Bon-Jun Ku

Forward link capacity of the WCDMA system using high altitude platform stations

High Altitude Platform Station (HAPS) system is considered as one of the most effective solutions to provide high quality wireless communication services, such as IMT-2000 services. In this paper, we provide a method to estimate the reverse link capacity of the wideband code division multiple access (WCDMA) system using HAPS, and demonstrate the results. HAPS would be located at 17 km to 22 km above sea level with a multi-beam antenna system and it leads to considering new channel conditions and system design criteria different from those of the conventional terrestrial system. Therefore, we use a practical system model which represents the HAPS system most appropriately, and it leads to realistic estimation results. We estimate the reverse link capacity of the HAPS WCDMA system considering a multi-cell and multi-HAPS model and compare it to that of the conventional terrestrial system. The estimation results show that the capacity in the border cells is decreased and the capacity of the HAPS WCDMA system is about 1.2 to 1.67 times larger than that of the conventional terrestrial system.

Compatibility study on terrestrial radio system operated in the coverage of multi-beam satellite system

Studies on frequency sharing techniques have been conducted for the efficient utilization of limited frequency resource. In satellite communications, the frequency sharing with other services is important because the service coverage is generally very wide and overlaps with those of other wireless services. This paper introduces a new method to mitigate interference into the terrestrial stations from the Earth station in the same frequency band by means of band segmentations which are portions of the overall operation frequency band divided by frequency reuse factor. We consider a multi-beam satellite system, where frequency bands are reused in each satellite cell. The terrestrial stations in the satellite cell use band segments of adjacent satellite cells and this may decrease the interferences. In addition, we take the concept of exclusion area in order to enhance the interference mitigation performance. By this way, the terrestrial and satellite systems can share the same frequency bands efficiently. The simulation is performed at frequency reuse factors, seven and three.1.

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

Reverse link capacity of the WCDMA system using high altitude platform stations

The high altitude platform station (HAPS) system is considered as one of the most effective solutions to provide high quality wireless communication services, such as IMT-2000 services. In this paper, we provide a method to estimate the reverse link capacity of the wideband code division multiple access (WCDMA) system using HAPS, and demonstrate the results. HAPS would be located at 17 km to 22 km above sea level with a multi-beam antenna system and it leads to a consideration of new channel conditions and system design criteria different from those of the conventional terrestrial system. Therefore, we use a practical system model which represents the HAPS system most appropriately, and it leads to realistic estimation results. We estimate the reverse link capacity of the RAPS WCDMA system considering a multi-cell and multi-HAPS model and compare it to that of the conventional terrestrial system. The estimation results show that the capacity in the border cells is decreased and the capacity of the HAPS WCDMA system is about 1.2 to 1.67 times larger than that of the conventional terrestrial system.

Interference analysis of cellular system due to HAPS system to provide IMT-2000 service

An interference evaluation study is necessary for the frequency sharing between a HAPS (high altitude platform station) system and existing terrestrial communication systems. Appropriate closed form equations for power calculation are derived, taking into account the antenna pattern of the HAPS airship, and interference is evaluated in terms of the interference-to-noise power ratio (I/N) with various parameters.

Design and measurements of Ka-band waveguide dielectric rod antenna for 7 channel digital beamformer for HAPS

HAPS system is required to have strict specification to reduce the interference between adjacent cells. One of the most efficient ways to suppress the grating lobe in visible rang is to shape FTEP (flat-topped element pattern). This work presents the design and experimental results of 7 waveguide dielectric rod array antennas for shaping FTEP in the Ka-band. The calculated element pattern and the measured element pattern are also compared. This prototype antenna will be applied to the multibeam antenna to generate 7 beams using digital beamformer.

Receiver memory management method for HARQ in LTE-based satellite communication system

Summary For the successful deployment of the long term evolution (LTE)-based mobile satellite service, the price of a user terminal is one of the major factors. A user terminal for the LTE-based satellite communication needs to be implemented with a similar hardware size that is used for a terrestrial LTE user terminal. However, for quality of service provision, the satellite user terminal needs a larger size of memories than the terrestrial terminal does. This is very evident by considering that the N-channel stop and wait hybrid automatic repeat request requires proportionally increasing memory size by the propagation delay, resulting in unmanageable amount of memories in the satellite system. To resolve this problem, we propose an efficient memory management method at the user terminal when the size of memory is insufficient. The simulation results in this paper reveal that the proposed method can increase the throughput about 20.7% when a user terminal is operated under very low throughput condition with an insufficient memory size, compared with the case without memory management scheme. In addition, we show that the additional throughput gain can be obtained by the packet scheduling using the information of receiver memory status. Copyright

An efficient MIMO scheme for integrated mobile satellite system

In this paper, we present an efficient interleaving method for SM-MIMO scheme in a cooperative satellite and terrestrial system. In the proposed scheme, we are not only utilizing bit-interleaver for both the satellite and terrestrial paths, but also employ a symbol-interleaver for the satellite path. The interleaver improves the performance by achieving a large diversity gain across the codewords. We present details about the interleaving process for the cooperative technique in an integrated mobile satellite system. Simulation results demonstrate that the proposed interleaving method improves the performance with a reasonable hardware complexity.

A scheduling algorithm for selective repeat HARQ type II in the mobile satellite system

The terrestrial LTE system uses N-channel stop-and-wait(SAW) hybrid automatic repeat request (HARQ). However, N-channel SAW HARQ of Geostationary Earth Orbit (GEO) based mobile satellite communication system needs much more memory than that of the terrestrial system. Therefore, we try to consider the application of the selective repeat HARQ with the insufficient memory. In this paper, we analyze the receiver buffer overflow, which is the problem of the application of the selective repeat HARQ with the insufficient memory, and try to resolve the problem through the packet scheduling. We demonstrate the performance of our algorithm through simulations.

An enhanced cooperative transmit diversity in integrated MSS systems

In this paper, we propose an enhanced cooperative transmit diversity scheme in integrated mobile satellite service (MSS) systems. The proposed scheme is an efficient technique to adapt various power differences between a satellite signal and CGC signals, depending on the position of user equipments in integrated MSS systems. In the proposed scheme, we utilize modified space-time block coding (STBC) in order to realize the transmit diversity for the mobile satellite system with several complementary ground components (CGCs). The satellite and two groups of CGCs operate in unison the send the encoded signals, so that the receiver may realize diversity gain. The simulation results show that the proposed method can provide stable improved performance.