Cross-layer adaptive resource allocation for OFDM systems with hybrid smart antennas

Orthogonal frequency division multiplex (OFDM) has become one of the most popular air-link technologies for future broadband wireless communications. To further improve its bandwidth efficiency and system performance, adaptive resource allocation and smart antenna techniques have been widely used in the OFDM system. However, the use of fully adaptive beamforming in an OFDM system significantly increases the complexity of the medium access control layer design and thus affects the implementation of adaptive resource allocation. A novel cross-layer adaptive resource allocation strategy with hybrid adaptive array and switched- beam smart antennas suitable for the OFDM systems has been proposed. With the help of different smart antennas schemes based on different users' quality of service requirements, the strategy effectively reduces the complexity of adaptive resource allocation in an OFDM system, while still maintaining a satisfactory system performance.     

Triple-band wireless local area network monopole antenna

A triple-band Bluetooth (BT) and wireless local area network (WLAN) monopole antenna has been proposed based on concepts called capacitive loading/de-loading and inductive loading/de-loading. It has been demonstrated that BT and triple-band WLAN operations, including the BT 2.4 GHz (2.4-2.484 GHz), the WLAN IEEE 802.11 2.4 GHz (2.4-2.484 GHz), 5.2 GHz WLAN (5.15-5.35 GHz) and WLAN 5.8 GHz (5.725- 5.825 GHz) can be achieved by using the monopole antenna with an overall size 8.0 x 11.5 x 1.0 mm³, which is one of the most compact WLAN monopole antennas covering the three frequency bands.     

Equalisation of SIMO-OFDM systems with insufficient cyclic prefix in doubly selective channels

Time variations of a doubly selective wireless channel and insufficient cyclic prefix (CP) length of an orthogonal frequency division multiplexing (OFDM) transmission system cause intercarrier interference (ICI) and interblock interference (IBI) as significant limitations. This paper investigates the problem of joint ICI and IBI mitigation in single-input multiple-output OFDM (SIMO-OFDM) systems. It is assumed, unlike most existing literature, that the channel delay spread is larger than the CP, and also the channel varies on each OFDM block. First, doubly selective channel is modelled using basis expansion model (BEM) and a closed-form expression for signal-to-interference-plus-noise ratio (SINR) is derived. Then, a time-domain equaliser is developed, which maximises the SINR for all subcarriers. Moreover, a frequency-domain equalisation approach is proposed which is based on the MSE minimisation per tone. A low-complexity implementation of the pertone equaliser is also derived. An important feature of the proposed equalisers is that no bandwidth expansion or redundancy insertion is required except for the CP. Finally, complexity comparison and simulation results over Rayleigh fading channel are provided to illustrate the effectiveness of the proposed approaches. Since both equalisers are designed in the frequency domain, they provide significant interference cancellation.     

滤波器组多载波系统的干扰分析和性能验证

分析了多普勒频偏以及多径时延对滤波器组多载波(FBMC)系统的影响,给出了多普勒频偏以及多径时延造成干扰的闭合定量分析式,该分析式对正交频分复用(OFDM)系统同样适用,并据此对无线多径衰落信道场景中的FBMC系统与传统OFDM系统性能进行了对比.研究结果表明,FBMC系统对多普勒频偏的抵抗性优于OFDM系统,但是系统性能会随信道多径时延的增大而降低.在多径时延相对较小的快衰落信道中,符号间干扰并非影响系统性能的主要因素,FBMC系统可以利用简单的频域均衡获得足够好的性能,仿真结果验证了这一点.     

Quintuple Band Antenna for Wireless Applications with Small Form Factor

A coplanar waveguide-fed quintuple band antenna with a slotted circular-shaped radiator for wireless applications with a high isolation between adjacent bands is presented in this paper. The proposed antenna resonates at multiple frequencies with corresponding center frequencies of 2.35, 4.92, 5.75, 6.52, and 8.46 GHz. The intended functionality is achieved by introducing a circular disc radiator with five slots and a U-shaped slot in the feed. The proposed antenna exhibits coverage of the maximum set of wireless applications, such as satellite communication, worldwide interoperability for microwave access, wireless local area network (WLAN), long-distance radio telecommunications, and X-band/Satcom wireless applications. The simulation and measurement results of the proposed fabricated antenna demonstrate the high isolation between adjacent bands. A stable realized gain with an advantageous radiation pattern is achieved at the operating frequency bands. The proposed simple design, compact structure, and simple feeding technique make this antenna suitable for integration in several wireless communication applications, where the portability of devices is a significant concern. The proposed antenna is anticipated to be an appropriate candidate for WLAN, long-term evolution, and fifth-generation mobile communication because of its multi-operational bands and compact size for handheld devices.     

Compact wideband Koch fractal printed slot antenna

A compact wideband printed slot antenna, suitable for wireless local area network (WLAN) and satisfying the worldwide interoperability for microwave access (WiMAX) applications, is proposed here. The antenna is microstrip-fed and its structure is based on Koch fractal geometry where the resonance frequency of a conventional triangular slot antenna is lowered by applying Koch iterations. The antenna size inclusive of the ground plane is compact and has a wide operating bandwidth. The proposed second iteration Koch slot antenna operates from 2.33 to 6.19 GHz covering the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands. The antenna exhibits omnidirectional radiation coverage with a gain better than 2.0 dBi in the entire operating band. Design equations for the proposed antenna are developed and their validity is confirmed on different substrates and for different slot sizes.     

Inkjet Printed Metamaterial Loaded Antenna for WLAN/WiMAX Applications

In this paper, the design and performance analysis of an Inkjet-printed metamaterial loaded monopole antenna is presented for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications. The proposed metamaterial structure consists of two layers, one is rectangular tuning fork-shaped antenna, and another layer is an inkjet-printed metamaterial superstate. The metamaterial layer is designed using four split-ring resonators (SRR) with an H-shaped inner structure to achieve negative-index metamaterial properties. The metamaterial structure is fabricated on low-cost photo paper substrate material using a conductive ink-based inkjet printing technique, which achieved dual negative refractive index bands of 2.25–4.25 GHz and 4.3–4.6 GHz. The antenna is designed using a rectangular tuning fork structure to operate at WLAN and WiMAX bands. The antenna is printed on 30 × 39 × 1.27 mm3 Rogers RO3010 substrate, which shows wide impedance bandwidth of 0.75 GHz (2.2 to 2.95 GHz) with 2 dB realized gain at 2.4 GHz. After integrating metamaterial structure, the impedance bandwidth becomes 1.25 GHz (2.33 to 3.58 GHz) with 2.6 dB realized gain at 2.4 GHz. The antenna bandwidth and gain have been increased using developed quad SRR based metasurface by 500 MHz and 0.6 dBi respectively. Moreover, the proposed quad SRR loaded antenna can be used for 2.4 GHz WLAN bands and 2.5 GHz WiMAX applications. The contribution of this work is to develop a cost-effective inject printed metamaterial to enhance the impedance bandwidth and realized the gain of a WLAN/WiMAX antenna.     

V-BLAST/OFDM系统的多用户分集性能研究

为改善V-BLAST/OFDM系统的性能,提出了子载波动态分配准则.该准则可以有效地利用多用户分集,明显提高V-BLAST/OFDM系统的整体性能.采用随机矩阵和排序统计的数学方法对取得的性能增益作了定量分析,仿真试验结果证明了分析的正确性.将取得的性能增益与空间分集系统中取得的多用户分集增益进行了比较,比较结果说明,将基于V-BLAST的多用户OFDM系统与子载波动态分配相结合,更能改善系统的整体性能.     

多相分解滤波器在OFDM高速水声通信中的应用

影响OFDM浅海高速水声通信的一个重要的因素是多普勒,多普勒频率会导致OFDM子载波间的正交性被破坏,进而带来OFDM子载波间干扰,严重影响OFDM水声通信的质量,因此必须对如何消除多普勒进行研究。在水声通信中消除多普勒的影响通常分两步：首先对多普勒因子正确估计,进而对接收数据变采样。在仿真实现变采样的基础上,利用多相分解降低其运算量,实现了高速率的变采样滤波器,并将算法运用到OFDM系统仿真中,最终对OFDM湖试数据进行解码,取得了满意的结果,很大程度上降低了多普勒频移对OFDM水声通信系统的影响。     

Compact multiband planar monopole antennas for smart phone applications

A compact multiband planar monopole antenna is discussed. Tuning techniques, including offset feed, etching meandered slot and cutting tuning inset, are applied to the radiator in order to maximise the operating frequency range of the antenna. Experimental results demonstrate that the proposed design covers the operating bands of seven wireless services including the DCS/PCS/W-CDMA/2.4-/5-GHz WLANs/Bluetooth and the WiMAX in United States. The design concept, step-by-step guidelines, radiation mechanism and the simulated and experimental results are carefully investigated. The finite-size ground plane effect is taken into account as well. This antenna features multiband operations, almost omnidirectional radiation patterns in one of the principal cuts, and a compact size of 22.75 times 20 mm². It is especially suitable for smart phone applications which are involving in integrating multiple wireless services into a single hand-held unit.     

一种双频MIMO天线的T型枝节解耦设计

本文设计了一种T型枝节解耦的双频MIMO天线.两个工作频段分别覆盖WLAN频率2.45 GHz/5.2 GHz/5.8 GHz.低频谐振单元为倒F天线,通过在低频枝节上增加短截线,用以产生高频谐振,实现双频工作.将天线单元沿水平方向对称放置形成二单元的MIMO天线,并采用在两个天线单元之间添加T型枝节的方法进行解耦.对...     

Iterative bit and power allocation for multi-cell orthogonal frequency division multiplexing with minimum variance distortionless response beamforming

This paper develops bit and power allocation schemes with beamforming for multi-cell orthogonal frequency division multiplexing (OFDM) systems on uplink. The model of the multi-cell channel with frequency reuse is considered. The transmit signal from each mobile causes interference to the received signals of other base stations. The schemes aim to minimise the total mobile transmit power while satisfying the required data rate and the bit error rate (BER) of each mobile. The proposed schemes offer better performance than that of the fixed bit allocation method. The proposed distributed allocation scheme reduces computational complexity compared to the proposed centralised multi-user greedy method with insignificant performance degradation. The simulation results are presented to demonstrate the efficacy of the proposed schemes.     

Wireless Industrial Monitoring and Control Using a Smart Sensor Platform

A wireless smart sensor platform (based on patent pending technologies, Ramamurthy ) targeted for instrumentation and predictive maintenance systems is presented. The generic smart sensor platform with "plug-and-play" capability supports hardware interface, payload and communications needs of multiple inertial and position sensors, and actuators, using a RF link (Wi-Fi, Bluetooth, or RFID) for communications, in a point-to-point topology. The design also provides means to update operating and monitoring parameters as well as sensor/RF link specific firmware modules "over-the-air." Sample implementations for industrial applications and system performance are discussed     

Frequency Reconfigurable Antenna for Portable Wireless Applications

In this paper, the design and experimental evaluation of a hexagonal-shaped coplanar waveguide (CPW)-feed frequency reconfigurable antenna is presented using flame retardant (FR)-4 substrate with size of 37 × 35 × 1.6 mm³. The antenna is made tunable to three different modes through the status of two pin diodes to operate in four distinct frequency bands, i.e., 2.45 GHz wireless fidelity (Wi-Fi) in MODE 1, 3.3 GHz (5G sub-6 GHz band) in MODE 2, 2.1 GHz (3G Long Term Evolution (LTE)-advanced) and 3.50 GHz Worldwide Interoperability for Microwave Access (WiMAX) in MODE 3. The optimization through simulation modeling shows that the proposed antenna can provide adequate gain (1.44~2.2 dB), sufficient bandwidth (200~920 MHz) and high radiation efficiency (80%~95%) in the four resonating frequency bands. Voltage standing wave ratio (VSWR) < 1.5 is achieved for all bands with properly matched characteristics of the antenna. To validate the simulation results, fabrication of the proposed optimized design is performed, and experimental analysis is found to be in a considerable amount of agreement. Due to its reasonably small size and support of multiple frequency bands operation, the proposed antenna can support portable devices for handheld 5G and Wireless LAN (WLAN) applications.     

Reconfigurable angular diversity antenna with quad corner reflector arrays for 2.4 GHz applications

The authors propose a reconfigurable angular diversity antenna, constructed with quad corner reflector arrays and switching control, that can provide effective polarisation. With switches in the control unit of the base station, a high radiation gain antenna to provide cross-pair polarisations for receiving operations, as well as an omni-directional radiation pattern for transmitting, has been reconfigured. Simulation and measurement results including frequency responses, radiation patterns and three-dimensional polar plots demonstrate the design of an antenna. Diversity measurements with correlation and root mean square (RMS) error vector magnitude (EVM) are presented in order to evaluate the proposed antennas. The angular diversity technique can be applied to wireless local area network (WLAN) and multiple-input and multiple-output (MIMO) systems.     

Broadband flexible comb-shaped monopole antenna

A broadband comb-shaped monopole antenna is proposed. The antenna has dimensions of 19 mm x 12 mm. The measured results show good agreement with the numerical prediction, and broadband operation with 10 dB impedance bandwidth of 44.75% (1.7-2.68 GHz). The antenna is built on one side of a flexible-printed circuit board (PCB) dielectric substrate. Folded and rolled antenna structures, which are transformed by the proposed planar antenna structure, are presented. Each antenna has a broadband impedance bandwidth that covers the PCS, UMTS, WiBro, WLAN and SDMB bands. Also, omni-directional radiation patterns over the operating bands have been obtained. The proposed antennas are suitable for mobile communication applications requiring a small antenna.     

A simple dual-band microstrip-fed printed antenna for WLAN applications

A novel microstrip-fed dual-band printed antenna for wireless local area network (WLAN) is presented. The antenna comprises a rectangular and a circular radiating element, which generate two resonant modes to cover 2.4/5.2/5.8 GHz WLAN bands. The design was experimentally verified by constructing the antenna on a FR4 (ϵr = 4.4) dielectric substrate (47 mm x 26 mm x 0.76 mm) and measuring its impedance and radiation characteristics at both the bands. The measured 10 dB return loss (VSWR 2:1) bandwidth in the 2.4G Hz band is 550 MHz (2.1?2.65 GHz) and it covers the bandwidth required for 2.4 GHz WLAN. The 5.2/5.8 GHz resonant mode has a bandwidth of 950 MHz (5.15?6.1 GHz) covering 5.2/5.8 GHz WLAN bands. A rigorous experimental evaluation confirmed that the dual-band printed antenna maintained good radiation characteristics with minimum cross-polarisation levels.     

The SVM-Based Smart Antenna for Estimation of the Directions of Arrival of Electromagnetic Waves

Microwave systems for object detection and imaging usually illuminate a given scene and measure the reflected signals. One of the most important tasks is a rapid and efficient detection of the angular positions of the scatterers present in the scene. This task can be accomplished by designing a smart antenna composed of multiple receiving elements, which is able to estimate the angles of incidence of the incoming electromagnetic waves. In this paper, a new efficient method based on a support vector regression is proposed for the detection of arriving electromagnetic waves scattered by objects located both in the far-field and near-field regions of the smart antenna. The effectiveness of the proposed approach is evaluated by means of several numerical simulations     

A Novel Compact Highly Isolated UWB MIMO Antenna with WLAN Notch

This paper presents a compact Multiple Input Multiple Output (MIMO) antenna with WLAN band notch for Ultra-Wideband (UWB) applications. The antenna is designed on 0.8 mm thick low-cost FR-4 substrate having a compact size of 22 mm × 30 mm. The proposed antenna comprises of two monopole patches on the top layer of substrate while having a shared ground on its bottom layer. The mutual coupling between adjacent patches has been reduced by using a novel stub with shared ground structure. The stub consists of complementary rectangular slots that disturb the surface current direction and thus result in reducing mutual coupling between two ports. A slot is etched in the radiating patch for WLAN band notch. The slot is used to suppress frequencies ranging from 5.1 to 5.9 GHz. The results show that the proposed antenna has a very good impedance bandwidth of |S11| < −10 dB within the frequency band from 3.1–14 GHz. A low mutual coupling of less than −23 dB is achieved within the entire UWB band. Furthermore, the antenna has a peak gain of 5.8 dB, low ECC < 0.002 and high Diversity Gain (DG > 9.98).     

低交叉极化高隔离的双极化天线

设计了一种应用于WLAN的具有低交叉极化和高隔离度的双极化天线.天线由3层功能层和2层介质基板间隔层叠而成.3层功能层分别为1个方形辐射贴片,2个带有发夹谐振器的馈电网络和1个刻蚀H形缝隙的接地板.发夹谐振器和辐射贴片构成一个二阶滤波天线用以展宽天线的带宽.通过在接地板上蚀刻H形缝隙降低了天线端口间的耦合电流,改善了天...