Turbo equalization for MIMO SC-FDMA underwater acoustic communications

Long Term Evolution (LTE) has adopted Single Carrier Frequency Division Multiple Access (SCFDMA) technique for uplink and Orthogonal Frequency Division Multiple Access (OFDMA) for downlink. SCFDMA is often called as Discrete Fourier Transform (DFT) spread OFDMA. In this paper, Wavelet based SCFDMA is proposed for analyzing Bit Error Rate (BER) performance. Analysis is carried out using different wavelets and different modulation schemes under AWGN channel. This analysis will show that the reduction in BER takes place by using wavelet transform in SCFDMA. Thus wavelet based SCFDMA provides better BER performance than that of DFT based SCFDMA.

Long Term Evolution (LTE) chose Single Carrier Frequency Division Multiple Access (SC-FDMA) for uplink communications due to lower signal envelope changes in SC-FDMA signal. This enables low peak to average power ratio (PAPR) in SC-FDMA in contrast to Orthogonal Frequency Division Multiple Access (OFDMA). High PAPR cannot be ignored as it reduces energy efficiency due to the requirement of large range linear power amplifiers. As the mobile devices are power restricted, there is a requirement to mitigate PAPR in the uplink SC-FDMA systems, especially for higher order modulations. Companding is an attractive technique to mitigate PAPR without any bandwidth extension. This paper suggests a companding transform using exponential function to mitigate PAPR in SC-FDMA systems. The suggested transform maintains the average signal power contrary to $\mu$ law companding. Simulation results demonstrate that exponential companding technique without any decompanding operation reduces PAPR by a significant value by maintaining the average signal power and BER performance.

The aim of paper is to design SCFDMA system using SFBC and receiver diversity which provides satisfactory performance over fast fading channel environment. The performance evaluation will be checked through MATLAB R2009b simulator. There are comparisons of performance among 1x1 SCFDMA system, 2x1 SCFDMA system using SFBC, 1x2 SCFDMA system using receiver diversity and 2x2 SCFDMA system using SFBC and receiver diversity. We describe design of SCFDMA system using transmitter diversity technique and receiver diversity technique. We have compared the performance of these systems with the conventional SCFDMA system. The main focus is on design of SCFDMA system using SFBC and receiver diversity which enables desired system to combat detrimental effects of fast fading.Keywords3rd Generation Partnership Project Long Term Evolution(3GPP-LTE)Binary Phase Shift Keying(BPSK)Discrete Fourier Transform(DFT)Inverse Discrete Fourier Transform(IDFT)Localized Frequency Division Multiple Access(LFDMA)Maximum Ratio Receiver Combining(MRRC)Multiple Input Multiple Output(MIMO)Orthogonal Frequency Division Multiple Access (OFDMA)Peak to average power ratio(PAPR)Single Carrier Frequency Division Multiple Access(SCFDMA)Space Frequency Block Code(SFBC)

Carrier frequency offset (CFO) and phase noise are challenging problems in single carrier frequency division multiple access (SC-FDMA) system. In this study, the authors have studied single-carrier space frequency block coding (SC-SFBC) to reduce the peak to average power ratio (PAPR) of the multiple-input multiple-output (MIMO) SC-FDMA signal, in which Alamouti SFBC will change the signal spectrum structure, break the single-carrier property and increase PAPR. Also, the authors propose a joint algorithm to suppress the inter-carrier interference (ICI) caused by phase noise and CFO. Conventional methods are to estimate phase noise and CFO in other algorithms, which are pretty difficult and complicated to obtain accurate estimation results. Unlike the conventional works, the novelty of the authors proposed algorithm is that it directly calculates the interference components and then reconstructs the ICI matrix. Thus, it avoids the degrading interactions between phase noise and CFO estimations. The proposed algorithm exploits block-type pilot, which is a common pilot pattern in SC-FDMA communications and is used in other wireless communication standards. Simulation results show that the suppression performance keeps smooth while phase noise and CFO varies, and BER performance degradation can be significantly reduced in 3 dB.

The Long Term Evolution (LTE) standards are generated by the Third Generation Partnership Project (3GPP) for the Fourth Generation (4G) wireless communication systems. The Fourth Generation (4G) wireless communication standards use new physical layer signaling techniques in their physical layer. Single Carrier Frequency Division Multiple Access (SC-FDMA) and Orthogonal Frequency Division Multiple Access (OFDMA) are the two major signaling techniques used in LTE. OFDMA is used in the downlink of the Fourth Generation (4G) wireless communication systems for its high spectral efficiency and SC-FDMA is used in the uplink of the Fourth Generation (4G) wireless communication systems for its high power efficiency. The main objective of this paper is to design and implement the reliable and energy efficient architecture for LTE uplink system using FPGA. IFDMA is the most energy efficient subcarrier mapping scheme of SC-FDMA multiple access scheme. In IFDMA, the data symbols subcarrier mapping is not one to one instead each subcarrier carries a part from each data symbol transmitted at that time instant. The reason for the selection of IFDMA subcarrier mapping along with SC-FDMA multiple access scheme for LTE uplink comes mainly from its advantage to provide a low peak to average power ratio (PAPR) for the transmitted waveform. This results in less power consumption in the mobile station during uplink transmission. The reliability of the system is improved using interleaving process by avoiding packet loss. Convolution codes are less complex and are used to provide error free transmission. The enhancement of energy efficiency is done using the convolution coded IFDMA. The chosen energy efficient architecture must be more power efficient and support high data rates, which is the main requirement for the mobile user. The proposed reliable and energy efficient architecture for LTE uplink system is implemented using Xilinx system generator tool.

Non-Gaussian noise is one of the most common noise models observed in wireless channels. This type of noise has severe impact on wireless systems detection devices. In this paper, the issue of OFDM and SCFDMA PAPR in non-Gaussian noise channel is addressed. Single carrier frequency division multiple access (SCFDMA) is developed form the Orthogonal Frequency Division Multiple access, (OFDM), and is a promising technique for high data rate uplink communications in the cellular systems. SCFDMA has similar throughput performance and essentially the same overall complexity as OFDM. One of the most important advantages of SCFDMA is the peak-to-average power ratio (PAPR), which is lower than that of OFDM. SCFDMA is employed in the uplink multiple access scheme in the Long Term Evolution (LTE) of cellular systems, and identified by the Third Generation Partnership Project (3GPP). In this paper, we show the performance differences of the OFDM and SCFDA system under different noise scenarios. The performance measure is the PAPR.

Orthogonal frequency division multiple access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) are the two major multiple access schemes for 4G wireless communications. In long term evolution (LTE) the downlink multiple access scheme is based on OFDMA and the uplink multiple access scheme is based on SC-FDMA. In this letter, we derive the fundamental performance difference between OFDMA and SC-FDMA, and present the general performance comparison between them. Analytical results show that OFDMA performance upper bounds SC-FDMA in the sense of capacity. The conclusion is further confirmed by numerical results.

A low complexity iterative equalization technique for OFDMA and SC-FDMA uplink systems with Tx-Rx IQ imbalance and CFO under doubly selective channels

Quadrature Orthogonal Frequency Division multiple access (Q-OFDMA) has been renowned as a promising technique which provides a solution to the high PAPR (Peak to average power ratio), sensitivity to carrier frequency offset (CFO) problem and design complexity as introduced by the normal OFDMA systems. Exploiting this Q-OFDMA systems on the Multi-Input Multi-Output (MEMO) architecture, leads to a remarkable improvement in achievable rates. A critical part of this technology is to design the full-rate diversity codes for two transmit and two receive antennas. This paper endeavours to identify key factors and trade-offs issues associated with designing Q-OFDMA systems. We proposed a Space Time Block Codes and spatial multiplexing technique as well as low complexity detection methods for more than 2×2 antennas at the cost of low complexity. This performs well for different fading channel environments and improves the overall system performance such as diversity gain, SNR (Signal to Noise Ratio), Coding gain and BER (bit error rate. The proposed scheme can be easily applied in OFDMA and Single-Carrier Frequency Division Multiple Access (SC-FDMA) by adjusting the parameters of Q-OFDMA.

Single-carrier frequency division multiple access (SC-FDMA) has been adopted as a possible air interface for future wireless networks. It combines most of the advantages of orthogonal frequency division multiple access and the low peak to average power ratio (PAPR) of single carrier (SC) transmission. Existing transmit antenna diversity techniques such as space-time block coding and space-frequency block coding are incompatible either with the system constraints or with the SC nature of SC-FDMA. We propose a novel space-frequency flexible coding scheme compatible with SC-FDMA and we prove its good performance both in terms of PAPR and bit error rate (BER) on frequency selective multiple input multiple output channels.

Similar to the orthogonal frequency division multiple access (OFDMA) system, the single-carrier frequency division multiple access (SC-FDMA) system also suffers from frequency mismatches between the transmitter and the receiver. As a result, in this system, the carrier frequency offsets (CFOs) disrupt the orthogonality between subcarriers and give rise to inter-carrier interference (ICI) and multiple access interference (MAI) among users. The authors present a new minimum mean square error (MMSE) equaliser, which jointly performs equalisation and carrier frequency offsets (CFOs) compensation. The mathematical expression of this equaliser has been derived taking into account the MAI and the channel noise. A low complexity implementation of the proposed equalisation scheme using a banded matrix approximation is presented here. From the obtained simulation results, the proposed equalisation scheme is able to enhance the performance of the SC-FDMA system, even in the presence of estimation errors.

Single carrier-frequency division multiple access (SC-FDMA) utilizes single carrier modulation at the transmitter and frequency domain equalization at the receiver. It has almost similar performance and essentially the same overall structure of an orthogonal frequency division multiple access (OFDMA) system with low peak to average power ratio (PAPR). Recently, the SC-FDMA has drawn great attention as an attractive alternative to OFDMA, in the uplink communications where lower PAPR greatly benefits the mobile terminal in terms of manufacturing cost as well as transmit power efficiency. Such power efficiency can provide considerable performance improvements in future wireless communication networks. This article outlines the basic principles of SC-FDMA systems with different types of sub-carrier mapping schemes. Simulation results demonstrate the performance of different sub-carrier mapping schemes under ideal and pedestrian channel condition.

In recent years, the constant-envelope orthogonal frequency-division multiplexing (CE-OFDM) has been considered as a candidate waveform in broadband satellite systems as it has a 0-dB peak-to-average power ratio (PAPR). However, the carrier frequency offset (CFO) estimation scheme for CE-OFDM broadband satellite systems directly affects system performance. In this paper, we analyze the network architecture and the propagation environment of CE-OFDM broadband satellite systems, and we propose a data-aided CFO estimation strategy based on the frequency domain pilot symbols. The Cramer–Rao bound (CRB) of our CFO estimator is given by mathematical analysis, and the effect of the number of pilot symbols on the estimation performance is analyzed. The pilot symbol-based CFO estimator is composed of a phase demodulator and a discrete Fourier transform (DFT) module, and it can obtain a large estimation range under a small pilot overhead. The simulation results show that the CE-OFDM broadband satellite systems can achieve a good bit error rate (BER) performance by using the proposed strategy to estimate and compensate the CFO.

Single-Carrier Frequency Division Multiple Access (SC-FDMA) has been selected as the uplink transmission scheme in the 3GPP Long Term Evolution standard. SC-FDMA has reduced sensitivity to phase noise and a lower Peak-to-Average Power Ratio (PAPR) compared to Orthogonal Frequency Division Multiple Access. In this paper we propose joint Tomlinson-Harashima Precoding and transmit power allocation for SC-FDMA. We derive the optimum power allocation for SC-FDMA transmission for both Zero-Forcing (ZF) and Minimum Mean-Square Error (MMSE) LE receivers in order to maximize the achievable data rate subject to constant transmit power. Although this improves the system's performance and offers a 1-2 dB improvement over Frequency-Domain Decision Feedback Equalization (FD-DFE), when the proposed transmit power allocation scheme is combined with decision feedback equalization the system incurs a performance degradation due to error propagation. In this paper we propose a joint implementation of the derived power allocation scheme with THP. Here we show that the system's performance is further improved over both FD-LE and FD-DFE when transmit power allocation is applied.

Peak-to-average power ratio (PAPR) is a hot issue in orthogonal frequency division multiplex (OFDM) technology. High PAPR of OFDM system limits its application in underwater acoustic communications. The DFT-s-OFDM technology has been widely used in long term evolution (LTE) and fifth-generation new radio (5G NR) uplink transmission schemes for wireless communications due to its good PAPR performance. However, it is difficult to adapt to time-varying underwater acoustic channels by using time-multiplexed training. We use the DFT-s-OFDM technology of the sideband tone reservation method to suppress the PAPR of the system. At the same time, for the DFT-s-OFDM system, it is impossible to insert data and pilots in a single symbol block at the same time to track the channels. A low-power training sequence is superimposed with symbols, and the training sequence is transmitted over all time. It is used to enhance the tracking channel capability with a small energy overhead and is used to process time-varying channels. Field experiments were carried in Qiandao Lake in 2021, and the results verify the effectiveness of the proposed scheme.