Until now, various techniques for predicting fault-prone modules have been proposed and evaluated in terms of their prediction performance; however, their actual contribution to business objectives such as quality improvement and cost reduction has rarely been assessed. This paper proposes using a simulation model of software testing to assess the cost effectiveness of test effort allocation strategies based on fault prediction results. The simulation model estimates the number of discoverable faults with respect to the given test resources, the resource allocation strategy, a set of modules to be tested, and the fault prediction results. In a case study applying fault prediction of a small system to acceptance testing in the telecommunication industry, results from our simulation model showed that the best strategy was to let the test effort be proportional to "the number of expected faults in a module × log(module size)." By using this strategy with our best fault prediction model, the test effort could be reduced by 25 percent while still detecting as many faults as were normally discovered in testing, although the company required about 6 percent of the test effort for metrics collection, data cleansing, and modeling. The simulation results also indicate that the lower bound of acceptable prediction accuracy is around 0.78 in terms of an effort-aware measure, Norm(Popt). The results indicate that reduction of the test effort can be achieved by fault prediction only if the appropriate test strategy is employed with high enough fault prediction accuracy. Based on these preliminary results, we expect further research to assess their general validity with larger systems.

The next-generation wireless access system named DPC-OF/TDMA, which is capable of achieving 100 Mbps carrier bit rate under high mobility environment, has been proposed and is being developed. For the realization of this system, large size of cellular zone is required in order to increase system capacity. However, propagation delays between an access point (AP) and mobile stations (MSs) managed by the AP increase as the cellular zone size is large. These increased propagation delays falls system throughput. In this paper, application of PR-DSMA, which is robust against large propagation delays, to the MAC layer protocol of DPC-OF/DMA is proposed to solve this problem. This paper also conducts performance evaluation in terms of Automatic Request control (ARQ) and cell radius by computer simulation.

This paper proposes a novel time alignment control (TAC) for uplink dynamic parameter controlled orthogonal frequency and time division multiple access (DPC-OF/TDMA), which has been suggested for development of new generation mobile communication system. The purpose of the proposed TAC is reducing an influence of multiple access interference (MAI) by propagation delays (PDs) due to differences of distances between accessing mobile stations (MSs) and an access point (AP). The proposed TAC estimates PDs of all MSs and informs the estimates to them. MSs accessing to AP control their transmission timings according to the informed estimates and compensate PDs. This paper examines the uplink DPC-OF/TDMA with the proposed TAC in term of slot error rate (SER) performances by computer simulation. The result shows that the proposed TAC performs precisely to compensate PDs, and that the uplink DPC-OF/TDMA with proposed TAC enables an equivalent performance to an ideal one under no PDs condition.

We propose a new simple timing synchronization method for the orthogonal frequency division multiplexing (OFDM) packet transmission systems in this paper. The conventional synchronization method adopts to calculate signal correlation by multiplication employing the feature of preamble or cyclic prefix in burst packet. However, multiplication circuit makes volume of digital signal processing (DSP) larger and more complex. In order to design a low-complex receiver, we replace the complex process by multiplication with the simple one by subtraction in the proposed method. We evaluated the performance of the proposed method from view points of timing offset mean, variance and bit error rate (BER) performance by computer simulation. Adopting simpler process, the proposed method shows that it can acquire quite smaller variance of timing offset and has equivalent BER performance to the conventional method under both slow and fast multipath fading environments.

This paper considers the call dropping probability in cellular systems with multihop wireless networking, and evaluates the relation between the call dropping probability and mobility patterns of the nodes. Also, this paper considers the difference between a cellular network with multihop networking and a multihop network without base stations. To compare these networks, the call dropping probability and the mean lifetime of a path are considered.

This paper proposes a new amplitude and phase compensation scheme for OFDM packet transmission systems in order to compensate severe and time-variant fluctuation of the received signal amplitude and phase under fast fading environment. The proposed scheme, in addition to the conventional scheme that averages and updates the estimated propagation characteristics on each subchannel, detects subchannels that are momentarily distorted by noise and inter-carrier-interference (ICI) over the fast frequency-selective channels, or by the sudden intercept owing to the shadowing effects. The information of the detected subchannel is used to improve accuracy of the compensation when update the estimated propagation characteristics. The performance of the proposed OFDM packet transmission system was evaluated from several aspects by computer simulation. As a result, by using the proposed scheme, packet error rate (PER) is improved under a high-mobility environment in comparison with the conventional scheme.

An adaptive zone configuration system for land mobile communications was examined using a developed circular, 8-element array antenna. Simulations were performed to investigate the effectiveness of the adaptive zone configuration system compared with the present omni directional zone system. It was found that the adaptive zone configuration system was more effective than the omni zone system in controlling the blocking rate (BR) and the ratio of the mean power of the communication zone.

We consider the structure of a flow network realized from a given terminal capacity matrix. As a result, we show a necessary and sufficient condition that a terminal capacity matrix is possible of realizing any graph. And in the case that the correspondence relation of vertices in a graph G and columns of an elementary terminal capacity matrix T/sub E/ are given, we show a sufficient condition and a necessary condition for the structure of the fundamental graph, for which is possible to realize T/sub E/.

Abstract The concept of vulnerability of a network, by which we mean the susceptibility of the network to attack, is very useful for the design of networks such as computer networks and communication networks. In this paper, a directed flow network, in which a nonnegative real number called edge capacity or capacity is associated with each edge is considered. If an edge in a network is destroyed, the value of maximum flow between two vertices in the network is decreased in general. If the decrease of the value of maximum flow by the destruction is large, the degree of influence of the edge on the vulnerability of the network is considered to be large. Two indices measuring the degree of influence of an edge on the vulnerability in the above sense are proposed and their properties are studied in this paper. Furthermore, the two indices are generalized to functions measuring the degree of influence of an edge on the vulnerability in a network.