Multi-site MIMO (Multiple Input Multiple Output) is a key technology to enable next generation cellular networks to achieve high throughput in the cell-edge areas. This paper presents a scheduling algorithm that can be applied to a multi-site MIMO cellular system. Our proposed scheduling scheme, named finite-automaton type scheduler (FA-scheduler), aims to achieve further improvement of cell-edge user throughput. The FA-scheduler is a simple scheme. Here we introduce one setting parameter for user throughput in order to prioritize user terminals whose throughput is lower than the setting parameter. The simulation results show that the user terminals whose user throughput is near the setting parameter are in the majority when the FA-scheduler is applied. The improvement of the cell-edge user throughput depends on the setting parameter.

This paper presents a prediction of the trend in radio resource availability in cognitive radio. In this paper, cognitive radio is defined as the wireless communication technology in which each node communicates via an optimal wireless system based on recognition of the radio resource availability in heterogeneous wireless communication systems. We focused on the prediction of the network allocation vector (NAV) value for radio resource availability in IEEE 802.11, which is one of the candidates for installation in a cognitive radio [1]. We verified the prediction of the future value of the trend in the NAV time series; based on an auto-regressive model (AR model) and using captured data within a real environment. Based on the results of the verification, we show that prediction based on the AR model with suitable parameters is applicable in comparison when the average of the last 10 samples is used as a predicted value and the case where prediction is not applied. Furthermore, it is possible to set up a long update interval for the regression coefficients.

A number of wireless systems have recently adopted an adaptive modulation scheme to improve frequency efficiency. Unlike mobile systems, FWA (fixed wireless access) systems including IEEE 802.16 systems used for MAN (metropolitan area network) are allowed to use quasi-millimeter and millimeter bands, but those are vulnerable to rain attenuation. Adaptive modulation scheme is effective in those systems to improve the availability of wireless links. A 26 GHz-band broadband FWA system with a five-level (1024 QAM to BPSK) adaptive modulation scheme was proposed and developed by the authors for field experiments. This paper introduces field experimental results concerning switching thresholds for adaptive modulation controls using the developed FWA system. The numerical results reveal that conventional ideas, in which identical switching thresholds in terms of BER (bit error rate) apply to all modulation methods and switching thresholds maximizing Layer-2 throughput, can neither obtain the maximum TCP (transmission control protocol) throughput nor satisfy the upper limit of the UDP (user datagram protocol) packet loss rate.

The demand for high-speed data communication and the use of real-time applications in mobile networks is becoming increasingly high and communication systems that specialise in downlink packet transfer are being developed and deployed. In these high-speed downlink packet networks, scheduling at the base station is one of the key technologies to accomplish such high speed. A scheduling algorithm that is based on the proportional fair criterion is widely used in commercial networks, but the problem with such an algorithm is that it does not schedule real-time application traffic efficiently. This paper proposes a new scheduling algorithm for real-time applications that does not need substantial change in the existing system and coexists efficiently with the proportional fair criterion. We evaluate the characteristics of the proposed algorithm through computer simulation and show that the efficiency of the proposed algorithm is better than that of existing algorithms.

Some channel-sensitive scheduling algorithms for mobile packet systems are designed to support real-time traffic. They schedule time slots depending on the channel state and queue length in the base station. Although queue length is correlated with the QoS of real-time applications, the essential performance measure of real-time applications is the playout buffer starvation probability. This study proposes a new scheduling algorithm, the playout-buffer-sensitive (PB) rule, which can efficiently support a mixture of real-time and elastic traffic. The PB rule achieves sufficient QoS for the real-time class as well as allocating higher throughput for the best effort class than the existing algorithms. We numerically show that the efficiency of the PB rule is much closer to the theoretical upper bound than the other algorithms.

In satellite communications systems, in addition to frequency resources, total satellite transmitting power, (i.e., satellite power) is a crucial radio resource, due to the limited capacity of onboard electric generators. To increase system capacity, satellite power constraints have to be taken into account, as well as the frequency constraints. As one approach to this issue, we propose a traffic distribution algorithm using linear programming, which maximizes the accommodated traffic in a multiple-satellite system under satellite power constraints. The algorithms are applicable to all types of satellite systems with multiple satellites (geosynchronous Earth orbit, medium Earth orbit, low Earth orbit, or a combination of any) to increase system capacity with respect to the total amount of traffic accommodated by the systems. Finally, this paper evaluates the performance of the proposed algorithm by distributing traffic demand on the earth's surface to cells irradiated by spot-beams of a satellite and allocating frequency resources to the cells. By using the algorithm that permits power constraints, the ratio of accommodated traffic in a system was improved 12% compared with the case when no power constraints were used.

The basic concept of a novel architecture called statistical lambda multiplexing network (SLAMNet) was proposed to provide a pair of routers with multiple transparent wavelength paths in a dense wavelength division multiplexing (DWDM) network. The architecture achieves statistical multiplex gain in use of limited wavelength resources by dynamically adjusting the number of wavelength paths according to the volume of traffic on a best-effort basis. The most striking feature of the architecture is to switch the wavelength paths without signaling between nodes operated asynchronously. Fundamental performance of the architecture was verified on an experimental system. The basic concept assumes a single hop network of switched wavelength paths, and the assumption limits flexibility and efficiency of network operation. In this paper, the basic concept is extended in order to apply SLAMNet to a multihop network of switched wavelength paths. Based on the extended concept, circuit-based and burst-based wavelength path assignment methods are discussed as implementation scenarios of the architecture.

In a mesh wireless network system that consists of plural wireless nodes, it is important that all wireless nodes share the same time. For example, in a TDD wireless system, the frequency resources utilization over the network can be improved by acquiring TDD frame synchronization. This paper proposes a novel scheme that autonomously realizes the synchronization in a whole wireless network without centralized control. The proposed scheme just needs information from adjacent wireless nodes and other mechanisms are not necessary. In addition, this scheme maintains synchronization in the link connected-area, if the network topology changes or node failure occurs in a local area. The proposed scheme responds flexibly to changing the network topology. The scheme is applicable in the case where many nodes join in and out frequently in the network, such as in nomadic wireless access. This paper discusses the procedures of the proposed synchronization scheme and presents examples of establishment network-wide synchronization and recovery from link failure.

Broadband fixed wireless access (BFWA) systems with multi-hop mesh topology have attracted considerable attention as a promising approach for the next generation high quality, high capacity and high density access infrastructure. This paper deals with the problem of adaptive allocation of radio channels and the routing of the communications traffic by the traffic engineering in the multi-hop mesh wireless networks. A mathematical model and formulation are first presented for the problem and a solution algorithm with a heuristic approach is then proposed. Finally, the performance and the characteristics of the proposed algorithm are evaluated through the numerical results for some example network scenarios.

Broadband fixed wireless access (BFWA) networks with Multipoint-to-Multipoint (MP-MP) systems of mesh topology have recently been considered as a promising approach to realize high quality and high performance networks. Needless to say, it is of prime importance to adopt an effective frequency assignment method suitable for MP-MP systems in order to make maximum use of frequency resources over the system. From the viewpoint of the scalability to network growth, a distributed architecture is preferable compared to a centralized architecture for assigning frequency. This paper firstly identifies constraints on frequency assignment for MP-MP systems and then, proposes an autonomous frequency assignment method. The proposed method dynamically determines an optimum frequency slot for every radio channel in every wireless link, where the number of radio channels is adaptively changed to deal with traffic and link quality changes. In the method, the optimum frequency slot is selected by using an evaluation function. This paper introduces three kinds of evaluation functions and investigates their performances from simulation results.

Broadband fixed wireless access (BFWA) networks with multipoint-to-multipoint (MP-MP) system of mesh topology have attracted considerable attention as a promising approach to realize high quality and performance networks. Selection of a suitable duplex mode plays an important role to attain efficient frequency resource utilization in wireless systems. This paper is intended to identify the optimum duplex mode for MP-MP networks carrying asymmetric traffic. Numerical evaluation of duplex modes-FDD(frequency division duplex), single-carrier TDD (time division duplex), and multi-carrier TDD, which have not been studied in detail, is presented to achieve the purpose of this paper. In addition, two resource allocation algorithms are introduced for multi-carrier TDD to attain an efficient usage of the frequency resources and it is demonstrated that one of the algorithms realizes not only efficient usage of the resources but also robustness to the traffic change. It is concluded that the multi-carrier TDD is the optimal selection from the viewpoints of the resource utilization and the system implementation.

In satellite communications systems, the total satellite transmitting power (in short, 'satellite power') is one of the important radio resources, as well as spectrum resources, because of the limited capability of onboard electric generators. Therefore, for attaining optimum satellite radio resource utilization, it is not enough to just consider the spectrum resources but also to take account of the satellite power. This paper proposes algorithms using the linear programming for optimally distributing the traffic demand to multiple satellites in a system. The algorithms are applicable to any kind of satellite system with multiple satellites (GEO, MEO, LEO or combination of any) to increase the system capacity in terms of the total amount of traffic accommodated by the system. Numerical examples demonstrate that the proposed algorithms contribute to maximizing the system capacity.

FDMA/TDMA non-GEO MSS (mobile satellite services) systems generally require a pre-planned pool of radio resources, i.e., frequency and time slot plan (FTSP), for each gateway Earth station (GES) prior to the real-time channel allocation by the multiple GESs sharing the resources harmoniously. The time-variant nature of those systems implies that a dynamic FTSP planning method is crucial to the operation to cope with time-variant traffic demand and inter-beam interference condition. This paper proposes and compares two resource assignment algorithms (spread type algorithm and concentrated-type algorithm). Numerical evaluation demonstrates that the spread type algorithm is very effective and promising in the FTSP generation for such systems.