Phase noise reduction techniques for multigigabit per second OFDM systems operating at 60 GHz

Singular value decomposition (SVD) is a useful technique to mitigate co-space interference (CSI) in multiple input multiple output (MIMO) systems employing orthogonal frequency division multiplexing (OFDM) scheme. The SVD based frequency-domain broadband beamforming (FBBF) approach uses the beamforming matrices in both transmitter and receiver sides for each subchannel matrix. However, when the MIMO- OFDM system has a large number of subchannels, the FBBF technique is very complex due to computing the SVD of each subchannel separately. In this paper, we propose a new approach to eliminate CSI and intersymbol interference (ISI) in time- domain and frequency-domain, respectively. By the use of polynomial matrix SVD based on SBR2 algorithm, the MIMO- OFDM system is decomposed to the parallel decoupled single input single output (SISO) OFDM systems. In this way, the CSI is eliminated by time-domain broadband beamforming (TBBF) in both transmitter and receiver sides and ISI is mitigated in each SISO-OFDM system by frequency-domain equalization. The performance of the proposed method is evaluated by computer simulations for fixed broadband wireless communication system developed based on the WiMax. Simulation results show that the proposed method achieves good performance in concerned SNR interval.

OFDM (orthogonal frequency division multiplexing) systems are very sensitive to carrier frequency offset. Although frequency offset is generally compensated for by an automatic frequency control (AFC), residual frequency offset remains after the AFC. Moreover, OFDM signals are also affected by phase noise. Thus, a kind of phase tracking is needed to compensate for these effects. In an OFDM system such as IEEE 802.11a, a phase tracking scheme that uses pilot subcarriers to detect the phase rotation caused by residual frequency offset and phase noise is employed. However, the spectrum of the AFC output signal is shifted by residual frequency offset. That is, the detected phase is the composite phase of the pilot subcarrier and the adjacent subcarrier because of inter-carrier interference (ICI). The compensation based on the composite phase sometimes overcorrects or undercorrects the phase rotation. In this paper, we propose a phase tracking scheme using iterative estimation of residual frequency offset in OFDM systems. The proposed phase tracking scheme estimates residual frequency offset in the frequency domain, and compensates for it in the time domain. The compensation in the time domain mitigates the spectrum shift of the AFC output. Therefore, the proposed scheme can reduce ICI, and track phases more accurately than the conventional phase tracking scheme.

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.

In this paper, we consider out-of-band radiations caused by high sidelobes in orthogonal frequency division multiplexing (OFDM) system. Suppression of sidelobes in OFDM system allows higher spectral efficiency and less interference with existing legacy systems in OFDM based overlay system. We combine different sidelobe suppression techniques to suppress the sidelobes in OFDM system. The multiple-choice sequence (MCS) is combined with cancellation carriers (CCs) and also MCS is combined with subcarrier weighting (SW) technique. MCS is applied prior to CCs or SW techniques. Simulation results show that combining MCS with CCs and MCS with SW techniques the sidelobes in OFDM system can be significantly reduced, which allow a successful co-existance between OFDM overlay system and an existing legacy system.

This paper presents an in-depth analysis of effect of oscillator phase noise (PN) on the performance of orthogonal frequency division multiplexing (OFDM) systems in sub-terahertz (Sub-THz) band. We use the empirical PN measurement of current Sub-THz signal sources to propose a two-part PN model that captures the unique characteristics of PN in Sub-THz band. Subsequently, the proposed model is used to analyze the performance of OFDM systems affected by PN. Our analysis reveals some key distinctions between the effect of PN on the OFDM systems operating at Sub-THz and the same systems operating at conventional microwave frequency bands. In particular, we show that in these systems: 1) the PN floor has a significant effect on the performance degradation, 2) the assumption of PN being a low-pass process is inaccurate, and 3) the existing OFDM PN mitigation schemes are less effective. To verify our analysis the upper bound on the signal-to-interference-and-noise ratio (SINR) after using the existing PN mitigation schemes under limited computational complexity constraint is derived and the effect of PN floor on the SINR is analytically calculated.

Phase noise, introduced by the receiver local oscillator, has severe effects on the performance of orthogonal frequency division multiplexing (OFDM) systems. The common compensation method can only correct common phase error (CPE) caused by the low-frequency part of the phase-noise spectrum, and cannot compensate phase noise thoroughly. A new method, per-symbol phase noise detection and compensation method, is proposed. Based on a frequency-domain linearized parametric model for phase noise, the method not only deals with CPE more effectively, but also compensates most of the intercarrier interference (ICI) induced by the high-frequency part of the phase-noise spectrum. This method well compensates phase noise in higher SNRs and lower quality tuners.

ABSTRACTWhile inter-symbol interference is not of concern, inter-carrier interference that is caused by carrier frequency offset (CFO) is more concerned in orthogonal frequency division multiplexing (OFDM) systems. The estimation of channel impulse response (CIR) is another important parameter of interest in the system. Recently, a number of approaches for the joint estimation of CFO and CIR in OFDM systems have been proposed in the literature, and most of them are traditional maximum-likelihood-based approaches. In this paper, we propose a number of mixture cost-reference particle filtering (CRPF) approaches for joint estimation of CIR and CFO, and a couple of them can be applied without the knowledge of both state and measurement noise statistics. Conventional least mean squares algorithm or recursive least squares algorithm is jointly employed with recently developed CRPF for nonlinear and multiple parameters estimation in OFDM systems. The computer simulation results show that mixture CRPFs are more robust against particle impoverishment (PI) problem than standard mixture particle filtering (PF) and mixture regularized PF (RPF) approaches although RPF was particularly developed to tackle the PI problem. In this paper, we investigate a number of mixture PF approaches including ones that do not need the information of noise statistics for the joint estimation of CFO and channel in OFDM systems.

Orthogonal frequency division multiplexing (OFDM) systems suffer from high sidelobes level. In some applications, as cognitive radios, this phenomenon can be a serious matter. This paper proposes Minimum shift keying (MSK)-OFDM to address this problem. The proposed method is an OFDM system using MSK modulation in each subcarrier. The corresponding transmitter and receiver are introduced. The method doesn't entail great changes in the main parts of OFDM. Like OFDM systems, the transceiver can be implemented using DFT/IDFT. Simulation results show great reduction in out of band radiation in comparison with conventional OFDM.

In this paper, we investigate and compare the performance of single- and multi-carrier modulation schemes for indoor visible light communication (VLC). Particularly, the performances of single carrier frequency domain equalization (SCFDE), orthogonal frequency division multiplexing (OFDM) and on-off keying (OOK) with minimum mean square error equalization (MMSE) are analyzed in order to mitigate the effect of multipath distortion of the indoor optical channel where nonlinearity distortion of light emitting diode (LED) transfer function is taken into account. Our results indicate that SCFDE system, in contrast to OFDM system, does not suffer from high peak to average power ratio (PAPR) and can outperform OFDM and OOK systems. We further investigate the impact of LED bias point on the performance of OFDM systems and show that biasing LED with the optimum value can significantly enhance the performance of the system. Bit-interleaved coded modulation (BICM) is also considered for OFDM and SCFDE systems to further compensate signal degradation due to inter-symbol interference (ISI) and LED nonlinearity.

Low complexity blind detection in OFDM systems with phase noise

A three-dimensional (3D) orthogonal frequency division multiplexing (OFDM) system with peak-to-average power ratio (PAPR) reduction method for the wireless sensor networks (WSNs) is presented. The transmit power of wireless nodes in an ad hoc network is strictly limited. Thus, high PAPR of the 3D OFDM system is a possible drawback when it is considered as a physical layer transmission scheme for the WSNs. Here, we propose an improved partial transmit sequence (PTS) technique to reduce PAPR of the OFDM system with 3D modulation formats. In the proposed algorithm, the components of 3D signals are assigned to different subblocks using a diagonal rule (DR), increasing randomness of the signals in the disjoint subblocks forcibly. As a result, the proposed method reduces PAPR of the 3D OFDM system significantly without increase in computational complexity. Hence, the proposed algorithm makes the 3D OFDM system be a possible candidate for a physical layer transmission scheme in future WSNs.

Orthogonal frequency division multiplexing (OFDM) system has been widely used for the high speed digital communication area and it is very promising for the next generation communication standard because of high data rate capability. However, OFDM system has inherent serious problem of high peak-to-average power ratio (PAPR) that makes the OFDM signal be distorted in the nonlinear HPA (high power amplifier). In this paper, CI (carrier interferometry)-OFDM system is considered to overcome this problem and is newly analyzed in the selective fading and narrow-band interference channel. CI-OFDM system distributes each parallel data to all sub-carriers in differently phase-rotated form. So, PAPR becomes lowered and it shows the frequency diversity effects. BER (bit error rate) performance is analyzed in the selective fading and narrow-band interference environment. From the simulation results, it is confirmed that CI-OFDM system calms down the high PAPR problem and CI-OFDM system is more robust than the ordinary OFDM system in the selective fading and narrow-band interference channel.

In this paper, an integrated Orthogonal Frequency Division Multiplexing (OFDM) system is developed to improve Bit Error Rate (BER) performance of communication systems in order to meet the requirements of advanced communication systems like long term evaluation advanced (LTE –A). The proposed OFDM system consists of channel estimation using comb type pilot arrangement and convolution encoder with the best known Coding Bounds and Maximum A Posteriori (MAP) decoder. Using pilot symbols, the channel quality is estimated. The BER performance of OFDM system is improved using pilot carriers, channel estimation schemes and MAP decoder at the best known coding bounds. The system performance is analyzed with recursive systematic and non-systematic convolution codes, ML and MAP decoders. From the results, it is evident that the proposed OFDM system with channel estimation and MAP decoder at the best known coding bounds improves the system performance significantly.

Based on the symmetry characteristic of subcarriers in the traditional orthogonal frequency division multiplexing (OFDM) system, we propose a half symbol OFDM (HS-OFDM) modulation method to further improve the bandwidth efficiency of communication system, the method applicable to OFDM systems whose subcarriers are modulated by BPSK or PAM. The spectra overlap percentage of adjacent subcarriers is raised from 50% to 75%, and the bandwidth efficiency upper limit of the passband OFDM system is raised from 1Baud/Hz to 2Baud/Hz, which is twice the efficiency of the traditional OFDM system.

Conventional orthogonal frequency division multiplexing (OFDM) system utilizes cyclic prefix (CP) to remove the channel-induced inter-symbol interference (ISI) at the cost of lower spectral efficiency. In this paper, a generalized sidelobe canceller (GSC) based equalizer for ISI suppression is proposed for uplink multi-antenna OFDM systems without CP. Based on the block representation of the CP-free OFDM system, there is a natural formulation of the ISI suppression problem under the GSC framework. By further exploiting the signal and ISI signature matrix structures, a computationally efficient partially adaptive (PA) implementation of the GSC-based equalizer is proposed for complexity reduction. The proposed scheme can be extended for the design of a pre-equalizer, which pre-suppresses the ISI and realizes CP-free downlink transmission to ease the computational burden of the mobile unit (MU). Simulation results show that the proposed GSC-based solutions yield equalization performances almost identical to that obtained by the conventional CP-based OFDM systems and are highly resistant to the increase in channel delay spread.