Search

Dual-functional radar communication (DFRC) is extremely attractive in the sixth generation systems, since it can simultaneously support communication and detection by a unified hardware platform with real-time cooperation. Considering the appealing features of multiple beams, this paper designs a dual mode multi-beam scheme composed of static and dynamic beams, so that it can simultaneously support multi-user transmission and high-accuracy targets detection. Besides, an integrated continuous phase modulation and linear frequency modulation signal is exploited to improve both range resolution of radar and bit error rate (BER) of users. To unify communication and radar systems, we define radar rate, and set the maximum sum-rate composed of communication and radar rates as the objective function. Since the optimization problem is non-convex, the problem is divided into two sub-issues, i.e., user selection, and joint beamforming design with power allocation. A successive maximum rate algorithm is presented for the former one, which can balance the performances between the sum-rate and complexity; and maximum minimization - Lagrange multiplier iteration algorithm is utilized to solve the latter one. In addition, some theoretical analyses, e.g., spectrum, BER, ambiguity function, false alarm and detection probabilities are deduced for the proposed system. Simulation results show that our proposed DFRC system can provide better sum-rate than the classical communication and radar separated systems.

To deal with channel estimation in the near-field area, previous studies have introduced orthogonal matching pursuit (OMP)-based algorithms, which are generally with high computational overhead. To tackle this issue, a novel approach based on discrete fractional Fourier transform (DFrFT) called DFrFT-clean is proposed in this letter. Instead of employing OMP, our method identifies the peaks of the DFrFT of the processed received signal to estimate the parameters of each path component of the channel. Additionally, it implements a cleaning procedure to mitigate the interference of strong paths on weaker paths. Simulation results show that the proposed DFrFT-clean method can significantly reduce the computational complexity while maintaining comparable or even favorable normalized mean square error (NMSE) performance compared to the benchmark algorithms.

Cell-free integrated sensing and communication (ISAC) offers simultaneous high-quality communication and robust target sensing, boasting superior spectral efficiency. This approach has emerged as a crucial technique in meeting the demanding requirements of 6G systems. For such a system, we investigate Voronoi-cluster multi-resolution assemblages, which involves the creation of a multi-resolution hierarchical codebook designed to support robust channel estimation and accurate latency estimation. Compared with the classical channel estimation method, the proposed scheme achieves a balance between search efficiency and detection accuracy. Leveraging on the benefits of the cell-free structure, we also propose a joint correlation multiple targets sensing algorithm to acquire the round-trip latencies of multiple targets. Moreover, we evaluate the performances of normalized mean square error, detection rate and latency estimation rate. Simulation results demonstrate that the proposed cell-free ISAC architecture provides superior detection performances than the classical centralized ISAC counterpart.

Traditional intra-aircraft communication systems were designed based mainly on electrical wired links for information exchange, which significantly increases the weight and fuel consumption of aircrafts. It is extremely difficult to examine these systems or replace defective wiring. Wireless avionics intra-communication (WAIC) is an emerging technology to mitigate these problems. This article presents an architecture of a next-generation WAIC network that uses reconfigurable intelligent surface (RIS) and focuses mainly on the wideband (WB) and millimeter wave (mmWave) communications of WAIC systems. We discuss the propagation characteristics of WB mmWave WAIC channel models inside aircrafts. Then, we introduce channel codes for WAIC systems. In particular, we propose novel low-density parity-check (LDPC) codes called collective-encoded LDPC codes (CE-LDPC). In addition, several important physical-layer techniques - for example, transceiver design, multiple-access, beamforming, RIS, and so on - are discussed with their related issues.

Opportunistic beamforming (OBF) is an appealing technique in wireless communications, since it can achieve multiuser diversity gains with low complexity. However, when the number of the waiting users is small, the system performances decline rapidly. In order to deal with the performance loss with a small number of waiting users scenario, this article presents a downlink multiuser OBF system, where each user equips multiple receive antennas. Three kinds of combining criteria are taken into consideration, which are selection combining (SC), equal gain combining (EGC), and maximum ratio combining (MRC) criteria. The statistical characteristics of equivalent channels are discussed in Nakagami-$m$ fading channels. Then, we derive the closed-form expressions of the ergodic capacities. And the influences of channel quality indication (CQI) quantization are also deduced. Numerical results show that the proposed system can achieve better ergodic capacity than the conventional beamforming schemes with the limited feedback, regardless of the number of waiting users.