Wireless Local Area Network Systems Research Articles

Performance analysis of IEEE 802.11ac based WLAN in wireless communication systems

<p><span lang="EN-US">IEEE 802.11ac based wireless local area network (WLAN) is emerging WiFi standard at 5 GHz, it is new gigabit-per-second standard providing premium services. IEEE 802.11ac accomplishes its crude speed increment by pushing on three distinct measurements firstly is more channel holding, expanded from a maximum of 80 MHz up to 160 MHz modes. Secondly, the denser modulation, now using 256-QAM, it has the ability to increase the data rates up to 7 Gbps using an 8×8 multiple input multiple output (MIMO). Finally, it provides high resolution for both narrow and medium bandwidth channels. This work presents a study to improve the performance of IEEE 802.11ac based WLAN system.</span></p>

A Proposal of Transmission Power Minimization Extension in Active Access-Point Configuration Algorithm for Elastic Wireless Local-Area Network System

Nowadays, the wireless local-area network (WLAN) has become common in the low-cost Internet access solution using wireless communications between access points (APs) and hosts. In WLAN, traffic demands from users tend to fluctuate according to day and time. To minimize the power consumption of active APs, we have studied the elastic WLAN system and implemented the testbed using Raspberry Pi for the AP. Also, the active AP configuration algorithm has been proposed to optimize the active AP configuration with channel assignments and host associations for the elastic WLAN system. In this paper, we propose the transmission power minimization extension in the active AP configuration algorithm to further minimize the power consumption. After the previous algorithm is applied with the maximum transmission power, it minimizes the power of each active AP such that it satisfies the minimum throughput constraint. The effectiveness of our proposal is verified through simulations using the WIMNET simulator and experiments using the testbed in several network scenarios.

PCS Threshold Selection for Spatial Reuse in High Density CSMA/CA MIMO Wireless Networks

Multiple-input multiple-out (MIMO) equipment improves the spectral efficiency of wireless local area network (WLAN) systems. However, in a large-scale or dense MIMO WLANs, overlapping radio cells or basic service sets (BSSs) are inherent. This prevents multiple concurrent transmissions and degrades spatial reuse. The inability to separate multiple simultaneous transmissions in space is detrimental to overall system performance. The carrier sense multiple access collision avoidance (CSMA/CA) protocol uses the physical carrier sensing (PCS) threshold to determine channel state at the physical layer (PHY) and decide on the number of concurrent transmissions allowed per time slot. Since the PCS threshold determines the spatial reuse under the CSMA/CA protocol, which consequently determines the interference level and the network aggregate throughput, we address PCS threshold selection for dense uplink (UL) MIMO WLAN systems. A closed-form expression is derived for selecting the PCS threshold based on the fundamental parameters of the network where nodes are randomly placed according to a Poisson point process (PPP). We obtain the PCS threshold value that maximizes the spatial density of throughput (SDT) and study the effectiveness of the proposed framework under moderate to high node density. In addition, we analyze the effect of WLAN density on interference from concurrent transmitters. The key observation is that PCS threshold selection should take into account key network characteristics including node density, target SINR or threshold, path-loss exponent and antenna configuration.

Direct Sequence and Frequency Hopping Signals Classification Based on Co-Occurrence Matrix and Clustering Techniques

Spread Spectrum techniques (SS) were first developed for military applications, but currently, they have commercial applications. SS provides secure communication and allows multiple accesses for same radio spectrum. So, most Wireless Local Area Network (WLAN) systems use it, as do Cognitive Radios (CR), space systems and Global Positioning Systems (GPS). Direct Sequence Spread Spectrum (DSSS) and frequency hopped spread spectrum (FHSS) are the two most-used techniques today. Nowadays radio spectrum has become very crowded and so now there is a need for spectrum efficiency. Automatic SS classification presents a rather difficult problem, especially if the parameters, such as the signal power, carrier frequency, etc., are unknown. This research takes a new direction; it deploys the Gray Level Co-occurrence Matrix (GLCM) to capture statistical features of SS signals. Using GLCM, 22 features are extracted for each vector of signal. Analyzing the signals is done in the time domain which measures the variation of amplitude of signals with time. Therefore, the main contribution is to apply and show how GLCM improves the identification accuracy of the two signals in presence of noise. The proposed model achieves considerably accurate results even with a low SNR. GLCM features help classifiers to achieve average accuracy 84% and reach 100% signal identification at a zero SNR. To prove the superiority of these features, a variety of clustering methods are applied, such as centroid, connectivity, model-based and message-passing models. Clustering performance results based on GLCM features are compared With Principal Components Analysis (PCA), Kernel-based Principal Components Analysis (KPCA) and fast Independent Components Analysis (Fast-ICA). Clustering results are evaluated with external and internal validity indices. The accuracy was tested over 26 levels of Signal-to-Noise Ratios (SNR).

Bandwidth enhancement using modified L-probe fed slotted patch antenna for WLAN and UMTS applications

AbstractIn this paper, two different radiating structures fed with modified L-probe, are reported using a circuit theory concept. The proposed antennas are operating in wireless local area network (WLAN) and universal mobile telecommunications system (UMTS) frequency bands. In the first design, an E-shaped patch is studied to increase the bandwidth. It is observed that the bandwidth is directly proportional to notch dimensions. In the second design, E-shaped patch is modified to reduce the antenna size up to 30% with high bandwidth. In the first design, measured bandwidth and gain achieved are 32.68% (1.92–2.67 GHz) and 8.43 dBi while in second design it is 34.19% (1.94–2.74 GHz) and 8.39 dBi, respectively. Radiation patterns for both the antennas are symmetrical and broadside in nature. The proposed antennas are fabricated and measured results compare well with the theoretical and simulated results.

Dual Carrier Modulation in Channel Aggregation for 60 GHz WLAN Systems

Dual carrier modulation (DCM) is a well-known transmission scheme for achieving frequency diversity in wireless communications. On the other hand, channel aggregation (CA) can fully utilize the available discontinuous spectrums and obtain much higher throughput. In this letter, we propose an approach to apply DCM transmission for two channel aggregation in 60 GHz wireless local area network (WLAN) systems based on the single carrier mode defined in the 60 GHz WLAN standard. We also investigate different detection algorithms and propose an optimized solution for frequency diversity combining. Our simulation results show that the proposed DCM transmission approach with the optimized detection algorithm can obtain more than 1.5 dB gain comparing with non-DCM approaches in CA.

A Coplanar Waveguide Fed UWB Antenna using Embedded E-shaped Structure with WLAN Band-rejection

Abstract A compact coplanar waveguide (CPW)-fed ultra-wideband (UWB) monopole antenna using embedded E-shaped structure with wireless local area network (WLAN) band-rejection is presented. The introduction of this E-shaped structure working as the radiator can enhance the impedance bandwidth of the UWB antenna without increasing the overall size. For preventing the interference from WLAN system, a pair of L-shaped stubs are connected to the ground of UWB antenna to create the rejected band. The center frequency of this rejected band is about 5.5 GHz with the rejection range of 5.2~5.8 GHz. Good agreement can be observed between the simulated and measured results.

Design of a Wideband Omnidirectional Antenna With Characteristic Mode Analysis

A low-profile horizontally polarized (HP) omnidirectional metasurface-inspired antenna is presented. To realize HP omnidirectional radiation pattern, the theory of characteristic mode is utilized to facilitate the analysis of three antenna structures. Then, by properly exciting the desired characteristic mode, the antenna with a wide bandwidth and good omnidirectionality, which is based on the modification of the standard patch antenna, is obtained. The simulated results show that the proposed antenna not only can obtain a low profile of 0.06 λ 0 (where λ 0 is the free-space wavelength at 5.2 GHz), but also has a wide operating bandwidth of 16.6%. Finally, the metasurface-inspired antenna is manufactured and the error analysis between the simulated and measured results is also provided. The antenna can be applied to 5G wireless local area network systems.

Throughput performance of NOMA in WLANs with a CSMA MAC protocol

The existing medium access control (MAC) protocols are not able to utilize the full opportunities from power-domain non-orthogonal multiple access (NOMA) technique in wireless local area networks (WLANs). In this paper, we propose a carrier sense multiple access (CSMA) MAC protocol to increase downlink throughput by utilizing the opportunities offered by NOMA technique in downlink access of WLANs. For downlink transmission, an algorithm is developed to select an optimal user-set with appropriate power allocation from a randomly selected user-set. We then develop an analytical model to compute the uplink and downlink throughputs of a WLAN under the proposed MAC protocol by modelling the WLAN system as a discrete time Markov chain. The uplink and downlink throughputs of a WLAN under the proposed MAC protocol are determined by means of the analytical model and the accuracy of the analytical model is verified via extensive simulation. It is demonstrated that the proposed NOMA based MAC protocol improves the downlink throughput significantly compared to an orthogonal multiple access (OMA) based traditional CSMA MAC protocol without reducing the uplink throughput considerably. For a reasonable configuration, the downlink throughput gain is found to be more than 250%. We also study the throughput performance of the proposed MAC protocol for different transmit power levels, user medium access rates, data rates, path loss exponents and number of users in WLAN. We find that the throughput gain obtained by the proposed MAC protocol increases with increasing the transmit power and decreases with increasing the data rates and path loss. However, the change in the throughput gain obtained by the proposed MAC protocol is not significant for increasing the number of users and the user medium access rate.

A Compact Antenna with WiMAX and WLAN bands notched for UWB applications

A Compact antenna with WiMAX and WLAN bands notched for ultra wide band (UWB) applications is proposed. The proposed antenna is designed for the planar ultra wide band (UWB) antenna and ultra wide band (UWB) antenna having two band rejections. The proposed antenna overall size is 30mm x 40mm x 1.6mm. The antenna consists of a rectangular patch on the top of FR4 substrate with 50ohm feed with defected ground structure. This patch consists of one round cut at each corner having radius 1.575mm. The simulated band width with return loss (RL) >=10db is 3.1 to 11.2 GHz with VSWR<2. It works for the applications of WiMAX system at 3.5GHz (3.3 – 3.7 GHz), C-band satellite communication (3.7 - 4.2 GHz), wireless local area network (WLAN) system at 5GHz (5.15 – 5.825 GHz), X-band satellite communication system (7.25 - 7.75 GHz). The ultra wide band frequency range for these wireless systems causes interference. To diminish obstruction, the band rejection is made. WiMAX and WLAN groups are dismissed by designing slots on the patch. This antenna has an incredible pick up in the Gain while a sharp drop in the rejected groups.

In brief

PAGE 395 A solution to avoid relay attacks on keyless entry systems in vehicles is proposed in work from Korea. In conventional systems, the proximity of the key to the vehicle is approximated using received signal strength. The proposed approach applies an additional layer of security using a channel correlation-based proximity authentication scheme to prevent relay attacks. PAGE 376 Researchers in the USA report the use of a digital filter with adaptive coefficients to correct current sensing and temperature variation in DC/DC switch mode power supplies. Tighter output voltage regulation is achieved with this filter and current sensing can be applied to systems without adaptive voltage positioning. The filter is suitable for computing, telecom, and storage applications. A channel correlation-based proximity authentication scheme for keyless entry systems for vehicles. PAGE 385 Digital television signals in urban environments are used to improve passive radar target detection performance in work from China. This work combines traditional polarisation theories with passive radar detection to reduce interference within built up urban environments using a dual-polarisation antenna array. Correct current sensing with a digital filter with adaptive coefficients for DC/DC switch mode power supplies. PAGE 336 Researchers in Japan make a combined wireless local area network system and smart antenna to suppress interference in busy locations, such as shopping malls and stadiums. The device has eight internal antennas that are dynamically selected by high-speed switching to maintain network service. A large improvement in interface suppression with this device is demonstrated in comparison with centralised antennas. Passive target detection in urban areas is improved by taking advantage of polarisation diversity in digital television signals. PAGE 359 Electromagnetic reflectivity from twill-weave carbon fibre reinforced polymers (CFRP) is measured in work from Austria. Different fibre patterns of the CFRP were investigated, including unidirectional, shredded and twill-weave fibres. Twill-weave fibres showed a sharp angular dependency in reflectivity in response to millimetre waves at 60 GHz. The fibres are manufacturing materials for vehicles and are targets for millimetre wave radar. Integration of eight internal antennas into a wireless local area network system to suppress interference in busy locations. The electromagnetic reflectivities of different patterns of carbon fibre reinforced polymers are measured.

Broadband Planar Aperture‐Coupled Antenna Array for WLAN and ITS Beam‐Steering Applications

AbstractA broadband multilayer beam‐steering antenna array with a modified mushroom‐like radiating element is introduced. The two‐layer aperture‐coupled array consists of four equal sets of mushroom‐like elements, each of which is made of 16 unit cells in a 4 × 4 configuration. The feeding network is a modified quasi‐Butler matrix, which benefits from improved double‐box branch line couplers. The network has an isolation bandwidth between 4 and 7.9 GHz (65%) and a transmission bandwidth from 4.8 to 7.1 GHz (39%), which operates acceptably in most of the C‐band, especially at wireless local area network and Intelligent Transport Systems (ITS). A broadband Butler matrix uses broadband 3 dB couplers and a middle network. The geometry of the element and feeding network is utilized in array form to enhance the impedance bandwidth and radiation efficiency of the antenna. The results show that the antenna impedance bandwidth covers 3.82 to 8.2 GHz (port 1) and 3.8 to 8.28 GHz (port 2) for Snn ≤ −10 dB, which covers the C‐band fully (4–8 GHz). Moreover, it has a 3 dB gain‐bandwidth of 2.25 GHz that extends from 4.65 to 6.9 GHz with a peak value of 13.65 dBi. The antenna array has a 3 dB axial ratio bandwidth of 1.65 GHz that extends from 4.9 to 6.55 GHz and involves wireless local area network (5.15–5.825 GHz) and ITS (5.795–6.400 GHz). The radiation efficiency of the array for both port excitations is in excess of 75% when circular polarization is achieved. Two firing beams at elevation angles of 20° and −35° are obtained for ports 1 and 2 upon excitation, respectively.

Low latency IR-HARQ for multiband WLAN system

This paper proposes a low latency incremental redundancy hybrid ARQ (IR-HARQ) scheme for a multiband wireless local area network (WLAN) system. The proposed scheme can reduce a retransmission delay and ensure backward compatibility with WLAN devices by using a clear to send (CTS) frame of a current WLAN system and rate compatible low-density parity-check (RC-LDPC) codes. Additionally, it can minimize the retransmission delay by selecting an optimal retransmission data length on the basis of the accumulated mutual information (ACMI) for available frequency bands. The results of computer simulations show that the multiband WLAN system using the proposed scheme has shorter retransmission delay and higher system throughput than the current WLAN system.

An Overview of China Millimeter-Wave Multiple Gigabit Wireless Local Area Network System

An Overview of China Millimeter-Wave Multiple Gigabit Wireless Local Area Network System

Dynamic Access-Point Configuration Approach for Elastic Wireless Local-Area Network System and Its Implementation Using Raspberry Pi

Recently, Wireless Local Area Networks (WLANs) have increased popularity around the world, where users can easily access to the Internet through associations with access points (APs) using mobile devices like smart phones, tablets, and laptops. In a WLAN, it is common that the number of users is always changing by time and users are not evenly distributed in the field. To optimize the number of active APs and the host associations in the network depending on traffic demands from users, previously, we proposed the AP configuration algorithm for the elastic WLAN system. Unfortunately, this algorithm can find the solution for the fixed user state in the network, although users often repeat joining and leaving the network. In this paper, we propose the extension of the AP configuration algorithm to deal with this dynamic nature. Here, as practical situations, this extension considers that at most one host may join or leave at the same time, and any communicating AP cannot be suspended and any communicating host cannot change its associated AP. Through numerical experiments using the WIMNET simulator in two network instances, the effectiveness of the proposal is demonstrated. Furthermore, it is implemented in the elastic WLAN system testbed using Raspberry Pi for the AP. The performance of this implementation is verified through experiments in four scenarios.

A throughput estimation model under two-link concurrent communications with partially overlapping channels and its application to channel assignment in IEEE 802.11n WLAN

Currently, the IEEE 802.11n wireless local-area network (WLAN) has been deployed world-wide due to flexibility and low costs. A key challenge in the WLAN deployment is to provide high data-rate under strong interferences due to the limited frequency channels. In WLAN, the adjacent channels are partially overlapped with each other, called partially overlapping channels (POCs). Then, the optimal POC assignment to the access-points (APs) in WLAN using the mathematical model is important to improve the performance, particularly for usage of the channel bonding. In this paper, we propose the throughput estimation model extension for concurrent communications of two IEEE 802.11n links under interferences using POCs and the channel bonding, from extensive measurement results under a variety of conditions. Then, based on this model, we present the channel assignment extension in the active AP configuration algorithm for the elastic WLAN system, which dynamically optimises the topology depending on network conditions. For the evaluation, we verify the model accuracy through comparing estimated throughputs with measured ones under various conditions. On top of that, we confirm throughput improvements by adopting POCs from using merely orthogonal channels (OCs) in simulations and experiments in several topologies.

A throughput estimation model under two-link concurrent communications with partially overlapping channels and its application to channel assignment in IEEE 802.11n WLAN

Currently, the IEEE 802.11n wireless local-area network (WLAN) has been deployed world-wide due to flexibility and low costs. A key challenge in the WLAN deployment is to provide high data-rate under strong interferences due to the limited frequency channels. In WLAN, the adjacent channels are partially overlapped with each other, called partially overlapping channels (POCs). Then, the optimal POC assignment to the access-points (APs) in WLAN using the mathematical model is important to improve the performance, particularly for usage of the channel bonding. In this paper, we propose the throughput estimation model extension for concurrent communications of two IEEE 802.11n links under interferences using POCs and the channel bonding, from extensive measurement results under a variety of conditions. Then, based on this model, we present the channel assignment extension in the active AP configuration algorithm for the elastic WLAN system, which dynamically optimises the topology depending on network conditions. For the evaluation, we verify the model accuracy through comparing estimated throughputs with measured ones under various conditions. On top of that, we confirm throughput improvements by adopting POCs from using merely orthogonal channels (OCs) in simulations and experiments in several topologies.

MIMO host location optimisation in active access-point configuration algorithm for elastic WLAN system

Recently, a wireless local-area networks (WLANs) has become prevalent around the world due to the low-cost and flexible internet access by wireless communications between user hosts and access points (APs) in the network. Previously, we proposed the active AP configuration algorithm for the elastic WLAN system that dynamically optimises the network configuration by activating/deactivating APs and assigning the channels and associated hosts depending on network situations. However, it assumed that only single-input-single-output (SISO) links are used, although multiple-input-multiple-output (MIMO) links have become popular for fast communications. Currently, most commercial APs can use MIMO, while a subset of hosts can use it, referred as MIMO hosts in this paper. Then, by optimising the locations of MIMO hosts, the performance of the network is expected to be improved. In this paper, we present the MIMO host location optimisation as the extension of the active AP configuration algorithm. Through simulations in two network topologies using the WIMNET simulator, the throughput improvements by this proposal are confirmed.

Traffic Offloading in LTE System Based Heterogeneous Networks

The continuous growing developments in the traffic of mobile data limits the data throughput and capacity of cellular networks. “Heterogeneous Networks (HetNets)” are efficient solution to realize such demands. However, in HetNets, the congestion on the overloaded cellular network can be increased when the traffic of data is pushed from a cellular network to the Wi-Fi. In practice, offloading the cellular data traffic to a Wireless Local Area Network (WLAN) depending on the signal quality is a broadly deployed method to solve such problem. The use of Device to Device (D2D) communication further enhances the traffic offloading in WLAN systems and helps to obtain better throughput, end-to-end delay and network load. However, the critical offloading potential and its impacts on the whole performance is not totally understood. In this paper, the offloading of Long Term Evolution (LTE) traffic is presented using a WLAN for voice and video applications. A comparison is performed among two WLAN mechanisms; Distributed coordination function (DCF) and Point Coordination Function (PCF). As well, the effect of adding a D2D technology to the PCF is discussed. The WLAN effectively offloaded nodes at their Signal to Interference and Noise Ratio (SINR) becomes more than a specific threshold. Results presented that the PCF mechanism outperforms the DCF one in terms of packet loss ratio, throughput and the maximum load of the entire network. In addition, the use of a D2D serviced in the PCF helps in further reduction in the network load.

Saturation throughput analysis of a carrier sensing based MU-MIMO MAC protocol in a WLAN under fading and shadowing

In wireless local area networks (WLANs), the traditional carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol cannot use the full benefits from multiuser multiple-input multiple-output (MU-MIMO) technique due to random medium access of the users. In this paper, we propose a carrier sensing based MAC protocol for a MU-MIMO based WLAN with full utilization of MU-MIMO technique. By modeling the WLAN system under the proposed MAC protocol as a discrete time Markov chain, we develop an analytical model for computing the saturation throughput in presence of path loss, Rayleigh fading and log-normal shadowing. The analytical model is then validated via simulation. By means of numerical and simulation results, we demonstrate that the proposed MAC protocol significantly improves throughput performance than the traditional CSMA/CA MAC protocol. Further, we compare the performance of the proposed MAC protocol with a MU-MIMO MAC protocol called Uni-MUMAC protocol and find that the proposed MAC protocol performs better than the Uni-MUMAC protocol. We also explore the effect of some of the network and wireless channel parameters on the performance of the proposed MAC protocol.