Space-Time Parallel Cancellation Orthogonal Frequency Division Multiplexing in Power Line Communications

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.

Orthogonal frequency division multiplexing (OFDM) systems work well if the subcarriers are orthogonal to each other. However, the orthogonality among subcarriers may not exist and result in inter-carrier interference (ICI) at the receiver. This may cause by residual carrier frequency offset, time variations due to Doppler shift or phase noise. Further developing the parallel cancellation (PC) scheme to mitigate the ICI of OFDM systems, we expand this OFDM symbol-based PC scheme into a space-frequency (SF) coded system. This new simple space- frequency parallel cancellation (SFPC) scheme is a technique that combines the SF and PC schemes together. Computer simulations indicate that OFDM systems using the SFPC scheme outperform the regular PC and SF systems in slow and fast frequency selective fading channels, specifically at a high signal-noise-ratio (SNR). Furthermore, the error floor of the SFPC-OFDM system is significantly lower than that of the PC and SF systems without increasing computational load. Additionally, the SFPC scheme is a simple multiple input and multiple output (MIMO) system.

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.

In this paper, we propose a novel receiver design for orthogonal frequency division multiplexing (OFDM) transmission over doubly (time- and frequency-) spread channels, where the receiver employs a turbo message passing (TMP) algorithm for joint channel estimation and data detection. We show that the proposed TMP-based receiver is able to make more efficient use of the prior information about the channel and the data for inter-carrier interference (ICI) cancellation than the existing iterative receivers. The proposed TMP algorithm can be further combined with a soft-input soft-output (SISO) decoder for joint channel estimation, data detection and decoding. Numerical results are presented to demonstrate the performance superiority of our proposed TMP-based OFDM receiver.

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.

In this paper, we propose a statistics-based channel estimation and inter-carriers interference (ICI) mitigation scheme for the orthogonal frequency division multiplexing (OFDM) transmission over high speed railway communication. The proposed scheme offers a new channel estimation method based on compressed sensing by utilizing the sparsity of high speed train (HST) in the time domain channel. The wireless channel is expressed by a weighted time-domain channel interpolation. The interpolation weights are designed according to the channel statistics, and the position of the selected parameter of each path is designed based on coherence of the model structure. Furthermore, by utilizing the channel statistics, we develop the receive post-processing in the receiver for ICI mitigation. Numerical and simulation results verify the effectiveness of the proposed schemes.

One of the widely adopted multicarrier modulation technique in wireless communication system is Orthogonal Frequency Division Multiplexing (OFDM), because of its enhanced robustness against channel dispersion. However, Inter Carrier Interference (ICI) caused by time varying wireless channel and Peak to Average Power Ratio (PAPR) due to the presence of a large number of subcarriers with varying amplitude are the critical issues faced in OFDM. One of the efficient ICI self-cancellation scheme is correlative precoder but it introduces increased PAPR. To overcome this shortcoming a new form of circulantly precoded OFDM system is implemented to enhance ICI reduce and also employed with Selective Mapping (SLM) which is effective in PAPR reduction and uncomplicated. BER performance of correlative and circulantly precoded OFDM system is evaluated for LMMSE and OLMMSE equalizers. Simulation results show that circulantly precoded OFDM with SLM can achieve jointly better ICI self cancellation and PAPR reduction than correlative precoding technique over time varying channel.

Traditionally, jamming to the wireless in-home system is a fatal threat for Smart Grid communications, which impedes the two-way data transmission between electric devices and the smart meter, and thus deteriorates the reliability of the in-home communication of Smart Grid. To enhance Home Area Network (HAN) security for Smart Grid application, in this paper, orthogonal frequency division multiplexing (OFDM)-based power line (PL) system is incorporated into HAN, and a hybrid model of PL and wireless communications are proposed with transmit diversity. For the combinational model with transmit diversity, Alamouti code is employed at the transmitter part. Simulation results validate the feasibility of the presented combinational solution, and furthermore show that the hybrid model could tolerate jamming to the wireless system effectively.

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.

This paper extends the previous proposition of Precoded Subcarrier Nulling (PSUN) [1], a novel orthogonal frequency division multiplexing (OFDM) transmission scheme for operation in the 3.5 GHz Band, to consideration of imperfect sensing of radar pulse parameters. We take into consideration existence of Environmental Sensing Capability (ESC), a sensing functionality of the 3.5 GHz Band coexistence architecture. We provide an analysis framework where variables representing impacts of imperfect sensing on an OFDM system are generalized. The framework demonstrates impacts of sensing errors by an ESC and parameter changes by a radar. Our results show that PSUN still is effective in suppressing inter-carrier interference (ICI) even with imperfect sensing.

Power Line Communications have been the subject of an important research work. At the same time, the growing demand for multimedia communications provides a good prospect for PLC as a promising transmission technique for the “last mile” access network. Orthogonal Frequency Division Multiplexing (OFDM) is a spectrally efficient multicarrier modulation technique for high speed data transmission over multipath fading channels. High Peak-to-Average Power Ratio (PAPR) is a major drawback of OFDM. The high PAR of the OFDM signal has to be considered when setting the range of the digital-to-analog converter (DAC) and dimensioning the line-driver. This paper introduced an improved PAPR reduction scheme using constant envelope modulation. Furthermore, by utilizing continuous phase modulation (CPM) in a CE-OFDM system, the PAPR can be effectively reduced to 0 dB. The paper describes a CE-OFDM based modem for Power Line Communications (PLC) over the low voltage distribution network. Relying on a preliminary characterization of a PLC network, a complete description of the modem is given.

This paper considers an adaptive orthogonal frequency-division multiplexing (OFDM) transmission scheme for narrowband (NB) power line communication (PLC). The NB PLC channel is found to show strong cyclostationary characteristics due to the periodic mains voltage. However, conventional systems do not use these time-varying channel features. An improvement of the performance is achieved by exploiting the cyclic properties of the channel. Therefore, adaptive bit and power loading methods are of great interest for PLC. In this work, we will evaluate a cyclic loading method for an OFDM system in the CENELEC A-band. Our analysis is based on noise measurements at three different locations over an observation time of 23 hours. Our contribution includes an OFDM system model comprising both additive noise and channel attenuation. Furthermore, we present a method for limiting the amplitude and power spectral density to comply with narrowband regulations. In conclusion, our proposed method achieves a lower bit error rate at all locations. The improvement reaches up to a 102 times lower bit error rate compared to non-adaptive carrier allocation at the same data rate.

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.

In this paper, we propose an enhanced iterative ICI (Inter Carrier Interference) cancellation method for cooperative STBC-OFDM (Space Time Block Coded-Orthogonal Frequency Division Multiplexing) system. In cooperative STBC-OFDM system, ICI cancellation is necessary because ICI due to the independent local oscillators always exits. The conventional iterative ICI cancellation method has severe performance degradation due to the initial estimation error. Also the performance degradation increases as CFOs (Carrier Frequency Offsets) and modulation order increases. Therefore, in this paper, we propose an enhanced iterative ICI cancellation method which can reduce the initial estimation error by giving a priority to initial estimation and cancellation process. Through the complexity and performance comparisons, we verify that the proposed method has better performance with approximately same complexity compared with the conventional method.

A novel encryption scheme using chaotic Zadoff-Chu matrix transform (ZCMT) precoding is proposed to improve both of the data security and performances in orthogonal frequency-division multiplexing (OFDM) transmission, where the security is significantly enhanced with a huge key space of ∼10400 provided by hyper digital chaos. The chaotic ZCMT matrix is generated with the reconfigurable parameters and row permutation of ZCMT matrix, both of which are predetermined by a hyper digital chaos. The OFDM data encryption using the chaotic ZCMT precoding effectively reduces the peak-to-average power ratio (PAPR) and consequently improves the OFDM transmission performance, if compared with the traditional OFDM transmission. The significant PAPR reduction is numerically analysed via the autocorrelation and the complementary cumulative distribution function (CCDF).