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Carrier sense multiple access with collision notification (CSMA/CN) is a typical representation of physical-layer (PHY)/medium access control (MAC) co-designs, where the MAC control frames are implemented or detected using PHY techniques. With CSMA/CN, the sender detects an unsuccessful transmission, with the aid of a collision notification (CN) from the receiver. In this paper, we first theoretically study the crucial impact of the CN attributes (namely, the detection threshold and the length) on system throughput in a wireless local area network (WLAN). We identify that the false-alarm probability of CN (more generally, the control frames in PHY/MAC co-designs) is a dominating metric that influences system performance. This paper will help developers select optimal CN attributes to balance various factors influencing CN detection performance. Extensive simulation results verify that our performance model is very accurate. [ABSTRACT FROM PUBLISHER]

In this paper, the scaling law of the network throughput of a special type of heterogeneous networks is studied, where a secondary network composed of cognitive users shares the same resources opportunistically with a primary network of licensed users. Some pioneering works in this area showed that this type of heterogeneous networks performs as well as two stand-alone networks under the dense network model. A key assumption behind this conclusion is that the density of the secondary network is higher than that of the primary network in the order sense, which essentially decouples the two overlaid networks as the secondary network dominates asymptotically. In this paper, we endeavor to investigate this problem with a weaker condition that the dimensions of the two overlaid networks are on the same order, under the extended network model. Our analysis shows that, with the ratio of the two network sizes larger than a threshold, this weaker (and arguably more practical) condition does not degrade either network throughput scaling. Our result further reveals the potential of cognitive radio (CR) technology in real applications. [ABSTRACT FROM PUBLISHER]

Densely deployed cellular wireless networks, which employ small cell technology, are being widely implemented. Mitigating the impact of inter- and intracell signal interferences induced by the operations of these networks is a challenging yet essential task. In this paper, we consider adaptive rate scheduling for a transmitting node, regardless of whether it is a base station (BS) or a mobile user. We aim to maximize the system's throughput through the employment of fractional frequency reuse (FFR) schemes. Each BS employs either an omnidirectional or a directional antenna system. We derive the optimal configuration of the FFR scheme and evaluate the ensuing system's performance behavior under absolute and proportional fairness requirements. To maximize the attained throughput by mobiles, we determine the best method to use to classify cell users into interior and edge mobiles. The bandwidth levels allocated for serving interior and edge mobiles are optimized. We derive approximate closed-form mathematical expressions for calculating the probability distributions of the interference signal levels measured at the destined receivers. We account for the impact of the classification process on intercell interference power levels. Under an absolute fairness requirement, we show that optimally configured FFR schemes lead to much enhanced performance. We show that the optimally configured directional-FFR schemes increase the throughput capacity by a factor of about 60% relative to that obtained by using optimal omnidirectional-FFR schemes. The analyses and simulation results presented in this paper serve to characterize the performance behavior attainable by using such small cell deployed cellular wireless network systems when employing the underlying configurations. [ABSTRACT FROM AUTHOR]

Recently, multiple concurrent transmission techniques have been proposed for smartly exploiting interference to improve network throughput. This paper considers zero-forcing (ZF) precoding that allows two interfering links to concurrently transmit under certain situations. This paper focuses on identifying appropriate schedule schemes that efficiently utilize the ZF precoding opportunities to improve network throughput. With this motivation, we define novel link models to formulate our concerned problem. We also develop a distributed scheduling algorithm by using belief propagation. Finally, we conduct extensive simulation experiments to evaluate the efficiency of ZF in improving network throughput in multihop wireless networks. Our simulations confirm that intelligently utilizing ZF in multihop networks is very effective in improving throughput. [ABSTRACT FROM PUBLISHER]

The large spectral bandwidth at millimeter-wave (mmWave) frequencies provides a mean to achieve very high data rates in wireless communication systems. A unique characteristic of mmWave is that mmWave links are very sensitive to blockage and have large propagation path loss, which exhibits low line-of-sight (LoS) probability, unstable connectivity and unreliable communication. This paper studies the influence of the blockage in pedestrian scenario, explains in detail how blockage affects the mmWave propagation characteristics. In particular, we study the behavior of the blockage due to human mobility and how it affects the timescale for outage due to blockage using knife-edge diffraction model (KED). One of the existing solutions to overcome the influence of blockage, is to associate the user equipment (UE) with other available base stations (BSs) by handover (HO) if the serving BS is blocked. In this paper, for a pedestrian scenario, we propose two reinforcement learning (RL) based user association algorithms, which accounts for the past experience of the blockage on the position of the UE. One focuses on the reward to increase the sum LoS probability and is named as blockage-aware user association (BAUA). The other focuses on the reward to balance the trade-off between the throughput and the LoS probability and is named as modified BAUA. We compare the proposed algorithm with the conventional user algorithms such as the maximum throughput based algorithm and the maximum SINR based algorithm. Simulation results show that to increase the sum LoS probability BAUA would be suitable, and to increase the average throughput maximum throughput based method would be suitable. [ABSTRACT FROM AUTHOR]

The level crossing rate (LCR) is an important second-order statistical quantity that characterizes the rate of occurrence of fading time intervals. In this paper, we investigate the LCR of multiantenna flat-fading channels in the presence of additive white Gaussian noise and cochannel interferers with unequal received powers and Doppler shifts. We first present a unified approach to derive the exact LCR of the signal-to-interference-noise ratio at a receiver, where maximum ratio combining is deployed over spatially correlated or uncorrelated systems. Through the exact LCR derivation, we identify an accurate approach to obtain a simplified approximate LCR expression in the spatially uncorrelated system case. Benefits of the LCR expressions derived in the paper are demonstrated in two important applications: 1) the packet error rate is evaluated through the finite-state Markov channel model; and 2) the optimum packet length to maximize the throughput of the system with the stop-and-wait automatic repeat request protocol is derived. The analytical results are validated by simulations. [ABSTRACT FROM PUBLISHER]

Device-to-device (D2D) communications underlaying cellular networks have been recently considered as a promising means to enhance resource utilization of the cellular network and local user throughput among devices in proximity to each other. In this paper, we investigate the joint resource block assignment and transmit power allocation problem to optimize the network performance in such a scenario. Specifically, we model the interference relationships among different D2D and cellular communication links as a novel interference graph with unique attributes and propose a corresponding joint resource-allocation scheme that can effectively lead to a near-optimal solution at the base station, with low computational complexity. Simulation results confirm that, with markedly reduced complexity, our proposed scheme achieves a network throughput that approaches the one corresponding to the optimal resource-sharing scheme obtained via exhaustive search. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a heterogenous network in which low-power indoor femtocells are deployed in the coverage area of the existing macrobase station (MBS). This paper proposes a novel coordinated random beamforming and user-scheduling strategy to improve the throughput of users served by the femtocell access point (FAP) while satisfying the quality-of-service (QoS) requirements of users served by both MBS and FAP. The strategy, termed as QoS-aware coordinated scheduling (QACS), requires limited coordination between the MBS and FAP, i.e., only the indexes of the qualified beams are shared. Exact statistical analysis for the ergodic achievable rate of both FAP and MBS with the proposed strategy are presented. Scheduling fairness is also addressed for the proposed QACS. [ABSTRACT FROM PUBLISHER]

This paper uses a spatial Aloha model to describe a distributed autonomous wireless network in which a group of transmit–receive pairs (users) shares a common collision channel via slotted-Aloha-like random access. The objective of this study is to develop an intelligent algorithm to be embedded into the transceivers so that all users know how to self-tune their medium access probability (MAP) to achieve overall Pareto optimality in terms of network throughput under spatial reuse while maintaining network stability. While the optimal solution requires each user to have complete information about the network, our proposed algorithm only requires users to have local information. The fundamental of our algorithm is that the users will first self-organize into a number of nonoverlapping neighborhoods, and the user with the maximum node degree in each neighborhood is elected as the local leader (LL). Each LL then adjusts its MAP according to a parameter R, which indicates the radio intensity level in its neighboring region, whereas the remaining users in the neighborhood simply follow the same MAP value. We show that by ensuring R \le \text{2} at the LLs, the stability of the entire network can be assured, even when each user only has partial network information. For practical implementation, we propose each LL to use R=\text{2}$ as the constant reference signal to its built-in proportional and integral controller. The settings of the control parameters are discussed, and we validate through simulations that the proposed method is able to achieve close-to-Pareto-front throughput. [ABSTRACT FROM PUBLISHER]

To support a tremendous amount of traffic demands via wireless access in 2020 and beyond, limited bandwidth of the licensed bands has been a major obstacle to boosting further the capacity of wireless services. To fundamentally break through this predicament, an emerging technology known as heterogeneous carrier communications has been launched into standardization in the form of licensed-assisted access (LAA) to the unlicensed bands. Integrating the heterogeneous cloud radio access networks and carrier aggregation, and although LAA-empowered cellular networks gain wider bandwidth from the unlicensed bands, communications may suffer from intersystem interference. To avoid interference, listen-before-talk has been designated as a mandatory function; however, it leads to significant challenges of the hidden-terminal problem. To address this open issue in LAA, in this paper, we consequently propose a resource-optimal scheme using a minimum amount of replicated radio resources to achieve the most essential latency guarantees for real-time applications. To further support non-real-time applications, a new resource control as well as the mathematical architecture inspired by so-called political communications is proposed to further maximize the throughput of packet delivery. Our scheme not only optimizes resource utilization in time and spatial domains but also suggests optimum energy efficiency and computation efficiency, to successfully deploy cellular networks on the unlicensed bands. [ABSTRACT FROM PUBLISHER]

The advancement of integrated millimeter-wave products opens the possibility of leveraging communications in 60-GHz band to meet the unprecedented traffic demand in WLAN. Despite the vast bandwidth available, millimeter-wave signals suffer from high attenuation and weak diffraction ability. Therefore, wireless communication at 60 GHz is characterized by the inherent directivity and susceptibility to blockage. Multiple Access Point (AP) architecture is proposed for 60-GHz WLAN to enhance spatial reuse and survive blockage. In the presence of multiple APs in the network, this paper addresses the important problem of user-AP association and resource allocation. We study three schemes of different complexity and investigate how to maximize user throughput with joint consideration of AP assignment and transmission scheduling. To solve the formulated problem, we propose a branch-and-cut-based solution procedure. We perform a detailed comparative analysis of the three schemes and advocate to use one-shot AP assignment-based scheduling scheme due to its simplicity and good performance. To deal with real-time traffic and human blockage, we propose an online algorithm to implement the one-shot AP assignment-based scheme to avoid frequent service disruption. Our results show that the proposed online algorithm is competitive when compared with the optimal offline algorithm. [ABSTRACT FROM AUTHOR]

Device-to-device (D2D) based offloading stands out as a promising approach to mitigate the pressure over cellular networks. From the perspectives of both operators and users, an ideal solution is expected to maximize the offloading efficiency (ratio) while guaranteeing the quality-of-service (QoS) of users. However, existing approaches seldom jointly take into consideration offloading efficiency optimization and QoS guarantee. In this paper, we study how to maximize the percentage of total offloaded traffic of mobile content downloading via D2D, while guaranteeing the user minimum throughput under limited buffer size. The major challenge is how to incorporate all potential D2D opportunities to maximize the offloading performance. We propose a spatial–temporal dynamic graph (STDG) to capture all possible D2D opportunities in D2D-based traffic offloading. Based on STDG, we mathematically formulate an optimization problem of maximizing the offloading efficiency, subject to throughput requirement and buffer size constraint. The formulated problem is a linear-fractional problem and can be transformed into an equivalent linear program, whose solution reveals the maximum offloading ability that D2D achieves under QoS satisfaction. Trace-based simulations validate the superiority of our approach over three benchmark approaches. [ABSTRACT FROM AUTHOR]

Heterogeneous cellular networks (HetNets) are to be deployed for future wireless communications to meet the ever-increasing mobile traffic demand. However, the dense and random deployment of small cells and their uncoordinated operation raise important concerns about energy efficiency. On the other hand, discontinuous transmission (DTX) mode at the base station (BS) serves as an effective technology to improve energy efficiency of the overall system. In this paper, we investigate energy efficiency under a finite local delay constraint in the downlink HetNets with the random DTX scheme. Using a stochastic-geometry-based model, we derive the local delay and energy efficiency in a general case and obtain closed-form expressions in some special cases. These results give insights into the effect of key system parameters, such as path-loss exponents, BS densities, signal-to-interference-ratio (SIR) threshold, and mute probability on system performance. We also provide the low-rate and high-rate asymptotic behavior of the maximum energy efficiency. It is analytically shown that it is less energy efficient to apply the random DTX scheme in the low-rate regime. In the high-rate regime, however, a random DTX scheme is essential to achieve the finite local delay and higher energy efficiency. Finally, we extend the analysis to the load-aware DTX scheme, where the mute probability depends on the user activity level. [ABSTRACT FROM AUTHOR]

Coordinated multipoint (CoMP) is corroborated to be an effective technology in mitigating cochannel interference (CCI) and enhancing system performance in picocell systems, which consist of a large number of pico base stations (BSs). In picocell systems, effective CoMP clustering schemes could provide significant gains of system performance such as throughput and cell-edge spectrum efficiency (SE). Moreover, an intrinsic problem of densely deployed networks is the cost of signaling overhead and data exchange between BSs in clusters. In this paper, a novel semidynamic clustering scheme based on affinity propagation for CoMP-Pico is presented to maximize user SE and throughput under the constraint of backhaul cost. Our proposed scheme consists of online and offline stages that can achieve good performance and low complexity. Simulation results show that the proposed scheme yields significant gains of SE and throughput and low running time compared with the existing clustering schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate multiuser scheduling with joint user pairing, resource allocation, and power control (PC) in Long-Term Evolution (LTE) uplink cellular networks. We first derive the received signal-to-interference-plus-noise ratio (SINR) in spatial multiuser single-carrier frequency-division multiple-access (SC-FDMA) systems with frequency-domain minimum mean square error (MMSE) equalization. Based on this, we formulate an optimization problem as joint multiuser pairing, resource allocation, and PC to maximize the weighted throughput of the system. We then divide it into a two-step optimization problem, which is suboptimal but significantly reduces the complexity. The two-step problem first performs optimal frequency resource allocation and user pairing for a given transmit power value and then adjusts the transmit power to maximize the weighted throughput when frequency resources are allocated and users are paired. With the help of high-interference indicators exchanged among multiple base stations (BSs), we develop an iterative distributed and low-complexity algorithm to further simplify the two-step problem. System-level simulation results show that the proposed algorithm can effectively mitigate interference and significantly outperforms the existing algorithms. [ABSTRACT FROM PUBLISHER]

Spectrum scarcity and intercell interference (ICI) are two fundamental limiting factors in wireless cellular systems. Soft frequency reuse (SFR) has been proposed as an effective way to manage the spectrum and reduce ICI in cellular systems. In a static SFR scheme, the allocations of transmit power or subcarriers in each cell are fixed prior to system deployment. This limits the potential performance of the SFR scheme. In this paper, we propose an intercell resource-allocation algorithm, which is referred to as the adaptive SFR algorithm (ASFR), that dynamically optimizes subcarrier and power allocations for multicell wireless networks to improve system capacity. The ASFR first finds the subcarrier and power allocations in each cell by using exhaustive search and greedy descend methods and then iteratively repeats among cells until a predefined convergence criterion is satisfied. The theoretical analysis proves the convergence of the ASFR algorithm. Simulation results show that the ASFR achieves a higher system throughput and better cell edge user performance than existing frequency reuse schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a non orthogonal multiple access (NOMA) system using coexisting narrow and wide beams to increase total capacity. In our proposed system, a base station considers the state of user mobility and supports users with either a narrow or a wide beam according to the mobility state. The proposed NOMA system uses the beam gain between a narrow and a wide beam, as well as the power gain from the pathloss difference in NOMA scheme. The system is thus less influenced by user mobility at the point of NOMA pairing. In the proposed system, we consider two power allocation schemes, namely the max and fair power allocation methods, and propose a pairing algorithm to maximize the capacity by minimizing the interference between narrow and wide beam user. The result verifies that the proposed system improves sum throughput, compared with the OMA and conventional NOMA system. [ABSTRACT FROM AUTHOR]

The mounting content sharing among users has resulted in a considerable rise in wireless data traffic, pressurizing the cellular networks to undergo a suitable upheaval. A competent technology of the fifth-generation (5G) networks for efficiently supporting proximity-based applications is device-to-device (D2D) communication, underlaying cellular networks. Significant advances have been made till date, for allocating resources to D2D users in cellular networks, such that sharing of spectral resources between cellular and D2D users is carried out in a coordinated manner. In this paper, a sector-based radio resource allocation (SBRRA) algorithm for resource block (RB) allocation to D2D pairs has been proposed, where the number of resource blocks (RBs) is allocated to each D2D pair in an adaptive manner, based on the demanded application by each pair. Different applications demand a varying number of RBs, in accordance with their priority. This algorithm focuses on the use of sectored antennas at the base station, for a better performance and low complexity. Extensive simulations are carried out, considering real-time scenario, for ensuring satisfactory quality of service (QoS) and quality of experience (QoE) by the users. The efficiency of the proposed scheme is proved by comparing it with the RB allocation using hidden Markov model. [ABSTRACT FROM AUTHOR]

One of the key challenges in wireless networking is allocating the available radio resources to maximize key service delivery parameters such as the aggregate throughput and the multimedia quality of experience (QoE). We propose a novel and effective scheduling policy that allocates resource blocks, such that interference power is shifted toward capacity-saturated users, while improving the throughput of unsaturated users. The highlight of this paper is that the proposed scheme can dramatically improve the performance of cells that have a high discrepancy in its signal-to-noise ratio (SNR) distribution, which is typical in urban areas. The results show that a free-lunch (FL) solution is possible, whereby for negligible performance degradation in the saturated users, a large improvement in the nonsaturated users can be obtained. However, on average, the number of FL user pairings is low. By relaxing the degradation constraints, the non-FL (NFL) solution can yield a greater multiuser throughput gain. Motivated by a surge in mobile multimedia traffic, we further demonstrate that the proposed scheduling may have a profound impact on both energy efficiency and QoE of multimedia service delivery. [ABSTRACT FROM PUBLISHER]

Cooperative communications has received tremendous interests in wireless systems. The communication performance of a single source–destination pair can be enhanced via the help of relays in traditional cooperative communications. Recent advances in interference cancelation (IC) can further enhance the performance of parallel cooperative transmissions between multiple source–destination pairs. Although some works have been done on cooperative communications, most existing works are focused on link-level physical-layer issues. Consequently, the potential benefits of cooperative communications on network-level upper layer issues, such as topology control, are largely ignored in existing works. In this paper, we study the impacts of cooperative communications, particularly IC-based cooperative communications, on topology control in wireless ad hoc networks (WANETs). We propose a distributed cooperative topology control scheme with opportunistic IC (COIC) to improve network capacity in WANETs by jointly considering both upper layer network capacity and physical-layer cooperative communications with IC. We show that the benefits brought by cooperative communications are opportunistic, which rely on network structures and channel conditions. These opportunistic advantages have significant impacts on network capacity, and our proposed COIC can effectively capture these opportunities to substantially improve network capacity. [ABSTRACT FROM PUBLISHER]

This paper investigates the performance of a non-orthogonal multiple access (NOMA) network with simultaneous wireless information, and power transfer (SWIPT) based battery-assisted energy harvesting (EH) full-duplex relay (FDR). In each signalling interval, the base-station communicates directly to a near user (NU), and through an EH FDR to a far user (FU). Considering the power-splitting (PS) protocol with a non-linear EH model, we derive closed-form expressions for the NU, and FU outage probabilities. We also demonstrate how the battery energy, and PS parameter can be chosen to maximize the FU throughput while ensuring a desired NU throughput when there is imperfect interference cancellation at the NU. Computer simulation results validate the accuracy of the derived expressions, and demonstrate that augmenting the harvested energy with a small quantum of the relay's battery energy can considerably improve the FU performance. [ABSTRACT FROM AUTHOR]

Millimeter wave (mmWave) has been widely considered as a promising technology in the next generation wireless communication systems. Various beam-based directional transmission techniques have been proposed to compensate high pathloss caused by mmWave properties. However, mobility effect of users potentially causes severe inter-beam interferences, which has not been fully-investigated in existing studies. In this paper, we have analyzed different types of mobility-aware beam interference models. Additionally, the theoretical SINR is derived based on channel statistics and the trajectories of users. We propose a mobility-aware subband and beam resource allocation (MSBA) scheme for the mmWave subband-beam massive multi-input multi-output (SB-MMIMO) systems. The proposed MSBA benefits from reduced computation complexity for maximizing system throughput constrained by quality-of-service (QoS) demands of users. The first phase of MSBA scheme is responsible for resource block assignment; while the second phase allocates beamwidth and beam directions according to the analytical derivations. Numerical results show that the proposed MSBA scheme can effectively achieve the highest system throughput and the lowest complexity compared to existing schemes in open literatures. [ABSTRACT FROM AUTHOR]

In Long-Term Evolution (LTE) random access (RA) systems, upon an access failure, the user equipment not only performs a backoff to randomly spread the retransmission attempt over a certain time period but also increases the transmission power for the retransmission, which is called a power ramping (PR) scheme. This paper analyzes the RA performance of LTE-based two-tier small-cell networks, in which the PR scheme may be a source of uplink cross-tier interference to the macrocell and small cells. To reduce cross-tier interference, we propose a scheme for partial sharing (PS) of orthogonal random access preambles (RAPs), in which small cells are allowed to use a subset of RAPs, whereas the macrocell uses the whole set of RAPs. We compare the PS scheme with a full-sharing scheme, in which the entire set of RAPs is shared by the macrocell and small cells. Our study characterizes the RA performances of LTE-based two-tier small-cell networks in terms of throughput, access delay, mean power consumption, and RAP-dropping probability and shows the benefits of the PS scheme and its trade-off between throughput and access delay of small cells. [ABSTRACT FROM PUBLISHER]

In this paper, the problem of mode switching in multiple-input–multiple-output (MIMO) broadcast channels utilizing the Per-User Unitary Rate Control (PU2RC) transmission scheme is considered. Since there is no mathematical expression for the achievable rate of the PU2RC systems, it is proposed to approximate them using proper bounds. It is shown that certain simple feedback distributions will lead to tight bounds on the achievable rates of the PU2RC systems. The proposed bounds are used for the calculation of mode-switching points and maximization of the system rate under different multiplexing order conditions. The asymptotic behavior of the preferred modes is also studied under high-signal-to-noise-ratio (SNR) and low-SNR conditions, and it is shown that the single-user transmission mode is the preferred mode for both regimes. [ABSTRACT FROM PUBLISHER]

In this paper, we study the issues of medium access control (MAC) for multihop wireless networks with directional antennas. Existing solutions to directional antenna MAC problems rarely account for the impact of minor lobes and typically assume that the neighboring nodes' locations are known a priori. As a result, they are not applicable to practical systems or mobile nodes. In this paper, we propose a reservation-based directional medium access control (RDMAC) protocol for multihop wireless networks based on the IEEE 802.11 distributed coordination function. The design objective of RDMAC is to increase the network throughput by reducing interference among neighboring nodes. We then develop an analytical model for RDMAC to investigate the throughput performance of RDMAC under arbitrary node density. The analytical model provides insights into RDMAC parameter settings. We also evaluate the performance of the proposed RDMAC through ns-2 simulations. The results validate the accuracy of our analytical model and show that our mechanism outperforms existing solutions, in terms of higher throughput. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a new concept of a knowledge management framework to enable a self-optimizing and self-learning for wireless system operation in real time. The framework encapsulates both environment and intelligent agent to reach optimal operation through sensing, perception, reasoning, and learning in a truly autonomous fashion. The agent derives adequate knowledge from previous actions improving the quality of future decisions. Domain experience was provided to guide the agent while exploring and exploiting the set of possible actions in the environment. Thus, it guarantees low-cost learning and achieves a near-optimal network configuration addressing the non-deterministic polynomial-time hardness problem of joint channel and location optimization in a wireless system. Extensive simulations are run to validate its fast convergence, high throughput, and resilience to dynamic interference conditions. We deploy the framework on off-the-shelf wireless devices to propose autonomous self-optimization with knowledge management. [ABSTRACT FROM AUTHOR]

The emerging non-orthogonal multiple access (NOMA) technology can effectively improve the throughput performance of Internet of Things (IoT) devices. Besides throughput maximization, ensuring throughput fairness is a practical design issue when implementing NOMA in wireless powered communication networks (WPCN). To this end, we investigate the joint transmission time and power allocation problem for NOMA communication, aiming to improve the sum-throughput while guaranteeing different wireless devices’ (WDs’) throughput in multi-cell WPCN. In particular, we first analyze the feasibility of the problem by deriving the necessary and sufficient conditions for the existence of feasible solutions and propose an efficient algorithm to obtain the set of feasible values of transmission time allocation. We then propose an efficient algorithm for the transmission time allocation to improve the sum-throughput. During each search iteration, we adopt the successive convex approximation (SCA) approach to transform the non-convex power allocation problem into a sequence of convex problems and obtain the locally optimal transmit power under a fixed transmission time. Numerical simulations show that the proposed algorithm can improve the sum-throughput while guaranteeing each WD’s throughput. [ABSTRACT FROM AUTHOR]

We present in this paper a novel proactive interference avoidance scheme for mobile-to-mobile (M2M) communication as an underlay in Long-Term Evolution (LTE) downlink networks. The proposed scheme introduces an intelligent user-selective resource allocation algorithm that aims to proactively avoid interference between M2M pairs and LTE regular users while achieving a satisfactory link budget for both M2M and LTE regular links. The proposed resource allocation algorithm is based on a novel low-complexity interference estimation approach that requires only channel quality indicator (CQI) information (CSI). Since the CQI reporting mechanism has been already implemented in current LTE systems, the proposed algorithm is indeed practical and standard compatible, compared with the existing works that require perfect knowledge of the channel state information (CSI). In this research, achievable data throughput with LTE-compliant adaptive modulation and coding has been adopted as the optimization measurement, rather than the information-theoretic capacity. Therefore, the performance of the proposed scheme is practically realizable in LTE communication systems. Since the performance of the proposed scheme highly relies on the accuracy of CQI feedback, we also carry out performance analysis to evaluate the impact of CQI estimation error and delay. The simulation results show that the total achievable data throughput for LTE networks is dramatically enhanced by M2M communication with this proposed interference avoidance resource allocation scheme. [ABSTRACT FROM PUBLISHER]

Device-to-device (D2D) communications can help in achieving the higher data rate targets in emerging wireless networks. The use of D2D communication imposes certain challenges such as interference with the cellular and D2D users. A well-designed joint admission control, network mode selection, and power allocation technique in a cellular network with D2D capability can improve overall throughput. The proposed technique jointly maximizes the total throughput and number of admitted users in cellular networks under quality-of-service (QoS) and interference constraints. The joint admission control, mode selection, and power allocation problem (JACMSPA) falls into a class of mixed-integer nonlinear constraint optimization problems that are generally NP-hard. Due to the combinatorial nature of the problem, its optimal solution needs exhaustive search of integer variables whose complexity increases exponentially with the number of user pairs. In this paper, we invoke outer approximation approach (OAA)-based linearization technique to solve the JACMSPA. The proposed method gives guaranteed $\varepsilon$- optimal solution with reasonable computational complexity. Simulation results verify the effectiveness of the proposed approach method. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel tractable approach for accurately analyzing both the coverage probability and the achievable throughput of cellular networks. Specifically, we derive a new procedure referred to as the equivalent uniform-density plane-entity (EUDPE) method for evaluating the other-cell interference. Furthermore, we demonstrate that our EUDPE method provides a universal and effective means to carry out the lower bound analysis of both the coverage probability and the average throughput for various base-station distribution models that can be found in practice, including the stochastic Poisson point process (PPP) model, a uniformly and randomly distributed model, and a deterministic grid-based model. The lower bounds of coverage probability and average throughput calculated by our proposed method agree with the simulated coverage probability and average throughput results and those obtained by the existing PPP-based analysis, if not better. Moreover, based on our new definition of cell edge boundary, we show that the cellular topology with randomly distributed base stations (BSs) only tends toward the Voronoi tessellation when the path-loss exponent is sufficiently high, which reveals the limitation of this popular network topology. [ABSTRACT FROM PUBLISHER]

Relay nodes (RNs), as important components of heterogeneous networks introduced in Long-Term Evolution-Advanced systems, are employed to improve network capacity and extend cell coverage in a cost-effective manner. In heterogeneous relay networks, there are two types of user access connections: the direct link and the two-hop link. The former is used when a user accesses the base station (BS) directly, whereas the latter, which is composed of a backhaul link and an access link, is used when a user accesses the BS via an RN. For the RNs with in-band wireless backhauls, two-hop links operate in shared spectrum, and thus, resource allocation is a challenging issue to provide sufficient capacity for backhaul links while maintaining fair sharing of resources with normal macro users. In this paper, we develop a hierarchical game based on the Stackelberg model to address the resource allocation in heterogeneous relay networks. The proposed game consists of two subgames, namely, the backhaul-level game (BLG) and the access-level game (ALG), respectively. In the game model, RNs in backhaul links as leaders play the BLG, whereas mobile stations (MSs) in access links as followers play the ALG. By estimating the achievable rates of MSs, the leaders choose their optimal resource-allocation strategies, and then, the followers do the best responses to the leaders' strategies. Simulation results demonstrate that our proposed hierarchical game can guarantee the throughput balance between backhaul and access links, and thus, improve the user data rates and the overall system resource utilization, as compared with the resource-allocation schemes that consider backhaul and access links separately. [ABSTRACT FROM PUBLISHER]

In this paper, we study a wireless mesh network (WMN), where a number of access points (APs) form a wireless infrastructure and provide communications to the mobile stations (MSs). Different APs share the same frequency channel. We study how to provide fair long-term throughput for the MSs while efficiently utilizing the channel resources through effective handoff management and channel timeline allocations, where the channel time is allocated at two levels: first among the APs and then among the MSs. An optimization problem is first formulated and solved. The optimum solution is based on the assumption of having global information about the channel conditions of all the MSs and cannot be easily implemented in a practical WMN. Two distributed schemes are proposed by decoupling the handoff management and channel time allocations. The HO-CA scheme performs heuristic handoff decisions for the MSs based on their link gains to nearby APs and then optimizes the channel time allocations through an iterative process. The CA-HO scheme allocates the channel time to individual APs based on interfering relationship of the APs and then allows the MSs to make handoff decisions based on possible utilities from nearby APs. In both schemes, individual APs solve a local optimization problem to allocate channel time for their associated MSs. Numerical results indicate that both the proposed schemes can achieve very good fairness and that the HO-CA scheme achieves higher throughput. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a two-phase non-orthogonal multiple access (NOMA) scheme with cooperative relaying. In the first phase, an access point (AP) linearly combines the signals of near-user $\mathrm U_1$ and far-user $\mathrm U_2$ and then broadcasts the superimposed signal to $\mathrm U_1$ and multiple relays. $\mathrm U_1$ tries to decode its desired data by treating the signal of $\mathrm U_2$ as interference. In a cooperative zone between AP and $\mathrm U_2$ , multiple relays try to decode the signal of $\mathrm U_2$ by decoding and canceling the signal of $\mathrm U_1$. In the second phase, a decodable relay is selected to forward the far-user's signal and, meanwhile, if $\mathrm U_1$ fails to decode its desired signal in the first phase, it will try to decode and cancel the far-user's signal to further decode its desired signal again. We analyze the system throughput and investigate the impacts of various parameters. Numerical results show that our proposed scheme can greatly outperform the time division multiple access and the non-cooperative NOMA schemes in terms of throughput for most system settings. [ABSTRACT FROM AUTHOR]

Channel-width adaptation can optimize multiple performance metrics of a wireless communication link, including transmission rate, communication range, resilience to delay spread, and power consumption. Supporting variable channel width has been considered one of the most critical features of a communication radio. How to leverage a channel-width adaptive radio to improve throughput of a wireless network is a challenging problem in the medium access control (MAC) layer. So far, there exist research results on either theoretical analysis or protocol implementation for a point-to-multipoint (PMP) infrastructure network. However, the impact of channel width to a multihop wireless network has not been fully investigated yet. More specifically, how to exploit variable channel width to enhance throughput of a multihop wireless network remains an unresolved research issue. This paper addresses this issue in wireless mesh networks (WMNs) considering orthogonal frequency-division multiple-access (OFDMA)-based channel-width adaptation. Theoretical analysis is first carried out to identify appropriate algorithms for channel width adaptation. To this end, resource allocation with OFDMA-based channel-width adaptation is formulated as an optimization problem, which is proved to be NP-complete. To reduce the computational complexity, a greedy algorithm is derived to obtain a suboptimal solution. Based on such a greedy algorithm, a distributed MAC protocol is designed for channel-width adaptation for OFDMA-based WMNs. It takes advantage of variable channel width in different time slots to achieve highly efficient resource allocation. Simulation results illustrate that the distributed MAC protocol significantly outperforms MAC protocols based on traditional channel-width adaptation. [ABSTRACT FROM PUBLISHER]

Device-to-device (D2D) communications bring significant benefits to mobile multimedia services in local areas. However, these potential advantages hinge on intelligent resource sharing between potential D2D pairs and cellular users. In this paper, we study the problem of energy-efficient uplink resource sharing over mobile D2D multimedia communications underlaying cellular networks with multiple potential D2D pairs and cellular users. We first construct a novel analytical model of energy efficiency for different sharing modes, which takes into account quality-of-service (QoS) requirements and the spectrum utilization of each user. Then, we formulate the energy-efficient resource sharing problem as a nontransferable coalition formation game, with the characteristic function that accounts for the gains in terms of energy efficiency and the costs in terms of mutual interference. Moreover, we develop a distributed coalition formation algorithm based on the merge-and-split rule and the Pareto order. The distributed solution is characterized through novel stability notions and can be adapted to user mobility. From it, we obtain the energy-efficient sharing strategy on joint mode selection, uplink reusing allocation, and power management. Extensive simulation results are provided to demonstrate the effectiveness of our proposed game model and algorithm. [ABSTRACT FROM PUBLISHER]

Traffic offloading via device-to-device communications is expected to play a major role to meet the exponential data traffic growth in wireless networks. In this paper, we focus on the problem of user capacity maximization in ultra-dense heterogeneous networks with device-to-device cooperation, where a large number of users in a given geographical area request common data content, such as video on demand streaming, with strict quality of service guarantees. We aim at finding the best strategy for delivering the content either over long range connectivity from the access points or short range connectivity from peer mobile terminals while meeting a target rate per served user. We formulate the multiuser resource management problem as an optimization problem including traffic offloading and channel allocation considering a very high user density reaching up to 1.75 users per square meter. We extend the system model to include mobile terminals acting as content owners by having the content cached locally, in order to further enhance the network capacity and coverage. We then propose an iterative resource management solution, which first solves the optimization subproblem of traffic offloading with orthogonal channels, and then optimally allocates channels to the transmitters with minimized interference due to channel reuse. We also propose efficient suboptimal hierarchical tree-based algorithms that operate in real time with dynamic and fast solutions for ultra-dense networks. For performance evaluation, we consider a realistic scenario consisting of a stadium topology with thousands of mobile terminals active simultaneously. We generate results as a function of a wide range of system parameters, and demonstrate that the proposed algorithms achieve near-optimal performance with notably low time complexity. [ABSTRACT FROM AUTHOR]

This paper develops an adaptive cooperative transmission scheme with relays harvesting wireless energy. Two relays are adopted to alternately forward source data to the destination using the two-path successive relaying (TPSR) protocol. When one relay forwards previous data along with source transmitting current data, using the power-splitting technique, the other relay will harvest energy and decode the current data from the received composite signal. If the TPSR cannot be performed due to the failure of data decoding at either relay, the decode-and-forward (DF) protocol will be performed by selecting a better relay. If one relay joins in the DF relaying, it will harvest energy and decode source data using the PS technique, while the other relay will always harvest energy from the received signal. If neither TPSR nor DF relaying can be performed, the source will transfer wireless power to both relays. The transmit powers of relays and the PS ratio are judiciously determined through analyzing the occurrence probability, average power fading, and success probability of each case. Numerical results show that our adaptive relaying scheme can achieve a much higher throughput than the single-relay DF scheme and the TPSR-only scheme. [ABSTRACT FROM PUBLISHER]

Beyond third-generation (3G) wireless systems will support real-time (inelastic) and nonreal-time (elastic) traffic over a common packet-switched radio channel using quality-of-service (QoS) mechanisms to differentiate the traffic. A key challenge in accurately modeling user and system performances is to be able to simultaneously account for the impacts of mixed traffic types, QoS mechanisms, and varying radio channels. This paper presents a novel way of extending and combining a number of techniques into a single approximate analytic methodology for providing fast and accurate performance analysis of multiple inelastic- and elastic-traffic classes, which is subject to preemptive priority for the inelastic traffic. The methodology is compared with the simulation for a range of guaranteed bit-rate requirements for the inelastic traffic and overall system traffic loads, with the results showing excellent agreement between the model and simulation. [ABSTRACT FROM PUBLISHER]

In this paper, we propose an adaptive-rate transmission scheme with opportunistic scheduling in a two-hop relay network over a Rayleigh fading environment. We assume that only channel state information (CSI) at receivers is available in a decentralized network, where n source-to-destination pairs are completely independent and m half-duplex relays cooperate by exchanging their selected source IDs at the beginning of the two-hop transmission. In the limit of large n and fixed m, the system throughput of the scheme scales as (m/ \2)\log\, \log\, n. It is shown that this is the same achievable scaling even with perfect CSI assumptions at transmitters and full cooperation among nodes. Furthermore, it is shown that the optimal scaling of m is \Theta(\log\, n), under which a linear increase in throughput with m is obtained. A closed-form delay expression of the proposed scheme is also presented. [ABSTRACT FROM PUBLISHER]

In this paper, a new power/rate control scheme is proposed to increase the network throughputs of carrier-sense-multiple-access-with-collision-avoidance (CSMA/CA)-based wireless ad hoc networks with multiple transmission rates. The design principle of the scheme is to utilize the space–time resource efficiently. For this purpose, a new measure that evaluates the space–time resource consumption per bit transmission is introduced. Simulation results show that the proposed scheme is effective in improving network throughputs under the two-ray ground reflection model and the Ricean model. [ABSTRACT FROM PUBLISHER]

Most slot assignment algorithms that are proposed for spatial time-division multiple-access (STDMA) mesh networks use a simplified transmission model that does not consider the time-varying fading characteristic of a wireless channel. In addition, these algorithms are usually link based, and scheduling in each slot is fixed and done for links. When the scheduled link is in deep fade or has no traffic, the slot that is given to that link will be wasted. In this paper, we present a node-based slot assignment scheme in which scheduling in each slot is done for nodes and not links. Because a node has multiple links, it can exploit multiuser diversity, i.e., different links have different traffic and fading conditions, to achieve much better performance. [ABSTRACT FROM PUBLISHER]

The emergence of high-density wireless local area network (WLAN) deployments in recent years is a testament to the insatiable demands for wireless broadband services. The increased density of WLAN deployments brings with it the potential of increased capacity, extended coverage, and exciting new applications. However, the corresponding increase in contention and interference can significantly degrade throughputs, unless new challenges in channel assignment are effectively addressed. In this paper, a client-assisted channel assignment scheme that can provide enhanced throughput is proposed. A study on the impact of interference on throughput with multiple access points (APs) is first undertaken using a novel approach that determines the possibility of parallel transmissions. A metric with a good correlation to the throughput, i.e., the number of conflict pairs, is used in the client-assisted minimum conflict pairs (MICPA) scheme. In this scheme, measurements from clients are used to assist the AP in determining the channel with the minimum number of conflict pairs to maximize its expected throughput. Simulation results show that the client-assisted MICPA scheme can provide meaningful throughput improvements over other schemes that only utilize the AP's measurements. [ABSTRACT FROM PUBLISHER]

In multihop ad hoc networks over 802.11, the real bandwidth-delay product (BDP) cannot reach a value as large as in wired networks due to contention through wireless shared channels. As a result, conventional congestion-control algorithms cause an overshooting window problem and result in poor throughput in ad hoc networks. In this paper, we split the real round-trip time (RTT) into two parts: 1) congestion RTT and 2) contention RTT. We reveal that the contention RTT has nothing to do with the BDP and that the BDP is determined by only the congestion RTT if a link with the worst contention status does not lead to link breakage. An inadequate use of contention RTT causes a Transmission Control Protocol (TCP) congestion window overshooting problem. We propose a novel mechanism called congestion window adaptation through contention detection, which provides a more accurate method of estimating the contention status. Based on this mechanism, we present a congestion window adaptation method to limit the window size from overshooting. Simulation results show that our proposed mechanism outperforms the conventional TCP and the enhanced mechanisms called TCP with contention control and TCP with a maximum window. [ABSTRACT FROM PUBLISHER]

Multi-transmit–receive capability is fast becoming a significant feature of next-generation wireless mesh networks. It enables routers to transmit or receive distinct packets from multiple neighbors simultaneously. A key problem, however, is designing a distributed link-scheduling algorithm that ensures high network capacity. In this paper, we propose dMaxQ, which is a novel queue-length-aware distributed link scheduler that requires only one-hop neighbors' queue information and uses the celebrated max-weight policy in a distributed manner. We have evaluated the performance of dMaxQ in different network topologies for both single-hop and multihop traffic models and compared it against other approaches, including two queue-length-aware centralized algorithms and state-of-the-art distributed approaches: JazzyMAC and receive-oriented multiple access. The results show that for single-hop and multihop traffic scenarios, dMaxQ obtains, respectively, 100% and 90% of the throughput achieved by the theoretical centralized policy. Other distributed algorithms, such as JazzyMAC, only managed 25% of the theoretical throughput. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a general framework to evaluate the tradeoff between energy efficiency (EE) and spectral efficiency (SE) in cognitive radio networks (CRNs). The proposed framework is discussed in three typical CRN paradigms: underlay CRNs (UCRNs), overlay CRNs (OCRNs), and interweave CRNs (ICRNs). The EE–SE relation for three CRNs is expressed in the closed-form formulation, in which the optimal (suboptimal) EE solution as the function of SE is deduced with the corresponding limits. The theoretical analysis and numerical results indicate that the EE–SE relation in CRNs is not contrary, i.e., an optimal EE–SE tradeoff can be achieved. The proposed framework provides a useful guidance in the design of practical green CRNs. [ABSTRACT FROM AUTHOR]

Opportunistic spectrum access (OSA) in cognitive radio has been proposed to improve spectrum efficiency in which secondary users (SUs) can access the unused portion of the primary users' (PUs) spectrum temporally or spatially. OSA by multiple SUs is controlled by the medium access control (MAC) protocol. OSA MAC protocols have to avoid or prevent collisions during transmission. In addition, OSA MAC protocols have to deal with the interference between the primary and secondary systems. The key challenge is to provide service to the secondary system while not causing interruption to the primary system. In this paper, we propose an opportunistic matched filter-based (OMF) MAC protocol to jointly consider spectrum access of the idle portion of the spectrum and coordination among SUs. We first model the channel as an on–off process and then apply renewal theory to deal with spectrum access and derive the expression for the expected accumulated interference interval in terms of the transmission time. Using this expression for interference interval, we model the coordination and competition among SUs as a discrete-time Markov chain. We then perform throughput and delay analysis to derive the closed-form expressions for the aggregate secondary system throughput and average secondary packet delay. Finally, we present simulation results to verify our analysis. [ABSTRACT FROM AUTHOR]

We investigate the problem of distributed channel selection in cognitive radio networks (CRNs) by taking the demands of the users into account. In most existing channel selection approaches, it is assumed that cognitive radio (CR) users can transmit on only one channel, which leads to a problem that the users usually cannot obtain enough transmission rates to satisfy their demands. We propose a demand-aware multichannel selection strategy focusing on optimizing CR users' satisfaction. In the proposed strategy, CR users can transmit on more than one channel simultaneously. Since there is no central controller and the users are autonomous, we propose a local interaction game to achieve global optimization for the network satisfaction problem distributedly. In existing local interaction game, the players need to exchange information with all the neighboring users, which results in heavy communication overhead. We design a new local interaction game, in which CR users only need to exchange information with part of the neighboring users instead of all neighboring users. As a result, the exchanged information is significantly reduced. Simulation results show that the proposed method achieves higher network satisfaction and better fairness than the existing single-channel selection approach. [ABSTRACT FROM PUBLISHER]

This paper studies how to perform joint congestion control and scheduling with network coding in wireless networks. Under network coding, a node may need to buffer a sent packet for decoding a packet to be received later. If sent packets are not forgotten smartly, much buffer space will be taken up, leading to dropping of new incoming packets. This unexpected packet dropping harms the final throughput obtained, although optimal scheduling has been used. To solve the problem, we introduce a new node model incorporating a transmission-mode preassignment procedure and a scheduling procedure. The introduced transmission-mode preassignment avoids memorizing several sent packets to reduce buffer overhead. We develop a new scheduling policy based on our node model and analyze formally the stability property of a network system using the proposed policy. We finally evaluate the efficiency of our algorithm through simulations from the perspectives of throughput and packet loss ratio. [ABSTRACT FROM PUBLISHER]

In this paper, we propose two cross-layer algorithms, namely, the Power-optimal Scheduling Algorithm (PSA) and the Throughput-optimal Scheduling Algorithm (TSA), to minimize energy consumption and to maximize throughput, respectively, in multihop wireless networks. Our algorithms guarantee a flow-based minimum data rate and jointly integrate congestion control, power allocation, routing, and link rate scheduling. Different from traditional algorithms that assume infinite buffers, the proposed algorithms deterministically upper bound the flow-based packet queue length and thus can be employed in multihop networks with finite buffers. In addition, the algorithms achieve a power expenditure/throughput “\epsilon-close” to the optimal value, with a tradeoff of order O(\1/\epsilon) in buffer size. The average end-to-end delay upper bound can also be derived from the finite buffer property. Finally, numerical results are presented to show the performance of the two algorithms with different system parameters. [ABSTRACT FROM PUBLISHER]

This paper investigates transmit antenna selection for linearly precoded multiuser multiple-input–multiple-output (MU-MIMO) systems. First, in some precoded single-user MIMO systems, using all transmit antennas does not always lead to the best performance due to ill-conditioned channel matrices. This condition motivates us to investigate whether a similar result can be obtained in MU-MIMO systems. Based on the derived analytical results, we found that, for a given number of transmit antennas, decreasing the number of active transmit antennas [number of radio frequency (RF) units] always degrades system performance in the linearly precoded MU-MIMO systems. However, in practical systems, RF units are expensive. To reduce the hardware cost, antenna selection is usually used to reduce the number of RF units. Thus, we further analyze the performance loss due to transmit antenna selection (TAS). These analytical results provide good design references for using TAS in practical systems. Moreover, based on the analytical results, we proposed several simple TAS algorithms for linearly precoded MU-MIMO systems. Complexity analysis and simulation results show that the computational complexity of the proposed algorithms can significantly be reduced, whereas the performance is still comparable with the optimal selection scheme. As a result, the analyzed results enable us to better understand how TAS affects the MU-MIMO systems. In addition, the proposed algorithms make TAS more feasible to be used in practical systems. [ABSTRACT FROM PUBLISHER]