Uplink Direction Research Articles

Fractional Frequency Reuse in Random Hybrid FD/HD Small Cell Networks With Fractional Power Control

Small cells are regarded as a promising solution for improving the coverage and spectral efficiency of the fifth generation (5G) cellular networks. Small cell networks utilize low transmission power levels and thus, are appropriate for deploying full-duplex (FD) technology. In this paper, a hybrid full/half duplex (FD/HD) small cell network exploiting fractional frequency reuse (FFR) and fractional power control (FPC) for interference mitigation is considered. Theoretical expressions for the coverage probability and the average sum-rate in uplink and downlink directions are derived for systems that make use of conventional frequency reuse, hard FFR, and soft FFR. The impact of various system parameters, such as power control parameter, small base station (SBS) density, and self-interference cancellation (SIC) parameters on system performance are investigated. The numerical experiments show that SBSs tend to operate in FD mode for large values of SBS density and SIC level. Also, interestingly, the optimal sum-rate is achieved when all SBSs operate either in FD or in HD mode. Finally, it is observed that exploiting FFR techniques in FD networks making use of FPC, significantly improves downlink coverage probability.

Estimation of the surface user distribution influence on the interference from adjacent cells in CDMA network

Abstract In this paper we consider the network of mobile users where CDMA technique is used in cells. The dependence of disturbances/interference in the uplink direction as a result of surface user distribution in the neighbouring cells is determined. Three user distribution types are considered: the uniform one, decreasing from the cell centre to the rim and the increasing one. The interference calculation is performed using mean values of user distance from the cell centre. It is proved in the paper that interference caused by decreasingly and increasingly distributed users may differ from the interference caused by the cell with uniform user distribution by not more than ±75%.

Greedy Based Radio Resource Allocation Algorithm with SARSA Power Control Scheme in D2D Underlaying Communication

Device-to-Device (D2D) underlaying communication system is a solution in reducing the workload of eNodeB and increasing the system data rate. This communication system consists of two users, namely Cellular User Equipment (CUE) and D2D pair, where CUE will share its resources with the D2D pair. This sharing resources also causes interference and should be managed using the resource allocation algorithm. In this work, the resource allocation scheme occurs in a single cell with an uplink communication direction. The resource allocation process uses greedy and joint greedy algorithms. After CUE allocates all of its resources, SARSA algorithm performs the power allocation process. The resource allocation process involves the scheduled CUE and D2D pair. After all the resource and power are allocated, parameter performance of the system is calculated. Based on the work results, joint greedy algorithm with power allocation using SARSA algorithm have performance results 1.375 × 107 bps/Watt in energy efficiency, 43.105 bps/Hz in spectral efficiency, and 0.993 in D2D fairness index.

Low Complexity Resource Allocation Techniques for Symmetrical Services in OFDMA Systems

The popularity of symmetrical services like video conferencing, telemedicine etc. is in an upsurge. With the rapid increase in the number of customers for such services, the demand for reliable and computationally feasible resource allocation techniques satisfying all the users are also intensifying. This paper proposes two computationally feasible techniques for allocation of resources in OFDMA system specifically for services that demand similar quality in the uplink and downlink directions. The resource allocation problem is multiobjective in nature with the objectives to maximize the data rates in both directions meanwhile minimizing the difference in the bidirectional data rates for each user. Fairness has been incorporated as a major constraint in the formulation of the optimization problem. Equal Power allocation and weighted sum method are implemented for power allocation while subcarrier allocation is carried out using an evolutionary technique. The solution for subcarrier allocation is represented in a novel manner such that the complexity is reduced to a great extent at the same time attaining acceptable data rates.

Low complexity based scheduling methods for multi-user MIMO systems

The process of joint user and receive antenna scheduling is very vital in the uplink direction of multi-antenna wireless data communications system with multiple users. With higher number of receive antennas and active users, the search space becomes huge for the joint user and receive antenna scheduling process. It is very difficult to accomplish the searching through the entire search space within the wireless communication time frame. In this paper, low complexity based methods for joint scheduling of users and receive antennas have been proposed. Here, this has been shown that low complexity based scheduling scheme is able to attain system throughput which is quiet close to that of exhaustive search algorithm (by searching the entire search space). Moreover, an interesting observation can be made that the number of complex multiplications and additions required by these low complexity methods is quite less than that of exhaustive search algorithm.

Performance evaluation of OFDMA and MU-MIMO in 802.11ax networks

IEEE 802.11ax defines a new access method called Orthogonal Frequency Division Multiple Access (OFDMA) which can be used in both downlink (DL) and uplink (UL) directions. OFDMA divides the bandwidth into several Resource Units (RUs) and allows multiple stations to transmit or to receive simultaneously. UL OFDMA supports Scheduled Access (SA) RUs and Random Access (RA) RUs. Only scheduled stations are allowed to send on SA RUs, while the other stations should contend for the RA RUs. Moreover, 802.11ax defines UL MU-MIMO and enhances DL MU-MIMO. In this paper, we introduce and evaluate the efficiency of DL and UL multi-user transmissions using OFDMA and MIMO. Our results show that UL OFDMA is particularly useful when multiple stations regularly need to transmit few MPDUs. In this case, UL OFDMA may outperform full bandwidth access with up to 400%. Moreover, we find that increasing the number of RA RUs does not effectively reduce the collision rate but significantly decreases the throughput. Furthermore, we show that UL MU-MIMO significantly improves the network throughput and that the performance of DL MU-MIMO is clearly enhanced thanks to the decreased duration of the channel sounding procedure.

Resource allocation for SWIPT-enabled energy-harvesting downlink/uplink clustered NOMA networks

In this paper, the problem of network sum-rate maximization in energy-harvesting clustered non-orthogonal multiple-access (NOMA) networks with simultaneous wireless information and power transfer (SWIPT) is considered. The aim is to maximize the network sum-rate in the downlink (DL) and uplink (UL) directions via joint subcarrier assignment, time-switching and power allocation (J-SA-TS-PA), while ensuring users’ quality-of-service (QoS). Particularly, each user cluster is to be assigned a subcarrier for data transmission in both link directions. However, problem J-SA-TS-PA happens to be non-convex, and NP-hard, and thus is computationally-intensive. Alternatively, a near-optimal low-complexity iterative solution procedure is devised to solve problem J-SA-TS-PA by splitting it into two sub-problems: (1) joint time-switching and power allocation per (user cluster, subcarrier) pair, and (2) one-to-one subcarrier assignment. Simulation results are presented to evaluate the proposed solution procedure, which is shown to yield comparable network sum-rate to the J-SA-TS-PA scheme (solved via a global optimization package), and superior to its OMA-based counterpart, while satisfying QoS constraints in both link directions.

Power Allocation for D2D Communications Using Max-Min Message-Passing Algorithm

The approach of factor-graphs (FGs) is applied in the context of power control and user pairing in Device-to-Device (D2D) communications as an effective underlay concept in wireless cellular networks. D2D communications can increase the spectral efficiency of wireless cellular networks by establishing a direct link between devices with limited help from the evolved node base stations (eNBs). A well-designed user pairing and power allocation scheme with low complexity can remarkably improve the system's performance. In this paper, a simple and distributed FG based approach is utilized for power control and user pairing implementation in an underlay cellular network with D2D communications. A max-min criterion is proposed to maximize the minimum rate of all active users in the network, including the cellular and multiple D2D co-channel links in the uplink direction. An associated message-passing (MP) algorithm is presented to distributedly solve the resultant NP-hard maximization problem, with a guaranteed convergence compared to game theoretic and Q-learning based methods. The complexity and convergence of the proposed method is analyzed and numerical results confirm that the proposed scheme outperforms alternative algorithms in terms of complexity, while keeping the sum-rate of users nearly the same as centralized counterpart methods.

Towards centralized transmission coordination in WLANs: a cross-layer approach

The world is becoming more dependent on wireless networks for ubiquitous computing. Wireless local area network (WLAN) is one kind of widely-deployed wireless networks used in this context. Its network performance, which is always limited by the severe mutual interference among mobile nodes, directly affects the user experience of ubiquitous computing. In this paper, we present concurrency-based coordination mechanism (CCM), a cross-layer protocol to achieve higher performance in WLANs through making nodes coordinated centrally and effectively to avoid data packet interference, resulting in higher user experience. The design of CCM contains OpenCCM which is based on the architecture of software defined networking to schedule the transmissions in both the uplink and downlink directions centrally to maximize transmission concurrency. It also contains an interference-resistant mechanism in the physical layer that can make the control message transmitted with the data packet simultaneously to eliminate the coordination overhead, while both mutual interfered information can be detected successfully. Experiment results with USRP2 demonstrate the feasibility of the interference-resistant mechanism, and the simulations by ns-2 show that CCM can outperform other protocols significantly.

Resource allocation algorithm for symmetrical services in OFDMA systems

<p><span>The widespread acceptance of symmetrical services has urged for performance betterment techniques in wireless communication systems. In this paper, we propose an algorithm for resource allocation in MIMO-OFDMA system for applications that demand similar quality in uplink and downlink direction. The problem is formulated as multiobjective optimization problem with objectives to maximize the bidirectional data rates for individual users and to minimize the difference between the uplink and downlink data rate for each user. Fairness has been considered as a constraint in the optimization problem. The power allocation for each subcarrier in the OFDMA system is carried out using Linear Programming (LP) techniques, while the subcarrier allocation problem has been undertaken using an innovative multiobjective optimization technique that employs the concept of non-dominance in evolutionary algorithms. The results are extremely encouraging as they outperform the algorithms reported in literature using linear programming techniques or evolutionary algorithms solely. </span></p>

Joint relay assignment and energy‐efficiency maximization in energy‐harvesting downlink/uplink clustered nonorthogonal multiple‐access networks

AbstractIn this article, the problem of joint relay assignment and energy‐efficiency maximization (J‐RA‐EE‐MAX) in energy‐harvesting downlink (DL) and uplink (UL) clustered nonorthogonal multiple‐access (NOMA) networks is considered. Specifically, the aim is to perform relay assignment to user clusters in the DL and UL directions, while simultaneously maximizing energy efficiency (EE) over each relay via multiobjective optimization, and satisfying users' quality‐of‐service (QoS) constraints. However, problem J‐RA‐EE‐MAX happens to be nonconvex in each link direction, and thus is computationally prohibitive. Alternatively, a low‐complexity solution procedure is devised to solve problem J‐RA‐EE‐MAX in each link direction by: (i) optimally solving the energy‐efficiency maximizing power allocation (EE‐MAX‐PA) for each (user cluster, relay) combination to construct the relays' preference profile, and (ii) performing relay assignment via Gale's top trading cycles (TTC) matching mechanism. In particular, the optimal solution of the EE‐MAX‐PA problem is obtained by transforming it into a concave maximization problem, while the TTC mechanism is executed in linear time‐complexity so as to obtain a stable relay assignment. Simulation results are presented to validate the proposed solution procedure, which is shown to yield comparable user cluster sum‐rate and relay EE to the J‐RA‐EE‐MAX scheme, and superior to other schemes in both link directions, however, at lower computational complexity, while satisfying users' QoS constraints. Finally, this work sheds light on the importance of decoupling relay assignment in the DL/UL directions, which significantly improves user cluster sum‐rate and relay EE in comparison to coupled relay assignment schemes, and thus serves the requirements of 5G networks and beyond.

A full‐duplex radio over fiber architecture employing 12 Gbps 16 × 16 optical multiple input multiple output for next‐generation communication networks

SummaryIn this article, a full‐duplex millimeter wave (mm‐wave) enabled radio‐over‐fiber architecture is proposed for distributed antenna systems. This architecture is capable of achieving transmission of 16 × 16 optical multiple input multiple output spatial streams at 12 Gbps per spatial stream by employing wavelength division multiplexing and exploiting its other degrees of freedom such as polarization states and modes of wavelengths. A single laser source based multiwavelength comb and wavelength reuse techniques along with plastic optical fiber are employed to make the proposed architecture cost efficient. Optical heterodyne detection is performed at the radio access unit to generate mm‐wave carrier frequency at 60 GHz. Channel equalization is achieved for pulse amplitude modulation data signal by employing least mean square equalizer to mitigate the optical fiber channel effects. Our proposed system supports 16 × 12 Gbps for downlink (DL) and uplink (UL) transmissions. To evaluate the performance of the proposed system, we compare the receiver sensitivities at forward error correction limit of 3.8 × 10−3 of bit error ratio of back to back system, employing no fiber effects, with its counterparts. We show that acceptable power penalties for the fiber lengths of 200 and 400 m are achieved for both LP01 and LP11 modes in DL and UL directions.

Corrections to “Beam Coverage Comparison of LEO Satellite Systems Based on User Diversification”

In the above article [1] , there is a misquotation in Section I, part A, paragraph 6, the fourth sentence. It should read: “The DRA will be able to form at least 16 beams in the uplink direction and at least 16 additional beams in the downlink direction and will have the capability of beamforming, its power, bandwidth, size, number, and boresight dynamically assigned to each beam to maximize system performance and minimize interference with GSO and NGSO satellites [2] .”

Downlink ratio impact on downstream traffic performances on WiMAX

Worldwide Interoperability for Microwave Access (WiMAX) offers high speed data transfer with various quality of service (QoS) for different applications. One of the services is the downlink ratio adjustment. Theoretically, the parameter allows users to manage bandwidth for uplink and downlink direction. As there is no related work to proof this parameter adjustment, this paper examines the impact through network simulator for downlink streaming. With limited total capacity of the simulated network, by using 4 nodes with downlink traffics varied from 5 to 15 kbps, simulation proofs that by changing downlink ratio from 0.1 to 0.9, the downlink stream performance is increasing with delay decrement up to 5.34 ms, jitter decrement 9.1 ms and packet loss reduction about 97.62%.

Probability bounds of cross‐layer interference in femtocell‐underlay cellular networks employing interference alignment

In a conventional cellular network underlaid with femtocells, the authors employ interference alignment (IA) to restrict cross-layer co-channel interference (X-interference). In their scenario, locally obtained channel state information is allowed to be conveyed between heterogeneous nodes to construct a decentralised IA-based scheme. Furthermore, they provide closed-form formulas for the upper bounds of X-interference in both uplink and downlink directions and characterise how they asymptotically approach zero for big enough channel dimensions used by individual nodes. Simulation results demonstrate that X-interference is always bounded by the above-mentioned limits and prove accuracy of their analytical formulas.

LTE‐DSRC hybrid vehicular communication system using DFT‐spread OFDM in uplink

SummaryTechnologies are advancing at a rapid rate in the current era. People are advancing with the advancement of technologies, be it in education industry, health industry, and providing luxury. With the advent of autonomous luxury‐in‐motion car that provides in‐car‐entertainment (ICE), vehicular communication is the prerequisite towards achieving this goal. Dedicated short range communication (DSRC) is a matured vehicular communication standard, and Long‐Term Evolution (LTE) is the most competing technologies in the cellular communication. In this paper, we focus on the uplink performance of the LTE‐DSRC hybrid infrastructure. The basic transmission scheme for uplink direction is based on single carrier transmission in the form of discrete Fourier transform (DFT)‐spread Orthogonal Frequency Division Multiplexing (OFDM) with a minimum mean square error (MMSE) receiver at the LTE Evolved Node B (eNodeB) and a DSRC OFDM transmitter. A comprehensive bit error rate (BER) performance simulative study has been made on a color image transmission in uplink hybrid LTE‐DSRC system, and the results obtained are encouraging that the proposed convergence is possible, as it provides a substantial decrease in the BER with a gradual increase in the signal ‐to‐ noise ratio Signal to Noise Ratio (SNR).

A Feasibility Study of IEEE 802.11 HCCA for Low-Latency Applications

Existing optical and wireless networks designed to support today’s services may not be suitable for the emerging services, such as machine-to-machine applications of the Internet-of-Things paradigm and tactile-haptic applications of the Tactile Internet paradigm. Some of these applications must adhere to stringent quality of service requirements, especially an ultra-low end-to-end latency constraint of approximately 1 ms. In this paper, we investigate the feasibility of the wireless local area network (WLAN) infrastructure, specifically the IEEE 802.11 HCF Controlled Channel Access (HCCA) media access control (MAC) protocol, in supporting low-latency applications. The scenario considered is tactile-haptic data transmission between body-worn data collection devices and a wireless access point. In particular, we focus on uplink direction rather than downlink direction, because uplink data transmission forms a latency bottleneck of this particular network. In this paper, we first formulate an analytical model of the HCCA using a queuing theory to evaluate the average uplink latency. We then carry out global sensitivity analyses to understand the implications of various timing and network parameters on the uplink latency. Using these insights, we propose a novel strategic parameter selection (SPS) algorithm that effectively reduces uplink latency of the IEEE 802.11 WLAN. This paper provides insights into WLAN design such that latency-sensitive applications can be supported in the near future.

Bridging the Transition from IEEE 802.11ac to IEEE 802.11ax: Survival of EDCA in a Coexistence Environment

TGax aims at developing the IEEE 802.11ax protocol to provide enhanced throughput and power efficiency in dense WiFi deployment environments. The new specification shifts the focus from EDCA access to point coordination access, which aims at improving network utilization and power efficiency. Furthermore, it introduces, for the first time, the concept of RU allocation and orthogonal frequency division multiple access (OFDMA) techniques. The new specification addresses the spectral inefficiency in existing transmission by including schedule-based multi-user multiple-input, multiple- output (MU-MIMO) and multi-user OFDMA (MU-OFDMA) techniques to facilitate multi-user uplink transmission for high efficiency (HE) devices. However, complete adoption of the HE protocol is likely to take place over a period of time to offset the deployment cost. To ensure the coexistence of non-HE devices during the transition period, EDCA based single user transmission will remain the basic access technique and a focal point of spectral inefficiency for non-HE devices in the uplink direction. Motivated by our work on the performance of IEE 802.11ac, we propose an EDCA based uplink transmission technique for non-HE devices that allows multi-user transmission to improve spectral efficiency in coexistent WLAN networks.

Request-Based Polling Access: Investigation of Novel Wireless LAN MAC Scheme for Low-Latency E-Health Applications

For hospital e-health systems, a novel medium access control (MAC) scheme that achieves delay-sensitive healthcare traffic (DSHT) delivery in the uplink direction of wireless local area networks (WLANs) is proposed and investigated. By introducing a slotted request uploading period and informing hubs to upload their transmission requests orderly during the period, overhead cost associated with frequent transmitter/receiver transitions can be reduced and polling empty hubs can be eliminated. Consequently, the proposed scheme results in in-time polling of hubs, thereby optimizing packet queuing delay. Moreover, due to centralized coordination, the proposed scheme avoids contention and back-off. Such an MAC scheme is critical to the Internet of Things (IoT)-based delay-sensitive healthcare applications (DSHAs), such as unmanned patient tending and tele-diagnose/surgery in future e-health systems. Our simulation results show that under a delay constraint of $200~\mu \text{s}$ , the proposed scheme outperforms both the conventional point coordination function (PCF) and distributed coordination function (DCF) schemes in terms of DSHT throughput and has a good DSHT delivery stability performance.

Driver’s physiological responses to negotiating urbanization highways of varying complexity

In the progress of urbanization, serious crashes on curved sections of urbanization highway are a significant problem. The main reason is that urbanization highways have an impact on drivers’ physiological status. In this paper, three road simulation scenarios were implemented in a driving simulator: ‘non-urbanization highway’, ‘semi-urbanization highway’ and ‘urbanization highway’. Drivers’ physiological features were studied by observing their heart rate growth rates. The results demonstrate that heart rate growth rate was significantly affected by the degree of urbanization of the highway. On curved segments of urbanization highway, heart rate growth rate changes and vehicle speed fluctuations were significant. Moreover, heart rate growth rates in the uplink direction of curves were higher than those in the downlink direction. Speed and heart rate growth rate were highly correlated. Within the same degree of urbanization highway, drivers’ heart rate growth rates first decreased and then increased with increasing speed. A correlation model of the degree of urbanization, vehicle speed and heart rate growth rates is proposed and used to derive safety thresholds based on heart rate growth rate. The safety thresholds of heart rate growth rate were 7.6%, 22.0% and 37.0% at ‘good’, ‘fair’ and ‘poor’ levels, respectively. The main results provide a basis for identifying dangerous road sections and improving the driving comfort and safety of urbanization highways.