Frequency domain discrete fourier transform spread generalized multi-carrier system and its performance analysis

Abstract

Discrete fourier transform spread generalized multi-carrier (DFT-S-GMC) scheme is a promising candidate for the uplink transmission of the new generation broadband mobile communications due to its lower peak-to-average power ratio and its robustness to the multi-user interference if compared with the conventional orthogonal frequency division multiple (OFDM)-based transmission schemes. However, the time domain DFT-S-GMC system has a relatively high implementation complexity and is difficult to analyze its signal-to-interference plus noise ratio (SINR). In addition, the existing link-to-system mapping methods for OFDM-based systems cannot be utilized in the DFT-S-GMC systems. In this paper, we first propose a novel frequency domain transceiver model for the DFT-S-GMC system, which can effectively simplify the SINR analysis. Then, we derive the closed-form SINR expressions for the link-to-system mapping of DFT-S-GMC system with Alamouti-like space–time block-coding (STBC). It is demonstrated that the theoretical SINR expressions match the simulation results very well.

Introduction

Next generation wireless communication systems are required to provide a much higher throughput to mobile users than the current systems [1], [2]. Therefore, multiple access schemes should offer a higher spectral efficiency at a reasonable complexity. The design of an efficient multiple access and multiplexing scheme is even more challenging on the uplink due to multiple-to-one nature in the uplink transmissions. Moreover, since the power efficiency is very critical for mobile users due to limited transmit power, the peak-to-average power ratio performance becomes one of the most important criteria in selecting the multiple access scheme for the uplink.

Many schemes have been proposed in various international standardization working group meetings, focusing on the selection of the best multiple access scheme for the uplink, such as multi-carrier-WCDMA (MC-WCDMA), MC-time duplex-synchronized CDMA (MC-TD-SCDMA), orthogonal frequency division multiple access (OFDMA) [1], and single carrier frequency division multiple access (SC-FDMA) [3]. Among them, OFDMA is proposed as the dominated multiple access scheme in uplink as well as downlink for FDD by some companies [8]. However, OFDMA has a high peak-to-average power ratio, which will reduce the power efficiency and thus the coverage efficiency in the uplink. Comparably, SC-FDMA, which includes IFDMA (interleaved FDMA) [4], DFT-S-OFDM (DFT-spread OFDM) [5], and DFT-S-GMC (DFT spread generalized multi-carrier) [6], [7], is a more promising candidate for the uplink transmission, since it has lower peak-to-average power ratio than OFDMA.

The DFT-S-GMC transmitter consists of DFT for spectrum spreading, inverse filter-bank transform (IFBT) with specific guard band between neighboring sub-bands for FDMA, and circulating of transmission signal for data block construction [6]. In addition, a specific cyclic prefix (CP) is added before the data block for transmission and the corresponding single carrier frequency domain equalization (SC-FDE) is applied at the receiver to mitigate the impact of channel impairment. As a result, the overall DFT-S-GMC system can be viewed as a filter-bank-based counterpart of the DFT-S-OFDM system. As seen from [6], the DFT-S-GMC system is more robust to multiple access interference than the DFT-S-OFDM system. However, the existed DFT-S-GMC transceiver is implemented by using time-domain filter-bank structure, thus resulting in a high implementation complexity.

Within standardization bodies it is commonly agreed that the link-to-system mapping method should be studied for system level performance evaluation [10]. Moreover, the SINR analysis is essential for link adaptation, such as adaptive modulation and coding (AMC) and channel quality indicator measurement [11], [12], [13]. In recent 3GPP contributions, several link-to-system mapping methods have been proposed for multi-carrier systems by using the concept of effective SINR [14], e.g., exponential effective SINR mapping and mutual information-based effective SINR mapping [14], [15]. However, these effective SINR methods cannot be directly utilized in DFT-S-GMC system which has different time-frequency structure from the existing multiple access systems, e.g., OFDMA and DFT-S-OFDM. In addition, the conventional DFT-S-GMC hardware in the time domain is complex for implementation and SINR analysis.

In this paper, a novel frequency domain transceiver model for DFT-S-GMC is proposed, which reduces the complexity and simplifies the SINR analysis. Different from the conventional time-domain counterparts that require SC-FDE and filter-bank demodulation in the time domain, the proposed model carries out equalization and demodulation in the frequency domain. Moreover, since SC-FDE is employed at the receiver side, an Alamouti-like space–time block-coding (STBC) [9] can be used as a spatial diversity scheme for DFT-S-GMC, which will be referred to as DFT-S-GMC-STBC hereafter. Based on this proposed frequency domain model, a closed-form SINR expression for link-to-system mapping is derived for DFT-S-GMC and DFT-S-GMC-STBC. The simulation results are presented to show the efficiency of the SINR prediction method.

The rest of the paper is organized as follows. A brief description on the time-domain DFT-S-GMC scheme is given in Section 2. Then, we propose the corresponding simplified frequency domain transceiver model as well as the structure of DFT-S-GMC-STBC in Section 3. Furthermore, the derivation of SINR expressions for the proposed frequency domain DFT-S-GMC and DFT-S-GMC-STBC are detailed in Section 4. We present simulation results in Section 5, followed by the conclusion of the paper in Section 6.

Before going to the detail analysis, we list the notations used in this paper as follows. The bold upper (lower) case letters are used to denote matrices (column vectors). ${\mathbf{F}}_N$ represents an $N\times N$ Fast Fourier Transform (FFT) matrix, and ${\mathbf{I}}_N$ stands for an $N\times N$ identity matrix. Notation “$\text{diag}\{·\}$” represents a diagonal matrix with its elements included in the bracket. Superscripts $(·{)}^{*}$, $(·{)}^T$ and $(·{)}^H$ represent the complex conjugate, transpose and conjugated transpose, respectively. $((·){)}_Q$ denotes modulo-Q operation, and $\otimes$ represents the circular convolution operation.