A Novel Architecture of Single-Carrier Block Transmission DS-CDMA

Abstract

Single-carrier (SC) block transmission [1][2]is an efficient scheme in multipath channels. With frequency-domain equalization, SC block transmission avoids complex time-domain equalization. There are also several systems proposed that combine SC-FDE with code-division multiple access (CDMA). However, unlike conventional direct-sequence (DS) CDMA, the present CDMA systems with FDE may be not suitable for asynchronous users, for lack of a signal model that could suitably express the despread signal in frequency domain.In this paper, we propose a novel architecture of SC block transmission DS-CDMA that can be applied for asynchronous users. A new signal model is derived that represents spreading, channel effect, and despreading as a series of circular convolutions. This signal model helps in deriving a new frequency-domain minimum mean-square error (MMSE) equalization algorithm for SC block transmission CDMA. Based on the proposed signal model, we also propose a simple channel estimation algorithm. Our architecture and signal model can be applied for further development of multi-user detection algorithms.

Adaptive Frequency-Domain Group-Based Shrinkage Estimators for UWB Systems

“…where the spreading matrix S k ∈ C M×M , M = N × N c , is a circulant Toeplitz matrix and its first column consists of the spreading codes and zero-padding [26]. The equivalent Mdimensional expanded data vector is…”

Single-Carrier Frequency Domain Equalization and Wireless Applications

“…For the conventional signal model of SC block transmission, if the receiver despread the received signal before FFT, the TD circular convolution may be distort and there is no clear signal model proposed for the FFT of the despread signal. Literature [18] proposed a new architecture and derived a FDE algorithm for SC block transmission DS-CDMA that is suitable for asynchronous users. The transmitter is roughly the same as the conventional block transmission systems.…”

Adaptive Detector for SC-FDE in Multiuser DS-UWB Systems Based on Structured Channel Estimation with Conjugate Gradient Algorithm

“…However, if we go directly with the signal model used for the SCE scheme, the resulting adaptive filter for DA schemes will be in an M -by-N matrix form which means very high complexity. Thanks to the new signal model proposed in [10], we can explore the structure of the MMSE detector in SC-FDE systems more efficiently. In this work, we adopt this new signal model and extend it to simplify the design of the adaptive filters.…”

“…In [9], a lowcomplexity channel estimation algorithm is proposed for single user communication. A new SC block transmission structure was proposed in [10], where a novel despreading scheme was employed in the frequency domain before channel estimation and equalization. In [11]- [13], frequency-domain linear multiuser detection and channel estimation was performed and a linear MMSE equalization scheme was described.…”

“…Prior work on adaptive frequency domain algorithms is limited to single-user systems [27] and do not exploit the structure created by multiuser UWB systems with a cyclic prefix. In order to obtain a simplified filter design, we adopt the signal expression described in [10] and extend it into an adaptive parameter estimation implementation. After obtaining the matrix form of the MMSE design of such a filter, we convert it into a vector form and develop LMS, RLS and CG algorithms in the frequency domain that enables the linear suppression of ISI and MAI.…”