Kunseok Kang

Performance Enhancement in Future Mobile Satellite Broadcasting Services

Multimedia broadcast and multicast services have started to outpace simple data unicast services. A hybrid satellite-terrestrial network can provide a cooperative system in such a way as to provide high-quality seamless MBMS effectively. In this article we discuss two promising techniques that can improve the performance of a mobile satellite broadcasting system with HSTN. The objective of the first technique is to obtain diversity gain from independent signal paths; this can be achieved by using the space-time coding technique jointly operated on both the satellite and terrestrial repeaters. The goal of the second scheme is to obtain power gain by using a layered channel coding scheme with which a user terminal adapts to the channel condition. We demonstrate various simulation results for both schemes on the prescribed network structure, and the results show substantial improvements in performance.

A satellite radio interface for IMT-Advanced system using OFDM

In this paper, we introduce a new satellite radio interface technology to provide efficient IMT-Advanced services. Maximizing the commonalities with the terrestrial system is one of the most important factors for cost-effective service delivery, which will finally bring successful deployment of the system. For this purpose, we adopt an OFDM based radio interface. At the same time, the interface should be tailored in order to compensate a long round trip delay of satellite systems. In this paper, we present a number of satellite specified techniques which was developed for this purpose, including frequency reuse technique, uplink synchronization technique, random access technique, and interleaving technique combined with adaptive modulation and coding.

Reduced search for optimum code sets to reduce PAPR in MC-CDMA system

In this paper, we propose a reduced search algorithm to find optimum Walsh-Hadamard (WH) code sets which can maintain almost the minimum peak to average power ratio (PAPR) in multi-carrier (MC) CDMA system. It was discovered that the PAPR of MC-CDMA system can be reduced by suitably allocating the user codes. The code allocation table must be made before the system operation, in order to dynamically allocate the optimum WH code when a user requests a connection. Searching for the optimum code set for each number of users in connection with the reasonable code set size incurs prohibitive computations even with a small alphabet sized modulation scheme such as BPSK or QPSK. The proposed search algorithm shows a tremendous reduction of computational time to search for optimum code sets.

Analysis of interference and availability between satellite and ground components in an integrated mobile-satellite service system

Summary An integrated mobile-satellite service (MSS) system is one of the most promising infrastructures for the efficient use of satellite frequency, and the satellite coverage can be extended by reusing the satellite frequency in its ground components. However, the co-channel interferences caused by the frequency reusing technique may lead to the performance degradation. This paper presents the interference analysis for an integrated MSS system that is composed of a multi-beam satellite, complementary ground components (CGCs), and mobile earth stations, by using statistical simulations. These statistical results are then used to evaluate the availability of the system. Our simulation results reveal that the satellite frequency reuse in the CGCs of the integrated MSS system can increase efficiency of satellite spectrum utilization with a tradeoff between CGC network capacity and intra-system interferences. Copyright

SAT-OFDM: a satellite radio interface for the IMT-advanced system

Summary This paper presents the satellite orthogonal frequency division multiplexing (SAT-OFDM) technology as a satellite radio interface for international mobile telecommunications (IMT)-Advanced. The SAT-OFDM radio interface is designed to provide various advanced IMT services in satellite environments. For cost-effective deployment of a satellite IMT-Advanced system, the radio interface must have a high degree of commonality with third-generation partnership project long-term evolution (3GPP LTE) technology for IMT-Advanced, but it also has a number of different features. Those features are needed to adapt the 3GPP LTE technology for satellite-specific environments such as long round-trip delay, large cell size, and slow-fading satellite channel. In this paper, we summarize the key features of the SAT-OFDM technology and propose satellite specific features included in the SAT-OFDM technology as an adaption way of LTE over satellite. Then we show the performance evaluation results of the SAT-OFDM technology to see the feasibility of LTE over satellite. Copyright

Residual frequency offset compensation-embedded turbo decoder

We propose a modified iterative turbo decoder, which inherently compensates the residual frequency offset remained in the decoder input. Based on the recently proposed phase offset compensation scheme which embeds phase compensation into iterative turbo decoding, we extend it to cover up to the frequency offset compensation. At each iteration, we estimate the residual frequency offset remained in the soft decoder output and compensate it for the next iteration. As iteration goes on, frequency offset is gradually and drastically reduced. Consequently, the severe turbo decoding failure due to even small residual frequency offset can be significantly recovered and then, almost the ideal decoding performance is achieved. Especially for power limited communications under very low SNR environment where the even tiny frequency offset is critical to turbo decoding, the proposed scheme is efficient since it does not require additional transmission power for compensation.

Efficient Time and Frequency Synchronization for OFDM based Wireless Indoor Communication over Rician Fading Channel

We present joint frame synchronization and frequency offset estimation using a new preamble with pseudo-noise sequences in time domain for orthogonal frequency division multiplexing (OFDM) based wireless communication over Rician fading channel. By the proposed scheme, the accuracy of the timing offset estimator is definitely 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 pilot symbol which has lower PAPR than those in conventional schemes. The performance of the proposed method is shown by simulation

HARQ–ARQ interaction method for LTE‐based mobile satellite communication system

SUMMARY Hybrid automatic repeat request (HARQ) and automatic repeat request (ARQ) of the terrestrial long-term evolution (LTE) system are designed considering the very short propagation delay of terrestrial environment. Therefore, when HARQ and ARQ are applied to the LTE-based mobile satellite communication system, the inefficiency is caused by the long propagation delay of satellite environment. This paper proposes the interaction method between HARQ and ARQ for the decrease of inefficiency in the LTE-based mobile satellite communication system. The existing concept of layered architecture about HARQ and ARQ is also maintained in our interaction method. Simulation results reveal that our proposed scheme can provide the larger spectrum efficiency than that of the non-interaction scheme in all environments. The performance improvement can be up to 2.04 times through the interaction method. Copyright

Efficient utilization of an adaptive modulation and coding for mobile satellite systems using LTE-Advanced

One of the most important features of the IMT-Advanced system is to utilize adaptive modulation and coding (AMC) in order to counteract time and/or frequency varying channel conditions. Due to increasing importance of integrated satellite and terrestrial networks, a satellite system specification needs to be designed by considering compatibility with terrestrial systems. In this paper, we propose an efficient utilization of AMC scheme for mobile satellite systems compatible with the LTE-Advanced. Due to a long round-trip delay (RTD) of a satellite system, the adaptation strategy of a satellite system should be quite different from that for the terrestrial system. In our scheme, a variable margin is allocated along with AMC in a comparatively slow fading condition such as open environment, while a long time interleaver is utilized along with AMC in a comparatively fast fading condition such as sub-urban area.

Performance analysis for terrestrial radio waveform for control and non-payload communication of unmanned aircraft systems

Necessity for interoperable control and non-payload communication technology and system deployment is increased for safe unmanned aircraft system (UAS) operation as well as extension of UAS applications. For this, C-band frequency was globally allocated only for CNPC in world radio conference 2012 (WRC-12). The technology development and standardization activities for high reliable UAS CNPC operating in the C-band frequency has already been kicked off in US and efficient radio communication technologies are being considered with respect to the size, weight, power and cost (SWaP-C) of UAS. In this paper, we analyze the terrestrial radio waveform standardized in radio technical commission for aeronautics (RTCA) and make some proposals for its performance enhancement.