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This paper presents a new design of spread spectrum signals with the minimally sufficient dimension from the view point of frequency diversity. Letting the signature signal duration and the bandwidth be denoted by *T* and *B*, respectively, we can nominally represent a signature signal of either Direct Sequence (DS) or MultiCarrier (MC) spread spectrum system as the sum of *N*=*BT* sinusoidal signal units with their frequencies separated by 1/*T* or its multiples. In our design,assuming the maximum expected channel delay spread σ_{d} « *T* as usual, one signature signal viewed in the frequency domain is made up of the minimum number *K*_{d}*B* of sinusoidal signal units which are arranged so as there is placed at least one unit in coherence bandwidth 1/(2πσ_{d}) in which the fading channel transfer function has strong correlation. Although the signature signal does not make use of all the units in the given frequency domain as in the ordinary spread spectrum systems, but uses only skipped units, it can be shown that almost the same frequency diversity effect is attained. And it is also shown that the immunity to the external interfering signals is by no means inferior. If every *L*=*N*/*K**T*/(2πσ_{d}) consecutive sinusoidal signal units are assigned to the *K* signal units of a signature signal, *L* different signature signals are simultaneously available mutually orthogonal when the synchronous demodulation is performed in the same *T* period. We call each of the orthogonal sinusoidal signal sets a Frequency Devision (FD) signal set. Now, CDMA can be independently realized on each of the *L* FD signal sets provided the operation is synchronous or quasi-synchronous with respect to the symbol demodulation (or signature) period. Partitioning the simultaneous users among the FD sets, it is possible to decrease the number of CDMA users to be processed, retaining the total number of simultaneous users. Owing to this effect, the multiple access performance for the FD/CDMA system is shown to be superior to that of the ordinary DS or MC/CDMA system, assuming matched filter reception based on the complete estimation of the channel characteristics for the both cases. The decrease of the number of CDMA users per FD set makes it practical for the receiver to employ multiple access interference cancellation and even the maximum likelihood detection. Curiously, any FD signal set can be represented in the time domain as *L* repetition of a sequence with its period equal to *K* in the number of 1/*B* duration time chips.

- Publication
- IEICE TRANSACTIONS on Fundamentals Vol.E83-A No.11 pp.2093-2101

- Publication Date
- 2000/11/25

- Publicized

- Online ISSN

- DOI

- Type of Manuscript
- Special Section PAPER (Special Section on Spread Spectrum Techniques and Applications)

- Category

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Masahiro FUJII, Makoto ITAMI, Kohji ITOH, "Performance of Frequency-Division CDMA Systems for Channels with Frequency Selective Fading" in IEICE TRANSACTIONS on Fundamentals,
vol. E83-A, no. 11, pp. 2093-2101, November 2000, doi: .

Abstract: This paper presents a new design of spread spectrum signals with the minimally sufficient dimension from the view point of frequency diversity. Letting the signature signal duration and the bandwidth be denoted by *T* and *B*, respectively, we can nominally represent a signature signal of either Direct Sequence (DS) or MultiCarrier (MC) spread spectrum system as the sum of *N*=*BT* sinusoidal signal units with their frequencies separated by 1/*T* or its multiples. In our design,assuming the maximum expected channel delay spread σ_{d} « *T* as usual, one signature signal viewed in the frequency domain is made up of the minimum number *K*_{d}*B* of sinusoidal signal units which are arranged so as there is placed at least one unit in coherence bandwidth 1/(2πσ_{d}) in which the fading channel transfer function has strong correlation. Although the signature signal does not make use of all the units in the given frequency domain as in the ordinary spread spectrum systems, but uses only skipped units, it can be shown that almost the same frequency diversity effect is attained. And it is also shown that the immunity to the external interfering signals is by no means inferior. If every *L*=*N*/*K**T*/(2πσ_{d}) consecutive sinusoidal signal units are assigned to the *K* signal units of a signature signal, *L* different signature signals are simultaneously available mutually orthogonal when the synchronous demodulation is performed in the same *T* period. We call each of the orthogonal sinusoidal signal sets a Frequency Devision (FD) signal set. Now, CDMA can be independently realized on each of the *L* FD signal sets provided the operation is synchronous or quasi-synchronous with respect to the symbol demodulation (or signature) period. Partitioning the simultaneous users among the FD sets, it is possible to decrease the number of CDMA users to be processed, retaining the total number of simultaneous users. Owing to this effect, the multiple access performance for the FD/CDMA system is shown to be superior to that of the ordinary DS or MC/CDMA system, assuming matched filter reception based on the complete estimation of the channel characteristics for the both cases. The decrease of the number of CDMA users per FD set makes it practical for the receiver to employ multiple access interference cancellation and even the maximum likelihood detection. Curiously, any FD signal set can be represented in the time domain as *L* repetition of a sequence with its period equal to *K* in the number of 1/*B* duration time chips.

URL: https://global.ieice.org/en_transactions/fundamentals/10.1587/e83-a_11_2093/_p

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@ARTICLE{e83-a_11_2093,

author={Masahiro FUJII, Makoto ITAMI, Kohji ITOH, },

journal={IEICE TRANSACTIONS on Fundamentals},

title={Performance of Frequency-Division CDMA Systems for Channels with Frequency Selective Fading},

year={2000},

volume={E83-A},

number={11},

pages={2093-2101},

abstract={This paper presents a new design of spread spectrum signals with the minimally sufficient dimension from the view point of frequency diversity. Letting the signature signal duration and the bandwidth be denoted by *T* and *B*, respectively, we can nominally represent a signature signal of either Direct Sequence (DS) or MultiCarrier (MC) spread spectrum system as the sum of *N*=*BT* sinusoidal signal units with their frequencies separated by 1/*T* or its multiples. In our design,assuming the maximum expected channel delay spread σ_{d} « *T* as usual, one signature signal viewed in the frequency domain is made up of the minimum number *K*_{d}*B* of sinusoidal signal units which are arranged so as there is placed at least one unit in coherence bandwidth 1/(2πσ_{d}) in which the fading channel transfer function has strong correlation. Although the signature signal does not make use of all the units in the given frequency domain as in the ordinary spread spectrum systems, but uses only skipped units, it can be shown that almost the same frequency diversity effect is attained. And it is also shown that the immunity to the external interfering signals is by no means inferior. If every *L*=*N*/*K**T*/(2πσ_{d}) consecutive sinusoidal signal units are assigned to the *K* signal units of a signature signal, *L* different signature signals are simultaneously available mutually orthogonal when the synchronous demodulation is performed in the same *T* period. We call each of the orthogonal sinusoidal signal sets a Frequency Devision (FD) signal set. Now, CDMA can be independently realized on each of the *L* FD signal sets provided the operation is synchronous or quasi-synchronous with respect to the symbol demodulation (or signature) period. Partitioning the simultaneous users among the FD sets, it is possible to decrease the number of CDMA users to be processed, retaining the total number of simultaneous users. Owing to this effect, the multiple access performance for the FD/CDMA system is shown to be superior to that of the ordinary DS or MC/CDMA system, assuming matched filter reception based on the complete estimation of the channel characteristics for the both cases. The decrease of the number of CDMA users per FD set makes it practical for the receiver to employ multiple access interference cancellation and even the maximum likelihood detection. Curiously, any FD signal set can be represented in the time domain as *L* repetition of a sequence with its period equal to *K* in the number of 1/*B* duration time chips.

keywords={},

doi={},

ISSN={},

month={November},}

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TY - JOUR

TI - Performance of Frequency-Division CDMA Systems for Channels with Frequency Selective Fading

T2 - IEICE TRANSACTIONS on Fundamentals

SP - 2093

EP - 2101

AU - Masahiro FUJII

AU - Makoto ITAMI

AU - Kohji ITOH

PY - 2000

DO -

JO - IEICE TRANSACTIONS on Fundamentals

SN -

VL - E83-A

IS - 11

JA - IEICE TRANSACTIONS on Fundamentals

Y1 - November 2000

AB - This paper presents a new design of spread spectrum signals with the minimally sufficient dimension from the view point of frequency diversity. Letting the signature signal duration and the bandwidth be denoted by *T* and *B*, respectively, we can nominally represent a signature signal of either Direct Sequence (DS) or MultiCarrier (MC) spread spectrum system as the sum of *N*=*BT* sinusoidal signal units with their frequencies separated by 1/*T* or its multiples. In our design,assuming the maximum expected channel delay spread σ_{d} « *T* as usual, one signature signal viewed in the frequency domain is made up of the minimum number *K*_{d}*B* of sinusoidal signal units which are arranged so as there is placed at least one unit in coherence bandwidth 1/(2πσ_{d}) in which the fading channel transfer function has strong correlation. Although the signature signal does not make use of all the units in the given frequency domain as in the ordinary spread spectrum systems, but uses only skipped units, it can be shown that almost the same frequency diversity effect is attained. And it is also shown that the immunity to the external interfering signals is by no means inferior. If every *L*=*N*/*K**T*/(2πσ_{d}) consecutive sinusoidal signal units are assigned to the *K* signal units of a signature signal, *L* different signature signals are simultaneously available mutually orthogonal when the synchronous demodulation is performed in the same *T* period. We call each of the orthogonal sinusoidal signal sets a Frequency Devision (FD) signal set. Now, CDMA can be independently realized on each of the *L* FD signal sets provided the operation is synchronous or quasi-synchronous with respect to the symbol demodulation (or signature) period. Partitioning the simultaneous users among the FD sets, it is possible to decrease the number of CDMA users to be processed, retaining the total number of simultaneous users. Owing to this effect, the multiple access performance for the FD/CDMA system is shown to be superior to that of the ordinary DS or MC/CDMA system, assuming matched filter reception based on the complete estimation of the channel characteristics for the both cases. The decrease of the number of CDMA users per FD set makes it practical for the receiver to employ multiple access interference cancellation and even the maximum likelihood detection. Curiously, any FD signal set can be represented in the time domain as *L* repetition of a sequence with its period equal to *K* in the number of 1/*B* duration time chips.

ER -