Packet scheduling is one of the key mechanisms that will be employed in the network nodes (routers and switches) for supporting multiple quality of services. In this paper we propose a new packet scheduling algorithm called Urgency-based Round Robin (URR) which computes an index for flows in order to keep track of instantaneous bursts. Basically the index is employed as a measure of the time-dependent service necessity for each flow thus making it possible to detect those flows which might be in need of momentary service. Also, we propose a novel weight allocation scheme to be used together with the scheduler with the aim of preventing network underutilization. Our algorithm can be considered as a version of Weighted Round Robin (WRR) with improved delay characteristics. We show analytically that URR has the desired capability of upper-bounding unfairness. We also show, by simulation, that URR can improve delay performance even under extremely bursty traffic conditions without bandwidth overprovisioning. We also give simulation results for network traffic which exhibits long range dependency (self-similarity) and show that URR is again more effective than a plain round robin multiplexer.

This paper presents experimental results obtained in indoor broad-band transmission experiments using a QPSK-100 Mbps modem in the 37 GHz band. Transmission performance is measured at many antenna locations in an office. The zone coverage, defined points where as the BER was less than 10-7, was derived in order to evaluate the possibility of high-speed transmission. It was found that adjusting the receiving antenna position a few centimeters greatly improves the zone coverage in utilizing millimeter waves. This result indicates the effectiveness in improving zone coverage of space diversity reception with an antenna spacing of several centimeters. Experimental results obtained show that zone coverage of up to 70% in the measured range is achieved by space diversity reception. Thus, the feasibility of 100 Mbps indoor wireless transmission, conventionally thought to be impossible, is experimentally confirmed.

In order to improve fairness and stability of TCP best-effort service we propose a new congestion control algorithm using packet loss information obtained from Selective Acknowledgments (SACK), and evaluate its effectiveness by simulation. The proposed scheme is for an environment consisting of Random Early Detection (RED) routers which drop each arriving packet with a certain probability after a threshold. The proposed mechanism adjusts the decrease in congestion window for Fast Recovery and the increase in congestion window per ACK during the congestion avoidance phase according to the number of lost packets. Simulation results show that not only the bandwidth allocation fairness is improved but also throughput deviation is markedly reduced resulting in more stable transport capability.

A new broadband space diversity (B-SD) combining method, which is a key technique in the growth of digital microwave radio system, is proposed. In this B-SD combining method, two received signals, whose bandwidths are 280 MHz, are combined. To develop this combining method, an optimum control algorithm is developed that monitors power levels of all primary carriers and controls the endless phase shifter so that the higher level signal is decreased and the lower level signal is increased. This paper describes the proposed B-SD combining method which effectively operates over a wide bandwidth. Performance evaluations based on simulations and theoretical estimations are given. It is proven that this combining method offers the same performance obtained by the conventional narrowband SD combining method and can be applied to over 50% cases of the propagation paths observed in Japan. The suitability of the proposed combining method and the calculation methods adopted is demonstrated experimentally.

In the digital terrestrial TV broadcasting system, it is important to evaluate both quantitative levels and sources of overreach interference, because it can degrade the TV service quality. This paper newly proposes an overreach measurement method that simultaneously monitors RSSI (Received Signal Strength Indicator) and CNR (Carrier to Noise power Ratio) of the TV waves and RSSI of FM waves. The results of measurements conducted in Hiroshima prefecture show that our proposed method can evaluate the level of overreach interference in the TV waves and also identify the source of the interference. Total 43 overreach interference events were found in the proposed method from one-year measurement in 2012. Based on M profile data, this paper also shows that the main factor of the overreach interference in this measurement is duct propagation due to meteorological condition.

In wireless access system, we need to use a limited frequency and electric power efficiently. And so we propose the fixed wireless access network using 5 GHz frequency which band has a good propagation performance in line of sight (LOS). In the proposed network, the several multi-level modulation methods are combined and identical frequency is reused by considering on the antenna directivity. As constructing this network, we can efficiently use frequency in 5 GHz band and enlarge system capacity. In this paper, it is assumed that user terminals are distributed nonuniformly over the service area. We analyze accommodation number of user terminals and the optimum combination of modulation methods. Numerical results show that most effective method is the combination of 16QAM and 256QAM, which can accommodate up to about 1.4 times as many users as only QPSK modulation method.

This paper describes the design and performance of a new adaptive IF equalizer for correcting amplitude and group delay dispersion due to selective fading in a 200 Mb/s, 16 QAM digital radio system. This equalizer contains only a simple variable-resonance circuit automatically controlled by a microcomputer. This adaptive equalizer can reduce both amplitude and delay dispersions due to minimum phase fading and amplitude dispersion due to non-minimum phase fading. In field trial tests (over-water, 52.6 km span), outage time for 16 QAM signals was significantly reduced by about 80% during severe fading periods by about 97.5% during two fading months using this equalizer. Additionally, the in-band amplitude dispersion probability was reduced by about 99%.

One of the most important topics of recent years is use of multimedia technology in radio systems for video, voice and data transmission. On the other hand, a major problem in such systems is the occurrence of errors due to multipath or interference noise. Forward error correction (FEC) is commonly used as a means of eliminating these errors. When employing the FEC technique, it is important to ensure that coding rate and coding gain requirements are met. In multimedia systems, however, the requirements differ with the type of media involved such as real-time voice, real-time video and data transmission. This paper proposes a variable-rate FEC method for multimedia systems as a means of overcoming this problem. The paper begins by presenting an information box and an ATM wireless LAN as examples of multimedia radio communication, and describes how the proposed variable-rate FEC method can be applied to these systems. Next, it shows in some detail how the ATM cells used in the variable-rate FEC are constructed. Then, it analyzes the effects of variable-rate FEC by employing a parameter called the Information Transmission Rate (ITR), which is defined as the product of the throughput rate and the coding rate. Finally, it shows the effects which the variable-rate FEC has on a typical quantity of traffic.