• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12A
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• pp.1339-1345
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• 2007

An important drawback in Lattice Reduction (LR) aided detectors has been investigated. For the solution, an improved LR aided detection with ignorable complexity overhead is proposed for MIMO system, where the additional correction operation is performed for the case of unreliable symbol decision. We found that LR aided detection errors mainly occur when the lattice points after the inverse lattice transform in the final step fall outside the constellation point set. In the proposed scheme, we check whether or not the lattice point obtained through LR detection is out of constellation. Only for the case of out of constellation, we additionally perform ML search with reduced search region restricted to the neighboring points near to the obtained lattice points. Using this approach, we can effectively and significantly improve the detection performance with just a slight complexity overhead which is negligible compared to full searched ML scheme. Simulation results show that the proposed scheme achieves the detection performance near to that of the ML detection with a lower computational complexity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.11
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• pp.2021-2026
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• 2016

In this paper, a system model for transmission of 3-dimensional (3-D) signals is presented and its performance is analyzed. Unlike 2-D signals, no quadrature form expression for the 3-D signals is available. Exploiting a set of orthogonal basis functions, the 3-D signals are transmitted. As a result of computer simulation using very higher-level signal constellations, the 3-D transmission system has significantly improved error performance as compared with the 2-D system. It is considered that the principal reason for such performance improvement is much increased minimum Euclidean distance (MED) of the 3-D lattice constellations compared with the corresponding 2-D ones. When the MEDs of 2-D and 3-D lattice constellation are compared to confirm the analysis, the MED of 3-D 1024-ary constellation is around 2.6 times larger than that of the quadrature amplitude modulation (QAM). Expanding the constellation size to 4096, the MED of 3-D lattice constellation is increased by 3.2 times of the QAM.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.4
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• pp.715-720
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• 2016

In this paper, a method to design 3-dimensional (3-D) cross-lattice signal constellations with increased compactness is presented and analyzed. Here, the symbols located at the outermost sides in the conventional lattice constellation are moved symmetrically to fill in empty sides and sunken corners. While the minimum Euclidean distance (MED) among adjacent symbols remains unchanged, the presented cross-lattice constellations have 3~5% reduced average power and upto 25% reduced total volume as compared with the conventional ones. Due to the increase compactness, average power of the new 3-D constellations is lower than that of the conventional ones. As a result, computer simulation verifies that the presented cross-lattice constellations can improve symbol error performance of a digital transmission system about 0.4 [dB]. Hence, the proposed 3-D cross-lattice constellations are appropriate for low-power and high-quality digital communication systems.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.5
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• pp.88-94
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• 2009

We propose a scheme which reduce the computational complexity of the lattice reduction (LR) aided detector in MIMO system. The performance of the ML detection algorithm is good but the computational complexity grows exponentially with the number of antenna elements and constellation points. LR aided detector shows the same diversity with the ML scheme with relatively less complexity. But the LR scheme still requires many computations since it involves several iterations of size reduction and column vector exchange. We notice that the LR process depends not on the received signal but only on the channel matrix so we can apply LR process offline and store the results in Look-Up Table (LUT). In this paper we propose an algorithm to generate the LUT which require less memory requirement and we evaluate the performance and complexity of the proposed system. We show that the proposed system requires less computational complexity with similar detection performance compared with the conventional LR aided detector.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.1
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• pp.10-18
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• 2013

Recently, a fixed complexity LR(fcLR) technique was proposed. Also QR-LRL signal detection method was proposed in which all constellation symbols are tried as the symbol corresponding to the least reliable layer (LRL), thereby achieving high error performance. In this paper, we combine these two efficient methods to propose a novel detection method. When the LRL is disregarded in the process of LR, the worst case complexity of LR is significantly reduced. Also, the proposed method is shown to be superior to the conventional fcLR-based detection method from the perspective of error performance. Simulations are performed to demonstrate the efficacy of the proposed method.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.117-121
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• 2005

In this work, we first present our study on the decoding schemes for space-time block code as well as our comments on their complexity. Then, we propose a new modified complex sphere decoding scheme, which has lower computational load than that of conventional complex sphere decoders. In the proposed scheme, the boundary for searching is defined by the intersection of an approximate polygon of searching circle and disk of lattice constellation. Therefore, the proposed scheme can reduce the searching boundary and it can avoid missing searching points as well. The performance of the proposed scheme, which is verified by computer simulations, consolidates our scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.8
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• pp.1833-1839
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• 2014

In this paper, a systematic demapping algorithm for three-dimensional (3-D) lattice signal constellations is presented. The algorithm consists of decision of an octant, computation of a distance from the origin, and determination of the coordinates of a symbol. Since the algorithm can be extended systematically, it is applicable to the larger lattice constellations. To verify the algorithm, 3-D signal transmission systems with field programmable gate array (FPGA) and $Matlab^{(R)}$ are implemented. And they are exploited to carry out computer simulation. As a result, both hardware and software based systems produce almost the same symbol error rates (SERs) in an additive white Gaussian noise (AWGN) environment. In addition, the hardware based system implemented with an FPGA generates waveforms of 3-D signals and recovers the original binary sequences perfectly. Those results confirm that the algorithm and the implemented 3-D transmission system operate correctly.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.5
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• pp.229-236
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• 2014

Quadrature Amplitude Modulation (QAM) is widely used in contemporary wired and wireless communications systems. In this paper, I propose a generalized triangular quadrature amplitude modulation (gTQAM) that includes the square quadrature amplitude modulation (SQAM), TQAM, and ${\Theta}$-QAM as special cases. Therefore, the proposed gTQAM forming a lattice of arbitrary triangles provides a versatile structure in signal constellations compared to other QAM schemes. For M-ary gTQAM, I derive an exact closed-form expression for the bit error rate (BER), and present the optimal signal constellations for given SNR values from the derived BER expression. Finally, I validate the derived BER results through computer simulations.