High Bandwidth Efficiency Research Articles

A design technique to improve harmonic suppression in high efficiency wideband Class E RF power amplifier

A design technique to improve harmonic suppression in high efficiency wideband Class E RF power amplifier

A Universal Low-Complexity Symbol-to-Bit Soft Demapper

High-order constellations are commonly used for achieving high bandwidth efficiency in most communication systems. However, the complexity of the multiplication operations associated with the standard max-sum approximation of the maximum a posteriori probability in the log-domain (Max-Log-MAP) symbol-to-bit demapper is very high. In this contribution, we conceive a low-complexity universal soft demapper, which reduces the demapper's complexity considerably for the binary-reflected Gray-labeled pulse amplitude modulation (PAM), phase shift keying (PSK), quadrature amplitude modulation (QAM), and amplitude phase-shift keying (APSK) relying on product constellation labeling (product-APSK). Our theoretical analysis demonstrates that the proposed demapper has exactly the same performance as the Max-Log-MAP demapper for the Gray-labeled PAM, PSK, and QAM. Our theoretical analysis and simulation results also demonstrate that for the Gray-labeled product-APSK, the performance degradation of the proposed simplified soft demapper is negligible for both 64-ary and 256-ary constellations compared with the Max-Log-MAP demapper.

The Research of High-Level Modulation in Visible Light Communication

Visible light communication system using light emitting diode as light source, the system has the dual role of lighting and communication, thereby greatly saving energy .The bandwidth of LED modulation is a major obstacle to development of VLC technology. Researchers have put forward a variety of techniques to extend the modulation bandwidth and improve the transmission rate, such as Blu-ray filtering, equalization, multiple-input multiple-output (MIMO) technology, high ray modulation format, the wavelength division multiplexing technology, discrete multi-tone modulation and so on. The transmission rate of VLC system can be greatly improved by a combination of these techniques in a technical or several techniques. This paper analyzes the effect of OFDM technology each sub-carrier modulation with MQAM to visible light communication. It gives a brief introduction of the visible light communication system; it also shows the average power spectral density and error rate from SIMULINK simulation. It proves further the high-level quadrature amplitude modulation (MQAM) with higher bandwidth efficiency and smaller error rate, the bandwidth efficiency of 256QAM modulation is the twice of 16QAM modulation.

High-Power Wideband $L$-Band Suboptimum Class-E Power Amplifier

This paper presents a high-power high-efficiency wideband suboptimum Class-E RF power amplifier based on a packaged high-power GaN HEMT. It uses a simple double-reactance compensation and impedance transformation load network that includes device intrinsic capacitance, package parasitics, low-loss microstrip transmission lines, and lumped components. This load network makes the GaN HEMT operate in suboptimum Class-E from 900 to 1500 MHz (50% fractional bandwidth at 1200 MHz). The amplifier can operate both in continuous wave and pulsed modes over its full bandwidth without tuning. It delivers up to 180-W output power with up to 85% drain efficiency and PAE=81%. To the best of the authors' knowledge, the amplifier proposed in this work outperforms commercial grade amplifiers that operate in the same frequency band with similar output power levels. Direct applications for this amplifier include mobile satellite communications transmitters, envelope elimination and restoration digital audio broadcasting transmitters, and power stages for primary and secondary RADAR transmitters.

Bandwidth efficient power‐aided semi‐blind channel estimation for multiple‐antenna systems

This study presents a semi-blind channel estimation scheme for multiple-antenna systems. With the aid of channel covariance and received signal power, the proposed scheme derives channel estimates using pilot symbols transmitted by only one of its antennas. Other transmit antennas in the scheme do not need to transmit any pilot symbols. As such, the proposed scheme has higher bandwidth efficiency compared with conventional pilot symbol-based multiple-antenna channel estimation schemes, where every antenna is required to transmit pilot symbols. It is shown that the proposed scheme is able to deliver performance on par with the conventional minimum mean-square error and least-square error multiple-channel estimation schemes. The strength of the proposed scheme lies in its ability to exploit received signal power for channel estimation.

An Effective Scheme of M-Ary Spread Spectrum System Based on Orthogonal Spread Spectrum and CPSK

A hybrid M-ary spread spectrum (SS) communication scheme which combined with orthogonal SS and CPSK technique is proposed. Based on dual orthogonal SS, every SS code is treated as original code to adopt CPSK modulation, the unattached synchronous code is chosen to achieve system synchronization. At the receiver, A circular correlator based on transform domain processing is employed to de-spread the received signals. Compared with M-ary SS and CPSK, the proposed scheme is able to obtain higher bandwidth efficiency, stronger anti-intercept capability, and better synchronous performance. The Monte-Carlo simulation results demonstrate that the proposed scheme can achieve better synchronous and bit error rate (BER) performance under additional white gauss noise channel models.

An Extended-Bandwidth Three-Way Doherty Power Amplifier

This paper expounds a three-way Doherty power amplifier (3W-DPA) as a solution to the need for high-efficiency wideband power amplifiers when driven by multi-standard signals. The paper begins with a theoretical analysis of 3W-DPA architecture from which the governing equations are derived. This analysis enables the identification of circuit parameters for maximizing bandwidth. A comprehensive methodology was devised to address the practical design challenges resulting from the transistor nonidealities: nonlinear input capacitance, transistor package, and output capacitance. Based on this methodology, a fully analog 30-W 3W-DPA was designed and implemented using GaN packaged transistors. The 3W-DPA prototype maintained an average drain efficiency of 55% at an output back-off of up to 9 dB, over the frequency range of 0.73-0.98 GHz. The 3W-DPA was successfully linearized when driven with 20-MHz four-carrier wideband code division multiple access (WCMDA) signals. 830- and 900-MHz power-added efficiencies of 47% and 53% was achieved at 32- and 35-dBm average output power, corresponding to a peak-to-average power ratio of 11.7 and 7.14 dB, respectively.

Collision-Free Bandwidth-Variable Optical Burst Switching Ring Network

Recently, flexible bandwidth allocation has been proposed in an orthogonal frequency division multiplexing based elastic optical network, which is a promising technology for 100G and beyond optical networks. In this paper, for the first time we introduce flexible bandwidth to an optical burst switching (OBS) ring network and propose a novel bandwidth-variable OBS (BV-OBS) ring network. In the proposed BV-OBS ring network, the durations of bursts are fixed to one timeslot in the time domain, while the bandwidths are variable in the frequency domain according to the burst size. With fixed burst duration and variable bandwidth, the BV-OBS ring can achieve the state of being collision free with high bandwidth efficiency. Simulation results show that a BV-OBS ring network outperforms previous OBS rings proposed in wavelength division multiplexing networks in both network throughput and end-to-end delay.

Distributed probabilistic medium access with multipacket reception and Markovian traffic

Enabling multipacket reception (MPR) at the physical layer is a promising way to achieve higher bandwidth efficiency while reducing the complexity of the medium access control layer in distributed wireless networks. We study distributed probabilistic access where transmitting nodes access the shared wireless medium with a probability based on the node's information about the aggregate traffic carried by the network. We model bursty traffic by rate-controlled two-state Markov sources and introduce a parameter that describes the "burstiness" level of the offered traffic. A throughput-optimal medium access strategy utilizing limited feedback is then described and its performance is examined for traffic with different levels of burstiness. It is shown that the bursty nature of the traffic in data networks allows for improvement of the bandwidth efficiency. Bounds on the system throughput are proposed and the queuing delay is analyzed.

Low complexity zero-forcing beamforming for distributed massive MIMO systems in large public venues

Distributed massive MIMO systems, which have high bandwidth efficiency and can accommodate a tremendous amount of traffic using algorithms such as zero-forcing beamforming (ZFBF), may be deployed in large public venues with the antennas mounted under-floor. In this case the channel gain matrix H can be modeled as a multi-banded matrix, in which off-diagonal entries decay both exponentially due to heavy human penetration loss and polynomially due to free space propagation loss. To enable practical implementation of such systems, we present a multi-banded matrix inversion algorithm that substantially reduces the complexity of ZFBF by keeping the most significant entries in H and the preceding matrix W. We introduce a parameter p to control the sparsity of H and W and thus achieve the tradeoff between the computational complexity and the system throughput. The proposed algorithm includes dense and sparse preceding versions, providing quadratic and linear complexity, respectively, relative to the number of antennas. We present analysis and numerical evaluations to show that the signal-to-interference ratio (SIR) increases linearly with p in dense precoding. In sparse preceding, we demonstrate the necessity of using directional antennas by both analysis and simulations. When the directional antenna gain increases, the resulting SIR increment in sparse precoding increases linearly with p, while the SIR of dense precoding is much less sensitive to changes in p.

Silicon micromirrors with three-dimensional curvature enabling lensless efficient coupling of free-space light

Miniaturized optical benches process free-space light propagating in-plane with respect to the substrate and have a large variety of applications, including the coupling of light through an optical fiber. High coupling efficiency is usually obtained using assembled micro-optical parts, which considerably increase the system cost and integration effort. In this work, we report a high coupling efficiency, monolithically integrated silicon micromirror with controlled three-dimensional (3D) curvature that is capable of manipulating optical beams propagating in the plane of the silicon substrate. Based on our theoretical modeling, a spherical micromirror with a microscale radius of curvature as small as twice the Gaussian beam Rayleigh range provides a 100% coupling efficiency over a relatively long optical path range. Introducing dimensionless parameters facilitates the elucidation of the role of key design parameters, including the mirror's radii of curvature, independent of the wavelength. A micromachining method is presented for fabricating the 3D micromirror using fluorinated gas plasmas. The measured coupling efficiency was greater than 50% over a 200-μm optical path, compared to less than 10% afforded by a conventional flat micromirror, which was in good agreement with the model. Using the 3D micromirror, an optical cavity was formed with a round-trip diffraction loss of less than 0.4%, resulting in one order of magnitude enhancement in the measured quality factor. A nearly 100% coupling was also estimated when matching the sagittal and tangential radii of curvature of the presented micromirror’s surface. The reported class of 3D micromirrors may be an advantageous replacement for the optical lenses usually assembled in silicon photonics and optical benches by transforming them into real 3D monolithic systems while achieving wideband high coupling efficiency over submillimeter distances. Scientists from France and Egypt have developed spherical micromirrors that can couple optical fibres with almost 100% efficiency. Yasser Sabry and colleagues fabricated their monolithically-integrated mirrors in a silicon platform by a technique incorporating fluorinated gas plasmas and then coating the etched surface with a 100-nm-thick layer of aluminium. The resulting broadband mirrors had curvatures of 30–200 μm and exhibited reflectivities of >92% in the visible and near-infrared spectral regimes. The combination of high reflectivity and almost perfect coupling to optical fibres allows for the creation of miniature integrated optical cavities with a round trip transmission of better than 99.6% multiplied by the mirror reflectivity and an overall Q-factor of around 3000. This performance is an order of magnitude better than that achieved using flat mirrors.

Quality of service guarantee for real-time VBR traffic flows with different delay bound and loss probability requirements in WLANs

The medium access control of IEEE 802.11e defines a novel coordination function, namely hybrid coordination function (HCF), which allocates transmission opportunity (TXOP) to stations taking their quality of service (QoS) requirements into account. However, the reference TXOP allocation scheme of HCF controlled channel access, a contention-free channel access function of HCF, is only suitable for constant bit rate traffic. For variable bit rate (VBR) traffic, serious packet loss may occur. In this article, we generalize the reference design with an efficient TXOP allocation algorithm, a multiplexing mechanism, and an associated admission control unit to guarantee QoS for VBR flows with different delay bound and packet loss probability requirements. We define equivalent flows and aggregate packet loss probability to take advantage of both intra-flow and inter-flow multiplexing gains so that high bandwidth efficiency can be achieved. Moreover, the concept of weighted-loss fair service scheduling is adopted to allocate the aggregate TXOP to individual flows. From numerical results obtained by computer simulations, we found that our proposed scheme meets QoS requirements and results in much higher bandwidth efficiency than previous algorithms.

Application of differential amplitude and phase-shift keying in underwater acoustic communication based on orthogonal frequency division multiplexing

With the increase of of marine resource and underwater users, developing a high-bit-rate underwater acoustic communication has become a hot topic. Amplitude and phase-shift keying (APSK) is a modulation technique having high efficiency in spectrum utilization, it attracts more and more attention in high-bit-rate underwater acoustic communication. Differential APSK (DAPSK) is modulated using differential amplitude and phase code in time domain, and it has higher bandwidth efficiency and be easier to realize the system than APSK. A transmission system based on DAPSK modulation and OFDM is presented to solve the problems of effectiveness and reliability in high-bit-rate underwater acoustic communication. Simulation results show that the system using DAPSK modulation has a better performance than those using APSK and QAM modulation.

Open research issues in multi-hop cognitive radio networks

Cognitive radio networks hold the key to achieving better radio bandwidth utilization and improving the quality of wireless applications. The next step in this fast emerging paradigm is the multi-hop cognitive radio network. Well designed multi-hop cognitive radio networks can provide high bandwidth efficiency by using dynamic spectrum access technologies as well as provide extended coverage and ubiquitous connectivity for the wireless end users. However, the special features of multi-hop cognitive radio networks also raise several unique design challenges. In this article, we survey these unique challenges and open research issues in the design of multi-hop cognitive radio networks as well as discuss potential approaches to address these challenges. This article specifically focuses on the medium access control (MAC) and network layers of the multi-hop cognitive radio protocol stack. Issues considered include efficient spectrum sharing, optimal relay node selection, interference mitigation, end-to-end delay, etc.

S-MIM: a novel radio interface for efficient messaging services over satellite

This article presents a radio interface recently standardized by ETSI under the name of S-band Mobile Interactive Multimedia (S-MIM) and especially designed to provide ubiquitous messaging services over S-band GEO satellites using low-power terminals. Thanks to low terminal cost and high bandwidth efficiency, this standard allows the development of new satellite services, particularly for vehicular and machine-to machine applications. The S-MIM standard relies on a broadcasting radio interface such as DVB-SH or ETSI SDR in the forward link, and reuses 3GPP W-CDMA technology properly adapted to the scope in the return link. Thanks to the use of spread spectrum ALOHA, terminals can access the channel in a totally asynchronous manner. The use of a packet-optimized iterative successive interference cancellation (i- SIC) algorithm at the receiver allows exploiting the inherent power imbalance among terminals in order to boost the throughput with respect to conventional SSA systems. In addition, advanced packet transmission control techniques have been adopted to maximize the probability of successful packet reception in the challenging land mobile satellite channel. Finally, the S-MIM link layer provides efficient and reliable transport of IP datagrams over the forward and return link radio interfaces.

A Blind Hammerstein Diversity Combining Technique for Flat Fading Channels

Diversity combining techniques play an important role in combating the destructive effects of channel fading in wireless communication systems. In this work we present a blind diversity combining technique for Rayleigh flat fading channels based on Hammerstein type filters. We show that the performance of this technique is very close to ideal MRC system which is accepted as an optimum receiver over fading channels in presence of AWGN. This is a valuable result especially because higher bandwidth efficiency is also achieved as compared with MRC. We also show that in our proposed technique the variation of the combiner output values around the values of transmitted symbols is less than the corresponding variation in MRC system. Hence, for soft decision applications it is superior to MRC technique.

DFT Based MMSE Equaliser in MIMO-OFDM

MIMO-OFDM is considered as a fast growing technology now days. OFDM is a multi carrier modulation technique in which the carriers are Orthogonal to each others as a result of which it provides high bandwidth efficiency and multiple carriers share the data among themselves. During the research equalizer is always a matter of strategies. When a signal is transmitted over a radio channel, it is subject to reflection, refraction and diffraction and also the type of modulation technique selected at transmitter. In this paper Bit Error Rate performance of OFDM under Rayleigh fading channel is analysed, and compared with Additive White Gaussian Noise Channel.

An Interference Nulling Based Channel Independent Precoding for MIMO-OFDM Systems with Insufficient Cyclic Prefix

In this paper, a new interference nulling based channel independent precoding for MIMO-OFDM systems of nt transmit and nr receive antennas with insufficient cyclic prefix (CP) is proposed. By employing the notion of interference nulling, we show that our proposed channel independent precoding scheme can eliminate the inter-block interference (IBI) caused by the insufficient CP with higher bandwidth efficiency than the conventional zero-padded or a sufficient CP added block transmission system when nr ≤ nt. It is also shown that when nr >; nt, the IBI can be eliminated without the need of any zero-padding or adding CP or precoding when the OFDM block length is not too small.

A critically coupled Germanium photodetector under vertical illumination

We propose and study a practical design of a Germanium photodetector implemented on a Silicon-on-insulator substrate to reach the critical coupling regime under vertical illumination at 1310 nm wavelength. With appropriate optimization procedures, a high efficiency bandwidth product larger than 50 GHz and a large 3dB spectral full width around 30 nm can be obtained given realistic material parameters and fabrication constraints. Our device is fully compatible to the state-of-art CMOS process technology, and may serve as a high performance, low cost solution for the optical receiver in Silicon photonics based optical interconnects.

Power-Efficient Calibration and Reconfiguration for Optical Network-on-Chip

Recent advances in nanophotonic fabrication have made the optical network-on-chip an attractive interconnect option for next-generation multi-/many-core systems, providing high bandwidth and power efficiency. Both postfabrication and runtime calibration of the optical components (ring resonators) are essential to building a robust optical communication system, as they are highly sensitive to process and thermal variation. Existing tuning methods based on bias voltage and temperature adjustment require excessive power to fully compensate for these variations. In this work, we propose a set of complementary techniques to address this challenge and significantly reduce the tuning power consumption: 1) a subchannel remapping scheme to decrease the required tuning from the free spectral range to less than one channel (typically less than 1 nm); 2) a transceiver-based network topology capable of building and tuning far fewer rings while maintaining the same system throughput. Our results show that the proposed methods can together reduce the tuning power by as much as 99.85%.