This paper presents a monolithic interface application-specific integrated circuit (ASIC) for a MEMS disk resonator gyroscope (DRG) with low zero-rate output (ZRO) drift and low scale factor (SF) nonlinearity. The ASIC is implemented under a high-precision force-to-balanced (FTR) mode combined with an easily integrable self-excitation drive loop. The ASIC improves the performance in two ways: First, based on an analysis of electrical errors in MEMS DRG performance, a time-domain anti-coupling architecture is proposed to reduce electrical coupling effects on ZRO drift and SF nonlinearity. This architecture also eliminates the need for high-bandwidth signal processing compared to traditional frequency-domain architectures. Second, the first-order linear relationship between ZRO drift and drive amplitude voltage in the FTR mode is analyzed and validated, and a low hardware compensation circuit is designed to correct ZRO drift. The ASIC is fabricated using a$0.35\mu $m BCD process with a chip area of 4.3 mm$\times 4.2$mm. Combined with the MEMS structure, it achieves a bias instability (BI), angle random walk (ARW), and SF nonlinearity of 0.018°/h, 0.0055° h, and 108 ppm, respectively.

Due to the large number of antennas in the antenna array, channel estimation for millimeter-wave (mm-Wave) massive MIMO becomes complex. Leveraging the sparsity of mm-Wave channels is an effective approach to reduce complexity and improve accuracy. For channel estimation methods that utilize the prior probability distribution of the sparse channel vector, the accuracy of the probability distribution is critical to the performance of channel estimation. This paper proposes a higher-order Markov prior model combined with the Turbo-OAMP framework, which is suitable for mm-Wave channel estimation scenarios where channel sparsity changes rapidly. Numerical simulation results show that the proposed method achieves better estimation accuracy and robustness in time-varying sparse mm-Wave channels.

In this paper, the weighted fractional Fourier transform (WFRFT) signal domain is introduced to enhance the security performance of two-way trusted relay systems at the signal level. The proposed scheme, which requires only a single relay node, leverages the multi-component energy distribution characteristics of WFRFT signals to improve security with low complexity and high power efficiency. The inherent security mechanism of WFRFT analyzed in this paper can be simply summarized as follows: the superposition of components in WFRFT signals that do not satisfy specific constraints will result in the inability to perfectly reconstruct the message signal. Based on this, confidential information is encoded into WFRFT signals with private transform orders, allowing legitimate users to achieve perfect decoding. Since WFRFT signals exhibit energy concentration only in specific transformation domains, mismatched transform orders adopted by the eavesdropper cause energy loss in the information-bearing signal, leading to inter-component interference that further degrades the quality of the recovered signal. The advantages of the proposed scheme in limiting information leakage and improving the achievable secrecy sum rate (SSR) are analyzed. Numerical results validate the theoretical analysis and demonstrate the secrecy performance of the proposed scheme.

Affine Frequency Division Multiplexing (AFDM) is a chirp-transform modulation technique that has shown reliable performance in high-mobility scenarios, making it an attractive option for next generation communication systems. Recent literature suggests that under chirp parameter adjustment, AFDM can achieve optimal diversity performance in delay-doppler channels with maximum likelihood (ML) detection. However, the performance of AFDM with minimum mean square error equalization (MMSE-Eq) has not been extensively investigated in the existing literature. In this paper, we analyze the performance of AFDM with MMSE-Eq, derive a lower bound for the theoretical bit error rate (BER) of the AFDM system, and discuss the relationship between chirp parameters and performance degradation. To optimize BER performance, we propose two distinct chirp parameter selection strategies for frequency selective and doubly selective channels, respectively. These strategies offer the advantage of avoiding extensive computations. Additionally, we propose a low-complexity and high-performance iterative MMSE-Eq algorithm based on time-domain channel matrix operations. The algorithm resolves the issue encountered in existing low-complexity methods, where different chirp parameter selections significantly impact the complexity. Simulation results demonstrate the efficacy of our proposed parameter selection strategies and the outstanding BER performance achieved by the iterative MMSE-Eq algorithm.

In this paper, we investigate hybrid precoder design to enhance the physical layer security of the millimeter-wave (mmWave) system with multiple eavesdroppers. Differing from traditional spatial domain-based schemes, we introduce an extra signal domain dimension and propose a multi-component-based security mechanism for the hybrid precoding system model. The model integrates both signal and spatial domains for designing baseband and analog precoders, ensuring that the received signal at the legitimate user complies specific signal domain characteristics. Consequently, all received energy becomes available for signal reconstruction, whereas the distorted signal at eavesdroppers inevitably forms inter-component interference. By introducing general multi-fractional Fourier transform (GMFRFT) signal domain into the model, we propose a specific GMFRFT-based scheme for subarray architectures. The secrecy performance is analyzed, and power allocation methods between multiple components are designed. Additionally, to optimize the utilization of spatial domain resources, we propose a GMFRFT-based scheme with dynamic subarrays, along with a low-complexity subarray partitioning algorithm. Furthermore, a GMFRFT-based scheme for fully connected architectures is investigated. It is verified to be equivalent to a lower-complexity weighted fractional Fourier transform (WFRFT)-based analog beamforming scheme, the efficacy of which hinges on the adherent secrecy provided by WFRFT signals. Both theoretical analysis and numerical results demonstrate the effectiveness of the proposed schemes.

Accurately estimating channels with fractional Doppler and delay is a challenging task for orthogonal time-frequency space (OTFS) systems. This paper proposes using the bilinear vector approximate message passing (Bi-VAMP) algorithm to sparsely estimate integer delay and Doppler shifts and learn fractional delay and Doppler shifts separately. The scalar coefficients of uncertain matrices are extended to vector form, transforming the first-order approximation model of the effective delay-Doppler (DD) domain channel response into an uncertain matrix estimation model. Furthermore, considering the characteristics of OTFS channels, this paper provides some suggestions to enhance the convergence robustness of the Bi-VAMP algorithm. Simulation results validate that compared to other on-grid and off-grid methods, the proposed off-grid Bi-VAMP OTFS channel estimation scheme exhibits significant advantages in normalized mean square error (NMSE) performance metrics.

The Cyclic prefix (CP) in traditional OFDM systems is used to combat inter-symbol Interference (ISI) and inter-carrier Interference (ICI), which simplifies the design of the equalizer by converting the linear convolution (LS) between symbols and the channel into cyclic convolution (CC). However, the overhead of CP reduces the system’s spectral efficiency and energy efficiency. This paper proposes a CP-free OFDM system called TSE-OFDM by exploiting a truncated symbol extrapolation (TSE) module. The TSE module categorizes the received OFDM symbols into reliable and unreliable parts based on their susceptibility to ISI. By iteratively extrapolating the reliable portion unaffected by ISI, the TSE module restores the CC characteristic of the received symbols. We conduct noise analysis and simulations to evaluate the performance of the extrapolation algorithm, demonstrating its robustness against out-of-band noise. Furthermore, we simulate the TSE-OFDM system to assess its bit error rate (BER) and spectral efficiency (SE). The simulation results show that TSE-OFDM significantly improves SE while maintaining satisfactory BER performance. Compared to other CP-free OFDM schemes, TSE-OFDM exhibits ample tolerance to symbol timing offset (STO) and channel estimation errors.

Space-air-ground integrated network (SAGIN), as an integration of interconnected space, air, and ground network segments, is expected to see prevalent usage as part of intelligent transportation systems (ITS), providing an enhanced service provision in terms of coverage, flexibility and reliability. However, restricted by the limited and unbalanced network resources, the efficiency and security of the underlying connectivities of SAGIN are of utmost concern for ITS applications. In this paper, a weighted fractional Fourier transform (WFRFT) based parallel complex spreading (PCS) approach is proposed to improve the communication efficiency and security of SAGIN at the physical (PHY-) layer. The concept of WFRFT along with the direct sequence spread spectrum technology establish the security kernel of the proposed scheme. The practicability of the complex-valued WFRFT-spreading architecture is verified by studying the correlation properties of the WFRFT-spreading signals. Taking advantages of the signal uniqueness of WFRFT, the proposed scheme is capable of providing more flexibility in signal characteristic control. Moreover, the complex-valued WFRFT-spreading processing makes the proposed scheme inherently robust against the large Doppler shift distortions in SAGIN. Simulation results demonstrate the superiority of the proposed WFRFT-PCS scheme in terms of communication efficiency and PHY-layer security. Finally, as a proof of concept, an all-digital FPGA prototype system is designed to show the practicability and the performance enhancement of the proposed scheme.

The weighted-type fractional Fourier transform (WFRFT)-based hybrid carrier (HC) system has been proposed to bridge the gap between orthogonal frequency division multiplexing (OFDM) system and single-carrier system with frequency domain equalization (SC-FDE). In this paper, we propose a novel HC system based on efficient fast-convolution (FC) without a cyclic prefix to meet the requirements of complex scenarios towards future communications. The proposed system can achieve flexible optimization of system performance, such as minimizing out-of-band emission (OOBE), peak to average power ratio (PAPR) and bit error rate (BER). This efficient FC based hybrid carrier (FCHC) system is among the most competitive waveforms. The closed-form BER expressions are derived and analyzed over additive white Gaussian noise (AWGN) and frequency-selective fading channels. A modified equalizer over frequency-selective channels is also provided to resist the inter-block interference (IBI). Moreover, the banded minimum mean-square error (MMSE) equalization based on FC can be embedded in the proposed system over doubly-selective channels, and then the interference caused by fading channels can be further suppressed through the combination of FC and HC. The simulation results demonstrate the superiority of the proposed system over the conventional HC system in terms of OOBE, PAPR and BER. The significant flexibility and combined performance advantages make the proposed system a potential scheme for future communications.

In this paper, we propose a security scheme based on extended weighted fractional Fourier transform to guarantee the physical layer security of wireless communication. The proposed scheme extends the existing fractional Fourier transform and reduces the equivalent signal-to-noise ratio and recognition probability of the eavesdropper by utilizing the anti-interception characteristics of the extended hybrid carrier signal, which guaranteed the robust nonzero security capability and anti-recognition performance. Moreover, due to the extension of parameter dimension, the diversity and design flexibility of EWFRFT also have adverse impacts on wiretapping. In addition, the self-interference property of the EHC signal is proposed and analyzed in detail to further enhance the security performance. Theoretical analysis and numerical simulation results show the superiority of the EWFRFT method. Compared with the existing HC system, the proposed scheme reduces the possibility of interception by eavesdroppers without extra computational complexity, which effectively guarantees the security of the system.

In this paper, a two-dimensional weighted fractional Fourier transform (2DWFRFT) based secure spatial modulation (SM) scheme is proposed to enhance the physical layer security (PLS) of the wireless communication system. In the proposed scheme, 2DWFRFT is implemented as the security kernel for PLS provision. The invertibility and uniqueness of the 2DWFRFT effectively protect the confidential messages from being intercepted by the eavesdroppers while imposing no performance degradation on the legitimate receiver. Both the signal generation strategy and the ergodic secrecy rate analysis under discrete-input continuous-output memoryless (DCMC) channel have been elaborated to depict the security mechanism of the proposed scheme. The maximum likelihood (ML) detector and the separate detection (SD) algorithm are formulated to correctly recover the received signal of our system. Simulation results demonstrate that the proposed scheme can achieve a much higher secrecy capacity than artificial noise schemes without requiring additional jamming power consumption.

In this paper, we propose an adaptive multi-attributes based physical layer authentication framework for enhanced authenticity provisioning. Instead of optimizing the "threshold" for a preset PHY-layer signature, this paper resort to exploiting and selecting multiple historical better performed PHY-layer attributes for authentication enhancement. In particular, the authenticator of the proposed scheme is designed to be capable of recording the historically performance of each potential attribute. Based on which, the most effective PHY-layer attributes (MEA) would be chosen to improve the reliability of the PHY-layer authentication. This paper experimentally proves that the dimension extension on PHY-layer signature attributes effectively enhances authenticator's capability in signal discrimination. However, with more attribute to observe, it also complicates the predicting and authenticating procedure. Therefore, a learning-based search algorithm is then formulated to facilitate the MEA selection procedure. Both theoretical analysis and experiment results are given to demonstrate the efficiency and superiority of the proposed scheme.

With the high mobility, flexibility and manoeuvrability, unmanned aerial vehicles (UAVs)‐enabled mobile edge computing (MEC) plays an important role in many applications that lack of available terrestrial infrastructures, such as disaster response, emergency relief and military scenarios. However, the high mobility of UAVs may severely degrade the implementation of UAV‐enabled MEC in computation‐intensive or delay‐sensitive scenarios from a physical layer signalling perspective, e.g. frequency selective fading effect caused by the low altitude and low elevation angle routes of UAVs. In this study, a generalised weighted‐type fractional Fourier transform (GWFRFT) based signal energy‐spreading transmission (EST) scheme is proposed for signalling and quality of service (QoS) provisioning for UAV‐enabled MEC. In the proposed scheme, the communication signal energy is redistributed evenly at the time‐frequency plane to enhance the robustness of UAV communications against the severe fading channels. The signalling provisioning mechanism of the GWFRFT‐EST scheme is analysed and simulated under poor air‐to‐ground channels with low Rician K ‐factor. Simulation results show that the proposed method greatly improves the bit error rate performance with a negligible computational complexity increase.

In systems that aim to mitigate the inter-carrier interference (ICI) caused by doubly selective (DS) channels, the partial Fast Fourier Transform (PFFT) has emerged as an interesting alternative to the conventional FFT. In this letter, we propose a novel PFFT demodulation scheme based on fast convolution (FC) structure. The proposed scheme uses the overlap-save operation of FC to further suppress the residual interference (RI) to improve performance over DS channels, including in terms of bit error rate (BER), while, at the same time, allowing for an improvement in spectral efficiency by avoiding the use of a cyclic prefix (CP). We provide a theoretical analysis of RI and numerical simulations to demonstrate the superiority of the proposed scheme in terms of BER performance.

The major drawback of orthogonal frequency division multiplexing (OFDM) systems is the high peak-to-average power ratio (PAPR) problem. Some PAPR reduction methods have been proposed in the literature, and clipping and filtering (CAF) has been recognized as the simplest one. However, the CAF method introduces in-band distortion. In this paper, weighted fractional Fourier transform (WFRFT) is utilized to enhance the CAF method to improve the PAPR performance and mitigate the in-band distortion, which is called WFRFT-CAF method. The proposed WFRFT-CAF method is compared with existing PAPR reduction methods, based on computation complexity, PAPR reduction capacity, power spectral density (PSD), and bit error rate (BER) performance. Through simulations, it is validated that the WFRFT-CAF method can obtain better PAPR and BER performance than existing PAPR reduction methods considering the transmit power gain and path loss.

The long term evolution-advanced (LTE-A) and worldwide interoperability for microwave access (WiMAX) standards are the two main contenders in the 4th generation (4G) wireless systems, which adopt the single carrier-frequency division multiplexing access (SC-FDMA) and orthogonal frequency division multiplexing access (OFDMA) schemes in the uplink, respectively. However, these two schemes have certain advantages and disadvantages. As the weighted fractional Fourier transform (WFRFT)-based system can merge the SC- FDMA scheme with the OFDMA scheme, it inherits these two schemes' characteristics and has the potential to obtain better performance. For enhancing the bit error rate (BER) performance of the future uplink communication, in this paper, we propose a new order selection method for the WFRFT- based system to obtain better BER performance than the existing conventional uplink SC-FDMA or OFDMA scheme concerning the peak-to-average power ratio (PAPR) and the uplink power control (UPC) parameter under frequency selective fading channels.

In this paper, the performance of hybrid carrier (HC) systems based on weighted fractional Fourier transform (WFRFT) is investigated in an uplink non‐orthogonal multiple access (NOMA) scenario. NOMA is a promising technology to improve the system capacity, in which two users (far‐user and near‐user relative to a base station) are allocated to use the same time‐frequency resources, and the successive interference cancellation (SIC) technique is implemented to decode signals at the receiver. Considering the actual error decoding in the SIC process (i.e. imperfect SIC), NOMA cannot avoid the inter‐user interference (IUI) and residual interference (or error propagation). Therefore, firstly IUI and residual interference are analysed, and signal to interference plus noise ratio (SINR) of the far‐user is expressed mathematically considering the residual interference. Then, based on the analysis of IUI, considering different WFRFT orders, a near‐user BER expression over additive white Gaussian noise (AWGN) channels is derived. Furthermore, the optimal WFRFT order selection to minimise the interference influence in the uplink is formulated and solved efficiently. Simulation results have verified the mathematical expression of SINR, the near‐user theoretical BER expression, and the proposed optimal WFRFT order selection to obtain the maximum sum spectral efficiency.

This paper proposes a Weighted fractional Fourier transform (WFRFT) based cooperation scheme to improve PHY layer security against eavesdropping in wireless communications. Rather than dissipating valuable transmission power to jam the eavesdropper, by leveraging the features of WFRFT, the information bearing signal can create “Artificial Noise” effect at the eavesdropper while imposing no effect on the legitimate receiver. Specifically, the proposed WFRFT based cooperation is performed in a two-phase manner, whereby the source first broadcasts its message to the intermediate nodes which then perform WFRFT operation to relay the message to the destination, with the objective of boosting the secrecy rate of the source-destination pair. Simulation results are provided, which demonstrate that the WFRFT-based user cooperation scheme can acehieve a significant performance gain, in terms of secrecy ergodic capacity, compared with conventional security-oriented user cooperation schemes.

In this paper, we propose a novel user cooperation scheme based on weighted fractional Fourier transform (WFRFT), to enhance the physical (PHY) layer security of wireless transmissions against eavesdropping. Specifically, instead of dissipating additional transmission power for friendly jamming, by leveraging the features of WFRFT, the information bearing signal of cooperators can create an identical artificial noise effect at the eavesdropper while causing no performance degradation on the legitimate receiver. Furthermore, to form the cooperation set in an autonomous and distributed manner, we model WFRFT-based PHY-layer security cooperation problem as a coalitional game with non-transferable utility. A distributed merge-and-split algorithm is devised to facilitate the autonomous coalition formation to maximize the security capacity while accounting for the cooperation cost in terms of power consumption. We analyze the stability of the proposed algorithm and also investigate how the network topology efficiently adapts to the mobility of intermediate nodes. Simulation results demonstrate that the WFRFT-based user cooperation scheme leads to a significant performance advantage, in terms of secrecy ergodic capacity, compared with the conventional security-oriented user cooperation schemes, such as relay-jamming and cluster-beamforming.

In this paper, weighted fractional Fourier transform (WFRFT) is employed to safeguard the physical layer (PHY) security of wireless communications. By leveraging the features of WFRFT, we propose a PHY security modulation scheme, which significantly degrades the equivalent signal-to-noise ratio (SNR) of the unauthorized receiver while imposing no impact on the legitimate receiver. With the proposed scheme, a robust nonzero secrecy capacity can be guaranteed. Moreover, the proposed scheme can conceal the actual modulation paradigms to prevent malicious signal detection, due to the variation in signal characteristics. A higher order statistics (HOS) based classifier is used to investigate the anti- recognition performance. Meanwhile, the secrecy performance of the proposed scheme is evaluated in terms of both secrecy capacity and average bit error rate (BER) by numerical simulations. Finally, as a proof-of-concept, an all-digital field programmable gate array (FPGA) based prototype system is developed to validate the practicability of the proposed scheme.

Sparse code multiple access (SCMA) is a new modulation and non-orthogonal multiple access scheme for 5G systems, in which the coded bits are mapped to multidimensional sparse codewords, and the message passing algorithm (MPA) is employed to detect multi-user signals. Device-to-Device communications underlaying cellular network is also a key technique in 5G networks; hence the sparse codes allocation between D2D users and cellular users is a new issue to be studied. Based on the short-range characteristics of D2D communications, this paper proposes a sparse codes allocation scheme between D2D users and cellular users. The proposed scheme allocates orthogonal resource blocks to the cellular users, whereas the D2D links reuse resources with cellular users in a non-orthogonal mode. By limiting the distance from the D2D transmitter to the base station, the proposed scheme enlarges the power diversity of the interfering symbols, which makes the interfering symbols at a resource block more easily separated. Simulation results show that, compared to the allocation scheme without distance limitation, the proposed scheme performs better in BER performance and the convergence behavior.

Exploiting physical layer (PHY) characteristics has great potential to complement and secure upper-layer authentication protocols. Unlike existing PHY authentication mechanisms requiring special hardware designs, in this paper, we propose a practical PHY- aided authentication approach based on weighted fractional Fourier transform (WFRFT). Instead of exploiting the channel or hardware characteristics that are out of control, the proposed scheme can provide two-fold protection on upper-layer protocols by leveraging the intrinsic PHY features of the transmitted signal. Firstly, WFRFT can hide and forge the modulation paradigm to mislead attackers in signal demodulation. Secondly, WFRFT signal can be adjusted among different patterns automatically and dynamically to provide more security and freedom in PHY authentication, similar to frequency-hopping systems. Numerical simulations and analyses demonstrate that the proposed scheme can achieve more secure authentication with tolerate computational overhead.

The performance of Device-to-Device (D2D) commu- nications in a cellular network depends on the resource sharing scheme between D2D links and cellular users. Existing research on resource sharing mainly focuses on power allocation under the condition that each D2D pair shares one cellular user's entire resources upon approval. Unlike conventional resource sharing schemes, this paper focuses on the low energy characteristics of the filtered OFDM signals in the guard band, and provides a novel resource sharing strategy which allows D2D pairs to share only part of one cellular user's resources. In the proposed approach, the base station allocates the resource blocks in the guard band to the D2D pairs first; if the allocated resource blocks can't meet the D2D communication requirement, the base station allocates part of the downlink resource blocks to the D2D users. The proposed scheme can further suppress the cellular-user-induced interference, and thereby improves the D2D capacity performance while guaranteeing the stability of cellular communications. Numerical results show that the proposed resource sharing strategy provides better D2D capacity performance.

This paper addresses the multi-antenna relay beamforming problem in single-carrier frequency division multiple access (SC- FDMA) systems with imperfect channel state information (CSI) at the relay. Under the deterministic model of CSI errors, we formulate the optimizing problem as a minimax problem, which is to minimize the maximum mean-squared-errors (MSE) among all channels in the uncertainty sets. Despite of the non- convexity of the optimizing problem, we prove that the problem can be solved in closed form. More specifically, the saddle-point property for this minimax problem is established and the non- convex complex- vector optimizing problem is transformed into a convex real-value power allocation problem and solved in closed form. The simulation results verify the excellent performance and robustness of our proposed scheme.

Signal to leakage and noise ratio (SLNR) based precoding algorithm is widely researched in CoMP-JP system. Nevertheless, the equivalent channel gain for each stream can be severely unbalanced in multi-stream transmission, and the overall performance is limited by the worst data stream. An improved SLNR based precoding algorithm is presented, which generates new precoding matrix with the method of weighting and linear transformation based on original SLNR vectors to eliminate the disparity of performance among streams, and optimize overall performance in multi-stream system. The simulation results demonstrate that our proposed algorithm can achieve considerable gains in error performance over the original SLNR and eliminate co-channel interference (CCI) among UEs at the same time for multi-stream transmission.

In TD-LTE-A downlink, multi-user beamforming is used to decrease co-channel interference of different users and increase system performance, and Signal-to-Leakage-and-Noise Ratio (SLNR) beamforming algorithm has been proved to have better performance in terms of sum capacity and average BER performance compared with other beamforming algorithms with moderate complexity. In order to further improve the performance, the power allocation algorithm is combined with the framework of SLNR beamforming. Based on the combined algorithm, we can maximize sum capacity and guarantee users' requirements in multiuser downlink scenario with multiple-input-multiple-output (MIMO). The problem is transformed into convex optimization and then solved by geometric programming. Simulation results show that sum capacity of the proposed algorithm is slightly inferior to water-filling algorithm, however, the proposed algorithm can satisfy users' requirement while water-filling algorithm cannot. Then, a sub-optimal algorithm is also proposed to reduce implementation complexity at the cost of 10% sum capacity loss.

This paper compares the achievable sum rates of multiple-input multiple-output (MIMO) single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) systems with linear receivers in spatially uncorrelated frequency selective Rayleigh fading channels. Zero forcing (ZF) and linear minimum mean-squared error (MMSE) receivers are considered. We derive closed form expressions for lower bounds on the achievable sum rates of SC- FDMA so as to compare them with the achievable sum rates of OFDMA. In addition, the comparison in the asymptotic regimes of high and low signal-to-noise ratios (SNRs) is also presented. It is analytically demonstrated that, for ZF and MMSE receivers, the achievable sum rate of SC-FDMA is approximately equal to that of OFDMA when the number of transmitter and receiver antennas grows with a fixed ratio of less than one, in both high and low SNR regimes. The results apply to scenarios with arbitrary numbers of subcarriers and arbitrary-length channels.

This paper investigates the achievable sum rates of multiple-input multiple-output (MIMO) single carrier frequency division multiple access (SC-FDMA) systems with different receivers in spatially uncorrelated frequency selective Rayleigh fading channels. Zero forcing (ZF), linear minimum mean-squared error (MMSE) and the proposed per subcarrier maximum likelihood (PSML) receivers are considered. Closed form expressions for the upper and lower bounds on the achievable sum rates of ZF, MMSE and PSML receivers are derived. Through these expressions, we characterize the behavior of the receivers in various scenarios of different channel lengths and subcarrier numbers. It is found that compared with the optimal receiver, the PSML receiver can obtain the optimal sum rate with significantly reduced computational complexity in flat fading channels. In addition, for ZF or MMSE receivers, either the upper or lower bound can be an accurate approximation of the achievable sum rate under certain conditions and can also provide a theoretical reference to practical systems.

To mitigate the inter-carrier interference (ICI) of doubly-selective (DS) fading channels, we consider a hybrid carrier modulation (HCM) system employing the discrete partial fast Fourier transform (DPFFT) demodulation and the banded minimum mean square error (MMSE) equalization in this letter. We first provide the discrete form of partial FFT demodulation, then apply the banded MMSE equalization to suppress the residual interference at the receiver. The proposed algorithm has been demonstrated, via numerical simulations, to be its superior over the single carrier modulation (SCM) system and circularly prefixed orthogonal frequency division multiplexing (OFDM) system over a typical DS channel. Moreover, it represents a good trade-off between computational complexity and performance.

ABSTRACT The fractional Fourier transform (FRFT)—a generalization of the well‐known Fourier transform (FT)—is a comparatively new and powerful mathematical tool for signal processing. Many results in Fourier analysis have currently been extended to the FRFT, including the ordinary convolution theorem. However, the extension of the ordinary convolution theorem associated with the FRFT has been developed differently and is still not having a widely accepted closed‐form expression. In this paper, a generalized convolution theorem for the FRFT is proposed, and the dual of it is also presented. The ordinary convolution theorem and some of its existing extensions related to the FRFT are shown to be special cases of the derived results. Moreover, some applications of the derived results are presented. Copyright © 2012 John Wiley & Sons, Ltd.

Recently, two fire-new modulation schemes: the so-called hybrid carrier (HC) modulation based on weighted-type fractional Fourier transform (WFRFT) and the modulation based on energy spreading transform (EST), have emerged as promising solutions to repress the inter-sample and inter-carrier interference caused by doubly selective channels. In this paper, we propose an iterative frequency domain minimum mean-square-error (MMSE) equalization scheme for systems with WFRFT and EST precoders in order to achieve a better tradeoff between the interference-repression performance and complexity. During the process of the proposed iterative equalization, priors-aided linear MMSE estimations (LME) are performed iteratively in the frequency domain, and the priors are updated in precoding domains. During the iterations, the prior information is estimated more accurately in WFRFT and EST based modulation systems than those in conventional orthogonal frequency division multiplexing (OFDM) and single carrier (SC) systems. Simulation results manifest that the proposed iterative frequency domain MMSE equalization (IFME) scheme outperforms existing iterative MMSE equalization schemes proposed for OFDM and SC architectures in terms of bit-error-ratio.

Abstract Cognitive ultra‐wideband (C‐UWB) systems have recently received much attention because the huge bandwidth of ultra‐wideband (UWB) systems can better exploit the advantages of cognitive radio (CR) systems. Dynamic spectrum access (DSA) is a key technique in CR systems to implement dynamic spectrum change and can be easily implemented by changing the transmitted pulse shape in a C‐UWB communication system. In this paper, we propose an orthogonal expansion based pulse shaping method to implement DSA and to compensate for antenna distortion, which uses the orthogonal Hermite functions as the orthogonal basis. In order to eliminate the direct current (DC) component existing in even orthogonal Hermite functions and to reduce the computational complexity, two modified methods and a simplification procedure are also proposed. Our results indicate that the proposed orthogonal expansion based pulse shaping methods have a much lower computational complexity than the semi‐definite programming (SDP) method, while achieving a high power efficiency. Furthermore, we demonstrate that the distortion caused by the antenna effects can also be compensated during the pulse shaping process and a better signal‐to‐noise ratio (SNR) can thus be achieved. Therefore, the proposed method is very suitable for practical application in C‐UWB communications, in which the spectrum environment changes rapidly. Copyright © 2009 John Wiley & Sons, Ltd.

In order to achieve efficient dynamic spectrum access (DSA) in Cognitive Ultra-Wideband (C-UWB) systems, an orthogonal wavelets based dynamic pulse shaping method is proposed to obtain pulses which can adapt to any given spectral requirements. Using Meyer wavelet set as the orthogonal basis, pulses with high power efficiency can be achieved. The compact support property of Meyer wavelets enables us to efficiently reduce the computational complexity in dynamic pulse shaping calculation. Moreover, we demonstrate that the proposed method is easy to implement and can achieve a good balance between power efficiency and system complexity.

In impulse radio (IR) type Ultra-Wideband (UWB) communications, orthogonal waveforms confirm to given spectral mask are desired to improve system capacity. Therefore, in this paper, an orthogonal wavelet based pulse shaping algorithm is proposed and compactly supported Meyer wavelet is used as an example to show how to obtain orthogonal pulses. Simulation results show that the proposed algorithm can obtain orthogonal pulses with high power efficiency and the pulse generator can be implemented simply as well.