Wei-Chang Chen

Spectrally Precoded OFDM and OFDMA with Cyclic Prefix and Unconstrained Guard Ratios

Spectrally precoded orthogonal frequency-division multiplexing with cyclic prefix (SP-CP-OFDM) and SP-CP-OFDM multiple access (SP-CP-OFDMA) are investigated in this paper. A general constraint on spectral precoding is developed for both SP-CP-OFDM and SP-CP-OFDMA signal formats with unconstrained guard ratios and arbitrary input data statistics to ensure very small power spectral sidelobes decaying asymptotically as f-2J-2, with J a predesigned integer-valued parameter. In the SP-CP-OFDM signaling format, new spectral precoders are devised to meet the constraint. It is shown that the proposed SP-CP-OFDM signals can provide much smaller spectral sidelobes than the previously designed SP-CP-OFDM signals with block partitioning and constrained guard ratios. In the SP-CP-OFDMA signaling format, a general procedure is proposed to facilitate the precoder design for SP-CP-OFDMA signals with arbitrary subcarrier allocation for each user and some spectral precoders are accordingly devised. It is shown that the proposed SP-CP-OFDMA signals can suppress sidelobe powers effectively and thus achieve higher spectral compactness than nonprecoded rectangularly-pulsed CP-OFDMA.

Spectral Precoding for Cyclic-Prefixed OFDMA With Interleaved Subcarrier Allocation

Spectrally precoded orthogonal frequency-division multiple access (OFDMA) using cyclic prefix and interleaved subcarrier allocation (IOFDMA) is a useful rectangularly pulsed OFDMA signaling format for it exploits high spectral compactness and frequency diversity characteristics. In this paper, two new spectral precoders of the largest precoding rate are developed for IOFDMA in order to provide improved spectral compactness and reduce implementation complexity, respectively. Specifically, a new correlative precoder is developed and shown to minimize the dominant spectral coefficient among all correlative precoders of the largest precoding rate and thus can construct IOFDMA signals providing extremely high spectral compactness. Besides, a multiple-stage spectral precoding technique is proposed to construct a low-complexity orthogonally precoded IOFDMA with power spectral sidelobes decaying as f^{-2L-2} for L>1, where L is the number of stages. The corresponding orthogonally precoded IOFDMA signals conveying independent zero-mean data are shown to provide the same power spectrum as existing orthogonally precoded IOFDMA signals of the largest precoding rate while requiring much less complexity.

Spectral Sidelobe Decaying Property of Walsh-Hadamard Code in MC-CDMA Systems

In this letter, a spectral sidelobe-decaying property of the Walsh-Hadamard code employed in multicarrier code-division multiple access (MC-CDMA) systems is exploited. It is shown that the sidelobe-decaying characteristic of the MC-CDMA signal can be properly described by the code index of the underlined Walsh-Hadamard codeword.

Realizable Bandlimited DS-CDMA System Occupying Nyquist Bandwidth

In this letter, the realizable direct-sequence code-division multiple-access (DS-CDMA) system occupying Nyquist bandwidth is developed. Several frequently-adopted spreading codes are examined for realization feasibility in the bandlimited DS-CDMA system. It is shown that Nyquist chip-rate transmission can be practically achieved for the bandlimited DS-CDMA system using frequently-adopted spreading codes at the sacrifice of very little user capacity.

Orthogonal Multirate Modulation

In this letter, the orthogonal multirate (MR) modulation signal is constructed by the orthogonal multiplexing of block-precoded component modulation waveforms occupying the Nyquist bandwidth and shown to outperform the conventional nonorthogonal MR modulation signal in error performance, while giving the same bandwidth efficiency.

An Improved Spectral Precoding Technique for Constant-Envelope OFDM

In this paper, a new spectral precoding scheme is developed for constant-envelope orthogonal frequency-division multiplexing (CE-OFDM) signals to provide very small power spectral sidelobes. It is shown that the proposed spectrally precoded CE-OFDM scheme can provide higher spectral compactness than previously designed spectrally precoded CE-OFDM block scheme and continuous-phase CE-OFDM scheme.

OFDM with Spectral Precoding and Specific-Band Power Minimization

In this paper, the specific-band power minimization precoding technique is incorporated with spectrally precoded OFDM to suppress near spectral sidelobes more efficiently and thus improve the spectral compactness. When the total number of redundant symbols introduced by both spectral precoder and specific-band power minimization precoder is fixed, the proposed OFDM system can find a balance between near sidelobe power suppression capability and sidelobe decaying capability to meet the desired spectral performance by properly allocating redundancy to the two precoders.