Brent R. Petersen

Suppression of adjacent-channel, cochannel, and intersymbol interference by equalizers and linear combiners

We describe the ability of a linear equalizer/combiner or decision-feedback equalizer to suppress all received adjacent-channel, intersymbol, and cochannel interference. The emphasis is on values among transmitter bandwidth, receiver bandwidth, carrier spacing, and antenna diversity which provide the best opportunities for interference suppression. Through analyses of the number of degrees of freedom and constraints in generalized zero-forcing equalizers, and partial comparisons to calculations of equalizer minimum-mean-square performance, four results are obtained. First, with one antenna and a linear equalizer, arbitrarily large receiver bandwidths allow for marginal improvements in spectral efficiency through decreased carrier spacing, because the carrier spacing cannot be reduced to a value below the symbol rate without incurring unsuppressible interference. Second, large receiver bandwidths assist multiple antennas in improving the spectral efficiency in that carrier spacing values may go below the symbol rate, even in the presence of cochannel interference. Third, the use of equalizers and linear combiners, together with large receiver bandwidths, allows large transmitter bandwidths to be used. Fourth, for cochannel interference and intersymbol interference, the number of interferers that may be suppressible by a generalized zero-forcing linear equalizer/combiner increases linearly with the product of the number of antennas and the truncated integer ratio of the total bandwidth to the symbol rate. >

Minimum mean square equalization in cyclostationary and stationary interference-analysis and subscriber line calculations

Equalization in cyclostationary interference, which occurs when similar neighboring digital communication systems cause interference (crosstalk), is considered. An expression is derived on the minimum mean square performance of a continuous-time infinite-length decision feedback equalizer in the presence of multiple cyclostationary interferers and additive white noise. This expression is calculated for a subscriber line system to show the performance improvements over the situation where the interference is stationary with the same power spectrum. Linear equalizer performance curves were also added to the comparisons. These results show two techniques which can provide opportunities for improved equalizer performance by enhancing the cyclostationarity of the interference. The first is by decreasing the misalignment of the phases of the transceiver clocks in the central office transmitters. The second is by using transmitter pulse bandwidths which are wide relative to the symbol rate. >

A Smart Microcontroller-Based Iridium Satellite-Communication Architecture for a Remote Renewable Energy Source

With an increased focus on the utilization of green technologies and greater demands on the electric power grid, renewable energy is an important form of current and future power generation. With remote generation deployments, such as those based on wind energy, a cost-effective communication system with global coverage using satellite technology would be advantageous. The monitoring of remote generators for performance and maintenance issues is certainly necessary for any distributed-generation system. To offer a cost-effective satellite solution, a cost-optimization algorithm for minimizing data transmission while maximizing relevant telemetry data is required. This paper proposes a low-cost smart communications architecture using an Iridium Satellite System 9601 short-burst data transceiver and simple microcontroller technology. The microcontroller allows for simple optimization routines to be performed on the locally stored data. This proposed system was implemented and tested and recommendations are drawn on the usability of the developed communication system for monitoring a remote generation site.

Symbol-wavelength MMSE gain in a multi-antenna UWB system

Ultra wideband (UWB) technology has the potential to provide high speed data services. These speeds can be greatly increased by using multiple input multiple output (MIMO) techniques. Multiple antennas are used to achieve spatial diversity and these antenna elements must be separated properly to have uncorrelated communication signals. The separation can be on the scale of a symbol wavelength ([speed of light]/[symbol rate]). We have designed a printed circular disc monopole and measured the UWB radio channel. Finally, we used the measurements to show the minimum mean squared error (MMSE) performance gain which occurs when the receiver antennas are separated on the scale of a symbol wavelength

Exploiting cyclostationary subscriber-loop interference by equalization

Equalization in cyclostationary interference, a situation that occurs in communication systems where neighboring channels carry digital data at similar symbol rates and in which the interference is composed of a few dominant or phase-aligned interferers, is discussed. A minimum-mean-square performance bound is derived for a continuous-time infinite-length decision-feedback equalizer in the presence of multiple cyclostationary interferers and additive white noise. This bound is evaluated in a subscriber-loop system example to show the performance improvements that can occur over the situation in which the interference is stationary, but has the same mean power spectrum as the cyclostationary interferers. These results show two important techniques which can provide opportunities for improved equalizer performance in cyclostationary interference: decreasing the misalignment of the phases of the transceiver clocks at the central office and using transmitter-pulse bandwidths which are wide relative to the symbol rate.<<ETX>>

Signalling wavelength in an antenna array for space-time wireless over LOS channels

We consider the inter-antenna separation in a distributed antenna array. We introduce a new separation constraint with respect to the signalling wavelength, which equals the chip wavelength in DS-CDMA systems and the symbol wavelength in non-spread systems. This constraint ensures the phases of the frequency responses are exercised over 2/spl pi/ in the baseband channel matrix. The diverse phases provide a better channel matrix for signal detection. The multiuser performance improvement due to this constraint has been named as the signalling wavelength antenna placement (SWAP) gain.

Performance Evaluation of Conductive-Paper Dipole Antennas

The feasibility of electrically conductive paper as a low-cost and eco-friendly alternative to copper is presented for application as an antenna conductor in UHF radio-frequency identification (RFID) systems. The conductivity of the paper is determined to be 50 S/m and the effect of such a low conductivity on the radiation performance of a half-wavelength dipole is investigated through simulation and experimental measurements. The radiation efficiency of a dipole cut from a 0.4 mm thick conductive paper sheet is measured to be 5.0%, which translates to an RFID tag read range of 22% of that obtained using copper. This performance is deemed unacceptable for most antenna applications. However, through simulation a conductivity of 500 S/m is identified as a reasonable target for the developers of conductive paper as the current distribution and terminal properties of the resulting antenna become similar to those observed when using copper. The radiation efficiency is projected at 56 % in this case, resulting in an RFID read range of 73% of that obtained using copper.

Suppression of adjacent-channel interference in digital radio by equalization

The ability of a linear or decision-feedback equalizer to suppress adjacent-channel interference in digital radio systems is described. The emphasis is on values among transmitter bandwidth, receiver bandwidth, carrier spacing, diversity, and cochannel interference which provide the best opportunities for interference suppression. Through analysis of a generalized zero-forcing linear equalizer and calculations of equalizer minimum-mean-square performance, it is shown that a substantial amount of adjacent-channel interference can be suppressed. The ability to suppress the interference is enhanced by using equalizers with wide receiver bandwidths because they are able to exploit the cyclostationary properties of the adjacent-channel interference.<<ETX>>

Blind Channel Estimation for HomePlug Power-Line Communications: A Feasibility?

The feasibility of blind channel estimation without the aid of any pilot-training symbols is investigated for the HomePlug power-line standard. This standard uses orthogonal frequency-division multiplexing (OFDM) and a custom windowing function for the purposes of spectral shaping. The latter feature makes blind channel estimation a difficult challenge. Theoretical and simulation results demonstrate that blind channel estimation is possible, however, through the exploitation of certain HomePlug standard signal features and eigenvalue decomposition. It should be noted that this paper is not a comparison of various channel estimation techniques (i.e., trained versus semiblind versus blind), but an assessment of 1) whether a blind estimation technique is feasible with the HomePlug power-line standard and 2) to determine its effectiveness in a typical power-line setting.

Optimum 2-D LOS MIMO Performance Using Omni-directional Antennas Attained through Genetic Algorithms

The application of genetic algorithm (GA) optimization has been proven to be highly successful in the area of nonlinear optimizations. For a multiple-input, multiple-output (MIMO) wireless communication system, the optimum performance of the users with respect to the arrangement of antennas is a highly non-linear function which a genetic algorithm seems highly suited to. In this paper, a four-by-four MIMO system model is considered using a simplified 2-D LOS radio channel with additive white noise. Placing the users in a known arrangement, the optimum placement of the four antennas is determined through a genetic algorithm optimization using the average MSE of the four users as the fitness function. Initial results show a tendency towards an arrangement in which at least two antennas seen by the all transmitters are separated by a symbol wavelength.