Multiple-subcarrier modulation for nondirected wireless infraredcommunication

We examine multiple-subcarrier modulation (MSM) schemes for wireless infrared digital communication in the indoor environment. Intensity modulation with direct detection (IM/DD) is employed, which results in equivalent baseband channels with a nonnegativity constraint on the input. The power efficiencies of modulation schemes are compared at 30 Mb/s and 100 Mb/s over an ensemble of experimentally determined multipath channels. Carrier selection and power shaping are examined as methods for improving MSM performance. It is found that MSM schemes can allow operation at higher data rates than single-carrier modulation schemes without equalization. Moreover, MSM schemes can be more bandwidth-efficient and also can provide a simple and flexible method for multiple access to the channel. However, they are not as power efficient as single-carrier schemes, and this will limit their use to applications which are not power limited     

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.     

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。     

无线光通信中PPM的RS级联编码调制研究

在脉冲位置调制(PPM)直接检测光通信系统中插入RS级联编码构成一种新的PPM光通信系统(RS-PPM),该方式对PPM直接检测光通信系统进行了改进,并用Mat l ab对编码系统和未编码系统的误比特率进行了仿真比较,仿真结果表明,基于RS级联编码的PPM系统具有较好纠错和抗干扰能力。     

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.     

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.     

Wavelet packet modulation for wireless communications

As proven by the success of OFDM, multicarrier modulation has been recognized as an efficient solution for wireless communications. Waveform bases other than sine functions could similarly be used for multicarrier systems in order to provide an alternative to OFDM. In this paper, we study the performance of wavelet packet transform modulation (WPM) for transmission over wireless channels. This scheme is shown to be overall quite similar to OFDM but with some interesting additional features and improved characteristics. A detailed analysis of the system's implementation complexity as well as an evaluation of the influence of implementation‐related impairments are also reported. Copyright © 2004 John Wiley & Sons, Ltd.     

Implementation of pulse interval modulation based on dualmapping technique for optical wireless communications

Aiming at implementing the digital pulse interval modulation（DPIM） for optical wireless communications（OWC）,a dual-mapping technique is presented.The scheme of DPIM train based upon the dual-mapping technique is given.Its slot error rate is derived for the avalanche photonic diode（APD） receiver model,and is compared with that of classical DPIM.Simulation results show that the dual-mapping DPIM（D-DPIM）,which has a fixed slot length,only has marginally inferior error performance,but can solve waiting slots or buffer overflowing in comparison with DPIM.Hence,it is suitable for the optical wireless communication systems.     

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.     

Trellis-coded multiple-pulse-position modulation for wireless infrared communications

We present new trellis codes based on multiple-pulse-position modulation (MPPM) for wireless infrared communication. We assume that the receiver uses maximum-likelihood sequence detection to mitigate the effects of channel dispersion, which we model using a first-order lowpass filter. Compared to trellis codes based on PPM, the new codes are less sensitive to multipath dispersion and offer better power efficiency when the desired bit rate is large, compared with the channel bandwidth. For example, when the bit rate equals the bandwidth, trellis-coded (17 2)-MPPM requires 1.4 dB less optical power than trellis-coded 16-PPM having the same constraint length.     

Single-channel imaging receiver for optical wireless communications

A novel and simple single-channel imaging receiver for high-speed portable wireless infrared communications is proposed. The receiver is able to aim automatically at the ceiling areas with better signal-to-noise ratio. The self-orienting capability, together with the very narrow field of view employed, drastically reduces the path loss, background noise and multipath distortion. Moreover, its single-channel structure minimizes hardware complexity in contrast to conventional angle diversity receivers. Our simulation results indicate that the proposed receiver, operating in a multispot diffusing configuration, offers significant gains in power requirements and channel bandwidth compared to angle diversity receivers.     

Digital pulse interval modulation for optical communications

This article presents a study of digital pulse interval modulation (DPIM) for optical wireless communications using intensity modulation with direct detection. The DPIM code properties are discussed, and expressions for the transmission capacity, power spectrum, and error probability are presented. We show that for a given number of bits per symbol, DPIM has a higher transmission capacity, a similar spectral profile, and only a marginally inferior error probability performance compared with pulse position modulation, and is rather less complex to implement. Finally, problems associated with the nonuniform symbol length characteristics of DPIM together with possible solutions are discussed     

SPC-APPM coded modulation for deep-space optical communications

A coded modulation scheme for deep-space optical communications is proposed,which is composed of an outer singleparity-check(SPC)-based product code,an interleaver,a bit-accumulator and a pulse-position modulation(PPM).It is referred as SPC-APPM code,which is decoded with an iterative demodulator-decoder using standard turbo-decoding techniques.Investigations show that the scheme has the advantages of low encoding and decoding complexities,good performance and flexible code rate for all rates above 1/2.Meanwhile,simulation results demonstrate that the SPC-APPM provides the performance similar to the low-density parity-check-APPM(LDPC-APPM),superior to the LDPC-PPM and product accumulate code-PPM(PA-PPM),although inferior to serially concatenated PPM(SCPPM).At the bit error rate(BER) of 10-5,the performance of SPC-APPM is about 0.7 dB better than LDPC-PPM and 1.2 dB better than PA-PPM.     

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.     

光通信中基于脉冲调制的联合编码调制研究

为了研究无线光通信中数字脉冲调制与信道编码的联合编码调制问题,在给出调制时域结构的基础上,采用理论推导和数值仿真相结合的方法,分析了基于二进制线性分组码的开关键控、数字脉冲位置调制和数字脉冲间隔调制系统的差错性能,得出了信道编码纠错能力与调制阶数的结合关系。结果表明,采用开关键控调制的系统,其汉明距离与欧式距离等价,故不存在调制与信道编码参量匹配问题;脉冲位置调制系统在纠错个数大于调制阶数时,可取得较明显的编码调制增益,当纠错个数能被调制阶数整除时,编码和调制达到匹配;由于数字脉冲间隔调制的符号时隙不固定,存在错误传播现象,不宜与差错编码联合使用。所得结果可为无线光通信链路的设计提供参考。     

Adaptive multicarrier modulation: a convenient framework fortime-frequency processing in wireless communications

A historical perspective of orthogonal frequency-division multiplexing (OFDM) is given with reference to its literature. Its advantages and disadvantages are reviewed, and its performance is characterized over highly dispersive channels. The effects of both time- and frequency-domain synchronization errors are quantified, and a range of solutions proposed in the recent literature are reviewed. One of the main objectives of this review is to highlight the recent thinking behind adaptive bit allocation and turbo coding in the context of OFDM. This paper concludes with a wide-ranging throughput comparison of the schemes discussed herein under the unified constraint of a fixed target bit error rate of 10^-4     

Differential space-frequency modulation via smooth logical channel for broadband wireless communications

In this letter, a differential space-frequency modulation (DSFM) scheme is proposed for multiple input multiple-output (MIMO)-orthogonal frequency-division multiplexing (OFDM) systems in broadband wireless communications. We assume that the fading channels keep constant only within each OFDM block, and may change independently from one OFDM block to another. The differential schemes proposed for MIMO-OFDM systems in the literature cannot successfully decode with such a rapidly fading channel, since the successful decoding of the previously existing schemes relies on the assumption that the fading channel keeps constant within a period of several OFDM blocks, and it changes slowly from a period of several OFDM blocks to another. In our proposed DSFM scheme, the transmitted signals are differentially encoded in the frequency domain within each OFDM block. Thus, the differential decoding can be performed over subcarriers within each single OFDM block. Furthermore, if a statistical channel power-delay profile (PDP) is known at the transmitter, we propose to create a smooth logical channel to improve the performance of the DSFM scheme. We obtain the smooth logical channel by sorting the channel frequency responses over subcarriers from a statistical point of view. If the logical channel is not smooth enough, we further consider a pruning process in which we use only the "good" part of the channel and get rid of the "bad" part of the channel. Simulation results show that the proposed DSFM scheme over a smooth logical channel (with pruning, if necessary) performs well for various channel PDPs.     

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.