Reduced-state Sequence Estimation Research Articles

A Reduced Complexity Ungerboeck Receiver for Quantized Wideband Massive SC-MIMO

Employing low resolution analog-to-digital converters in massive multiple-input multiple-output (MIMO) has many advantages in terms of total power consumption, cost and feasibility. However, such advantages come together with significant challenges in channel estimation and data detection due to the severe quantization noise present. In this study, we first derive linear minimum mean-square-error channel estimator for cyclic-prefix (CP) free single carrier MIMO (SC-MIMO) under frequency-selective channel. Then, we propose a novel iterative receiver for quantized CP-free uplink wideband SC-MIMO for uncorrelated or correlated Rayleigh and Rician fading channels. This detector utilizes an efficient message passing algorithm based on Bussgang decomposition, reduced state sequence estimation and Ungerboeck factorization. Therefore, it achieves remarkable complexity reduction and exhibits significant performance advantages compared to the existing quantized SC-MIMO receivers from the literature.

Iterative Processing Structure for the Single-Channel Mixture of Digital-Modulated Adjacent-Frequency Source Signals

Considering the high cost and complexity of multiple-channel blind source separation, single-channel solutions have elicited a significant amount of interest in source separation. Joint maximum likelihood sequence estimation implemented by the Viterbi algorithm (VA) is a seemingly ultimate solution to the problem of data transmission over dispersive channels. However, both joint reduced-state sequence estimation (JRSSE) and joint delayed-decision feedback sequence estimation (JDDFSE) have numerous shortcomings when applied to single-channel blind signal separation. Hence, joint double-direction DDFSE (JDD-DDFSE) is proposed in this article. JDD-DDFSE employs joint VA (JVA) of the low-order channel twice. The estimated symbols from the initial JVA are utilized to equalize the causal and non-causal taps of the channel beyond the trellis state in the second JVA. A method that can derive the log likelihood ratio of the estimated symbols is provided; the complexity of this method is considerably lower than that of soft-output VA or the BCJR algorithm. Hence, the entire computation complexity of the iterative separation structure basically remains unchanged compared with that of the no-iteration structure. For the non-causal channel, the proposed algorithm has the lowest computation complexity and demonstrates a separation performance similar to that of conventional JVA, JRSSE, and JDDFSE algorithms.

PN-PAM scheme for short range optical transmission over SI-POF \u2014 an alternative to Discrete Multi-Tone (DMT) scheme

BackgroundHow to deal with the time-dispersive channel is the main challenge faced by the short-range optical communication systems. In this work a novel pseudo-noise sequence (PN) assisted pulse-amplitude modulated (PN-PAM) transmission scheme for short-range optical communication systems is proposed in this work. With the help of the PN based channel estimation, minimum-phase pre-filter and reduced-state sequence estimation based equalizer, the proposed PAM transmission scheme can significantly reduce the training overhead for channel estimation in the classical PAM systems using decision feedback equalizer (DFE). In addition, the proposed PAM transmission scheme can effectively avoid the error propagation phenomenon in the classical DFE.ResultsTheoretical study shows that the proposed PAM scheme can achieve a 1.5 dB SNR gain with PAM-8 modulation over 50 m step-index polymer optical fiber (SI-POF) channel at a desired BER level of 1×10−3 and 1.2 Gbps transmission rate. Furthermore the hardware experiment using commercially available components proves the improvements in the proposed PAM transmission scheme.ConclusionThe novel PAM transmission scheme is compared to the optimized discrete multi-tone (DMT) transmission with bit-loading. The experimental results show that for a transmission distance less than 50 m over SI-POF, DMT systems outperform the PAM systems. However, for a SI-POF transmission over the distance longer than 50 m, the proposed scheme can reach a better performance than the DMT systems thanks to the advantage of a lower peak-to-average-power ratio.

Multihead Multitrack Detection for Next Generation Magnetic Recording, Part II: Complexity Reduction — Algorithms and Performance Analysis

To achieve large storage capacity on magnetic hard disk drives, very high track density is required, causing severe intertrack interference (ITI). Multihead multitrack (MHMT) detection has been proposed to better combat the effects of ITI. Such detection, however, has prohibitive implementation complexity. Reduced-state sequence estimation (RSSE) is a promising technique for significantly reducing the complexity, while retaining good performance. In this paper, several different MHMT models are considered, including symmetric and asymmetric 2H2T systems, and a symmetric 3H3T system. By carefully evaluating the effective distance between two input symbols, we propose optimized set partition trees for each channel model. Different trellis configurations for RSSE are constructed based on the desired performance/complexity tradeoff. Simulation results show that the reduced MHMT detector can achieve near maximum-likelihood (ML) performance with a small fraction of the original number of trellis states. We also use error event analysis to explain the behavior of RSSE. The proposed algorithm could be potentially applied to next generation magnetic recording systems, especially when the ML detector is infeasible due to the high computational complexity.

Low-Complexity Adaptive Threshold Detection for Molecular Communication.

This paper studies detection algorithms for diffusion-based molecular communication systems, where molecules freely diffuse as information carrier from a transmitter to a receiver in a fluid medium. The main limitations are strong intersymbol interference due to the random propagation of the molecules, and the low-energy/low-complexity assumption regarding future implementations in so-called nanomachines. In this contribution, a new biologically inspired detection algorithm suitable for binary signaling, named adaptive threshold detection, is proposed, which deals with these limitations. The proposed detector is of low complexity, does not require explicit channel knowledge, and seems to be biologically reasonable. Numerical results demonstrate that the proposed detector can outperform the common low-complexity fixed threshold detector under certain conditions. As a benchmark, maximum-likelihood sequence estimation (MLSE) and reduced-state sequence estimation (RSSE) are also analyzed by means of numerical simulations. In addition, the effect of molecular denaturation on the detection performances is studied. It is shown that denaturation generally improves the detection performances, while RSSE is able to outperform MLSE in the case of no denaturation.

Multihead Multitrack Detection With Reduced-State Sequence Estimation

To achieve ultra-high storage capacity, the data tracks are squeezed more and more on the magnetic recording disks, causing severe intertrack interference (ITI). The multihead multitrack (MHMT) detector is proposed to better combat ITI. Such a detector, however, has prohibitive implementation complexity. In this paper we propose to use the reduced-state sequence estimation (RSSE) algorithm to significantly reduce the complexity, and render MHMT practical. We first consider a commonly used symmetric two-head two-track (2H2T) channel model. The effective distance between two input symbols is redefined. It provides a better distance measure and naturally leads to an unbalanced set partition tree. Different trellis configurations are obtained based on the desired performance/complexity tradeoff. Simulation results show that the reduced MHMT detector can achieve near maximum-likelihood (ML) performance with a small fraction of the original number of trellis states. Error event analysis is given to explain the behavior of RSSE algorithm on 2H2T channel. Search results of dominant RSSE error events for different channel targets are presented. We also study an asymmetric 2H2T system. The simulation results and error event analysis show that RSSE is applicable to the asymmetric channel.

A Reduced-State Ungerboeck Type MAP Receiver with Bidirectional Decision Feedback for M-ary Quasi Orthogonal Signaling

In this paper, we propose a generic receiver based on optimum maximum likelihood sequence estimation (MLSE) employing a generalized Ungerboeck metric with significantly reduced complexity for the general class of M-ary quasi orthogonal signaling (MOS) in severe multipath fading channels. First, by using the factor graph (FG) of the obtained generalized Ungerboeck metric for MOS and sum-product algorithm (SPA) framework, a highly efficient reduced state sequence estimation (RSSE) algorithm is proposed that operates on forward and backward directions and is directly applied to unwhitened channel matched filter (CMF) and code matched filter outputs at symbol rate. The proposed structure, generating the a posteriori probabilities (APP) by bidirectional RSSE recursions, are substantiated with symbol rate bidirectional decision feedback (BDF) based on surviving paths in order to eliminate the post- and pre-cursor inter-symbol interference (ISI) as well as multi code interference (MCI) due to the non-ideal properties of the signaling waveforms and multipath channel. It appears as the unification of Ungerboeck type reduced trellis equalization framework for MOS and achieves near-optimum performance especially for channels with large dispersion. Second, we identify a bias term through an error probability analysis which helps us improve the proposed receiver's performance. Furthermore, a tight approximation for the bit error rate (BER) of the proposed receiver is derived. These analyses lead to significant insight on the selection of system parameters and clearly demonstrate the high performance and efficiency of the proposed scheme by a proper choice of the signaling parameters.

Adaptive Selective State-Transition Decoding: A Combined Approach for Trellis Coded Modulation Scheme

We are presenting a new suboptimum decoding strategy, namely, Adaptive Selective StateTransition Decoding (ASSTD) for Trellis Coded Modulation schemes transmission over band-limited ISI channels. The ASSTD is a combined approach provides an improved error performance over Reduced State Sequence Estimation (RSSE) techniques which are in practical use. The ASSTD operates on two different concepts and has the flexibility to work with a controlled complexity. Simulation results are obtained for static band-limited ISI channels. The results show that the ASSTD can be extended to fading channels.

Channel-Based Multi-Dimensional Set Partitioning for MIMO Reduced-State Sequence Estimation

A multi-dimensional set partitioning (MDSP) is proposed for reduced-state sequence estimation of multi-path fading multiple input multiple output (MIMO) channels. The proposed MDSP takes channel state information into account when making a set partition because MIMO channels change the distance between symbol vectors in a multi-dimensional constellation. To reduce complexity of the proposed MDSP, we propose an efficient MDSP algorithm which exploits only typical error vectors for partitioning.

Sphere constrained detection of complementary code keying signals transmitted over frequency-selective channels

In the wireless local area network (WLAN) standard IEEE 802.11b, complementary code keying (CCK) modulation has been adopted for the high data rate transmission mode. In this paper, complexity reduction for block reduced-state sequence estimation (bRSSE), tailored for CCK transmission over frequency-selective channels, is considered. A trellis diagram for the chip phases of the codewords fully describes the CCK code properties. Subset trellises are derived from the full CCK trellis diagram based on set partitioning of the multidimensional CCK code set. The CCK subset trellises connect consecutive bRSSE states forming a compound trellis. The Viterbi algorithm (VA) with per-survivor processing is applied to the compound trellis to take the inter-chip interference into account. Inter-codeword interference is also accounted for by state-dependent decision feedback. The resulting scheme is denoted as bRSSE-pS and has a significantly lower complexity than bRSSE with bruteforce search over the entire CCK code set. By introducing a sphere constraint on the overall decoding trellis (SC-bRSSEpS), the complexity of bRSSE-pS can be further reduced. Omitting states in the CCK subset trellises that violate the sphere constraint, edges that emanate from such states can be pruned, and the average number of metric calculations per CCK trellis segment can be reduced. All presented schemes are also specialized to the case of a single bRSSE trellis state, resulting in block decision-feedback equalization (bDFE) algorithms with per-survivor processing and sphere decoding (bDFE-pS and SC-bDFE-pS, respectively). Simulation results show that the performance of bRSSE-pS (bDFE-pS) and SC-bRSSE-pS (SCbDFE-pS), respectively, is essentially equivalent to that of bRSSE (bDFE) with brute-force search over the entire CCK code set, while complexity is significantly reduced.

Reduced-State Sequence Estimation with Level Adaptation for High-Density Disc

We report a new data-reproducing scheme for a high density of over 40 Gbytes with a commercial Blu-ray recordable disc. Bit error rates (bERs) of 3×10-5 and 3.3×10-3 with 45 and 50 Gbytes, respectively, were experimentally obtained using this new data-reproducing scheme, which indicates the possibility of achieving 50 Gbytes data storage with a commercial single-layer Blu-ray disc.

Field Tests of Digital Audio Broadcasting in the FM Band Based on Continuous Phase Modulation

We propose a new broadcasting scheme for the transmission of digital audio signals simultaneously with existing analog frequency modulation radio (88-108 MHz) in adjacent channels, denoted as in-band-adjacent channel system (IBAC) . This broadcasting scheme enables the transmission of digital audio data in CD quality with a data rate of up to 156 kb/s within an FM 200 kHz channel. The digital transmission is based on continuous phase modulation (CPM) and a proper reduced-state sequence estimator. CPM is the digital equivalent of the analog FM and has a constant envelope, too. This is a great advantage, because on the one hand existing nonlinear amplifiers can be reused to achieve good efficiency and low out-of-band radiation, on the other hand it enables the broadcasting companies to reuse the existing infrastructure (amplifiers, antennas, frequency bands) which reduces the investment costs and improves the chances for an introduction of CPM as a new broadcasting standard. With the proposed method, the power level and the symbol rate of the transmitter signal is determined in a manner that the interference the CPM signal poses for the analog FM signal in adjacent channels remains below a level according to the radio frequency emission mask defined by international rules. Due to the multipath propagation of the transmitted signal, the transmission behavior of typical radio channels is characterized by high dispersion of up to 85 . For the parameterization of this demonstrator, the channel memory amounts 14 bits. Due to the implementation of the hardware, the symbol duration is different in this case from the one in . Since Viterbi detection is not feasible due to the number of channel states, detection is performed by a reduced-state sequence estimator that is able to eliminate the complete channel interferences by decision feedback . We will describe in this paper the underlying algorithms of synchronization and channel estimation, since they are important components of a real receiver. To underline the suitability of the CPM based broadcasting scheme, we have conducted field tests in the city area of Hanover with a real broadcasting evaluation system based on the proposed CPM broadcasting scheme with support of the northern German broadcast service (NDR) in Hanover with encouraging results.

Transmission and Reception Concepts for WLAN IEEE 802.11b

State-of-the-art wireless local area network (WLAN) IEEE 802.11b terminals employ complementary code keying (CCK) as modulation format. In this paper, receiver concepts tailored for CCK transmission over frequency-selective fading channels are presented in a unified and systematic framework. First, optimum maximum-likelihood (ML) detection for CCK signaling is considered. Second, for complexity reduction, minimum mean-squared error block decision-feedback equalization (MMSE-DFE) is investigated and reduced-state sequence estimation (RSSE) is considered on the basis of an Ungerbock-like set partitioning of the multidimensional CCK code wordset. In order to improve the reliability of CCK transmission over fading channels, time-reversal space-time block codes (TR-STBCs) combined with receive diversity are applied. Simulation results of the considered suboptimum receivers are compared with a performance approximation for optimum detection. Our results demonstrate the excellent performance of the advocated equalization schemes and the significant gains that can be achieved with TR-STBCs and receive diversity in typical WLAN environments

A novel RSSE-PSP equalizer with an adaptive pre-filter

A reduced-state sequence estimation (RSSE) receiver based on per-survivor processing (PSP) in conjunction with an adaptive pre-filter is proposed in this paper. In RSSEPSP, each survivor path holds an estimated value of the channel impulse response (CIR), which is updated by adaptive algorithm during the data transmission. Based on the different estimated channel values of each survivor path, corresponding pre-filters are calculated via the Levinson-Durbin algorithm, which can track the time-varying channel adaptively. Computer simulations indicate that the RSSE-PSP equalizer with the new adaptive pre-filter works much better than those with the prevenient pre-filters in ISI channel.

Decision-Feedback Sequence Estimation for Time-Reversal Space–Time Block-Coded Transmission

In this correspondence, we consider three different decision-feedback sequence-estimation (DFSE) schemes originally proposed for single-input-single-output channels for time-reversal space-time block coding (TR-STBC). The first scheme is called unwhitened DFSE (U-DFSE) and performs reduced-state sequence estimation based on the output of the spatio-temporal matched filter (MF), typically employed in TR-STBC. The second approach improves upon U-DFSE by subtracting a bias term caused by anticausal interference from the U-DFSE metric. In the third scheme, the noise component in the output of the spatio-temporal MF is first whitened using a prediction-error filter and, subsequently, whitened DFSE (W-DFSE) is performed. As a relevant example, all three DFSE schemes are compared for the global system for mobile communications/enhanced data rates for GSM evolution (GSM/EDGE) system and typical channel profiles. Our results show that for binary modulation (as used in GSM) U-DFSE and its improved version can approach the performance of W-DFSE for the full range of delay spreads relevant for GSM and EDGE. On the other hand, for high-level modulation (as used in EDGE) only W-DFSE gives a satisfactory performance, if a low trellis complexity is desired.

Digital audio broadcasting in the fm band based on continuous phase modulation

A method for broadcasting digital audio signals simultaneously with existing analog frequency modulation radio (88-108 MHz) in adjacent channels is presented. The digital transmission is based on continuous phase modulation (CPM) and a proper reduced-state sequence estimator. With the proposed method, the power level and the symbol rate of the transmitter signal is determined in a manner that the interference the CPM signal poses for the analog FM signal in adjacent channels remains below a level according to the radio frequency emission mask defined by international rules. Due to the multipath propagation of the transmitted signal, the transmission behavior of the radio channel is determined by high dispersion up to 85 /spl mu/s. With the selected bit rate, the receiver has to cope with a channel memory of up to 17 bits. Since Viterbi detection is not feasible due to the number of channel states, detection is performed by a reduced-state sequence estimator that is able to eliminate the complete channel interference by decision feedback. Simulation results show that the detector almost achieves the detection quality of the optimum receiver. CPM achieves data rates of up to 200 kb/s inside a 200 kHz FM channel, which is sufficient for transmission of digital compressed audio signals at compact disc quality. The encouraging results of field tests will be published in another paper.

Efficient equalization and symbol detection for 8-PSK EDGE cellular system

A new method is presented for channel equalization and symbol detection of an enhanced data rate for Global System for Mobile (GSM) communication and IS-136 evolution (EDGE) cellular system in which eight phase-shift keying (8-PSK) modulation is employed. The new method iteratively minimizes the Euclidean distance between the detected and received signal sequences, with neighbor symbol perturbation to reduce the computational complexity. The new algorithm is computationally efficient and can also be easily implemented into commercial signal processors. Simulation results comparing our method with the reduced-state sequence-estimation (RSSE) method, both with and without set partitioning, are presented.

On reduced complexity equalisation for EDGE

A reduced complexity equaliser involving the novel reduced-state sequence estimation is presented. It is difficult to employ maximum likelihood sequence estimation for EDGE since it uses the 8PSK modulation scheme and hence high computational complexity is incurred. Consequently, a sub-optimum technique offering an approximation to the optimum performance is required. The proposed method is capable of equalisation with four states, at the expense of only 1dB trade-off in performance.

Equalization concepts for EDGE

An equalization concept for the novel radio access scheme Enhanced Data rates for GSM Evolution (EDGE) is proposed by which high performance can be obtained at moderate computational complexity. Because high-level modulation is employed in EDGE, optimum equalization as usually performed in Global System for Mobile Communications (GSM) receivers is too complex and suboptimum schemes have to be considered. It is shown that delayed decision-feedback sequence estimation (DDFSE) and reduced-state sequence estimation (RSSE) are promising candidates. For various channel profiles, approximations for the bit error rate of these suboptimum equalization techniques are given and compared with simulation results for DDFSE. It turns out that a discrete-time prefilter creating a minimum-phase overall impulse response is indispensable for a favorable tradeoff between performance and complexity. Additionally, the influence of channel estimation and of the receiver input filter is investigated and the reasons for performance degradation compared to the additive white Gaussian noise channel are indicated. Finally, the overall system performance attainable with the proposed equalization concept is determined for transmission with channel coding.

On the distribution of zeros of mobile channels with application to GSM/EDGE

The distribution of zeros of mobile channels is investigated and the results obtained are applied to the GSM/EDGE system. The taps of the discrete-time overall impulse response can be modeled as correlated complex Gaussian random variables, where the correlations depend on the transmit filter, the power delay profile of the channel, and the receiver input filter. For calculation of the density of zeros of the overall transfer function, a result from the mathematical literature is used. From this density, two cumulative distributions which are relevant for the design of suboptimum receivers are derived. Our investigations show that for the power delay profiles specified for GSM/EDGE, an allpass prefilter which transforms the impulse response in its minimum phase equivalent should be employed if decision-feedback equalization (DFE) or reduced-state sequence estimation (RSSE) are used at the receiver. On the other hand, if impulse response truncation using a linear prefilter is applied, the truncated impulse response should have a length of three as shown.