Constant envelope orthogonal frequency-division multiplexing (CE-OFDM) has attracted increasing attention as a power-efficient modulation scheme for Internet of Things (IoT) networks, particularly in energy-constrained scenarios such as space–air–ground integrated networks (SAGINs). Despite its inherently low peak-to-average power ratio (PAPR), CE-OFDM suffers from significant bit error rate (BER) degradation due to nonlinear phase wrapping caused by phase modulation. To address this limitation, we propose a selective mapping (SLM)-aided CE-OFDM scheme, in which the transmit sequence with the minimum number of phase jumps is selected from a pre-defined set of candidates. This strategy effectively mitigates the impact of phase wrapping and significantly improves BER performance. Furthermore, to eliminate the spectral overhead caused by conventional side information transmission, we propose an embedded side information (ESI) mechanism that seamlessly incorporates index data into the transmitted signal without requiring additional bandwidth. Simulation results verify that the proposed SLM-aided CE-OFDM scheme, equipped with ESI, achieves substantial BER improvements over conventional CE-OFDM systems, while maintaining the low-PAPR property essential for energy-constrained IoT devices.

In the field of constant envelope orthogonal frequency division multiplexing (CE-OFDM), the use of phase modulation heralds a paradigm with an extremely reduced peak-to-average power ratio (PAPR) of zero. However, the non-linear characteristics inherent to phase modulation pose a formidable challenge to the integration of modern channel coding strategies aimed at improved bit error rate (BER) results. To address this issue, we present an efficient low-complexity log-likelihood ratio (LLR) computation strategy based on the traditional phase receiver, anchored in an effective approximation to the phase noise variance. Furthermore, this foundation paves the way for an innovative receiver architecture, namely the near-maximum likelihood (NML) receiver, designed to improve decoding performance without incurring significant computational overhead. Comparative analyses of encoded CE-OFDM across different receiver models not only confirm the accuracy and superiority of the proposed LLR estimation, but also underscore the dual advantages of our proposed NML receiver in optimising BER and detection complexity, positioning CE-OFDM as an optimal candidate for scenarios requiring high-efficiency power amplifiers (PAs).

Constant envelope orthogonal frequency division multiplexing (CE-OFDM) is a promising power-efficient wave-form with a peak to average power ratio (PAPR) of 0 dB, which allows it to avoid power backoff and nonlinear distortion when passing through a high power amplifier (HPA). Never-theless, compared to orthogonal frequency division multiplexing (OFDM), the sensing accuracy of CE-OFDM is relatively poor. In this paper, an offset CE-OFDM (OCE-OFDM) scheme is introduced for integrated sensing and communication (ISAC), which enhances the communication and sensing performance with the aid of adjusted power distribution among subcarriers. Specifically, a element-constrained maximum likelihood (ML) estimator is proposed to mitigate the equivalent sensing noise in OCE-OFDM, whose Cramer-Rao Lower Bound (CRLB) and parameter setting are further analyzed. Theoretical analysis and simulation results under mm Wave channel model show that the proposed OCE-OFDM scheme is capable of achieving better trade-off between sensing and communication performance compared to conventional OFDM and CE-OFDM system.

Recently, the reconfigurable intelligent surface (RIS), capable of adjusting the phase shifts (PSs) of the reflecting signals through its low-cost elements, has emerged as a promising technology for next-generation wireless communications. However, the RIS may be manipulated by an illegal passive attacker (Wyn) due to the shared nature of wireless channels. In this paper, a Wyn-controlled RIS is considered to attack multiple-input single-output (MISO) communications via passive beamforming based on existing localization and Rician factor estimation techniques. Specifically, we propose an alignment cancellation (AC) scheme to minimize the achievable rate (AR), where the closed-form expressions for location, reflecting element number, and PSs are derived. Furthermore, the computational complexity is quantified to evaluate the low-cost characteristics of this algorithm. Simulation results demonstrate that the proposed AC scheme outperforms other benchmark schemes in degrading the AR with efficient and low-complexity designs.

The problem of high peak-to-average-power-ratio (PAPR) is a major drawback of orthogonal frequency-division multiplexing (OFDM) technique, which is also the challenge of OFDM-based non-orthogonal multiple access (NOMA) for next-generation communications. To address this issue, this paper introduces constant envelope (CE) OFDM waveform, which is capable of achieving a PAPR of 0dB, for downlink NOMA. The proposed hybrid NOMA structure, namely CE-TF-NOMA, superposes conventional CE-OFDM and DFT spread (DFT-s)-CE-OFDM over the time-frequency domain, which significantly mitigates the time-domain fluctuation of transmitted signal and improve the power efficiency of high power amplifiers (HPA). Furthermore, two receiver schemes on the tradeoff between computational complexity and detection accuracy are presented. The system performance of the proposed TF-CE-NOMA is evaluated by comparison with the OFDM-based power-domain NOMA (PD-NOMA) and time-frequency domain NOMA (TF-NOMA), respectively. Simulation results demonstrate that CE-TF-NOMA is capable of achieving improved BER and constraint capacity with significantly reduced PAPR performance.

Constant envelope orthogonal frequency division multiplexing (CE-OFDM) has been extensively studied due to its ability to achieve low peak-to-average power ratio (PAPR) waveforms. However, CE-OFDM may encounter the phase ambiguity problem when the modulation index is relatively large. To mitigate this issue, we incorporate companding technique into CE-OFDM successfully enhance the overall system performance. Moreover, companding scheme requires a balanced consideration between the degree of signal compression and phase ambiguity problem. Therefore, this paper derives the optimal parameter selection by analysing the signal-to-interference-plus-noise ratio (SINR) of the scheme. Simulation results demonstrate that the proposed approach enhances the performance of CE-OFDM effectively by reducing the phase ambiguity as well as minimizing the interference caused by the companding technique.

In order to mitigate the high peak-to-average power ratio (PAPR) of the uplink waveform, the frequency domain spectrum shaping (FDSS) and $\frac{\pi }{2}$ BPSK modulation are adopted to DFT spread orthogonal frequency-division multiplexing (DFT-s-OFDM) for both data and pilot transmission in 5G new radio (NR). However, generating such pilot sequences with acceptable orthogonality and reduced PAPR causes a computationally intensive search. This paper introduces the constant envelope (CE) OFDM waveform for both pilot and data transmitting with a PAPR of 0dB. Especially, an modified channel estimation scheme with the optimized selection of modulation index is proposed to overcome the non-flat power spectral density caused by phase modulation in CE-OFDM. Numerical results prove the superiority of the proposed low-PAPR waveform over the classical NR signal in terms of both PAPR and BER performance.

Multiple-input multiple-output and orthogonal frequency division multiplexing with index modulation (MIMO-OFDM-IM) deliver information bits by both the indices of activated subcarriers and conventional constellations, enabling a trade-off between spectral efficiency (SE) and system performance. To obtain the channel state information (CSI) without reducing the SE of the system, a superimposed pilot transmission scheme for MIMO-OFDM-IM, along with multiple superimposed pilot patterns, is proposed in this paper. Meanwhile, a modified channel estimation process is explored to cancel the mutual interference between pilots and information signals, improving the channel estimation and the bit error rate (BER). The simulation results demonstrate that within a tolerable complexity, the proposed MIMO-OFDM-IM assisted with superimposed pilot scheme exhibits higher SE than the conventional comb-type pilot scheme without loss of BER performance.

Millimeter wave (mmWave) band communication has attracted extensive attention for high-data-rate transmission at the cost of increasing distortion from the degraded power efficiency of high power amplifier (HPA). Constant envelope orthogonal frequency division multiplexing OFDM (CE-OFDM) technique is capable of obtaining a 0dB peak-to-average-power-ratio (PAPR) signal and better resistance to phase noise in a multipath channel. However, current CE-OFDM suffers from the tradeoff between bit error rate (BER) performance and receiving complexity. This paper proposes an offset CE-OFDM (OCE-OFDM) scheme, which improves the carrier to noise ratio of subcarriers at higher frequency by adjusting the real component of the signal. Both theoretical and computer simulations make a comparison between the proposed OCEOFDM and conventional CE-OFDM, and demonstrate that the proposed scheme realizes a better BER performance using the low-complexity receiver in both AWGN and 60GHz mmWave channels with nonlinear HPA.

Constant envelope orthogonal frequency division multiplexing (CE-OFDM) has been proposed to overcome the primary drawback as high peak-to-average power ratio (PAPR) in original OFDM at the cost of considerable out-of-band emission. The novelty of this contribution is that the concept of N-continuous signaling is integrated with CE-OFDM in order to suppress the sidelobe. More specifically, the scheme advocated is capable of enhancing the continuity between adjacent CE-OFDM symbols and their higher order derivatives. Moreover, the related signal-to-interference-plus-noise ratio (SINR) of the proposed scheme is analyzed in this paper. The performance results show that the sidelobe suppression can be achieved with slight cost of bit-error rate (BER).

Offset spatial modulation orthogonal frequency division multiplexing (OSM-OFDM) is demonstrated to offer a simple radio frequency (RF) switching structure with comparable bit error rate (BER) performance to conventional SM-OFDM. However, the OSM-OFDM waveform inherits the large peak-to-average power ratio (PAPR) of original OFDM, and suffers performance loss in terms of BER due to the nonlinear noise from high power amplifier (HPA). As a class of efficient PAPR reduction techniques, the BER performance of clipping-aided OSM-OFDM is first evaluated through theoretical analysis. Furthermore, in this contribution, we conceive a new antenna offset structure as grouped OSM-OFDM toward low PAPR, while its upper BER bound is quantified through theoretical analysis. Through simulation results, we demonstrate that compared to the original OSM-OFDM, both grouped OSM-OFDM and clipped OSM-OFDM are capable of striking a better balance between PAPR and BER performance, while the former one is without extra computational complexity and the later one needs distortion recovery at the receiver side.

In this paper, the idea of offset spatial modulation (OSM) is integrated with orthogonal frequency division multiplexing (OFDM), toward an efficient design to bridge their advantages. Compared to its conventional counterpart as spatial modulation (SM)-OFDM, the proposed OSM-OFDM scheme aims at providing a simplified implementation structure with less number of radio frequency (RF) chains, by introducing an offset between the RF chain and the index of the activated transmit antenna on each subcarrier. Specifically, three types of offset antenna selection (OAS) methods are developed to meet different scene requirements for different number of available RF chains. Furthermore, through theoretical analysis, we quantify the bit error rate upper bounds of OSM-OFDM with different types of OAS methods. Finally, extensive computer simulations demonstrate that OSM-OFDM provides a flexible tradeoff among implementation cost, computation complexity and error performance.

Non-terrestrial network (NTN) based on orthogonal frequency-division multiplexing (OFDM) can provide robust high-speed data transition over geographically wide-range radio links between terrestrial ends and the satellite platforms. In this paper, we firstly investigate the performance of OFDM signal over a nonlinear channel caused by group delay and nonlinear distortion from the electronic processing and high power amplifier (HPA), respectively. By comparing with the conventional single-carrier waveform, simulation results show that the OFDM system can achieve a comparable BER performance with higher frequency efficiency in group delay channel, but suffers BER degradation from nonlinear distortion by HPA. To improve the BER performance, we propose a pre-distortion-based index- modulated OFDM (IM-OFDM) for the terrestrial-satellite radio link in the non-terrestrial network. The proposed scheme, taking the advantage of sparse allocation of the partially active subcarriers in IM-OFDM waveform, remaps the nonlinear distortion noise into an extended constellation space independently among the active and non-active subcarriers, thus to mitigate the effect of distortion noise to block-wise symbol detection. Simulations show that the proposed pre-distortion-based IM-OFDM signal is capable of achieving a better tradeoff among BER performance and HPA efficiency, compared with both the conventional OFDM and the IM-OFDM system.

An N-continuous generalized frequency division multiplexing (GFDM) transceiver architecture is studied with the objective of striking a balanced trade-off between the bit error rate (BER) and the sidelobe suppression performance. More specifically, in the proposed N-continuous GFDM signaling, the basis signals constructed allow one to make the GFDM signal N-continuous and attain a compact spectrum as an explicit benefit of sidelobe suppression. We further reveal that compared to conventional N-continuous orthogonal frequency division multiplexing (NC-OFDM), N-continuous GFDM introduces relatively low interference through evaluating the signal-to-interference ratio (SIR). Secondly, a signal recovery algorithm is presented by constructing a recovery matrix to eliminate the interference. Finally, it is demonstrated that the proposed N-continuous GFDM scheme outperforms its N-continuous OFDM counterpart in terms of sidelobe suppression, while achieving moderate BER performance degradation as opposed to original OFDM.

Internet of Things (IoT) as a prospective platform to develop mobile applications, is facing with significant challenges posed by the tension between resource-constrained mobile smart devices and low-latency demanding applications. Recently, mobile edge computing (MEC) is emerging as a cornerstone technology to address such challenges in IoT. In this paper, by leveraging social ties in human social networks, we investigate the optimal dynamic computation offloading mode selection to jointly minimize the total tasks' execution latency and the mobile smart devices' energy consumption in MEC-aided low-latency IoT. Different from the previous studies, which mostly focus on how to exploit social tie structure among mobile smart device users to construct the permutation of all the feasible modes, we consider dynamic computation offloading mode selection with social awareness-aided network resource assignment, involving both the computing resources and transmit power from heterogeneous mobile smart devices. On the one hand, we formulate the dynamic computation offloading mode selection into the infinite-horizon time-average renewal-reward problems subject to time average latency constraints on a collection of penalty processes. On the other hand, an efficient solution is also developed, which elaborates on a Lyapunov optimization-based approach, i.e., drift-plus-penalty (DPP) algorithm. Numerical simulations are provided to validate the theoretical analysis and assess the performance of the proposed dynamic social-aware computation offloading mode selection method considering different configurations of the IoT network parameters.

In this paper, we investigate performance of partial transmit sequence (PTS) for peak-to-average-power (PAPR) reduction in orthogonal frequency division multiplexing with index modulation (OFDM-IM), where three patterns of subcarrier grouping are considered. Firstly, the PAPR performance in terms of the independence of candidate sequences generated by three subcarrier grouping patterns are analyzed, respectively. Both theoretical analysis and numeric simulation show that PTS can achieve somewhat better PAPR performance in OFDM-IM than that in OFDM system. Moreover, the issue of imperfect side information(SI) at the receiver is investigated for exposing the relationship between SI transmitting scheme and BER performance. In the context, the comparison of OFDM and OFDM-IM signal shows that the BER performance of PTS aided OFDM-IM is more robust than that of OFDM signal.

Orthogonal frequency division multiplexing with index modulation (OFDM-IM), which uses the indices of activated subcarriers to carry additional information bits, is a novel multicarrier transmission technique. In this paper, a profile-based power management relying on maximal minimum Euclidean distance (MED) criterion is proposed. Moreover, a low-complexity subset searching method based on the normalized maximal MED criterion and corresponding reception scheme are proposed. Simulation results show that, without any forward side information or additional complexity for reception, the proposed profile-based power allocation scheme is capable of providing bit error rate (BER) performance improvement over conventional OFDM-IM system.

Differential spatial modulation (DSM) is a novel attractive alternative technique for coherent spatial modulation (CSM) without channel state information (CSI) at the receiver. In this paper, iterative detection is firstly employed to improve the performance of DSM schemes. With the Hamming distance of two matrices reduced to the sum of simple elements, a lowcomplexity iterative detection scheme for recursive systematic convolutional (RSC) coded DSM scheme is proposed. Simulation results show that the proposed detector is capable of approaching a near- capacity performance with a great complexity reduction compared to the maximum a posteriori (MAP) detector.

Conventional energy harvesting (EH) communications are limited by energy unsteadiness and causality. In this paper, a novel technique namely energy borrowing (EB) is specifically designed as an efficient way to bridge energy harvesting and power grid in wireless communications. The EH nodes are capable of adaptively borrowing and returning energy from the power grid, at the cost of paying extra energy interest. In order to maximize the transmission throughput, the packets scheduling problem in the proposed EB-aided EH systems is investigated and adaptive solutions are developed. Simulation results show that the proposed EB-aided EH system provides throughput improvement over the conventional one without EB, while achieving extra energy benefits for the power grid.

Energy efficiency is of high attention these days due to the development of green communications. Previous resource allocation algorithms in orthogonal frequency division multiple access (OFDMA) mainly focused on maximizing the energy efficiency (EE) of all the users and cannot ensure fairness in advance. To strike a balance between EE and user fairness, this paper proposes an energy-efficient proportional resource allocation algorithm. During subcarriers allocation, the priority of users is adaptively determined by both overall EE and the ratio of users' EE to proportionality. Then a low-complexity power allocation algorithm is extended to uplink OFDMA by searching the water level with constraints on maximum power and minimum rate requirements of each user. Simulation results show that the proposed schemes achieve a substantially proportional fair on EE among users as well as a relatively high over EE.

N-continuous orthogonal frequency division multiplexing (OFDM) is a promising sidelobe suppression technique by enhancing the continuity between adjacent symbols with higher-order derivatives. However, it has high computational complexity due to the large-scale matrix operations in frequency domain. In this paper, a low-complexity time-domain signal processing (TDSP) algorithm for N-continuous OFDM is proposed. Based on linear combination of basis vectors, it utilizes small-scale matrix operations to generate the coordinates to construct N-continuous OFDM signal. Simulation results approve that the proposed algorithm achieves dramatic complexity reduction with identical sidelobe suppression and BER performance compared to conventional frequency-domain processed N-continuous OFDM.

As a cognitive radio (CR) modulation technique, transform domain communication system (TDCS) has been proposed by utilizing white space spectrum for the network access and achieving low probability of interception (LPI). In the previously reported TDCS- based cognitive radio networks (CRN), however, the non-zero periodic correlation function between any pair of users results in multiuser interference (MUI). In this paper, a novel framework under the CR constraints is presented by employing a two- dimension spreading scheme (i.e., time and frequency domains). We first obtain a class of spreading sequences with almost perfect periodic correlation function for arbitrary spectrum utilization pattern. Then, an universal criteria is presented for synchronous MUI-free CRNs when employing TDCS. Simulation results demonstrate that the proposed TDCS-based CRN architecture is a preferable candidate for distribution wireless networks, such as CR Ad-hoc wireless sensor networks.

Energy efficiency is becoming more and more important for mobile devices in future green radio network. This paper addresses the tradeoff between energy-efficiency (EE) and spectral efficiency (SE) in uplink multiuser orthogonal frequency division multiple access (OFDMA) systems. In this paper, EE is measured by the sum of instantaneous bits-per-Joule of each user, and it is optimized with the restrictions on both the minimum rate requirements and available transmit power over frequencyselective channels. Based on this optimization model, a novel low-complexity energy-efficient resource allocation algorithm is proposed. Simulation results demonstrate that the proposed scheme provides a better tradeoff between SE and EE than the conventional schemes with reduced complexity.

Peak-cancellation is a pre-distortion technique for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. The distortion introduced to the transmitted signals can be mitigated on the condition that the signal attenuation factor is known at the receiver. In this paper, to alleviate the distortion and disclose the signal feature of peak-cancellation combined OFDM signals, the signal attenuation factor is analyzed and hence evaluated, which is supported by simulation results.

In this letter, a low-complexity structure of PAPR reduction scheme, user grouping, in multicarrier code-division multiple access (MC-CDMA) is introduced. The proposed structure is based on joint spreading and inverse fast Fourier transform (S-IFFT) processing, and a class of low-complexity structure of user grouping scheme is proposed on the tradeoff between computational complexity and storage size. Comparison with the conventional PTS schemes, it shows that the proposed low-complexity scheme can achieve similar PAPR reduction with lower complexity.

Partial transmit sequence (PTS) is an attractive distortless peak-to-average power ratio (PAPR) reduction technique for orthogonal frequency division multiplexing (OFDM) system. However, the complexity of PTS increases exponentially with the number of sub-blocks as it requires an exhaustive searching over all phase factor combinations. In this paper, we explored the correlation among the multiple candidate signals of PTS and proposed a modified scheme with lower complexity. The main idea is based on selecting a subset from the whole set of candidate signals by analyzing the correlation of candidate signals. Simulation results show that the performance of the modified scheme is close to the theoretical lower bound and outperforms selected mapping (SLM) scheme with the same computational complexity.

Selected mapping (SLM) is a promising peak-to-average power ratio (PAPR) reduction technique for orthogonal frequency division multiplexing (OFDM) system. In SLM, phase sequences are combined with the data for generating alternative signals, so as to reduce the PAPR. In this paper, a new criterion is developed to examine the effects of different phase sequence sets in SLM-OFDM based on the mathematical correlation analysis among the alternative signals. Furthermore, according to the proposed criteria, the chaotic phase sequence set is introduced for improving the PAPR reduction performance in SLM. Simulation results show that the improved SLM outperforms conventional methods such as proposed in [6].

The high peak-to-average power ratio (PAPR) is one of the main drawbacks of multicarrier code division multiple access (MC-CDMA) system. To alleviate this problem, in this paper, we propose a novel user grouping scheme for PAPR reduction in the downlink of MC-CDMA. The basic principle is to partition the users into subgroups, and generate multiple alternatives to achieve considerable PAPR reduction. The proposed scheme can be regarded as a modified version of partial transmit sequence (PTS), but with improved performance. And simulation results show that the user grouping scheme is more effective than the conventional PTS in MC-CDMA system.