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Information Communication Technologies Conference (ICTC)

Maximum Likelihood Detection Based on Warm-start Quantum Optimization Algorithm

Xinlin He, Han Zeng, Xutao Yu

Published May 10, 2024• 2 citations
Publisher

Abstract

Quantum computing, with its powerful parallel computing capabilities, is considered one of the promising candidates for solving complex communication problems. This paper proposes a new detection scheme by combining quantum approximation optimization algorithms (QAOA) with maximum likelihood (ML) detection. The scheme addresses the computational complexity problem faced by ML detection in large-scale multiple-input multiple-output (MIMO) channels. The primary focus lies in the warm-start optimization based on the QAOA-ML detection. We use semi-definite relaxation (SDR) to calculate the temporary solution of ML for initializing quantum circuits. The feasibility of the scheme is verified through simulation. The proposed detection scheme is evaluated and compared with classical computer-based ML detection and Minimum Mean Square Error (MMSE) detection, demonstrating similar bit error rate (BER) performance. The enormous potential of quantum algorithms in computing power solving the drawbacks of traditional ML detection algorithms provides new possibilities for improving detection efficiency.

DOI
10.1109/ictc61510.2024.10602129

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Quantum computing, with its powerful parallel computing capabilities, is considered one of the promising candidates for solving complex communication problems. This paper proposes a new detection scheme by combining quantum approximation optimization algorithms (QAOA) with maximum likelihood (ML) detection. The scheme addresses the computational complexity problem faced by ML detection in large-scale multiple-input multiple-output (MIMO) channels. The primary focus lies in the warm-start optimization based on the QAOA-ML detection. We use semi-definite relaxation (SDR) to calculate the temporary solution of ML for initializing quantum circuits. The feasibility of the scheme is verified through simulation. The proposed detection scheme is evaluated and compared with classical computer-based ML detection and Minimum Mean Square Error (MMSE) detection, demonstrating similar bit error rate (BER) performance. The enormous potential of quantum algorithms in computing power solving the drawbacks of traditional ML detection algorithms provides new possibilities for improving detection efficiency.
Recent advances in quantum technologies pave the way for noisy intermediate-scale quantum (NISQ) devices, where the quantum approximation optimization algorithm (QAOA) constitutes a promising candidate for demonstrating tangible quantum advantages based on NISQ devices. In this paper, we consider the maximum likelihood (ML) detection problem of binary symbols transmitted over a multiple-input and multiple-output (MIMO) channel, where finding the optimal solution is exponentially hard using classical computers. Here, we apply the QAOA for the ML detection by encoding the problem of interest into a level-pppQAOA circuit having2p2p2pvariational parameters, which can be optimized by classical optimizers. This level-pppQAOA circuit is constructed by applying the prepared Hamiltonian to our problem and the initial Hamiltonian alternately inpppconsecutive rounds. More explicitly, we first encode the optimal solution of the ML detection problem into the ground state of a problem Hamiltonian. Using the quantum adiabatic evolution technique, we provide both analytical and numerical results for characterizing the evolution of the eigenvalues of the quantum system used for ML detection. Then, for level-1 QAOA circuits, we derive the analytical expressions of the expectation values of the QAOA and discuss the complexity of the QAOA based ML detector. Explicitly, we evaluate the computational complexity of the classical optimizer used and the storage requirement of simulating the QAOA. Finally, we evaluate the bit error rate (BER) of the QAOA based ML detector and compare it both to the classical ML detector and to the classical minimum mean squared error (MMSE) detector, demonstrating that the QAOA based ML detector is capable of approaching the performance of the classical ML detector.
Data detection in large-scale multiple-input multiple-output (MIMO) systems with higher-order quadrature amplitude modulation (QAM) remains a challenging problem due to the exponential complexity of the classical maximum likelihood (ML) detector. This challenge is further amplified by Gray-coded modulation, which introduces nonlinear symbol-to-bit mappings and transforms the problem into a higher-order unconstrained binary optimization (HUBO) formulation. To address this problem, this paper presents a hybrid quantum-classical detection framework that leverages a warm-start linear-ramp Quantum Approximate Optimization Algorithm (WSLR-QAOA) for solving the resulting HUBO problem. A structured warm-start based on a low-rank semidefinite relaxation, solved via a block coordinate descent (BCD) method, provides an efficient and high-quality initialization, while a linear ramp parameterization guides the QAOA optimization. Simulation results show that the proposed framework outperforms classical methods in terms of symbol error rate (SER) and converges faster than standard QAOA, while achieving performance close to the optimal ML detector. Furthermore, the WSLR-QAOA algorithm is validated on actual IBM quantum hardware, where it achieves near-ML performance at low SNR and maintains competitive accuracy at higher SNR despite moderate degradation due to hardware noise. This demonstrates the practical potential of the HUBO-based WSLR-QAOA algorithm for large-scale MIMO data detection.
In the massive multiple-input and multiple-output (Massive MIMO) systems, the maximum likelihood (ML) detection problem is NP-hard and becoming classically intricate with the number of transmitting antennas and symbols increasing. The quantum approximate optimization algorithm (QAOA), a leading candidate algorithm running in the noisy intermediate-scale quantum (NISQ) devices, can show quantum advantage for approximately solving combinatorial optimization problems. In this paper, we propose the QAOA based on the maximum likelihood detection solver of binary symbols. In the proposed scheme, we first conduct a universal and compact analytical expression for the expectation value of the 1-level QAOA. Second, a Bayesian optimization based parameters initialization is presented, which can speedup the convergence of the QAOA to a lower local minimum and improve the probability of measuring the exact solution. Compared to the state-of-the-art QAOA based ML detection algorithm, our scheme has the more universal and compact expectation value expression of the 1-level QAOA, and requires few quantum resources and has the higher probability to obtain the exact solution.
Quantum-approximate optimization algorithm (QAOA) is promising in Noisy Intermediate-Scale Quantum (NISQ) computers with applications for NP-hard combinatorial optimization problems. It is recently utilized for NP-hard maximum-likelihood (ML) detection problem with fundamental challenges of optimization, simulation and performance analysis for n x n multiple-input multiple output (MIMO) systems with large n. QAOA is recently applied by Farhi et al. on infinite size limit of Sherrington-Kirkpatrick (SK) model with a cost model including only quadratic terms. In this article, we extend application of QAOA on SK model by including also linear terms and then realize SK modeling of massive MIMO ML detection by ensuring independence from specific problem instance and size n while preserving computational complexity of O(16p) designed by Farhi et al. We provide both optimized and extrapolated angles for p in the set [1, 14] and signal-to-noise (SNR) < 12 dB achieving near-optimum ML performance for 25 x 25 MIMO system with p >= 4 in extensive simulations where 236500 different QAOA circuits are simulated. We present two conjectures about the concentration properties of QAOA and its near-optimum performance for massive MIMO systems with large sizes covering n < 300 promising significant performance for next generation massive MIMO systems.
Quantum-approximate optimization algorithm (QAOA) is promising in Noisy Intermediate-Scale Quantum (NISQ) computers with applications for NP-hard combinatorial optimization problems. It is recently utilized for NP-hard maximum-likelihood (ML) detection problem with challenges of optimization, simulation and performance analysis forn×nmultiple-input multiple output (MIMO) systems with largen. QAOA is recently applied by Farhi et al. on infinite size limit of Sherrington-Kirkpatrick (SK) model with a cost model including only quadratic terms. In this article, we extend the model by including also linear terms and then realize SK modeling of massive MIMO ML detection. The proposed design targets near ML performance while with complexity includingO(16p) initial operations independent from problem instance and sizenfor optimizing QAOA angles andO(n2p) quantum operations for each instance. We provide both optimized and extrapolated angles forp∈ [1, 14] and signal-to-noise (SNR)p≥ 4 for 25×25 and 12 × 12 MIMO systems modulated with BPSK and QPSK, respectively. We present two conjectures about concentration properties of QAOA and near-optimum performance for next generation massive MIMO systems coveringn< 300.
Quantum approximate optimization algorithm (QAOA) with layer depthpis promising near-optimum performance and low complexity for NP-hard maximum-likelihood (ML) detection inn×nmulti-input multi-output (MIMO) systems. Experimental challenges for ML detection on Noisy Intermediate-Scale Quantum (NISQ) computers arise from accumulated errors with largepandn. Recursive QAOA (RQAOA) is promising with smallpby reducing complexity overnsteps. In this article, we modify RQAOA forp≪nwith cost sorting and post-selection inm≪nsteps, and then integrate it with majority voting (MV) and successive interference cancellation (SIC) into the QAOA-MVSIC algorithm to tackle experimental challenges. We truncate QAOA circuits to further improve experimental feasibility. Simulations withn= 24 and 12 for BPSK and QPSK modulations, respectively, show near-optimum bit-error rate (BER) withp= 1 andm≤ 4. Truncated version requiresO(m n p) quantum andO(m n2) classical operations with low complexity. We experimentally implement QAOA combined with MV (QAOA-MV) fornϵ [17; 64] in IBM Eagle processor by observing superior performance of QAOA-MV over QAOA and reducing problem dimensions by at leastn/4. We generalize QAOA as cost-restricted uniform sampling (CRUS) oracle and approximately simulate forn≤ 128 to obtain comparison benchmark for future QAOA experiments.