Showing papers on "Smart antenna published in 1995"

Direction finding and "smart antennas" using software radio architectures

Abstract: Operational tests and demonstrations of systems based on software radios are currently being performed in the 800 MHz mobile cellular radio band. These field trials are for mobile unit geolocation systems and adaptive phased array "smart antenna" applications. The geolocation system trials are in response to the demand for high confidence geolocation of mobile units for enhanced emergency 911 service and for use in the US Department of Transportation's Intelligent Vehicle Highway System (NHS) initiative. The smart antenna array application addresses the cellular service providers' need for more user channel capacity and/or geographic coverage from existing base station installations. Software radio architectures were selected because of their ability to provide superior performance at low life cycle cost. These systems use 4 to 8 wideband coherent channels and fully characterize the arriving RF energy to either geolocate the emitter or to maximize the carrier-to-interference ratio. >

Synthesis of antenna arrays using genetic algorithms

Abstract: The synthesis of the radiation pattern of linear antenna arrays is an interesting problem in radiating systems. When the synthesis of antennas is subject to many restrictions the problem is very complex and becomes difficult to solve by classical optimization techniques because they are vulnerable to local minima problems. One relatively novel technique which could be used for the antenna synthesis is the use of Genetic Algorithms (GAs). In this article two methods for the synthesis of the radiation pattern of a linear array antenna based on GAs are presented. With these techniques it is possible to synthesize a radiation pattern specified by shaped beams and nulls in given directions. Results for different cases are presented.

Advanced adaptive null steering concepts for GPS

Abstract: The problem of protecting the GPS signal from interference is addressed. A number of null steering techniques for use in conjunction with antenna arrays are compared and contrasted in terms of efficient use of available degrees of freedom and computational complexity. The techniques investigated range from the simple well known power minimization approach to a subspace constrained power minimization method that makes use of DOA estimates provided by a 2D version of ESPRIT. Limitations of the methods are addressed as well.

Smart antenna system using microelectromechanically tunable dipole antennas and photonic bandgap materials

Abstract: An antenna system includes a set of symmetrically located center-fed and segmented dipole antennas embedded on top of a frequency selective photonic bandgap crystal. A two-dimensional array of microelectromechanical (MEM) transmission line switches is incorporated into the dipole antennas to connect the segments thereof. An MEM switch is located at the intersection between any two adjacent segments of the antenna arm. The segments can be connected (disconnected) by operating the switch in the closed (open) position. Appropriate manipulation or programming of the MEM switches will change the radiation pattern, scanning properties and resonance frequency of the antenna array. In addition, an MEM switch is inserted into the crystal to occupy a lattice site in the 3-dimensional crystal lattice. The crystal will have a broadband stopgap if the MEM switch operates in the closed position (perfect symmetry of the crystal), and will produce a narrowband absorption line inside the stopgap if the MEM switch is in the open position, thereby permitting change in real time of the frequency response of the crystal.

Center-fed grid array antennas

Abstract: Single- and double-layer grid array antennas are numerically investigated. A radiation beam normal to the antenna plane is realized by using appropriate configuration parameters. The difference of the gains between the upper-fed and lower-fed grid arrays is very small (0.5 dB over a frequency range of 12.5 to 12.75 GHz).

Multiuser blind channel estimation and spatial channel pre-equalization

Abstract: In this paper, we study two of the fundamental operations of a TDD smart antenna system, namely, the uplink channel and sequence identification and downlink selective transmission. For uplink, our focus is on the development of a blind estimation algorithm which is capable of resolving a multiuser system without the use of training sequence or any input statistics. For downlink, we propose a spatial channel pre-equalization scheme which simultaneously eliminates the intersymbol interference (ISI) and the co-channel interference (CCI) for all users using FIR filters. Both algorithms were validated by RF experiments using the smart antenna testbed developed in the University of Texas at Austin.

Recursive adaptive beamforming for wireless CDMA

Abstract: The increasing demand for mobile communication services without corresponding increases in RF spectrum allocation requires new techniques to improve spectrum utilization. Spatial processing using antenna arrays at the base-station has been proposed to reduce co-channel interference and reduce fading of the desired signal, leading to an increase in system capacity. The use of base station antenna, arrays in wireless CDMA is studied. A recursive, fast, and numerically stable algorithm estimating the array response vector and the optimum beamforming weights is derived. Our approach uses a space-time processing approach for estimating-the array response vector, and hence the optimum beamforming weights. Simulation results are also presented.

Jitter diversity in multipath environments

Abstract: The lack of capacity in mobile communication systems is an increasing problem. A channel model for the use of antenna arrays at the base station is presented. A new diversity scheme, jitter diversity, is suggested with a simple algorithm. The technique is to use an antenna array and move the main beam slightly to avoid deep fades, giving substantial improvement in the fading distribution and the mean power. Linear antenna arrays with 1-19 elements are applied to propagation environments with different scatterer spread. The influence of the environments on the received antenna pattern, such as the effective gain, is investigated. Experiments support the main findings, namely that the environments reduce the directivity of the perceived antenna diagram by several dB. Jitter diversity is a very simple approach, compared to other combining methods, as it only includes the variation of a single parameter, the phase between elements. It should therefore be simple to implement in practice.

A direction-finding antenna system using an integrated six-port circuit

Abstract: A new method to measure the complex ratio of signals at adjacent elements of an array is presented. The circuit used for the measurement is an integrated six-port junction operated as an homodyne vectorial analyzer. A procedure that uses three known and many unknown incident or radiated fields conditions to calibrate the junction embedded in the antenna feed network is implemented. Experimental results are shown for a basic two-element array used as a receiving antenna. The direction of arrival of an incoming plane wave computed from the six-port measurements can be determined with a good accuracy. The monitoring system presented may find applications in direction-of arrival estimation.

Performance enhancement and trade-offs of smart antennas in CDMA cellular networks

Abstract: In this paper, we study the improvement in the reverse link budget due to base-station smart antennas in CDMA cellular networks. Considering a typical multipath propagation environment, we quantify the excess energy per bit to interference plus noise ratio /spl gamma//sub b/ due to smart antenna processing at the base station as a function of the number of sensors, their separation, and scattering angle, With this excess /spl gamma//sub b/, we evaluate different trade-offs between different performance measures such as capacity, area coverage, and mobile transmitted power. Both theoretical and simulation results are presented.

Near-far effects in adaptive SDMA systems

Abstract: In an adaptive SDMA system users can share the same channel which is made possible by using adaptive array antennas at the base station site and forming multiple independent beams to serve the users. Though the enormous capacity enhancements of this approach are obvious, there are two constraints which limit its performance: 1. Any two users sharing the same channel should be located in different directions and 2. the difference between the received power levels should not be too large. If one of these constraints is violated, the users cannot be separated, i.e. one of the connections is blocked or lost. While the capacity increase of SDMA taking into account the first constraint have been analysed in a previous paper [18], this paper is focused on the implications of the second constraint, which represents a near-far problem similar to those encountered in CDMA systems. To solve the near-far problem, grouping of the mobile users into power classes is suggested. The resulting channel allocation scheme is analysed, and it will be shown that the gain reduction caused by the second constraint will be only marginal in most realistic environments, i.e. still a large capacity gain can be achieved. Fig. 1: Typical scenario for A-SDMA application * This wok has been supported by EU within the RACE project TSUNAMI 0-7803-3002-1/95 $4.00 0 1 995 I E E E 1293

Experimental direction of arrival and spatial signature measurements at 900 MHz for smart antenna systems

Abstract: Smart antenna systems which utilize adaptive beamforming techniques on both uplink and downlink transmissions will allow mobiles located at shorter reuse distances and mobiles located at spatially distinct angles from the base station to operate on the same frequency channel, thus providing significant capacity increase over conventional antenna. This paper presents some preliminary results of experimental studies of smart antenna systems for wireless communications. The purpose of this paper is to investigate the change in DOAs and spatial signatures of stationary moving transmitters to provide some insight into the advantages of DOA-based beamforming over spatial signature beamforming for downlink transmissions.

Experimental study of antenna arrays in indoor wireless applications

Abstract: A spatial signature is the response vector of an antenna array to a mobile unit at a certain location. The mobile subscribers at different locations exhibit different spatial signatures. The exploitation of spatial diversity (or difference of spatial signatures) is the basic idea of the so-called space-division-multiple-access (SDMA) scheme, which can be used to significantly increase the channel capacity and quality and combat multipath fading in a wireless communication system. The purpose of this paper is to describe indoor experiments conducted with our antenna array (or smart antenna) testbed to study the vector channel propagation characteristics in various indoor scenarios. The results to be presented include indoor DOA angle spread and spatial signature variation due to terminal displacement. The experimental results show the rich spatial diversity and potential benefits of using an antenna array for indoor wireless applications, such as wireless local area networks (LANs).

Reconfigurable array antennas with phase-only control of quantized phase shifters

Abstract: In this paper a new synthesis method for electronically controlled, reconfigurable array antennas for future wireless communication systems such as vehicle to roadside communications or cellular telephone systems is presented. Quantized phase shifters can already be taken into account during synthesis. The shape of the main beam as well as the sidelobe level can be reconfigurated with phase-only control of quantized phase shifters. The amplitude of the weighting factors in the antenna beamforming network remains constant resulting in only one antenna beamforming network for several antenna patterns. Results for linear as well as planar array antennas show the efficacy of the new synthesis method.

Optical multiple beam-forming systems for wireless communication antennas

Abstract: 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

Performance Enhancement IQf DS-CDMA PCS C4llular Networks with Smart Antennas

Abstract: This paper considers the performance of a OS-COMA system which employs adaptive antenna technology at the basestation site. By utilising the capability of ray-tracing to provide the complex channel impulse response, a new ray-based simulation methodology for an adaptive antenna in a DS-CDMA system is presen ted. Results for a typical microceUular environment highlight the behaviour of the adap tive antenna. Finally, with the help of a OS-COMA capacity analysis, the potential spectrum efficiency enhancement is evaluated.

System and method for frequency multiplexing antenna signals

Abstract: There is disclosed an antenna system and method of operation which allows for a large number of antennas to transmit signal streams to a similarly large number of receiver/transmit ports over a single communication channel. In operation, there is created a plurality of frequency bands each identified with a particular one of the antennas. The signal streams from each antenna are mixed so that they fall within the frequency band assigned to that antenna. The reduced signal streams, which now all fall within a preselected frequency band for each antenna, are then combined into a single wide band signal stream and communicated over a single communication channel to the remote end where the signals are separated into their respective signal streams and the separated signal streams are then mixed to recreate the originally received frequencies. The system can be arranged such that a selection process allows multiple radios to connect to any channel of any antenna.

A method for selecting two antennas

Abstract: A base site (100) employs a method and apparatus for selecting two of a plurality of antennas (101-106) from which to receive a communication signal. A first signal quality metric is measured for a communication signal received from a first antenna (102) and a second signal quality metric is measured for the communication signal received from a second antenna (103). When the first signal quality metric differs from the second signal quality metric by a threshold, a signal receiver (113) is coupled to a third antenna (e.g., 101) and a third signal quality metric is measured for the communication signal received from the third antenna (101). Based on the three signal quality metrics, a primary antenna and a secondary antenna are selected from which to receive the communication signal.

Performance enhancement of DS-CDMA PCS cellular networks with smart antennas

Abstract: This paper considers the performance of a DS-CDMA system which employs adaptive antenna technology at the basestation site. By utilising the capability of ray-tracing to provide the complex channel impulse response, a new ray-based simulation methodology for an adaptive antenna in a DS-CDMA system is presented. Results for a typical microcellular environment highlight the behaviour of the adaptive antenna. Finally, with the help of a DS-CDMA capacity analysis, the potential spectrum efficiency enhancement is evaluated.

Simulated annealing approach for the design of unequally spaced arrays

Abstract: A synthesis method aimed at designing an array antenna is proposed. Simulated annealing (SA), which is a probabilistic methodology used to solve combinatorial optimization problems, has been utilized to optimize the position and the weighting coefficients of the array elements in order to improve the antenna performance. The sensor position and related weighting coefficients are considered as parameters to be tuned in order to constrain the directivity function (i.e., the beam power pattern) of an antenna to satisfy specific requirements. Conventional beamforming is utilized to compute the beam power pattern having the desired properties, such as a narrow width of the main lobe, and side lobe amplitudes under a certain threshold, etc., taking into account the need to reduce to number of sensors with a small spatial aperture. Several results are presented showing a notable improvement in the antenna performance utilizing the SA approach with respect to those considered in the literature.

Smart skin spiral antenna with chiral absorber

Abstract: Recently there has been considerable interest toward designing 'smart skins' for aircraft. The smart skin is a composite layer which may contain conformal radars, conformal microstrip antennas or spiral antennas for electromagnetic applications. These embedded antennas will give rise to very low radar cross section (RCS) or can be completely 'hidden' to tracking radar. In addition, they can be used to detect, monitor or even jam other unwanted electromagnetic field signatures. This paper is designed to address some technical advances made to reduce the size of spiral antennas using tunable dielectric materials and chiral absorbers. The purpose is to design, develop and fabricate a thin, wideband, conformal spiral antenna architecture that is structurally integrable and which uses advanced Penn State dielectric and absorber materials to achieve wideband ground planes, and together with low RCS. Traditional practice has been to design radome and antenna as separate entities and then resolve any interface problems during an integration phase. A structurally integrable conformal antenna, however, demands that the functional components be highly integrated both conceptually and in practice. Our concept is to use the lower skin of the radome as a substrate on which the radiator can be made using standard photolithography, thick film or LTCC techniques.

Linearity considerations in adaptive antenna array applications

Abstract: The use of adaptive antenna in mobile communications base stations is self-explanatory. It offers the potential of increased spectrum efficiency, extended range of coverage and reduced delay spread. However, one major concern for adaptive antenna system is the non-linearity effects of the RF/IF chain upon digital baseband beamforming network. This contribution investigates these effects on the performance of adaptive antennas and suggests the use of linearised transceiver system to tackle the nonlinearity problem.

Impact of the antenna set-up and arrays on mobile radio systems

Abstract: This paper outlines the impact of the antenna set-up and antenna array configurations on mobile radio system at millimetre-wave frequencies. Simulations in typical indoor environments using directive antennas have shown a significant reduction in the channel time dispersion and in power requirements. Also in a typical city street, specially when some objects (cars, buses, etc.) are present, it gives significant performance improvements when compared with an omnidirectional antenna. The significant reduction of channel time dispersion achieved with directional antennas, associated to the fact that a mobile terminal must be able to communicate in any direction, indicates that the best performance of a broadband system is obtained with either switchable beams or antenna arrays. The propagation channel is modelled with a ray tracing tool that takes into account the propagation environment and the antennas used.

Space Geodesy Techniques: An Experimental and Theoretical Study of Antenna Related Error Sources

Abstract: This thesis presents work associated with antenna related error sources, as well as antenna design, in space geodesy utilizing the techniques of Very-Long-Baseline Interferometry (VLBI) and the Global Positioning System (GPS). Geodetic VLBI uses large radio telescopes, often in global networks observing at least a few times per year. As the number of dedicated antennas for this purpose is limited, also antennas designed for radio astronomical research are used. However, new feed systems are needed to handle the simultaneous dual-frequency observations and the large bandwidth in geodetic VLBI. This thesis describes and numerically evaluates such a feed system. The design has the advantage of not interfering with existing front-end receivers of traditional Cassegrain antennas. In contrast to VLBI antenna systems, GPS antennas have low directivity in order to receive signals from the satellites in different directions simultaneously. The disadvantage with such antennas is the relatively high susceptibility to scattering from structures close to the antenna. Two studies presented in this thesis show that signal scattering from structures associated with the mounting of the antenna to the pillar and with the pillar itself, might be a significant source of error. As nearby structures are in general located below the antenna, scattering from these structures may be minimized using antennas with reduced side- and back-lobe levels. This thesis presents results from a preliminary study of two new designs of such antennas. The Swedish permanent GPS network, SWEPOS, consists of 20 stations distributed across Sweden. One of the scientific motivations for this network is to monitor crustal motions associated with postglacial rebound. This thesis describes SWEPOS, and results from almost 18 months of daily observations are presented and compared to models of postglacial rebound. The results from SWEPOS have also uncovered two major error sources. One of them is the scattering effect mentioned above. The other, which also is investigated in this thesis, is related to snow accumulated on the top of the pillars and on the radomes that covers the antennas. This accumulation appears to refract and delay the GPS signals, and thus degrade the positioning accuracy.

Performance of CDMA smart antenna systems

Abstract: Preliminary radio frequency (RF) field experiments were conducted to evaluate the performance of smart antenna systems for code-division multiple access (CDMA) systems. Besides conventional multipath fading problems, CDMA schemes are subject to near-far problems. The IS-95 CDMA system uses a 1/3 convolutional encoder and an interleaver to mitigate the fading problem and uses feedback power control schemes to equalize the powers of all the uplink co-channel signals. We evaluate the performance of the IS-95 standard implemented on a smart antenna system in a slow-fading environment. In particular, we evaluate the effects of imprecise power control, convolutional coding, and different beamforming techniques for a CDMA smart antenna system. Our results show that the smart antennas are not so sensitive to imperfect power control and that the optimal (Wiener) beamforming technique outperforms the simple beamforming approach. The most interesting result is that the effect of convolutional coding is not so significant for a smart antenna system than for an single antenna system. Based on our limited experimental results, we found that the 3 times bandwidth dedicated to the 1/3 convolutional encoding is better used to increase the spreading factor in a CDMA smart antenna system, leading to reduced cost and perhaps better performance.

Non-linearity effects on adaptive antennas

Abstract: The effects of nonlinearity on the performance of adaptive array antennas has been presented. The feed forward linearisation technique is identified as the most suitable for mobile communication base station applications. This is because that the large bandwidth requirement and multiple carrier operations at base stations. The effect of using linearised amplifiers in the communications system has also been briefly discussed.

Non-linear amplifier effects in transmit beamforming arrays

Abstract: The effects of memoryless (no feedback) amplifiers with amplitude non-linearities on the output of transmit beamforming arrays is studied. These studies are limited to "small signal" cases where the output signal is not undergoing significant compression by the amplifier; and where the amplifier non-linearities can be approximated well by a cubic polynomial. The performance of three "optimal" beamforming techniques are compared and contrasted when both linear and non-linear amplifiers are used in a two dimensional array. The two dimensional array considered is designed to simultaneously transmit two narrowband signals, at different frequencies, through a common aperture. Attention is focused on the non-linearity induced interaction of the stimulus signals, and the effect this has on the array's outputs as a function of the beamforming technique.

Motor vehicle multi-antenna testing method

Abstract: The method for testing motor vehicle antennas, especially multi-antennas with selective operating antenna diversity uses a test impulse or impulse sequence (PI) via the radio receiver (6) or externally via a test device by a test connector and connecting cable. The impulse is converted to dc levels, based on the control of the antenna switch (4) of the diversity switch, switching to a selected antenna (1) or a switching sequence of antennas. A HF signal is applied to the antenna under test, the quality and level of the received signal is measured through the complete path.

Propagation measurements for 1.9 GHz high-gain antenna design

Abstract: This paper addresses the benefits achievable with advanced base station antennas for 1.9 GHz personal communications services (PCS). High-gain antennas, multiple sub-aperture diversity combining, and adaptive array processing are all parts of the advanced antenna concept. A measurement program was carried out in urban and suburban environments to preview the performance achievable with large antennas. Results indicate that very tall narrow antenna subarrays can produce the desired high gain while minimizing the amount of beam-steering and beamforming required.

Pattern shaping for handset antennas

Abstract: Traditional handset designs for personal communications have used simple antennas and it appears that little attempt has been made to shape the radiation pattern in a systematic way. Although diversity designs have been discussed, e.g. by Jensen and Rahmat-Samii (see IEEE Trans. Antennas and Propagation, vol.42, p.1106-1113, 1994), and Ogawa and Uwano (see IEEE Trans. Antennas and Propagation, vol.42, p.1342-1345, 1994), a clear analysis of what constitutes a "good" handset pattern has not yet been made. The authors discuss these questions, suggest a classification for the possible structures, and present some work on modelling and measurements of prototypes for the new generation of systems working around 1.8-2 GHz. >