Cross-polarization Interference Cancellation Research Articles

Joint XPI and ISI Cancellation for Dually-Polarized Radio Systems over Earth-Space Links

Using dually-polarized technology to double the spectral efficiency is very attractive in satellite communication systems. However, the cross polarization interference (XPI) which is inevitable will degrade the performance of the system. In order to eliminate it, a cross polarization interference cancellation (XPIC) is necessary, at least under unfavourable propagation conditions. This paper mainly studies the issue of cross polarization interference cancellation for dually-polarized radio systems over earth-space links. A joint XPIC and DEAF is presented, and compared with conventional XPIC, DEAF and other equalizer structures. The study shows that even under the circumstances with XPI only, the combination of XPIC and DEAF are necessary, for the XPI in the signal will cause ISI during the signal processing which can not be eliminated by the XPIC. And the simulation results also show that the joint XPIC and DEAF have the best performance among them.

Frequency Asynchronous Cross-Polarization Interference Canceller for Variable Polarization Frequency Division Multiplexing (VPFDM)

This paper proposes a frequency asynchronous cross-polarization interference canceller for Vertical/Horizontal (V/H) polarization multiplexing satellite communications. In satellite communications, V/H polarization signals are likely to experience different frequency fluctuations, and so the cross-polarization undergoes two different frequency fluctuations. To cancel this cross-polarization interference, a new frequency asynchronous cross-polarization interference canceller that removes interference and frequency offsets is proposed. Computer simulations are carried out to evaluate its fundamental performance. The results show that the proposed canceller can remove the cross-polarization interference created by the two different frequency offsets, simultaneously.

Cross polarization interference cancellation for fiber optic systems

One method of improving the bandwidth efficiency of a fiber optic communication system is to use polarization multiplexing, where independent signals are transmitted with orthogonal polarizations. A receiver can reconstruct both signals without interference by tracking their polarizations as long as they remain orthogonal. Since orthogonality is lost to some extent during propagation through an optical fiber, a polarization tracking system will incur a signal crosstalk penalty. A new and practical method using cross polarization interference cancellation (XPIC) is proposed to correct for the loss of orthogonality incurred during propagation through an optical fiber. The system optimally reconstructs both signals at the receiver and eliminates the need for conventional polarization tracking. XPI cancellation uses fewer lasers than conventional polarization interleave multiplexing and can also mitigate effects that currently limit link performance such as chromatic and polarization mode dispersion (PMD).

A simple polarization-recovery algorithm for dual-polarized cellular mobile-radio systems in time-variant faded environments

Dual-polarized signaling constitutes an effective frequency-reuse technique to enhance the cell capacity in cellular mobile-radio systems. In the present paper, we present a new cross-polarization interference canceler (XPIC) which accomplishes the polarization-recovery task in time-division multiple-access (TDMA)-based cellular radio systems. The main new attractive feature of the proposed XPIC is that it is able to work even in the presence of unknown and possibly time-variant random phase fluctuations, as those due to imperfect phase recovery at the receiver side.

A modular neural network for enhancement of cross-polar radar targets

A polarimetric radar navigation system makes use of polarization rotating twist-grid retroreflectors in order to navigate a confined waterway, even in inclement weather or after dark. Despite the polarization diversity offered by such a radar target, depolarization allows significant cross-polar clutter to obscure the reflector return. A novel modular neural network solution integrates an adaptive cross-polar interference canceller, a radial basis function network, and a conventional cell-averaging CFAR processor to successfully demonstrate the enhancement and detection of a polarization target. The modular solution outperforms any one of the aforementioned methods on their own. This is indicated subjectively through the display of the resultant processed images, and objectively by the estimates of target-to-clutter ratio and receiver operating curves. A post-detection processor uses a priori information about the reflector location along the water-land boundary of the waterway. A fuzzy processor combines primary detection information with the output from a vision-based edge detector to effectively remove false alarms.

Architecture and circuit design of a 6-GOPS signal processor for QAM demodulator applications

A QAM processor for applications in QAM demodulators with baud rates of up to 60 Mbaud and modulation schemes of up to 1024 QAM has been implemented on a single chip. The chip performs 11-tap complex-valued adaptive time-domain equalization and the complete digital base-band signal processing of high-capacity QAM demodulators. This includes frequency-domain slope equalization and the digital parts of the timing and carrier recovery as well as the gain and offset control for the A-to-D converters. The equalizer can be operated in baud spaced and half-baud spaced mode and can also be applied for cross-polarization interference cancellation. The computational power of the QAM processor exceeds 6 giga-multiply-accumulate operations per second. Fabricated in an 1.0-/spl mu/m CMOS technology on a silicon area of 185 mm/sup 2/ this 800 K-transistor chip demonstrates the potential of such low-cost technologies. The maximum clock frequency under worst-case conditions is 60 MHz. The corresponding power dissipation is 4.2 W. >

Orthogonal Cochannel Operation for High Spectrum Efficiency Based on the Example of 16 QAM-140 Mbit/s Systems Using Rolloff 0.19

In view of the rapidly increasing demands for transmission capacity of public networks and the limited number of radio frequencies available, the band efficiency of existing systems in general will become insufficient for future high-capacity requirements. This fact is becoming increasingly evident for 16 QAM-140 Mbit/s radio systerns at 3.9, 6.7, and 11.2 GHz which are in widespread use in todays long-haul transmission networks. Conceptual and technological measures for making cochannel operation feasible and practical are presented using the example of a system family. By these means, even the capacity of existing 16 QAM-140 Mbit/s radio routes with 40 MHz interleaved channel arrangements can be doubled with the particular advantage of reutilizing the existing antennas and radio equipment with only minor modifications. A progressive filter concept makes orthogonal cochannel transmission possible with negligible adjacent channel spectrum interference. Surface acoustic wave IF filters are used to convert existing systems from 0.5 rolloff to 0.19 rolloff. Special RF channel/antenna arrangements were developed for the transmission of all RF channels in both directions, including space diversity and using only two antennas. A field experiment verified the feasibility of the concept and indicated that a crosspolar interference canceller is generally not necessary for 16 QAM140 Mbit/s cochannel operation.

Digitalized Cross-Polarization Interference Canceller for Multilevel Digital Radio

This paper proposes a newly developed, highly precise cross-polarization interference canceller (XPIC), utilizing digitalized transversal filters. Performance of the digitalized XPIC is solely determined by quantization and tap numbers and is not affected by any circuit imperfection. Moreover, it can be universally applied to different bit rates and various modulation schemes. Performance of the XPIC is analytically estimated for various modulation schemes and various interference conditions. Then, the digitalized XPIC is realized and applied to a 12.5 MB 256 QAM digital radio system. Experimental results have closely conformed with theoretical estimations and it is confirmed that the XPIC is a powerful countermeasure against multipath fading for a future digital radio.

Cross-Polarization Interference Cancellation and Nonminimum Phase Fades

In this paper we examine the effects of nonminimum phase fades on dual-polarized M-state quadrature amplitude-modulated signals. Performance is evaluated in the presence of a baseband cross-polarization interference canceler described in another paper. Results indicate that the canceler performance is practically transparent to the fade type.

Baseband Cross-Polarization Interference Cancellation for M-Quadrature Amplitude-Modulated Signals Over Multipath Fading Radio Channels

In this paper we propose a novel baseband structure capable of adaptively mitigating cross-polarization interference in a dual-polarized, M-state quadrature amplitude-modulated received signal. We show that by using this canceler, performance signatures very close to single-polarized system signatures can be achieved for dually polarized digital radio systems.

Performance of Cross-Polarized M-ary QAM Signals Over Nondispersive Fading Channels

This paper presents performance analysis of dual-polarized M-ary Quadrature Amplitude Modulated (QAM) signals over nondispersive radio channels. In particular, dual-polarized, 16-QAM signals are examined. A simple method for adaptive cancellation of static and fade-induced cross-polarization interference is introduced. The cancellation is performed at baseband. For this canceler, two adaptation methods are studied. The results indicate that dual-polarized M-ary QAM is not feasible over fading channels unless means of adaptive cancellation of the cross-polarization interference are provided. The results also indicate that the adaptive algorithm employed in cross-polarization interference cancellation should take into account noise power reduction.

Signal-to-Noise Ratio Statistics for Nondispersive Fading in Radio Channels with Cross Polarization Interference Cancellation

The signal-to-noise ratio (SNR) statistics of a crosspolarized interference cancellation scheme is derived in terms of the statistics of nondispersive fading of the signals in the radio channels. The results are applied to certain digital radio channels subjected to nondispersive fading. It is found that error rates not exceeding 10-6could be maintained during 99 percent of the duration of a 30 dB fade in a 26.4 mi path. The method and data presented support the feasibility of cross polarization interference cancellation. They are applicable to the determination of SNR budget in the transmission system.