• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.5
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• pp.31-41
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• 1995

In this paper, the relationship between k consecutive outputs of the conventional differential detector and output of differential detector with k-symbol periods delay for differential MSK and GMSK systems is investigated. It is hown that there exists periodity in modulo-2 sum and product of k successive outputs of the conventional differential detector with the output of a detector with k-symbol periods delay circuit. This relationships are used to achieve performance gains over conventional differential detection. The error rate performance of the method is carried out by computer simulation and performance improvement is achieved for differential MSK and GMSK systems.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.6
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• pp.1-8
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• 1998

This paper presents an asynchronous DS/CDMA multiuser detector, which is a two stage, symbol-by-symbol scheme consisting of conventional detectors followed by linear decorrelating detectors. The conventional detector first makes temporal decisions and the detected symbols are delayed by one symbol period to be used for the selection of decorrelating bases in the subsequent decorrelaing detection stage. It also employs a bank of early-late correlators in place of a bank of single correlators taking the small offset of chip timing asynchronism into account. The proposed detector requires only the coarse knowledge of relative time delays of interfering users and is suitable for digital implementation. To verify the detector performance, the analytical BER performance will be given and compared with the simulation results for BPSK DS/CDMA signals in AWGN channel. While the performance of the proposed detector will be analyzed for time-limited signal, the simulation is carried out for both the time-limited and band-limited signals. As can be seen in the simulation results, the proposed scheme shows good results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11C
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• pp.932-939
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• 2008

Recently lattice-reduction (LR) has been used in signal detection for multiple-input multiple-output (MIMO) systems. The conventional LR aided detection schemes are combinations of LR and signal detection methods such as zero-forcing (ZF) and minimum mean square error (MMSE) detection. In this paper, we propose the Lattice-Reduction-aided scheme based on extended noise variance matrix to search good candidate symbol set in quantization step. Then this scheme estimates transmitted symbol with Semidefinite Relaxation by candidate symbol set. Simulation results in a random MIMO system show that the proposed scheme exhibits improved performance and a slight increase in complexity.

• Journal of Communications and Networks
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• v.9 no.3
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• pp.219-228
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• 2007

In this paper, we present a novel blind adaptive multiuser detector structure and three robust recursive filters to improve the performance in CDMA environments: Sigma point kalman filter (SPKF), particle filter (PF), and Gaussian mixture sigma point particle filter (GMSPPF). Our proposed robust recursive filters have superior performance over a conventional extended Kalman filter (EKF). The proposed multiuser detector algorithms initially use Kalman prediction form to estimated channel parameters, and unknown data symbol be predicted. Second, based on this predicted data symbol, the robust recursive filters (e.g., GMSPPF) is a refined estimation of joint multipaths and time delays. With these estimated multipaths and time delays, data symbol detection is carried out (Kalman correction form). Computer simulations show that the proposed algorithms outperform the conventional blind multiuser detector with the EKF. Also we can see it provides a more viable means for tracking time-varying amplitudes and time delays in CDMA communication systems, compared to that of the EKF for near-far ratio of 20 dB. For this reason, it is believed that the proposed channel estimators can replace well-known filter such as the EKF.

• ETRI Journal
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• v.29 no.2
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• pp.143-152
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• 2007

In this paper, we propose a time-varying modified minimum mean-squared error (MMSE) detector for the detection of higher data rate signals in a multirate asynchronous code-division multiple-access (CDMA) system which is signaled in a fast Rayleigh fading channel. The interference viewed by a higher data rate symbol will be periodic due to the presence of a lower data rate symbol which spans multiple higher data rate symbols. The detection is carried out on the basis of a modified MMSE criterion which incorporates differential detection and the ratio of channel coefficients in two consecutive observation intervals inherently compensating the fast variation of the channel due to fading. The numerical results obtained by the MMSE detector with time-varying detection show around 3 dB (M=2) and 6 dB (M=4) performance improvement at a BER of $10^{-3}$ in the AWGN channel, while introducing more computational complexity than the MMSE detector without time-varying detection. At a higher $E_b/N_0$, the proposed scheme can achieve a BER of approximately $10^{-3}$ in the presence of fast channel variation which is an improvement over other schemes.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.7
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• pp.28-38
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• 1997

Previously, we have proposed the M-BECM(Modified-Band Edge Component Maximization), which is a symbol synchronization algorithm based on spectral line method for all-digital high speed digital communications. However, Until now, the characteristics of the timing detector based on the spectral line method including M-BECM was not analyzed, particularly the effect of a timing offset at the optimal convergence pont. In this paper, we analyze the timing dtector's characteristics of the M-BECM and present optimal design value. First, the expression for the timing detector's mean value(often called its S-Curver) as a function of the normalized symbol timing offset is derived. Next, the P $D_{bias}$, the value for compensating the timing offset at an optimal convergence point, and the bandwidth of bandpass filter in the timing detector are calculated. It is also shown and analyzed that the P $D_{bias}$ is affected by varuous factors such as the excess bandwidth of input signal, frequency offsets, noise and particularly, the excess bandwidth of input signal is a major parameter to decide P $D_{bias}$. Finally, analytic resutls are compared to simulation results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12A
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• pp.933-940
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• 2009

This paper proposes a robust detection scheme for quasi-orthogonal space-time block code over time-selective fading channels. The proposed detector performs interference cancellation and decision feedback equalization to remove the inter-antenna interference and inter-symbol interference when the channel varies from symbol to symbol. Cholesky factorization is used on the channel Gram matrix after performing interference cancellation to obtain feed forward equalizer and feedback equalizer. It is shown by simulations that the proposed detection scheme outperforms the conventional detection schemes and the exiting detection schemes to time-selectivity.

• The Journal of the Acoustical Society of Korea
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• v.24 no.8
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• pp.462-468
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• 2005

In this paper, we present a frame synchronization scheme for high oversampling rate based QPSK receiver system in the underwater acoustic burst transmission. The proposed frame synchronization scheme determines the frame synchronization by comparing a threshold value with the correlation between the received symbol sequence and rotated 16-symbol length CAZAC sequence, which is made by dividing into two 8-symbol length sequences and then concatenating the latter sequence and the former one. If the correlation value is bigger than the threshold value, the frame detector determines that the frame synchronization is achieved at that sample. Also, the approximated performance of designed frame detector is derived and it is well fit the simulated result.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.5
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• pp.25-32
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• 2011

In this paper, we propose a subspace search-based detector (SSD) with low-complexity to achieve near optimal performance for multiple-input multiple-output systems. As an effective solution to reduce the prohibitive computational complexity of the optimal maximum likelihood detector, a partial candidate symbol vector is generated through a partitioned search space but not the entire search space. In addition, based on a partial candidate symbol vector, an ensemble candidate symbol vector generation considering the whole search space is introduced to produce a near optimal solution. As a result, the proposed SSD achieves near-maximum-likelihood performance while having a significantly reduced computational complexity.

• Journal of IKEEE
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• v.10 no.1 s.18
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• pp.69-74
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• 2006

In this paper, we present symbol detection methods for decision feedback equalizers (DFE) in trellis coded modulation systems. The proposed symbol detectors improve symbol error rate (SER) by exploiting the coding structure of trellis coded modulation (TCM). For example, for 8-PAM signals the achieved SER with the proposed detection scheme is improved to $2{\times}10^{-5}$ from $2.5{\times}10^{-2}$ of the conventional symbol-by-symbol detector under AWGN channel at 20dB SNR. This SER improvements mitigate error propagation of DFE.and produces significant over-all SER improvement for under multipath channels (for example, from 0.26 to 0.01 and 0.005 under a severe multipath channel 20dB SNR as shown in the simulation result of this paper).