0007

Type of Manuscript: Special Section PAPER (Special Section on Discrete Mathematics and Its Applications)

Category: communication

Authors

Tomoko K. MATSUSHIMA
Polytechnic University
Shoichiro YAMASAKI
Polytechnic University

Keyword

DS-CDMA, OVSF codes, complex sequences, polyphase orthogonal codes

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Tomoko K. MATSUSHIMA, Shoichiro YAMASAKI, "Complex Orthogonal Variable Spreading Factor Codes Based on Polyphase Sequences" in IEICE TRANSACTIONS on Fundamentals, vol. E103-A, no. 10, pp. 1218-1226, October 2020, doi: 10.1587/transfun.2019DMP0007.
Abstract: The direct sequence code division multiple access (DS-CDMA) technique is widely used in various communication systems. When adopting orthogonal variable spreading factor (OVSF) codes, DS-CDMA is particularly suitable for supporting multi-user/multi-rate data transmission services. A useful property of OVSF codes is that no two code sequences assigned to different users will ever interfere with each other, even if their spreading factors are different. Conventional OVSF codes are constructed based on binary orthogonal codes, called Walsh codes, and OVSF code sequences are binary sequences. In this paper, we propose new OVSF codes that are constructed based on polyphase orthogonal codes and consist of complex sequences in which each symbol is represented as a complex number. Construction of the proposed codes is based on a tree structure that is similar to conventional OVSF codes. Since the proposed codes are generalized versions of conventional OVSF codes, any conventional OVSF code can be presented as a special case of the proposed codes. Herein, we show the method used to construct the proposed OVSF codes, after which the orthogonality of the codes, including conventional OVSF codes, is investigated. Among the advantages of our proposed OVSF codes is that the spreading factor can be designed more flexibly in each layer than is possible with conventional OVSF codes. Furthermore, combination of the proposed code and a non-binary phase modulation is well suited to DS-CDMA systems where the level fluctuation of signal envelope is required to be suppressed.
URL: https://global.ieice.org/en_transactions/fundamentals/10.1587/transfun.2019DMP0007/_p

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@ARTICLE{e103-a_10_1218,
author={Tomoko K. MATSUSHIMA, Shoichiro YAMASAKI, },
journal={IEICE TRANSACTIONS on Fundamentals},
title={Complex Orthogonal Variable Spreading Factor Codes Based on Polyphase Sequences},
year={2020},
volume={E103-A},
number={10},
pages={1218-1226},
abstract={The direct sequence code division multiple access (DS-CDMA) technique is widely used in various communication systems. When adopting orthogonal variable spreading factor (OVSF) codes, DS-CDMA is particularly suitable for supporting multi-user/multi-rate data transmission services. A useful property of OVSF codes is that no two code sequences assigned to different users will ever interfere with each other, even if their spreading factors are different. Conventional OVSF codes are constructed based on binary orthogonal codes, called Walsh codes, and OVSF code sequences are binary sequences. In this paper, we propose new OVSF codes that are constructed based on polyphase orthogonal codes and consist of complex sequences in which each symbol is represented as a complex number. Construction of the proposed codes is based on a tree structure that is similar to conventional OVSF codes. Since the proposed codes are generalized versions of conventional OVSF codes, any conventional OVSF code can be presented as a special case of the proposed codes. Herein, we show the method used to construct the proposed OVSF codes, after which the orthogonality of the codes, including conventional OVSF codes, is investigated. Among the advantages of our proposed OVSF codes is that the spreading factor can be designed more flexibly in each layer than is possible with conventional OVSF codes. Furthermore, combination of the proposed code and a non-binary phase modulation is well suited to DS-CDMA systems where the level fluctuation of signal envelope is required to be suppressed.},
keywords={},
doi={10.1587/transfun.2019DMP0007},
ISSN={1745-1337},
month={October},}

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TY - JOUR
TI - Complex Orthogonal Variable Spreading Factor Codes Based on Polyphase Sequences
T2 - IEICE TRANSACTIONS on Fundamentals
SP - 1218
EP - 1226
AU - Tomoko K. MATSUSHIMA
AU - Shoichiro YAMASAKI
PY - 2020
DO - 10.1587/transfun.2019DMP0007
JO - IEICE TRANSACTIONS on Fundamentals
SN - 1745-1337
VL - E103-A
IS - 10
JA - IEICE TRANSACTIONS on Fundamentals
Y1 - October 2020
AB - The direct sequence code division multiple access (DS-CDMA) technique is widely used in various communication systems. When adopting orthogonal variable spreading factor (OVSF) codes, DS-CDMA is particularly suitable for supporting multi-user/multi-rate data transmission services. A useful property of OVSF codes is that no two code sequences assigned to different users will ever interfere with each other, even if their spreading factors are different. Conventional OVSF codes are constructed based on binary orthogonal codes, called Walsh codes, and OVSF code sequences are binary sequences. In this paper, we propose new OVSF codes that are constructed based on polyphase orthogonal codes and consist of complex sequences in which each symbol is represented as a complex number. Construction of the proposed codes is based on a tree structure that is similar to conventional OVSF codes. Since the proposed codes are generalized versions of conventional OVSF codes, any conventional OVSF code can be presented as a special case of the proposed codes. Herein, we show the method used to construct the proposed OVSF codes, after which the orthogonality of the codes, including conventional OVSF codes, is investigated. Among the advantages of our proposed OVSF codes is that the spreading factor can be designed more flexibly in each layer than is possible with conventional OVSF codes. Furthermore, combination of the proposed code and a non-binary phase modulation is well suited to DS-CDMA systems where the level fluctuation of signal envelope is required to be suppressed.
ER -