Multiple-symbol Detection Research Articles

Research on FM Telemetry Software Demodulation Algorithms

Aimed at the problem that the demodulation threshold of non-coherent demodulation technology of PCM/FM telemetry system using frequency modulation in the present situation of aerospace measurement and control is higher, research a kind of multiple symbol detection based on maximum likelihood thought (Multi-Symbol Detection, MSD) demodulation method. This paper introduces the principle of multiple symbol detection and aiming at the shortcomings of the previous synchronization method, studies a kind of symbol decision process and synchronization of the combination of synchronization method.

Research on Soft Demodulation of Telemetry Signal Based on the Orthogonal Complex Baseband Rotating MSD

For PCM/FM telemetry signal demodulation, compared to traditional demodulation method, multiple Symbol Detection technology (Multi - Symbol Detection, MSD) is an effective method for a lower demodulation threshold.[ For software MSD demodulation in the process of PCM/FM telemetry signal algorithm is too complex and cause a large computation takes longer problem, research based on baseband complex rotating orthogonal MSD soft PCM/FM signal demodulation method, this algorithm can greatly reduce the amount of calculation of MSD and performance with the ordinary MSD are basically identical. The simulation and test results verify the effectiveness of the proposed method.

BER Analysis of Decision-Feedback Multiple-Symbol Detection in Noncoherent MIMO Ultrawideband Systems

In this paper, we investigate noncoherent multiple-input-multiple-output (MIMO) ultrawideband (UWB) systems where the signal is encoded by differential space-time block code (DSTBC). DSTBC enables noncoherent MIMO UWB systems to achieve diversity gain. However, the traditional noncoherent symbol-by-symbol differential detection (DD) for DSTBC-UWB suffers from performance degradation compared with coherent detection. We introduce a noncoherent multiple-symbol detection (MSD) scheme to enhance the performance of DSTBC-UWB systems. Although the MSD scheme can boost the performance more as the observation window size becomes larger, the complexity of the exhaustive search for MSD also exponentially increases in terms of the window size. To decrease the computational complexity, the concept of decision feedback (DF) is introduced to the MSD for DSTBC-UWB in this paper. The resultant DF-MSD yields reasonable complexity and solid performance improvement. We provide the bit-error-rate analysis for the proposed DF-MSD. Both theoretical analysis and simulation results validate the proposed scheme.

Successive AF/DF Relaying in the Cooperative DS-CDMA Uplink: Capacity Analysis and Its System Architecture

A successive-relaying-aided network (SRAN) is designed for a multiuser spread-spectrum scenario conceived for noncoherent (NC) detection to convert the typical 50% half-duplex relaying induced throughput loss to a potential user-load reduction of the code-division multiple-access (CDMA) system, where the NC allows us to avoid the extra power consumption imposed by channel estimation. We commence by evaluating the NC discrete-input-continuous-output memoryless channel (DCMC) capacity of both the amplify-and-forward-based (AF) and decode-and-forward-based (DF) SRANs in the direct-sequence CDMA (DS-CDMA) uplink (UL). While NC detection has the added benefit of eliminating both the pilot overhead and the power-hungry channel estimation, it tends to form an error floor at high Doppler frequencies. We mitigate this problem using multiple-symbol detection, which increases the detection complexity upon extending the detection window. Finally, a relay-aided soft-input-soft-output multiple-symbol differential sphere detection (SISO-MSDSD) CDMA regime is proposed, which significantly reduces the system's complexity without sacrificing its performance.

The Problems in Signal Detection of Multi-Band Spread Spectrum

Compared with the traditional direct sequence spread spectrum technology，Multi-band Spread Spectrum have great advantages. According to the basic principle of Multi-band Spread Spectrum, this paper Established the Multi-band Spread Spectrum system model, discusses the signal detection problems in terms of multi-band spread spectrum. Based on the results, it obtained the ruling methods of Gaussian white noise channel under multiple symbols detection and binary bits detection and likelihood ratio information theoretical expressions. And it finds that the two tests have the same mistake-symbol performance through the simulation. The experimental results show that multiple symbol detection and RS code used in conjunction with will achieve better performance.

Decision-feedback multiple symbol detection for differential space-time block coded UWB systems

The symbol-by-symbol differential detection scheme, originally employed to detect differential space-time block coded (DSTBC) ultra-wideband (UWB) signal in previous work, suffers from a performance degradation compared with coherent detection. In this paper, a noncoherent multiple symbol detection (MSD) scheme is proposed to enhance the performance of DSTBC-UWB system. After the signal model of DSTBC-UWB is analyzed, the optimal maximum likelihood (ML) MSD is derived and then a suboptimal ML-MSD is obtained by channel approximating. However, exhaustive search based MSD is impractical in DSTBC-UWB systems since its complexity increases exponentially with observation window size. To decrease the computational complexity, the decision-feedback (DF) scheme is introduced to MSD. The resultant DF-MSD yields reasonable complexity and solid performance improvement.

Soft-Input Soft-Output Multiple Symbol Differential Detection for UWB Communications

Multiple-symbol differential detection (MSDD) is a promising technique to enhance the performance of ultra-wideband (UWB) communications without estimating the channel explicitly. In this context, the generalized log-likelihood ratio test (GLRT) for MSDD was developed, and the hard-output multiple-symbol detector was proposed, which exhibits considerable bit-error-rate (BER) performance improvement over transmitted reference transmissions. In this paper, we further improve the system performance by incorporating error correction code (ECC) and iterative processing at the receiver. The soft-input soft-output (SISO) MSDD is developed to deliver a posteriori information to the outer ECC decoder and enables iterative detection and decoding. Simulations show that the iterative processing achieves significant gains over the existing MSDD in UWB communications.

Designing Low-Complexity Near-Optimal Multiple-Symbol Detectors for Impulse Radio UWB Systems

Multiple-symbol detection has recently caught attention in ultrawideband (UWB) communications because of its high performance without requiring explicit channel estimation. In this context, the generalized likelihood ratio test (GLRT) for multiple-symbol detection problem is developed to jointly detect multiple symbols, which exhibits considerable error performance improvement over transmitted reference transmissions methods. Unfortunately, the GLRT is a Boolean quadratic programming (BQP) problem, which is generally nondeterministic polynomial hard (NP-hard). In this paper, we propose two near-optimal detectors with polynomial complexity. The first detector performs semidefinite relaxation to approximately solve the BQP problem (called SDP-MSD). The second detector is based on a sphere-based relaxation of the BQP problem [we refer to this as modified unconstrained relaxation multiple-symbol detector (MUR-MSD)]. Both detectors achieve near-optimal performance, while the SDP-MSD performs slightly better than the MUR-MSD at the price of higher computational complexity. Furthermore, the MUR-MSD can be treated as a further nontight relaxation of SDP-MSD. Simulations are utilized to validate our findings and to demonstrate performance robustness to multiaccess interference.

Multiple-symbol M-sphere Detection based on Linear Radius for Differential Unitary Apace-time Modulation Systems

Abstract In view of the problems of high computational complexity and difficulties in pipelining and parallel processing existed in sphere decoding (SD) algorithm for multiple-symbol differential detection (MSDD) system, the M-SD detection which combined M algorithm with SD is presented.. In M-SD, a new spherical radius scheme called linear radius is proposed to reduce the retained branches. It largely reduces the times of computing Frobenius norm square by a gradually decreasing radius with signal-to-noise ratio (SNR) increases. Based on the linear radius, M algorithm is combined with SD at low SNR to maintain a stable retained branch size and further reduce complexity. Simulation results show that M-SD detection with the constraint of linear radius significantly reduces the overall complexity compared with regular SD and its complexity is more stable. , Especially the complexity of M-SD can get more than 90% reduction when SNR £ 5dB, while the bit error rate (BER) performance is very close to SD within 0.1dB loss.

Sphere Decoding Based Multiple Symbol Detection for Differential Space-Time Block Coded Ultra-Wideband Systems

In this letter, a sphere decoding (SD) based noncoherent multiple symbol detection (MSD) scheme is proposed for differential space-time block coded (DSTBC) ultra-wideband (UWB) impulse radio systems. Exhaustive search based maximum likelihood (ML) MSD is impractical in DSTBC-UWB systems since its complexity exponentially increases with observation window size. To decrease the computational complexity, the original MSD metric is transformed into another equivalent form which can be implemented by SD for DSTBC-UWB systems.

Differential Encoding by a Look-Up Table for Quadrature-Amplitude Modulation

In this paper, we propose a novel differential encoder for QAM (quadrature-amplitude modulation), by a look-up table instead of a rule. Using a table for differential encoding has the advantages of both low complexity and good error performance. We propose algorithms to construct the table for maximizing the minimum noncoherent distance and minimizing the number of different data bits between two codewords with small noncoherent distance. For 16QAM and 32QAM, we show that the differential encoders obtained by the proposed algorithms are optimal in terms of minimum noncoherent distance. Differential detectors for QAM, including a reduced-complexity two-symbol detector and multiple-symbol detectors, are proposed as well. Simulation results of 16QAM show that the proposed differential encoder provides significant gain over existent differential encoders as expected by distance analysis, and the proposed low-complexity multiple-symbol differential detector can further improve the error performance.

Fast multiple-symbol detection for free-space optical communications

In this paper, we investigate noncoherent detection, i.e. detection assuming the absence of channel state information at the receiver, of on-off keying in an intensity modulation and direct detection (IM/DD) free-space optical (FSO) system. To partially recover the performance loss associated with symbol- by-symbol noncoherent detection, we consider the application of multiple-symbol detection (MSD), in which block-wise decisions are made using an observation window of several bit intervals. Specifically, we develop a fast search algorithm for optimal MSD and propose a reduced-complexity decision metric suitable for suboptimal MSD; performance results confirm that the optimal and suboptimal metrics perform comparably well. Significantly, the complexity of our receiver, on a per bit-decision basis, is only logarithmically dependent on the observation window size. We also present the framework for a decision-feedback receiver and obtain performance expressions for the ideal case of error-free feedback; these expressions serve as an upper bound to the performance of MSD. Analytical and simulation results indicate that as the observation window size increases, the performance of the MSD receiver approaches that of detection with channel state information. The conclusion is reached that the proposed implementation provides an attractive low-complexity mechanism for performing noncoherent MSD in FSO systems.

Multiple-symbol detection for photon-counting MIMO free-space optical communications

We employ a photon-counting signal model of a multiple-input multiple-output (MIMO) free-space optical (FSO) system and investigate detection assuming the absence of channel state information (CSI) at the receiver, in moderate to strong atmospheric turbulence. The considered modulation format is on-off keying with repetition coding across the transmitters. To partially recover the performance loss associated with symbol-by-symbol detection without CSI, we consider the application of multiple-symbol detection (MSD) to equal gain combined (EGC) statistics. We develop a fast search algorithm for EGC-MSD and propose a suboptimal closed-form decision metric suitable for reduced-complexity implementation; performance results confirm that the true and suboptimal metrics perform comparably well. Significantly, the complexity of our receiver, on a per bit-decision basis, is only logarithmically dependent on the observation window length N, and is effectively independent of the size of the MIMO array. We also present the framework for a decision-feedback receiver and obtain performance expressions for the ideal case of error-free feedback; these expressions serve as an upper bound to the performance of EGC-MSD. Analytical and simulation results indicate that the system effectively realizes the diversity gains expected from a MIMO configuration and that the performance of the EGC-MSD receiver approaches the EGC with CSI lower bound with increasing N.

Noncoherent Multiple-Symbol Detection in Coded Ultra-wideband Communications

Recently, ultra wideband (UWB) impulse radio systems based on noncoherent detection, such as transmitted reference and differential modulation systems, have drawn a lot of attention for their potential applications in low-rate and low-cost communications. In this paper, a unified approach is presented to develop and analyze a noncoherent multiple-symbol detection (MSD) algorithm for various UWB signaling formats in multi- path environments. Pair-wise error probabilities of coherent and noncoherent MSD algorithms are derived and compared. The intrinsic connection between the coherent and noncoherent MSD algorithms is revealed, tradeoff curves between their performance and complexity are obtained, and optimal transmission signal design rules for noncoherent detection are provided. The bit error rates are shown through simulations to verify the analysis and to evaluate the performance of the developed algorithms in realistic environments.

On Multiple Symbol Detection for Diagonal DUSTM Over Ricean Channels

This letter considers multiple symbol differential detection for multiple-antenna systems over flat Ricean-fading channels when partial channel state information (CSI) is available at the transmitter. Using the maximum likelihood (ML) principle, and assuming perfect knowledge of the channel mean, we derive the optimal multiple symbol detection (MSD) rule for diagonal differential unitary space-time modulation (DUSTM). This rule is used to develop a sphere decoding bound intersection detector (SD-BID) with low complexity. A suboptimal MSD based decision feedback DD (DF-DD) algorithm is also derived. The simulation results show that our proposed MSD algorithms reduce the error floor of conventional differential detection and that the computational complexity of these new algorithms is reasonably low.

Improved autocorrelation demodulation receivers based on multiple-symbol detection for UWB communications

The autocorrelation demodulation (ACD) has potential for use in medium-range low-cost UWB communications, however, its weak performance is a bottle neck. To improve ACD's performance, it is proposed to combine the multiple-symbol detection with ACD to form a multiple-symbol-based ACD receiver. In contrast to ordinary ACD scheme that uses symbol-by-symbol decision, the proposed structure uses block-based multiple-symbol joint decision. Performance of the new scheme is evaluated analytically for arbitrary block sizes employing Gaussian approximation approach. The accuracy of the method is verified by computer simulation. The evaluation shows that the proposed scheme offers several dB improvement in performances with only a moderate increase in complexity.

Noncoherent Receivers for Multichip Differentially Encoded DS-CDMA

We design and analyze novel noncoherent receivers for direct-sequence code-division multiple access (DS-CDMA) with multi-chip (MC) differential encoding (DE). The proposed receivers for MC-DE are based on multiple-symbol detection and decision-feedback differential detection, which have been previously applied for symbol-level DE. While the complexity of the proposed receivers is moderate, it is shown that they enable large performance gains over conventional differential detection for various channel environments, such as additive white Gaussian noise (AGWN) channels, Rayleigh and Ricean fading channels, and channels with frequency offset and phase noise. Furthermore, we show that in most cases MC-DE outperforms single-chip differential encoding and, in addition, decreases receiver complexity. Another result of this paper is that quaternary differential phase-shift keying (QDPSK) is more suitable for chip-level DE than binary DPSK.

A soft-detector based on multiple symbol detection for double differential modulation

We consider the problem of soft-detection for communication systems employing double differential modulation and forward error correction codes, for example, a convolutional code. We propose a soft-detector (based on the multiple symbol heuristic detector) with low computational complexity. Simulation results are provided to show the superior performance of the new soft-detector.

Trellis-Coded Differential Unitary Space-Time Modulation with Multiple-Symbol Detection

Summary Multiple-symbol detection (MSD) of differential unitary space-time modulation (DUSTM) uses maximum likelihood sequence detection of μ symbols to achieve a performance gain over conventional 2 symbol differential detection (DD). Using results from MSD, an additive symbol by symbol metric is developed for noncoherent detection of trellis-coded DUSTM (TC-DUSTM). In the Rayleigh fading channel, performance is almost as good as the performance of coherent detection of TC-DUSTM when μ is large, while computational complexity increases only linearly with the size of μ.

Multiple-symbol double-differential detection based on least-squares and generalized-likelihood ratio criteria

Two algorithms for double-differential detection of multiple phase-shift keying modulation are proposed, based on a least-squares criterion and a generalized-likelihood ratio test, respectively. While both algorithms take advantage of the performance gain obtained by observing the received signal over an observation interval longer than that required for symbol-by-symbol detection, the former has the important advantage of reduced implementation complexity, whereas the latter offers better performance.