Zero-forcing Equalizer Research Articles

Performance Analysis of a Proposed Pre-FEC Structure for a DVB-C2 Receiver

To increase the spectral efficiency of HFC network, the standard of digital video broadcasting for cable systems (DVB-C2) was completed in 2010 and products that support the DVB-C2 is expected to be released within years. Before making products for DVB-C2 receiver, the performance of them should be investigated under various channel conditions first. Thus, we show the performance of the proposed structure for a pre-FEC in DVB-C2 receiver considering the channel model including additive white Gaussian noise (AWGN), a frequency offset, and echo channels to provide information about the implementation of DVB-C2 receiver. Based on the simulation results, we implement the pre-FEC using two field programmable gate arrays (FPGAs) and show the measured symbol error rate (SER) between the transmitted and received quadrature amplitude modulation (QAM) symbols with respect to various symbol timing estimations (STEs) of synchronization (SYNC) and powers of analog-to-digital converter (ADC) input. Because the STE makes the received pilot symbols in preamble rotated and these rotated pilot symbols are used in channel estimation, it affects the channel estimation and SER of pre-FEC. In addition, the channel estimation impaired by the STE causes the received QAM symbols to have biased mean values compared with the transmitted 4096QAM symbols. Since this degrades the performance of pre-FEC, the automatic gain control (AGC) is added after zero-forcing linear equalizer (ZF-LE) to improve the performance of pre-FEC. As the power of ADC input decreases, the SER increases due to the noise enhancement of ZF-LE.

Continuous Phase Modulation for Digital Video Broadcasting

ABSTRACT In this paper, we study the performance of the Digital Video Broadcasting- Terrestrial (DVB-T) system with Continuous Phase Modulation Orthogonal Frequency Division Multiplexing (CPM-OFDM). The proposed structure combines the advantage of mitigating the Peak-to-Average Power Ratio (PAPR) problem in the Power Amplifier (PA)in addition to exploiting the channel frequency diversity and power efficiency of CPM. The proposed CPM-OFDM DVB-T system is implemented with Frequency-Domain Equalization (FDE) to avoid the complexity of the equalization. Two types of frequency domain equalizers are considered and compared for performance evaluation of the system; the Zero-Forcing (ZF) equalizer and the Minimum Mean Square Error (MMSE) equalizer. Simulation results show that the performance of the CPM-OFDM DVB-T system with multi-path fading is better than its performance with single-path fading. Keywords DVB-T; OFDM; CPM; ZF Equalizer; MMSE Equalizer; PAPR.

Parallel Channel Estimator and Equalizer for Mobile OFDM Systems

Mobile OFDM refers to OFDM systems with fast moving transceivers, in contrast to traditional OFDM systems whose transceivers are stationary or have a low velocity. In this paper, we use the basis expansion model (BEM) to model time-varying OFDM channels. Using different BEM’s, we investigate various architectures to implement the least-squares (LS) channel estimation and its corresponding zero-forcing (ZF) channel equalization. The experimental results show that our implementation for mobile OFDM systems is capable of combatting the time variation of mobile OFDM channels, and more hardware resource utilization is necessary compared with a traditional OFDM design which fails in a time-varying scenario. For mobile OFDM systems, different BEM’s are available for the channel modeling. We observe that the so-called Critically sampled Complex-Exponential BEM (CCE-BEM) leads to the most efficient hardware architecture while still maintaining high modeling accuracy.

ANALYSIS AND SOLUTION FOR MULTI-BAND ORTHOGONAL FREQUENCY-DIVISION MULTIPLEXING ULTRA WIDE BAND SYSTEM IN REAL ENVIRONMENT FOR VEHICLE TO INFRASTRUCTURE APPLICATION

Many researches in the world deal with driving on the road to ensure optimum safety. In this context, several telecommunication technologies are often used to connect the vehicles via continuous wireless communication with the infrastructure, exchange data and information relevant to increase overall road safety and enable cooperative traffic management. These systems are not reliable for all situations and the difficulties encountered by the drivers. We have been proposed the Multi-band Orthogonal Frequency- Division Multiplexing system based on Ultra Wide Band (MB-OFDM UWB) as a good candidate to insure a Vehicle to Infrastructure (V2I) communication with high data rate and good performances in terms of Bit Error Rate (BER). However, Inter-Carrier Interference (ICI) resulting from Doppler shift phenomenon degrades MB-OFDM UWB system performance and raises a significant challenge in wireless mobile environment. In this study, V2I communication based on the MB-OFDM UWB technology is studied and analyzed for 200 Mbit/s, over multipath channel using the IEEE802.15.4a channel model with Doppler shift for different speeds. The theoretical formulas of BER in Additive White Gaussian Noise (AWGN) and Rayleigh channels are calculated and are compared to the simulation results in MB-OFDM UWB system. The comparison shows that simulation results are consistent with theoretical formulas. The degradation in the performance of the proposed system solution becomes worse with a high speed 250 Km h1, so it's necessary to use new receiver solutions. The Extended Kalman Filer (EKF) and the Maximum Likelihood (ML) estimation with ZF equalizer have been proposed and have been compared to Zero-Forcing (ZF) in order to combat the ICI effect. For high value of speed (250 Km h1), the EKF method performs better than the ML method, better than the ZF equalizer and offers much improvement in performance in term of BER

Maximum-Likelihood Detection in Few-Mode Fiber Transmission With Mode-Dependent Loss

In this letter, the performance of maximum-likelihood (ML) detection is evaluated and compared with the zero-forcing (ZF) and minimum mean square error (MMSE) equalizers for a 3 × 158-Gb/s mode-division multiplexed dual-polarization quadrature phase shift keying orthogonal frequency division multiplexing transmission impaired by mode-dependent loss. The receiver schemes are compared in terms of performance and complexity. The simulations show that the ML approach outperforms both ZF and MMSE equalization for strongly coupled modes. However, the complexity of the ML detection is significantly higher and increases faster with the number of modes used for transmission and the modulation format order.

MC-CDMA System Identification and Equalization Using the LMS Algorithm and Takagi-Sugeno Fuzzy System

Abstract In this paper we are focused on the Multi-Carrier Code Division Multiple Access (MC-CDMA) equalization problem. The equalization is performed using the Minimum Mean Square Error (MMSE) and Zero Forcing (ZF) equalizer based on the identified parameters representing the indoor scenario (European Telecommunications Standards Institute Broadband Radio Access Networks (ETSI BRAN A) channel model), and outdoor scenario (ETSI BRAN E channel model). These channels are normalized for fourth-generation mobile communication systems. However, for such high-speed data transmissions, the channel is severely frequency-selective due to the presence of many interfering paths with different time delays. The identification problem is performed using the Least Mean Squares (LMS) algorithm and the Takagi-Sugueno (TS) fuzzy system. The comparison between these techniques, for the channel identification, will be made for different Signal to Noise Ratios (SNR).

On the Study of a Novel Decision Feedback Equalizer with Block Delay Detection for Joint Transceiver Optimization

This paper presents a novel decision feedback equalizer (DFE) with block delay detection for the joint transceiver design that uses channel state information (CSI). The block delay detection in the proposed DFE offers a degree of freedom for optimizing the precoder of the transmitter, provided the transmission power is constrained. In the proposed DFE, the feedforward matrix is devised to enable a block-based equalizer that can be cooperated with an intrablock decision feedback equalizer for suppressing the intersymbol interference (ISI) for the transmitted block with a certain block delay. In this design, the interblock interference (IBI) for the delay block is eliminated in advance by applying the recently developed oblique projection framework to the implementation of the feedforward matrix. With knowledge of full CSI, the block delay and the associated block-based precoder are jointly designed such that the average bit-error-rate (BER) is minimized, subject to the transmission power constraint. Separate algorithms are derived for directly determining the BER-minimized block delays for intrablock minimum mean-squared error (MMSE) and zero-forcing (ZF) equalization criteria. Theoretical derivations indicate that the proposed MMSE design simultaneously maximize the Gaussian mutual information of a transceiver, even under the cases of existing IBI. Simulation results validate the proposed DFE for devising an optimum transceiver with CSI, and show the superior BER performance of the optimized transceiver using proposed DFE. Relying on analytic results and simulation cases also builds a sub-optimum MMSE design of the proposed DFE using the BER-minimized block delay for ZF criterion, which exhibits almost identical BER performance as the proposed MMSE design in most of the signal-to-noise ratio (SNR) range.

A Cyclic Shift Relaying Scheme for Asynchronous Two-way Relay Networks

Perfect time synchronization among multiple relay nodes is quite difficult to realize in distributed relay networks. In this paper, we proposed a cyclic prefix (CP) assisted cyclic shift relaying (CFR) scheme for asynchronous two-way amplify-and-forward (AF) relay networks over flat fading channels. In the proposed scheme, a CP is inserted at the two source nodes to combat the asynchronous delays. Each relay amplifies the received mixed asynchronous signals after CP removal, and a cyclic delay is introduced to further improve the system performance. With the CP and the cyclic delay, the multiple flat fading relay channels are transformed into a multipath fading channel. As a result, low complexity frequency domain equalizers, such as zero-forcing and minimum mean square error (MMSE) equalizer, can be used to recover the transmit signal. Furthermore, the performance of the proposed CFR scheme with MMSE equalizer is analyzed and closed-form expression for the lower bound of uncoded bit error rate (BER) performance is derived. Based upon this lower bound, we also investigate the power allocation among the sources and the relays to improve the system performance. Finally, extensive numerical results are provided to show the BER and frame error rate performance of the proposed CFR scheme.

Exploiting Equalization Techniques for Improving Data Rates in Organic Optoelectronic Devices for Visible Light Communications

This paper presents the use of equalization techniques in visible light communication (VLC) systems in order to increase the data rate. Here we investigate two VLC links a silicon (Si) light emitting diode (LED) and an organic photodetector (OPD), and an organic LED (OLED) plus an Si photodetector (PD), together with three equalization schemes of an RC high pass equalizer, a fractionally spaced zero-forcing equalizer (ZF) and an artificial neural network (ANN). In addition we utilize a pre-distortion scheme to enhance the performance of the digital equalizers. For both systems the bit rate achieved are 750 kb/s from a raw bandwidth (BW) of 30 kHz and 550 kb/s from a raw BW of 93 kHz.

Performance Evaluation of DWT-OFDM and FFT-OFDM for Multicarrier Communications Systems using Time Domain Zero Forcing Equalization

Other than the conventional fast Fourier transform (FFT) for multicarrier modulation, a new approach for multicarrier modulation (MCM) has been known. Meanwhile, multicarrier modulation involves dividing the broadband channel into many orthogonal but overlapping narrowband carriers. In an OFDM modulation based multicarrier system using the FFT, a cyclic prefix (CP) is inserted after each symbol frame to combat the effects of inter symbol interference (ISI). By inserting the CP, which results in spectral inefficiency OFDM schemes trades up to 25% of the transmit bandwidth. A new MCM approach that is void of the expense is the wavelet transform-based systems. These systems also have very suppressed side-lobes and exhibit improved BER performance. In wavelet based systems, the latest challenge in its implementation is in the channel estimation. In this work we have studied the performance of the FFT based OFDM system against wavelet transform (WT) based multicarrier system using a simple zero forcing (ZF) equalization in time domain. The studied system shows some improved BER performance.

Efficient Image Transmission with Multi-Carrier CDMA

This paper presents a new approach for efficient image transmission over Multi-Carrier Code Division Multiple Access (MC-CDMA) systems using chaotic interleaving. The chaotic interleaving scheme based on Baker map is applied on the image data prior to transmission. The proposed approach transmits images over wireless channels, efficiently, without posing significant constraints on the wireless communication system bandwidth and noise. The performance of the proposed approach is further improved by applying Frequency-Domain Equalization (FDE) at the receiver. Two types of frequency-domain equalizers are considered and compared for performance evaluation of the proposed MC-CDMA system; the Zero-Forcing equalizer and the Linear Minimum Mean Square Error (LMMSE) equalizer. Several experiments are carried out to test the performance of the image transmission with different sizes over the proposed MC-CDMA system. Simulation results show that image transmission over wireless channels using the proposed chaotic interleaving approach is much more immune to noise and fading. Moreover this chaotic interleaving process adds a degree of encryption to the transmitted data. The results also show a noticeable performance improvement in terms of the Root Mean Square Error and Peak Signal-to-Noise Ratio values when applying FDE in the proposed approach, especially with the LMMSE equalizer.

Achieving Joint Diversity in Decode-and-Forward MIMO Relay Networks with Zero-Forcing Equalizers

Wireless MIMO relay networks have received significant interests in recent years. However, most MIMO relay techniques require high complexity equalizers and error free forwarding at the relay to collect diversity. In this paper, we propose high-rate and low-complexity decode-and-forward (DF) MIMO relay designs that achieve cooperative diversity, receive diversity or joint diversity. We introduce a power-scaling strategy for MIMO relays to enable cooperative diversity. Zero-forcing equalizers are employed at both relay and destination to maintain low-complexity. We also develop a channel-controlled ARQ scheme to collect receive diversity. Through mathematical analysis, we prove the diversity order achieved by each proposed design and numerical simulations confirm the theoretical claims.

Joint Low-Complexity Equalization and Carrier Frequency Offsets Compensation Scheme for MIMO SC-FDMA Systems

Due to their noise amplification, conventional Zero-Forcing (ZF) equalizers are not suited for interference-limited environments such as the Single-Carrier Frequency Division Multiple Access (SC-FDMA) in the presence of Carrier-Frequency Offsets (CFOs) . Moreover, they suffer increasing complexity with the number of subcarriers and in particular with Multiple-Input Multiple-Output (MIMO) systems. In this letter, we propose a Joint Low-Complexity Regularized ZF (JLRZF) equalizer for MIMO SC-FDMA systems to cope with these problems. The main objective of this equalizer is to avoid the direct matrix inversion by performing it in two steps to reduce the complexity. We add a regularization term in the second step to avoid the noise amplification. From the obtained simulation results, the proposed scheme is able to enhance the system performance with lower complexity and sufficient robustness to estimation errors.

Regularized MIMO Equalization for SC-FDMA Systems

In this paper, we propose an efficient frequency domain equalization scheme for Multiple Input Multiple Output (MIMO) Single-Carrier Frequency-Division Multiple Access (SC-FDMA) systems. The proposed scheme avoids the complexity problem associated with the conventional MIMO Zero-Forcing (ZF) equalizer as well as the noise enhancement problem. The matrix inversion process associated with the proposed equalization scheme is performed in two steps to reduce complexity. A regularization term is added in the second step of the matrix inversion to avoid the noise enhancement. Simulation experiments on uplink MIMO SC-FDMA systems show that the proposed equalization scheme provides better performance than that of the ZF equalizer and its complexity is far less than that of the ZF equalizer.

Performance of a novel LED lamp arrangement to reduce SNR fluctuation for multi-user visible light communication systems

This paper investigates the performance of our recently proposed LED lamp arrangement to reduce the SNR fluctuation from different locations in the room for multi-user visible light communications. The LED lamp arrangement consists of 4 LED lamps positioned in the corners and 12 LED lamps spread evenly on a circle. Our studies show that the SNR fluctuation under such a LED lamp arrangement is reduced from 14.5 dB to 0.9 dB, which guarantees that users can obtain almost identical communication quality, regardless of their locations. After time domain zero-forcing (ZF) equalization, the BER performances and channel capacities of 100-Mbit/s and 200-Mbit/s bipolar on-off-keying (OOK) signal with most significant inter-symbol interference (ISI) are very close to that of the channel without any ISI caused by this LED lamp arrangement.

Application of Student's t and Behrens–Fisher distributions to the analysis of enhanced noise after zero-forcing frequency domain equalisation

Since many years the Gaussian or normal distribution has been a useful tool to model data observations in fields as physics or astronomy. In communication systems, for instance, this distribution is widely used to model thermal noise. However, there exist many natural physical phenomena that exhibit tails decay following a power law that cannot be modelled by the classical Gaussian distribution. In many of these cases, Student's t distributions can be useful for modelling these kind of data because they allow heavy tails which are more realistic. This study provides a brief introduction to those distributions and their convolutions, which are distributed according to the Behrens–Fisher distributions. The goal is to highlight the potential application of non-Gaussian distributions to the analysis of communication systems. With this purpose, the authors present their work applying those distributions to describe the enhanced noise when zero-forcing (ZF) equalisation is used to compensate the effects of a selective fading Rayleigh channel. Obtained results allows the analysis of enhanced noise in three different scenarios: an orthogonal frequency division multiplexing (OFDM) transmission, an OFDM-based relay network and a single carrier frequency division multiple access (SC-FDMA) transmission.

Inter Carrier Interference Analysis of SCFDMA System using Frequency Domain Equalization

Single Carrier Frequency Division Multiple Access (SCFDMA) system performs better than multicarrier transmission systems due to its inherent single carrier structure. It is a strong candidate for uplink communication due to its lower peak to average power ratio (PAPR) but it is high sensitive to carrier frequency offset. However the problem of intercarrier interference (ICI) in SCFDMA system is not addressed. In this paper conjugate cancellation method is used to reduce the effect of frequency offset in SCFDMA system. Bit error rate of OFDMA and SCFDMA system is compared in different multipath channels using zero forcing equalizer (ZFE) and Minimum mean square error (MMSE) equalizers. Simulation results shows that ZFE performs better for additive white gaussian noise (AWGN) and pedestrian channels but its performance gets degraded in vehicular channels. MMSE equalizer performs better than zero forcing equalizer up to 0.2 normalized frequency offset in vehicular channels.

Low-Cost Perturbation-Based ICI Equalizers for OFDMA Mobile Systems

SUMMARY For advanced mobile communication systems that adopt orthogonal frequency-division multiple access (OFDMA) technologies, intercarrier interference (ICI) significantly degrades performance when mobility is high. Standard specifications and concerns about complexity demand low-cost methods with deployment readiness and decent performance. In this paper, novel zero forcing (ZF) and minimum mean-square error (MMSE) equalizers based on per-subcarrier adaptive (PSA) processing and perturbation-based (PB) approximation are introduced. The proposed equalizers strike a good balance between implementation cost and performance; therefore they are especially suitable for OFDMA downlink receivers. Theoretical analysis and simulations are provided to verify our

OFDM Based on Low Complexity Transform to Increase Multipath Resilience and Reduce PAPR

This paper introduces a new multicarrier system using a low computational complexity transform that combines the Walsh-Hadamard transform (WHT) and the discrete Fourier transform (DFT) into a single fast orthonormal unitary transform. The proposed transform is used in a new orthogonal frequency division multiplexing ( T-OFDM) system, leading to a significant improvement in bit error rate (BER) and reasonable reduction in the peak-to-average power ratio (PAPR). Use of the proposed transform with OFDM has been found to attain high frequency diversity gain by combining all data samples resulting in the transmission over many subcarriers. Consequently, the detrimental effect arising from channel fading on the subcarrier power is minimized. Theoretical analysis of the uncoded T-OFDM performance over additive white Gaussian noise (AWGN), flat fading, quasi-static (fixed within the entire period of OFDM symbol transmission) frequency selective fading channel models with zero-forcing (ZF) and minimum mean square error (MMSE) equalizers is presented in this work. Moreover, the low superposition of the subcarriers passing through the T-transforms leads to a reduction in the high peak of the transmitted signal whilst preserving the average transmitted power and data rate. Analytical results confirmed by simulations demonstrated that the proposed T-OFDM system achieves lower PAPR and the same BER over AWGN and flat fading channels. Compared to OFDM, T-OFDM is found to have better BER when MMSE equalizer is used, but slightly worse when ZF equalizer is used.

User Arrival in MIMO Interference Alignment Networks

In this paper we analyze a constant multiple-input multiple-output interference channel where a set of active users are cooperating through interference alignment while a set of secondary users desire access to the channel. We find the minimum number of secondary transmit antennas required so that a secondary user can use the channel without affecting the sum rate of the active users, under a zero-forcing equalization assumption. When the secondary users have enough antennas, we derive several secondary user precoders that approximately maximize the secondary users' sum rate without changing the sum rate of the active users. When the secondary users do not have enough antennas, we perform numerical optimization to find secondary user precoders that cause minimum degradation to the sum rate of the active users. Through simulations, we confirm that i) with enough antennas at the secondary users, gains equivalent to the case of all the users cooperating through interference alignment is obtainable, and ii) when the secondary users do not have enough antennas, large rate losses at the active users can be avoided.channels