Cooperative Covert Communication in Multi-Antenna Broadcast Channels

With the gradual popularization of 5G communications,the application of multi-antenna broadcasting technology has become widespread.Therefore,this study aims to investigate the wireless covert communication in the two-user cooperative multi-antenna broadcast channel.We focus on the issue that the deteriorated reliability and undetectability are mainly affected by the transmission power.To tackle this issue,we design a scheme based on beamforming to increase the reliability and undetectability of wireless covert communication in the multi-antenna broadcast channel.We first modeled and analyzed the cooperative multi-antenna broadcasting system,and put forward the target question.Then we use the SCA(successive convex approximation)algorithm to transform the target problem into a series of convex subproblems.Then the convex problems are solved and the covert channel capacity is calculated.In order to verify the effectiveness of the scheme,we conducted simulation verification.The simulation results show that the proposed beamforming scheme can effectively improve the reliability and undetectability of covert communication in multi-antenna broadcast channels.

Multi-User Semantic Fusion for Semantic Communications over Degraded Broadcast Channels

Degraded broadcast channels(DBC) are a typical multiuser communication scenario, Semantic communications over DBC still lack in-depth research. In this paper, we design a semantic communications approach based on multi-user semantic fusion for wireless image transmission over DBC. The transmitter extracts semantic features for two users separately and then effectively fuses them for broadcasting by leveraging semantic similarity. Unlike traditional allocation of time, power, or bandwidth, the semantic fusion scheme can dynamically control the weight of the semantic features of the two users to balance their performance. Considering the different channel state information(CSI) of both users over DBC,a DBC-Aware method is developed that embeds the CSI of both users into the joint source-channel coding encoder and fusion module to adapt to the channel.Experimental results show that the proposed system outperforms the traditional broadcasting schemes.

Joint Dirty Paper Coding and Linear Receiver Design for Multiuser MIMO Broadcast Channels

A multiuser multiple input multiple output (MIMO) broadcast scheme was proposed through applying dirty paper coding (DPC) at the transmitter and linear equalization at the receiver. Assuming single data stream communication for each user, joint transmitter and linear receiver design were done to enhance the system performance. Furthermore, a multiuser scheduling algorithm was presented to exploit multiuser diversity when the number of the users is larger than that of transmit antennas. The proposed system achieves the sum rate close to the Sato bound and is superior to some of the existing schemes.

Science Letters:Peak-power reduction by the lattice-reduction-aided closest point search for MIMO broadcast channels

In this letter, we present a modified vector-perturbation precoding scheme for the multiple-input multiple-output broadcast channel, where a perturbation vector is chosen to take into account both the instantaneous power and the instantaneous peak power of the transmitted signal. This perturbation vector is obtained by using the closest point search, with the aid of the lattice-reduction algorithm. Simulation results show that the proposed scheme yields a tradeoff among power efficiency, peak-to-average power ratio reduction, and complexity.

Maximizing dirty-paper coding rate of RIS-assisted multi-user MIMO broadcast channels

We consider a downlink multi-user scenario and investigate the use of reconfigurable intelligent surfaces(RISs)to maximize the dirty-paper-coding(DPC)sum rate of the RIS-assisted broadcast channel.Different from prior works,which maximize the rate achievable by linear precoders,we assume a capacity-achieving DPC scheme is employed at the transmitter and optimize the transmit covariances and RIS reflection coefficients to directly maximize the sum capacity of the broadcast channel.We propose an optimization algorithm that iteratively alternates between optimizing the transmit covariances using convex optimization and the RIS reflection coefficients using Riemannian manifold optimization.Our results show that the proposed technique can be used to effectively improve the sum capacity in a variety of scenarios compared to benchmark schemes.

Power duality for multi-antenna OFDM system in broadcast channel with user scheduling

This paper deals with design and analysis of user scheduling and power allocation for multi-antenna OFDM systems with DPC,ZF-DPC,ZF-BF and TDMA transmit strategies.We consider the general multi-user downlink scheduling problem and power minimization with multi-user rate constraints.According to the channel state,it is shown that there is a power optimal policy which selects a subset of users in each scheduling interval.We present user selection algorithms for DPC,ZF-DPC,ZF-BF and TDMA for multi-antenna OFDM system in broadcast channels,and we also present the practical water-filling solution in this paper.By the selected users with the consideration of fairness,we derive the power optimization algorithm with multi-user rate constraints.We also analyze the power duality of uplink-downlink for the transmit strategies of DPC,ZF-DPC and ZF-BF.Simulation results show that the present user-scheduling algorithm and power minimization algorithm can achieve good power performance,and that the scheduling algorithm can guarantee fairness.

Capacity Region of a Class of Gaussian Cognitive Degraded Broadcast Channel

This paper studies the cognitive broadcast channel in which the primary user communicates to the primary receiver, while the secondary user has noncausal knowledge of the primary radio's codeword and expects to communicate to two secondary receivers. Comparing with the existing cognitive radio channel which considers only one secondary receiver, cognitive broadcast channel studies the case that there are multiple secondary receivers.To this end, we investigate the fundamental limits of the performance of the Gaussian cognitive broadcast channel from the information theoretic perspective. Specifically, we derive the capacity region of the Gaussian cognitive degraded broadcast channel with weak interference.

HIGH SNR SUM CAPACITY ANALYSIS OF BD MIMO BC SYSTEMS WITH IMPERFECT CSI

We investigate the sum capacity of Block Diagonalization precoding Multiple Input Mul-tiple Output Broadcast Channels(BD MIMO BC) with imperfect Channel State Information(CSI) at the base station.Since it is difficult to obtain the exact expression,a lower and an upper bounds of the sum capacity under Gaussian channel estimation errors are drived instead.Analyses show that the gap between two bounds is considerably tight at all Signal to Noise Ratio(SNR) region.From the lower bound of the sum capacity,we can see that the multiplexing gain tends to be zero at high SNR region,which indicates that the BD MIMO BC system with channel estimation errors is interference-limited at high SNR.

Wireless Communication and Broadcasting Convergence Network Throughput

Wireless communication and broadcasting convergence networks provide a potential solution to greater traffic throughput in the future. In this paper, the throughput of a convergence network is analyzed based on the standardization project for specific requirements for local and metropolitan area networks in China, referred to as broadband wireless multimedia systems. The convergence network is modeled as a combination of a broadcasting channel and a multi-access channel with interference. The throughput is then given as a function of the time resource allocation by calculating the channel capacity with interference. The maximum throughput and the optimal time resource allocation are then determined for a given delay constraint and traffic requirements. The results give guidelines for time resource allocation and system design for convergence networks.

Novel limited feedback scheme under the MIMO broadcast system

By deducing the distribution of the normalized channel covariance matrix,a novel limited feedback scheme is proposed under multiple users（MU） multiple-input multiple-output（MIMO） broadcast channel（BC） system.The proposed scheme has advantages in three aspects.First,it has no constraints on the number of users or antennas.Second,each user＇s feedback bits are independent of the number of receiving antennas.Third,the proposed scheme avoids the storage of large-size codebook on the transceivers.Simulation results show that the performance of the proposed scheme is close to the perfect channel state information（CSI） case and it just needs a small number of feedback bits.

Capacity Comparison of CDMA and TDMA in Vector Broadcast Channel

The sum-rate capacity of CDMA and TDMA in vector broadcast channel is researched. An upper bound of sum-rate capacity in CDMA system and a lower bound of sum-rate capacity in TDMA system are derived respectively. According to these two bounds, the ratio of the two bounds at most can achieve min(M,K). Here M is the antenna number of the transmitter and K is the number of the user in this vector broadcast channel.

On the MAC-BC duality of multiuser non-regenerative MIMO relay systems

Multiple input multiple output （MIMO） relaying techniques can greatly improve the spectral efficiency and extend network coverage for future wireless systems. This article investigates a multiuser MIMO relay channel, where a base station （BS） with multiple antennas communicates with multiple mobile stations （MS） via a relay station （RS） with multiple antennas. The RS applies linear processing to the received signal and then forwards the processed signal. The dual channel conditions between MIMO relay multiple access channel （MAC） and broadcast channel （BC） are first developed for single-relay scenario with white Gaussian noise. Then the MAC-BC duality for MIMO relay systems is established by proving that the capacity region of MIMO relay MAC is equal to that of dual MIMO relay BC under the same total network transmit power constraint. In addition, the duality is also extended to multi-relay scenario with arbitrary noise. Finally, several simple general numerical examples are provided to better illustrate the effectiveness of the MIMO relay MAC-BC duality.