Inter-carrier interference cancelation for Alamouti coded single frequency network

We have been conducting research on a transmission system using ultra-multilevel orthogonal frequency division multiplexing (OFDM) technology and dual-polarized multiple-input multiple-output (MIMO) technology based on the digital terrestrial broadcasting signal format, ISDB-T. As a technology of a single frequency network (SFN) for the next-generation of digital broadcasting, we studied a space time coding (STC) - space division multiplexing (SDM) transmission in which STC and dual-polarized MIMO-OFDM are used together. In this paper, we studied a scattered pilot (SP) scheme for the channel estimation in STC-SDM transmission and the coding schemes. Computer simulations confirmed the advantages of STC-SDM transmission compared with the conventional SFN scheme in environments in which the desired to undesired signal ratio (D/U) is low. We also show the results that STC-SDM transmission with space time block coding (STBC) and space frequency block coding (SFBC) has the same characteristics as transmissions under fixed reception conditions.

Multi-carrier code division multiple access (MC-CDMA)has been considered as a strong candidate for next generation wireless communication system due to its excellent performance in multi-path fading channel and simple receiver structure. However, like all the multi-carrier transmission technologies such as OFDM, the inter-carrier interference (ICI) produced by the frequency offset between the transmitter and receiver local oscillators or by Doppler shift due to high mobility causes significant BER (bit error rate) performance degradation in MC-CDMA system. Many ICI cancellation methods such as windowing and frequency domain coding have been proposed in the literature to cancel ICI and improve the BER performance for multi-carrier transmission technologies. However, existing ICI cancellation methods do not cancel ICI entirely and the BER performance after ICI cancellation is still much worse than the BER performance of original system without ICI. Moreover, popular ICI cancellation methods like ICI self-cancellation reduce ICI at the price of lowering the transmission rate and reducing the bandwidth efficiency. Other frequency-domain coding methods do not reduce the data rate, but produce less reduction in ICI as well. In this paper, we propose a novel ICI cancellation scheme that can eliminate the ICI entirely and offer a MC-CDMA mobile system with the same BER performance of a MC-CDMA system without ICI. More importantly, the proposed ICI cancellation scheme (namely Total ICI Cancellation) does not lower the transmission rate or reduce the bandwidth efficiency. Specifically, by exploiting frequency offset quantization, the proposed scheme takes advantage of the orthogonality of the ICI matrix and offers perfect ICI cancellation and significant BER improvement at linearly growing cost. Simulation results in AWGN channel and multi-path fading channel confirm the excellent performance of the proposed Total ICI Cancellation scheme in the presence of frequency offset or time variations in the channel, outperforming existing ICI cancellation methods.

The standard Alamouti space-frequency block code (SFBC) suffers from performance degradation when used over highly frequency-selective channels because the channel frequency response is not necessarily flat over the Alamouti block. In this paper, we present an enhanced Alamouti space frequency block decoding scheme for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems over highly frequency selective channels. The enhanced Alamouti scheme uses the channel frequency variations in consecutive subcarriers to adapt the Alamouti decoder. Simulation results of DVB-T2 system confirm that the proposed method has substantial performance improvement in terms of bit error rate when compared to standard Alamouti decoder mainly over highly frequency-selective channels such as single frequency networks (SFN). 2011 IEEE.

Orthogonal frequency division multiplexing (OFDM) is a method suitable for high-rate data transmission in wireline and wireless communications. However, it is very sensitive to frequency offset due to Doppler shifts and carrier synchronization errors. This frequency offset results in inter-carrier interference (ICI) and, as a result, the performance of the OFDM system degrades drastically. Consequently, it, is necessary to remove as many ICI effects as possible to achieve the desired OFDM system performance. Therefore, in this paper, we propose a new method based on a nonlinear adaptive filter to suppress these ICI effects. In addition to showing that the ICI effects can be reduced significantly, the results also demonstrate that the nonlinear filter scheme is superior to the conventional linear filter.

Performance improvement of a power line communication system is presented here considering the noise as a cyclostationary non-white Gaussian random process. Performance of a power line communication system is severely deteriorated by fading and multipath effect. The impulsive noise has been considered time variant, has short duration, random occurrence with a high power spectral density (PSD). It causes bit error in the signal. Using orthogonal frequency division multiplexing (OFDM) technique, the effect of impulsive noise and fading can be improved greatly. An analytic approach is presented to evaluate the performance of a power line communication link in the presence of the above limitations. The simulation results show that there is deterioration in system BER due to time and frequency dependence of noise and the degradation is found to be significant at higher bit rates and bandwidth. The system suffers penalty in receiver sensitivity due to non-white nature of the noise process. In this paper, an analytical approach using diversity reception is carried out to examine the performance improvement of a power line channel in fading and impulsive noise. The system bit error rate (BER) is compared numerically for both binary phase shift keying (BPSK) and OFDM system. The BER results show that there is significant improvement in OFDM. Also the performance is remarkably upgraded using diversity reception.

Orthogonal frequency-division multiplexing (OFDM) is robust against frequency selective fading because of the increase of the symbol duration. However, the time-varying nature of the channel causes inter-carrier interference (ICI) which destroys the orthogonal of sub-carriers and degrades the system performance severely. To alleviate the detrimental effect of ICI, there is a need for ICI mitigation within one OFDM symbol. We propose an iterative Inter-Carrier Interference (ICI) estimation and cancellation technique for OFDM systems based on regularized constrained total least squares. In the proposed scheme, ICI aren’t treated as additional additive white Gaussian noise (AWGN). The effect of Inter-Carrier Interference (ICI) and inter-symbol interference (ISI) on channel estimation is regarded as perturbation of channel. We propose a novel algorithm for channel estimation o based on regularized constrained total least squares. Computer simulations show that significant improvement can be obtained by the proposed scheme in fast fading channels.

This paper discusses a cyclic prefixed single carrier frequency-domain equalization (SC-FDE) scheme with two types of transmit diversity. Firstly, we propose a SC-FDE system with space-frequency block coding (SFBC). The transmit sequence of the proposed system is designed to have spatial and frequency diversities, which is equivalent to the SFBC. The corresponding combining receiver is derived under a minimum mean square error (MMSE) criterion. It is shown that the proposed system significantly outperforms the SC-FDE system with space-time block coding (STBC) over fast fading channels, while providing lower computational complexity than orthogonal frequency division multiplexing (OFDM) combined with SFBC. We verify the performance of two-branch transmit diversity systems including the proposed one through bit error rate (BER) analysis. Secondly, as a scheme that combines STBC and SFBC, a space-time-frequency block code (STFBC) SC-FDE system is presented. Computer simulation results show that the proposed STFBC SC-FDE system has better immunity to the distortion caused by both fast fading and severe frequency selective fading, compared to the SC-FDE system with the STBC or the SFBC scheme. Complexity analysis is also conducted to compare their computational loads of the transceiver. It is shown that the proposed STFBC SC-FDE system has lower computational complexity than the STFBC OFDM system.

Two transmitter diversity techniques for turbo coded orthogonal frequency division multiplexing (OFDM) are presented: space-time block coding (STBC) and space-frequency block coding (SFBC). With different channel environment and block size, STBC and SFBC have different performance. Also, with the increase of interleaver size (equal to block size for BPSK), turbo has better performance. So the performance of STBC and SFBC with different transmission environment and block size is simulated and discussed. Some important conclusions about the transmitter diversity for turbo coded OFDM systems are achieved.

It is well known that Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from intercarrier interference (ICI) in mobile environment due to loss of orthogonality among subcarriers caused by Doppler shifts. There exist many ICI mitigation techniques in the literature to improve the performance of OFDM systems. However, most of the existing ICI mitigation techniques assume the OFDM transmission bandwidth is narrow enough that the frequency offsets on all subcarriers are identical. In a wideband OFDM transmission or a non-contiguous OFDM spanning over large bandwidth, the Doppler shifts on different subcarriers are different, especially in high speed aerial vehicle communication systems. In this paper, we analyze the wideband OFDM system in high mobility environment where the frequency offsets vary from subcarrier to subcarrier. We then propose a novel ICI cancellation scheme to eliminate the ICI effect and offer the wideband OFDM system significantly improved BER performance. Simulation results in AWGN channel and multipath fading channel confirm the effectiveness of the proposed scheme in the presence of frequency offset and time variations in the channel, offering the best BER performance available which matches the BER performance of wideband OFDM system without ICI. To our knowledge, this paper is the first to address the ICI problem of varying frequency offsets across subcarriers in wideband OFDM system.

The convergence of high data rate multimedia services such as speech, audio, video, image and data will be the main features of future wireless systems. Multi-carrier code division multiple access (MC-CDMA) is one of the powerful techniques to meet the requirements of next generation broadband and wireless mobile communication systems. MC-CDMA system allows many users to get the benefit of both orthogonal frequency division multiplexing (OFDM) technique and code division multiple access scheme (CDMA). It offers high spectral efficiency, high data rate, low transmit power, lower implementation complexity, large system capacity and narrowband interference rejection capability. Multicarrier systems are very sensitive to carrier frequency offset (CFO) caused by Doppler shifts and imperfections of transmitter and receiver oscillators, which leads to loss of orthogonality among the subcarriers resulting in intercarrier interference (ICI). In this paper, a low complexity receiver phase rotated conjugate cancellation (RPRCC) algorithm using an iterative maximum likelihood (ML) based CFO estimation is proposed. The proposed method reduces the ICI which in turn reduces the multiple access interference (MAI) and subsequently increases the system capacity. Simulation results show that the RPRCC method provides better carrier to interference ratio (CIR) and bit error rate (BER) performance compared to transmitter phase rotated conjugate cancellation (PRCC) technique and conventional conjugate cancellation (CC) scheme.

In systems using Orthogonal Frequency Division Multiplexed (OFDM) all transmitters in a radio broadcasting network may transmit identical signals in the same frequency block, forming a so called Single Frequency Network (SFN). The simultaneous transmission creates a severe artificial multipath propagation causing interference at the receiver. This interference consists not only by intersymbol interference (ISI), but also interchannel interference (ICI) due to orthogonality losses between OFDM scheme‘s subcarriers. A method that is often used to counter the ’’self-interference‘‘ is to insert a guard interval between consecutive OFDM frames combined with an increased symbol duration. The receiver in an SFN is normally experiencing a diversity gain of receiving several signals. Doubts concerning the performance has been raised due to the OFDM scheme‘s sensitivity to frequency errors. If the received signals are exposed to different carrier offsets it will lead to ICI, resulting into reduced coverage. In this paper we apply pulse shaping to reduce the effects of ISI and ICI. Pulse shaping of the transmitted OFDM signal is shown to give significant reductions in self-interference. It is hereby possible to achieve the same coverage with a reduced amount of transmitters. The system also becomes less sensitive to time and frequency synchronisation errors. A method to analyse the performance for time limited pulse shapes is presented using weight functions describing the amount of useful and interfering powers. In the receiver analysis, generalised expressions are given using Fourier transforms and series.

For Orthogonal Frequency Division Multiplex (OFDM)-based wireless communication systems, mobile receivers could suffer significant performance degradation due to intercarrier interference (ICI). ICI cancellation becomes necessary to achieve good detection. We proposed a novel iterative decision-directed ICI cancellation technique (IDDICI) and its low-complexity implementation (LC-IDDICI), and showed its performance by simulation. In this paper, we first present a theoretical analysis to obtain the achievable performance of an OFDM receiver using IDDICI. Next, we show analytically that the "sub-optimal" LC-IDDICI actually provides better ICI cancellation than the original IDDICI. Finally, the LC-IDDICI is compared to two other published ICI cancellation techniques, which are also standard conformable. The comparison shows that the LC-IDDICI requires the lowest complexity while providing comparable performance.

Ultrasonic communication is a desirable method for information transfer through solid channels such as metallic bars, plates, or pipes by overcoming the physical barriers that prevent conventional wired or radiofrequency transmission. In this paper, we investigate the architecture of a reconfigurable software-defined ultrasonic communication (SDUC) platform that can make use of the complete channel bandwidth for real-time video transmission through a highly reverberant solid channel. Reverberations in solid channels are complex and generated by surface wave, lamb wave, longitudinal wave, shear wave, reflection, refraction, dispersion, mode conversion, and scattering phenomena. To explore the multipath and fading effects on bitrate, experimental studies were performed using an aluminum rectangular bar (ARB) of 25, 40, and 50 cm channel length. We investigated the feasibility of utilizing orthogonal frequency-division multiplexing (OFDM) combined with quadrature amplitude modulations (QAM) for peak bitrate performance. Design strategies and guidelines have been established for the best solutions to combat intersymbol interference caused by the severe reverberation inherent to ultrasonic solid channels. A practical solution for video transmission, adhering to the Digital Video Broadcasting Terrestrial (DVB-T) standard, is also examined for video streaming transmission of 240p, 480p, and 720p resolutions at 20 frames per second across an ARB channel. For experimental studies and performance evaluation, we designed a high-performance reconfigurable system-on-chip (SoC) SDUC platform for video transmission and bit error rate (BER) assessment. Through experimental studies for ultrasonic channel analysis, we achieved a peak video transmission rate of 1074 kbps with 3.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10 ^{-4}$ </tex-math></inline-formula> BER despite reverberation, the multipath effect, and signal fading within the ARB channel.

A radio is adaptive if it can autonomously analyze the communications environment and instantly modify its settings to achieve the best possible efficiency. In orthogonal frequency division multiplexing (OFDM) transmissions, identifying the space frequency block coding (SFBC) category utilized is one of the most important tasks of an adaptive receiver. Previous approaches to this problem did not take into consideration the fact that real systems typically suffer from transmission defects. This study offers a novel maximum likelihood recognizer capable of distinguishing between SFBC OFDM waveforms in the context of inphase and quadrature phase differences (IQDs). The theoretical findings show that IQDs arising from the transmitter and recipient can be combined with channel paths to generate so-called effective channel paths. The conceptual examination demonstrates that the outlined maximum likelihood strategy of the SFBC recognition and effective channel estimation processes is implemented by an expectation maximization tool utilizing the error control decoders’ soft outputs. The simulations results reveal that the suggested strategy delivers a much greater recognition accuracy than the typical approaches outlined in the comparable literature. At a signal-to-noise ratio (SNR) of 14 dB, for example, the proposed approach achieves a bit error rate (BER) of 0.00002, which is very close to the case of perfect estimation and compensation for IQDs, outperforming the previous reported works which achieved BERs of 0.01 and 0.02.

The nonlinearity of high power amplifiers (HPAs) exhibits amplitude and phase distortions, which cause loss of orthogonality among the subcarriers in orthogonal frequency division multiplexing (OFDM) systems, and hence, inter-carrier interference (ICI) is introduced in the transmitted signal. The ICI power is proportional to the amplitude of the signal at the amplifier input and it may cause a considerable bit error rate (BER) degradation. Due to the ICI is a random process and has unknown distribution function, it is difficult to evaluate the theoretical BER when the ICI is taken into account. This paper evaluates the BER analytically using sequence development approach (SDA) for OFDM systems perturbed by the HPA. In comparison to the state-of-the-art technique, the evaluation of the BER using this approach achieves superior approximation at the expense of additional computational complexity.