Insufficient Guard Interval Research Articles

Optimal Filter Length and Zero Padding Length Design for Universal Filtered Multi-Carrier (UFMC) System

Universal filtered multi-carrier (UFMC) systems offer a flexibility of filtering arbitrary number of subcarriers to suppress out of band (OoB) emission, while keeping the orthogonality between subcarriers and robustness to transceiver imperfections. Such properties enable it as a promising candidate waveform for Internet of Things (IoT) communications. However, subband filtering may affect system performance and capacity in a number of ways. In this paper, we first propose the conditions for interference-free one-tap equalization and corresponding signal model in the frequency domain for UFMC system. The impact of subband filtering on the system performance is analyzed in terms of average signal-to-noise ratio (SNR), capacity and bit error rate (BER) and compared with the orthogonal frequency division multiplexing (OFDM) system. This is followed by filter length selection strategies to provide guidelines for system design. Next, by taking carrier frequency offset (CFO), timing offset (TO), insufficient guard interval between symbols and filter tail cutting (TC) into consideration, an analytical system model is established. In addition, a set of optimization criteria in terms of filter length and guard interval/filter TC length subject to various constraints is formulated to maximize the system capacity. Numerical results show that the analytical and corresponding optimal approaches match the simulation results, and the proposed equalization algorithms can significantly improve the BER performance.

Filtered OFDM Systems, Algorithms, and Performance Analysis for 5G and Beyond

Filtered orthogonal frequency division multiplexing (F-OFDM) system is a promising waveform for 5G and beyond to enable the multi-service system and spectrum efficient network slicing. However, the performance for F-OFDM systems has not been systematically analyzed in the literature. In this paper, we first establish a mathematical model for an F-OFDM system and derive the conditions to achieve the interference-free one-tap channel equalization. In the practical cases (e.g., insufficient guard interval, asynchronous transmission, and so on), the analytical expressions for inter-symbol interference, inter-carrier interference, and adjacent-carrier interference are derived, where the last term is considered as one of the key factors for asynchronous transmissions. Based on the framework, an optimal power compensation matrix is derived to make all of the subcarriers having the same ergodic performance. Another key contribution of this paper is that we propose a multi-rate F-OFDM system to enable low-complexity low-cost communication scenarios, such as narrow-band Internet of Things, at the cost of generating inter-subband interference (ISubBI). Low computational complexity algorithms are proposed to cancel the ISubBI. The result shows that the derived analytical expressions match the simulation results, and the proposed ISubBI cancelation algorithms can significantly save the original F-OFDM complexity (up to 100 times) without significant performance loss.

Orthogonal Chirp Division Multiplexing

Chirp waveform plays a significant role in radar and communication systems for its ability of pulse compression and spread spectrum. This paper presents a principle of multiplexing a bank of orthogonal chirps, termed orthogonal chirp-division multiplexing (OCDM) for high-speed communication. As Fourier transform is the kernel of orthogonal frequency-division multiplexing (OFDM), which achieves the maximum spectral efficiency (SE) of frequency-division multiplexing, Fresnel transform underlies the proposed OCDM system, which achieves the maximum SE of chirp spread spectrum. By using discrete Fresnel transform, digital implementation of OCDM is introduced. According to the properties of Fresnel transform, the transmission of OCDM signal in linear time-invariant channel is studied. Efficient digital signal processing is proposed for channel dispersion compensation. The implementation of the OCDM system is discussed with the emphasis on its compatibility to the OFDM system; it is shown that it can be easily integrated into the existing OFDM systems. Finally, the simulations are provided to validate the feasibility of the proposed OCDM. It is shown that the OCDM system can efficiently exploit multipath diversity and thus outperforms the OFDM, and that it is more resilient against the interference due to insufficient guard interval than single-carrier frequency-domain equalization.

A single‐input multiple‐output transceiver architecture to ‘Blindly’ null unknown interference for block‐based single‐carrier transmission with an insufficient guard interval

This paper proposes a new way to realize a maximum-SINR beamformer for block-based cyclically prefixed single-carrier modulation. Here, SINR stands for ‘signal to interference plus noise’ ratio, at the beamformer output. This spatial beamformer will ‘blindly’ pass the signal-of-interest; and this beamformer will ‘blindly’ null any co-channel interference, any adjacent-channel interference, any out-of-system interference, and/or any spatio-temporally correlated additive noises. This proposed scheme is made possible by zero-padding an insufficient guard interval, which may be shorter than the temporally spreading channel's order. The proposed receiver will first undergo frequency-domain equalization, to ‘clear’ the data of any signal-of-interest's energy in the zero-padded guard interval, in order to facilitate the estimation of the interference and noise. This interference-and-noise estimate will then be eigen-subtracted from the signal-and-interference-and-noise dataset by the aforementioned ‘blind’ beamformer in the spatial dimension.

基于DCO OFDM的帧内信号时域调整技术研究

In conventional OFDM system,an OFDM symbol will exceeds its guard interval(GI)and seriously interfere with its neighboring symbols when channel characteristic is unsatisfactory.This will cause inter-symbol interference(ISI)and inter-carrier interference(ICI).In high-speed incoherent optical OFDM communication system,a novel time domain reshuffling method for mitigating ISI and ICI based on DCO-OFDM was proposed.This scheme utilized the properties of Fourier Transform.By simple preprocessing subcarrier channels in frequncy domain,sampling sequence of a DCO-OFDM symbol in time domain was exchanged interactively.Thus signal energy was centralized in the central part of a symbol.Numerical simulation indicates that ISI and ICI is significantly reduced and system BER performance is improved effectively due to signal surpassing the GI.In optical OFDM systems with insufficient GI for the popurse of higher information transmission efficiency,the reshuffling scheme also has a great value.

Application of 3GPP LTE and IEEE 802.11p Systems to Ship Ad-Hoc Network with the Existence of ISI

In order to provide high data rate and real time services under maritime environment, link-level performance of ship ad-hoc network (SANET) based on 3GPP LTE and IEEE 802.11p (WAVE) specifications are investigated and discussed in this paper. The measured maritime channel, whose delay spread is longer than the length of guard interval (GI) of both 3GPP LTE and IEEE 802.11p specifications, is adopted for the link-level simulations. For the purpose of eliminating inter-symbol interference (ISI) due to insufficient GI length, double antenna pattern (DAP) scheme and advanced time-domain decision-feedback equalizer (DFE) are proposed for LTE and WAVE systems, respectively. The proposed DFE removes the ISI in a same manner as the residual inter-symbol interference cancellation (RISIC) algorithm, but the inter-carrier interference (ICI) is reduced via cyclicity removal instead of cyclicity restoration used in the RISIC algorithm. Compared with existing schemes, our proposed DFE is a robust technique to overcome the severe ISI channel which has a comparatively large delay spread. Based on simulation results, not only comparisons between systems are discussed, but also some reformative suggestions are given.

Precoder/two-stage equaliser for block-based single-carrier transmission with insufficient guard interval

Proposed is a zero-inserting precoder and a two-stage linear equaliser, to shorten the guard interval in block-based single-carrier modulation. The first-stage equaliser consists of a linear single-tapper-subcarrier frequency-domain equaliser. The second-stage equaliser maximises the SINR, in the time-domain, based on the interference-plus-noise estimated from the zero-padded sub-intervals of the single-carrier modulation. This proposed scheme is applicable even without cyclic prefixing.

Linear prediction based semiblind channel estimation for multiuser OFDM with insufficient guard interval

To meet the demand of high data rate transmissions for multimedia wireless communications, orthogonal frequency division multiplexing (OFDM) systems in conjunction with multiple-input multiple-output (MIMO) signal processing have been considered one of the central techniques in advanced wireless communications. In the paper, two semiblind channel estimation algorithms are proposed for the uplink multiuser OFDM systems with insufficient guard interval, in contrast to sufficient guard interval assumed in most of the prior works. A zero-padding OFDM system, which zero-pads rather than cyclicly prefixing each block, is considered in this paper. By utilizing the relation between the linear prediction error filters (LPEFs) of the received signal with multiple prediction orders and the transmitted data sequence, the first proposed algorithm, namely the multistage LP (MLP) based algorithm, can estimate the MIMO channel coefficients, with only a single pilot OFDM block used. To reduce the sensitivity of the proposed algorithms to the channel order overestimation, it is proposed to implement the LPEFs with a QR-decomposition based approach. This QRdecomposition based approach alternatively computes the LPEFs without direct inversion of the received signal correlation matrix, thus exhibiting robustness against channel order overestimation. Some simulation results are presented to demonstrate the effectiveness and robustness of the proposed algorithms.

Combination of interference cancellation with channel estimation for OFDM transmission over mobile radio channels

AbstractThis paper proposes a new method, which combines interference cancellation with channel estimation for an orthogonal frequency division multiplexing (OFDM) system in the case of insufficient guard interval (GI) length. To avoid the problem of causing additional errors of conventional cancellers in the presence of strong additive noise, the proposed cancellation scheme uses the channel state information (CSI) and the so‐called remodulation technique to reproduce the interference distortions. Then, these distortions in both the received pilot symbols and the data symbols are iteratively cancelled. Consequently, the channel estimation as well as the data equalisation performances are iteratively enhanced. In the range of high signal‐to‐noise ratio (SNR), the proposed scheme improves significantly the performance of the system. It does not cause any additional errors to the received signal, when the system suffers from very low SNR. In comparison to the case of sufficient GI length, the required SNR can be reduced by 0.5 dB to achieve the same symbol error rate (SER). Moreover, the spectral efficiency of the system can be increased, because the GI length is allowed to be insufficient. The proposed method is applicable to future OFDM‐based wireless local area networks (WLANs). Copyright © 2007 John & Sons, Ltd.

Per-Tone Equalization for Single Carrier Block Transmission with Insufficient Cyclic Prefix

This paper proposes per-tone equalization methods for single carrier block transmission with cyclic prefix (SC-CP) systems. Minimum mean-square-error (MMSE) based optimum weights of the per-tone equalizers are derived for SISO (single-input single-output), SIMO (single-input multiple-output), and MIMO (multiple-input multiple-output) SC-CP systems. Unlike conventional frequency domain equalization methods, where discrete Fourier transform (DFT) is employed, the per-tone equalizers utilize sliding DFT, which makes it possible to achieve good performance even when the length of the guard interval is shorter than the channel order. Computer simulation results show that the proposed equalizers can significantly improve the bit error rate (BER) performance of the SISO, SIMO, and MIMO SC-CP systems with the insufficient guard interval.

Parameter Acquisition Techniques for Multiuser Detection with ISI Cancellation in a Quasi-Synchronous Reverse Link MC-CDMA System

In a quasi-synchronous reverse link multicarrier code division multiple access system, the signal detection is vulnerable to the interference due to the insufficient guard interval. A multiuser detection with intersymbol interference cancellation is a potential solution to overcome this problem. In this paper, we proposes a parameter acquisition technique based on a specially designed training sequence for the receiver. The concerned parameters are the transformed signature sequences and the ISI generation sequences. We analyze a criterion for the training sequences to achieve the minimum mean square error and propose the systematic generation of the optimum training sequences. We also propose the noise variance estimator for providing information about noise variance to some classes of multiuser detection. Simulation results prove relevant benefits of the proposed techniques and give useful insights into the system designs.

Zero-Forcing Frequency-Domain Equalization for Generalized DMT Transceivers with Insufficient Guard Interval

We propose a zero-forcing frequency domain block equalizer for discrete multitone (DMT) systems with a guard interval of insufficient length. In addition to the insufficient guard interval in the time domain, the equalizer takes advantage of frequency domain redundancy in the form of subcarriers that do not transmit any data. After deriving sufficient conditions for zero-forcing equalization, that is, complete removal of intersymbol and intercarrier interference, we calculate the noise enhancement of the equalizer by evaluating the signal-to-noise ratio (SNR) for each subcarrier. The SNRs are used by an adaptive loading algorithm. It decides how many bits are assigned to each subcarrier in order to achieve a maximum data rate at a fixed error probability. We show that redundancy in the time domain can be traded off for redundancy in the frequency domain resulting in a transceiver with a lower system latency time. The derived equalizer matrix is sparse, thus resulting in a low computational complexity.