A* Algorithm Inspired Memory-Efficient Detection for MIMO Systems
Summary (1 min read)
Introduction
- Best-first search (BFS) detection schemes [2]–[6] based on the Dijkstra’s (or ) algorithm maintains a list of nodes sorted in some defined cost and explores the nodes in such order.
- Imposing a memory constraint [6] facilitates hardware implementation and reduces the search complexity at the cost of some performance degradation.
- The proposed methods are described Manuscript received June 18, 2012.
II. TRANSMISSION SYSTEM AND BEST-FIRST DETECTION
- Transmitted symbol vector x̃c contains uncorrelated entries selected equiprobably from the squared quadrature amplitude modulation (QAM) alphabet S = {a + ib | a, b ∈ Q} and has zero mean and covariance matrix σ2xINT , where Q is the pulse amplitude modulation (PAM) alphabet and INT is the NT ×NT identity matrix.
- Hc has independent and identically distributed (i.i.d.).
- Gaussian entries with zero mean and covariance matrix σ2HINR , where σ2H = 1.
- The channel information is assumed perfectly known to the receiver.
- The authors reach (9) by rewriting the objective function, where the second and third terms do not depend on xk−11 .
A. Complexity Evaluation
- Here, the authors evaluate the overall computational complexity of the proposed algorithms in comparison with conventional methods.
- Since all processing is conducted on real values based on (2), all the calculations below refer to real operations.
- The complexity of a tree-search detection scheme is evaluated in terms of the number of nodes visited and expanded (defined respectively by nodes that ever occupy a position and become the best node in the node list).
- Similar calculations can be carried out for the BFS-LA2 algorithm.
B. Simulation Results
- Here, the authors present the simulation results: symbol error rate (SER) performance in Fig. 1, memory usage in Fig. 2, and complexity in terms of floating-point operations in Table I (one real multiplication/addition each counts a flop).
- Similar observations can be made in Fig. 1(b).
- Fig. 2 illustrates the memory-reduction capability of the proposed schemes.
V. CONCLUSION
- Modified BFS-based MIMO detection algorithms incorporating an efficient look-ahead mechanism have been presented.
- Simulation results demonstrated that the proposed algorithms maintain exact ML detection capability while achieving memory savings and enhanced performance in memory-constrained scenarios.
- Complexity analysis was conducted to confirm the computational feasibility of the proposed algorithms.
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References
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"A* Algorithm Inspired Memory-Effici..." refers background in this paper
...Modifying the sorting criterion such as the use of a biased cost [3] can improve the error and complexity performance of a BFS scheme in memoryconstrained scenarios, yet at the loss of detection optimality....
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...The cost can be a node’s path metric d [4]–[6], or its biased path metric d − k [3] if this node is in layer k, where > 0 is the bias....
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"A* Algorithm Inspired Memory-Effici..." refers methods in this paper
...We compute matrix/vector computations by direct multiplications and accumulations, matrix inverse by the efficient LDL decomposition method [10], and λmin by the power method [11] applied on ( R T R )−1 to obtain its dominant (largest) eigenvalue....
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"A* Algorithm Inspired Memory-Effici..." refers methods in this paper
...The optimal detection performance in memory-constrained scenarios is guaranteed in the proposed scheme in [7] that combines the memory-efficient sphere decoder and the computationally-efficient Dijkstra’s algorithm....
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13 citations
"A* Algorithm Inspired Memory-Effici..." refers methods in this paper
...numbers of multiplications and additions in the complexity of the power method approximated by 4(k− 1)2+3(k− 1) [11]....
[...]
...We compute matrix/vector computations by direct multiplications and accumulations, matrix inverse by the efficient LDL decomposition method [10], and λmin by the power method [11] applied on ( R T R )−1 to obtain its dominant (largest) eigenvalue....
[...]