We provide an exact analysis of orthogonal frequency-division multiplexing (OFDM) performance in the presence of phase noise Unlike most methods which assume small phase noise, we examine the general case for any phase noise levels After deriving a closed-form expression for the signal-to-noise-plus-interference ratio (SINR), we exhibit the effects of phase noise by precisely expressing the OFDM system performance as a function of its critical parameters This helps in understanding the meaning of small phase noise and how it reflects on the proper parameters selection of a specific OFDM system In order to combat phase noise, we also provide in this paper a general phase-noise suppression scheme, which, by analytical and numerical results, proves to be quite effective in practice

OFDM systems in the presence of phase noise: consequences and solutions

OFDM suffers from severe performance degradation in the presence of phase noise. In particular, phase noise leads to common phase error (CPE) as well as intercarrier interference (ICI) in the frequency domain. Some approaches in the literature mitigate phase noise by directly evaluating and then compensating for CPE or ICI, while others choose to correct phase noise in the time domain. A new parametric model of OFDM signals is proposed in this paper which shows that, in the presence of phase noise, each received frequency-domain subcarrier signal can be expressed as a sum of all subcarrier signals weighted by a vector parameter. Then, two reduced-complexity techniques are presented to estimate this weighting vector. The first is a maximum likelihood (ML) method whereas the second one is a linear minimum mean square error (LMMSE) technique. Using the obtained estimates, we also propose two approaches, i.e., a decorrelator and an interference canceler, to mitigate phase noise. It is shown that most conventional methods can be readily obtained from our approaches with some approximation or orthogonal transform. Theoretical analysis and numerical results are provided to elaborate the proposed schemes. We show that the performance of both approaches is superior to that of conventional methods. Furthermore, LMMSE gives the best performance, while ML provides a much simpler yet effective way to mitigate phase noise

Phase Noise Estimation and Mitigation for OFDM Systems

In multiple access OFDM systems (OFDMA) the separation of different users is achieved by exploiting the orthogonality of the subcarriers. However, a well-known problem in OFDM-based systems is the vulnerability to synchronization errors which leads to a loss of orthogonality. In this paper, a method is proposed to counteract the effect of different frequency offsets among users in an OFDMA uplink system with a frequency selective Rayleigh fading channel. The multiple access interference due to the user frequency misalignments is reduced by reconstructing and removing the interfering signals in the frequency domain. This is performed by means of a successive or selective cancellation method. In particular, the performance of these cancellation schemes is analyzed by assuming either an ideal or estimated frequency offset. Simulation results show that it is possible to achieve, with the interference cancellation, a performance close to the ideal case, i.e., without frequency offset among users.

Multiuser interference cancellation receivers for OFDMA uplink communications with carrier frequency offset

This paper investigates wireless access schemes, in the forward link that are suitable for wireless broadband packet transmission in a multi-cell environment. The single-carrier (SC)/DS-CDMA, multi-carrier (MC)/DS-CDMA, and MC-CDMA schemes are compared in terms of packet error rate (PER) performance taking into account the impact of other-cell interference assuming the use of cell-site diversity. The results show that, while SC/DS-CDMA (64 Mcps) and MC/DS-CDMA (number of sub-carriers 4, 16 Mcps per sub-carrier) cannot attain the average PER=10/sup -2/ for more than two users, MC-CDMA (number of sub-carriers=512, 156 ksps per sub-carrier) achieves much better performance and realizes simultaneous transmission of approximately 10 users with antenna diversity reception, when the total bandwidth is 80 MHz and the information bit rate per user is 2 Mbps.

https://ieeexplore.ieee.org/iel5/7084/19094/00883259.pdf

Forward link capacity of coherent DS-CDMA and MC-CDMA broadband packet wireless access in a multi-cell environment

In this paper, we consider OFDM channel estimation in the presence of frequency offset and phase noise. In the literatures, most channel estimation methods assume perfect frequency synchronization and the knowledge of channel statistics. Phase noise and residual frequency offset cause inter-carrier interference (ICI), which consequently impairs the accuracy of channel estimation. The lack of knowledge of channel statistics can make channel estimation much harder. To resolve these problems, we propose with the aid of cyclic prefix (CP) based frequency offset estimation statistics-independent channel estimation. We iteratively search for the most likely channel impulse response (CIR) length, and use it not only for the optimum compensation of frequency offset, but also for finding the optimum window to filter the least square (LS) channel estimate which further suppress the effects of ICI and noise. The proposed scheme is compared with conventional methods for both non-interpolation and interpolation cases. Numerical results are presented to illustrate the effectiveness of the proposed scheme.

OFDM channel estimation in the presence of frequency offset and phase noise

Orthogonal frequency division multiplexing (OFDM) is believed to be an important technique for future wireline and wireless communications. One of the major disadvantages of such a multi-carrier modulation is the sensitivity of the performance to a frequency offset. The frequency offset can result from a Doppler shift due to mobile movement as well as from a carrier frequency synchronization error. Such a frequency offset causes a loss of the carriers' orthogonality, and hence inter-carrier interference (ICI). A previously proposed method to estimate and correct the frequency offset uses the retransmission of a data symbol, thus reducing the bandwidth efficiency. Another method, which merely reduces the effects of the ICI instead of completely correcting for effects of the frequency offset is based on repetition coding in the frequency domain, hence also reducing the throughput. In this paper, we propose a blind method using the correlation of the samples at the output of the discrete Fourier transform (DFT) to estimate the frequency offset. As no training sequence or symbol retransmission is required there is no loss in bandwidth efficiency. Additionally, we develop an adaptive algorithm for the frequency offset correction. The derived algorithm is basically a stochastic gradient algorithm which minimizes the mean squared frequency offset error.

A novel method for blind frequency offset correction in an OFDM system

Conventional multiuser code division multiple access (CDMA) suffers from the well-known near-far problem. Both the conventional decorrelator and an adaptive separator termed bootstrap algorithm were used to mitigate this problem and obtain near-far resistant receivers. These approaches still require the knowledge of which users are active and their respective codes. Eliminating this requirement is advantageous for downlink communication as only the desired user is of interest. Furthermore, in a multipath environment the use of the RAKE receiver adds to the complexity. A transmission method called multicarrier CDMA (MC-CDMA) uses multiple narrowband subcarriers and, as a result, the channel is flat-fading at each subcarrier. In this paper, a receiver for downlink MC-CDMA is proposed that does not require the knowledge of which users are active. This is achieved by replacing the bank of matched filters of the full dimensional multiuser detector by 2 matched filters; one for the desired user and one representing all the interfering users combined in a specific way. Additionally, this significantly reduces the number of adaptively controlled weights. The performance of this system is analyzed and simulation results are obtained for the Rayleigh fading channel with and without correlation between the subcarriers.

Adaptive Reduced Complexity Multicarrier CDMA (MC‐CDMA) Structure for Downlink PCS

Conventional multi-user Code Division Multiple Access (CDMA) suffers from the well-known near-far problem. Both the conventional decorrelator and an adaptive separator termed Bootstrap algorithm were used to mitigate this problem and obtain near-far resistant receivers. Nevertheless, those approaches still require the knowledge of which users are active and their respective powers. Eliminating this requirement is advantageous for downlink communication as we are only interested in one desired user. Furthermore, in a multipath environment the use of the RAKE receiver adds to the complexity. A transmission method called Multi-Carrier CDMA (MC-CDMA) uses multiple narrowband subcarriers and as a result the channel is flat-fading at each sub carrier. However, due to frequency selective fading the fading at adjacent subcarriers will be correlated. We propose a downlink MC-CDMA communication system which has a special structure and requires less complex hardware at the receiver. The performance of this system is analyzed and simulation results are obtained for the AWGN channel and the Rayleigh fading channel with and without correlation between the subcarriers.

Adaptive Multi-Carrier CDMA (MC-CDMA) Structure for Downlink PCS

Orthogonal Frequency Division Multiplexing (OFDM) is believed to be an important technique for future wireline and wireless communications. One of the major disadvantages of such a multi-carrier modulation is the sensitivity of the performance to a frequency offset. The frequency offset can result from a Doppler shift due to mobile movement as well as from a carrier frequency synchronization error. Such a frequency offset causes a loss of the carriers’ orthogonality, and hence Inter Carrier Interference (ICI). A previously proposed method to estimate and correct the frequency offset uses the retransmission of a data symbol, thus reducing the bandwidth efficiency. Another method, which merely reduces the effects of the IC1 instead of completely correcting for effects of the frequency offset is based on repetition coding in the frequency domain, hence also reducing the throughput. In this paper, we propose a blind method using the correlation of the samples at the output of the Discrete Fourier Transform (DFT) to estimate the frequency offset. As no training sequence or symbol retransmission is required there is no loss in bandwidth efficiency. Additionally, we develop an adaptive algorithm for the frequency offset correction. The derived algorithm is basically a stochastic gradient algorithm which minimizes the mean squared frequency offset error.

http://ieeexplore.ieee.org/iel4/5930/15794/00734676.pdf

A Novel Method for lind Frequency ffset Correction in an OFD

In this paper we describe various applications of bootstrap based blind adaptive signal separators. Schemes are developed for multiuser detection (MUD) for downlink MC-CDMA, frequency offset correction (FOC) for OFDM and joint MUD and FOC for downlink MC-CDMA.

Matthijs A. Visser

Papers

A novel method for blind frequency offset correction in an OFDM system

Adaptive Reduced Complexity Multicarrier CDMA (MC‐CDMA) Structure for Downlink PCS

Adaptive Multi-Carrier CDMA (MC-CDMA) Structure for Downlink PCS

A Novel Method for lind Frequency ffset Correction in an OFD

Blind Adaptive Interference Cancelation for Multicarrier Modulated Systems