Communications: directive radio wave systems and devices (e.g. – Directive – Including antenna pattern plotting
Reexamination Certificate
1999-08-17
2001-05-22
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including antenna pattern plotting
C342S372000, C342S169000
Reexamination Certificate
active
06236363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention most generally relates to the simulation and testing of smart antenna systems. More particularly, it pertains to methods and apparatus for verifying the functionality and performance of a smart antenna processor by simulating multipath signals and co-channel signals received at a multi-sensor antenna array, including the coordinated effects of delay spread, Doppler spread, and angular spread for all the sensors of the antenna array.
2. Background of the Invention
The personal communication services industry in the wireless market has seen a substantial growth, particularly in the cellular telephone segment. The deregulation of the telecommunications industry has fueled the fire of this rapid expansion, and pushed the technological envelope to new heights. The increased demand requires that innovative systems be developed that allow for more users, greater coverage, improved reception, lower costs, less power, and geo-location ability. And, for those that are using the cellular communications for data transfer and not just voice communication, there is a desperate need for increased speed and tighter bandwidths. Some argue that the existing wire based systems are inadequate to handle the growing need for high-speed telecommunications, and that wireless systems are a viable alternative to expensive fiber optic or cable installations into every home.
In addition, conventional wire connections no longer satisfy the mobile and harried worker who requires instant access anytime and anywhere. The transition from a wire based connective society to a wireless form is also a necessary transition in some applications. Remote areas that have no access to any wiring or do not have access to a high-speed wire network require a dependable and inexpensive way to communicate. The various forms of transportation, including car, train, plane and boat also need to communicate over wireless communication means.
Thus, the need for dependable wireless systems is a necessity in order to sustain the growth of the telecommunications industry, and the high technology sector as a whole. As more and more people experience the convenience and performance capabilities of wireless communications, the consumer demand will further increase.
One of the leading technologies in the wireless market is the smart antenna. The term smart antenna has been used to describe those antenna systems with multiple antenna elements controlled by complex software algorithms that favor the user's signal or the user's location and adapt to the transmission and reception conditions to enhance performance. The geo-location advantages of obtaining data from multiple points and processing this data can be illustrated by a person's bearing ability. As the ear picks up a sound, both ears and the processing of the brain combine to allow the source of the noise to be accurately determined. Listening with a single ear does not give the necessary focus to determine the location.
Smart antenna systems use signal processing methods in conjunction with multiple antennas to achieve significant improvements in capacity and range for wireless mobile communications. Temporal and spatial filtering techniques are devised to effectively mitigate co-channel interference and remove multipaths in all its forms. There are numerous temporal/spatial processing techniques that have been proposed for uplink as well as downlink communications. Each technique is most applicable to a specific multiple access air interface and for deployment under specific operating environment.
The key role of the multiple element antenna arrays at the base station in cellular mobile radio communications is to sample, at different points in space, the waveforms propagating from users who are accessing the same communication channel. The effectiveness of spatial sampling in reducing co-channel interference and mitigating multipath effects depends on an employed signal processing technique that combines the information over time from the different antennas. The aim of any smart antenna system is to recover the user signal of interest (SOI) and produce an output with significantly improved carrier-to-interference ratio. For uplink processing, the offerings and expectations of smart antennas, however, depend on how they exploit the communication channel characteristics and remove its effect on the statistical and deterministic properties of the desired and undesired components of the waveforms incident on the base station.
There are different types of communication formats and systems that are well known in the industry. But all are subject to the same problems and limitations, namely; channel capacity, spectrum efficiency, limited range coverage, co-channel interference, multipath fading, and system complexity. Associated with these problems and limitations are the expensive and time-consuming processes of monitoring and testing the base stations to ensure that they are functioning within prescribed limits for the conditions encountered.
The basic access protocols used for mobile communications, include frequency domain multiple access (FDMA), time domain multiple access (IDMA), and code domain multiple access (CDMA). FDMA uses different frequencies to distinguish the users. In TDMA, different time slots and interleaving allow the users to be distinguished. The CDMA scheme is a spread spectrum method that uses a separate code for each user. The pseudo noise (PN) sequence spreads the spectrum over a larger bandwidth, and reduces the spectral density of the signal. A number of CDMA signals occupy the same bandwidth and appear as random noise to each other.
An additional scheme, space diversity multiple access (SDMA) uses a dynamically changing antenna to distinguish signals, using multipath signals that hit different antenna elements in the array at different times. This delay is used to differentiate the users through spatial distribution and correlation.
Spatial correlation relates to the difference between signals received by separate sensors of a multisensor array. This correlation between the data received by two or more sensors can be measured at the same or at different time instants. Thus, spatial correlation depends on the temporal correlation of received waveforms as well as other variables related to spatial dimension, such as: the narrow and broadband properties of the transmitted signal, the array sensor spacing, the mutual coupling between the adjacent and distant sensors, the height of the antennas and their polarization, the array manifold and the omni-directional features of the array sensors, and the channel dynamics including Doppler, delay, and angular spreads.
Temporal correlation is the correlation between two data samples at the same or different time instant, so it is a correlation across time and only a function of the statistical properties of the transmitted waveforms. Strong correlation makes it easier to differentiate between directional and non-directional components of the data. The non-directional components, .such as thermal noise, are often assumed to be independent from one sensor to another.
Directional components are those generated by near or far transmitters and follow propagation, attenuation, scattering, diffraction, and refraction laws before reaching the receiver. The directional components contain information about the transmitting sources, and this information can be extracted with proper processing in the smart antenna. Thus, the working environment of the antenna contributes significantly to the transmission and reception characteristics. The environment determines the amount of multipath and interferer signals that are introduced in the antenna reception.
Multipath propagation refers to those signals arriving at a receiving antenna as a result of a combination of various components from different directions. Multipath propagation effects depend upon buildings, structures, terrain conditions, and other such objects that can reflect or refrac
Amin Moeness G.
Robbins David F.
Asmus Scott J.
Maine Vernon C.
Micronetics Wireless
Mull Fred H
Tarcza Thomas H.
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