Multipath Interference Cancellation Research Articles

Multistage interference cancellation for cyclic interleaved frequency division multiplexing

AbstractCyclic interleaved frequency division multiplexing (CIFDM), a variant of IFDM, has recently been proposed. While CIFDM employs cyclic interleaving at the transmitter to make multipath components resolvable at the receiver, the current approach of matched filtering followed by multipath combining does not fully exploit the diversity available. This is primarily because the correlation residues among the codes have a significant impact on multipath resolution. As a solution, we introduce a novel multipath successive interference cancellation (SIC) technique for CIFDM, which replaces the conventional matched filtering approach. We have examined the performance of this proposed CIFDM‐SIC technique and compared it with the conventional CIFDM‐matched filter bank and IFDM schemes. Our simulation results clearly demonstrate the superiority of the proposed scheme over the existing ones.

Successive Multipath Interference Cancellation for CP-Free OFDM Systems

Traditional orthogonal frequency-division multiplexing (OFDM) systems mitigate multipath interferences with the help of a cyclic prefix (CP) appended between two adjacent OFDM blocks. The length of the CP must be made longer than channel delay spread to avoid intersymbol interference (ISI). The use of CPs degrades spectrum efficiency significantly, which is a deal price paid in all existing OFDM systems. Motivated to deal with this issue, this paper proposes a CP-free OFDM scheme with successive multipath interference cancellation (SMIC), which does not require CPs and removes ISI before fast Fourier transform (FFT) at a receiver using stored feedback equalization (SFE). The SFE operation leaves a CP gap between adjacent OFDM blocks, and the CP is regenerated with estimated signals. In this way, we convert linearly shifted OFDM blocks induced by multipath propagation back to cyclically shifted OFDM blocks for successful FFT operation. SMIC-OFDM achieves a much higher spectrum efficiency than traditional OFDM owing to the save of CPs in transmission signals. The performance of SMIC-OFDM in terms of the bit error rate, capacity, and computational complexity is compared to that of traditional OFDM to verify the effectiveness of the proposed SMIC-OFDM scheme.

3D Printing Using a 60 GHz Millimeter Wave Segmented Parabolic Reflective Curved Antenna

This paper proposes a segmented parabolic curved antenna, which can be used in the base station of a 60 GHz millimeter wave communication system, with an oblique Yagi antenna as a feed. By analyzing the reflection and multi-path interference cancellation phenomenon when the main lobe of the Yagi antenna is reflected, the problem of main lobe splitting is solved. 3D printing technology relying on PLA (polylactic acid) granule raw materials was used to make the coaxial connector bracket and segmented parabolic surface. The reflective surface was vacuum coated (via aluminum evaporation) with low-loss aluminum. The manufacturing method is environmentally friendly and the structure was printed with 0.1 mm accuracy based on large-scale commercial applications at a low cost. The experimental results show that the reflector antenna proposed in this paper achieves a high gain of nearly 20 dBi in 57–64 GHz frequency band and ensures that the main lobe does not split.

Wideband Optical Multipath Interference Cancellation Based on a Dispersive Element

A novel scheme is proposed for analog multipath interference cancellation based on two polarization modulators (PolMs) and a dispersive element. Multiple optical compensation branches are formed by an array of tunable lasers. By adjusting the wavelength and the optical power of each tunable laser, the delay and the magnitude of the known interference signal can be finely tuned, so that the multipath interference can be accurately reconstructed for counter-phase cancellation. The dispersion-induced RF power fading in a dispersive optical link can also be compensated because of the PolM-based intensity modulation scheme, so the best cancellation depth can be obtained at any desired frequency. Experimental result shows that the proposed system can achieve more than 44-dB cancellation depth for wideband signals.

Indoor Multipath Interference Cancellation Using MMSE-CMA Estimator with 2.45 GHz of MIMO Channel Measurement

This paper studies an indoor multipath interference cancellation using the MMSE-CMA estimator for the unlicensed at 2.45 GHz of wireless communication systems. The proposed of the MMSE-CMA estimator can mitigate a superposition of the multipath interference at the receiver. As the result, the magnitudes of the channel characterization in the time domain are shown between the measured and estimated channel as a difference of number of iterations. Furthermore, we also confirm the multipath interference cancellation with the eye diagrams.

A Digital Golay-MPIC Time Domain Equalizer for SC/OFDM Dual-Modes at 60 GHz Band

In this paper, a digital time domain equalizer (TDE) for 60 GHz radio frequency transmission systems is presented. Significantly, the TDE supports both single carrier (SC) and orthogonal frequency-division multiplexing (OFDM) operation modes for digital baseband receiver. In order to improve the performance, the proposed TDE adopts Golay sequence aided one-shot channel estimation and modified multi-path interference cancellation (MPIC) equalization. Targeting on the line-of-sight (LOS) channel characteristic, MPIC is simplified with single-tap for complexity reduction. From the area efficiency point of view, both SC and OFDM modes are designed within a single hardware to yield 99% of area sharing. The Golay-MPIC TDE structure is realized as feed-forward data path with 8X-parallelism to achieve 2.64 GS/s at 330 MHz clock rate. The Golay-MPIC TDE is fabricated as a part of a digital baseband with 65 nm 1P9M general purpose process. The area of Golay-MPIC TDE occupies 1.05 mm2 with 405 K gate counts. Besides, the power dissipations for SC and ODFM modes are 56.71 mW@220 MHz (1 V) and 91.29 mW@330 MHz (1.1 V), respectively. Finally, the chip can provide the maximum throughput 15.84 Gb/s (2.64 GS/s with 64-QAM modulation).

A Novel Analog Photonic Method for Broadband Multipath Interference Cancellation

A novel analog optical technique for multipath interference cancellation of broadband signals is proposed. Multiple optical compensation branches are utilized to replicate wireless multipath channel effects. The duplicated signal is subtracted from the total received signal to recover the signal of interest while suppressing interference. The proposed architecture achieved 40 dB of cancellation over 200 MHz and 50 dB over 10 MHz. The depth and broadband nature of the cancellation demonstrates the precision of optical components and the validity of our interference cancellation scheme.

Multipath Interference Cancellation in MIMO Mobile Cellular system

Wireless network widely used today include, cellular network, wireless mesh network (WMNs), wireless local area network and personal area network. The increasing demand for these networks has turned spectrum into a precious resource. For this reason, there is always a need for methods to pack more bits/Hz. A particular solution is to use multiple antenna at both transmitter and receiver side. Such a system is called multiple-input multiple-output (MIMO) system. In real propagation environment of cellular communication, channel reuse will cause the co-channel interference which will degrade the MIMO channel performance. The interference cancellation (IC technology) can handle efficiently the cochannel interference. In this paper comparison computer simulation for zero forcing successive interference cancellation (ZF-SIC) minimum mean square error (MMSE equalizer) and maximum likelihood (ML) for two transmitting and two receiving antenna is shown.

Multipath Interference Cancellation Technique for High Precision Tracking in GNSS Receiver

Multipath is one of the major error sources that deteriorates tracking performance in global navigation satellite system (GNSS). In this letter, the orthogonal matching pursuit (OMP) algorithm is used to estimate multipaths which are highly correlated with the line of signal (LoS) signal. The estimated multipaths are subtracted from the received signal such that the autocorrelation function of the received signal is restored to optimize the tracking performance. The performance of the proposed technique is verified via computer simulations under the multipath environment of GNSS.

A Refined Channel Estimation Method for STBC/OFDM Systems in High-Mobility Wireless Channels

In this paper, we investigate channel estimation for orthogonal frequency division multiplexing (OFDM) systems with space-time block code (STBC) in mobile wireless channels. Our proposed method consists of two-stage processing and is developed on the basis of the classical discrete Fourier transform (DFT)-based channel estimation method. In the initialization stage, we employ a multipath interference cancellation technique to estimate multipath delays and multipath complex gains. In the tracking stage, we develop a refined decision-feedback (DF) DFT-based channel estimation method in which a few pilot tones inserted in OFDM data symbols are applied to form an optimal gradient vector at the first iteration such that the error propagation effect is mitigated. In order to reduce computational complexity, an approximate weighting matrix is adopted to avoid matrix inversion. We demonstrate the proposed method through computer simulation of an STBC/OFDM system with two transmit antennas and a single receive antenna. The results show that our method outperforms the classical DFT-based method, the STBC-based minimum mean square error (MMSE) method, and the Kalman filtering method as well, and that significant signal-to-noise ratio (SNR) performance improvement can be achieved, especially when a high-level modulation scheme, e.g. 16QAM, is adopted in high-mobility environments.

A multipath interference cancellation technique for WCDMA downlink receivers

AbstractIn this paper, we present a simple interference cancellation technique for the downlink of wideband code‐division multiple‐access (WCDMA) systems in multipath environment. With the same knowledge required by a RAKE receiver, the present method acts as an equalizer and cancels the interfering multipath signals from the received signal to retrieve the orthogonality property of the received signal. The present receiver has a simple structure and it has significant performance gain against the RAKE receiver. In addition, the noise enhancement is negligible when there is a line of sight path or the channel power delay profile has an exponential decaying form. Copyright © 2006 John Wiley & Sons, Ltd.

A new multipath interference mitigation technique for high-speed packet transmission in WCDMA downlink

In order to increase throughput using high order data modulations in wide-band code-division multiple-access (WCDMA) downlink, it is necessary to eliminate multipath interferences. In a multipath interference canceller (MPIC) was proposed, which enables the use of high order modulations in multipath fading channels. However, only packet channels and pilot channels were considered as transmitted code channels. Code channels dedicated to other users and remaining common code channels coexist in practice, and such unknown code channels degrade the performance of MPIC significantly. In this letter, we propose a multipath interference mitigation scheme that removes all the intracell interferences by orthogonal variable spreading factor (OVSF) code characteristics. Simulation results show that the proposed scheme makes it possible to improve total throughput using high order modulations in WCDMA downlink.

Comments on "A noncoherent tracking loop with diversity and multipath interference cancellation for direct-sequence spread-spectrum systems"

For original paper see IEEE Trans. Commun., vol.46, p.1516-24 (1998 November). In the original paper, the authors presented a noncoherent tracking loop with diversity and multipath interference cancellation to improve the loop performance on frequency-selective fading channels. However, the effects of imperfections in multipath interference cancellation have been dropped out in the statistical analyses, and only evaluated by using computer simulations. The present authors show that such effects can change the error characteristic, at least in the mean sense, and thus make the analyses of jitter performance improper.

Multipath interference canceller for high-speed packet transmission with adaptive modulation and coding scheme in W-CDMA forward link

This paper proposes a multipath interference canceller (MPIC) associated with orthogonal code-multiplexing that achieves much higher peak throughput than 2 Mbit/s with adaptive data modulation for high-speed packet transmission in the wideband direct sequence-code division multiple access (W-CDMA) forward link, and evaluates its throughput performance by computer simulation. The simulation results elucidate that sufficient multipath interference (MPI) suppression is achieved by a four-stage MPIC with 6-12 orthogonal code-multiplexing using one iterative channel estimation with pilot and decision feedback data symbols and further that the interference rejection weight control according to the number of observed multipaths is effective in improving the throughput. It is also demonstrated that MPIC exhibits a superior MPI suppression effect to a chip equalizer in the lower received signal energy per bit-to-background noise spectrum density (E/sub b//N/sub 0/) channel around 0-3 dB owing to the successive channel estimation at each stage. We show that the maximum peak throughput using MPIC is approximately 2.1 fold that without MPIC in a two-path and three-path Rayleigh fading channel and that the peak throughput of 8.0 Mbit/s is achieved using 64 QAM data modulation in a two-path fading channel within a 5 MHz bandwidth. Furthermore, the required average E/sub b//N/sub 0/ for satisfying the same throughput with MPIC is decreased by more than 2.0 dB.

A modified PN code tracking loop for direct-sequence spread-spectrum communication over arbitrarily correlated multipath fading channels

A modified fully digital pseudonoise code tracking loop is proposed for direct-sequence spread-spectrum communication. By taking advantage of the inherent diversity, a modified code tracking loop is embedded into a RAKE receiver in order to avoid problems caused by unstable locked points of error signals. Such unsteadiness of locked points often occurs with a conventional code tracking loop because the error signals may be randomly biased by multipath fading. Thus, a robust pull-in capability can be provided over a time-variant fading channel where multiple propagation paths are arbitrarily correlated. Furthermore, an effective multipath interference regeneration and cancellation technique is also proposed to improve the error characteristics of the proposed technique. Analytical expressions of the error characteristics and error signals are derived and then confirmed by means of extensive computer simulation results. In addition, several simulation results for the timing jitter and the mean time to lose lock are also presented. The very attractive behavior obtained using the proposed technique is verified.

A noncoherent tracking loop with diversity and multipath interference cancellation for direct-sequence spread-spectrum systems

A noncoherent tracking loop with diversity reception and multipath interference cancellation is proposed for direct-sequence spread-spectrum systems on frequency-selective multipath fading channels. The basic idea of the loop is to reproduce the multipath interference and remove it from the received signal, and then a path diversity is embedded in the loop to improve the loop performance. The tracking error performance of the loop is evaluated by linear analyses and computer simulations. Numerical results show that the proposed tracking loop outperforms the traditional delay locked loop and performs very well under all considered fading conditions.

Criteria of the possibility of multipath interference cancellation

AbstractA case exists in which cancellation of interference is not possible with an interference canceler which cancels the interference wave from ground radio stations mixing into the ground station for the satellite communication. It is found experimentally that this is caused by the difference in the frequency characteristics of the input signals to the two antennas by the multipath effects.Further, a method is proposed to discriminate whether the arriving interferences can be cancelled. Its effectiveness is confirmed experimentally. Whether or not the interferences can be cancelled can be determined by the amount of variation of the received electric field intensity of the interferences. If there is a signal with a constant‐shaped spectrum, the distortion of the shape can be used for discrimination. As a result, the condition and limit of applications of the interference canceler are found.