4,444 research outputs found
Waveform Design for 5G and Beyond
5G is envisioned to improve major key performance indicators (KPIs), such as
peak data rate, spectral efficiency, power consumption, complexity, connection
density, latency, and mobility. This chapter aims to provide a complete picture
of the ongoing 5G waveform discussions and overviews the major candidates. It
provides a brief description of the waveform and reveals the 5G use cases and
waveform design requirements. The chapter presents the main features of cyclic
prefix-orthogonal frequency-division multiplexing (CP-OFDM) that is deployed in
4G LTE systems. CP-OFDM is the baseline of the 5G waveform discussions since
the performance of a new waveform is usually compared with it. The chapter
examines the essential characteristics of the major waveform candidates along
with the related advantages and disadvantages. It summarizes and compares the
key features of different waveforms.Comment: 22 pages, 21 figures, 2 tables; accepted version (The URL for the
final version:
https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119333142.ch2
A DHT-Based Multicarrier Modulation System with Pairwise ML Detection
This paper presents a complex-valued discrete multicarrier modulation (MCM) system based on the real-valued discrete Hartley transform (DHT) and its inverse (IDHT). Unlike the conventional discrete Fourier transform (DFT), the DHT cannot diagonalize multipath fading channels due to its inherent properties, and this results in mutual interference between subcarriers of the same mirror-symmetrical pair. We explore this interference pattern in order to seek an optimal solution to utilize channel diversity for enhancing the bit error rate (BER) performance of the system. It is shown that the optimal channel diversity gain can be achieved via pairwise maximum likelihood (ML) detection, taking into account not only the subcarrier's own channel quality but also the channel state information of its mirror-symmetrical peer. Performance analysis indicates that DHT-based MCM can mitigate fast fading effects by averaging channel power gains of each mirror-symmetrical pair of subcarriers. Simulation results show that the proposed scheme has a substantial improvement in BER over the conventional DFT-based MCM system
Mixed numerologies interference analysis and inter-numerology interference cancellation for windowed OFDM systems
Extremely diverse service requirements are one of the critical challenges for the upcoming fifth-generation (5G) radio access technologies. As a solution, mixed numerologies transmission is proposed as a new radio air interface by assigning different numerologies to different subbands. However, coexistence of multiple numerologies induces the inter-numerology interference (INI), which deteriorates the system performance. In this paper, a theoretical model for INI is established for windowed orthogonal frequency division multiplexing (W-OFDM) systems. The analytical expression of the INI power is derived as a function of the channel frequency response of interfering subcarrier, the spectral distance separating the aggressor and the victim subcarrier, and the overlapping windows generated by the interferer's transmitter windows and the victim's receiver window. Based on the derived INI power expression, a novel INI cancellation scheme is proposed by dividing the INI into a dominant deterministic part and an equivalent noise part. A soft-output ordered successive interference cancellation (OSIC) algorithm is proposed to cancel the dominant interference, and the residual interference power is utilized as effective noise variance for the calculation of log-likelihood ratios (LLRs) for bits. Numerical analysis shows that the INI theoretical model matches the simulated results, and the proposed interference cancellation algorithm effectively mitigates the INI and outperforms the state-of-the-art W-OFDM receiver algorithms
Performance analysis and optimization of DCT-based multicarrier system on frequency-selective fading channels
Regarded as one of the most promising transmission techniques for future wireless communications, the discrete cosine transform (DCT) based multicarrier modulation (MCM) system employs cosine basis as orthogonal functions for real-modulated symbols multiplexing, by which the minimum orthogonal frequency spacing can be reduced by half compared to discrete Fourier transform (DFT) based one. With a time-reversed pre-filter employed at the front of the receiver, interference-free one-tap equalization is achievable for the DCT-based systems. However, due to the correlated pre-filtering operation in time domain, the signal-to-noise ratio (SNR) is enhanced as a result at the output. This leads to reformulated detection criterion to compensate for such filtering effect, rendering minimum-mean-square-error (MMSE) and maximum likelihood (ML) detections applicable to the DCT-based multicarrier system. In this paper, following on the pre-filtering based DCT-MCM model that build in the literature work, we extend the overall system by considering both transceiver perfections and imperfections, where frequency offset, time offset and insufficient guard sequence are included. In the presence of those imperfection errors, the DCT-MCM systems are analysed in terms of desired signal power, inter-carrier interference (ICI) and inter-symbol interference (ISI). Thereafter, new detection algorithms based on zero forcing (ZF) iterative results are proposed to mitigate the imperfection effect. Numerical results show that the theoretical analysis match the simulation results, and the proposed iterative detection algorithms are able to improve the overall system performance significantly
Interference Localization for Uplink OFDMA Systems in Presence of CFOs
Multiple carrier frequency offsets (CFOs) present in the uplink of orthogonal
frequency division multiple access (OFDMA) systems adversely affect subcarrier
orthogonality and impose a serious performance loss. In this paper, we propose
the application of time domain receiver windowing to concentrate the leakage
caused by CFOs to a few adjacent subcarriers with almost no additional
computational complexity. This allows us to approximate the interference matrix
with a quasi-banded matrix by neglecting small elements outside a certain band
which enables robust and computationally efficient signal detection. The
proposed CFO compensation technique is applicable to all types of subcarrier
assignment techniques. Simulation results show that the quasi-banded
approximation of the interference matrix is accurate enough to provide almost
the same bit error rate performance as that of the optimal solution. The
excellent performance of our proposed method is also proven through running an
experiment using our FPGA-based system setup.Comment: Accepted in IEEE WCNC 201
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