Pilot-free dynamic phase and amplitude estimations for wireless ICI self-cancellation coded OFDM systems

OFDM has the advantage over the conventional single-carrier modulation schemes in the presence of frequency-selective fadings. Nevertheless, intercarrier-interference (ICI) due to Doppler frequency drift, phase offset, local oscillator frequency drift, and sampling clock offset will be a severe problem in the wireless OFDM systems. Previous ICI self-cancellation coding schemes can greatly reduce the ICI, but they are very sensitive to the phase ambiguity, which is due to the composite effect of the phase offset, the multipath fading and the local oscillator frequency drift. In this paper, a novel receiver which combines the current ICI self-cancellation coding techniques with a new pilot-free joint phase/amplitude estimation and symbol detection scheme is proposed. Based on the energy modulation or the irregular symbol constellation, our new technique does not have any requirement of pilot symbols and it can operate on all kinds of phase error ranges. The proposed scheme is promising in comparison with other existing methods at different noise levels through OFDM simulations.     

Joint phase/amplitude estimation and symbol detection for wireless ICI self-cancellation coded OFDM systems

OFDM has been applied in the current wireless local-area networks and digital video broadcasting systems since it has the advantage over the conventional single-carrier modulation schemes when the frequency-selective fadings are present. Nevertheless, intercarrier-interference (ICI) due to Doppler frequency drift, phase offset, local oscillator frequency drift, and multipath fading will be a severe problem in OFDM systems. Previous ICI self-cancellation coding schemes can greatly reduce the ICI, but they are very sensitive to the phase ambiguity, which is due to the composite effect of the phase offset, the multipath fading and the local frequency drift. In this paper, the phase ambiguity and amplitude ambiguity problems in ICI self-cancellation coded OFDM receivers will be formulated and discussed. Then, a novel receiver which combines the current ICI self-cancellation coding techniques with a new expectation-maximization-based joint phase/amplitude estimation and symbol detection scheme is proposed. The outstanding performance of this proposed scheme is shown and compared with other existing methods at different noise levels through OFDM simulations.     

Robust ICI Self-cancellation OFDM Receiver with Dynamic Phase and Amplitude Estimations

Orthogonal frequency division multiplexing (OFDM) has been applied in the current wireless local-area networks and digital video broadcasting since it is robust against the frequency-selective channels. However, there is still a crucial intercarrier-interference (ICI) problem due to Doppler effect, local frequency drift and sampling clock offset, associated with OFDM systems. Recently ICI self-cancellation schemes have been proposed to significantly reduce the ICI and empirically they greatly outperform the convolutional coding schemes adopted by the IEEE 802.11 standard. However, all existing ICI self-cancellation receivers are still sensitive to the phase and amplitude ambiguities due to the phase offset, the local oscillator frequency drift and the multipath reflections. Therefore, in this paper, a novel receiver design integrating the ICI self-cancellation with a proposed dynamic phase and amplitude estimation mechanism is introduced, which can well solve the ambiguity problem. The Monte Carlo simulation results show that our phase and amplitude estimators can greatly decrease the error probability for the final symbol detection in the ICI self-cancellation OFDM receivers.     

Analysis of ICI cancellation scheme in OFDM systems with phase noise

Phase noise in orthogonal frequency division multiplexing (OFDM) systems destroys the orthogonality of the subcarriers and inter-carrier interference (ICI) is caused. In this paper, the ICI self-cancellation scheme is adopted to combat the ICI caused by phase noise in OFDM systems. Moreover, the error coefficients are defined and the theoretical expressions of carrier to interference ratio (C/I) with and without the ICI self-cancellation scheme are separately derived. From the simulation results, it is verified that the ICI self-cancellation scheme obviously decreases the amount of the ICI caused by phase noise and the improvement of C/I could reach 10 dB when the normalized 3 dB bandwidth of phase noise is 0.4. However, the convolutional coding OFDM (COFDM) system could supply more performance gain at the expense of increasing decoder complexity compared to OFDM system with the ICI self-cancellation scheme in the frequency-selective channel.     

Phase Noise Correction Based on TPS Symbols for the Chinese DTTB System

In orthogonal frequency division multiplexing (OFDM) system, phase noise (PHN) from oscillator can severely reduce the performance by causing: common phase error (CPE) and inter-carrier interference (ICI). The impact of PHN on received signal can be characterized by the circular convolution of the transmitted signal and the discrete Fourier transform (DFT) of PHN signal in frequency domain. Digital television/terrestrial multimedia broadcasting (DTMB), announced as the Chinese digital television terrestrial broadcasting (DTTB) standard, adopted the time-domain synchronous OFDM system (TDS-OFDM) system which has 36 continuous transmission parameter signaling (TPS) symbols in frequency domain which be used for PHN suppression. Based on a linearized parametric model for PHN, least squared (LS) estimation and fast Fourier transform (FFT) approaching method for PHN correction are proposed in this paper. The effects of the PHN on channel estimation in both TDS-OFDM system and conventional cyclic prefix OFDM (CP-OFDM) are also investigated. Simulations show that the proposed algorithm can effectively reduce the PHN and improve the symbol error rata (SER) of TDS-OFDM systems over both additive white Gaussian noise (AWGN) and broadcasting multipath channel. In practice, the FFT-approaching method can be applied to the DTMB receiver-chip design directly with low implementation cost.      

An Exact Error Probability Analysis of OFDM Systems with Frequency Offset

In this paper, we derive exact closed form bit error rate (BER) or symbol error rate (SER) expressions for orthogonal frequency division multiplexing (OFDM) systems with carrier frequency offset (CFO). We consider the performance of an OFDM system subject to CFO error in additive white Gaussian noise (AWGN), frequency flat and frequency selective Rayleigh fading channels. The BER/ SER performances of BPSK and QPSK modulation schemes are analyzed for AWGN and frequency-flat Rayleigh fading channels while BPSK is considered for frequency-selective Rayleigh fading channels. Our results can easily be reduced to the respective analytical error rate expressions for the OFDM systems without CFO error. Furthermore, the simulation results are provided to verify the accuracy of the new error rate expressions.     

Intercarrier interference self-cancellation space-frequency codes for MIMO-OFDM

Space-frequency (SF) codes that exploit both spatial and frequency diversity can be designed using orthogonal frequency division multiplexing (OFDM). However, OFDM is sensitive to frequency offset (FO), which generates intercarrier interference (ICI) among subcarriers. We investigate the pair-wise error probability (PEP) performance of SF codes over quasistatic, frequency selective Rayleigh fading channels with FO. We prove that the conventional SF code design criteria remain valid. The negligible performance loss for small FOs (less than 1%), however, increases with FO and with signal to noise ratio (SNR). While diversity can be used to mitigate ICI, as FO increases, the PEP does not rapidly decay with SNR. Therefore, we propose a new class of SF codes called ICI self-cancellation SF (ISC-SF) codes to combat ICI effectively even with high FO (10%). ISC-SF codes are constructed from existing full diversity space-time codes. Importantly, our code design provide a satisfactory tradeoff among error correction ability, ICI reduction and spectral efficiency. Furthermore, we demonstrate that ISC-SF codes can also mitigate the ICI caused by phase noise and time varying channels. Simulation results affirm the theoretical analysis.     

Probability of error calculation of OFDM systems with frequencyoffset

Orthogonal frequency-division multiplexing (OFDM) is sensitive to the carrier frequency offset (CFO), which destroys orthogonality and causes intercarrier interference (ICI), Previously, two methods were available for the analysis of the resultant degradation in performance. Firstly, the statistical average of the ICI could be used as a performance measure. Secondly, the bit error rate (BER) caused by CFO could be approximated by assuming the ICI to be Gaussian. However, a more precise analysis of the performance (i.e., BER or SER) degradation is desirable. In this letter, we propose a precise numerical technique for calculating the effect of the CFO on the BER or symbol error in an OFDM system. The subcarriers can be modulated with binary phase shift keying (BPSK), quaternary phase shift keying (QPSK), or 16-ary quadrature amplitude modulation (16-QAM), used in many OFDM applications. The BPSK case is solved using a series due to Beaulieu (1990). For the QPSK and 16-QAM cases, we use an infinite series expression for the error function in order to express the average probability of error in terms of the two-dimensional characteristic function of the ICI     

An Improved ICI Reduction Method in OFDM Communication System

Orthogonal frequency division multiplexing (OFDM) is a promising technique for the broadband wireless communication system. However, the inter-sub-carrier-interference (ICI) produced by the phase noise of transceiver local oscillator is a serious problem. Bit error rate (BER) performance is degraded because the orthogonal properties between the sub-carriers are broken down. In this paper, ICI self-cancellation of data-conjugate method is studied to reduce ICI effectively. CPE (common phase error), ICI and CIR (carrier to interference power ratio) are derived and discussed by the linear approximation of the phase noise. Then, the system performance of the data-conjugate method is compared with those of the original OFDM and the conventional data-conversion method. As results, it can be shown that CPE becomes zero in the OFDM of the data-conjugate method. Besides, in the OFDM system with phase noise, the data-conjugate method can make remarkable improvement of the BER performance and it is better than the data-conversion method and the original OFDM with or without convolution coding.     

Joint estimation of channel response, frequency offset, and phase noise in OFDM

Accurate channel estimates are needed in orthogonal frequency-division multiplexing (OFDM), and easily obtained under the assumption of perfect phase and frequency synchronization. However, the practical receiver encounters nonnegligible phase noise (PHN) and carrier frequency offset (CFO), which create substantial intercarrier interference that a conventional OFDM channel estimator cannot account for. In this paper, we introduce an optimal (maximum a posteriori) joint estimator for the channel impulse response (CIR), CFO, and PHN, utilizing prior statistical knowledge of PHN that can be obtained from measurements or data sheets. In addition, in cases where a training symbol consists of two identical halves in the time domain, we propose a variant to Moose's CFO estimation algorithm that optimally removes the effect of PHN with lower complexity than with a nonrepeating training symbol. To further reduce the complexity of the proposed algorithms, simplified implementations based on the conjugate gradient method are also introduced such that the estimators studied in this paper can be realized efficiently using the fast Fourier transform with only minor performance degradation. EDICS: SPC-MULT, SPC-CEST, SPC-DETC.     

OFDM系统中相位噪声的影响及ICI自消除方案

相位噪声也能引起信道间干扰( ICI) ,本文系统的分析了采用ICI自消除方案前后相位噪声对OFDM系统的影响,得出了载波干扰比和信噪比的近似计算公式,在AWGN信道上仿真了系统的误码性能。从仿真结果看,ICI自消除的方案能够显著提高系统的载波干扰比和误码率     

Blind frequency-offset estimator for OFDM with general symbol constellation

An efficient feedforward blind carrier frequency offset (CFO) estimator for orthogonal frequency division multiplexing (OFDM) systems with general symbol constellation is presented. The proposed estimator requires only one OFDM symbol period to blindly and accurately estimate the CFO in Gaussian and multipath fading channels.     

Error probability of MPSK OFDM impaired by carrier frequency offset in AWGN channels

In this letter, we evaluate the symbol error probability of orthogonal frequency division multiplexing (OFDM) with M-ary (M>4) phase shift keying (MPSK) impaired by carrier frequency offset (CFO). A signal space decomposition (SSD) approach is proposed for additive white Gaussian noise (AWGN) channels, and then the symbol error rate (SER) performance is expressed as the sum of an infinite series with the Beaulieu series. The derived theoretical expression agrees well with the simulation results     

CO-OFDM系统中融合迫零与自消除算法的新颖相位噪声补偿算法

针对激光器的相位噪声会严重影响相干光正交频分复用(CO-OFDM)系统的性能问题,提出了一种将迫零算法与自消除算法相结合的新颖相位噪声补偿算法。该算法利用导频信息,通过迫零算法将每个OFDM符号的相位噪声补偿到较小的范围内,再通过自消除算法进一步补偿相位噪声。仿真结果表明,与迫零算法相比,该补偿算法不但能有效补偿相位噪声,也能补偿部分加性高斯白噪声,改善系统的误码性能,降低系统对激光器线宽的要求。     

Inter‐carrier Interference Reduction Scheme for SFBC‐OFDM Systems

In this paper, we first analyze carrier‐to‐interference ratio performance of the space–frequency block coded orthogonal frequency‐division multiplexing (SFBC‐OFDM) system in the presence of phase noise (PHN) and residual carrier frequency offset (RCFO). From the analysis, we observe that conventional SFBC‐OFDM systems suffer severely in the presence of PHN and RCFO. Therefore, we propose a new inter‐carrier interference (ICI) self‐cancellation method — namely, ISC — for SFBC‐OFDM systems to reduce the ICI caused by PHN and RCFO. Through the simulation results, we show that the proposed scheme compensates the ICI caused by PHN and RCFO in Alamouti SFBC‐OFDM systems and has a better performance than conventional schemes.     

Decision Feedback Frequency Offset Estimation and Tracking for General ICI Self-Cancellation Based OFDM Systems

Inter-carrier interference (ICI) self-cancellation schemes were often employed in many OFDM systems as a simple and effective approach to suppress ICI caused by carrier frequency errors. The same procedure, however, can not perform very well at high frequency offsets. We propose a simple decision feedback scheme based on the general ICI self-cancellation scheme to perform estimation and tracking of the carrier frequency offsets. A system with the scheme does not consume additional bandwidth since it used the same data symbols employed for ICI cancellation for the estimation. After an initial estimation is completed, the scheme switches to the tracking mode to carry out the estimation of deviations in the frequency offsets. Finally this fine-tuned estimate is applied to the ICI self-cancellation scheme concurrently for frequency offset correction and hence improved the system performance greatly. Simulation results showed that our scheme allowed up to 9% of random variations in the frequency offset. The effectiveness of our scheme is further verified by calculating the bit error rate performance of various OFDM receivers.     

An Enhanced Inter-carrier Interference Reduction Scheme for OFDM System with Phase Noise

Inter-carrier interference (ICI) reduction techniques achieve a better carrier-to-interference ratio (CIR) in OFDM system in the presence of synchronisation errors. However, the frequency diversity available on the frequency-selective channel has not been utilised by conventional ICI reduction techniques. In this paper, the frequency diversity of ICI reduction methods in the presence of phase noise over frequency-selective fading channels is analysed. Based on the analysis, an ICI reduction technique is proposed, enhanced symmetric data-conjugate (ESDC) technique, to enhance the frequency diversity in multipath fading channel. The carrier-to-interference ratio (CIR) and common phase error (CPE) of the proposed ICI reduction scheme are derived and the BER performance of the proposed system is compared with the conventional ICI reduction methods such as adjacent data-conjugate (ADC) and symmetric data-conjugate (SDC) methods. Simulation results reveal that the proposed ICI reduction scheme provides an improvement in BER performance over a fading channel and it is also better than conventional ICI reduction techniques in the presence of ICI due to phase noise.     

BER Analysis of OFDM Systems Impaired by Phase Noise in Frequency-Selective Fading Channels

In this paper, we study the effect of finite-power, phase-locked loop based phase noise on the bit-error-rate (BER) performance of orthogonal frequency division multiplexing (OFDM) systems in frequency-selective fading channels. It is well known the impact of phase noise on the performance of an OFDM system can be divided into a multiplicative term called common phase error (CPE) and an additive term called intercarrier interference (ICI). Based on the conditional Gaussian approximation technique, we first derive the BER formulas for BPSK, QPSK, 16-QAM, and 64-QAM modulated OFDM signals in frequency-selective Rayleigh fading channels. To further quantify the individual influence of the CPE and the ICI on system performance for different phase noise spectra, we derive the BER expressions for perfect CPE compensation cases. The analytical results obtained for frequency-selective Rayleigh fading channels are then generalized to frequency-selective Rician fading channels. Simulation results not only validate the accuracy of our analysis but also show the dependency of BERs on the shapes of phase noise spectra.     

Probability of Error Analysis of BPSK OFDM Systems with Random Residual Frequency Offset

In this paper, we derive closed form bit error rate (BER) expressions for orthogonal frequency division multiplexing (OFDM) systems with residual carrier frequency offset (CFO). Most of the published work treats CFO as a nonrandom parameter. But in our study we consider it as a random parameter. The BER performance of binary phase shift keying (BPSK) OFDM system is analyzed in the cases of additive white Gaussian noise (AWGN), frequency-flat and frequency-selective Rayleigh fading channels.We further discuss how these expressions can be related to systems with practical estimators. The simulation results are provided to verify the accuracy of these error rate expressions.     

针对DTMB-A系统的相位噪声消除算法

相位噪声会破坏OFDM (Orthogonal Frequency Division Multiplex) 符号内频域子载波的正交性,产生公共相位误差（CPE, Common Phase Error）和子载波间干扰（ICI, Inter-Carrier Interference）,对系统性能造成严重影响。针对数字电视地面广播传输标准演进方案（DTMB-A）的相位噪声问题,本文提出了一种两步结合的相位噪声估计和消除算法。首先,利用相邻两帧的帧头符号中所包含的PN（Pseudo Noise）序列,对帧体符号内的公共相位误差进行粗估计;随后,对帧体数据子载波进行标记,选取合适的子载波集合用于估计公共相位误差和子载波间干扰的精确结果。由此获得相位噪声频域估计结果后,通过快速傅立叶变换（FFT, Fast Fourier Transform）得到时域估计结果并进行消除。和现有基于判决反馈的相位噪声估计算法对比,本文所提算法的创新性在于采用了粗估计和精确估计结合的方法,同时利用子载波标记的方法有效降低了由于错误判决导致的误码扩散。仿真结果表明在现有算法已经不能正常工作的情况下,本文所提算法还可以有效的抑制相位噪声对系统性能的影响。