Wireless data communications are currently being implemented by the complementary technologies of RF and IR. The RF options provide larger area coverage than wireless optical communications but are limited in full bandwidth throughput to about 5 Mbps whereas infrared systems using IR-LED have achieved data rates up to 125 Mbps which makes them suitable for use in FDDI, Fast Ethernet and ATM wireless connectivity as well as Token Ring, Ethernet and PABX (voice).
In this paper, we utilize the embedded hybrid fiber-optic/coaxial CATV network for wireless bidirectional communications with a star-ring fiber-optic network to distribute broadcasting cable TV programs and simultaneously to provide bidirectional transmission of wireless signals. At the head end, there are two lasers: the downlink laser is split into two parts (one as the local oscillator for the uplink coherent detection and the other being externally modulated by the combined TV and wireless signals); the uplink laser connects to the ring network with the cascaded phase modulators schemes. For the star-ring topology, the total hub number are limited by the CNR of TV signals and the radius between head end and hub as: the total hub number of this system to be 14 and 20 for r of 5 km and 1 km, respectively, with the CNRU and CNRD larger than 15 dB together with CNRTV larger than 50 dB.
The bandwidth limitations of spread spectrum RF technology are easily removed by use of optical carriers. A variety of wireless connectivity system applications have been achieved using IR LED (not laser) at data rates up to 125 Mbps and with low frequency corners below 100 Kbps. By use of the UWINTM principle it is possible to achieve wireless communications which are protocol independent. Thus, an urgent installation which must serve today as an Ethernet or Token Ring wireless connection in the future can be used at FDDI, Fast Ethernet, 100 VG Anylan or ATM without any modification to the original installation. In this paper we describe three separate applications of this principle where there are significant trade-offs between range and angular coverage.
In this paper, with ideal power control and ideal interleaving, the optimization between the processing gain and the coding gain of a constant bandwidth direct-detection spread-spectrum system operating in the environment of Rician fading channel is presented. The BPSK modulation is considered, and binary BCH codes are employed to illustrate the benefit with the optimum design. Also, optimization of the code rate for this channel is presented and discussed numerically. The results of this paper may be a useful guideline for spread spectrum system design.
For portable, civil or military, communication systems, the characterization of the radiated field poses specific problems. First of all, due to its poor directivity, the radiated field has to be determined over a full sphere surrounding the test antenna. Secondly, the user has an evident but rather random effect on the radiating properties, and the knowledge of such effects is required to perform reliable predictions of the radiated field. Finally, due to their small volume, the measurement process can be seriously perturbed by the cable(s) used to feed the portable system. This paper presents a Near- Field (NF) approach which offers a convenient solution for the two first aspects. The third one has been solved by using an optical link to feed the portable equipment under test. The performances of this optical link have been assessed by comparison to standard RF coaxial feeding and to numerical results predicted from a computer code. The NF approach has allowed to investigate the effects of the user on the Far-Field (FF) radiation pattern of his telephone, both in co- and cross- polarization. Preliminary assessments, conducted in the Socrate spherical NF facility of the Centre d'Etudes de Gramat (CEG), have demonstrated the flexibility and the accuracy of the NF approach.
The paper gives a set of new low power radio propagation models in the picocell environments suitable to some urban and rural conditions in China. A number of propagation measurements was taken by the authors using two antenna height of 3.2 m to 7.5 m at frequency 900 MHZ. Test settings were chosen in rural open areas, suburban streets, and urban streets, crossroads and overbridges in order to study propagation in variety of environments. Based on the obtained data in different environments, this paper takes the further steps to discuss the variations of signal strength with distance that have distinct near and far regions separated by a breakpoint and the effect of antenna height and type by analyzing the two ray model, and then gives a new propagation model, which was proved well-fitted to the measured results in some places. Moreover, this model was applied to make the radio propagation prediction for CT2 Campus Network, which is now running well. This also shows the practicality and reliability of the model in Chinese environments. Up to present, the measurement database has been established and a CAD software package which can predict the radio coverage area for rural and urban in China is going to be finished.
On overview of optical technologies, active and passive components, and systems that are deemed suitable for wireless communications is presented in this paper. Specifically addressed is the use of onboard photonics in advanced spacecraft, satellite, etc. for applications in wireless communications. To assess its viability in potential commercial applications, the state-of-the-art of phonics technology and future prospects for economical large capacity multi-channel services is briefly reviewed.
The problem of optimum signal transmission/reception is addressed under a wireless acoustics data communications framework. The ocean waveguide can be modeled as an inhomogeneous dispersive medium with a frequency- dependent Green's function. An FDM-type reception scheme with non- overlapping acoustic subchannels is proposed. This methodology exploits the optimal propagation frequencies along specific ducts and paths in the ocean waveguide. The parallel data transmission system used frequency division multiplexed (FDM) channels to avoid equalization techniques which introduce higher-order computational complexity to the receiver. Multicarrier modulation (MCM) ameliorates the effects of multipaths, and allows operation at multiples of the single-carrier transmission rate. The long symbol time used in multicarrier modulation increases the system margins against noise, intersymbol interference (ISI) and fast fades. Network topology issues are considered to determine optimum network architectures for underwater acoustic LAN's. A central network topology supported by a blind adaptive equalization (BAE) transmission technique is proposed as superior to a distributed topology in terms of power, bandwidth efficiency, setup simplicity, and elimination of overhead bits for short data packet exchange. Included is an investigation on the factors controlling the system's power efficiency.
Fiber optic components are the building blocks in the construction of microcellular networks for cellular and personal communications services. In this paper, we explored the performances and applications of optical fibers, optical couplers, optical amplifiers, polarization- insensitive optical isolators, fused and filter wavelength division multiplexers, optical circulators, optical polarization controllers, LiNbO3 electro-optic modulators (EOMs) in microcellular wireless networks and microcell modules.
The theoretical foundations for code division multiple access (CDMA) are similar for microwave and optical implementations, and the advantages of this form of multiple access communications are similar, also. The advantages include the ability to support bursty, asynchronous, concurrent communications and to tolerate multipath interference. Optical implementations of CDMA are different in that they tend to require guided lightwaves (e.g., fiber cable), the coding is imposed on the intensity rather that on the amplitude of the lightwave, the various codes are not strictly orthogonal, and the receiver uses direct detection. This gives rise to the term 'optical CDMA'. These pseudo- orthogonal CDMA codes usually require wide bandwidths to represent the encoded data, so that optical CDMA is sometimes considered bandwidth inefficient. Two classes of optical CDMA codes which ar sufficiently bandwidth efficient for wireless communications applications are (1) incoherent spectral CDMA and (2) optical matrix CDMA. In addition, the wireless communications applications may need to support various data rates (for the various services), and these two classes of optical CDMA are both very tolerant of data rate variations. An appropriate topology for applications such as a local area network (LAN) is a star and, for multimedia data distribution, a tree.
This paper describes a simple and low cost transceiver for indoor wireless LAN system to be operated in 60 GHz for ultra-high speed data (e.g. 156 Mbps) transmission, along with design of system parameters such as frequency selection, radio link parameters featuring very low RF power of 10 mW suitable to MMIC performances and high gain antennas. Without using route diversity and adaptive delay equalizers making up for shadowing and multipath reflection of RF signals, new layout of hub and user stations and line-of-sight transmission scheme are adopted. In addition, partially applied radio absorber helps effectively to reduce the undesired co-channel interference signal to the neglectful level, which system is named minimum delay spread (MDS0 local area network (LAN). This paper also presents the idea of effective applying absorber on ceiling which is derived from simulation and some useful measured data of absorbing construction materials, and presents main features of developed MMIC chip set workable in 60 GHz.
As data communications rates climb toward 10 Gbits/s, clock recovery and synchronization become more difficult, if not impossible, using conventional electronic circuits. The high-speed photonic clock regenerator described in this article may be more suitable for such use. This photonic regenerator is based on a previously reported photonic oscillator capable of fast acquisition and synchronization. With both electrical and optical clock inputs and outputs, the device is easily interfaced with fiber-optic systems. The recovered electrical clock can be used locally and the optical clock can be used anywhere within a several kilometer radius of the clock/carrier regenerator.
Fiber Optic microwave links for microcellular mobile communications have gained wide spread attention in the recent years. This paper reports the analysis of a fiber optic microwave link that employs a metal semiconductor metal photodiode (MSM-PD) as an optoelectronic mixer (OEM). The OEM can considerably reduce the base station hardware in a typical microcell environment and thus economize the overall system cost. The nonlinearities inherent in the MSM-PD OEM are examined by modeling its dc responsivity as a third order polynomial function of applied bias voltage. The OEM has been analyzed in terms of its conversion loss and noise figure. The link quality has been estimated in terms of the carrier to noise ratio (CNR).
Several new systems and concepts using optical technology are introduced for the wireless communication antenna. These include antenna-design limitations on frequency reuse in cellular architectures, optical beamforming, adaptive filtering, and direction finding, optical receive- mode IF combining, use of ultra-short optical time delay methods for millimeter wave antenna arrays, and the use of space-time coding of electro-optically steered lasers for multiple access communications.
A microcellular system with radio signals transmitted over a passive optical network is proposed. External amplitude- and phase-modulation are employed in the base station (BS) and the radio port (RP), respectively. A remodulation scheme is used at RPs to eliminate the need of active optical source. An optical local oscillator is employed at BS receiver for heterodyne detection to eliminate the distortions caused by remodulation. Theoretical analysis is carried out and the system capacity is also estimated. It shows that two 200 mW and 25 mW and 25 mW Nd:YAG lasers can serve 16 microcells and provide a total number of 1600 channels for a macrocell with radius 5 km.
Interest is growing in indoor cellular communications systems using very small cell sizes (tens of meters) to meet the demand for wideband wireless networks. Millimeterwave systems are attractive because they offer large bandwidths and small size. Achieving high data rates requires efficient and adaptive antenna systems. Antenna radiation patterns should be shaped for best cell illumination and capable of being altered to cope with multipath and changing propagation conditions. Microstrip ring slot and annular rings offer potential for low cost beam shaping and steering. They are compatible with MMIC technology making integration easy and are low cost. A brief discussion of antenna requirements is given. The operation of these microstrip antennas is presented along with a description of low cost adaptive arrays.