Changho Yun

Transmission rate control of ASO-TDMA in multi-hop maritime communication network

We consider a ship ad-hoc network (SANET) that extends the service coverage for data communication with the multi-hop connectivity among the ships. In this paper, we propose two means of transmission rate control to maximize the system throughput subject to the reservation-based random access that is is inherent to the ad-hoc self-organizing TDMA (ASO-TDMA) protocol in SANET. It has been demonstrated that the proposed control schemes can maintain the maximum system throughput adaptively as the number of ships varies for the different hop ranges and their target attempt rates.

Statistical Analysis of VHF Channel Over the Sea Surface for Various Ranges

VHF is generally used for data or voice communications between ships and land stations. Although there exist many analytical and empirical channel models for radio waves on land, over-the-sea models are very limited to basic description. In this paper, a VHF channel is measured using vertical and/or horizontal whip antennas on shore and a moving ship for various ranges. The results show that the Doppler shift and changes in power for various ranges are observed. We can also find that the statistical analysis results in that the statistical parameters are rapidly changes, especially for V/H and H/V channels.

The Conceptual Design and User Requirement Analysis of the HCI Multi-function Console for Ship

The multi-function console system in ships has currently exposed operational difficulties due to its complex interfaces although it supports a variety of functionalities. In this paper the concept of a human computer interaction (HCI) based multi-function console system is proposed, which can support intuitive operation environments by the analysis of users needs to shipboard systems. Expert interviews and surveys are carried out in order to obtain users requirements. Through the survey results, the HCI based multi-function console system is conceptually designed, which is optimized to the input of multi-touch screen. It is expected that the HCI based multi-function console system can provide ship operators with easy interfaces to the console system as well as safe operation in a rough ocean environment.

Baseband Receiver Design for Maritime VHF Digital Communications

In this paper a design of /4-DQPSK baseband receiver for the exchange of digital data and e-mail between shore and ship stations and/or among ship stations in the maritime mobile service VHF channels is described. Due to the permitted relatively big frequency instability of local oscillators at the transmitter and the receiver of maritime communication system, the designed baseband receiver should have the capabilities of correct estimation and compensation of the synchronization parameters, such as symbol timing and frequency offset, from the received signal which might include relatively big frequency error. Simulated BER results show that the designed baseband receiver works less than 0.5dB loss under AWGN channel when the normalized frequency offset of the received signal is more then 20%.

Underwater acoustic QPSK receiver implementation and its test results at the very shallow water

In this paper, we describe an DSP based implemented QPSK receiver prototype for 25kHz carrier frequency and 5 kHz symbol rate with excess bandwidth 0.35, and its test results at the very shallow water of the South Sea of Korea. The implemented digital receiver prototype for underwater communication is composed of analog and digital signal processing parts. The analog part, composed of an implemented omni-directional acoustic sensor and a bi-directional deriving unit, is in charge of acquiring the acoustic signal and of converting the acoustic signal into an electric signal. The sampled passband signal should be converted into a baseband signal and then the baseband signal is further processed to enhance the signal quality and reduce decision error by synchronizer, equalizer, and Viterbi decoder. The joint synchronizer detects the packet synchronization and estimates the coarse symbol timing and phase offset at the same time. After synchronization, the received baseband signal is decimated to take 4 samples per symbol which is the input of channel equalizer. The channel equalizer improves the quality of signal by reducing the multipath interference and tracking the phase and frequency offsets. The Viterbi decoder decides the transmitted information using the output of equalizer. The implemented QPSK receiver prototype is tested the BER performance by transmitting 160pixel*100pixel*8bit/pixel images with horizontal transmission distances of 1km, 2km and 3km at the very shallow water (approximately 25m water depth). Test result shows that BER is 0, 2.3×10−5, and 1.8×10−3 for the 1km, 2km and 3km transmission distance, respectively.

The least-cost network selection scheme for delay-constrained transmission in the multi-band maritime communication system

As various types of wireless systems are characterized by its own individual reliability and transmission cost in the multi-band maritime communication network, a means of selecting a least-cost system is required for transmitting the shipment information within a pre-specified time constraint. In this paper, a simple decision criterion for a least-cost network selection has been derived with a stochastic Markov decision process, so as to warrant the delay-constrained transmission in a distributed manner. Our simulation results show that the proposed approach can reduce the transmission cost dramatically under the varying channel conditions of the different networks.

The Minimum-cost Network Selection Scheme to Guarantee the Periodic Transmission Opportunity in the Multi-band Maritime Communication System

This paper presents the minimum-cost network selection scheme which determines the transmission instance in the multi-band maritime communication system, so that the shipment-related real-time information can be transmitted within the maximum allowed period. The transmission instances and the corresponding network selection process are modeled by a Markov Decision Process (MDP), for the channel model in the 2-state Markov chain, which can be solved by stochastic dynamic programming. It derives the minimum-cost network selection rule, which can reduce the network cost significantly as compared with the straight-forward scheme with a periodic transmission.