A new OFDM‐CDMA Uplink Concept with <i>M</i>‐ary Orthogonal Modulation

Dekorsy, Armin; Kammeyer, Karl‐Dirk

doi:10.1002/ett.4460100407

Cited by 22 publications

(10 citation statements)

References 19 publications

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“…The interleaved version of vector at the output of is fed to the OFDM-CDMA transmitter. 1 This transmitter consists of the following parts [8]. First, the symbols are scrambled with a user-specific sequence , .…”

Section: System Descriptionmentioning

confidence: 99%

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Low-rate channel coding with complex-valued block codes

Dekorsy¹,

Kuehn

Kammeyer

2003

IEEE Trans. Commun.

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This paper addresses aspects of channel coding in orthogonal frequency-division multiplexing-code-division multiple access (OFDM-CDMA) uplink systems where each user occupies a bandwidth much larger than the information bit rate. This inherent bandwidth expansion allows the application of powerful low-rate codes under the constraint of low decoding costs. Three different coding strategies are considered: the combination of convolutional and repetition codes, the code-spread system consisting of one single very low-rate convolutional code and a serial concatenation of convolutional, Walsh-Hadamard and repetition code. The latter scheme is improved by combining the Walsh-Hadamard codes with an additional -phase-shift keying modulation resulting in complex-valued Walsh-Hadamard codes (CWCs). Analytical performance evaluations will be given for these codes for the first time. The application of CWCs as inner codes in a serial code concatenation is also addressed in this paper. We derive a symbol-by-symbol maximum a posteriori decoding algorithm in the complex signal space in order to enable iterative decoding for the entire code. A comprehensive performance analysis by simulation of all the proposed coding schemes shows that the Walsh-Hadamard-based schemes are the best choice for low-to-medium system load. Note that even for fully loaded OFDM-CDMA systems, the concatenation with an inner complex-valued Walsh-Hadamard code leads to a bit-error rate less than 10 5 for an 0 of about 6 dB. Index Terms-Block codes, code-division multiple access (CDMA), concatenated coding, iterative decoding, orthogonal frequency-division multiplexing (OFDM), turbo codes. where he conducts research projects on UMTS. His current research interests are mainly smart antenna solutions and interference cancellation techniques, as well as radio resource management algorithms for third-generation mobile standards.Volker Kuehn (M'00) was born in Paderborn, Germany, in 1966. He received the M.Sc. degree in electrical and electronics engineering from the University of Paderborn, Paderborn, Germany, in 1993, and the Ph.D. degree in communications engineering in 1998 from the same university.Currently, he is with the Department of Communications Engineering at the University of Bremen, Bremen, Germany. His main fields of interest are error-correcting codes and iterative decoding, as well as CDMA.Karl-Dirk Kammeyer (M'95) received the M.Sc. degree in electrical engineering In 1995, he was appointed Professor for Telecommunications at the University of Bremen, Bremen, Germany. His research interests are digital (adaptive) systems and signal processing in mobile communication systems (GSM, UMTS, multicarrier systems). Since 1989, he has been active in the field of higher order statistics. He holds 14 patent families, and has published two course books as well as 75 technical papers.

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Section: System Descriptionmentioning

confidence: 99%

“…V. Kuehn multicarrier CDMA (MC-CDMA) [5]- [8]. In MC-CDMA, the entire bandwidth is divided into narrow subchannels.…”

Section: Introductionmentioning

confidence: 99%

Low-rate channel coding with complex-valued block codes

Dekorsy¹,

Kuehn

Kammeyer

2003

IEEE Trans. Commun.

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“…In this paper we investigate a multi-carrier CDMA (MC-CDMA) system [5,6] in an uplink situation. As multi-carrier technique we use Orthogonal Frequency Devision Multiplex (OFDM).…”

Section: Introductionmentioning

confidence: 99%

Combating Near Far Effects of Linear MMSE Multiuser Detection in Coded OFDM-CDMA

Feuersänger

Kühn

2002

Multi-Carrier Spread-Spectrum &Amp; Related Topics

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This paper deals with near far effects encountered in MMSE linear multiuser detection and proposes a method to mitigate the transmit-power dependent userspecific bit error rates by introducing an additional postprocessing by a combination of nonlinear parallel and successive interference cancellation. Throughout the paper we consider a quasisynchronous (i.e. asynchronous with coarse synchronization at the receiver) OFDM-CDMA uplink transmission as well as perfectly known channel impulse responses.

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“…In this paper, the uplink of a multicarrier CDMA (MC-CDMA) system [4], [5] is considered using OFDM (Orthogonal Frequency Division Multiplex) to combat the frequency selectivity of the mobile radio channel. Therefore, each subcarrier is affected by flat fading and a one tap equalizer suffices for eliminating channel distortion.…”

Section: Introductionmentioning

confidence: 99%

Combined MMSE-PIC in coded OFDM-CDMA systems

Kühn

GLOBECOM'01. IEEE Global Telecommunications Conference (Cat. No.01CH37270)

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Abstract-In this paper the performance of linear multi-user detection (MUD) and nonlinear parallel interference cancellation (PIC) is analyzed for a quasi synchronous OFDM-CDMA uplink transmission. Specifically, we investigate two different approaches concerning the combination of linear MUD techniques such as the decorrelator and the MMSE approach with nonlinear parallel interference cancellation (PIC). It is pointed out that OFDM-CDMA systems offer great advantages over single carrier systems due to flat fading conditions on each subcarrier leading to much lower implementation costs of MUD techniques.Assuming perfectly known channel impulse responses for each user and a rough synchronization it turns out that the application of the MMSE-MUD filter leads to an insufficient equalization of the channel. Therefore, we propose an approach where the PIC loop works directly on the channel output and the MMSE filter is only active in the initial iteration loop. With this approach, the combination of linear MMSE-MUD and PIC shows excellent performance even for very high system loads.

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A new OFDM‐CDMA Uplink Concept with M‐ary Orthogonal Modulation

Cited by 22 publications

References 19 publications

Low-rate channel coding with complex-valued block codes

Low-rate channel coding with complex-valued block codes

Combating Near Far Effects of Linear MMSE Multiuser Detection in Coded OFDM-CDMA

Combined MMSE-PIC in coded OFDM-CDMA systems

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