Block Linear Equalizer Research Articles

Joint time-frequency domain equalization of MSK signal over underwater acoustic channel

Minimum shift keying (MSK) shows better bandwidth efficiency than the phase shift keying owing to its high bandwidth usage efficiency and constant envelope property. The performance of frequency-domain block linear equalization (FD-BLE), which is commonly used for MSK communication, is limited in complex time-varying underwater acoustic (UWA) channel. In this paper, a time-domain adaptive decision feedback equalization (TD-ADFE) is proposed to address issues pertaining to MSK communications over UWA channel. Further joint time–frequency domain equalization (JTFDE) built on TD-ADFE and BLE is proposed to further reduce the bit error rate (BER). The proposed method can effectively track the time-varying UWA channel through the updated equalizer coefficient according to the output of de-mapper. Numerical simulation shows that the JTFDE performed better than TD-ADFE and FD-BLE over time-varying UWA channel by approximately 2 dB when the BER was 1 × 10−3.The sea trial results verified the proposed JTFDE and demonstrated that the BER of JTFDE was 82.5% and 88.9% lower than that of TD-ADFE and FD-BLE, respectively.

Joint detection based on the total least squares

Joint detection can eliminate the inter-symbol interference which is caused by Multipath propagation, and multiple access interference which is caused by non-orthogonal multiplexing. In multipath fading channels, the error of channel estimation is inevitable. It will propagate to system matrix. In this dissertation, we utilize the joint detection to analyze the effect of channel estimation error Considering the error of system matrix and noise. We present the total least squares (TLS) way that can be used to overcome the defect of Zero Forcing Block Linear Equalizer (ZF-BLE). The emulated data have turned out that our proposed receiver is superior than the conventional ZF-BLE method.

Comparative Study on Zero Forcing Block Linear Equalization for TD-SCDMA

3G standards such as TD-SCDMA use multi-user detection (MUD) at the base station to combat multi address interference (MAI) and inter-symbol interference (ISI). We review Cholesky factorization and Schur algorithm for Zero Forcing Block Linear Equalization. We compare the solutions of different algorithm for ZF-BLE by computation, and analyze the complexity of those methods.

A Unified Approach to Reduced-Redundancy Transceivers: Superfast Linear and Block-Iterative Generalized Decision Feedback Equalizers

This paper shows, under general input data models, how block memoryless equalizers should be formulated considering reduced-redundancy transmissions for superfast detection. We propose linear and DFE-based, both multicarrier (MC) and single-carrier-frequency-domain (SC-FD) transceivers, along with efficient methods for the equalizer calculation, in a unified manner. We argue that, under a one-tap block decision feedback, transmitted redundancy can be reduced below the minimum <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\lceil(L-1)/2\rceil$</tex></formula> samples allowed in the linear case, where <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L$</tex></formula> is the channel length, even down to zero-redundancy, with improved BER performance. This is quantified in light of the optimal reconstruction delay set for a minimum-norm zero-forcing feedforward matrix in terms of the channel zeros location. The proposed MC and SC-FD block DFEs do not cancel inter-block-interference (IBI) via zeros-jamming; Instead, it removes IBI completely, in part by decision-feedback, and in part by zero-padding, which allows for much lower redundancy transmissions. The remaining ISI is further eliminated through a one-step block-iterative-generalized-DFE (BI-GDFE) obtained in the minimum-mean-square-error (MMSE) sense. Unlike computationally demanding block DFEs that eliminate ISI via successive cancelation, the proposed DFE schemes are as efficient as a superfast block-linear equalizer, requiring at most 3 receive branches to realize the order- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$M$</tex></formula> feedforward matrices in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\cal O}(M \log M)$</tex></formula> operations.

Linear and Nonlinear Time Domain Block Equalizers on MIMO Frequency Selective Channels

Single-Carrier (SC) transmission with the same bandwidth as Multi-Carrier (MC) transmission (such as OFDM) may have far shorter symbol duration and is considered to be more robust against time selective fading. In this paper, we proposed the novel equalization and signal separation schemes in time domain for short block length transmission, i.e., Block Linear Equalization (BLE) and Block Nonlinear Equalization (BNLE) on MIMO frequency selective fading channels. The proposed BLE uses the MMSE based inverse matrix in time domain and the BNLE utilizes the QRD-M (QR Decomposition with M algorithm) with appropriate receiver complexity. We compared the computational complexity among the conventional SC-FDE (Frequency Domain Equalization) scheme and the proposed equalizers. We also used the Low-Density Parity Check (LDPC) decoder concatenated to the proposed BLE and BNLE.

Reduced Rank Technique for Joint Channel Estimation and Joint Data Detection in TD-SCDMA Systems

In time division-synchronous code division multiple access systems, the channel estimation for multiple subscribers requires the computation of very complicated algorithms through short training sequences. This situation causes mismodeling of the actual channels and introduces significant errors in the detected data of multiple users. This paper presents a novel channel estimation method with low complexity, which relies on reducing the rank order of the total channel matrix H. We exploit the rank deficient of H to reduce the number of parameters that characterizes this matrix. The adopted reduced rank technique is based on singular value decomposition algorithm. Equations for reduced rank-joint channel estimation (JCE) are derived and compared against traditional full rank-joint channel estimators: least square (LS) or Steiner, enhanced LS, and minimum mean square error algorithms. Simulation results of the normalized mean square error for the above mentioned estimators showed the superiority of reduced rank estimators. Multi-user joint data detectors based linear equalizers are used to suppress inter-symbol interference and mitigate intra-cell multiple access interference. The detectors: zero forcing block linear equalizer and minimum mean square error block linear equalizer algorithms are considered in this paper to recover the data. The results of bit error rate simulation have shown that reduced rank-JCE based detectors have an improvement by 5 dB lower than other traditional full rank-JCE based detectors.

Study on Channel Estimate and Joint Detection in 3G Network

In order to study the contribution of the channel estimation and joint measuring technology on the third generation mobile communications (3G), the channel estimation and joint detection model of the 3G system has been installed to analyze the channel estimation approaches grounded on emergency setups and training sequence. Pulse shaping filtering has been conducted by operations such as QPSK baseband modulation and Spread Spectrum on the User Data Source; then to channel estimate and joint measure the data received from base station via the Additive White Gaussian Noise channel. In line with the simulation results, with the increase of signal to noise ratio，the impulse response graph of the signal via the Steiner Estimator channel levels with that via the noise-free channel. Zero Forcing Block Linear Equalizer (ZF-BLE) has a good effect on eliminating the multipath interference and the inter-symbol interference in the system, which prove the good effects on the 3G system of using both the channel estimation technology of the Steiner Estimator and the joint measuring technology of the ZF-BLE, which is of good application prospects.

이중 선택적 채널 OFDM 시스템을 위한 블록 선형 MMSE 등화 방식의 성능 분석

본 논문에서는 이중 선택적 채널 OFDM 시스템을 위한 블록 선형 MMSE(Minimum Mean Square Error) 등화 방식의 성능을 컴퓨터 모의실험을 통하여 분석한다. 블록 선형 MMSE 등화 방식의 BER(Bit Error Rate) 성능은 SNR(Signal-to-Noise Ratio)이 증가함에 따라 BER이 처음에는 감소하다가 SNR이 일정 값을 넘어서면 BER이 오히려 증가하는 다소 특이한 현상을 나타낸다. 본 논문에서는 블록 선형 MMSE 등화 과정에 포함된 선형연립방정식 계수 행렬의 상태수(condition number) 분석을 통하여 이러한 블록 선형 MMSE 등화 방식의 BER 특성을 규명하고 높은 SNR 값에서의 BER 성능 저하를 개선하는 새로운 방안을 제시한다. In this paper, we analyze the performance of the block linear MMSE equalization for OFDM systems in doubly selective channels by computer simulations. The block linear MMSE equalization shows somewhat unusual BER characteristics in that the BER curve drops at first as SNR increases but then rises up as SNR increases further beyond some point. In this paper, we investigate the BER characteristics of the block linear MMSE equalization by analyzing the condition number of the coefficient matrix in the linear system involved in the equalization process, and propose a new method to avoid the BER performance degradation at high SNR.

Low-Complexity Block Turbo Equalization for OFDM Systems in Time-Varying Channels

We propose low-complexity block turbo equalizers for orthogonal frequency-division multiplexing (OFDM) systems in time-varying channels. The presented work is based on a soft minimum mean-squared error (MMSE) block linear equalizer (BLE) that exploits the banded structure of the frequency-domain channel matrix, as well as a receiver window that enforces this banded structure. This equalization approach allows us to implement the proposed designs with a complexity that is only linear in the number of subcarriers. Three block turbo equalizers are discussed: two are based on a biased MMSE criterion, while the third is based on the unbiased MMSE criterion. Simulation results show that the proposed iterative MMSE BLE achieves a better bit error rate (BER) performance than a previously proposed iterative MMSE serial linear equalizer (SLE). The proposed equalization algorithms are also tested in the presence of channel estimation errors.

Novel Bluetooth Receiver Structure Deploying Improved Zero-Crossing Detection

Bluetooth is a short-range communication system facilitating ad hoc networking between various devices and terminals, using Gaussian-frequency-shift-keying modulation. In this paper, the authors present and analyze a novel receiver structure for Bluetooth, which is based on zero-crossing detection in combination with zero-forcing block linear equalization. Simulation results are presented, showing a favorable performance compared to other detectors

Frequency Domain Realization of Space-Time Receivers in Dispersive Wireless Channels

In this paper, we present a class of low complexity space-time receivers for frequency-selective channels in multiple input and multiple output (MIMO) systems. The main idea is that under certain conditions the matrices involved in the implementation of linear and nonlinear equalizers for MIMO systems can be approximated with block circulant matrices which can be inverted via block DFT operations. As result, the computational complexity of the receiver implementation is drastically reduced. First, we extend to MIMO systems two linear approaches originally derived in the framework of joint detection techniques for code division multiple access. Next, we develop a hybrid zero-forcing block decision feedback equalizer (DFE) and a minimum mean square error block DFE for MIMO systems, by performing in the frequency domain the feedback processing as in Benvenuto and Sostrato and the block linear equalizer as in Vollmer , while interference cancellation is performed in the time domain. Last, we extend to the frequency domain the fully connected ordered successive interference cancellation DFE. We show that these receivers yield almost the same performance as the original space-time receivers implemented in the time domain, and their computational complexity is lower, even against state of the art fast time-domain realizations

Low-Complexity Banded Equalizers for OFDM Systems in Doppler Spread Channels

Recently, several approaches have been proposed for the equalization of orthogonal frequency-division multiplexing (OFDM) signals in challenging high-mobility scenarios. Among them, a minimum mean-squared error (MMSE) block linear equalizer (BLE), based on a band LDL factorization, is particularly attractive for its good tradeoff between performance and complexity. This paper extends this approach towards two directions. First, we boost the BER performance of the BLE by designing a receiver window specially tailored to the band LDL factorization. Second, we design an MMSE block decision-feedback equalizer (BDFE) that can be modified to support receiver windowing. All the proposed banded equalizers share a similar computational complexity, which is linear in the number of subcarriers. Simulation results show that the proposed receiver architectures are effective in reducing the BER performance degradation caused by the intercarrier interference (ICI) generated by time-varying channels. We also consider a basis expansion model (BEM) channel estimation approach, to establish its impact on the BER performance of the proposed banded equalizers.

Multi-User MIMO Mobile CDMA Uplink System Employing Turbo Coding and Joint Detection Through a Multipath Rayleigh Fading Channel

In this paper, a generalized multiple-input multiple-output (MIMO) antenna system that can be fitted to the uplink of a wireless communication system is considered for the general case of multi-user. At the transmitter, the information bits are Turbo coded, then interleaved and passed through a serial-to-parallel converter. The channel is assumed bad urban suffering from multipath Rayleigh fading resulting in inter-symbol and multiple access interferences (ISI and MAI). At the front-end of the receiver, a number of receiving antennas are used followed by a joint multi-user estimator based on the Minimum Mean Square Error Block Linear Equalizer (MMSE-BLE). Computer simulations demonstrate a significant performance improvement in both single user and multi-user cases.

On low-complexity joint-detection techniques for TD-CDMA

This paper is focused on low-complexity joint-detection (JD) algorithms, where the computational complexity is reduced using banks of discrete Fourier transformations. Mainly, we have developed a fast hybrid zero-forcing block decision-feedback equalizer (H-ZF-BDFE) combining the Fourier-based JD scheme (IEEE J. Sel. Areas Commun., vol. 19, p. 1461, 2001) with the fast decision-feedback structure (F-ZF-BDFE) IEEE J. Sel. Areas Commun., vol. 19, p. 245, 2001. In a Rayleigh frequency-selective fading channel, the new structure yields an improvement in E/sub b//N/sub 0/ of almost 2 dB against the fast block linear equalizer (BLE) (IEEE J. Sel. Areas Commun., vol. 19, p. 1461, 2001) at a bit error rate (BER)=10/sup -3/. Moreover, it has the same performance as the F-ZF-BDFE, but the computational complexity for the signal processing is reduced by almost 50%.

Time-varying FIR equalization for doubly selective channels

We propose a time-varying (TV) finite impulse response (FIR) equalizer for doubly selective (time- and frequency-selective) channels. We use a basis expansion model (BEM) to approximate the doubly selective channel and to design the TV FIR equalizer. This allows us to turn a complicated equalization problem into an equivalent simpler equalization problem, containing only the BEM coefficients of both the doubly selective channel and the TV FIR equalizer. The minimum mean-square error (MMSE) as well as the zero-forcing (ZF) solutions are considered. Comparisons with the block linear equalizer (BLE) are made. The TV FIR equalization we propose here unifies and extends many previously proposed serial equalization approaches. In contrast to the BLE, the proposed TV FIR equalizer allows a flexible tradeoff between complexity and performance. Moreover, through computer simulations, we show that the performance of the proposed MMSE TV FIR equalizer comes close to the performance of the ZF and MMSE BLE, at a point where the design as well as the implementation complexity are much lower.