Seog Geun Kang

An OFDM with 3-D signal mapper and 2-D IDFT modulator

In this letter, a novel orthogonal frequency division multiplexing (OFDM) is introduced. Here, a three-dimensional (3-D) signal mapper and two-dimensional (2-D) inverse discrete Fourier transform are used to allocate 3-D signals to OFDM subchannels and to modulate the signals, respectively. The minimum Euclidean distance of the 3-D mapper is much farther than that of the 2-D mapper if both mappers consisting of the same number of signal points are normalized to have the same average power. As a result, the proposed OFDM has significantly improved error performance when compared to the conventional one.

Closed-form expressions for the symbol error probability of 3-D OFDM

In this letter, closed-form expressions for the symbol error probability of 3-D orthogonal frequency division multiplexing in additive white Gaussian noise channel are derived. When a 3-D 4-ary constellation is used as signal mapper, we calculate the upper and the lower bound for the error probability, and also provide its approximation. Since decision boundaries of 8- ary constellation form an extended regular hexahedron, an exact symbol error probability can be computed. It is verified that the theoretical error probabilities are very close to or almost the same as simulation results.

Construction of Higher-Level 3-D Signal Constellations and Their Accurate Symbol Error Probabilities in AWGN

A simple and straightforward method of constructing higher-level three-dimensional (3-D) signal constellations for a reliable digital communication system is proposed in this paper. The new method expands basic 8-ary constellation into 3-D signal space systematically so that it produces lattice configurations. We also derive accurate closed-form symbol error probability (SEP) of cross-lattice constellations in additive white Gaussian noise (AWGN). It is verified that the theoretical SEPs are almost the same as simulation results. Minimum Euclidean distance (MED) of the higher-level 3-D constellations is increased at least 49% in comparison with quadrature amplitude modulation (QAM). When the number of symbols is 256, the 3-D constellation has around 105% longer MED than the 2-D QAM. Due to increase in MED, the 3-D constellations have much improved error performance compared to the QAM configurations. It is, therefore, considered that the higher-level 3-D constellations are appropriate for high-quality digital communications.

Probability of symbol error of OFDM system with 3-Dimensional signal constellations

In this paper, symbol error probabilities of orthogonal frequency division multiplexing (OFDM) with 3-Dimensional (3-D) signal constellations over additive white Gaussian noise is computed and analyzed. We present the exact closed-form expressions of the symbol error probabilities of the OFDM system with 3-D 8-ary and 32-ary constellations. In the case of 16-ary constellation, an approximation symbol error probability is computed. The higher level 3-D constellations can be built by extension of a basic structure consisting of the regular hexahedron. Simulation result verifies that the theoretical error performance found in this paper matches well with the experimental values. It is also noted that the OFDM systems with 3-D constellation have much lower symbol error probability than general OFDM systems.

Multi-envelope 3-dimensional constellations for polarization shift keying modulation

In this paper, multi-envelope 3-dimensional (3-D) constellations for polarization shift keying modulation (POLSK) are introduced. Signal points of the constellations are on the surfaces of two concentric spheres. In the receiver, two kinds of demodulation schemes are exploited. One is the conventional coherent detection (CD) of the Stokes parameters. The other is based on the maximum-likelihood (ML) algorithm. As a result of simulation, the 16-ary cube-in-cube (CIC) constellation with the ML receiver shows the best error performance in the additive white Gaussian noise (AWGN) environment.

Multistage waveform coding for voice communication over Zigbee networks

Zigbee standard includes no technical references for voice communication. Since the Zigbee standard has very limited size of data payload, high compression with good waveform recovery capability is essential to realize voice communication. This paper presents a voice coding scheme based on discrete wavelet transform (DWT) for Zigbee. Theoretical analysis and simulation verify that 2-stage DWT-based scheme is considered as a feasible method for voice communication over Zigbee networks.

A new design of OFDM for ultra-wideband systems

In this paper, a three-dimensional (3-D) orthogonal frequency division multiplexing (OFDM) is introduced. In the new OFDM, a 3-D signal mapper and 2-D inverse discrete Fourier transform are used to allocate 3-D signals to OFDM subchannels and to modulate the signals, respectively. The minimum Euclidean distance of the 3-D signal mapper is much farther than that of the 2-D mapper if both mappers are normalized to have the same average power. As a result, the proposed OFDM has much improved error performance as compared with the conventional scheme.

Three-Dimensional Modulation Formats with Constant Power for Optical Communications

In this paper, a new method of constructing three-dimensional modulation formats with constant power is introduced. Constellations designed by the method have slightly larger minimum Euclidean distances (MEDs) than the conventional ones. No repetitive algorithm to maximize MED is used so that the new method has little computational complexity. Since signal points in the new formats are distributed regularly and symmetrically, an error control coding with systematic set-partition is applicable. We also present theoretical symbol error probability (SEP) of the new constellations in an additive white Gaussian noise environment, and demonstrate that the theoretical results are accurate. As the new modulation formats have almost the same or slightly lower SEPs than the conventional ones, they are appropriate for implementing a highly reliable optical communication system.

Trellis coded 3-dimensional OFDM system

In this paper, the structure of a trellis-coded 3-dimensional orthogonal frequency division multiplexing (3-D OFDM) is proposed and its error performance in additive white Gaussian channel is analyzed. We present the set-partitioning of a 3-D 8-ary constellation for trellis coding. As a result, the trellis-coded 3-D OFDM system has around 6 dB coding gain over an uncoded one when an 8-ary constellation is exploited. And it also has around 3 dB better symbol error probability as compared to the uncoded system when a 4-ary constellation is employed. Thus, the proposed trellis-coded 3-D OFDM may be appropriate for an application in the high-quality wireless communication system for the next generation.

Performance of ML modulation classifier for multilevel QAM signals

In this paper, performance of the ML modulation classifier (MLMC) for multilevel QAM signals with respect to the number of observation samples is studied. A part of complex symbols are assumed to be shared by several modulation formats in common so that the smaller formats are subsets of the larger ones. As a result, correct classification ratio (CCR) of the MLMC algorithm is over 97 % in all SNR regions when the true constellation is 4 QAM. Even perfect classification can be achieved with triple-sample observation. In the case of the 16, 64 and 256 QAM, double-sample observation shows around 15 % increased CCR when compared to the single-sample observation scheme. And additional 10 % improvement can be obtained when three consecutive samples are exploited for the likelihood ratio tests. However, when the size of true constellation is increased, there are performance limits in single-and double-sample classification schemes. Such limits are mainly caused by the symbols shared by multiple constellations in common. Nevertheless, the MLMC with triple-sample observation shows almost perfect classification performance in high SNR region.