Observed time difference of arrival (OTDOA) is one of the trilateration based positioning techniques adopted in 3rd generation partnership project (3GPP) long term evolution (LTE) release 9. It can estimate user's location by using received time difference of positioning reference signals (PRS) from eNBs. When user detects PRS, quantization error can occur due to low sampling resolution of narrow bandwidth signal in time-domain, and it can seriously degrade positioning performance. For that reason, carrier aggregation (CA) based bandwidth extension has been discussed in recent 3GPP standardization meeting; however, it requires a single fast Fourier transform (FFT) suitable for the extended bandwidth, and it is only available with a new design of PRS and reporting table of reference signal's time difference (RSTD). Meanwhile, early-late gate detector (ELD) based timing synchronization algorithm can be considered. It can exactly estimate reception timing of PRS; however, quantization error still occurs during RSTD reporting due to the minimum resolution of the reporting table. Therefore, in this paper, we propose a novel quantization error reduction method using multiple PRS transmission. The proposed method utilizes a new sampling structure of higher resolution than the conventional ones which occur in case of PRS in LTE. The sampling points of the new structure can be derived from a relationship among the sampling points of multiple PRSs which have different size of bandwidth and sampling resolution. We verify that the proposed method can effectively reduce the quantization error without additional bandwidth extension or a new reporting table.

Device-to-device (D2D) communication has received considerable attention in recent years as one of the key technologies for future communication system. Among the typical D2D communication systems, FlashLinQ (FLQ) adopted single-tone orthogonal frequency division multiplexing (OFDM) transmission which enables wide-sense discovery by time domain spreading and very low peak to average power ratio (PAPR). Although synchronization based on a common external source (CES) is basically assumed in FLQ, a means to support devices when they are unable to use a CES is still necessary. In OFDM system, generally, carrier frequency offset (CFO) induces inter-carrier interference (ICI) which degrades overall system performance drastically. Especially in D2D system, ICI can be amplified due to not only different frequency selectivity but also different path losses between links. Accordingly, a precise estimation and compensation of CFO are very important. Therefore, in this paper, we propose a new CFO estimation method for OFDM based D2D system. In the proposed method, the estimation of CFO is obtained by using two correlation results in a symbol. The estimation procedure of the proposed method enables the independent estimation of CFO between links and the estimation range can be adaptively defined depending on the distance between the two windows. By numerical analysis and performance evaluation, we verified that the proposed method achieves precise estimation performance compared to the conventional method.

Recently, 3rd generation partnership project has adopted a new study item for device-to-device (D2D) communication service in long term evolution (LTE) system, called the group communication system enablers for LTE (GCSE_LTE). In GCSE_LTE, synchronization is an important issue; therefore, many synchronization methods of wireless sensor network and ad-hoc network can be considered. In these conventional methods, they only consider synchronizing the transmission time of signal. However, in case of ideal synchronization method, conventional methods cause a link delay spread (LDS) problem. LDS means a time difference between received signals which are caused by the different propagation delays among user equipments (UEs). The problem is that all UE need an extra length of cyclic prefix (CP) to receive multi-path delayed signals, and it can be a substantial resource waste. Therefore, in this paper, we propose a fine timing synchronization method by a master node which can reduce the maximum LDS in D2D group. We verify that the proposed method can reduce the average length of additionally required CP compared to conventional methods.

In this paper, multi-user multiple-input multiple output (MU-MIMO) transmission in long term evolution (LTE)-Advanced system is presented. To support dynamic scheduling of MIMO transmission, enhanced node B (eNB) does not inform user equipment (UE) of the existence of other co-scheduled UE. In this case, the UE cannot perform any interference mitigation scheme because it does not know whether the interference actually occured or not, so a multi-user interference (MUI)-detection which precedes the interference mitigation is essential. In order to overcome this problem, we propose a novel MUI detection method. The pro-posed method partially estimates interference using simple matrix operations. After that, we decide the existence of MUI by using a threshold-based interference detection method.

In this paper, we propose an enhanced iterative ICI (Inter Carrier Interference) cancellation method for cooperative STBC-OFDM (Space Time Block Coded-Orthogonal Frequency Division Multiplexing) system. In cooperative STBC-OFDM system, ICI cancellation is necessary because ICI due to the independent local oscillators always exits. The conventional iterative ICI cancellation method has severe performance degradation due to the initial estimation error. Also the performance degradation increases as CFOs (Carrier Frequency Offsets) and modulation order increases. Therefore, in this paper, we propose an enhanced iterative ICI cancellation method which can reduce the initial estimation error by giving a priority to initial estimation and cancellation process. Through the complexity and performance comparisons, we verify that the proposed method has better performance with approximately same complexity compared with the conventional method.

In this paper, we propose group Manchester code (GM) modulation scheme for medical in-body wireless body area network (WBAN) systems. In IEEE, the WBAN system is assigned as 802.15. Task Group 6 (TG6), and the related standardization is being progressed. Recently, in this Group, group pulse position modulation (GPPM), which can obtain data rate increase by grouping pulse position modulation (PPM) symbols, is proposed as a new modulation scheme for low-power operation of WBAN system. However, the conventional method suffers from BER performance degradation due to the absence of gray coding and its demodulation characteristics. Therefore, in this paper, we propose a modified GM scheme which groups Manchester code instead of PPM. In the proposed GM scheme, a low-complexity maximum likelihood (ML) demodulation method is employed in order to maximize the BER performances. Also, log likelihood ratio (LLR) decision method is proposed to employ the Turbo code as forward error correction (FEC). Finally, we verified that the proposed method has a good performance and is an appropriate scheme for in-body WBAN system through extensive performance evaluation.

In this paper, we propose an enhanced channel estimation method for multi-user multiple-input multiple output (MU-MIMO) based long term evolution (LTE)-Advanced system. In MU-MIMO based LTE-Advanced system, the orthogonality between co-scheduled layers is not perfectly guaranteed. In this case, significant performance degradation in channel estimation can occur due to the interference from transmit signals for co-scheduled users. To overcome this problem, the proposed method partially estimates and eliminates the multi-user interference using a simple pilot matrix inversion based scheme. After the interference mitigation, we apply an iterative two-dimensional minimum mean squared error (2-D MMSE) channel estimation scheme with adaptive noise and interference weighting method to increase the estimation accuracy. Various simulation results verify that the proposed method has superior performance compared with the conventional 2-D MMSE channel estimation scheme, with only a few times of iteration.

In this paper, we present the state of the art of communication technology related to the capsule endoscopes (CEs) and analyze the technologies and characteristics of commercialized CEs on the current global market. The study shows that the communication technology of human body communication (HBC) can reduce the power consumption and have a smaller size of CE compared to radio frequency (RF) communications technology, since the HBC doesn't use power consuming RF components and antenna.

In this paper, a novel diversity transmission technique using cooperative relay is presented. Although the conventional distributed space-time coded cooperative (DSTC) system achieves a diversity gain with single antenna user and relay, there is tradeoff between the diversity gain and resource requirements. Therefore, we propose a novel diversity transmission technique which can obtain diversity gain without additional time or frequency resources. From the performance evaluation, compared with the conventional method, the proposed method achieves 0.5 dB and 2.1 dB differences at BER=10-5for QPSK and 16-QAM modulation, respectively.

In this paper, we propose a fast AGC (Automatic Gain Control) scheme for 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) TDD (Time Division Duplex) system. Since the received signal has a large signal power difference between uplink and downlink subframe in wireless communication systems using a TDD scheme, conventional AGC scheme cannot sufficiently adjust the AGC gain because the AGC gain cannot converge fast enough to properly respond. Therefore, conventional AGC scheme leads to increased AGC gain variation, and the received signal will be attenuated by large AGC gain variation. To overcome this limitation, we propose an AGC scheme based on the average amplitude ratio calculation which can not only effectively increase convergence speed of the AGC gain but also maintain the stability of AGC operation in LTE TDD system. By using extensive computer simulation in various channel environments, we show that the proposed method can obtain a good behavior in terms of convergence speed for LTE TDD system and verify that the proposed method is attractive and suitable for implementation with stable operation.

In this paper, we propose two robust frequency offset estimation methods for OFDM systems in single frequency network (SFN) with large delay spread. Conventional guard-interval-based (GIB) estimation method is very sensitive to intersymbol interference (ISI) caused by long and strong echoes of the SFN channel. In order to minimize ISI-dependent performance degradation, we first introduce a suboptimal minimum variance unbiased (MVU) estimation method based on best linear unbiased estimation (BLUE) principle, and then we modify it to reduce the computational complexity. Simulation results verify that the proposed methods improve the root mean square error (RMSE) performance without error floor due to ISI in contrast with the conventional method. Also, the reduced-complexity method can achieve suboptimal performance in typical multi-path channel as well as the SFN channel.

To mitigate the asynchronous ICI (inter-cell interference), SCM (spatial covariance matrix) of the asynchronous ICI plus background noise should be accurately estimated for MIMO-OFDMA (multiple-input multiple-output-orthogonal frequency division multiple access) system. Generally, it is assumed that the SCM of the asynchronous ICI plus background noise is estimated by using training symbols. However, it is difficult to measure the interference statistics for a long time and training symbol is also not appropriate for MIMO-OFDMA system such as LTE (3GPP long term evolution). Therefore, a noise reduction method is required to improve the estimation accuracy. Although the conventional time-domain low-pass type weighting method can be effective for noise reduction, it causes significant estimation error due to the spectral leakage in practical OFDM system. Therefore, we propose a time-domain sine type weighing method which can not only reduce the noise effectively minimizing estimation error caused by the spectral leakage but also implement frequency-domain moving average filter easily. By using computer simulation, we show that the proposed method can provide up to 3 dB SIR (signal to interference ratio) gain compared with the conventional method, and verify that the proposed method is attractive and suitable for implementation with stable operation.

In this paper, we propose a robust soft decision method based on channel state information (CSI) for coded orthogonal frequency division multiplexing (COFDM) systems. In the presence of co-channel interference (CCI), conventional soft decision decoding is performed by a simple erasing method for frequency selective CCI. But the conventional method cannot obtain sufficient performance gain because the CCI power varies and a considerable number of bits are affected by the CCI. For this reason, we consider a novel weighting method based on the specific CSI such as statistical location and instantaneous power of the CCI as well as typical frequency-selective fading channel. Simulation results verify that the proposed CSI estimation is sufficiently reliable for digital video broadcasting-terrestrial (DVB-T) system with analog TV signals as the CCI. In addition, the proposed soft decision method guarantees superior coded bit error rate (BER) performance compared to the conventional method.

A precise estimation of SFO (Sampling Frequency Offset) is an important issue in OFDM (Orthogonal Frequency Division Multiplexing) system. However, the conventional method causes serious performance degradation of SFO estimation in low SNR (Signal to Noise Ratio) or large Doppler frequency environment. Therefore, in this paper, we propose a SFO estimation method which can achieve stable operation in low SNR and large Doppler frequency environment. The proposals for SFO estimation /compensation are mainly based on DVB (Digital Video Broadcasting) system, and we verified that the proposed method has a good performance and stable operation through extensive simulation.

In this paper, we propose a simple and robust iterative channel estimation algorithm in OFDM packet transmission systems. Iterative scheme with channel update process is effective to reduce the packet error rate. However, conventional iterative structure has a limit on improving the performance because error propagation often occurs while updating the channel in the low SNR. In order to overcome this problem, we introduce a novel moving average filter to enable estimating the channel more reliably. Simulation results show that the proposed algorithm outperforms the conventional scheme. In particular, combined performance of the proposed algorithm and the noise reduction method[1] is close to MMSE channel estimation algorithm.

We propose a polarity decision carrier recovery algorithm that is useful for carrier acquisition in high order-QAM (quadrature amplitude modulation). The PD (phase detector) output and its variance characteristics are mathematically derived and the simulation results are presented. We design a carrier recovery loop with this polarity decision PD and ATC (automatic transfer-mode controller), which is proposed to detect a proper time for mode change and to yield fine phase tracking error in the steady state. While the conventional DD (decision directed) algorithm can only acquire frequency offsets of less than /spl plusmn/10 kHz, the proposed carrier recovery algorithm can acquire up to /spl plusmn/200 kHz without AFC (automatic frequency control). We show the RMS (root mean square) phase error performance using the proposed carrier recovery PLL (phase locked loop).

The bit-error rate (BER) performance of a DS-CDMA/QPSK system taking into account the effect of fast fading and high frequency offset is analyzed. The performance is obtained by deriving the SNR of the demodulated signal as a function of the correlation between received signal values and estimated values of the channel estimator. The derived SNR shows that the conventional channel estimator using a single integrator structure has some problems such as the degradation of estimator's performance from fast phase change. We propose a new channel estimator using a double integrator structure that is not affected by fast phase change. We also show the performance comparison between EQOC-QPSK and NEQOC-QPSK data modulation in third generation DS-CDMA. Finally, chip-based simulation is presented to confirm the derived BER performance.

A new lock detection algorithm for digital quadrature phase-shift keying (QPSK) receiver is proposed. Analysis of the detector's output characteristics is given and is verified by using computer simulation. Performance degradation due to carrier jitter is also considered. Analytic and simulation results show that the proposed algorithm is very useful as a lock detector in digital receivers because it has a good detection performance and simple structure.

The well known methods for survivor path storage and decoding are the register-exchange method (REM) and the trace-back method (TBM). The REM is conceptually simple, but it is not appropriate for VLSI implementation because it requires large power consumption and large chip area. The TBM is the preferred method in the VLSI implementation of Viterbi decoders (VD) having large constraint length and high performance. However, the TBM requires last-in-first-out (LIFO) buffer and has to use multiple read operations for high speed operation. This multiple operation results in complex control logic. In this paper, we propose a new survivor memory management method called trace-delete method (TDM) and realize this algorithm in hardware (H/W) for VLSI implementation and we compare the TDM with the TBM in terms of latency, the number of memory elements, and the requirements of control logic. The main advantage of the proposed method can be found as short latency and less requirements on additional control logic. Especially, if we combine the TDM with block interleaving the implementation is even simpler than the TBM. The method is studied with particular relevance to HDTV.

We propose a new channel assignment algorithm called DVINS (distance variance insertion) to reduce intermodulation products (IMPs) in the one-level SCPC satellite systems. In addition, we propose a DELINS-INSDEL with SDELINS algorithm, which is well suited for improving the intermodulation advantage (IMA) performance. In obtaining sub-optimal channel assignment schemes, DVINS requires very short CPU time by using the variance of distribution for the elements in the distance triangle set. Since the DVINS algorithm does not need to calculate the IMP's levels by direct counting, it takes a shorter CPU time than any other published algorithms. We show the basic concept of the DVINS algorithm, and compare the performance of the DVINS algorithm with other algorithms in terms of the IMA and CPU time. The result shows that the new algorithm exhibits similar performance as other practical algorithms in terms of the IMA, while achieving a remarkable reduction in CPU time. Therefore, it would be highly desirable to use the proposed algorithm to obtain suboptimal channel assignment schemes in one-level SCPC satellite systems with many carriers.>