110 research outputs found
On the Detection of CE-OFDM Signals
In this letter, we study the optimum performance
of constant envelope orthogonal frequency division multiplexing
(CE-OFDM) signals in both ideal additive white Gaussian noise
channels and frequency-selective channels, and we compare it to
the performance of conventional CE-OFDM receivers based on
a phase detector. It is shown that the phase detector can achieve
optimum performance, but only in scenarios where the power
efficiency is very low. For this reason, the use of CE-OFDM
schemes in power-constrained scenarios may demand other type
of receivers, such as optimum-based receiver
Quantifying Potential Energy Efficiency Gain in Green Cellular Wireless Networks
Conventional cellular wireless networks were designed with the purpose of
providing high throughput for the user and high capacity for the service
provider, without any provisions of energy efficiency. As a result, these
networks have an enormous Carbon footprint. In this paper, we describe the
sources of the inefficiencies in such networks. First we present results of the
studies on how much Carbon footprint such networks generate. We also discuss
how much more mobile traffic is expected to increase so that this Carbon
footprint will even increase tremendously more. We then discuss specific
sources of inefficiency and potential sources of improvement at the physical
layer as well as at higher layers of the communication protocol hierarchy. In
particular, considering that most of the energy inefficiency in cellular
wireless networks is at the base stations, we discuss multi-tier networks and
point to the potential of exploiting mobility patterns in order to use base
station energy judiciously. We then investigate potential methods to reduce
this inefficiency and quantify their individual contributions. By a
consideration of the combination of all potential gains, we conclude that an
improvement in energy consumption in cellular wireless networks by two orders
of magnitude, or even more, is possible.Comment: arXiv admin note: text overlap with arXiv:1210.843
Near-Optimal Detection of CE-OFDM Signals with High Power Efficiency via GAMP-based Receivers
Proceeding of: 2022 IEEE Globecom Workshops (GC Wkshps), Rio de Janeiro, Brazil, 4-8 December 2022A quasi-optimum receiver based on the generalized approximate message passing (GAMP) concept is proposed for constant envelope orthogonal frequency division multiplexing (CE-OFDM) signals. Large modulation index results in large power efficiency for CE-OFDM, but the phase modulator introduces nonlinear distortion effects, precluding good performance for a simple phase detector. Our simulation results show that the GAMP receiver can achieve quasi-optimum performance and it can outperform the linear OFDM and CE-OFDM with phase detectors, for both additive white Gaussian noise (AWGN) and frequency selective channels.This work received funding from the European Union (EU) Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie ETN TeamUp5G, grant agreement No. 813391, the Spanish National Project IRENE-EARTH (PID2020-115323RB-C33) (MINECO/AEI/FEDER, UE) and Portuguese FCT Instituto de Telecomunicaçoes project UIDB/50008/2020
Theoretical Analysis and Performance Comparison of multi-carrier Waveforms for 5G Wireless Applications
5G wireless technology is a new wireless communication system that must meet different complementary needs: high data rate for mobile services, low energy consumption and long-range for connected objects, low latency to ensure real-time communication for critical applications and high spectral efficiency to improve the overall system capacity. The waveforms and associated signals processing, present a real challenge in the implementation for each generation of wireless communication networks. This paper presents the diverse waveforms candidate for 5G systems, including: CE-OFDM (Constant Envelope OFDM), Filter-Bank Multi Carrier (FBMC), Universal Filtered Multi-Carrier (UFMC) and Filtered OFDM (F-OFDM). In this work, simulations are carried out in order to compare the performance of the OFDM, CE-OFDM, F-OFDM, UFMC and FBMC in terms of Power spectral density (PSD) and of Bit Error Rate (BER). It has been demonstrated that (CE-OFDM), constitutes a more efficient solution in terms of energy consumption than OFDM signal. Moreover, the (F-OFDM), (UFMC) and (FBMC) could constitute a more efficient solution in terms of power spectral density, spectral efficiency and bit error rates. In fact, CE-OFDM reduces the Peak to Average Power Ratio (PAPR) associated with OFDM system, FBMC is a method of improving out-of-band (OOB) characteristic by filtering each subcarrier and resisting the inter-carrier interference (ICI). While, UFMC offers a high spectral efficiency compared to OFDM
Phase-domain Injected Training for Channel Estimation in Constant Envelope OFDM
Constant envelope orthogonal frequency division
multiplexing (CE-OFDM) is a multi-carrier waveform with 0 dB
peak-to-average power ratio (PAPR). This property enables the
exploitation of multi-carrier waveforms with non-linear power
amplifiers, avoiding the undesirable clipping effects. However,
the existing channel estimation techniques designed for OFDM
cannot be reused, since the use of a phase modulator makes
CE-OFDM a non-linear waveform. Previous works assumed that
the channel estimation process relies on the transmission of
preambles, and the data symbols are equalized using a frequency
domain equalizer (FDE). To avoid the overhead induced by
preambles, a phase-domain injected training (PIT) is proposed,
where the pilot sequence is embedded in the phase dimension of
the data symbols. This novel approach does not waste time and/or
frequency resources as in preamble-based schemes. Moreover, it
does not require additional power for the training. The received
symbols are averaged with a dual procedure, and owing to
the particular structure of CE-OFDM, the channel estimates
are recovered. Also, the analytical expression of the channel
estimation mean squared error (MSE) is derived. Finally, several
numerical results illustrate the performance of the proposal,
showing that the MSE, bit error rate (BER) and achievable rate
are improved, as compared to the existing works.This work was supported by the Spanish National Project IRENE-EARTH under Grant PID2020-115323RBC33/AEI/10.13039/501100011033. The work of Andrea M. Tonello was supported in part by the Chair of Excellence Program of the Universidad Carlos III de Madrid.Publicad
Constant Envelope DCT- and FFT- based Multicarrier Systems
Discrete Cosine Transform (DCT)- and Fast Fourier Transform (FFT)- based Orthogonal Frequency Division Multiplexing (OFDM) systems with a variety of angle modulations are considered for data transmission. These modulations are used with the purpose of achieving Constant Envelope (CE) transmitted signals, for superior power efficiency with nonlinear High Power Amplifier (HPA), typically used at the transmitter in OFDM systems. Specifically, four angle modulations are considered: i) Phase Modulation (PM); ii) Frequency Modulation (FM); iii) Continuous Phase Modulation (CPM); and iv) Continuous Phase Chirp Modulation (CPCM). Descriptions of DCT- and FFT- based OFDM systems with M-ary Pulse Amplitude Modulation (MPAM) mapper, with these modulations, are given and expressions for transmitted signals are developed. The detection of these signals in Additive White Gaussian Noise (AWGN) and multipath fading channels is addressed. The receiver structure consists of arctangent demodulator followed by the optimum OFDM receiver for memoryless PM and FM modulations. However, for CPM and CPCM modulations that have inherent memory, arctangent demodulator followed by correction with oversampling technique is used prior to the optimum OFDM receiver. Closed-form expressions for Bit Error Rate (BER) have been derived and are function of: i) Signal-to-Noise Ratio, (Eb/N0); ii) Modulation parameters; iii) Number of amplitude levels of M-PAM mapper; and iv) parameters of multipath fading environment. It is shown that, in general, BER performance of CE-DCT-OFDM system is superior compared to that of conventional DCT-OFDM system, when the effect of HPA in the system is taken into account. Also, it is observed that CE-DCT-OFDM system outperforms CE-FFT-OFDM system by nearly 3 dB. The DCT- and FFT- OFDM systems with CPM and CPCM modulations are superior in BER performance compared to PM and FM modulations in these systems. The use of CPCM in OFDM systems can provide attractive trade off between bandwidth and BER performance. The performance of CE-DCT-OFDM and CE-FFT-OFDM systems over Rayleigh and Rician frequency non-selective slowly-varying fading channels are illustrated as a function of channel parameters and the penalty in SNR that must be paid as consequence of the fading is determined
Multiuser equalizer for hybrid massive MIMO mmWave CE-OFDM systems
This paper considers a multiuser broadband uplink massive multiple input multiple
output (MIMO) millimeter-wave (mmWave) system. The constant envelope orthogonal frequency
division multiplexing (CE-OFDM) is adopted as a modulation technique to allow an efficient power
amplification, fundamental for mmWave based systems. Furthermore, a hybrid architecture is
considered at the user terminals (UTs) and base station (BS) to reduce the high cost and power
consumption required by a full-digital architecture, which has a radio frequency (RF) chain per
antenna. Both the design of the UT’s precoder and base station equalizer are considered in this work.
With the aim of maximizing the beamforming gain between each UT and the BS, the precoder analog
coefficients are computed as a function of the average angles of departure (AoD), which are assumed
to be known at the UTs. At the BS, the analog part is derived by assuming a system with no multi-user
interference. Then, a per carrier basis nonlinear/iterative multi-user equalizer, based on the iterative
block decision feedback equalization (IB-DFE) principle is designed, to explicitly remove both the
multi-user and residual inter carrier interferences, not tackled in the analog part. The equalizer
design metric is the sum of the mean square error (MSE) of all subcarriers, whose minimization is
shown to be equivalent to the minimization of a weighted error between the hybrid and the full
digital equalizer matrices. The results show that the proposed hybrid multi-user equalizer has a
performance close to the fully digital counterpart.publishe
Modulation Schemes for Cognitive Radio in White Spaces
In this paper we give an overview and a comparison of the possible waveforms for white space applications. Four physical layer schemes for cognitive radio are selected for study: Orthogonal Frequency Division Multiplexing (OFDM), DFT-Spread OFDM (DFTS-OFDM), Constant Envelope OFDM (CE-OFDM) and Filter Bank Multicarrier (FBMC). The comparison is mainly based on the side effects of various non-ideal analog components (power amplifier, local oscillator) and residual synchronization errors such as frequency offset. As we will show, each technique has different sensitivity to the various impairments. The comparisons will be performed via spectral density functions and bit error rates (BER)
Performance Analysis and Resource Allocation in MIMO-OFDM Systems
The paper deals with the analysis of the vital performance plot of SNR and BER in MIMO systems. The importance of the diversity orders and the variation of the SNR-BER plot with respect to it is also studied using the simulation outputs. The three types of fading channels are also analysed. It is also seen that the presence of diversity and other schemes like Maximal Ratio Combining, selection combining, alamouti scheme increases the overall efficiency. The importance of the optimisation techniques and the superiority of the Monte Carlo optimization to the theoretical system without optimisation is also clearly visualised. The paper also deals with resource allocation in MIMO-OFDM systems. The advantage of the constant envelope OFDM over OFDM is achieved. Also the power allocation using water-filling algorithm and bandwidth-power product minimisation is compared using the obtained results
Overhead-Free Channel Estimation based on Phase-domain Injected Training for FM-OFDM
Frequency-Modulated Orthogonal Frequency-Division Multiplexing (FM-OFDM) is a novel constant envelope multi-carrier waveform proposed to be exploited in high-mobility scenarios, which is a typical case to be coped in the 6G. Moreover, it also exhibits a strong robustness to phase noise and carrier frequency offsets. However, it assumes that the channel estimates are perfectly given. In this paper, phase injected training (PIT) is proposed in order to obtain accurate enough channel estimates with a zero overhead for the case of FM-OFDM, since the pilot symbols are embedded in the phase component of the data symbols. Theoretical expressions and numerical results prove the feasibility of FM-OFDM using a realistic channel estimation method
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