Suil Kim

Efficient frequency-hopping synchronization for satellite communications using dehop-rehop transponders

A simple and efficient method of frequency hopping synchronization for the dehop-rehop satellite transponder is proposed. This method enables simultaneous synchronization of the up- and downlinks through two steps only, which minimizes the overall acquisition time. The mean acquisition time of the method is mathematically derived and simulated. A comparison with conventional methods confirms the effectiveness of the proposed method. In addition, synchronization failure because of the drift of the satellite can be resolved.

Joint resource allocation, routing and CAC for uplink OFDMA networks with cooperative relaying

In this paper, we propose a joint resource allocation, routing, and connection admission control (CAC) scheme for uplink transmission in orthogonal frequency division multiple access (OFDMA) relay networks with cooperative relaying. For cooperative relaying, relay station can relay uplink data from mobile station (MS) to base station with cooperation of the MS using transmit diversity. Transmit diversity can be achieved by virtual MISO via distributed space–time coding. The proposed scheme jointly allocates OFDMA resources and selects path for each user with CAC to maximize the upink throughput of cooperative OFDMA relay networks. The basic OFDMA resource unit is considered as a resource element which is one subcarrier over one OFDMA symbol. An efficient multi-choice multi-dimensional knapsack (MMKP) algorithm is presented for the proposed scheme. The proposed MMKP algorithm provides a unified framework which is applicable to OFDMA networks with and without cooperative relaying. We evaluate the performance of the proposed scheme with and without cooperative relaying in a hilly terrain with heavy tree density by using OPNET-based simulation. We show that the cooperative relaying improve the uplink system throughput compared with non-cooperative relaying, and the proposed scheme outperforms the conventional link quality-based scheme in both cooperative and non-cooperative relay networks.

Performance analysis of OSTBC in gamma-gamma fading channels

The multi-input multi-output (MIMO) system with a subcarrier intensity modulation (SIM) scheme in free-space optics (FSO) has a huge merit for ultra wide band communications mainly due to its diversity gain to be able to mitigate the signal scintillation caused by the atmospheric turbulence. In this study, we have analyzed the performance of the orthogonal space-time block codes (OSTBCs) in FSO links. In particular, the power series expressions of the outage probability and average bit error rate (BER) of the OSTBC for any number of antennas are derived in gamma-gamma fading channels using the SIM scheme. According to the analysis, the 3×2 OSTBC scheme could achieve a significantly high signal-to-noise ratio (SNR) gain of 62.5 dB in a strong turbulence regime, and also a moderately high SNR gain of 48 dB in a moderate turbulence regime over the no diversity at the BER of 10-6. Monte Carlo simulation results verify the accuracy of our analysis.

Range estimation of turbo coded waveforms over vegetative mountain blockage using link budget analysis

This paper is on the estimation of radio delivery range of multimedia data using turbo coded waveforms under terrain blockage. To achieve high throughput of multimedia data transmission with limited power under hostile radio propagation environment, multiple turbo coded waveforms of QPSK, 8-PSK, 16 and 64-QAM are employed. Towards effective estimation of the maximum transmission range, models of ground to ground (GTG) communication scenario under mountain blockage with/without vegetation is considered at 800 MHz. The estimated range is obtained by using extensive link budget analysis (LBA) based on the major parameters of transmit power, transmit/receive antenna heights and path losses under different channel conditions including AWGN and Rayleigh fading. Results of LBA show that terrain blockage of vegetative mountain is the worst radio propagation region. Doppler Effect also impacts on the reduction of estimated ranges as data rate increases.

Performance analysis of FFH-FDMA satellite communication system using partial processing Dehop-Rehop Transponder (DRT) under jamming

This paper presents simulation results which illustrate the performance of a fast frequency hopped - frequency division multiple access (FFH-FDMA) satellite communication system using a partial processing Dehop-Rehop Transponder (DRT) under jamming. In the simulated system, convolutional coded symbols (using rates 1/2 or 1/4) are hopped with time diversity to enhance the anti-jamming (AJ) capacity. This study examines the combined effect of time diversity and channel coding under the influence of TWTA nonlinearity, jammer strength and up/down link channel noises on the end-to-end bit error rate (BER) of the DRT system. The simulated results show that under the considered jamming environments of partial band noise jamming (PBNJ) and band multi-tone jamming (BMTJ), excessive TWTA input back-off (IBOF) does not necessarily enhance the performance; rather, it greatly degrades the BER, particularly when channel noise is non-negligible. It was also verified that under the same conditions, time diversity and convolutional coding must be carefully combined to avoid possible degradation in FH-FDMA satellite channel.

Analysis of Iterative Erasure Insertion and Decoding of FH/MFSK Systems without Channel State Information

We analyze the symbol measures for iterative erasure insertion and decoding of a Reed-Solomon coded SFH/MFSK system over jamming channels. In contrast to conventional erasure insertion schemes, iterative schemes do not require any preoptimized threshold or channel state information at the receiver. We confirm the performance improvement using a generalized minimum distance (GMD) decoding method with three different symbol measures. To analyze performance, we propose a new analysis framework considering the “trapped-error” probability. From analysis and the simulation results, we show that ratio-based GMD decoding has the best performance among the one-dimensional iterative erasure insertion and decoding schemes.

Performance Analysis of Coherent FSO-OFDM Systems With Frequency Offset

In this letter, we investigate the performance of coherent free-space optical (FSO)-orthogonal frequency division multiplexing (OFDM) systems with multiple receivers over an atmospheric turbulence channel considering the frequency offset effect. In particular, we derive an exact average bit error probability (ABEP) of coherent FSO-OFDM systems in a turbulence-induced fading channel. To mitigate the atmospheric turbulence-induced amplitude fluctuations and phase aberrations, a modal compensation technique is assumed to be employed at the receivers. Numerical results confirm the validity of the derived ABEP expression.

Geometric programming applied to multipoint-to-multipoint MIMO relay networks

In this paper, we consider a relaying system which employs a single relay in a wireless network with distributed sources and destinations. Here, all source, destination, and relay nodes are equipped with multiple antennas. For amplify-and-forward relay systems, we confirm the achievable sum rate through a joint multiple source precoders and a single relay filter design. To this end, we propose a new linear processing scheme in terms of maximizing the sum rate performance by applying a blockwise relaying method combined with geometric programming techniques. By allowing the global channel knowledge at the source nodes, we show that this joint design problem is formulated as a standard geometric program, which can guarantees a global optimal value under the modified sum rate criterion. Simulation results show that the proposed blockwise relaying scheme with the joint power allocation method provides substantial sum rate gain compared to the conventional schemes.

Traffic-aware adaptive routing metrics for tactical ad hoc networks

In tactical environment, MANET (Mobile Ad Hoc Network) has the network characteristics which make highly dynamic nodes, self-organized in fully-distributed style. Also, it has a harsh wireless channel environment compared to the commercial networks. In these channel environments, optimal path decision suited for Quality of Service (QoS) of transmitted tactical traffics must be performed by recognizing various environmental factors of wireless channels and the status of tactical mobile radio nodes autonomously to construct reliable communication links. In this paper, we newly define the required QoS features of tactical traffics and the characteristics of routing metrics in tactical network environment. We also propose a new ad hoc routing algorithm to ensure an efficient communication in tactical environment by calculating the optimal path using adaptive selection of routing metrics according to traffic characteristics. Simulation results show that the proposed algorithm outperforms existing ad hoc routing schemes, especially when tactical network has a high mobility and a high traffic load.

Evaluation of multimedia quality of service parameters in on-board switching ATM network

As the demand for multimedia traffic via satellite increase, quality of service (QoS) management becomes more crucial, especially for the effective utilization of on-board switching capabilities of multi-beam satellite system. For multimedia services, parameters related to different requirements need to be evaluated in terms of delay, jitter, blocking probability and burstiness. This paper is on the evaluation of QoS parameters associated with the transmission of multimedia information including voice, video and data through satellite on-board ATM switching network by using various onboard switching algorithms and queueing analyses. Specifically, we evaluate and compare the performance of on-board switching algorithm of Djikstra, Bellman-Ford, and K-shortest path on the most efficient ATM network (Banyan, Benes, and Batcher-Banyan networks) along with M/G/1 queuing system. The parameters used for MF-TDMA uplink and TDM downlink simulations include: end-to-end delay, queuing delay, burstiness factor for varying traffic load on the network, and blocking probability for various holding time. Results show that, for small and medium size networks, Djikstras algorithm is most effective in terms of delay whereas K-shortest path algorithm is most effective for large network. Towards low blocking probability and burstiness factor, the Batcher-Banyan ATM network with the single server M/G/1 queue is most efficient.