Jp McGeehan

The performance enhancement of multibeam adaptive base-station antennas for cellular land mobile radio systems

The problem of meeting the proliferating demands for mobile telephony within the confinement of the limited radio spectrum allocated to these services is addressed. A multiple-beam adaptive base-station antenna is proposed as a major system component in an attempt to solve this problem. The approach is demonstrated by employing an antenna array capable of resolving the angular distribution of the mobile users as seen at the base-station site, and then using this information to direct beams toward either lone mobiles, or groupings of mobiles, for both transmit and receive modes of operation. The energy associated with each mobile is thus confined within the addressed volume, greatly reducing the amount of cochannel interference experienced from and by neighboring cochannel cells. To ascertain the benefits of such an antenna, the conventional and proposed antenna systems are modeled in a typical mobile radio environment. For a given performance criterion, the theoretical results indicate that a significant increase in the spectral efficiency, or capacity, of the network is obtainable with the proposed antenna. >

A comparison of the HIPERLAN/2 and IEEE 802.11a wireless LAN standards

At present, WLANs supporting broadband multimedia communication are being developed and standardized around the world. Standards include HIPERLAN/2, defined by ETSI BRAN, 802.11a, defined by the IEEE, and HiSWANa defined by MMAC. These systems provide channel adaptive data rates up to 54 Mb/s (in a 20 MHz channel spacing) in the 5 GHz radio band. An overview of the HIPERLAN/2 and 802.11a standards is presented together with software simulated physical layer performance results for each of the defined transmission modes. Furthermore, the differences between these two standards are highlighted (packet size, upper protocol layers etc.), and the effects of these differences on throughput are analyzed and discussed.

The application of a deterministic ray launching algorithm for the prediction of radio channel characteristics in small-cell environments

Propagation characteristics play a fundamental role in the design and implementation of radio systems. The application of broadband digital data services within the cordless environment requires close consideration of the dispersive nature of radio channels. A prediction algorithm is presented such that propagation characteristics can be estimated for small-cell high-data-rate systems. Through the use of geometric optics and geometric theory of diffraction the algorithm performs ray launching techniques in order to evaluate reflected, transmitted, and diffracted rays from a simplified description of a given environment. Both modeled and measured results are presented demonstrating the models ability to predict typical rms delay spread values. >

Optimizing microcell base station locations using simulated annealing techniques

The problem of choosing the optimum locations for base stations in a microcell communications system is considered. The factors affecting optimum selection are the non-uniform service areas in complex propagation environments, the mutual coverage and interference of multiple base stations, and the service objective which is usually defined by signal level but may also be defined by delay spread for certain digital systems. This optimization problem is addressed using simulated annealing (SA) techniques which offer a method to achieve near optimum solutions to complex combinatorial optimization problems, This research shows that SA is a viable approach for handling practical base station siting problems in an urban microcell environment.<<ETX>>

Wireless personal communications for the 21st century: European technological advances in adaptive antennas

Adaptive antennas are now regarded by many within the wireless communications industry as a core system component in future-generation mobile networks. In order to promote European research and development in this strategic area, the Commission of the European Community has funded, through the Research into Advanced Communications in Europe, RACE, and now the Advanced Communications Technologies and Services, ACTS, programs, the Technology in Smart Antennas for Universal Advanced Mobile Infrastructure, TSUNAMI, consortium in order to further technological advances for the next millennium, as reported here.

The application of GTD and ray launching techniques to channel modelling for cordless radio systems

Propagation characteristics play a fundamental role in the design and implementation of radio systems. The application of broadband digital data services within the cordless environment requires close consideration of the dispersive nature of radio channels. A prediction algorithm is presented such that the propagation characteristics can be estimated for small-cell high-data-rate systems. Through the use of geometric optics and geometric theory of diffraction (GTD) the algorithm performs ray launching techniques in order to evaluate reflected, transmitted, and diffracted rays from a simplified description of a given environment. Both modeled and measured results are presented, demonstrating the models ability to predict typical RMS delay spread values.<<ETX>>

Patterned growth of neuronal cells on modified diamond-like carbon substrates.

Diamond-like carbon (DLC) has been explored as a biomaterial with potential use for coating implantable devices and surgical instruments. In this study the interaction of DLC with mammalian neuronal cells has been studied along with its modifications to improve its function as a biomaterial. We describe the use of DLC, oxidised DLC and phosphorus-doped DLC to support the growth and survival of primary central nervous system neurones and neuroblastoma cells. None of these substrates were cytotoxic and primary neurones adhered better to phosphorus-doped DLC than unmodified DLC. This property was used to culture cortical neurones in a predetermined micropattern. This raises the potential of DLC as a biomaterial for central nervous system (CNS) implantation. Furthermore, patterned DLC and phosphorus-doped DLC can direct neuronal growth, generating a powerful tool to study neuronal networks in a spatially distinct way. This study reports the generation of nerve cell patterns via patterned deposition of DLC.

An analysis of microstrip with rectangular and trapezoidal conductor cross sections

The finite-difference time-domain (FDTD) technique is used to analyze boxed microstrip with both rectangular and trapezoidal cross sections. It is confirmed that the exact shape of the conductor has a marked effect on the effective permittivity of the microstrip. Results using this method are compared to the findings of K.A. Michalski et al. (1989) using the analytically more complicated boundary element method; very good agreement is observed. The effect of adding a thin passivation layer is also calculated and it is found that such an addition noticeably reduces the effective permittivity of the microstrip. It is shown that the FDTD technique is capable of treating microstrip with a general cross section and producing accurate results. >

Network planning for third-generation mobile radio systems

The success of UMTS relies not only on the development of a flexible air interface, efficient coding techniques, and handset technology; it is equally important to design a system that can support the underlying technology and to interface with other networks.<<ETX>>

Wireless propagation measurements in indoor multipath environments at 1.7 GHz and 60 GHz for small cell systems

Given the current interest being shown in the utilization of the frequency band around 1.7/1.8 GHz and 60 GHz, work has been undertaken to determine channel characteristics in these two ranges. The authors describe wideband measurements which have been conducted in a variety of indoor locations. RMS (root mean square) delay spreads were calculated and used to compare levels of multipath activity at the two frequencies. The levels of multipath measured at the two frequencies can be related to the size of the rooms involved and the measurement techniques. Any differences due to atmospheric absorption at 60 GHz were found to be negligible.<<ETX>>