Orthogonal Decoding Research Articles

Robust orbital-angular-momentum-based underwater acoustic communication with dynamic modal decomposition method.

Recently, acoustic communication employing orbital angular momentum (OAM) opens another avenue for efficient data transmission in aquatic environments. Current topological charge (TC) detection of OAM beams relies on the orthogonality among different-order OAM beams. However, such strategy requires measurements of the complete azimuthal acoustic pressure, which inevitably reduces the efficiency and increases the bit error rate (BER). To address these challenges, this study proposes a modified dynamic modal decomposition (DMD) method by partially sampling the acoustic field for precise TC detection. Numerical simulations confirm the accuracy of this approach in extracting single or multiple TCs magnitudes within a partially sampled acoustic field. We theoretically compare the performance of the modified DMD approach with conventional orthogonal decoding method. Simulation results indicate that our modified DMD scheme exhibits lower BER under the same noise interference and is more robust to the array misalignment. This research introduces an efficient demodulation solution for acoustic OAM communication, offering potential benefits for simplifying receiver array design and enhancing long-distance underwater data transmission.

High-Order Hadamard-Encoded Transmission for Tissue Background Suppression in Ultrasound Contrast Imaging: Memory Effect and Decoding Schemes.

Hadamard-encoded multipulses (HEM) transmit has recently been utilized for tissue background suppression in ultrasound contrast imaging to enhance the contrast-to-tissue ratio (CTR). Nonetheless, the second-harmonic component in HEM transmit results in residual tissue background after decoding and, thus, compromises the detection of contrast microbubbles. Theoretically, high-order HEM transmit can produce harmonic-free background but the memory effect, which considers the nonlinear contribution of previous bit waveform into the next one in the progress of harmonic generation, may limit the achievable tissue suppression. In this paper, three possible harmonic-free pairs using time-shifted subtraction (SH1, SH2, and SH3) in the fourth-order Hadamard decoding are analyzed and experimentally compared using hydrophone measurement and B-mode imaging. Moreover, the orthogonal decoding (OD) of HEM transmit is also proposed with pulse-inversion harmonic suppression (PIHS) to remedy memory effect on the tissue background. Results show that SH3, which utilizes the third and fourth rows for decoding, provides the lowest magnitude of tissue background among all possible decoding pairs and performs comparably to the reference PI and amplitude-modulation sequence in terms of CTR. For PIHS-OD, the pulse subtraction effectively removes the harmonic interferences from memory effect and, thus, further improves the CTR by 5.4 dB compared to SH3. For high-order HEM transmit, PIHS-OD can help to eliminate the residual tissue background due to memory effect and is comparable to Hadamard decoding in temporal resolution and possible motion artifacts.

Multi-Channel Detection System for Joint Position Based on Optical and Orthogonal Decoding

The multi-channel joint position detection system of measuring arm is of high precision, multi-channel and other special characteristic. This system uses hardware called DSPic30F microchip as the processing core. The detection system adopts optical encoder as joint angle sensor and orthogonal decoding and reversible chip HCTL-2032 to multi frequency the detected signal, which greatly reduces the system error and enhances the detection precision. Experiments of joint position detection are realized. Thirty times repeated experiments show that the maximum error is 0.009 °and the maximum relative deviation is 40.9 × 10-3 /%.

A simple asynchronous distributed STBC network scheme with full diversity

In this article, we propose a simple distributed space-time block code (STBC) network scheme for asynchronous relay network, where every two traditional relay nodes are combined to one node to amplify and forward the processed signals via the same transmission antenna. In the proposed distributed network scheme, we consider a wireless scenario with frequency selective fading channels. The orthogonal frequency division multiplexing (OFDM) symbols are broadcast from source to relay nodes in the first step, and in the second step, the received signals at the relay nodes are implemented with a simple operation and mixed partially and forwarded to destination. In this network scheme, the four by four quasi-orthogonal STBC (QO-STBC) is applied, and the orthogonal decoding algorithm can be used at the receiver because of the orthogonality of the re-constructed equivalent transmission matrix. Thus, the full rate and the full diversity are achieved at the transmitter and the receiver of the proposed distributed network scheme, respectively. Simulation result shows that the proposed distributed STBC network scheme has better performance than other network schemes.

A novel fast fractal super resolution technique

A novel supe-resolution method is proposed to construct a higher resolution image from a low resolution image using fractal coding. This super-resolution method utilizes a special type of orthogonal fractal coding method in which the fractal affine transform is determined by the range block mean and contrast scaling. The proposed non-adaptive fractal super-resolution procedure uses a fixed domain block and a fixed contrast scaling factor. Thus, no additional information must be stored for the fractal coding. Because the mean of each range block of the decoding series in the orthogonal fractal decoding is invariant, a higher resolution image consists of range blocks can be reconstructed from a low resolution image consisting of range block means. Experimental results are presented to show the impact of this method in terms of image quality and its computational requirements.

Distributed GABBA space-time codes in amplify-and-forward relay networks

Cooperative communications via distributed space-time codes has been recently proposed as a way to form virtual multiple-antennas that provide dramatic gains in slow fading wireless environments. In this paper, we consider the design of practical distributed space-time codes for wireless relay networks using the amplify-and-forward (AF) scheme, where each relay transmits a scaled version of the linear combinations of the received symbols and their complex conjugate. We employ GABBA codes, which are systematically constructed, orthogonally decodable, full-rate, full-diversity space-time block codes, in a distributed fashion. Our scheme is valid for any number of relays with linear orthogonal decoding in the destination, which make it feasible to employ large numbers of potential relays to improve the diversity order. We generalize the distributed space-time codes in AF mode when the source-destination link contributes in both phases of the transmission. Assuming MPSK or M-QAM constellations and maximum likelihood (ML) detection, we derive an approximate formula for the symbol error probability of the investigated scheme in Rayleigh fading channels. The analytical results are confirmed by simulations, indicating both the accuracy of the analysis, and the fact that low-complexity, flexible, and high-performing distributed space-time block codes can be designed based on GABBA codes.

Multidimensional Subcarrier Mapping for Bit-Interleaved Coded OFDM With Iterative Decoding

A power and bandwidth-efficient bit-interleaved coded modulation (BICM) with orthogonal frequency-division multiplexing (OFDM) and iterative decoding (BI-COFDM-ID) using combined multidimensional mapping and subcarrier grouping is proposed for broadband transmission in a frequency-selective fading environment. A tight bound on the asymptotic error performance is developed, which shows that subcarrier mapping and grouping have independent impacts on the overall error performance, and hence, they can be independently optimized. Specifically, it is demonstrated that the optimal subcarrier mapping is similar to the optimal multidimensional mapping for bit-interleaved coded modulation with iterative decoding (BICM-ID) in frequency-flat Rayleigh fading environment, whereas the optimal subcarrier grouping is the same with that of OFDM with linear constellation preceding (LCP). Furthermore, analytical and simulation results show that the proposed system with the combined optimal subcarrier mapping and grouping can achieve the full channel diversity without using LCP and provide significant coding gains as compared to the previously studied BI-COFDM-ID with the same power, bandwidth, and receiver complexity.

Unit-rate complex orthogonal space-time block code concatenated with turbo coding

Space-Time Block (STB) code has been an effective transmit diversity technique for combating fading due to its orthogonal design, simple decoding and high diversity gains. In this paper, a unit-rate complex orthogonal STB code for multiple antennas in Time Division Duplex (TDD) mode is proposed. Meanwhile, Turbo Coding (TC) is employed to improve the performance of proposed STB code further by utilizing its good ability to combat the burst error of fading channel. Compared with full-diversity multiple antennas STB codes, the proposed code can implement unit rate and partial diversity; and it has much smaller computational complexity under the same system throughput. Moreover, the application of TC can effectively make up for the performance loss due to partial diversity. Simulation results show that on the condition of same system throughput and concatenation of TC, the proposed code has lower Bit Error Rate (BER) than those full-diversity codes.