Network-Assisted Full-Duplex Cell-Free mmWave Massive MIMO Systems with DAC Quantization and Fronthaul Compression

In this paper,we investigate networkassisted full-duplex(NAFD)cell-free millimeter-wave(mmWave)massive multiple-input multiple-output(MIMO)systems with digital-to-analog converter(DAC)quantization and fronthaul compression.We propose to maximize the weighted uplink and downlink sum rate by jointly optimizing the power allocation of both the transmitting remote antenna units(T-RAUs)and uplink users and the variances of the downlink and uplink fronthaul compression noises.To deal with this challenging problem,we further apply a successive convex approximation(SCA)method to handle the non-convex bidirectional limited-capacity fronthaul constraints.The simulation results verify the convergence of the proposed SCA-based algorithm and analyze the impact of fronthaul capacity and DAC quantization on the spectral efficiency of the NAFD cell-free mmWave massive MIMO systems.Moreover,some insightful conclusions are obtained through the comparisons of spectral efficiency,which shows that NAFD achieves better performance gains than cotime co-frequency full-duplex cloud radio access network(CCFD C-RAN)in the cases of practical limited-resolution DACs.Specifically,their performance gaps with 8-bit DAC quantization are larger than that with1-bit DAC quantization,which attains a 5.5-fold improvement.

Cell-free biocatalysis coupled with photo-catalysis and electro-catalysis: Efficient CO_(2)-to-chemical conversion

The increasing atmospheric carbon dioxide (CO_(2)) concentration has exposed a series of crises in the earth's ecological environment.How to effectively fix and convert carbon dioxide into products with added value has attracted the attention of many researchers.Cell-free enzyme catalytic system coupled with electrical and light have been a promising attempt in the field of biological carbon fixation in recent years.In this review,the research progresses of photoenzyme catalysis,electroenzyme catalysis and photo-electroenzyme catalysis for converting carbon dioxide into chemical products in cell-free systems are systematically summarized.We focus on reviewing and comparing various coupling methods and principles of photoenzyme catalysis and electroenzyme catalysis in cell-free systems,especially the materials used in the construction of the coupling system,and analyze and point out the characteristics and possible problems of different coupling methods.Finally,we discuss the major challenges and prospects of coupling physical signals and cell-free enzymatic catalytic systems in the field of CO_(2) fixation,suggesting possible strategies to improve the carbon sequestration capacity of such systems.

Deep Reinforcement Learning Based Joint Cooperation Clustering and Downlink Power Control for Cell-Free Massive MIMO

In recent times,various power control and clustering approaches have been proposed to enhance overall performance for cell-free massive multipleinput multiple-output(CF-mMIMO)networks.With the emergence of deep reinforcement learning(DRL),significant progress has been made in the field of network optimization as DRL holds great promise for improving network performance and efficiency.In this work,our focus delves into the intricate challenge of joint cooperation clustering and downlink power control within CF-mMIMO networks.Leveraging the potent deep deterministic policy gradient(DDPG)algorithm,our objective is to maximize the proportional fairness(PF)for user rates,thereby aiming to achieve optimal network performance and resource utilization.Moreover,we harness the concept of“divide and conquer”strategy,introducing two innovative methods termed alternating DDPG(A-DDPG)and hierarchical DDPG(H-DDPG).These approaches aim to decompose the intricate joint optimization problem into more manageable sub-problems,thereby facilitating a more efficient resolution process.Our findings unequivo-cally showcase the superior efficacy of our proposed DDPG approach over the baseline schemes in both clustering and downlink power control.Furthermore,the A-DDPG and H-DDPG obtain higher performance gain than DDPG with lower computational complexity.

Optimal AP Deployment in Cell-Free Massive MIMO Systems with LoS/NLoS Transmissions:A Stochastic Geometry Approach

Cell-free massive multiple-input multipleoutput(MIMO)is a promising technology for future wireless communications,where a large number of distributed access points(APs)simultaneously serve all users over the same time-frequency resources.Since users and APs may locate close to each other,the line-of-sight(Lo S)transmission occurs more frequently in cell-free massive MIMO systems.Hence,in this paper,we investigate the cell-free massive MIMO system with Lo S and non-line-of-sight(NLo S)transmissions,where APs and users are both distributed according to Poisson point process.Using tools from stochastic geometry,we derive a tight lower bound for the user downlink achievable rate and we further obtain the energy efficiency(EE)by considering the power consumption on downlink payload transmissions and circuitry dissipation.Based on the analysis,the optimal AP density and AP antenna number that maximize the EE are obtained.It is found that compared with the previous work that only considers NLo S transmissions,the actual optimal AP density should be much smaller,and the maximized EE is actually much higher.

Secure symbol level precoding for cell-free network based on band-region constraint of the eavesdropper’s receiving signal

A symbol level secure precoding scheme based on band-region constraint of the eavesdropper’s receiving signal is proposed to enhance the energy efficiency of cell-free multiple-input multiple-output(MIMO)networks in the presence of an eavesdropper while guaranteeing the quality of service(QoS)of user and the security of system.Moreover,to lighten its high computational complexity,original problem is divided into several cascade sub-problems firstly,and then those sub-problems are handled by combining Lagrangian dual function and improved Hooke-Jeeves method together.Comparative ex-periment with other secure symbol-level precoding schemes demonstrate that proposed scheme can achieve the lower power consumption with almost same symbol error rate and QoS of user.

Clinical use of donor-derived cell-free DNA in kidney transplantation

Traditional monitoring of kidney transplant recipients for allograft dysfunction caused by rejection involves serial checks of serum creatinine with biopsy of the renal allograft if dysfunction is suspected.This approach is labor-intensive,invasive and costly.In addition,because this approach relies on a rise in serum creatinine above historical baselines,injury to the allograft can be extensive before this rise occurs.In an effort to address this,donor-derived cell-free DNA(dd-cf DNA)is being used with increasing frequency in the clinical setting as a means of diagnosing a rejection of the renal allograft early in the course.This can poten-tially allow for early intervention to minimize not only injury,but the intensity of antirejection therapy needed and the avoidance of side effects.Here,we will review the available methodology for the determination and quantification of dd-cf DNA,the data supporting its use in clinical practice and the limitations of this technology.

Cooperative Distributed Beamforming Design for Multi-RIS Aided Cell-Free Systems

Cell-free systems significantly improve network capacity by enabling joint user service without cell boundaries,eliminating intercell interference.However,to satisfy further capacity demands,it leads to high-cost problems of both hardware and power consumption.In this paper,we investigate multiple reconfigurable intelligent surfaces(RISs)aided cell-free systems where RISs are introduced to improve spectrum efficiency in an energy-efficient way.To overcome the centralized high complexity and avoid frequent information exchanges,a cooperative distributed beamforming design is proposed to maximize the weighted sum-rate performance.In particular,the alternating optimization method is utilized with the distributed closed-form solution of active beamforming being derived locally at access points,and phase shifts are obtained centrally based on the Riemannian conjugate gradient(RCG)manifold method.Simulation results verify the effectiveness of the proposed design whose performance is comparable to the centralized scheme and show great superiority of the RISs-aided system over the conventional cellular and cell-free system.

RIS-Assisted Cell-Free MIMO: A Survey

Cell-free(CF)multiple-input multiple-output(MIMO)is a promising technique to enable the vision of ubiquitous wireless connectivity for next-generation network communications.Compared to traditional co-located massive MIMO,CF MIMO allows geographically distributed access points(APs)to serve all users on the same time-frequency resource with spatial multiplexing techniques,resulting in better performance in terms of both spectral efficiency and coverage enhancement.However,the performance gain is achieved at the expense of deploying more APs with high cost and power consumption.To address this issue,the recently proposed reconfigurable intelligent surface(RIS)technique stands out with its unique advantages of low cost,low energy consumption and programmability.In this paper,we provide an overview of RIS-assisted CF MIMO and its interaction with advanced optimization designs and novel applications.Particularly,recent studies on typical performance metrics such as energy efficiency(EE)and spectral efficiency(SE)are surveyed.Besides,the application of RIS-assisted CF MIMO techniques in various future communication systems is also envisioned.Additionally,we briefly discuss the technical challenges and open problems for this area to inspire research direction and fully exploit its potential in meeting the demands of future wireless communication systems.

Cell-Free大规模MIMO系统中基于传输时延的缓存策略研究

为了满足未来移动互联网中用户的超低时延和超高可靠需求,将无线缓存技术与无小区大规模多输入多输出系统相结合,设计了基于AP间协作缓存及区域流行度评估的缓存模型。推导出涉及AP分簇、协作缓存以及区域流行度的传输时延表达式,并将内容放置问题表述为最小化总内容传输时延问题。通过对优化问题的NP-hard和拟阵约束下次模单调性的证明,提出了基于贪婪算法的缓存部署优化策略。仿真结果表明,所提策略可有效降低系统内容传输时延和提升缓存命中率。

Liquid biopsy in patients with hepatocellular carcinoma: Circulating tumor cells and cell-free nucleic acids

Hepatocellular carcinoma(HCC), with its high incidence and mortality rate, is one of the most common malignant tumors. Despite recent development of a diagnostic and treatment method, the prognosis of HCC remains poor. Therefore, to provide optimal treatment for each patient with HCC, more precise and effective biomarkers are urgently needed which could facilitate a more detailed individualized decision-making during HCC treatment, including the following; risk assessment, early cancer detection, prediction of treatment or prognostic outcome. In the blood of cancer patients, accumulating evidence about circulating tumor cells and cell-free nucleic acids has suggested their potent clinical utilities as novel biomarker. This concept, so-called "liquid biopsy" is widely known as an alternative approach to cancer tissue biopsy. This method might facilitate a more sensitive diagnosis and better decision-making by obtaining genetic and epigenetic aberrations that are closely associated with cancer initiation and progression. In this article, we review recent developments based on the available literature on both circulating tumor cells and cell-free nucleic acids in cancer patients, especially focusing on Hepatocellular carcinoma.

Wireless Powered IoE for 6G: Massive Access Meets Scalable Cell-Free Massive MIMO

A key challenge to the scalable deployment of the energy self-sustainability(ESS)Internet of Everything(IoE)for sixth-generation(6G)networks is juggling massive connectivity and high spectral efficiency(SE).Cell-free massive multiple-input multiple-output(CF mMIMO)is considered as a promising solution,where many wireless access points perform coherent signal processing to jointly serve the users.However,massive connectivity and high SE are difficult to obtain at the same time because of the limited pilot resource.To solve this problem,we propose a new framework for ESS IoE networks where the user activity detection(UAD)and channel estimation are decoupled.A UAD detector based on deep convolutional neural networks,an initial access scheme,and a scalable power control policy are proposed to enable the practical scalable CF mMIMO implementation.We derive novel and exact closed-form expressions of harvested energy and SE with maximum ratio(MR)processing.Using local partial minimum mean-square error and MR combining,simulation results prove that the proposed framework can serve more users,improve the SE performance,and achieve better user fairness for the considered ESS IoE networks.

Liquid biopsy in patients with pancreatic cancer: Circulating tumor cells and cell-free nucleic acids

Despite recent advances in surgical techniques and perioperative management, the prognosis of pancreatic cancer(PCa) remains extremely poor. To provide optimal treatment for each patient with Pca, superior biomarkers are urgently needed in all phases of management from early detection to staging, treatment monitoring, and prognosis. In the blood of patients with cancer, circulating tumor cells(CTCs) and cell-free nucleic acids(cf NAs), such as DNA, m RNA, and noncoding RNA have been recognized. In the recent years, their presence in the blood has encouraged researchers to investigate their potential use as novel blood biomarkers, and numerous studies have demonstrated their potential clinical utility as a biomarker for certain types of cancer. This concept, called "liquid biopsy" has been focused on as a less invasive, alternative approach to cancer tissue biopsy for obtaining genetic and epigenetic aberrations that contribute to oncogenesis and cancer progression. In this article, we review the available literature on CTCs and cfN As in patients with cancer, particularly focusing on PCa, and discuss future perspectives in this field.

Mesenchymal stem cell-derived exosomes: Toward cell-free therapeutic strategies in regenerative medicine

Mesenchymal stem cells(MSCs)are multipotent stem cells with marked potential for regenerative medicine because of their strong immunosuppressive and regenerative abilities.The therapeutic effects of MSCs are based in part on their secretion of biologically active factors in extracellular vesicles known as exosomes.Exosomes have a diameter of 30-100 nm and mediate intercellular communication and material exchange.MSC-derived exosomes(MSC-Exos)have potential for cell-free therapy for diseases of,for instance,the kidney,liver,heart,nervous system,and musculoskeletal system.Hence,MSC-Exos are an alternative to MSCbased therapy for regenerative medicine.We review MSC-Exos and their therapeutic potential for a variety of diseases and injuries.

Liquid biopsy of gastric cancer patients:Circulating tumor cells and cell-free nucleic acids

To improve the clinical outcomes of cancer patients, early detection and accurate monitoring of diseases are necessary. Numerous genetic and epigenetic alterations contribute to oncogenesis and cancer progression, and analyses of these changes have been increasingly utilized for diagnostic, prognostic and therapeutic purposes in malignant diseases including gastric cancer (GC). Surgical and/or biopsy specimens are generally used to understand the tumor-associated alterations; however, those approaches cannot always be performed because of their invasive characteristics and may fail to reflect current tumor dynamics and drug sensitivities, which may change during the therapeutic process. Therefore, the importance of developing a non-invasive biomarker with the ability to monitor real-time tumor dynamics should be emphasized. This concept, so called “liquid biopsy”, would provide an ideal therapeutic strategy for an individual cancer patient and would facilitate the development of “tailor-made” cancer management programs. In the blood of cancer patients, the presence and potent utilities of circulating tumor cells (CTCs) and cell-free nucleic acids (cfNAs) such as DNA, mRNA and microRNA have been recognized, and their clinical relevance is attracting considerable attention. In this review, we discuss recent developments in this research field as well as the relevance and future perspectives of CTCs and cfNAs in cancer patients, especially focusing on GC.

Quick recovery and characterization of cell-free DNA in seminal plasma of normozoospermia and azoospermia： implications for non-invasive genetic utilities

We established a quick and reliable method for recovering cell-free seminal DNA （cfsDNA）, by using the binding-washing-elution procedure on the DNA purification column. Low variations （below 15%） among the triplicate values of cfsDNA quantity verified the reproducibility of our cfsDNA recovery method. Similar cfsDNA yield and size distribution between seminal plasma acquired by filtration and centrifugation confirmed the presence of cfsDNA. To investigate the general characterization of cfsDNA, the quantitation and size distribution of cfsDNA from normozoospermic and azoospermic semen were analyzed by real-time PCR and electrophoresis, respectively. CfsDNA concentration in semen with normozoospermia （n = 11） was 1.34 ± 0.65 μg ·mL^-1, whereas a higher cfsDNA concentration was observed in azoospermia （2.56 ± 1.43 μg ·mL^-1, n = 9）. The continuous distribution of DNA fragments ranging from -1 kb to 15 kb and a spectrum of multiples of 180-bp fragments were observed in each normozoospermic and azoospermic sample. Distinct characteristic DNA ladder fragmentations in some azoospermic samples implicated that cfsDNA originate partly from apoptotic cells. CfsDNAs of 36 selected azoospermic patients with known information of Y chromosome microdeletion were subjected to the same microdeletion analysis by multiplex PCR and PCR amplification of sY114 （1 450 bp）. All multiplex PCR reactions with cfsDNA amplified successfully and provided the same result as leukocyte DNA. PCR amplification of sY114 gave a 1 450-bp amplicon as expected. Our data suggested the potential use of cfsDNA in search of biomarker or diagnostic procedures.

Beamforming Optimization for RIS-Aided SWIPT in Cell-Free MIMO Networks

Reconfigurable intelligent surface(RIS)is a promising technology that utilizes massive low-cost elements to reflect incident signals to desired direction.In this paper,we consider a RIS-aided cell free multiple-input multiple-output(MIMO)network that composed of multiple access points(APs),multiple RISs,multiple information receivers(IRs),and multiple energy receivers(ERs).Under the maximum transmit power constraints of the APs and the minimum total energy harvesting power constraints of the ERs,we aim to maximize the weighted sum-rate(WSR)by jointly optimizing the beamforming matrices and the passive RIS reflection matrices.However,the formulated problem is nonconvex and very challenging to solve.Therefore,we propose an alternating optimization algorithm to obtain a suboptimal solution.Explicitly,the proposed algorithm decomposes the original optimization problem into three subproblems that can be efficiently solved.To overcome the nonconvexity of the subproblems,a successive convex approximation(SCA)based algorithm is proposed to tackle the energy harvesting constraints.Moreover,an alternating direction method of multipliers(ADMM)based algorithm is proposed to optimize the constant modulus constrained RIS reflecting elements.Finally,simulations are conducted to demonstrate the performance advantages of the proposed algorithms.

Joint Flexible Duplexing and Power Allocation with Deep Reinforcement Learning in Cell-Free Massive MIMO System

Network-assisted full duplex(NAFD)cellfree(CF)massive MIMO has drawn increasing attention in 6G evolvement.In this paper,we build an NAFD CF system in which the users and access points(APs)can flexibly select their duplex modes to increase the link spectral efficiency.Then we formulate a joint flexible duplexing and power allocation problem to balance the user fairness and system spectral efficiency.We further transform the problem into a probability optimization to accommodate the shortterm communications.In contrast with the instant performance optimization,the probability optimization belongs to a sequential decision making problem,and thus we reformulate it as a Markov Decision Process(MDP).We utilizes deep reinforcement learning(DRL)algorithm to search the solution from a large state-action space,and propose an asynchronous advantage actor-critic(A3C)-based scheme to reduce the chance of converging to the suboptimal policy.Simulation results demonstrate that the A3C-based scheme is superior to the baseline schemes in term of the complexity,accumulated log spectral efficiency,and stability.

Cell membrane and bioactive factors derived from mesenchymal stromal cells: Cell-free based therapy for inflammatory bowel diseases

Inflammatory bowel diseases(IBD)are chronic inflammatory disorders of the gastrointestinal tract associated with multifactorial conditions such as ulcerative colitis and Crohn’s disease.Although the underlying mechanisms of IBD remain unclear,growing evidence has shown that dysregulated immune system reactions in genetically susceptible individuals contribute to mucosal inflammation.However,conventional treatments have been effective in inducing remission of IBD but not in preventing the relapse of them.In this way,mesenchymal stromal cells(MSC)therapy has been recognized as a promising treatment for IBD due to their immunomodulatory properties,ability to differentiate into several tissues,and homing to inflammatory sites.Even so,literature is conflicted regarding the location and persistence of MSC in the body after transplantation.For this reason,recent studies have focused on the paracrine effect of the biofactors secreted by MSC,especially in relation to the immunomodulatory potential of soluble factors(cytokines,chemokines,and growth factors)and extracellular vehicles that are involved in cell communication and in the transfer of cellular material,such as proteins,lipids,and nucleic acids.Moreover,treatment with interferon-γ,tumor necrosis factor-α,and interleukin-1βcauses MSC to express immunomodulatory molecules that mediate the suppression via cell-contact dependent mechanisms.Taken together,we present an overview of the role of bioactive factors and cell membrane proteins derived from MSC as a cell-free therapy that can improve IBD treatment.

Value of dynamic plasma cell-free DNA monitoring in septic shock syndrome: A case report

BACKGROUND Mortality due to septic shock is relatively high.The dynamic monitoring of plasma cell-free DNA(cfDNA)can guide the treatment of septic shock.CASE SUMMARY Herein,we present a typical case of septic shock syndrome caused by the bacilli Acinetobacter baumannii and Pantoea.The patient complained of abdominal pain,fever and chills upon admission to the Emergency Department.Marked decreases in white blood cells and procalcitonin(PCT)were observed after the patient received continuous renal replacement and extracorporeal membrane oxygenation.Plasma cfDNA levels were consistently high,peaking at 1366.40 ng/mL,as measured by a duplex real-time PCR assay with an internal control,which was developed as a novel method for the accurate quantification of cfDNA.The patient died of septic shock on HD 8,suggesting that cfDNA could be used to monitor disease progression more effectively than PCT and the other inflammatory factors measured in this case.CONCLUSION CfDNA may be a promising marker that complements other inflammatory factors to monitor disease progression in patients with septic shock.

A Successful Transmission Probability Based AP Clustering Scheme in User-Centric Cell-Free Networks

Cell-free network is a promising architecture with numerous merits in energy efficiency and macro diversity,which is easy and flexible to integrate with other communication technologies.However,its current network topology where access points(APs)are connected to a central processing unit(CPU)to jointly serve the users,causes huge burden to the fronthaul network.To deal with this problem,in this paper,we first combine thoughts in user-centric(UC)network where users are served by selected subset of APs.Then,we propose a successful transmission probability(STP)based AP clustering scheme to reduce the fronthaul capacity requirement(FCR).By using stochastic geometry and proper approximation methods,the approximated STP calculation expression is derived.Numerical simulations demonstrate that the obtained STP expression can provide a tight approximation compared to Monte Carlo simulation results under different system parameters while keeping the computation tractable.Furthermore,the relationship between the FCR and the STP threshold is formulated as a clustering optimization problem,which gives insights on clustering design in UC-CF network systems.We show by simulation results that the proposed scheme requires less fronthaul capacity than the original CF approach while ensuring the STP performance.