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IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC)

Quantum Partial Sorting for Efficient Signal Decoding in Spatially Modulated Wireless Systems

Abdulmohsen A. Alsaui, Ibrahim Al-Nahhal, Octavia A. Dobre

Published Jul 7, 2025• 1 citation
Publisher

Abstract

This paper introduces a novel quantum-assisted algorithm for partial sorting, which is integrated with a decoding algorithm for spatially modulated wireless signals. The decoder achieves near-optimal bit error rate performance, closely matching that of the maximum-likelihood decoder, while significantly reducing computational complexity. Additionally, integrating the quantum partial sorting algorithm lowers the query complexity. Although quantum algorithms introduce a small failure probability, resulting in an error floor, simulations validate the scalability and practical efficiency of the utilized decoder with quantumassisted sorting.

DOI
10.1109/spawc66079.2025.11143437

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This paper introduces a novel quantum-assisted algorithm for partial sorting, which is integrated with a decoding algorithm for spatially modulated wireless signals. The decoder achieves near-optimal bit error rate performance, closely matching that of the maximum-likelihood decoder, while significantly reducing computational complexity. Additionally, integrating the quantum partial sorting algorithm lowers the query complexity. Although quantum algorithms introduce a small failure probability, resulting in an error floor, simulations validate the scalability and practical efficiency of the utilized decoder with quantumassisted sorting.
Multiple-input multiple-output (MIMO) technology utilizes multiple antennas at the transmitter and receiver to enhance data transmission speeds and reliability. Traditional MIMO decoding methods, however, can become increasingly complex as the number of antennas and modulation order rises. Quantum computing brings forth a new realm of information processing with significant potential. This study investigates the applicability of quantum algorithms for decoding information in MIMO wireless communication systems. Specifically, the Dürr-Høyer quantum search, based on Grover’s algorithm, and optimal quantum sorting algorithms are leveraged to reduce the query complexity with an analysis of the complexity and achievable bit error rate performance of the quantum-assisted decoders. The study considers cases of MIMO diversity, spatial modulation, and multiplexing transmission using both maximum-likelihood and fixed-complexity sphere decoders. By examining a variety of communication scenarios, this work aims to assess the applicability of quantum algorithms across different operational regimes and aids in extending the methodology to other communication systems.
We propose a new quantum-assisted maximum likelihood detection (MLD) scheme for generalized spatial modulation (GSM) systems. To that end, we first present a novel MLD formulation for GSM, and then describe a corresponding novel method to prepare the initial state for an associated quantum-computing Grover adaptive search (GAS) algorithm. Simulation results are presented to show that our approach achieves optimal performance and reduces query complexity compared both to the classical MLD and to earlier quantum search methods, which do not achieve an advantage over classical MLD for some parameter settings.
We propose a quantum-assisted solution for the maximum likelihood detection (MLD) of generalized spatial modulation (GSM) signals. Specifically, the MLD of GSM is first formulated as a novel polynomial optimization problem, followed by the application of a quantum algorithm, namely, the Grover adaptive search. The performance in terms of query complexity of the proposed method is evaluated and compared to the classical alternative via a numerical analysis, which reveals that under fault-tolerant quantum computation, the proposed method outperforms the classical solution if the number of data symbols and the constellation size are relatively large.
The past, the current state-of-the-art and the future of wireless communications was briefly summarized in [1], [2]. Against this background, this presentation briefly reports on some of the recent quantum-aided design examples in the field of wireless communications. The high complexity of numerous optimal classic communication schemes, such as that of the Maximum Likelihood (ML) Multi-User Detector (MUD) often prevents their practical implementation [3], [4]. Fortunately the parallel-processing capability of quantum-domain algorithms is capable of potentially circumventing this limitation. In our first design example [5] we follow a quantum-aided approach to achieve the same performance as the optimal soft-input soft-output classic detectors by replacing them with a quantum algorithm which estimates the weighted sum of a function's evaluations. We propose a soft-input soft-output Quantum-assisted MUD (QMUD) scheme, which is the quantum-domain equivalent of the Maximum Likelihood (ML) MUD. We then demonstrate its application using the design example of a Direct-Sequence Code Division Multiple Access (DS-CDMA) system employing Bit-Interleaved Coded Modulation (BICM) relying on Iterative Decoding (ID), and compare it to the optimal ML MUD in terms of its performance and complexity. Both our EXtrinsic Information Transfer (EXIT) charts and Bit Error Ratio (BER) curves show that the performance of the proposed QMUD and that of the optimal classic MUD are equivalent, but the QMUD’s computational complexity is significantly lower. In our second design example [6] we have conceived a near-capacity code design for entanglement-assisted classical communication over the quantum depolarizing channel. The proposed system relies on efficient near-capacity classical code designs [7] for approaching the entanglement-assisted classical capacity of a quantum depolarizing channel. It incorporates an Irregular Convolutional Code (IRCC), a Unity Rate Code (URC) and a soft-decision aided Superdense Code (SD), which is hence referred to as an IRCC-URC-SD arrangement. Furthermore, the entanglement-assisted classical capacity of an N-qubit superdense code transmitted over a depolarizing channel is invoked for benchmarking. It is demonstrated that the proposed system operates within 0.4 dB of the achievable noise limit for both 2-qubit as well as 3-qubit SD schemes. More specifically, our design exhibits a deviation of only 0.062 and 0.031 classical bits per channel use from the corresponding 2-qubit and 3-qubit capacity limits, respectively. The proposed system is also benchmarked against the classical convolutional and turbo codes.
The high complexity of numerous optimal classic communication schemes, such as the maximum likelihood (ML) multiuser detector (MUD), often prevents their practical implementation. In this paper, we present an extensive review and tutorial on quantum search algorithms (QSA) and their potential applications, and we employ a QSA that finds the minimum of a function in order to perform optimal hard MUD with a quadratic reduction in the computational complexity when compared to that of the ML MUD. Furthermore, we follow a quantum approach to achieve the same performance as the optimal soft-input soft-output classic detectors by replacing them with a quantum algorithm, which estimates the weighted sum of a function's evaluations. We propose a soft-input soft-output quantum-assisted MUD (QMUD) scheme, which is the quantum-domain equivalent of the ML MUD. We then demonstrate its application using the design example of a direct-sequence code division multiple access system employing bit-interleaved coded modulation relying on iterative decoding, and compare it with the optimal ML MUD in terms of its performance and complexity. Both our extrinsic information transfer charts and bit error ratio curves show that the performance of the proposed QMUD and that of the optimal classic MUD are equivalent, but the QMUD's computational complexity is significantly lower.
This work presents a novel Generalized Space-Time Block Code (GSTBC) approach, which was inspired by Quantum Error Correction (QEC) to enhance wireless communication performance in hybrid Gaussian–quantum noise environments. The proposed approach integrates space-time fronthaul encoder-decoder compression, where the encoding process was optimized utilizing Singular Value Decomposition (SVD). To achieve the best eigen decomposition, this work employed the Variational Quantum Algorithm (VQA), which leveraged quantum-computing advantages in high-dimensional signal processing. The proposed approach was simulated using a MATLAB-based quantum communication simulator, showing high performance in mitigating noise effects and enhancing signal efficiency. The proposed approach was evaluated considering different user scenarios using the following metrics: Signal-to-Noise Ratio (SNR), Bit Flip Noise Error, and Mean Square Error (MSE). The findings from the simulation highlight the potential of Quantum-Assisted encoding-decoding approaches in future 6G wireless communication systems to provide efficient and reliable data transmission.