• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.8C
• /
• pp.681-688
• /
• 2007

Applying an appropriate received signal processing algorithm based on the channel characteristics is important to improve the receiver performance. Wireless channels in general exhibit various time-delay characteristics depending on their power delay profile. When the estimated channel power summation is used to determine the amount of time delay, a channel adaptive receiver structure can be implemented. In this paper, we derive a closed-form expression for the error probability of the channel classification when the estimated channel power summation is used to classify channel groups having different time delay characteristics, and present the performance gain utilizing multiple estimation results.

• Journal of Communications and Networks
• /
• v.10 no.2
• /
• pp.163-174
• /
• 2008

Performance of downlink transmission strategies exploiting cooperative transmit diversity is investigated for distributed multiple-input single-output (MISO) systems, for which geographically distributed remote antennas (RA) in a cell can either communicate with distinct mobile stations (MS) or cooperate for a common MS. Statistical characteristics in terms of the signal-to-interference-plus-noise ratio (SINR) and the achievable capacity are analyzed for both cooperative and non-cooperative transmission schemes, and the preferred mode of operation for given channel conditions is presented using the analysis result. In particular, we determine an exact amount of the maximum achievable gain in capacity when RAs for signal transmission are selected based on the instantaneous channel condition, by deriving a general expression for the SINR of such antenna selection based transmission. For important special cases of selecting a single RA for non-cooperative transmission and selecting two RAs for cooperative transmission among three RAs surrounding the MS, closed-form formulas are presented for the SINR and capacity distributions.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.15 no.1
• /
• pp.45-52
• /
• 2015

Since the broadcast message in satellite signals the security of the data is extremely poor compared to other communication technologies such as the broadcast signal. Thus, encryption of the communication satellite has become a very important issue, an analysis of the communication performance of a general service is always required. In this paper, In order to analyze the encrypted communication the turbo code in an IP-based satellite communication applies the code rate compatible punctured and The wireless channel in consideration of the actual satellite communication was constructed by placing a weight on the Rayleigh fading and the Rician fading two channels. Retransmission-based error control scheme were constructed in the best performance of H-ARQ Type-II, III scheme of a number of ways that are recently considered. we analyzed the effects of normal service against a satellite communication network The security services were configured with encryption algorithms AES, ARIA (CTR, CBC mode).

• Journal of Communications and Networks
• /
• v.5 no.2
• /
• pp.157-166
• /
• 2003

This paper deals with the problem of channel identification for Single Input Multiple Output (SIMO) slow fading channels using clustering algorithms. Due to the intrinsic memory of the discrete-time model of the channel, over short observation periods, the received data vectors of the SIMO model are spread in clusters because of the AWGN noise. Each cluster is practically centered around the ideal channel output labels without noise and the noisy received vectors are distributed according to a multivariate Gaussian distribution. Starting from the Markov SIMO channel model, simultaneous maximum ikelihood estimation of the input vector and the channel coefficients reduce to one of obtaining the values of this pair that minimizes the sum of the Euclidean norms between the received and the estimated output vectors. Viterbi algorithm can be used for this purpose provided the trellis diagram of the Markov model can be labeled with the noiseless channel outputs. The problem of identification of the ideal channel outputs, which is the focus of this paper, is then equivalent to designing a Vector Quantizer (VQ) from a training set corresponding to the observed noisy channel outputs. The Linde-Buzo-Gray (LBG)-type clustering algorithms [1] could be used to obtain the noiseless channel output labels from the noisy received vectors. One problem with the use of such algorithms for blind time-varying channel identification is the codebook initialization. This paper looks at two critical issues with regards to the use of VQ for channel identification. The first has to deal with the applicability of this technique in general; we present theoretical results for the conditions under which the technique may be applicable. The second aims at overcoming the codebook initialization problem by proposing a novel approach which attempts to make the first phase of the channel estimation faster than the classical codebook initialization methods. Sample simulation results are provided confirming the effectiveness of the proposed initialization technique.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.12A
• /
• pp.1219-1225
• /
• 2007

In this paper, we propose a new quasi-orthogonal space-time block code(QO-STBC) achieving full rate and full diversity for general QAM and quasi-static Rayleigh fading channels with four transmit antennas. This code possesses the quasi orthogonal property like the conventional minimum decoding complexity QO-STBC(MDC-QO-STBC), which allows independently a maximum likelihood(ML) decoding to only require joint detection of two real symbols. By computer simulation results, we show that the proposed code exhibits the identical BER performance with the existing MDC-QO-STBC. However, the proposed code has an advantage in the transceiver implementation since the original coding scheme may be modified so that increases of peak-to-average power ratio occur at only two transmit antennas, but the MDC-QO-STBC does at all of transmit antennas.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.12 no.3
• /
• pp.360-369
• /
• 2001

This paper proposes the groupwise serial cross interference cancellation(GSCIC) algorithm for coherent detection and analyzes the groupwise serial block interference cancellation(GSBIC) and GSCIC algorithm for an asynchronous wideband DS-CDMA system in a single cell over multipath fading channels. In general, the GSIC algorithm can be grouped into two classes: i.e., GSBIC and GSCIC algorithm. In this paper, the proposed GSCIC algorithm is to improve the performance of the GSBIC algorithm. We compare the performance of the GSCIC and existing GSBIC algorithm in a multipath fading channel to that of the existing SIC algorithm. As a result, the performance of GSCIC algorithm is somewhat better compared with the GSBIC algorithm according to reduction factor $R_{f}$ and is similar to that of the SIC algorithm. And also, the GSBIC and GSCIC algorithms have the advantage that it can be analyzed system performance easily, changing the number of users within a user group according to system capacity.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.2A
• /
• pp.91-99
• /
• 2011

Several repeater systems are used to enhance the cell coverage to location such as shadow and rural areas in mobile systems. But the general RF repeater solutions are not suitable for high power outdoor environment because it has the weakness such as self oscillation problem With adoption of a adaptive digital filter technology, feedback interference cancellation repeater prevents oscillation by detecting and canceling the unwanted feedback signal between transmission and receiver antenna. In this paper, dual NLMS based interference cancellation method is proposed and the step size adaptation can be implemented by the estimation of the feedback channel Doppler frequency characteristics. The performance of the proposed algorithm is quantified via analysis and simulation for the static and multipath fading feedback channels.

• Journal of IKEEE
• /
• v.9 no.2 s.17
• /
• pp.123-135
• /
• 2005

3GPP RLC protocol specification adopted a window-controlled selective-repeat ARQ scheme for provisioning reliable data transmission. Inevitably, the re-ordering issue arises in the 3GPP's ARQ since it belongs to the selective-repeat ARQ clan. A long re-ordering time results in the degradation of throughput and delay performance, and may invoke the overflow of the re-ordering buffer. Also, the re-ordering time must be regulated to meet the requirements of some services which are both loss-sensitive and delay-sensitive. In the 3GPP's ARQ, we may deflate the occupancy of the re-ordering buffer by reducing the window size and/or length of the status report period. Such a decrease, however, deteriorates the throughput and delay performance and encroaches the resource of the reverse channel. Aiming at reducing the occupancy at the re-ordering buffer while suppressing the degradation of throughput and delay performance, we propose threshold-dependent occupancy control schemes, identified as post-threshold and pre-threshold schemes, as supplements to the 3GPP's ARQ. For judging the effectiveness of the proposed schemes, we investigate peak occupancy, maximum throughput and average delay in the practical environment involving fading channels. From the simulation results, we observe that the proposed schemes invoke the performance trade-off between occupancy and throughput in general. Also, we reveal that the post-threshold scheme is able to improve the throughput and delay performance of the ordinary 3GPP's ARQ without inflating the occupancy of the re-ordering buffer.

• Proceedings of the KIEE Conference
• /
• 2004.11c
• /
• pp.196-199
• /
• 2004

This paper presents a structure of the searcher using the space diversity in array antenna system operating in the DS/CDMA signal environments. The new technique exploits the fact that the In-phase and Quadrature components of interferers can respectively be viewed as independent Gaussian noise at each antenna element in most practical CDMA (Code Division Multiple Access) signal environments. The proposed PN acquisition scheme is a single dwell serial PN acquisition system consisting of two stage, that is, the searching stage and the verification stage. The searching stage correlates the received signals with the local PN oscilator for obtaining the synchronous energy at the entire uncertainty region. The verification stage compares the searching energy with the optimal threshold, which is pre-designed in the Lock-Detector, and decides whether the acquisition is successful or fail. In this paper, we analyzed the relationship of both diversity order and the mean acquisition time. In general, It is known that the mean acquisition time decreases significantly as the number of antenna elements increases. But, the enhancement of the performance is saturated in terms of PN acquisition scheme. Therefore, to decrease the mean acquisition time, we must design the optimal array antenna system by considering the operating SNR range of the receiver, the detection probability, and the false alarm probability. The performance of the proposed acquisition scheme is analyzed in frequency-selective Rayleigh fading channels. In this paper, the effect of the number of antenna elements on acquisition scheme is considered in terms of the detection probability, false alarm probability. and the mean acquisition time.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.10A
• /
• pp.839-846
• /
• 2011

Link Adaptation should select the best modulation and coding scheme (MCS) which gives the highest throughput as channel conditions vary. Several link adaptation algorithms for wireless local area network (WLAN) have been proposed but for the future WLAN systems such as 802.11n system, these algorithms do not guarantee the best performance. In this paper, we propose a new link adaptation algorithm in which an MCS level is chosen by the received SNR plus the offset value obtained from the transmission results. The performance of proposed algorithm is simulated by an IEEE 802.11n system. From the analysis, we conclude the proposed algorithm performs better than the well-known link adaptation algorithms such as auto rate fallback and general SNR-based techniques. Particularly, the proposed algorithm improves throughput when the packet error ratio (PER) is constrained for fast fading channels.