Inter-carrier Interference Power Research Articles

Intelligent reflecting surface‐aided Doppler compensation for Low‐Earth orbit satellite networks: Joint power allocation and passive beamforming optimisation

AbstractDue to the reduction in costs of manufacture and launch of Low‐Earth orbit (LEO) satellites, LEO satellite communication (SATCOM) has become a promising solution to provide high data rates and low latency connectivity for future communications. However, due to the fast movement of LEO satellites, it has to face a large Doppler effect, leading to high inter‐carrier interference (ICI) power and severe received symbol error rate. To tackle this problem, a novel optimisation framework is proposed that boosts the achievable rate in LEO SATCOM networks by utilising passive beamforming of intelligent reflecting surface (IRS) to compensate for the Doppler effect. First, a carrier‐to‐interference‐noise ratio (CINR) was derived for each subcarrier and a joint optimisation problem of both power allocation is formulated to each subcarrier and passive beamforming of IRS. Moreover, a simultaneous iterative‐water‐filling‐algorithm (SIWFA) and semidefinite programing (SDP) are utilised, thereby striking a balance that minimises ICI power and maximises desired signal power. Numerical results demonstrate the superior achievable rate performance of the proposed IRS‐aided Doppler compensation for LEO SATCOM networks compared to benchmark schemes.

A TIME-MIRRORING (TM) SCHEME FOR ICI MITIGATION IN TIME-VARYING CHANNEL FOR DIGITAL VIDEO BROADCASTING (DVB) SYSTEMS

High mobility and high data speeds are now highly important requirements. The orthogonal frequency division multiplexing (OFDM) structure, which suffers from inter-carrier interference (ICI) in time-varying channels, is the basic core method in digital video broadcasting (DVB). Hence, the bit error rate (BER) is declined. In this paper, the time mirroring (TM) based on the symbol time compression (STC) technique for entire ICI suppression for DVB systems is proposed. In addition, some missing analysis for STC technique and ICI power analysis is introduced. Finally, the computational complexity of the proposed TM scheme is determined. The simulation results show that the proposed scheme reduces the ICI power by a significant amount when compared to the other traditional schemes. In comparison to traditional systems, the BER performance is greatly enhanced, and the eye diagram is entirely opened. In addition, as compared to traditional schemes, the proposed approach can handle normalized Doppler frequency by up to 40% and it has about the same computational complexity as the STC scheme but it is more efficient in terms of computational complexity than the traditional OFDM system.

Refined Bounds for Inter-Carrier Interference in OFDM Due to Time-Varying Channels and Phase Noise

Inter-carrier interference (ICI) due to time-variations of the channel and phase noise is a critical issue in current orthogonal frequency division multiplexing (OFDM) systems. For the discrete-time formulation of OFDM and the general case of partially occupied contiguous subcarriers, we present exact expressions for the average ICI power at each subcarrier. These lead to insightful lower and upper bounds for the bandwidth-averaged ICI power, which bring out the combined impact of Doppler spread and phase noise statistics. The bounds are tighter than those in the literature, which employ a tractable, but less accurate, continuous-time formulation and assume infinitely many subcarriers.

Impact of Subcarrier Allocation and User Mobility on the Uplink Performance of Multiuser Massive MIMO-OFDM Systems

This paper considers the uplink performance of a multi-user massive multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system with mobile users. Mobility brings two major problems to a MIMO-OFDM system: inter carrier interference (ICI) and channel aging. In practice, it is common to allot multiple contiguous subcarriers to a user as well as schedule multiple users on each subcarrier. Motivated by this, we consider a general subcarrier allocation scheme and derive expressions for the ICI power, uplink signal to interference plus noise ratio and the achievable uplink sum-rate, taking into account the ICI and the multi-user interference due to channel aging. We show that the system incurs a near-constant ICI power that depends linearly on the ratio of the number of users per subcarrier to the number of subcarriers per user, nearly independently of how the UEs distribute their power across the subcarriers. Further, we exploit the coherence bandwidth of the channel to reduce the length of the pilot sequences required for uplink channel estimation. We consider both zero-forcing and maximal-ratio combining at the receiver and compare the respective sum-rate performances. In either case, the proposed subcarrier allocation scheme leads to significantly higher sum-rates compared to previous work, owing to the near-constant ICI property as well as the reduced pilot overhead.

ICI and BEP analysis of hyperbolic FRFT based systems for satellite internet of things

In this paper, calculations of intercarrier interference (ICI) and bit error probability (BEP) of hyperbolic fractional Fourier transform (FRFT) based systems for the satellite internet of things applications, has been considered. Analysis of ICI power and BEP in Rician flat fading channels has been done, mathematically. Simulations approve that the systems based on the hyperbolic FRFT are resistant against carrier frequency offset in high-speed moving conditions. Also, in severely deep fade conditions, the hyperbolic FRFT based systems have an acceptable performance in the achieved bit error probability.

Pulse shaping methods for inter carrier interference reduction in OFDM system

The weakness of the orthogonal freuency division multiplexing (OFDM) system is susceptible to the existence of carrier frequency offset (CFO) which causes the emergence of inter carrier interference (ICI) which causes a degradation of performance OFDM systems. This study aims to apply the suggested rectangular (REC) pulse and improved sinc-power (ISP) pulse shaping methods on OFDM system and determines ICI reduction with the effects of CFO over flat fading Rayleigh channels. The performance of each pulse shaping method is evaluated and compared based on parameter ICI power vs. normalized frequency offset, signal to interference ratio (SIR) vs. normalized frequency offset and bit error rate (BER) vs. energy bit per noise (Eb/No). The simulation result in terms of BER vs. Eb/No indicated that REC and ISP pulse shaping has better performance dealing with ICI reduction compared to OFDM system no applied pulse shaping. In addition, the ISP is able to mitigate ICI better than REC.

Performance enhancement of generalized frequency division multiplexing with RF impairments compensation for efficient 5G wireless access

Fifth generation (5G) is expected to support diverse applications with reduced latency, reliability, high spectral efficiency, huge data rate and improved energy efficiency. Among the several waveforms, Generalized Frequency Division Multiplexing (GFDM) gained more attention and considered as one of the candidate waveform for 5G. Radio frequency (RF) impairments such as carrier frequency offset (CFO), intercarrier interference (ICI), out-of-band (OoB) emission, peak to average power ratio (PAPR) and in-phase (I) and quadrature phase (Q) imbalances greatly degrades the GFDM system performance. An efficient spectral shaping with advanced signal processing techniques is highly essential to counteract the RF impairments and to realize the robust physical layer for 5G applications. Hence a spectrally efficient precoder which comprises differential encoding followed by (1 + D) correlative coding with precise, low complex blind IQ imbalance compensation is proposed to preserve GFDM from RF impairments. Simulation results show that the proposed GFDM outperforms the conventional GFDM and OFDM in terms of bit error rate (BER), ICI power, PAPR and OoB radiations which enables the proposed GFDM is one of the solutions to meet the key requirements of 5G wireless access.

Intercarrier interference analysis for massive MIMO fractional Fourier transform‐OFDM systems over time‐varying channels

SummaryMassive multiple‐input multiple‐output orthogonal frequency division multiplexing (MIMO‐OFDM) system is an approach to increase data rate and spectral efficiency of 5G wireless communication systems. It's easy to analyze the performance of any system with the assumption of immobile users, but if the user is moving with varying velocity, then the communication between user and base station (BS) is very difficult to maintain. Under high mobility, rapidly fading, doubly dispersive, and nonstationary environment, the conventional system fails to respond and leads to the problem of intercarrier interference (ICI). To overcome these problems, fractional Fourier transform (FrFT) has been used in place of Fourier transform (FT) to increase the correlation coefficient, to mitigate effect of ICI, and to improve bit error rate. In this paper, novel formulae for correlation coefficient, average power of ICI, and closed form bit error expression have been derived for the proposed system by considering fast‐fading model and imperfect channel state information. Finally, the comparison of both the systems conventional and proposed proved that the proposed system has improved bit error rate by 40% and intercarrier interference cancelation by 70%.

ICI analysis of hyperbolic FRFT‐FBMC based on optimal order of transform for Internet of Things applications

This study aimed at analysing intercarrier interference (ICI) of filter bank multicarrier signals which are made by hyperbolic fractional Fourier transform, depend on optimum order of transform for the Internet of Things applications. Calculation of ICI power based on joint time and frequency selective fading channel has been derived. The upper bound of ICI power has been found as an applicable equation for the system design, which has been mathematically calculated. In order to minimise the amount of ICI power which is relative to the order of transform, the optimum order of transform with almost accurate formula has been computed. Simulations demonstrate the proposed signal is so robust to the frequency offset and by selecting the optimum order of transform, the acceptable amount of ICI is generated.

ICI Mitigation in OFDM System Using Negative Peak Augmented Raised Cosine Power Pulse

Orthogonal frequency division multiplexing (OFDM) is a digital modulation technique generally which is utilized in modern wireless applications to support high data rates. The carrier frequency offset (CFO), which models the frequency discrepancy between the transmitter and receiver oscillators, gives rise to inter carrier interference (ICI), along with destroying the orthogonality between the OFDM subcarriers. Thus the alleviation of an ICI power is extremely important in an OFDM system. Pulse shaping functions is a standout amongst the most generally utilized solutions with the end goal of lessening the ICI power. In this paper, an Adaptive pulse shaping filter based on the concept of Negative Peak Augmentation is proposed to mitigate the ICI and to enhance the performance of the OFDM system. The simulation results demonstrate the impact of the proposed pulse shaping function and performance investigation in terms of SIR, SNR and BER is carried out to show the superiority of the proposed pulse shaping function.

Throughput Analysis of Wavelet OFDM in Broadband Power Line Communications

Windowed orthogonal frequency-division multiplexing (OFDM) and wavelet OFDM have been proposed as multicarrier techniques for broadband communications over the power line network by the standard IEEE 1901. The windowed OFDM has been extensively researched and employed in different fields of communication, while the wavelet OFDM has been recently recommended for the first time in a standard. This paper is aimed to show that the wavelet OFDM, which basically is an extended lapped transform-based multicarrier modulation (ELT-MCM), is a viable and attractive alternative for data transmission in hostile scenarios, such as in-home power line communications (PLC). To this end, we obtain theoretical expressions for ELT-MCM of: 1) the desired signal power; 2) the inter-symbol interference power; 3) the inter-carrier interference power; and 4) the noise power at the receiver side. These expressions are used to derive the throughput. This paper includes several computer simulations that show that ELT-MCM is an efficient alternative to improve data rates in the PLC systems.

Low ICI Symbol Boundary Alignment for 5G Numerology Design

Symbol boundary alignment, with respect to waveform selection, has an important impact on the numerology design for fifth-generation mobile applications. The current symbol boundary alignment, along with orthogonal frequency division multiplexing (OFDM) waveform, strongly suffers from intercarrier interference (ICI) especially in unmanned aerial vehicles (UAV) communications. This happens when the mobility causes Doppler effect which results in loss of orthogonality in OFDM. The available solutions for overcoming the ICI problem suffer from high complexity, low spectral efficiency, and incompatibility with the current radio access technologies. This paper presents a novel symbol boundary alignment, called Low ICI Symbol (LICIS) boundary alignment numerology, to avoid the disadvantages of the available solutions. LICIS utilizes large subcarrier-spacing to reduce the ICI power (e.g., around 5-dB ICI power reduction with subcarrier spacing of 30 kHz in high-speed UAV communications). Moreover, LICIS is based on the same reference clock as local thermal equilibrium (LTE) which guarantees its compatibility with the current LTE numerology. In addition, this approach places only one guard-interval at the end of a sequence of OFDM symbols and creates a subslot. This leads to less overhead and preserves the spectral efficiency. Furthermore, a pre-fast Fourier transform (FFT) multipath channel equalizer is considered for removing the intersymbol interference between the OFDM symbols occurring within the subslot. Only one additional FFT and IFFT operations are required for the equalizer which creates an acceptable complexity increment compared to the complexity of other available solutions. Numerical and analytical evaluations show the superior performance of the proposed technique in terms of reliability and spectral efficiency

Improved Nyquist-I Pulses to Enhance the Performance of OFDM-Based Systems

Pulse shaping is used in orthogonal frequency division multiplexing (OFDM) based systems to reduce inter-carrier interference (ICI) power and peak-to-average power ratio (PAPR), which are considered the major weaknesses in OFDM-based systems. A novel family of Nyquist-I pulses called sinc exponential pulse (SEP) is proposed, and it is characterized by two new design parameters that provide extra degrees of freedom for a certain roll-off factor, ź. SEP effectively decreases the relative magnitude of the two largest side lobes of the SEP frequency function, which minimizes the ICI power and reduces the PAPR in OFDM systems. Furthermore, the SEP possesses a broader main lobe, which provides sufficient improvement in bit-error-rate (BER). The behavior of the SEP is examined in the time and frequency domain by tuning its design parameters to obtain the sub-optimum SEP. Theoretical and simulation results show that the sub-optimum SEP performs better than other existing pulses in terms of ICI power, signal-to-interference ratio (SIR) power, BER, and PAPR in OFDM-based systems.

Analysis of Uplink ICI and IBI in Heterogeneous Cellular Networks With Multiple Macrocells

This letter analyzes the effects of inter-carrier interference (ICI) and inter-block interference (IBI) on uplink reception of small cells (SCs) in orthogonal frequency division multiple access heterogeneous cellular networks. Tight upper and lower bounds of the power of ICI and IBI plus co-channel interference from nearby SCs, average rate, and symbol error rate (SER) per SC subcarrier are derived. Results show that the theoretical analysis is close to simulation. Importantly, the average rate and SER are seriously degraded by the interference at high signal-to-noise ratio.

Near-Optimal Angle of Transform in FrFT-OFDM Systems Based on ICI Analysis

In this paper, we establish an analytical framework to derive a closed form for a close approximation of the optimal angle of transform in fractional-Fourier-transform orthogonal-frequency-division-multiplexing (FrFT-OFDM) systems. In this framework, we derive a tight upper bound for the intercarrier interference (ICI) power and use this bound instead of the exact ICI power to obtain the near-optimal angle of transform. We also analyze the sensitivity of the FrFT-OFDM systems to the angle of transform. In other words, we derive the increase in the ICI power when we exploit a nonoptimal angle of transform due to channel estimation errors. We show that once the error in the channel state information (CSI) is reasonable, the ICI power increase is tolerable. For instance, for a two-path channel, if the error in estimating the slope of the channel spread function in the delay–Doppler plane is less than 20%, the ICI power increase is smaller than 0.1 dB.

Suppressing the effect of ICI power using dual sinc pulses in OFDM-based systems

Sensitivity to frequency offset in orthogonal frequency division multiplexing (OFDM)-based systems allow unwanted interference among the subcarriers, which results in intercarrier interference (ICI). A novel family of Nyquist-I pulses, named dual sinc pulses (DSPs), is proposed herein having three new design parameters, giving additional degrees of freedom to minimize ICI power in OFDM-based systems. Several Nyquist-I pulses have been studied and implemented to deal with the problem of frequency offset in OFDM-based systems. In this paper, we investigate the performance of DSPs in terms of ICI power, signal-to-interference power ratio (SIR), and bit error rate (BER) in OFDM-based systems. The frequency responses of the DSPs are studied by adjusting the values of the new design parameters. Theoretical and simulation results presented herein show that DSPs outperform other existing pulses in OFDM-based systems, in terms of ICI power, SIR power, and BER.

Proposal of DCS-OFDM-PON upstream transmission with intensity modulator and collective self-coherent detection

Abstract We introduce digital coherent superposition (DCS) into optical access network and propose a DCS-OFDM-PON upstream transmission scheme using intensity modulator and collective self-coherent detection. The generated OFDM signal is real based on Hermitian symmetry, which can be used to estimate the common phase error (CPE) by complex conjugate subcarrier pairs without any pilots. In simulation, we transmit an aggregated 40 Gb/s optical OFDM signal from two ONUs. The transmission performance with DCS is slightly better after 25 km transmission without relative transmission time delay. The fiber distance for different ONUs to RN are not same in general and there is relative transmission time delay between ONUs, which causes inter-carrier-interference (ICI) power increasing and degrades the transmission performance. The DCS can mitigate the ICI power and the DCS-OFDM-PON upstream transmission outperforms the conventional OFDM-PON. The CPE estimation is by using two pairs of complex conjugate subcarriers without redundancy. The power variation can be 9 dB in DCS-OFDM-PON, which is enough to tolerate several kilometers fiber length difference between the ONUs.

Intercarrier Interference Analysis for High-Speed Trains Based on Broadband Channel Measurements

This letter presents an analysis of intercarrier interference (ICI) in high-speed trains. The ICI is caused by the motion of the receiver together with the carrier frequency offset (CFO). It results in a degradation of the reliability of the OFDM transmission. The analysis is based on a channel sounding measurement campaign for cellular broadband wireless communications with high-speed trains that was carried out in the context of the CORRIDOR project. The considered scenario corresponds to a railway deployed network, where the base station is located directly next to the railway line. We present the ICI power obtained with the measurement campaign and some theoretical results for a simple channel model that captures the main effects observed in the measurements.

Family of Nyquist-I Pulses to Enhance Orthogonal Frequency Division Multiplexing System Performance

ABSTRACTA family of Nyquist-I pulses called sinc parametric linear combination pulse (SPLCP) is proposed. It is characterized by two novel design parameters that provide additional degrees of freedom to minimize the intercarrier interference (ICI) power due to frequency offset. Moreover, it reduces the high peak-to-average power ratio (PAPR) value in orthogonal frequency division multiplexing (OFDM) systems. Several Nyquist-I pulses were recently proposed to address the subject of high sensitivity to frequency offset and high PAPR in OFDM-based transmissions. In this paper, we investigate the performance of SPLCP in terms of ICI power, signal-to-interference ratio (SIR) power, bit error rate (BER), and PAPR. We additionally examine the behaviour of SPLCP with new design parameters for a certain roll-off factor, α. We compare the performance of SPLCP with other well-known pulses. Theoretical and simulation results show that the proposed SPLCP outperforms other existing pulses in terms of ICI power, SIR power, BER, and PAPR.

Enhanced performance of phase-conjugated OFDM subcarriers using digital coherent superposition

We have recently demonstrated the improved phase noise tolerance in coherent optical OFDM by digital coherent superposition of optical OFDM subcarriers, which are phase-conjugated pairs with Hermitian symmetry. In this approach, we realized DCS of OFDM subcarriers in single polarization (or channel), denoted as SP-DCS-OFDM. In this paper, we show that another approach is in dual polarizations, or DP-DCS-OFDM. According to the concept of phase-conjugated twin wave, both approaches can also mitigate the fiber nonlinearity to the first order. We prove that both approaches can cancel the inter-carrier interference (ICI) due to phase noise to the second order, and we derive the reduced ICI power to the fourth order using the Wiener phase noise model. In simulation, we show the enhanced tolerance to the laser phase noise and fiber nonlinearity.