Single-input Single-output Orthogonal Frequency Division Multiplexing Research Articles

MIMO-OFDM NB-PLC Designs in Underground Medium-Voltage Networks

In this paper, we investigate the application of multi-input multi-output (MIMO) orthogonal frequency-division multiplexing (OFDM) to narrowband powerline communications (NB-PLC) over medium-voltage (MV) underground (UG) networks. We study different MIMO transmission scenarios with different injection configurations utilizing both the cable conductor and sheath phases. Multiconductor transmission line theory is used to accurately characterize the UG MV NB-PLC channel transfer function and evaluate the spatial correlation between the different conductor phases. The achievable data rates are evaluated for all configurations at different line lengths after optimizing the transmit energy allocation across the different spatial information streams subject to a transmit power spectral density constraint. The achievable data rates for MIMO configurations are shown to be significantly higher (by up to three times higher) compared to single-input single-output OFDM transmission. Moreover, we investigate the effects of practical design constraints, such as cyclic prefix length and bit caps, on the achievable data rates. Finally, we show how to reduce the complexity of both the transmitter and receiver implementations while minimizing the data rate loss.

Secure resource allocation for the SISO‐OFDM wiretap channel

The broadcast nature of communication systems opens the possibility for attackers to eavesdrop the data and compromise data confidentiality. This study takes the information theoretic security at the physical layer of single-input single-output orthogonal frequency division multiplexing (SISO-OFDM) wiretap system into account, in which, different signal-to-noise ratio (SNR) values on the legitimate and eavesdropper's receivers are assumed. The optimisation problem for secure resource allocation is formulated. Then, the secrecy rate of the system is used as the objective function for resource allocation. Finally, a power allocation strategy is obtained. The upper bound of the secrecy capacity of the single-user system is proposed as a linear function of legitimate receiver's SNR (dB), based on the mentioned strategy. In addition, an iterative power allocation algorithm is proposed for two-user SISO-OFDM wiretap channel. Results showed that the proposed algorithm is fast and converges to the optimal value in the second iteration. The upper bound linear model is valid in a two-user case when there is a relatively large difference between Bob and Eve SNRs.

Bandwidth efficient transceiver design for differentially encoded OFDM system

In this paper, we present a bandwidth efficient non-coherent transceiver design for single input single output orthogonal frequency division multiplexing (SISO-OFDM) modulation with differential encoding. Under fast channel fading or in low signal-to-noise ratio (SNR) regime, pilot assisted channel estimation is not feasible. In such channel conditions, conventional non-coherent detection methods are not reliable resulting in poor throughput. We propose a frequency-spread time-encoded (FSTE) method for OFDM modulation, which exploits multipath diversity and achieves target energy-per-bit to noise spectral density $${E_b}/{N_0}$$Eb/N0 in low SNR regime by spreading differentially encoded information symbols along OFDM sub-carriers. We investigate the impact of spreading on bit-error rate (BER) and throughput under relative mobility and multipath fading scenarios. In order to maximize the throughput of the proposed method, we also optimize spreading factor and modulation order. The simulation results demonstrate significant BER and throughput performance gain as compared to prevailing differential encoding methods.

Optimized MIMO-OFDM design for narrowband-PLC applications in medium-voltage smart distribution grids

In this paper, a multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system is proposed for narrowband power-line communication (NB-PLC) applications in medium-voltage (MV) networks. Multi-conductor transmission line theory is used for accurate MV NB-PLC channel characterization and evaluation of the spatial correlation between the phase conductors. By optimizing the indices of the active OFDM sub-channels, the bit allocation across them, and the transmit power allocation across the spatial beams, the proposed MIMO-OFDM design can achieve significant data rate gains over single-input single-output OFDM transmission. The achievable MIMO-OFDM data rates are evaluated for an MV overhead network with different lengths, coupler impedances and branches, showing that the proposed MIMO-OFDM design is an efficient implementation of NB-PLC technology in MV smart distribution grids.

Performance Analysis of Adaptive Clipping Technique for Reduction of PAPR in Alamouti Coded MIMO-OFDM Systems

Like single-input single-output orthogonal frequency division multiplexing (SISO-OFDM), multi-input multi-output (MIMO) OFDM systems also suffer from the problem of high peak to average power ratio (PAPR). To account for this issue, amplitude clipping is one of the simplest techniques employed to reduce PAPR. However, it leads to additional distortion. In this paper, adaptive clipping technique is proposed to reduce PAPR of Alamouti coded MIMO-OFDM systems. In this scheme, successive peaks are clipped according to an adaptive algorithm. Simulation results reveal that the proposed clipping technique provides effective reduction in PAPR and better bit error rate (BER) performance. BER performance and PAPR reduction capability of the proposed algorithm in MIMO-OFDM systems are also compared with SISO-OFDM systems. Power spectral density (PSD) for conventionally clipped, adaptively clipped, and normal SISO-OFDM systems is analyzed and plotted. It can be revealed from the PSD plot that the spectral spreading due to the proposed scheme is less than the conventional clipping scheme.

Analysis of Optimal Sounding Signal Design in OFDM Systems

We focus on a sounding signal design for single-input single-output orthogonal frequency division multiplexing (SISO-OFDM) systems. We show that the frequency spectrum of an optimum sounding signal has a constant magnitude across the frequency band for the cases with or without Doppler effects. Simulation results show that the designed optimum sounding signal outperforms random sounding signals and that the performance of a maximal-length shift register sequence is indistinguishable from that of the optimum sounding signal.

Performance evaluation of variable transmission rate OFDM systems via network source coding

Studies related to the network source coding have addressed rate-distortion analysis in both noiseless and noisy channels. However, to the best of authors’ knowledge, no prior work has studied network source coding in the context of orthogonal frequency division multiplexing (OFDM) systems. In addition, the system performance using network source coding schemes also remains unknown. In this article, we first propose two variable transmission rate (VTR) OFDM systems by utilizing network source coding schemes, and then evaluate the system performance of these two proposed VTR-OFDM systems. For the proposed VTR single-input single-output OFDM system, we employ the concept of a network with intermediate nodes to develop a 3-stage encoder/decoder, and the proposed encoder provides three different coding rates from 0.5 to 0.8. As for the proposed VTR multi-band OFDM system, two correlated sources are simultaneously transmitted using the multiterminal source coding schemes, and two sources are encoded by different coding rates from 0.25 to 0.5. Finally, compared with the traditional uncoded OFDM system, the proposed VTR-OFDM systems have at least 1 to 4 dB gain in signal-to-noise ratio to achieve the same symbol error rate in the additive white Gaussian noise channel.

Semiblind frequency-domain timing synchronization and channel estimation for OFDM systems

In this article, we propose unit vectors in the high dimensional Cartesian coordinate system as the preamble, and then propose a semiblind timing synchronization and channel estimation scheme for orthogonal frequency division multiplexing (OFDM) systems. Due to the lack of useful information in the time-domain, a frequency-domain timing synchronization algorithm is proposed. The proposed semiblind approach consists of three stages. In the first stage, a coarse timing offset related to the delayed timing of the path with the maximum gain in multipath fading channels is obtained. Then, a fine time adjustment algorithm is performed to find the actual delayed timing in channels. Finally, the channel response in the frequency-domain is obtained based on the final timing estimate. Although the required number of additions in the proposed algorithm is higher than those in conventional methods, the simulation results show that the proposed approach has excellent performance of timing synchronization in several channel models at signal-to-noise ratio (SNR) smaller than 6 dB. In addition, for a low-density parity-check coded single-input single-output OFDM system, our proposed approach has better bit-error-rate performance than conventional approaches for SNR varying from 3 to 8 dB.

An Approximation Method for Evaluating SIMO-OFDM MRC System in Multipath Environment Where Delay Profile Exceeds the Guard Interval

Equivalent Transmission Path (ETP) model-based BER map method was proved to be used in fast estimating Bit Error Rate (BER) of Single-Input Single-Output Orthogonal Frequency Division Multiplexing (SISO-OFDM) system, where the delay spreading exceeds the guard interval. In this paper, we propose a method for evaluating transmission characteristics of Single-Input Multiple-Output Orthogonal Frequency Division Multiplexing (SIMO-OFDM) system with application to maximum ratio combining diversity at the reception. The simulation results show that the proposed approximation method is able to be used in estimating trasmission characteristics with high accuracy not only for SISO-OFDM system but also for SIMO-OFDM system.

MIMO-OFDM Channel Estimation Using Pilot Carries

A multiple-input multiple-output (MIMO) communication system combined with the orthogonal frequency division multiplexing (OFDM) modulation technique can achieve reliable high data rate transmission over broadband wireless channels. Channel state information for both single-input single-output (SISO) and MIMO systems based on pilot aided arrangement is investigated in this paper. The estimation of channel at pilot frequencies with conventional Least Square (LS) and Minimum Mean Square (MMSE) estimation algorithms is carried out through Matlab simulation. The performance of MIMO OFDM and SISO OFDM are evaluated on the basis of Bit Error Rate (BER) and Mean Square Error (MSE) level. Further enhancement of performance can be achieved through maximum diversity Space Time Block Coding (STBC) and Maximum Likelihood Detection at transmission and reception ends respectively. MMSE estimation has been shown to perform much better than LS but is more complex than LS for the MIMO system using pilot carriers.

Blind Channel Estimation for MIMO-OFDM Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> By combining multiple-input multiple-output (MIMO) communication with the orthogonal frequency division multiplexing (OFDM) modulation scheme, MIMO-OFDM systems can achieve high data rates over broadband wireless channels. In this paper, to provide a bandwidth-efficient solution for MIMO-OFDM channel estimation, we establish conditions for channel identifiability and present a blind channel estimation technique based on a subspace approach. The proposed method unifies and generalizes the existing subspace-based methods for blind channel estimation in single-input single-output OFDM systems to blind channel estimation for two different MIMO-OFDM systems distinguished according to the number of transmit and receive antennas. In particular, the proposed method obtains accurate channel estimation and fast convergence with insensitivity to overestimates of the true channel order. If virtual carriers (VCs) are available, the proposed method can work with no or insufficient cyclic prefix (CP), thereby potentially increasing channel utilization. Furthermore, it is shown under specific system conditions that the proposed method can be applied to MIMO-OFDM systems without CPs, regardless of the presence of VCs, and obtains an accurate channel estimate with a small number of OFDM symbols. Thus, this method improves the transmission bandwidth efficiency. Simulation results illustrate the mean-square error performance of the proposed method via numerical experiments. </para>