Neural network-based receiver for wireless communications

A novel approach, based on neural networks, for the design of a receiver for TDMA wireless communications is described. The receiver utilises three functional blocks: time-frequency analysis, feature extraction, and pattern classification. Computer simulation results are presented comparing the performance of the new receiver against a conventional MSK receiver for a Rayleigh fading multipath channel. The results show that the new receiver is capable of achieving a performance comparable to that of the MSK receiver without the regular transmission of a training sequence     

Gigabit receiver ICs for optical communications

The authors discuss gigabit receiver ICs for optical communications, focusing on their circuit and package design, the performance of receivers that were fabricated, and their application to a 1.6 Gb/s optical receiver. The key technologies for the receivers are discussed, and a design based on these key technologies is proposed. The proposed design is used to fabricate six receiver ICs (eight chips) using an ultra-high-speed bipolar process with transistors having a unity gain bandwidth of 6-8 GHz. The receivers are suitable for long-haul optical transmission at bit rates up to 1.6 Gb/s. Experimental results show that the 1.6 Gb/s receiver has an optical dynamic range of more than 23 dB without any adjustment, and the received average optical power required to maintain a 10^-11 error rate is less the -31 dBm     

Polarisation-insensitive optical heterodyne receiver for coherent FSK communications

An optical FSK heterodyne communications receiver is proposed using a polarisation diversity technique which has a reduced level of complexity. The proposed receiver is constructed and tested at 100kbit/s and shown to have a maximum fluctuation in sensitivity of 17% over conditions of originally complete polarisation fading.     

Capacity of wireless optical communications

We consider the ergodic capacity and capacity-versus-outage probability of direct-detection optical communication through a turbulent atmosphere using multiple transmit and receive apertures. We assume shot-noise-limited operation in which detector outputs are doubly stochastic Poisson processes whose rates are proportional to the sum of the transmitted powers, scaled by lognormal random fades, plus a background noise. In the high and low signal-to-background ratio regimes, we show that the ergodic capacity of this fading channel equals or exceeds that for a channel with deterministic path gains. Furthermore, knowledge of these path gains is not necessary to achieve capacity when the signal-to-background ratio is high. In the low signal-to-background ratio regime, path-gain knowledge provides minimal capacity improvement when using a moderate number of transmit apertures. We also develop expressions for the capacity-versus-outage probability in the high and low signal-to-background ratio regimes, by means of a moment-matching approximation to the distribution for the sum of lognormal random variables. Monte Carlo simulations show that these capacity-versus-outage approximations are quite accurate for moderate numbers of apertures.     

Multiple-subcarrier modulation in optical wireless communications

This article overviews multiple-subcarrier modulation techniques in optical wireless communications. The basic principles and characteristics of MSM techniques in optical wireless communications are presented. MSM optical wireless systems are explained where some block codes that convert information bits to be transmitted to the symbol amplitudes of subcarriers are used to increase the minimum value of the MS electrical waveform. MSM optical communications systems using subcarrier signal point sequences (SSPS) that can improve the power efficiency of MSM systems are also explained. The performance of MSM optical communications systems is presented in the intensity modulation with direct detection (IM/DD) channel without dispersion and in atmospheric optical communications where the effects of scintillation exist.     

无线光通信中的非成像集中器

在无线光通信领域,利用非成像光学设计的集中器能够聚集光辐射能量,而且相对于成像性集中器具有更紧凑的结构和更高的增益.利用光线追迹法对半球形集中器的性质进行了分析与研究.对好几种非成像集中器:半球形集中器,复合抛物线形集中器,介质内部全反射集中器,多表面集中器,多相介质集中器,从设计原理、增益和视场进行比较,并分析其应用场合.     

Guest editorial: optical wireless communications

Over the last two decades, wireless communications has gained enormous popularity, offering attractive options for many personal and organizational communication needs due to major intrinsic characteristics such as flexibility, cost effectiveness, and mobility.     

Adaptive polarisation diversity receiver configuration for coherent optical fibre communications

The authors describe an implementation of the polarisation diversity detection technique for coherent heterodyne communications which maintains the total IF amplitude at a constant level, irrespective of fluctuations in the state of polarisation of either the signal or local oscillator optical fields at the output polarisation beam-splitter.<>     

大气无线光通信系统中数字脉冲间隔调制研究

基于光强闪烁的大气无线光通信系统模型,研究了数字脉冲间隔调制(DPIM)方式的差错性能,分析了符号结构、发射功率、带宽需求等问题,并与 OOK(开关键控)和 PPM(脉冲位置调制)调制方式进行比较。理论和仿真研究结果表明,DPIM 调制方式较 PPM 方式有较高的功率效率和较少的带宽需求,特别是在系统实现上相对于 PPM 大大简化。因此 DPIM 应用于无线光通信系统具有一定优势。     

Petahertz communication: Harmonizing optical spectra for wireless communications

With the rapid deployment of Next-Generation Networks (NGN), the research community has initiated discussions on an entirely new suite of optical enabling techniques. To pave the way for the development of future wireless networks, this article aims to unify the existing infrared, visible light, and ultraviolet subbands while also exploring the potential of the Petahertz (PHz) band to support extremely bandwidth-thirsty telepresence style applications. Our focus is on the emerging Petahertz Communication (PetaCom) framework, scenario-dependent propagation channels, modulation schemes, system performance, multiple access techniques, and networking. We conclude with a range of PetaCom challenges and open research issues.     

Angle diversity and rate-adaptive transmission for indoor wireless optical communications

The main degrading factor in indoor wireless optical communication systems for bit rates up to several megabits per second is the shot noise induced by ambient light (sunlight and artificial light produced by incandescent and fluorescent lamps). Due to the directional nature of both signal and ambient light noise, the spatial distribution of the signal-to-noise ratio in indoor environments can show large variations. This article compares techniques that are able to mitigate the effect of such SNR variations: rate-adaptive transmission and angle diversity. In the first technique, the effective data rate is adjusted to the local SNR conditions by introducing different levels of redundancy. The second technique explicitly explores the directionality of the SNR by combining signals collected from different observation angles. We address the performance of rate-adaptive transmission and angle diversity techniques, and compare them based on experimental results obtained in a typical indoor environment.     

Low-noise current optoelectronic integrated receiver with internalequalizer for gigabit-per-second long-wavelength optical communications

An equalizer, which is essential in order to improve the sensitivity of receiver optoelectronic integrated circuits (OEICs) at a gigabit-per-second data rate, has been monolithically integrated on an InP substrate with a p-i-n photodiode and a high-impedance high-electron-mobility-transistor (HEMT) amplifier. The receiver operated up to 1.6 Gb/s and showed low noise current characteristics. The minimum noise current is less than 4 pA/√Hz. The sensitivity calculated from the noise current characteristics is -28.4 dBm for 1.6-Gb/s signals. The receiver chip, which was assembled on a ceramic mount, exhibited a sensitivity of -30.4 dBm at 1.2 Gb/s and 1.3-μm wavelength. The performance is as good as those of receiver OEICs with an external equalizer and sufficient for practical use in gigabit-per-second optical communication system     

Four-port homodyne receiver for optical fibre communications comprising phase and polarisation diversities

A new four-port homodyne receiver for optical fibre communications is proposed and studied experimentally. It comprises phase-and polarisation-diversity schemes, removing the need for phase locking and polarisation control. The bit-error-rate measurement is also reported.     

A feature extraction and pattern recognition receiver employing wavelet analysis and artificial intelligence for signal detection in diffuse optical wireless communications

Optical wireless diffuse indoor infrared communication systems have as yet large unrealized bandwidths that are not subject to the same regulatory control as radio frequency systems. Usually, well established RF techniques are used to combat channel imperfections for IR implementations. Here, we introduce a novel receiver system based on the multiresolution time-frequency feature extraction capabilities of wavelet analysis, coupled with the well recognized pattern recognition performance of artificial neural networks for mitigating the effects of bandwidth limiting channel-induced distortion.     

Turbo-MIMO for wireless communications

This article reviews an important class of MIMO wireless communications, known collectively as turbo-MIMO systems. A distinctive property of turbo-MIMO wireless communication systems is that they can attain a channel capacity close to the Shannon limit and do so in a computationally manageable manner. The article focuses attention on a subclass of turbo-MIMO systems that use space-time coding based on bit-inter-leaved coded modulation. Different computationally manageable decoding (detection) strategies are briefly discussed. The article also includes computer experiments that are intended to improve the understanding of specific issues involved in the design of turbo-MIMO systems.     

无线光通信中PPM的差错编码调制研究

文章推导了基于线性分组码的脉冲位置调制(PPM)通信系统纠错后的差错概率上限,分析了差错编码的纠错能力和PPM位分辨率的参数设置对差错性能的影响,并进行了仿真.结果表明,在纠错个数能被位分辨率整除时,PPM系统达到较高编码调制性能,同时指出适合PPM系统的纠错编码一般为高阶码.     

Polarisation-diversity receiver for coherent FSK communications

A polarisation-insensitive optical heterodyne receiver, in which two signals with orthogonal polarisations are independently detected and demodulated, and subsequently combined, has been demonstrated for FSK-modulated signals at 50 Mbit/s with a sensitivity of ?55.5 dBm (Pe=10?9). The receiver uses the entire received signal and local oscillator signal with only one photodiode in each branch. Differences between the two PINFET detectors result in a ±ldBm sensitivity variation for all polarisation states of the received signal.     

A CMOS imaging diversity receiver for gigabit free-space optical MIMO

A 7-channel imaging diversity receiver based on current-summing is implemented in a 180 nm CMOS technology for broadband free-space optical (FSO) multi-input/multi-output (MIMO) communication. Each channel employs a low input-impedance current mirror (CM) as the input stage, which allows the implementation of direct current-summing for equal-gain combining (EGC). The summed current signal drives a second stage transimpedance amplifier (TIA) to generate the output voltage. Electrical characterization was performed using a photodiode emulation circuit and chip-on-board FR-4 assembly, demonstrating a total transimpedance gain of 62 dBΩ, −3 dB bandwidth of 1.2 GHz, and eye diagrams up to 2 Gb/s for 0.25 pF photodiode capacitance. The theoretical sensitivity of the imaging receiver is −16.8 dBm for a bit error rate (BER) of 10⁻⁹ at a photodetector responsivity of 0.4 A/W. The simulated power consumption for a single front-end amplifier circuit is 4.2 mW, and for the second stage TIA is 10.3 mW from a single 1.8 V supply. The diversity receiver is flip-chip compatible to enable hybrid integration to a custom InGaAs photodetector array.     

Rate-adaptive transmission schemes in the context of runlength-limited-codes for optical wireless communications

In this letter, the performance evaluation of rate-adaptive transmission schemes for indoor unguided optical links has been analyzed in the context of runlength-limited (RLL) sequences. Here, the superiority of on-off keying (OOK) formats with runlength constraints based on silence periods has been corroborated in terms of code efficiency and peak-to-average optical power ratio (PAOPR) compared to a hybrid HHH (1,13) code, variable-rate signalling technique obtained by modifying the RLL (1,13) code specified in the very fast infrared (VFIr) standard by the infrared data association (IrDA). Additionally, the use of very simple decoding schemes based on Boolean logic has been proposed.