This paper proposes a new channel allocation algorithm for satellite communication systems. The algorithm is based on a spectrum division transmission technique as well as a spectrum compression transmission technique that we have developed in separate pieces of work. Using these techniques, the algorithm optimizes the spectrum bandwidth and a MODCOD (modulation and FEC error coding rate) scheme to balance the usable amount of satellite transponder bandwidth and satellite transmission power. Moreover, it determines the center frequency and bandwidth of each divided subspectra depending on the unused bandwidth of the satellite transponder bandwidth. As a result, the proposed algorithm enables flexible and effective usage of satellite resources (bandwidth and power) in channel allocations and thus enhances satellite communication (SATCOM) system capacity.

This paper proposes a novel satellite channel allocation algorithm for a demand assigned multiple access (DAMA) controller. In satellite communication systems, the channels' total bandwidth and total power are limited by the satellite's transponder bandwidth and transmission power (satellite resources). Our algorithm is based on multi-carrier transmission and adaptive modulation methods. It optimizes channel elements such as the number of sub-carriers, modulation level, and forward error correction (FEC) coding rate. As a result, the satellite's transponder bandwidth and transmission power can be simultaneously used to the maximum and the overall system capacity, i.e., total transmission bit rate, will increase. Simulation results show that our algorithm increases the overall system capacity by 1.3 times compared with the conventional fixed modulation algorithm.

To obtain large capacity, high quality mobile satellite communication systems in the future, we must use a multi-beam that can cope with extremely high levels of frequency reuse. This paper describes a novel resource allocation algorithm for multi-beam satellite communication systems that can dynamically adapt to maximum communication capacity without compromising quality. The algorithm combines two resource allocation schemes that enable it to contend with the ever-changing user distribution and inter-beam interference conditions. The first scheme optimizes the resources amongst beams. To minimize interference, the optimal constraint conditions are clarified when all clusters share and occupy the same bandwidth completely. These constraints are used in the optimization algorithm. The second scheme manages the various required resources and adapts them to the beam gain and interference levels at various user locations within a single beam. We propose a fixed power adaptive modulation scheme to obtain stable communications. This two-layered scheme can satisfactorily allocate multi-beam satellite resources to contend with the increasing communication capacity and still improve the quality.

This paper describes a novel channel allocation scheme that enables data to be collected from observation points throughout the ultra-wide area covered by a satellite communication system. Most of the earth stations in the system acquire pre-scheduled type data such as that pertaining to rainfall and temperature measurements, but a few of them acquire event-driven type data such as that pertaining to earthquakes. Therefore, the main issue pertaining to this scheme is how to effectively accommodate demand for the channels by a huge number of earth stations with limited satellite frequency bandwidth regardless of their acquired data types. To tackle this issue, we propose a channel allocation scheme built on a pre-assigned scheme to gather pre-scheduled type data but that also includes an additional procedure to gather event-driven type data reliably. Performance evaluations show that the proposed scheme achieves higher throughput and lower packet loss rate than conventional schemes.

This paper proposes a dynamic spectrum controlled (DSTC) channel allocation algorithm to increase the total throughput of satellite communication (SATCOM) systems. To effectively use satellite resources such as the satellite's maximum transponder bandwidth and maximum transmission power and to handle the propagation gain variation at all earth stations, the DSTC algorithm uses two new transmission techniques: spectrum compression and spectrum division. The algorithm controls various transmission parameters, such as the spectrum compression ratio, number of spectrum divisions, combination of modulation method and FEC coding rate (MODCOD), transmission power, and spectrum bandwidth to ensure a constant transmission bit rate under variable propagation conditions. Simulation results show that the DSTC algorithm achieves up to 1.6 times higher throughput than a simple MODCOD-based algorithm.

This paper proposes Direct Spectrum Division Transmission with spectrum editing technique. The transmitter divides the single carrier modulated signal into multiple “sub-spectra” in the frequency domain and arranges each sub-spectrum so as to more fully utilize the unused frequency resources. In the receiver, the divided sub-spectra are combined in the frequency domain and demodulated. By editing the divided spectrum in the frequency domain, the total bandwidth occupied by the multiple “sub-spectra” is less than that of the modulated signal. The proposed technique allows the unused frequency resources scattered across the bands to be better utilized. Simulations show that the proposed technique makes the bit error rate negligible.

This paper introduces distributed array antenna (DAA) systems that offer high antenna gain. A DAA consists of several small antennas with improved antenna gain. This paper proposes a technique that suppresses the off-axis undesired radiation and compensates the time delay by combining signal processing with optimization of array element positioning. It suppresses the undesired radiation by compensating the delay timing with high accuracy and deliberately generating the inter-symbol interference (ISI) in side-lobe directions. Computer simulations show its effective suppression of the equivalent isotropic radiated power (EIRP) pattern and its excellent BER performance.

Long-distance wireless local area networks (WLANs) are the key enablers of wide-area and low-cost access networks in rural areas. In a WLAN, the long propagation delay between an access point (AP) and stations (STAs) significantly degrades the throughput and creates a throughput imbalance because the delay causes unexpected frame collisions. This paper summarizes the problems caused in the medium access control (MAC) mechanism of the WLAN by a long propagation delay. We propose a MAC protocol for solving the delay-induced throughput degradation and the throughput imbalance between the uplink and the downlink in WLANs to address these problems. In the protocol, the AP extends NAV duration of CTS frame to protect an ACK frame and transmits its data frame to avoid delay induced frame collisions by piggybacking on the ACK frame transmission. We also provide a throughput model for the proposed protocol based on the Bianchi model. A numerical analysis using the proposed throughput model and simulation evaluation demonstrate that the proposed protocol increases the system throughput by 150% compared with that obtained using the conventional method, and the uplink throughput can be increased to the same level as the downlink throughput.