Hybrid Block Diagonalization Precoding for Multi-User Weighted Sum-Rate Maximization

This paper studies large-scale multi-input multi-output(MIMO)orthogonal frequency division multiplexing(OFDM)communications in a broadband frequency-selective channel,where a massive MIMO base station(BS)communicates with multiple users equipped with multi-antenna.We develop a hybrid precoding design to maximize the weighted sum-rate(WSR)of the users by optimizing the digital and the analog precoders alternately.For the digital part,we employ block-diagonalization to eliminate inter-user interference and apply water-filling power allocation to maximize the WSR.For the analog part,the optimization of the PSN is formulated as an unconstrained problem,which can be efficiently solved by a gradient descent method.Numerical results show that the proposed block-diagonal hybrid precoding algorithm can outperform the existing works.

Resource Allocation in Multi-User Cellular Networks:A Transformer-Based Deep Reinforcement Learning Approach

To meet the communication services with diverse requirements,dynamic resource allocation has shown increasing importance.In this paper,we consider the multi-slot and multi-user resource allocation(MSMU-RA)in a downlink cellular scenario with the aim of maximizing system spectral efficiency while guaranteeing user fairness.We first model the MSMURA problem as a dual-sequence decision-making process,and then solve it by a novel Transformerbased deep reinforcement learning(TDRL)approach.Specifically,the proposed TDRL approach can be achieved based on two aspects:1)To adapt to the dynamic wireless environment,the proximal policy optimization(PPO)algorithm is used to optimize the multi-slot RA strategy.2)To avoid co-channel interference,the Transformer-based PPO algorithm is presented to obtain the optimal multi-user RA scheme by exploring the mapping between user sequence and resource sequence.Experimental results show that:i)the proposed approach outperforms both the traditional and DRL methods in spectral efficiency and user fairness,ii)the proposed algorithm is superior to DRL approaches in terms of convergence speed and generalization performance.

Joint channel and carrier frequency offset estimation for multi-user MIMO-OFDM uplink transmissions

This article proposes a new algorithm of joint channel and carrier frequency-offset OCCFO） estimation for multi-user multi-input and multi-output orthogonal frequency division multiplexing （MIMO-OFDM） systems. A least square （LS） channel estimation and a carrier frequency offset （CFO） correlation estimation are combined in this contribution. CFOs are generally estimated using training sequences in a special synchronization timeslot. In this contribution, CFO estimation is further improved by taking advantages of channel estimation based on pilot symbols in traffic timeslots. The CFOs can be first obtained from the primary channel estimation. And then, with the knowledge of the CFOs estimated, channel estimation can be enhanced greatly. Computer simulation results indicate that the proposed JCCFO scheme is of good performance. Besides, the computational complexity is low.

基于混沌序列的MIMO-OFDM雷达通信一体化波形设计

为了解决多输入多输出的正交频分复用(multiple input multiple output orthogonal frequency division multiplexing,MIMO-OFDM)雷达通信一体化信号波形由于通信信息的不确定性导致模糊函数旁瓣水平较高以及系统雷达探测能力较差的问题,提出利用混沌序列对通信信息进行直接扩频。但普通单级混沌序列具有保密性低,可用数量少,容易被破解的缺点。因此采用一种基于加权算法优化的混合型级联混沌序列对通信信息进行扩频调制,然后再通过MIMO-OFDM一体化系统进行传输。由仿真结果可知,加权后的级联混沌序列相关性和误码率性能较m序列和Gold序列更好,经此序列扩频后的一体化信号模糊函数旁瓣水平会更低,故该一体化波形雷达探测性能更佳。且混沌序列越长,信号波形雷达探测能力越好。

基于深度学习的多用户MIMO-OFDM-IM系统符号检测技术

MIMO-OFDM-IM是将MIMO-OFDM(多输入多输出正交频分复用)和IM(索引调制)结合的一种新颖的多载波调制技术。为解决目前多用户MIMO-OFDM索引调制的符号检测技术仍存在的复杂度高和误码性能受用户数量影响严重的问题,提出一种基于深度学习的符号检测框架,在该框架中,编码器与解码器都由DNN(深度神经网络)构造,采用监督式学习训练数据。实验结果表明,该框架有效地解决了以上问题。

Resource allocation algorithm for multi-user MIMO-OFDM downlink with correlated channels

To minimize transmitting power,an adaptive resource allocation algorithm is proposed for multi-user multiple input multiple output-orthogonal frequency division multiplexing(MIMO-OFDM)downlink with correlated channels,which,based on the user’s grouping according to their spatial correlations,combines the shared manner and the exclusive manner to allocate sub-carriers.Between different groups the shared manner with a null steering method based on group marginal users is applied,whereas within a group the exclusive manner is applied.The simulations show that the power efficiency and spectral efficiency are improved;the base station transmitting antenna number and the computational complexity is decreased.

Joint Multi-User Detection with Weighting Factors for Unsourced Multiple Access

Multi-user detection techniques are currently being studied as highly promising technologies for improving the performance of unsourced multiple access systems. In this paper, we propose joint multi-user detection schemes with weighting factors for unsourced multiple access. First, we introduce bidirectional weighting factors in the extrinsic information passing process between the multi-user detector based on belief propagation (BP) and the LDPC decoder. Second, we incorporate bidirectional weighting factors in the message passing process between the MAC nodes and the user variable nodes in BP- based multi-user detector. The proposed schemes select the optimal weighting factors through simulations. The simulation results demonstrate that the proposed schemes exhibit significant performance improvements in terms of block error rate (BLER) compared to traditional schemes. .

Flexible paired-orthogonal codes for multi-user MIMO-OFDM

The work proposes two novel spreading codes, called extensive double-orthogonal code （EDOC） and flexible paired-orthogonal code （FPOC）, for multi-user downlink multiple-input multiple-output （M1MO） orthogonal frequency division multiplexing （OFDM） systems. The goal of code designs is to obtain an improved bit error rate （BER） performance without loss of bandwidth efficiency. The code designs achieve space diversity by employing multiple antennas at both transmit ends and receive ends. Codes are reasonably spread into time, frequency and space domain. The proposed codes are attractively characterized with length flexibility, which breaks the ＂power of two＂ constraint. The simulation results indicate that the proposed codes improve overall BER performance, by exploiting space diversity gains. The flexibility in code length also results in high spectral efficiency.

Power allocation for MIMO-OFDM systems with multi-user decoupling and scheduling

A power allocation scheme for multi-user multiple-input multiple-output orthogonal frequency division multiplexing （MI- MO-OFDM） systems with channel state information （CSI） on transmitter and receiver is pressed. Multi-user lower allocation can be decoupled into single user lower allocation throughout null space mapping of multi-user channel and lower allocation can be performed throughout spatial-spectral water-filling for per user.To deal with more users in system and fading correlation,scheduling is oerformed to maintain the gain of power allocation.The proposed scheme can substantially improve system＇s spectral efficiency with low complexity.Simulation results validate the accuracy of theoretic analyses.

Tensor Decomposition-Based Channel Estimation and Sensing for Millimeter Wave MIMO-OFDM V2I Systems

An integrated sensing and communication(ISAC)scheme for a millimeter wave(mmWave)multiple-input multiple-output orthogonal frequency division multiplexing(MIMO-OFDM)Vehicle-to-Infrastructure(V2I)system is presented,in which both the access point(AP)and the vehicle are equipped with large antenna arrays and employ hybrid analog and digital beamforming structures to compensate the path loss,meanwhile compromise between hardware complexity and system performance.Based on the sparse scattering nature of the mmWave channel,the received signal at the AP is organized to a four-order tensor by the introduced novel frame structure.A CANDECOMP/PARAFAC(CP)decomposition-based method is proposed for time-varying channel parameter extraction,including angles of departure/arrival(AoDs/AoAs),Doppler shift,time delay and path gain.Then leveraging the estimates of channel parameters,a nonlinear weighted least-square problem is proposed to recover the location accurately,heading and velocity of vehicles.Simulation results show that the proposed methods are effective and efficient in time-varying channel estimation and vehicle sensing in mmWave MIMOOFDM V2I systems.

低频部署下MIMO-OFDM通信系统的频谱利用效率分析

主要深入研究低频部署下多进多出-正交频分复用(Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing,MIMO-OFDM)通信系统的频谱利用效率,探讨低频部署对系统性能的影响,并提出相应的优化策略。详细分析低频部署对信号传输性能和频谱利用效率的影响,评估频谱利用效率,提出针对低频部署的MIMO-OFDM系统的优化策略,最后探讨低频部署下MIMO-OFDM系统的适用场景,为实际应用提供一些建议。

Closed BER expression of multi-user DS UWB systemsin indoor fading channel

The bit error rate （BER） performance of multi-user direct spreading bi-phase shift keying （DSBPSK） direct impulse ultra wideband （UWB） systems is analyzed and simulated based on a statistical indoor multi-path fading channel model. The BER of the system is theoretically derived and given in closed form, which is expressed in terms of channel parameters and system parameters such as pulse width parameter, pulse repeat period, user number and pulse waveform. With this BER expression, the effect of these parameters on the system performance can be evaluated in a uniform way. Simulation results well match the theory numerical results, and prove that the multi-access interference （MAI） of DS-BPSK UWB is a normal distribution.

Adaptive resource allocation in downlink multi-user MC-CDMA systems

The joint channel and power allocation in the downlink transmission of multi-user multi-carrier code division multiple access（MC-CDMA） systems are investigated and the throughput maximization problem is considered as a mixed integer optimization problem. For simplicity of analysis, the problem is divided into two less complex sub-problems： power allocation and channel allocation, which can be solved by a suboptimal adaptive power allocation （APA）algorithm and an optimal adaptive channel allocation （ACA） algorithm, respectively. By combining APA and ACA algorithms, an adaptive channel and power allocation scheme is proposed. The numerical results show that the proposed APA algorithm is more suitable for MC-CDMA systems than the conventional equal power allocation algorithm, and that the proposed channel and power allocation scheme can significantly improve the system throughout performance.

Optimal subcarrier allocation for cognitive radio with multi-user OFDM and distributed antenna

The subcarrier allocation problem in cognitive radio（CR）networks with multi-user orthogonal frequency-division multiplexing（OFDM）and distributed antenna is analyzed and modeled for the flat fading channel and the frequency selective channel,where the constraint on the secondary user（SU）to protect the primary user（PU）is that the total throughput of each PU must be above the given threshold instead of the ＂interference temperature＂.According to the features of different types of channels,the optimal subcarrier allocation schemes are proposed to pursue efficiency（or maximal throughput）,using the branch and bound algorithm and the 0-1 implicit enumeration algorithm.Furthermore,considering the tradeoff between efficiency and fairness,the optimal subcarrier allocation schemes with fairness are proposed in different fading channels,using the pegging algorithm.Extensive simulation results illustrate the significant performance improvement of the proposed subcarrier allocation schemes compared with the existing ones in different scenarios.

Multi-User Connection Performance Assessment of NOMA Schemes for Beyond 5G

Non-orthogonal multiple access(NOMA)is proved to be useful to satisfy the requirements of beyond 5th generation such as massive multi-user connection.Here we compare the performances of two NOMA schemes:low code rate spreading(LCRS)scheme and interleaver division multiple access(IDMA)scheme.It is found that LCRS is superior to IDMA when number of users is small due to coding gain achieved.While IDMA is preferred when number of users is high because repetition applied in IDMA can suppress multi-user interference effectively.And interleaver is important in IDMA for randomizing the interference.Also,this paper evaluates the impact of channel decoder.It is observed that Log-MAP decoder has much better performance than that of Max-Log-MAP when number of users is large.Thus,it is recommended to use Log-MAP decoder in NOMA in high user overloading case.We also compared the performance of NOMA by using different type of channel codes.We find that NOMA using specific convolutional code has a better performance than that of using specific LDPC code when number of users is high.

Complex field network-coded cooperation based on multi-user detection in wireless networks

Cooperative communication can achieve spatial diversity gains,and consequently combats signal fading due to multipath propagation in wireless networks powerfully.A novel complex field network-coded cooperation（CFNCC） scheme based on multi-user detection for the multiple unicast transmission is proposed.Theoretic analysis and simulation results demonstrate that,compared with the conventional cooperation（CC） scheme and network-coded cooperation（NCC） scheme,CFNCC would obtain higher network throughput and consumes less time slots.Moreover,a further investigation is made for the symbol error probability（SEP） performance of CFNCC scheme,and SEPs of CFNCC scheme are compared with those of NCC scheme in various scenarios for different signal to noise ratio（SNR） values.

Multi-User Detection for Spatial Modulation toward 5G Wireless Communications

Spatial modulation(SM) is a class of novel multiple-input multiple-output(MIMO) techniques toward future wireless communications,which activates only one transmit antenna in each time slot,so as to reduce the number of RF chains for saving the implement cost.Meanwhile,considering its application in 5G systems with multiple users,the detection of multi-user spatial modulation has drawn greater attention.In this paper,a pair of efficient detectors are proposed for multi-user spatial modulation.Specially,a threshold-aided approximate message passing(T-AMP) detector is proposed with the purpose of reducing the computational complexity of traditional structured approximate message passing(Str-AMP) detector.In addition,a novel probability sorting aided approximate message passing detector,called probability-ranking-aided AMP detector(P-AMP),is also proposed with the purpose of improving the performance.Simulation results show that the proposed T-AMP detector is able to achieve similar performance as traditional StrAMP with lower complexity,while the proposed P-AMP detector exhibits a better symbol error rate(SER) performance with similar complexity.

Virtual reality for immersive multi-user firefighter-training scenarios

Background Virtual reality(VR)applications can be used to provide comprehensive training scenarios that are difficult or impossible to represent in physical configurations.This includes team training for emergency services such as firefighting.Creating a high level of immersion is essential for achieving effective virtual training.In this respect,motion-capture systems offer the possibility of creating highly immersive multi-user training experiences,including full-body avatars.Methods This study presents a preliminary prototype that helps extin-guish a virtual fire on a container ship as a VR training scenario.The prototype provides a full-body and multi-user VR experience based on the synthesis of position data provided by the motion-capture system and orientation data from the VR headsets.Moreover,the prototype facilitates an initial evaluation of the results.Results The results confirm the value of using VR for training procedures that are difficult to implement in the real world.Furthermore,the results show that motion-capture-based VR technologies are particularly useful for firefighting training,in which participants can collaborate in difficult-to-access environments.However,this study also indicates that increasing the immersion in such training remains a challenge.Conclusions This study presents a prototypical VR application that enables the multi-user training of maritime firefighters.Future research should evaluate the initial results,provide more extensive training scenarios,and measure the training progress.

Cryptanalysis and Improvement of the Multi-User QPCE Protocol with Semi-Honest Third Party

In a recent work [Quantum Inf. Process 12 （2013） 1077], a multi-user protocol of quantum private comparison of equality （QPCE） is presented. Here we point out that if we relax the constraint of a semi-honest third party, the private information of the users will be totally leaked out to the third party. A special attack is demonstrated in detail. Furthermore, a possible improvement is proposed, which makes the protocol secure against this kind of attack.

Multi-user performance analysis of differential frequency hopping system over Rayleigh-fading channel

A novel non-coherent detection scheme for differential frequency hopping(DFH)system is proposedin asynchronous multi-user environments over Rayleigh-fading channels.The synchronous and asyn-chronous multi-user performances of DFH with the conventional detection scheme and this novel detectionscheme are analyzed,respectively.The performance results are validated with simulation.The results ofanalyses and simulations prove two conclusions.Firstly,the performance of asynchronous multi-user DFHsystem overcomes that of synchronous multi-user DFH system over Rayleigh-fading channel.Secondly,the novel detection scheme can achieve better performance than the conventional non-coherent detectionscheme in asynchronous multi-user environments.