Ho-Jin Lee

Timing estimation for OFDM systems by using a correlation sequence of preamble

In this paper, we propose a novel timing estimation method for orthogonal frequency division multiplexing (OFDM) systems. The most common approaches in estimating timing use correlation by using a given preamble. Thus, the estimation performance is directly dependent on the specific preamble type. The proposed algorithm estimates the timing by using a simple circular shift operation of the given preamble at the receiver. For this reason, the proposed method can be used for any of the OFDM systems regardless of their preamble structures. The simulation results investigated in this paper reveal that the proposed method remarkably increases the estimation performance by more than 5 dB in terms of the mean squared error compared to conventional methods. We also consider the computational complexity of the methods and introduce a simple structure to reduce the computational burden of the proposed method.

The very short frame of mobile DVB‐RCS: Code design and QoS Performance

SUMMARY In this paper, the design of a new very short frame introduced in the upcoming version of DVB-RCS standard targeting interactive mobile services will be described. The frame design with a special focus on channel coding and performance are addressed in detail, as well as an evaluation of the QoS performance for realistic traffic scenarios, propagation channel conditions, and carrier sizes. Copyright r 2009 John Wiley & Sons, Ltd.

Adaptive buffering scheme for streaming service in intersystem handover between terrestrial and satellite systems

In this paper, we propose an adaptive buffering scheme for streaming service during inter-system handover. In general, the buffering scheme of streaming service is used to compensate for delay jitter of networks. By the way, the terminal, which is served from wireless communication systems, can explore the discontinuation of receiving streaming packets during handover. Especially, in case of inter-system handover, the discontinuation of receiving packets is longer than that of intra-system handover. Therefore, existing buffering schemes cannot fully compensate for the degradation of QoS. The proposed method of this paper is an additional buffering scheme before handover. Using this method, we can prevent the discontinuation of streaming service during handover. This method is validated through simulations.

OFDM channel estimation with timing offset for satellite plus terrestrial multipath channels

In this paper, we propose a discrete Fourier transform (DFT)-based channel estimation and timing synchronization to cope with satellite plus intermediate module repeater (IMR) channels. Conventional DFT-based channel estimations suffer from the timing offset and incorrect channel impulse response, and this results in means square error (MSE) floor of channel estimations. Moreover, timing synchronization accuracy is also degraded on IMR channels. We, therefor, propose an improved DFT-based channel estimation by deciding significant channel taps based on a threshold and we derive this threshold with respect to MSE. Using results from proposed channel estimation, we compensate residual timing offset of conventional timing estimation

Direct sequence spectrum spreading techniques for next generation mobile broadband satellite services

The recently approved mobile version of the Digital Video Broadcasting Return Channel via Satellite (DVB-RCS+M) foresees the use of direct sequence spectrum spreading (DS-SS) in the forward link. The addition of a spreading mode, on top of the conventional time division signaling structure of the fixed DVB-S2, allows in fact for the efficient extension of DVB-S2 to mobile terminals with small aperture antennas operating in Ku (11–14u2009GHz) and Ka (20–30u2009GHz) bands. Spectrum spreading has been introduced to augment the received energy without increasing the transmitted power density, which is limited by regulatory constraints, and to enhance the waveform resilience to co-channel interference. In this paper, we report on the design and assessment of the DS-SS technique that we carried out for its inclusion in the DVB-RCS+M standard. In particular, by comparing the physical layer performance of the spread and nonspread modes in the specific DVB-RCS+M mobile scenarios, we show that the proposed DS-SS technique has no impact on the DVB-RCS+M data detection performance, while satisfying the requirements on interference resilience and received energy augmentation. In order to deal with the acquisition issues raised by the introduction of the DS-SS technique, we then propose and evaluate several synchronization sub-systems able to deal with the specific impairments of the mobile satellite scenarios, that is, large frequency offsets, phase noise, link obstructions, etc. Finally, a possible implementation of the DS-SS technique that fully accommodates the reuse of the specific hardware compatible with conventional DVB-S2 is also reported. Copyright

Inter-System Handover Analysis in Integrated Terrestrial and GEO Satellite Communication Networks for Seamless Mobility

In this paper, we propose the handover decision method for inter-system handover between satellite communication system and terrestrial communication system. The characteristics of signal of satellite communication system are not different from those of terrestrial communication system. Therefore, we analyze the characteristics of satellite signal, and we design the handover decision method to reflect those characteristics. The performance of proposed method is validated through simulations. The proposed method decreases the unnecessary handovers more than that of existing handover method which considers only hysteresis margin.

Satellite radio interfaces compatible to 3GPP WCDMA system

This paper provides an overview of a technical study on the satellite radio interfaces based on 3GPP WCDMA system. First, the outcome of the technical study is introduced, which has been carried out by the Mobile Satellite System Working Group of the ETSI Satellite Earth Satellite Technical Committee (ETSI TC SES MSS). The study dealt with the configurations and performance of the 3GPP WCDMA (UTRAN) radio interface over a satellite link. Second, as an evolution of satellite-specific radio interface, the study results are addressed on the possible adaptations of WCDMA to the satellite link in order to maximize the radio link performance. The resultant outcome of the study was reflected in a detail on the G and C families of the satellite radio interface of the ITU-R Recommendation M.1457, respectively. Copyright

Selective Repeat Hybrid ARQ Type II in the GEO Satellite Networks

Selective repeat hybrid ARQ is not used in terrestrial systems. However, selective repeat hybrid ARQ can largely improve the data throughput with the same memory size as N-channel stop and wait ARQ in GEO satellite environment. Therefore, we research the application of selective repeat hybrid ARQ. In this paper, we analyze the receiver buffer overflow phenomenon, which is the one of most important problem of the application of selective repeat hybrid ARQ. From this analysis, we can give the insight about the proper receiver buffer size. In addition, we propose the method of explicit buffer overflow notification for preventing consecutive packet errors of selective repeat hybrid ARQ type II.

Call Admission Control Scheme with Bandwidth Borrowing in Integrated GEO Satellite Networks

In this paper, we propose the bandwidth borrowing scheme to improve the performance of the blocking probability and analyze the performance of call admission control schemes with bandwidth borrowing and bandwidth reservation. In general, the target transmission rates of communications and streaming services are fixed, but data services do not have the target transmission rates. Therefore, we can control the transmission rates for data services flexibly according to the system loading situation. The bandwidth borrowing scheme is implemented by the transmission rates control of data services through packet scheduler. We make the queueing model about our system model. However, it is difficult to get the analytic solution, so we demonstrate the results through simulations. The simulation results show that there is a 8.7 – 35.2 dB gain at the total blocking probability according to the use of bandwidth borrowing scheme and the use of the bandwidth reservation scheme and the bandwidth borrowing scheme causes to decrease the handoff blocking probability.