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One of promising transmission technologies for beyond-5G wireless communication is cell-free massive MIMO where all the access nodes (ANs) cooperate to coherently serve all the user equipments (UEs). Based on the benefits from massive MIMO, the novel notion of cell-free network architecture is adequate to overcome the inter-cell interference limitation in ultra-dense network (UDN) environments, owing to the full cooperation among ANs. In this paper, we develop synergetic operations between the cell-free massive MIMO and mmWave ultra-wide frequency band, which is able to provide a genuine high-quality and robust wireless pervasive service by fully utilizing the basic three pillars for wireless capacity, such as bandwidth, spectral efficiency and network densification. For this goal, we study the impacts of analog precoding schemes to be combined with zero-forcing digital precoding on cell-free mmWave massive MIMO UDN systems. In addition, we investigate the effect of correlated shadowing and pilot assignment strategies on the average spectral efficiency performance for the proposed hybrid precoding schemes in both outdoor and indoor UDN environments.

This paper focuses on the downlink of a cell-free massive multiple-input multiple-output (MIMO) system in which each of the access nodes (ANs) is equipped with low-resolution digital-to-analog converters (DACs). In particular, the system is assumed to operate over mmWave frequency with practical considerations such as pilot contamination and hybrid precoding scheme. By mimicking the effect of few-bit DACs with the additive quantization noise model (AQNM), a tight approximate rate expression is derived and analyzed with some simulation results, which provide deep understanding of the impacts from the few-bit quantization as well as channel estimation error on the performance of cell-free mmWave massive MIMO.

Cell-free massive multiple-input multiple-output (MIMO) systems are envisioned to achieve the improved spectral efficiency by supporting users via nearby access points (APs). This work addresses the optimization of beamforming weights for cell-free massive MIMO systems. The connectivity level constraints are taken into account to accommodate finite-rate fronthaul links. The minimum rate maximization problem is tackled by the weighted minimum mean squared error (WMMSE) algorithm. Numerical results show that the proposed scheme achieves significantly improved performance than a baseline scheme in overall signal-to-noise ratio (SNR) regime.

This paper studies deep learning-based beamforming design schemes for multi-user downlink systems. Two distinct objectives are considered: sum-rate maximization and min-rate maximization. Each of formulations is first tackled by classical majorization-minimization (MM) algorithms that find a locally optimum point iteratively. To reduce computational overheads of the MM algorithms, deep neural networks (DNNs) are introduced which yield optimized beamforming solutions from channel vector inputs. Performance of trained DNNs is evaluated in terms of bit-error rate (BER) measure. Numerical results show that deep learning approaches achieve the BER performance very close to MM algorithms with much reduced complexity. Also, it is desirable to adopt the minimum-rate criterion to achieve low BER performance rather than sum-rate.

Cooperative beamforming across access points (APs) and fronthaul quantization strategies are essential for cloud radio access network (C-RAN) systems. The nonconvexity of the C-RAN optimization problems, which is stemmed from per-AP power and fronthaul capacity constraints, requires high computational complexity for executing iterative algorithms. To resolve this issue, we investigate a deep learning approach where the optimization module is replaced with a well-trained deep neural network (DNN). An efficient learning solution is proposed which constructs a DNN to produce a low-dimensional representation of optimal beamforming and quantization strategies. Numerical results validate the advantages of the proposed learning solution., accepted for publication on IEEE Wireless Communications Letters

Cell-free Massive MIMO (multiple-input multiple output), where all the access nodes (ANs) cooperate to coherently serve all the user equipments (UEs) and to overcome the inter-cell interference limitation in ultra-dense network environments, has attracted significant attention from both academia and industry as a promising technology for 5G and future wireless communication. In this paper, we investigate the impacts of RF beamforming schemes to be combined with zero-forcing baseband precoding on cell-free mmWave massive MIMO UDN systems.

In this paper, we consider a edge computing (EC)- enabled heterogeneous network. By using tools from stochastic geometry and queuing theory, we derive the service probability. Then, we formulate the service probability maximization problem with respect to (w.r.t.) the service caching decision. By using successive convex approximation (SCA), we obtain a stationary point of the non-convex problem. Finally, by using numerical results, we show the proposed solution achieves a higher service probability than the baseline schemes.

In recent years, an ultra-dense network (UDN) has received considerable attention as a promising technique for improving the network capacity. In this paper, we evaluate the performance of UDN with non-coherent joint transmission (NC-JT) scheme through system-level simulation including indoor UDN scenario. Numerical results demonstrate that the NC-JT with multi-panel reception in UDN environment has better area traffic capacity and 5th percentile user spectral efficiency performances than those of 5G requirements. This indicates that the inter-cell interference in UDN is well managed by using NC-JT with multi-panel reception.

One of promising transmission technologies for beyond-5G wireless communication is cell-free massive MIMO where all the access nodes (ANs) cooperate to coherently serve all the user equipments (UEs). Based on the benefits from massive MIMO, the novel notion of cell-free network architecture is adequate to overcome the inter-cell interference limitation in ultra-dense network (UDN) environments, owing to the full cooperation among ANs. In this paper, we develop synergetic operations between the cell-free massive MIMO and mmWave ultra-wide frequency band, which is able to provide a genuine high-quality and robust wireless pervasive service by fully utilizing the basic three pillars for wireless capacity, such as bandwidth, spectral efficiency and network densification. For this goal, we study the impacts of analog precoding schemes to be combined with zero-forcing digital precoding on cell-free mmWave massive MIMO UDN systems. In addition, we investigate the effect of correlated shadowing on the average spectral efficiency performance for the proposed hybrid precoding schemes in both outdoor and indoor UDN environments.

In the downlink of a fog radio access network (F-RAN) system, a cloud processor (CP) sends independent messages to user equipments (UEs) through a set of edge nodes (ENs). The ENs are connected to the CP via backhaul links which are modeled as orthogonal digital links. Since the ENs in F-RAN have signal processing functionalities, it is assumed that the CP transmits UEs’ messages to the ENs on the backhaul links, and the ENs perform channel encoding and linear precoding based on the received messages. Due to the finite capacity of backhaul links, it is not trivial to find the optimal connectivity level which defines the number of ENs that serve each UE. This work proposes a rate-splitting approach that resolve this problem by splitting the message for each UE into multiple submessages that are simultaneously communicated with different connectivity levels. The rate and linear precoding variables for the submessages are jointly optimized so that the proposed rate-splitting scheme always outperforms baseline schemes with fixed connectivity levels. Numerical results show the effectiveness of the proposed rate-splitting scheme.

In this paper, we propose a novel resource allocation algorithm for indoor user-centric ultra dense networks using millimeter-wave band. The objective of the proposed algorithm is to maximize network performance measured in terms of per area aggregated user rate. The idea of the proposed algorithm is to minimize the interference caused by sharing the same resources. Thus, we employ iterative minimum weight matching, where the the interference is defined as the weight. In particular, information of beam forming is utilized for estimating the location of a user equipment to calculate the weight. Simulation results show that the proposed algorithm outperforms the investigated benchmark algorithms.

This letter studies deep learning (DL) approaches to optimize beamforming vectors in downlink multi-user multi-antenna systems that can be universally applied to arbitrarily given transmit power limitation at a base station. We exploit the sum power budget as side information so that deep neural networks (DNNs) can effectively learn the impact of the power constraint in the beamforming optimization. Consequently, a single training process is sufficient for the proposed universal DL approach, whereas conventional methods need to train multiple DNNs for all possible power budget levels. Numerical results demonstrate the effectiveness of the proposed DL methods over existing schemes., Comment: to appear in IEEE Wireless Communications Letters (5 pages, 3 figures, 2 tables)

This work addresses the joint design of fronthaul and edge links for a cache-aided cloud radio access network (C-RAN) system with a wireless fronthaul link. Motivated by the fact that existing techniques, such as C-RAN and edge caching, come at the cost of increased energy consumption, an energy efficiency (EE) metric is defined and adopted as the performance metric for optimization. As the fronthaul links can be used to transfer quantized and precoded baseband signals or hard information of uncached files, both soft- and hard-transfer fronthauling strategies are considered. Extensive numerical results validate the impact of edge caching, as well as the advantages of the energy-efficient design over the spectrally-efficient scheme. Additionally, the two fronthauling strategies&mdash, the soft- and hard-transfer schemes&mdash, are compared in terms of EE.

This work studies distributed uplink reception for a device-to-device (D2D) underlaid cloud radio access network (C-RAN) system, in which cellular user equipments (UEs) communicate with a baseband processing unit (BBU) through a set of distributed remote radio heads (RRHs) that are connected to the BBU via finite-capacity fronthaul links. The uplink of C-RAN system is interfered by a number of D2D communication links that operate in the same frequency band. Most of prior works on C-RAN uplink systems prescribe that the noise signals of different RRHs do not have statistical correlation. However, in the D2D underlaid C-RAN uplink systems, the effective noise signals that contain the D2D interference signals may have inter-RRH cross correlation. This work proposes an improved distributed reception scheme which leverages the noise correlation information. To tackle non-convex sum-rate maximization problem, a successive convex approximation (SCA) based iterative algorithm is derived that guarantees monotonically non-decreasing sum-rates. Some numerical results are presented that validate the advantages of the proposed scheme.

Mobile WiMAX is emerging as one of the most promising systems for 4th generation mobile wireless networks in which it is foreseen that mobile TV services will proliferate. In general, TV applications are bandwidth hogs that cause a challenging capacity problem in wireless networks. To address this challenge, a novel scheme for mobile TV services over WiMAX network, called the wireless switched digital video (WSDV) scheme, is proposed in this paper. Compared with the conventional broadcast or unicast schemes, the hybrid approach introduced in our proposed WSDV approach exploits the merits of two conventional schemes and mitigates their demerits, which enables it to increase wireless capacity for mobile TV services. In addition, we present a WiMAX design tool, based on an analytical model, which facilitates analysis of the influence of some system parameters on wireless capacity. The analytical model can capture the details of WiMAX resource allocation and take into consideration the popularity of the mobile TV contents being viewed by users-enabling it to provide an accurate estimate of the amount of bandwidth required for WiMAX TV services and also enabling a designer to optimally select the number of channels via the WSDV service while meeting a desired level of blocking probability. In addition, we demonstrate that our proposed optimized scheme outperforms the conventional schemes with respect to blocking probability. Finally, an end-to-end solution to the WSDV scheme is also presented.

This letter analyzes the communication success probability of two randomly selected devices in mmWave wireless personal area networks (WPANs). Devices are randomly distributed in a piconet, each device is equipped with a directional antenna, and the antenna direction of each device is randomly chosen and fixed during the communication. The communication of the selected pair can be performed either directly or via relaying devices. In the analysis, the probability density function of the distance for devices is used and transmissions with ideal antenna and practical antenna are considered. Numerical results show an optimal beamwidth enables efficient spatial reuse to maximize the successful communication probability of a pair of devices. It also shows that the communication of a pair of devices is difficult when the directions of antennas of devices are fixed and the transmission through sidelobe of a transmitter gives a good effect in some circumstances. The obtained results will provide a criterion for the practical design of mmWave network systems, for implementing appliances using high data rate, and for developing the technology of mmWave band.

Heterogeneous network, which consists of macro-cells and small cells, is actively researched in Long Term Evolution (LTE) area. The present handover procedure is not considered for the heterogeneous network environment. As the coverage of a small cell is limited, more frequent handovers occur. Therefore, workloads of a Mobility Management Entity (MME) and a Serving Gateway (SGW) increase. We propose the micro mobility management to reduce the workloads of the MME and the SGW. The proposed scheme introduces the mobility anchor, which handles handover between small cells without the participation of the MME and the SGW. The mobility anchor hides the change of the data path of a User Equipment (UE) from the SGW. Also, the MME can receive the notification of the change of the control path for maintenance of the Non Access Stratum (NAS) channel between the MME and the UE. The MME no longer relays the data path control signal to the SGW. The simulation result shows the reduction of the handover latency due to the simplified handover procedure.

A Dual Connectivity architecture has been proposed by 3GPP for enhancement of small cells in long term evolution heterogeneous networks. A Master eNodeB (MeNB) handles handovers on behalf of the Mobility Management Entity (MME) and the Serving Gateway (SGW) for secondary eNodeBs (SeNB) located within the coverage of MeNB. Workloads of the MME and the SGW are moved to the MeNB. Small cells can be concentrated in crowded downtown or buildings in the heterogeneous network environment. The number of handovers may be increased due to concentrated small cells having small coverage, so the workload of the MeNB can be increased inside the hot spot. We propose a micro mobility management scheme to offload the workload of the MeNB to other components. The proposed scheme introduces a mobility anchor (MA) which processes the handovers between SeNBs on behalf of MeNB. Simulation results indicate the reduction of the workload of the MeNB due to the MA.

This paper presents a terminal-assisted frame-based packet reservation multiple access (TAF-PRMA) protocol, which optimizes random access control between heterogeneous traffic aiming at more efficient voice/data integrated services in dynamic reservation TDMA-based broadband access networks. In order to achieve a differentiated quality-of-service (QoS) guarantee for individual service plus maximal system resource utilization, TAF-PRMA independently controls the random access parameters such as the lengths of the access regions dedicated to respective service traffic and the corresponding permission probabilities, on a frame-by-frame basis. In addition, we have adopted a terminal-assisted random access mechanism where the voice terminal readjusts a global permission probability from the central controller in order to handle the 'fair access' issue resulting from distributed queuing problems inherent in the access network. Our extensive simulation results indicate that TAF-PRMA achieves significant improvements in terms of voice capacity, delay, and fairness over most of the existing medium access control (MAC) schemes for integrated services.

Today, MIMO has become an indispensable scheme for providing significant spectral efficiency in wireless communication and for future wireless system, recently, it goes to two extremes: massive MIMO and single-RF MIMO. This paper, which is put in the latter, utilizes load-modulated arrays with only reactance loads for single-RF transmission of spatially multiplexed QAM signals. To alleviate the need for iterative processes while considering mutual coupling in the compact antenna, we present a novel design methodology for the loading network, which enables the exact computation of the three reactance loads per antenna element and also the perfect matching to the source with the opportunity to select appropriate analog tunable loads. We verify the design methodology by comparing the calculated values for some key parameters with the values from the circuit simulation. In addition, as an evaluation of the proposed architecture, we perform the bit error rate (BER) comparison which shows that our scheme with ideal loading is comparable to the conventional MIMO., 5 pages with 2-column format

The 57-66GHz millimeter-wave (mmWave) spectrum has been dramatically drawing interest due to the worldwide availability of the extremely wide and unlicensed bandwidth which enable us to build up multi-gigabit wireless system (MGWS). The MGWS provides the opportunity to deliver high-quality uncompressed video wirelessly. In order to realize the uncompressed video transmission, we investigate the impact of unequal error protection (UEP) scheme which can be effectively used for graceful quality degradation under harsh wireless link conditions. To allow for improved quality maintenance and efficient wireless resource usage, this paper proposes a flexible UEP method with awareness of the uncompressed video context, which offers better visual-quality and resource usage over conventional UEP and equal error protection (EEP). Computer simulations using real uncompressed high-definition images indicate that the proposed UEP scheme outperforms conventional UEP and EEP schemes in terms of average weighted peak-signal-to-noise-ration (PSNR) under both poor channel and good channel condition.

Mobile WiMAX is emerging as one of the most promising systems for 4th generation mobile wireless networks where mobile TV services are foreseen to be proliferated. These applications are bandwidth hogs which cause a challenging capacity problem. To address this challenge, a novel mobile TV services over WiMAX network, called wireless switched digital video (WSDV), is proposed in this paper. Unlike with the conventional broadcast or unicast schemes, we use a hybrid approach that exploits adaptive modulation and coding (AMC) gain in unicast scheme and at the same time accommodates arbitrary many users watching the same channel like broadcast method, which enables to increase wireless capacity for mobile TV service. In addition, we present a WiMAX design tool, based on an analytical model, maximizing WiMAX capacity and study the influence of the most important traffic and system parameters. The analytical model can capture the details on WiMAX resource allocation and consider the popularity of the mobile TV contents from user, which provides an accurate estimate of the amount of bandwidth for WiMAX TV service and also enables a designer to optimally select the number of channels via WSDV schemes while meeting a desired level of blocking probability. Finally, we also demonstrate that the optimized scheme outperforms the conventional schemes in terms of blocking probability, and address the bandwidth sharing effect with other data services.

There have been great attentions on directional MAC (D-MAC) protocol recently in wireless ad hoc networks. Even if directional MAC has benefits such as spatial reuse and thus increased throughput, it has significant problems that have not been effectively rectified including hidden terminal and deafness problems. To tackle the hidden terminal and deafness problems, we propose a new D-MAC protocol that uses circular RTS (CRTS) and circular CTS (CCTS). We evaluate the performance of our protocol using ns-2 simulator. Performance evaluation shows that our proposed D-MAC protocol can reach up to 800% throughput gain with scenario 2 (24 nodes) against scenario 1 (3 nodes).

This paper presents a switched wireless video service which can swell the capacity by serving video channels through switched broadcast, switched multicast, or switched unicast instead of standard broadcast schemes. We extend the switched video service into wireless environment and then exploit WiMAX adaptive modulation and coding gain.

In this paper, we enhance the existing upstream scheduling algorithm for VoIP service in data-over-cable system interface specification (DOCSIS) MAC protocol which is, called unsolicited grant service with activity detection (UGS-AD), not able to efficiently support various VoIP codecs with variable bit rate (VBR) and silence suppression over the shared medium hybrid-fiber-coaxial (HFC) network. We modify the UGS-AD to minimize a waste of uplink resources for supporting the VBR VoIP service. This proposed scheme is compared with the existing UGS-AD through the capacity analysis. Results show that our proposed algorithm can support more up to 59% voice users compared with the existing UGS-AD.

IEEE 802.16 defines the air interface standard for fixed/mobile broadband wireless access (BWA) metropolitan area networks (MANs), which is expected to support quality of service (QoS) for real time application such as voice over IP (VoIP). However, three major technical problems that stand in the way are: 1) absence of MAC scheduling for supporting codecs with voice activity detector (VAD); 2) absence of mapping procedure between IEEE 802.16 service flow and network flow; 3) absence of efficient admission control for VoIP. This paper proposes two schemes, statistical UGS and UGS-rtPS combined scheduling, of MAC scheduling, addresses mapping RSVP FlowSpecs parameter into IEEE 802.16 QoS parameter, and devises simple admission control algorithm for VoIP services.

Data-over-cable service interface specification (DOCSIS) MAC protocol is the de facto standard for hybrid fiber coax (HFC) network, and has also given leverage to IEEE 802.16 MAC protocol. The primary medium access control (MAC) function is contention resolution algorithm (CRA), called frame-based truncated binary exponential back-off (F-TBEB), for bandwidth requests from cable modems. The DOCSIS MAC is on the upgrade by introducing channel bonding concept in that the multiple channels can be combined together to get greater aggregate bandwidth. This paper provides a simple analytical model to compute the F-TBEB delay and throughput in single DOCSIS channel. Furthermore, we give two solutions to the problem of CRA on multiple channels and use the analytical model to determine which solution is superior.

This paper proposes effective polling scheme to control a polling interval adaptively by considering the characteristics of real-time traffic and delay constraint. In this scheme, the initial polling token generation time of each source is set as the polling interval of each source, and whether source is serviced in the frame or not is decided by relationship between poling token generation time and frame length (T). The proposed scheme adjusts the polling interval dynamically, considering delay bound whenever AP detects the inactive transition of sources. The attractive feature of the proposed scheme is that is uses contention-free based mechanism for activity detection of real-time traffic and simultaneously revised polling token generation time used for activity detection can guarantee the delay bound of real-time traffic, still conforming to IEEE 802.11 standard. Therefore this method improves inefficiency of legacy contention or contention-free based activity detection scheme. Also the proposed mechanism increases system capacity through reduction of unnecessary delay caused by the transmission of polling message when a mobile station has no packet to be transmitted. Our simulation study demonstrates that capacity of the real-time traffic can be increased considerably.

In most of broadband wireless data access systems including the cdma2000 1xEV-DO system, a maximum possible data rate prescribed by the channel condition of a terminal is reflected into the priority metric in the course of packet scheduling. Particular examples of packet scheduling algorithms include the proportional fairness and modified largest weighted delay first (M-LWDF) packet scheduling schemes. We note that all of these existing algorithms suffer from a so-called rate-length mismatch problem, which may seriously degrade the system performance. In this paper, we devise a new priority metric based on a concept of virtual DRC (Data Rate Control) to solve this particular problem. It has been shown that our virtual DRC-based packet scheduling algorithm always works better than or at least equivalently to the conventional one.

In this paper, we propose a layered access control protocol, which incorporates a dynamic polling scheme on a burst level into the fair cell scheduling (polling-based wireless access burst scheduling: P-WABS) algorithms. Both the real-time and non-real-time multimedia services can be efficiently supported under the framework of the layered access control in the wireless ATM networks. Since it provides a contention-free access control mechanism, it turns out to be adequate for the multimedia services with the real-time constraints. Multimedia service traffic, including the constant bit rate (CBR), real-time variable bit rate (rt-VBR) and available bit rate (ABR) services, is considered to analyze the proposed scheme. Simulation results show that the proposed approach significantly improves the cell loss performance of rt-VBR services while a reasonable level of fairness is achieved for the ABR services.

The exact packet loss due to buffer overflow at the transmitter side of the wireless link is derived and a closed-form approximation for the corresponding wireless effective bandwidth is obtained. This discrete fluid flow analysis (FFA) is compared with existing continuous FFA and simulation analysis. Results show that packet loss performance by the discrete FFA is more accurate than that by the continuous FFA.