Unmanned aerial vehicles (UAVs), with the advantage in on-demand and cost-effective deployment, have emerged as an aerial communication platform for supporting constant high-data rate transmission services for terrestrial stations with different mobility patterns. To this end, developing high-accuracy localization functionality is of crucial importance in tracking the target users. However, the limited payload size of a single UAV restricts precise direction-of-arrival (DOA) estimation, and the UAV-swarm based collaborative estimation architectures have become a promising remedy. In this paper, the UAV swarm is utilized to form a nested array (NA) architecture to improve the DOA estimation accuracy. A two-stage alternating iterative approach is proposed to jointly estimate the UAV position errors and DOAs through iterative feedback. Specifically, position error estimation is performed using the gradient descent method, whereas DOA estimation is achieved through a novel NA-Bessel atomic transformation and norm minimization (NA-BATNM) framework, built upon an off-grid atomic norm minimization algorithm. Simulation results demonstrate that the proposed method achieves high-precision estimation of both DOAs and UAV position errors. Furthermore, the proposed NA-BATNM method exhibits superior performance compared to grid-based DOA estimation algorithms.

The partially cooperative repair model is an available technology to deal with multiple node failures in a distributed storage system, which does not depend on the heavy assumption of exchanging data with all new nodes, increasing the flexibility of the system. In this paper, constructions and repair schemes for codes with minimum storage overhead and optimal repair bandwidth, i.e., minimum storage partially cooperative regenerating codes are proposed. These constructions show that the theoretic bound on the repair bandwidth of the partially cooperative repair model is tight for the minimum storage cases. Notably, these codes with optimal repair bandwidth may have smaller sub-packetization compared with the known codes for this model.

Recently proposed splitting receivers, utilizing both coherently and non-coherently processed signals for detection, have demonstrated remarkable performance gain compared to conventional receivers in the single-antenna scenario. In this paper, focusing on a single-input multiple-output (SIMO) setup, we propose a multi-antenna splitting receiver, where the received signal at each antenna is split into an envelope detection (ED) branch and a coherent detection (CD) branch, and the processed signals from both branches of all antennas are then jointly utilized for recovering the transmitted information. We derive a closed-form approximation of the achievable mutual information (MI), in terms of the key receiver design parameters including the power splitting ratio at each antenna and the signal combining coefficients from all the ED and CD branches. We further optimize these receiver design parameters and demonstrate important design insights for the proposed multi-antenna ED-CD splitting receiver: 1) the optimal splitting ratio is identical at each antenna, and 2) the optimal combining coefficients for the ED and CD branches are the same, and each coefficient is proportional to the corresponding antenna’s channel power gain. Our numerical results also demonstrate the MI performance improvement of the proposed receiver over conventional non-splitting receivers.

Z-complementary code sets (ZCCSs) can support interference-free multi-carrier code-division multiple access (MC-CDMA) in quasi-synchronous channels due to their favourable correlation properties. In this letter, based on the existing optimal ZCCSs and CCCs, we propose new class of optimal ZCCSs using Kronecker product. The resultant sequence sets have enlarged set size and sequence lengths which have not been reported before.

Faster-than-Nyquist signaling (FTNs) is capable of improving the signaling rate of communication system, while yielding the inter-symbol interference (ISI) complicating the receiver design. However, due to the unavoidable detection performance degradation when compression factor τ drops considerably below the Mazo limit, the achievable gain is limited. In this paper, preceding the FTN modulation, a precoding based data spreading is utilized to introduce an artificial interference, which aims to support a smaller τ that corresponds to achieving a higher capacity, at the cost of detection complexity. Further, we optimize the precoder by minimizing the mean square error (MSE) of the equalizer's output. Meanwhile, the problem is transformed and reformulated as a non-convex quadratically constrained and quadratic programming with one constraint (QCQP-1), where the consensus-alternating directions method of multipliers (ADMM) algorithm is utilized to iteratively pursue the solution. Simulation results justify the proposed scheme, where the capacity of 64-, 128-, and even 256-QAM Nyquist signaling can be achieved by precoding the 16-QAM FTNs, even without SNR loss at bit error rate (BER) of 10-5.

When oriented to the needs of the future fifth generation (5G) networks, orthogonal frequency division multiplexing (OFDM), as a modulation scheme, has some drawbacks: high out‐of‐band emission (OOBE) of power, relatively low spectrum efficiency, and poor flexibility for allocating resources. In this study, a subband superposed OFDM (OFDM) scheme, based on a variable granularity spectrum allocation, is proposed to divide the transmission channel into several subbands considering the compromises between single‐carrier and multicarrier spectrum utilisation. For accommodating the diverse 5G scenarios, appropriate signalling parameters can be independently configured among the subbands. A multistage polyphase interpolator is developed in the transmitter to reduce the implementation cost of time‐domain filter depressing the OOBE. Extremely narrow frequency guard intervals between subbands are realised by filtering to maximise the spectrum utilisation. At the receiver, a subband decision feedback and feedforward equaliser, relying on the subband's oversampling architecture, is designed to utilise the diversity gains in both the Doppler and the multipath delay domains. Simulation results indicate that the spectral efficiency, in terms of the spectrum utilisation rate, is increased up to and that the bit‐error‐rate performance is significantly improved for the subbands experiencing high‐speed mobile channels while preserving a relatively low computational complexity.

Orthogonal frequency division multiplexing (OFDM) can not meet the diverse scenarios of the future fifth generation (5G) networks due to its high out-of-band emission (OOBE), relatively low spectrum efficiency, and poor flexibility. In this paper, a nonuniform subband superposed OFDM (NSS-OFDM) scheme, based on a variable granularity (VG) spectrum allocation technique, is proposed as a candidate waveform for 5G. The VG method is exploited to divide the transmission band into a certain amount of subbands, each of which is applied to a specified application scenario through configuring the signaling parameters. To reduce the computational complexity, a multistage polyphase subfiltering architecture is utilized. Additionally, with subtly designed filters, the OOBE is significantly suppressed, which can minimize the frequency guard intervals between subbands. At the receiver, bit-error- rate is investigated for the additive white Gaussian noise and frequency selective channel. Simulation results show that the spectral efficiency, in terms of spectrum utilization rate, is increased up to 98.85% when ignoring the BER performance loss.

Filtered orthogonal frequency division multiplexing (F-OFDM) system has a high computational complexity due to its high-order filter. In this paper, a subband superposed OFDM (SS-OFDM) scheme, utilizing a multistage polyphase subfiltering structure, is proposed to reduce the complexity. In the SS-OFDM system, the entire transmission channel is divided into several subbands and each subband employs relatively low order filtering to depress its out-of-band emission (OOBE). Moreover, all the subbands implement parallel transmission in time domain, which decreases the operating rate, meanwhile shortening the filter length. Simulation results show that the spectral efficiency (with respect to spectrum occupancy ratio) is increased up to about 99% for the LTE, DTMB, and DVB-T standards, while preserving a low implementation complexity.