Access Point Mode Research Articles

On the Sum Spectral Efficiency of Dynamic TDD-Enabled Cell-Free Massive MIMO Systems

We examine the sum spectral efficiency (SE) performance of a cell-free massive multiple-input multiple-output (CF-mMIMO) system, where each access point (AP) can operate either in the uplink or downlink mode in each slot, corresponding to dynamic time-division duplexing (DTDD) across the APs. We derive the sum SE of the system under a weighted combining of the signals received at the central processing unit. We show that the sum SE is a sub-modular function of the subset of active APs. We exploit this to develop a novel, low-complexity, greedy algorithm for choosing the mode of operation of the APs which is guaranteed to achieve within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(1-1/e)$ </tex-math></inline-formula> of the sum SE attained via a full-complexity brute-force search. Our results show that DTDD with greedy AP mode selection can nearly double the sum SE compared to a TDD based CF-system where all APs operate in the uplink or downlink modes simultaneously. Thus, it is a promising duplexing scheme for beyond 5G communications.

Learning Based Joint Cache and Power Allocation in Fog Radio Access Networks

The growing demand for rich content services and developments of industrial internet of things and vehicle-to-everything communications pose challenging requirements for the next-generation fog radio access networks (F-RANs). Though F-RANs are promising to support these enabling technologies by leveraging edge caching and edge computing, delay performance is still straightforward and should be optimized. A latency optimization problem for F-RANs is formulated, and to solve the problem, a deep reinforcement learning (DRL) based joint proactive cache placement and power allocation strategy is proposed in this paper. Furthermore, to enhance the content serving capability at the edge, we rigorously consider that a set of F-RAN nodes cooperatively serve the content request. The user's demand can be adaptively satisfied either through fog access point mode at the network edge or by centralized cloud computing mode at the cloud tier. The key idea of the proposal is to learn the user's demand and make an intelligent decision for caching appropriate content and allocating a significant amount of power resources. Simulation results show the effectiveness and performance gains of the proposal under maintaining throughput compared with other baselines.

Characterization of Wireless Data Transmission over Wi-Fi in a Biomechanical Information Processing System

This paper presents a characterization of the wireless transmission of biomechanical signals in an embedded system, where a TCP protocol is used in an IEEE 802.11 communications network (Wi-Fi). The embedded system under study, called Imocap, allows the collection, analysis and transmission of biomechanical signals in real-time for various applications, among which the analysis of the movement of the lower and upper extremities and the operation of various control systems stand out. To accomplish this, Imocap is equipped with a Wi-Fi transceiver module (ESP8266) and various input and output peripherals. The wireless communication performance of Imocap, exposed in this paper, was analyzed through different tests in miscellaneous conditions like indoors, outdoors and in the presence of interference, noise and other wireless networks. The different test protocols conducted result in the Imocap system: 1) has a maximum effective range of 45.6 m when in Access Point mode; 2) has a maximum effective range of 44.3 m when in Station mode. In indoors and under the same conditions, the Imocap system: 3) has a maximum effective range of 81.25 m2, either Access Point or Station mode. The results showed that the transmission of biomechanical information through Wi-Fi using the TCP protocol is efficient and robust, both indoors and outdoors, even in environments of radio frequency interference. The use of this protocol is emphasized since its use allows the transmission of packages to be carried out in a controlled manner, allowing the error handling and recovery. In this way, it is possible to carry out efficient and robust wireless communication through embedded and portable devices, focusing mainly on areas such as medicine, telemedicine and telerehabilitation.

Anti-fog System for High Speed Vehicles Using WI-FI

Smog is considered as a serious worldwide problem especially in Asian countries resulting sometimes in fatal injuries. Wireless communication can play a vital role in solving this problem effectively. In this paper, a novel offline system is proposed and designed to drive the vehicles safely in a dense smoggy atmosphere where nothing is visible to the driver. The system utilizes off the shelf wireless fidelity modules operating in station mode for moving vehicles and access point mode for immobile vehicles to enable the driver to drive along a smoggy path in case if any vehicle is stopped on the motorway due to any reason (accident, car breakdown etc.) along with the use of node microcontroller unit, ultrasonic sensors and accelerometer. Ultra Sonic sensors installed on vehicle show the distance of front objects to let him drive safely. Additionally, an android application is also designed so that the users having an Internet resource can see road hazards (speed breakers, potholes, debris etc) ahead. The K-means clustering method using elbow technique is used to analyze the mobile phone’s global positioning system coordinates and speed of vehicle to do effective road monitoring. The proposed system would not only be helpful for the drivers to drive smoothly on the road in foggy environment and avoid unforeseen catastrophes but can also be used for effective road monitoring.

Design and Deployment of UAV-Aided Post-Disaster Emergency Network

Designing a reliable, resilient, and quickly deployable emergency communication network is a key challenge for post-disaster management. In this paper, a UAV-assisted emergency Wi-Fi network is proposed to expedite the rescue operations by guiding the survivors to the nearest rescue camp location. Here, the Raspberry PI (RPI) development board, mounted on UAV is considered to form a Wi-Fi chain network over the disaster region. During network set-up, the proposed solutions for the design challenges like UAV synchronization, avoid communication disruption and surveillance data management are the key contributions of this paper. The designed UAV network is capable of doing on-site surveillance and transmitting the data to the relief center for better rescue planning. One major challenge is to alert a survivor about the emergency network, which is addressed by designing a captive portal. Furthermore, to extend the Wi-Fi network, an Android-based application is developed by which each smartphone acts as a relay for its neighbor. Three types of field experiment are carried out to evaluate the performance of the designed prototype. It is found from the field results; the Wi-Fi access point mode and user datagram protocol are more suitable for network design as compared to Ad-Hoc mode and transmission control protocol, respectively. It is also observed from the experiment that the maximum hop distance for the prototype is 280 meters and 290 meters for a Wi-Fi configuration following IEEE 802.11n and IEEE 802.11ac protocol, respectively.

A cm-Scale 2.4-GHz Wireless Energy Harvester With NanoWatt Boost Converter and Antenna-Rectifier Resonance for WiFi Powering of Sensor Nodes

The widespread use of WiFi in the 2.4-GHz ISM band creates the potential for RF powering using WiFi radios. This paper presents the design of a cm-scale RF-energy harvester including antenna, rectifier, and dc–dc boost converter for RF powering in the 2.4-GHz ISM band. The rectifier and boost converter are designed while considering cold-start operation and nanowatt-scale available power from the rectifier for RF incident power $\times $ and ~2 $\times $ improvement in range compared to prior art. Measurements using a commercial WiFi TX demonstrate the ranges of up to 1.25 m for 14-dBm output power with 1.3% TX duty-cycling in WiFi access-point mode, demonstrating the feasibility of powering sensors from RF power beacons in the 2.4-GHz ISM band as well as from background WiFi transmissions.

The Performance Of Wireless 802.11 B/G For Data Acquisition Utilization

This study aimed to increase the range of the wireless IEEE 802.11 b/g by adding the antenna gain, testing the performance of access point with router access point mode of the wireless IEEE 802.11 b/g, and comparing the performance of access point with router access point mode of the wireless IEEE 802.11 b/g.This research was conducted in Makassar. The method used was by performing direct performance measurement of end to end node, namely: delay time, throughput and Packet Loss. Wireless access point was placed on the SPN tower (Sekolah Tinggi Kepolisian Negara/College of Police of State) of Batua. Wireless clients were placed at 2.7 km, 5.36 km, 8.81 km and 10.82 km.The results showed that wireless IEEE 802.11 b/g can be used for data communications up to 10.82 km by adding 24 dB of antenna gain. Wireless with access point mode and router access point mode experienced 100% of packet loss with 60000 bytes of window size packets’ delivery and can handle only 1000 bytes of window size packets. The performance of wireless with access point mode was better than wireless with access point router mode, as follows: For access point packet: 0% of lost wireless, 8 ms of delay time, and 1 Mbps of throughput; On the other hand, for router access point packet: 30% of lost wireless, 26 ms of delay time, and 0.31 Mbps of throughput. Wireless 802.11 B/G can be used as data communication decive for cost-effective data acquisition and has not impact to carbon emission

A Self-Adaptive Model-Based Wi-Fi Indoor Localization Method.

This paper presents a novel method for indoor localization, developed with the main aim of making it useful for real-world deployments. Many indoor localization methods exist, yet they have several disadvantages in real-world deployments—some are static, which is not suitable for long-term usage; some require costly human recalibration procedures; and others require special hardware such as Wi-Fi anchors and transponders. Our method is self-calibrating and self-adaptive thus maintenance free and based on Wi-Fi only. We have employed two well-known propagation models—free space path loss and ITU models—which we have extended with additional parameters for better propagation simulation. Our self-calibrating procedure utilizes one propagation model to infer parameters of the space and the other to simulate the propagation of the signal without requiring any additional hardware beside Wi-Fi access points, which is suitable for real-world usage. Our method is also one of the few model-based Wi-Fi only self-adaptive approaches that do not require the mobile terminal to be in the access-point mode. The only input requirements of the method are Wi-Fi access point positions, and positions and properties of the walls. Our method has been evaluated in single- and multi-room environments, with measured mean error of 2–3 and 3–4 m, respectively, which is similar to existing methods. The evaluation has proven that usable localization accuracy can be achieved in real-world environments solely by the proposed Wi-Fi method that relies on simple hardware and software requirements.

Spiderman Handover for Railway Communications

In this paper, we propose a new mechanism, called the Spiderman Handover, for enabling Wi-Fi technology to support high speed mobility. It introduces two new 802.11 operational modes: the Spiderman mode and the Wireless Switch Access Point mode. We describe its operation, highlighting the Spiderman Handover and the Gratuitous ARP Loop routing update procedure as key elements for providing seamless horizontal handover for high-speed vehicles such as trains. We discuss and evaluate its operation theoretically and by means of simulation, concluding that the proposed mechanism is able to provide track-side connectivity with virtually no packet loss while keeping the observed latency invariant to the handover frequency.

Adaptive role switching for fair and efficient battery usage in device-to-device communication

By leveraging device-to-device communication, opportunistic networks promise to complement infrastructure-based networks, by enabling communication in remote areas or during disaster and emergency situations, as well as by giving rise to novel applications, such as location-based sharing. Yet, to become feasible in practice and accepted by users, it is crucial that opportunistic communication be energy-efficient. Through extensive and detailed measurements and analysis, we show in this paper, that all of today's device-to-device communication technologies suffer from two grave energy consumption problems: very expensive neighbor discovery and unfair connection maintenance. We consider the two most well-known technologies -- Wi-Fi Direct and Bluetooth, and a third solution based on the WLAN access point mode -- WLAN-Opp. We carefully design a measurement setup which allows us to isolate the energy consumption of individual operations (e.g. CPU sleeping/waking up, scanning/listening for neighbors etc) for thesetechnologies and compare the technologies based on these measurements. Our analysis reveals that neighbor discovery can quickly drain a device's battery, depending on the required scanning frequency. In addition, once a connection is established, the "host" of the connection consumes two to five times the energy needed by a "client". To solve this unfairness problem, we propose a strategy that periodically alternates the hosting role among the peers. Further, we minimize the cost of the role switching operation by using the distribution of the residual connection time of two peers to calculate an adaptive switching period. We examine the trade-off between fairness and switching cost on real-world connection traces and show that our scheme largely outperforms static role switching. Finally, we demonstrate that our fair role switching scheme is also effective when run on real devices.

A Seamless Handoff Scheme with Access Point Load Balance for Real-Time Services Support in 802.11 Wireless LANs

IEEE 802.11 wirelesses LANs (WLANs) have been rapidly deployed in enterprises, public areas, and households. Voice-over-IP (VoIP) and similar applications are now commonly used in mobile devices over wireless networks. Recent works have improved the quality of service (QoS) offering higher data rates to support various kinds of real-time applications. However, besides the need for higher data rates, seamless handoff and load balancing among APs are key issues that must be addressed in order to continue supporting real-time services across wireless LANs and providing fair services to all users. In this paper, we introduce a novel access point (AP) with two transceivers that improves network efficiency by supporting seamless handoff and traffic load balancing in a wireless network. In our proposed scheme, the novel AP uses the second transceiver to scan and find neighboring STAs in the transmission range and then sends the results to neighboring APs, which compare and analyze whether or not the STA should perform a handoff. The initial results from our simulations show that the novel AP module is more effective than the conventional scheme and a related work in terms of providing a handoff process with low latency and sharing traffic load with neighbor APs.

A Novel AP for Improving the Performance of Wireless LANs Supporting VoIP

Recently, wireless LANs based on the IEEE 802.11 standard have become popular and widely used, and Voice-over-IP (VoIP) is one of the most promising technologies to be used in mobile devices over wireless networks. Up-to-date, new technologies have improved, providing a high data rate to support various kinds of realtime applications. However, besides the need for higher data rates, seamless handoff is another important issue to be addressed in order to continue supporting real-time services across wireless LANs. In this paper we introduce a novel Access Point (AP) with two transceivers to improve network efficiency in terms of supporting seamless handoff and balancing the traffic load in a wireless network. In our proposed scheme, the novel AP will use the second transceiver to scan and find neighboring STAs in the transmission range and later send the result to its associate AP, which in turn compares and analyzes whether or not the STA should perform a handoff. The initial results from our simulations show the novel AP module is more effective than the conventional one in terms of providing a handoff process with low latency and support traffic load sharing with neighbor APs.