Kun Seok Kang

Adaptive modulation and coding for Long Term Evolution-based mobile satellite communication system

SUMMARY The adaptive modulation and coding (AMC) scheme is mandatory for modern wireless communication systems to overcome inevitable channel impairments. Many of the limitations using AMC are due to the long round-trip delay of a satellite system. This paper proposes an efficient AMC scheme with power control and symbol interleaving that can be effectively applied to satellite systems. In particular, we focus on mobile satellite systems that have maximum compatibility in a Long Term Evolution system. Simulations reveal that the proposed scheme can provide a maximum 10.2% increase of average beam spectral efficiency and a maximum of 8-dB power gain compared with a conventional AMC scheme. Copyright

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.

Advanced Power Control and Handover Algorithms for Mobile Satellite Communications Systems with Ancillary Terrestrial Component

In this paper, modified power control algorithms are proposed for a satellite mobile communications system with ancillary terrestrial component (ATC). In order to increase system capacity and reduce the transmitting power of the users equipment, we propose the modified power control scheme consisting of the modified closed-loop and open-loop power control. The modified closed-loop power control (CLPC) algorithm, combining the delay compensation algorithms and pilot diversity, is mainly applied to the ATC link in urban areas because it is more suitable to the short round-trip delay (RTD). In the case of rural areas where ATCs are not deployed or a signal is not received from ATCs, combining monitoring transmitting power equipment and open-loop power control (OLPC) algorithms using an efficient pilot diversity is mainly applied to the link between the users equipment and the satellite. Two power control algorithms are applied equally to the boundary areas where two kinds of signals are received in order to ensure coverage continuity. The simulation results show that the modified power control scheme has good performance compared to conventional power control schemes in a geostationary earth orbit (GEO) satellite system with ATC.

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.

Call Admission Control Scheme with Bandwidth Borrowing in Integrated Services Network

In this paper, we propose the bandwidth borrowing scheme to improve the performance of call admission control schemes and demonstrate the results. 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 situation. The bandwidth borrowing scheme is implemented by the transmission rates control of data services through the packet scheduler. We make the queuing model for our system model. However, it is difficult to get the analytic solution, so we demonstrate the results through the 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

Blind Time and Frequency Synchronization in OFDM Based Communication

We present joint frame/symbol timing and carrier frequency offset estimation using the first data symbol in a frame, the first half of the first data symbol is identical to the second half in the time domain. Approximately maximum likelihood (ML) estimation is proposed for timing offset and a fractional part of the frequency offset based on both the first data symbol and its cyclic prefix (CP) in time domain. We also find a integer part of the frequency offset with virtual carriers in frequency domain. By the proposed method, the accuracy of the frame/symbol timing synchronization is definitely improved and the timing metric has a peak only at the correct start point of a frame. The performance of the proposed method is shown analytically and by simulation.

Efficient Time and Frequency Offset Estimation for OFDM Based MSS Systems

We consider efficient time and frequency synchronization using one training symbol with a constant envelop for orthogonal frequency division multiplexing (OFDM) based mobile satellite service (MSS) systems over Rician fading channel. We propose a new preamble corresponding to only one OFDM symbol, where multiplication of a value of one sample and a conjugated value of its neighboring sample becomes CAZAC sequence in time domain, and present joint frame/symbol timing and frequency synchronization method through only time domain processing based on this preamble. By the proposed method, the accuracy of the frame/symbol timing synchronization is obviously improved and an estimation range of the frequency offset normalized by the carrier spacing is extremely extended to one half of the total signal bandwidth with only one preamble symbol which has lower peak to average power ratio (PAPR) than those in conventional schemes. The performance of the proposed method is shown by simulation.

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.

Satellite Frequency Reuse Method for Complementary Ground Components in an Integrated MSS System

As a next generation mobile satellite network, an integrated satellite and complementary ground component (CGC) network is recently considered in order to provide seamless,transparent and ubiquitous wireless coverage over the world. In this network, it is essential to reuse efficiently frequencies between satellite and CGC components under tolerable interference level. In this paper, we propose how the CGC can reuse satellite frequencies in an OFDMA based multi-beam mobile satellite system with frequency reuse factor 1. In our scheme, the CGC is operated via beam division multiple access (BDMA) for interference mitigation between satellite and CGC signals.

Coordinated Multi-point Transmission Combined with Cyclic Delay Diversity in Mobile Satellite Communications

In OFDMA based MSS system, the beam planning with frequency reuse factor 1 may induce severe inter-beam interference due to the usage of the same subcarrier between user equipments of adjacent beams. In order to solve this problem, this paper shows a coordinated multi-point transmission scheme combined with cyclic delay diversity. The proposed scheme improves frequency usage efficiency in a beam boundary area and minimizes the interference between adjacent beams in an OFDMA based mobile satellite communication. In addition, Simulation results show that it makes the received signal to noise ratio increased due to diversity gain from cyclic delayed multi-point transmitted signals. This performance gain could be achieved without any modification of a conventional Single-Input and Single-Output tranceiver, differently from the space-frequency transmit diversity scheme.