Modern Wireless Communication Systems Research Articles

Wideband and Multiband Antenna Design and Fabrication for Modern Wireless Communications Systems

One of the major challenges due to spectrum scarcity in modern wireless communication is on antenna design that can serve a non-contagious frequency spectrum. In this paper, wideband and multiband design approaches are proposed to produce antennas that can serve various wireless technologies using different frequencies from 2.3 to 6.0 GHz, covering WiFi frequencies at 2.4-2.48 GHz, 5,15-5,35 GHz and 5,725-5,825 GHz, as well as WiMax frequencies at 2.3-2.4 GHz, 2.495-2.695 GHz, 3.3-3.8 GHz, and 5.25-5.85 GHz. The wideband and multiband antenna were implemented on an 0.8 mm thick of FR4 epoxy dielectric substrate with permittivity er=4.3. The return loss of 10 dB can be achieved for 2.3 to 6 GHz in wideband antenna, and a tripe band of 2.3-2.8 GHz, 3.3-3.7 GHz, and above 4.6 GHz in multiband antenna. The gain of both antennas increases almost linearly from 0 dB at 2.3 GHz to around 4.5 dB at 6 GHz, except for the stop band at 2.8-3.3 GHz which has a significant drop of gain, corresponding to the stop frequency band. Antenna radiation pattern is bidirectional at x-y plane and nearly omnidirectional at y-z plane, and shows a similar patern for both wideband and multiband design approaches.

Pattern Synthesis of Nonuniformly Spaced Arrays Based on Unit Circle Representation and Taguchi Method

Unit circle representation techniques such as Schelkunoff null placement method have been extensively used to synthesize uniformly spaced linear arrays. In this work, it is attempted to extend the unit circle representation approach to synthesize nonuniformly spaced linear arrays with some desired null directions and minimum achievable sidelobe level. The problem is formulated as an optimization task upon which Taguchi method is employed to solve for the set of element positions. Illustrative examples are included to demonstrate the design effectiveness and flexibility for modern wireless communication system applications.

Compact and high-performance bandpass filter and diplexer based on SCMRC-loaded SIR

Bandpass filter (BPF) and diplexer, which are required to be compact size and high performance, are widely used in modern wireless communication systems. In this article, novel BPF and diplexer are designed using the proposed resonator called spiral compact microstrip resonator cell (SCMRC)-loaded stepped-impedance resonator (SIR). The SCMRC-loaded SIR is proposed using the slow-wave structure SCMRC to replace the low-impedance section of the conventional SIR. Compared with the conventional SIR, the new SCMRC-loaded SIR has a compacter size and can generate a transmission zero above its fundamental resonant frequency. As examples, a BPF with the central frequency at f 0 = 1 GHz and a diplexer operating at 0.9/1.57 GHz are designed and fabricated. The fabricated BPF occupies a compact size of 0.07 λ 0 × 0.035 λ 0 and has a −60 dB rejection level wide stopband from 1.2 f 0 to 3.8 f 0. The fabricated diplexer occupies a compact size of 0.076 λ 0 × 0.128 λ 0 and has an up to −50 dB output isolation. Good agreement can be observed between the simulations and the measurements.

Power Spectral Density Analysis of WLAN based OFDM System

is a technique used in modern broadband wireless communications systems. OFDM has been adopted for wireless standards such as IEEE 802.11a. In this paper, different Power Spectral Density (PSD) curves of OFDM signal based on WLAN with various pulse shapes are presented. OFDM waveform is analyzed in frequency domain response for different modulation techniques such as BPSK, QPSK, 16-QAM, 64-QAM and different block sizes such as 50 and 2048. Power spectral density increases with increase in levels of modulation. For high power spectral density of transmitter higher levels of QAM modulation techniques are preferred.

High-performance digital predistortion test platform development for wideband RF power amplifiers

In this paper, a complete design procedure, together with robust system validation approaches, is presented for implementing a high-performance re-configurable digital predistortion (DPD) test platform for compensating for nonlinear distortion and memory effects induced by radio frequency (RF) power amplifiers (PAs) in the transmitters of modern wireless communication systems. This hardware and software co-operated test system not only enables effective validation for DPD algorithm development, but also provides a high-performance and reliable hardware-based linearization test platform. The experimental test was applied on a medium power Doherty amplifier, which was designed for 3 G/4 G wireless communication base stations. By applying our DPD algorithms on the proposed platform, more than 30 dB improvements in adjacent channel power ratio can be achieved for Universal Mobile Telecommunications System and long-term evolution signal excitations.

RF power amplifier's nonlinear modelling with memory effect

Theoretically, memoryless nonlinear effect is the main concern for RF power amplifier (PA) modelling and analysis. However, the latest generation wireless communication systems, such as Wi-Fi, WiMAX and LTE, using wider bandwidth, add new problems for the analysis of RF PAs, which is the memory effect associated with the bandwidth. The memory effect causes additional distortion to the PA and affects the performance of digital predistortion (DPD) design. Previously, we predicted the memoryless spectrum regrowth of a PA related to its intercept points up to arbitrary high order for a few of wireless communication signals, such as TDMA, CMDA and OFDM. In this letter, we propose a simplified Hammerstein structure-based method to consider the memory effect as well in order to analyse the nonlinear characteristic of PAs more precisely and completely. The simplification greatly reduced the complexity of classic Hammerstein system identification for PAs. The result will be useful in the analysis of RF PAs with memory effect and the proposed PA model is intended to be used in predistorter design for modern wideband wireless communication systems.

Modeling, Analysis, and Experimental Validation of Frequency Dividers with Direct Injection

An analytical model and a methodology are presented for the analysis of CMOS injection-locked frequency dividers with direct injection, which are used in modern wireless communication systems. The amplitude and phase of the oscillation in the synchronous operation mode, as well as the locking range, are found in explicit form. The width of the locking range is determined by the condition of the existence and stability of synchronous oscillations. The accuracy of the model and of the presented formulas is validated through a comparison with experimental results, which are in good agreement with the analytical ones.

On Ultra Extended Cyclic Prefix in Orthogonal Frequency Division Multiplexing (OFDM) Systems: The Case of LTE Downlink

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier scheme used in modern broadband wireless communication systems to transmit data over a number of orthogonal subcarriers. When transmitted signals arrive at the receiver by more than one path of different length, the received signals are staggered in time; this is multipath propagation. To mitigate the effect of dispersed channel distortion caused by random channel delay spread, Cyclic Prefix (CP) is introduced to eliminate Inter-Symbol Interference (ISI). In the literature, researchers have focused on carrying out investigations (or studies) mainly on the two existing CP insertions, namely: normal and extended CPs. Both CPs have limitations with respect to handling channel delay spreads. In the current work, a new CP, herein referred to as “ultra extended” CP is proposed to address delay spreads beyond the limits of the normal and extended CPs. The efficacy of the proposed ultra extended CP is tested via simulation under different scenarios. It is shown by the results obtained that the proposed CP can efficiently handle delay spreads beyond the limits of the existing normal and extended CP, and can indeed be implemented in the design of future telecommunication systems to accommodate higher channel delay spreads and it ensures wider cell coverage.

A NOVEL BROADBAND ASYMMETRIC COPLANAR WAVEGUIDE (ACPW)-FED ZEROTH-ORDER RESONATOR ANTENNA BASED ON EPSILON NEGATIVE TRANSMISSION LINE

A broadband zeroth-order resonant (ZOR) antenna based on asymmetric coplanar waveguide (ACPW) is presented. By adopting the epsilon negative transmission line (ENG-TL), a zeroth-order resonance mode can be achieved. We employ an asymmetric coplanar waveguide structure which ofiers the design freedom to realize the broadband ZOR antenna, where the antenna's bandwidth is characterized by the equivalent circuit parameters. The antenna has the compact unit cell dimensions of 5 £ 13:8mm 2 . The measured results show that the operating bandwidth is about 1050MHz (1.90{ 2.95GHz), and the peak gain and radiation e-ciency are 2.46dBi and 91% at zeroth-order 2.3GHz. Owing to the characteristics of broad bandwidth, high e-ciency, omnidirectional radiation, and easy manufacturing, the proposed ACPW ZOR antenna is very suitable for modern wireless communication systems (UMTS, WLAN, WIMAX, LTE).

Energy Efficient Random Transmission Control for Cognitive Radio Systems

Cognitive radio technology will allow terminals to access licensed and unlicensed portions of the spectrum. This feature will improve end-user satisfaction and will partially solve bandwidth scarcity problems. However, this opportunistic access implies more transmission attempts and thus higher power consumption. This goes against the energy/power efficient design that underpins modern wireless communication systems. This paper partially addresses this issue by proposing a random transmission policy that is energy-efficient and that provides high throughput gains. To facilitate analysis, a reception model for Rayleigh channels is here proposed that allows the calculation of correct packet reception statistics in the presence/absence of interference between primary/secondary users. The analysis initially focuses on the derivation of the boundaries of two types of trade-off regions: primary vs. secondary throughput, and sum-throughput vs. power consumption. It is observed that secondary transmissions always increase power consumption, and in the case of low interference they always lead to higher sum-throughput at the expense of reduced primary performance. By contrast, in the case of high interference, secondary transmissions can reduce both sum-throughput and primary user performance, thus requiring more complex control. It is shown that the minimum sum-throughput solution is also the boundary of the region where primary/secondary contributions to sum-throughput start to become dominant. An optimum transmission policy is further derived that maximizes sum-throughput while keeping primary/secondary throughput and power consumption under control. Sketches of the trade-off regions show the benefits of the proposed transmission policy.

Bandwidth Enhancement of Asymmetric Coplanar Waveguide (ACPW)-Fed Antenna Based on Composite Right/Left-Handed Transmission Line

A novel wideband antenna based on composite right/left-handed transmission line (CRLH-TL) is presented. The bandwidth enhancement of the antenna can be achieved when the zeroth-order and first-positive-order modes are closely spaced and merged together. The uniplanar asymmetric coplanar waveguide (ACPW) is adopted as the host transmission line. The ACPW structure not only offers the design freedom to implement the circuit parameters, but also overcomes the design constraint of the traditional CPW. The measured results show that the operating bandwidth is 1720 MHz (2.1–3.82 GHz), corresponding to approximately 58.1% fractional bandwidth. Owing to the characteristics of wide bandwidth, enhanced efficiency, and omnidirectional radiation, the proposed antenna is a good candidate for modern wireless communication systems (LTE, WLAN, WiMAX).

A Compact Filtering Antenna With Flat Gain Response Within the Passband

A compact filtering antenna is designed for the modern wireless communication systems in this letter. First, a two-pole Butterworth bandpass filter is designed. Then, by substituting the second port and resonator with fan-shaped patch antenna (traditional antenna) with defected ground structure (DGS), a filtering antenna is formed. Compared to the traditional antenna, the filtering antenna obtains the flatter gain response within the passband, good selectivity at the passband edge, and the wider bandwidth. Measured results show that the filtering antenna can operate at 2.4 GHz and has a 460-MHz bandwidth and a 2.3-dBi peak gain within the passband. Moreover, a radiation zero occurs at 3 GHz.

ELECTRONICALLY RECONFIGURABLE BEAM STEERING ANTENNA USING EMBEDDED RF PIN BASED PARASITIC ARRAYS (ERPPA)

In this paper, an electronically reconflgurable beam steering antenna using embedded RF PIN switches based parasitic array (ERPPA) is proposed for modern wireless communication systems that operate at 5.8GHz frequency. In the proposed antenna, a single driven element is fed by a coaxial probe, while each of the two parasitic elements is integrated with an RF PIN switches that embedded inside the substrate. In the conventional reconflgurable antennas, the RF PIN switches are mounted on narrow slots created on the top or bottom layer of the radiator/parasitic elements, which could lead to the dimensional changes of the antenna and degrade the performance in terms of beam steering and return loss. However, this research proposes an exclusive solution where the RF PIN diodes at parasitic elements are embedded inside the substrate thus no additional slots have to be created to mount the SMCs on the antenna. In this regard, the proposed antenna is highly competent to eliminate the intermodulation efiect generated by the RF PIN diodes and the other passive elements associated with the PIN diodes. In this research, extensive investigations revealed that the parasitic element dimension and the selection of RF PIN switches signiflcantly in∞uence

Comparison of DoA Estimation Algorithms in SDMA System

With Space Division Multiple Access (SDMA) schemes employing digital signal processing algorithms in its smart antenna systems, it is possible to improve the system capacity of modern wireless communication systems by enabling user's angular separation. Angular separation ability enhances reception in Signal-of-Interest direction and minimizes interference in Signal-of-Not-Interest direction. Direction of Arrival (DoA) algorithms are used for estimation of a number of incident plane waves on the antenna array and their incidence angles. This paper compares performance of three DoA algorithms: MUSIC, root-MUSIC and Capon applied on the uniform linear array in the presence of uncorrelated white noise. The simulation results show that MUSIC outperformed root-MUSIC and Capon in both required number of snapshots and number of array elements as well as in signal-to-noise ratio requirements.

Wideband Antenna Design and Fabrication for Modern Wireless Communications Systems

Abstract One of major challenges in antenna design for modern wireless communication system is to construct a single antenna that can serve a non-contagious frequency allocation using various wireless technologies. In this paper, a wideband antenna design approach is proposed to produce a single antenna that can be used by various wireless technologies using different frequencies from 2.3 to 6.0 GHz, covering WiFi frequencies at 2.4-2.48 GHz, 5,15-5,35 GHz and 5,725-5,825 GHz, as well as WiMax frequencies at 2.3-2.4 GHz, 2.495-2.695 GHz, 3.3-3.8 GHz, and 5.25-5.85 GHz. The antenna construction consist of a truncated circular patch with a coplanar waveguide (CPW)-fed line, printed on an 0.8 mm thick of FR4 epoxy dielectric substrate with permittivity ɛr=4.3. Comparation of return loss, VSWR, gain, and radiation pattern between simulation and measurement results appears in close aggrements. Return loss of 9.54 dB or VSWR of 2 can be achieved for the desired 2.3 to 6 GHz frequency band from measurement results. The antenna gain increases almost linearly from 0 dB at 2.3 GHz to around 4.5 dB at 6 GHz. The antenna radiation pattern is found to have an apple-like pattern, which is bidirectional pattern in x-y plane and circular pattern in x-z plane.

Multi-Cell Multi-Stream Collaborative Transmission Incorporating Closed-Loop and Open-Loop Techniques

Abstract This paper addresses the inter-cell interference (ICI) issue in the multi-cell scenario in modern wireless communications systems which employ factor-one frequency reuse pattern, and proposes an effective solution to deal with the ICI. The proposed transmission structure takes advantage of the cooperation between base stations (BS), and combines both closed-loop and open-loop multiple-input multiple-output (MIMO) techniques. The cases of single-stream transmission and multi-stream transmission are both considered in this work. The proposed schemes can enhance the communications quality of the cell-edge mobile stations considerably while causing no additional system complexity. Analysis and simulation results show the effectiveness of the proposed transmission scheme against the inter-cell interference. In particular, the proposed transmission scheme can obtain comparable performance compared with local precoding of coordinated multipoint (CoMP) in terms of sum rate, and doubly reduce the feedback overhead as well.

High-Efficiency Doherty Power Amplifiers: Historical Aspect and Modern Trends

In modern wireless communication systems, it is very important to realize simultaneously high-efficiency and linear operation of power amplifiers. This paper-overview describes the historical aspect of the Doherty approach to the power-amplifier design introduced in 1936 and modern trends in Doherty amplifier (DA) design techniques using multistage and asymmetric multiway architectures. To increase efficiency over the power backoff range, the switchmode class-E, conventional class-F, or inverse class-F operation mode by controlling the second and third harmonics can be used in the load network. The DA with a series-connected load, and inverted, push–pull, balanced, and parallel Doherty architectures are also described and discussed. Finally, examples of the lumped DA implemented in monolithic microwave integrated circuits, digitally driven Doherty technique, and broadband capability of the two-stage DA are given.

Implementation Trade-Offs of Soft-Input Soft-Output MAP Decoders for Convolutional Codes

Soft-input soft-output (SISO) maximum a-posteriori (MAP) decoders for convolutional codes (CCs) are an integral part of many modern wireless communication systems. Specifically, SISO-MAP decoding forms the basis for turbo decoders, as, e.g., specified for HSDPA or 3GPP-LTE, or for iterative detection and decoding in multiple-input multiple-output wireless systems, such as IEEE 802.11n. In this paper, we investigate the silicon-area, throughput, and energy-efficiency trade-offs associated with SISO-MAP decoders based on the algorithm developed by Bahl, Cocke, Jelinek, and Raviv (BCJR). To this end, we develop radix-2 and radix-4 architectures for high-throughput SISO-MAP decoding of CCs having 4, 8, 16, 32, and 64 states and present corresponding implementation results in 180 nm, 130 nm, and 90 nm CMOS technology. We validate technology-scaling rules and finally demonstrate the use of the presented trade-off analysis by identifying the key design parameters for parallel turbo-decoder implementations.

Front-End Design for Compact MIMO Receivers: A Communication Theory Perspective

The front-end is a crucial component in modern wireless communication systems. For SISO systems minimizing the front-end noise factor is optimal, and this also applies to MIMO systems with i.i.d. noise. However, for compact MIMO receivers that may exhibit spatially correlated noise, e.g., through antenna mutual coupling, the optimal design procedure is not clear. In this paper we develop MIMO low-noise design principles from a communication theory perspective by deriving generalizations of SNR and noise factor from various MIMO communication schemes. As one result, we are able to derive optimal matching networks for a bank of uncoupled amplifiers.

Adaptive modulation and coding for Long Term Evolution‐based mobile satellite communication system

SUMMARYThe adaptive modulation and coding (AMC) scheme is mandatory for modern wireless communication systems to overcome inevitable channel impairments. Many of the limitations using AMC are due to the long round‐trip delay of a satellite system. This paper proposes an efficient AMC scheme with power control and symbol interleaving that can be effectively applied to satellite systems. In particular, we focus on mobile satellite systems that have maximum compatibility in a Long Term Evolution system. Simulations reveal that the proposed scheme can provide a maximum 10.2% increase of average beam spectral efficiency and a maximum of 8‐dB power gain compared with a conventional AMC scheme. Copyright © 2012 John Wiley & Sons, Ltd.