High-speed Wireless Local Area Networks Research Articles

A 200-MS/s 10-Bit SAR ADC Applied in WLAN Systems

This paper introduces a new high-performance successive approximation register (SAR) analog-to-digital converter (ADC) designed for high-speed and low-power wireless local area network (WLAN) applications using a SMIC 55 nm 1p8m CMOS process. The design employs several innovative techniques, including an improved bootstrap switch with high linearity, a 4-reference voltage method to minimize capacitive digital-to-analog converter (CDAC) mismatch, a kickback-canceling comparator to eliminate kick-back noise, and redundant design-assisted window-opening SAR logic to decrease conversion time. Experimental results reveal that the proposed ADC achieves an impressive signal-to-noise and distortion ratio (SNDR) of 55.3 dB and a spurious-free dynamic range (SFDR) of 66.6 dB at a sampling rate of 200 MHz with Nyquist frequency input while consuming a power of 2.8 mW at a 1.2 V power supply. This corresponds to a figure-of-merit (FoM) value of 29 fJ/conversion-step. Thanks to the incorporation of the 4-reference voltage method, the ADC demonstrates a significant area advantage compared to other designs with similar FOM values utilizing more advanced processes, occupying a mere 0.008 mm2 of core area.

BER PERFORMANCE ANALYSIS OF 4QAM/OFDM OVER DIFFERENT SCENARIOS OF LAPLACE FADING CHANNEL.

Multicarrier transmission, also known as (OFDM) Orthogonal Frequency Division multiplexing, in wireless communications, it has been proven to be an essential technique for countering multipath fading. It has been used successfully for HF radio applications and has been selected as the interface for digital audio transmission, digital terrestrial TV broadcasting, and high-speed wireless local area networks in Europe. In this paper, we suggested a new design for modeling multipath fading channels, such as the Laplace fading channel, in order to discover new simulation results and effects. Furthermore, the variance of the Laplace fading channel has been computed and the new Bit Error Rate (BER) derivation is established, and the performance of (M-QAM), M-ary Quadrature Amplitude Modulation (with M=4 over OFDM system under Laplace fading channels in Additive White Gaussian Noise (AWGN) is discussed and compared to the conventional M-QAM/OFDM system Rayleigh fading channel in AWGN. All the simulation results are examined using the optimum signal detection based on the Euclidean distance and evaluated using Monte-Carlo simulation.

An octagonal star shaped flexible UWB antenna with band-notched characteristics for WLAN applications

In this paper, a flexible UWB antenna with band notched characteristics for high speed WLAN applications is presented. The flexibility of the designed antenna is achieved by developing the antenna on a flexible Teflon substrate. The proposed antenna primarily consists of a slot loaded octagonal star-shaped patch with a partial ground plane for wide operating bandwidth. A split ring resonator (SRR) based stop band filter is embedded in the ground plane to realize a rejection band characteristic to mitigate the interference impact from wireless local area network (WLAN) IEEE802.11n (5.725–5.825 GHz) band. The measured result shows that the suggested antenna operates over 3.25 to 13 GHz with a fractional bandwidth of about 120% with a peak gain of 6.7 dBi. The measurement results also confirm the presence of the rejection band from 5.7–6.2 GHz. Also, in terms of flexibility, the antenna provides high robustness in the performance for different types of bending conditions. The obtained results depict that the proposed antenna is suitable for mounting on all types of surface area with band rejection characteristics.

Multi-User MAC Protocol for WLANs in MmWave Massive MIMO Systems With Mobile Edge Computing

Merging mobile edge computing (MEC) service with the wireless local area networks (WLANs) provides enormous benefits such as intensive computation capabilities. Access to high-speed WLANs has become an urgent challenge due to the fast rate of application development and user adoption. Providing increased wireless resources is one solution, but millimeter (mmWave) multi-user massive Multiple-Input Multiple-Output (MIMO) technology has also attracted attention due to a series of features such as high throughput, strong anti-interference ability, and small fading. Hence, exploring the potential of mmWave MIMO systems for WLAN could play a significant role in improving network performance, especially throughput. In this paper, we introduce mmWave and massive MIMO into traditional WLAN with MEC, which enables a large portion of spatial resources to be allocated among users, and mitigates inter-user interference. Moreover, we propose a novel media access control (MAC) protocol, named as LSMWN-MAC, to adapt to a series of unique characteristics of mmWave and massive MIMO, which adopts space division multiple access (SDMA) as one of the resource methods, taking full advantage of spatial resources. In addition, we modify the protocol and propose the MLSMWN-MAC protocol to allocate resources dynamically, a solution that is particularly suitable for scenes with 30-50 users. Simulation results show that compared to 802.11ad, the proposed two protocols can increase the saturated throughput by 4.7Gb/s and 5.4Gb/s respectively, which are close to the throughput upper limit of the mmWave MIMO system. Meanwhile, we observe that when the number of users exceeds the threshold, the performance of the LSMWN-MAC protocol using a static allocation method is superior to the MLSMWN-MAC protocol using a dynamic method. In other cases, the dynamic protocol has better performances.

Location Assisted Coding for FSO Communication

Recent years have witnessed an explosive growth in the number of wireless devices. This development has fueled much research in wireless access technologies to efficiently use radio frequency spectrum. On the other hand, recent advances in free space optical (FSO) technologies promise a complementary approach to increase wireless capacity. In this paper, we describe WiFO, a hybrid WiFi and FSO high-speed wireless local area network of femtocells that can provide high bit rates while maintaining seamless mobility. Importantly, we introduce a novel location-assisted coding (LAC) technique, based on which, the number of novel rate allocation algorithms is proposed to increase throughput and reduce interference for multiple users in a dense array of overlapped femtocells. Both theoretical analysis and numerical results show orders of magnitude increase in throughput using LAC over existing schemes for various random topologies.

Coexistence issues for a 2.4 GHz wireless audio streaming in presence of bluetooth paging and WLAN

Abstract. Nowadays, customers expect to integrate their mobile electronic devices (smartphones and laptops) in a vehicle to form a wireless network. Typically, IEEE 802.11 is used to provide a high-speed wireless local area network (WLAN) and Bluetooth is used for cable replacement applications in a wireless personal area network (PAN). In addition, Daimler uses KLEER as third wireless technology in the unlicensed (UL) 2.4 GHz-ISM-band to transmit full CD-quality digital audio. As Bluetooth, IEEE 802.11 and KLEER are operating in the same frequency band, it has to be ensured that all three technologies can be used simultaneously without interference. In this paper, we focus on the impact of Bluetooth and IEEE 802.11 as interferer in presence of a KLEER audio transmission.

Dynamic Multiuser Sub-Channels Allocation and Real-Time Aggregation Model for IEEE 802.11 WLANs

Wireless local area networks (WLANs) are becoming increasingly popular due to the recent availability of affordable devices providing multiple and high rate capabilities. New PHY and MAC layer enhancements have been introduced in different IEEE 802.11 WLAN standards. These improvements have given birth to a wide range of bandwidth channels (up to 160 MHz) and very high transmission data rates (> 1 Gbps) to keep up with current and up-coming multimedia applications. The MAC layer in current WLANs randomly allocates the entire channel to only one user as a single resource, which, unfortunately, reduces the efficiency of WLANs. One way to significantly improve WLAN performance is to reduce the channel width and create many sub-channels. Based on the user's channel conditions and QoS requirements, the PHY layer resources can be dynamically allocated to several users at the same time. In this paper, we shall present a novel sub-channels access approach, titled MU-Access, with new features suitable for the forth-coming high-speed MIMO-based WLAN products. We will evaluate its performance compared to state-of-the-art systems, using NS-3 under a variety of network conditions. Our experiments will then demonstrate that our proposed scheme enhances the performance of IEEE 802.11 devices with a much higher throughput.

Deafness-aware MAC protocol for directional antennas in wireless ad hoc networks

The use of directional antennas is a promising technique for the provision of high-speed wireless local and personal area networks such as IEEE 802.11ac, IEEE 802.11ad, and IEEE 802.15.3c. In this paper, we propose a new directional MAC protocol for wireless ad hoc networks that is referred to as deafness-aware MAC (DA-MAC). Although a significant number of directional MAC protocols have been proposed, they have not comprehensively resolved the deafness problem. Our proposed DA-MAC protocol can distinguish the deafness problem from collisions by employing logical data and control channels. We provide a discrete-time Markov chain model to analyze the impact of deafness for both an existing technique and DA-MAC. Through extensive simulations, we show that our DA-MAC protocol can significantly outperform the other existing techniques with respect to the throughput, deafness duration, energy consumption, and transmission fairness.

AN OPTIMIZED LOW POWER PIPELINE ANALOG-TO-DIGITAL CONVERTER FOR HIGH-SPEED WLAN APPLICATION

This paper presents the design and implementation of a 11-bit 160 MSPS analog-to-digital converter (ADC) for next generation super high-speed wireless local area network (WLAN) application. The ADC core consists of one front sample and hold stage and four cascades of 2.5 bit pipeline stages with opamp sharing between successive stages. To achieve low power dissipation at 1.2 V supply, a single stage symmetrical amplifier with double transimpedance gain-boosting amplifier is proposed. High speed on-chip reference buffer with replica source follower is also included for linearity performance. The ADC was fabricated in a standard 130-nm CMOS process and an occupied silicon area of 0.95 mm × 1.15 mm. Performance of 73 dB spurious-free-dynamic-range is measured at 160 MS/s with 1 Vpp input signal. The power dissipation of the analog core chip is only 50 mW from a 1.2 V supply.

Client-Weighted Medium-Transparent MAC Protocol for User-Centric Fairness in 60 GHz Radio-Over-Fiber WLANs

We present a novel client-weighted medium-transparent medium access control (CW-MT-MAC) protocol with enhanced fairness service delivery properties accompanied by a low-loss remote access unit (RAU) architecture for use in indoor, Gbps-capable, 60 GHz radio-over-fiber (RoF) wireless local area networks (WLANs). Our approach relies on incorporating a client-weighted algorithm (CWA) in the optical capacity allocation mechanism employed in the MT-MAC scheme, so as to distribute the available wavelengths to the different antenna units according to the total number of active users served by each individual antenna. The protocol’s throughput and delay fairness characteristics are evaluated and validated through both simulations and analytic modeling for saturated network traffic operational conditions. In addition, extended simulation-based performance analysis for nonsaturated network conditions and for different end-user distributions, traffic loads, and available optical wavelengths at 1 Gbps data rates is presented. Our results confirm that complete throughput equalization can be achieved even for highly varying user population patterns when certain wavelength availability conditions are satisfied. At the same time, the presented scheme manages to equalize the average packet delays amongst packets generated by all RAUs while concurrently dropping the packet delay variation metric that is essential for quality of service delivery. Finally the proposed RAU design reduces insertion losses by almost 14 dB compared to RAU elements used in MT-MAC-compatible bus networks, extending in this way the number of supported RAUs by an order of magnitude and enabling the formation of extended-reach, high-speed RoF WLANs.

Vertical Handover Over Intermediate Switching Framework: Assuring Service Quality for Mobile Users

Ensuring quality of service (QoS) for the mobile users during vertical handover between IEEE 802.11 wireless local area networks (WLAN) and data network provided by Ultramodern Telecommunication Systems (UMTS) is one of the key requirements for seamless mobility and transfer of existing connections from one network to another. QoS fulfillment is a complex problem and requires participation of both the mobile users as well as the connection networks. The QoS assurance criteria for existing connections can be affected by fluctuations of data rates when a user moves from the high speed WLAN network to the low speed UMTS network, even in the presence of another WLAN network in its vicinity. This can happen if the alternate WLAN network is highly loaded. Therefore handover from a high speed network to a low speed network should be avoided, whenever possible. This paper proposes a QoS based handover procedure that prioritizes the existing connection over the new connections so that rate fluctuations due to handover can be avoided if there exist another WLAN network in the range of the mobile user. Whenever the possibility of handover is detected, a pre-handover bandwidth reservation technique is used to reserve bandwidth at the alternate WLAN networks to avoid QoS degradation. The proposed scheme is implemented in Qualnet network simulator and the performance is analyzed and compared with traditional handover techniques.

골든 부호 기반의 공간 변조 다중 안테나 시스템

본 논문에서는 실내 근거리 무선 통신에 적합하고 대역폭 효율을 향상시키는 공간 변조(spatial modulation) 다중 안테나 시스템을 제안한다. 기존의 공간 변조 다중 안테나 시스템은 다중 송신 안테나 중 하나의 안테나를 사용하여 채널 간에 간섭을 피할 수 있어서 다중 경로가 많은 실내 환경에서 적합하다. 그러나 심벌 전송 구간마다 한 개의 안테나만을 선택하여 전송하므로 다중 안테나의 최대 부호 이득을 얻을 수 없다. 이를 극복하기 위하여 시공간블록부호화 방식을 적용한 공간 변조 다중안테나 시스템은 두 개의 안테나를 사용하여 수신 성능을 향상시키지만 대역폭 효율이 향상되지 않는 단점이 있다. 본 논문에서는 골든 부호(Golden code)를 적용한 공간 변조를 제안하여 공간 변조 다중 안테나 시스템의 수신 성능과 대역폭 효율을 개선한다. 그리고 컴퓨터 모의실험을 통하여 기존 시스템과 제안하는 시스템의 성능을 비교 평가한다.

Practical Rate Adaptation for Very High Throughput WLANs

Wireless Local Area Networks (WLANs) have become increasingly popular due to the recent availability of affordable devices providing multiple and high rate capabilities. Optimizing the performance of WLANs for emerging new Internet applications that demand High Throughput (HT) is an important and a highly challenging issue. In this paper, we present a new practical Rate Adaptation (RA) algorithm, termed L3S, which extends legacy schemes with new MIMO features suitable for the forthcoming 802.11n high-speed MIMO-based WLAN products. We have implemented our rate adaptation algorithm in real hardware devices and evaluated its performance and compared it to the existing rate control mechanisms. Our experiments demonstrate that our scheme allows the current 802.11n devices to have a greater adaptability to a variety of wireless channel conditions and performs better than state-of-the-art rate adaptation algorithms.

Wideband Parameters Analysis and Validation for Indoor radio Channel at 60/70/80GHz for Gigabit Wireless Communication employing Isotropic, Horn and Omni directional Antenna

Recently, applications of millimeter (mm) waves for high-speed broadband wireless local area network communication systems in indoor environment are increasingly gaining recognition as it provides gigabit-speed wireless communications with carrier-class performances over distances of a mile or more due to spectrum availability and wider bandwidth requirements. Collectively referred to as E-Band, the millimeter wave wireless technology present the potential to offer bandwidth delivery comparable to that of fiber optic, but without the financial and logistic challenges of deploying fiber. This paper investigates the wideband parameters using the ray tracing technique for indoor propagation systems with rms delay spread for Omnidirectional and Horn Antennas for Bent Tunnel at 80GHz. The results obtained were 2.03 and 1.95 respectively, besides, the normalized received power with 0:55fix10^8 excess delay at 70GHz for Isotropic Antenna was at 0.97.

Performance Analysis of Hybrid Wireless Networks Under Bursty and Correlated Traffic

Wireless local area networks (WLANs) have risen in popularity for in-car networking systems that are designed to make driving safer. Wireless mesh networks (WMNs) are widely deployed to expand the coverage of high-speed WLANs and to support last-mile connectivity for mobile users anytime and anywhere at low cost. Many recent measurement studies have shown that the traffic arrival process in wireless networks exhibits the bursty and correlated nature. A new analytical model is developed in this paper as a cost-effective performance tool to investigate the quality-of-service (QoS) of the WMN that interconnects multiple WLANs in the presence of bursty and correlated traffic. After validating its accuracy via extensive simulation experiments, the analytical model is then used to investigate the performance of the hybrid wireless networks.

Wideband E-Shaped Microstrip Antenna for Wireless Sensor Networks

Problem statement: Wireless Sensor Networks (WSN) is currently receiving significant attention due to their unlimited potential. It is still very early in the lifetime of such systems and many research challenges exist, out of which one of the challenges is sensor processing and fusion under limited capacities, the most important component in sensor is its TX/RX antenna. Approach: For high-speed wireless local area networks and other wireless communication systems covering the 5.33-5.71 GHz frequency band. In this frequency band microstrip antennas have attracted with its low-profile in nature. Microstrip antenna was proposed to meet the challenges, which combines the advantages of compactness with the low cost and low profile of a patch antenna. Results: The key parameters governing the antenna optimization have been determined with the help of High Frequency Simulation Software (HFSS). As a consequence, 5.5GHz microstrip antenna with size 22×16×3.2 mm had been realized on duroid with 2.2. Conclusion: This combination of performance metrics is highly desirable for autonomous distributed sensor network applications where a small sensor node volume and excellent power efficiency are required.

Enhanced performance of a patch antenna using spiral-shaped electromagnetic bandgap structures for high-speed wireless networks

This study describes the improvement of gain and bandwidth of a microstrip patch antenna achieved using a spiral-like electromagnetic bandgap (EBG) structure for high-speed wireless local area networks. The size of the antenna is only 45 × 45 × 2.47 mm and resonates at a frequency of 2.4 GHz. The gain and bandwidth of this antenna is 3 dBi and 67.4% greater than a conventional patch antenna. The working frequency of the patch antenna falls inside the EBG bandgap, which leads to the suppression of surface waves. Simulations of the antenna are conducted using the finite-difference time-domain analysis technique. The electromagnetic (EM) simulated and measured return loss, gain, directivity, radiation pattern, antenna efficiency and voltage standing wave ratio are presented for the proposed antenna array. These results allow one to determine the structures giving the best focusing performance and to obtain the frequency band for directive radiation.

Spatially variable insecticide applications for early season control of cotton insect pests

Our research has shown that cotton insect pests, specifically tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois) (Heteroptera: Miridae) can be controlled early season in commercial cotton fields in Mississippi, USA, using spatially variable insecticide applications. Technology was developed for using GIS-based map scouting and a technique called the line-intercept method for obtaining low-level insect population counts in both rapidly growing areas of cotton and poorer growing areas. Using these population characteristics in combination with heuristic knowledge of the cotton fields and with the GIS maps, a spatially sensitive map could then be developed that could drive a spatially variable insecticide application for the control of the insect pest. We outline the steps needed to develop an automated technology for overcoming the time-sensitive events for early season control of cotton pests. This technology not only includes software systems for processing multispectral images to spatially variable insecticide application maps for spray controllers in the field but also high-speed wireless local area network (WLAN) technology for automated delivery of these controller application maps and for acquisition of as-applied and harvest maps from the field.

Performance Study of Power Control Radio Resource Management Over WLANs

Wireless Local Area Networks (WLANs) based on IEEE 802.11 standard have been rapidly growing. With limitations of the WLAN standard and rapid increase in wireless application demand, the air interface acts as bottleneck even in high-speed WLAN standards such as IEEE 802.11a and 802.11g with expected data transmission rates of up to 54 Mbps. To improve the overall performance of IEEE 802.11 WLAN under large deployment and heavy application demand environment, Radio Resource Management (RRM) algorithms based on power control have been investigated and tested through simulation. The results show that controlling the Wireless Terminal's (WT) transmitter power to an optimum power level helps in increasing data throughput in WLANs and when the transmitter power level of a WT is increased beyond the optimum power level, the overall data throughputs drop drastically no matter how high the WT's transmitter power may be increased.

A WIDEBAND E-SHAPED MICROSTRIP PATCH ANTENNA FOR 5 - 6 GHZ WIRELESS COMMUNICATIONS

A wideband E-shaped microstrip patch antenna has been designed for high-speed wireless local area networks (IEEE 802.11a standard) and other wireless communication systems covering the 5.15-5.825 GHz frequency band. Two parallel slots are incorporated to perturb the surface current path, introducing local inductive effect that is responsible for the excitation of the second resonant mode. The length of the center arm can be trimmed to tune the frequency of the second resonant mode without affecting the fundamental resonant mode. A comprehensive parametric study has been carried out to understand the effects of various dimensional parameters and to optimize the performance of the antenna. A substrate of low dielectric constant is selected to obtain a compact radiating structure that meets the demanding bandwidth specification. The reflection coefficient at the input of the optimized E-shaped microstrip patch antenna is below -10 dB over the entire frequency band. The measurement results are in excellent agreement with the HFSS simulation results.