Yoshikuni Onozato

Region division assignment of orthogonal variable-spreading-factor codes in W-CDMA

This work focuses on the problem of efficient assignment of the orthogonal-variable-spreading-factor (OVSF) codes for multimedia communications in W-CDMA systems. Due to the problem of code blocking in OVSF-code assignment considered by Minn and Siu, and the different probability of requests for each data rate, the OVSF-code assignment algorithms proposed so far cannot efficiently serve the high-rate requests when traffic load is high. Even though Minn and Siu proposed the algorithm to completely eliminate the code blocking, a system implemented with such an algorithm has a lower number of simultaneous voice conversations than the system with the code blocking problem. To efficiently provide the services for all supported rates, we propose an OVSF-code assignment scheme called the region division assignment (RDA). The performance of the proposed RDA scheme is evaluated by simulation for voice and video sources based on the multiple access protocol in UMTS/IMT-2000.

Spatial correlation for a circular antenna array and its applications in wireless communication

In this paper, we derive spatial correlation functions of linear and circular antenna arrays for three types of angular energy distributions: a Gaussian angle distribution, the angular energy distribution arising from a Gaussian spatial distribution, and uniform angular distribution. The spatial correlation functions are investigated carefully. The spatial correlation is a function of antenna spacing, array geometry and the angular energy distribution. In order to emphasize the research and their applications in diversity reception, as an example, performance of the antenna arrays with MRC in correlated Nakagami fading channels is investigated, in which analytical formulas of average BER for the spatial correlation are obtained.

Generalized spatial correlation equations for antenna arrays in wireless diversity reception exact and approximate analyses

Multiple antenna systems are promising architectures for overcoming the effects of multi-path interference and increasing the spectrum efficiency. In order to be able to investigate these systems, in this article, we derive the generalized spatial correlation equations of a circular antenna array for two typical angular energy distributions: a Gaussian angle distribution and uniform angular distribution. The generalized spatial correlation equations are investigated carefully by exact and approximate analyses.

Hybrid OVSF code assignment scheme in W-CDMA

This paper focuses on an analysis of an orthogonal-variable-spreading-factor (OVSF) codes assignment scheme called the hybrid OVSF-code assignment (HCA). We propose HCA as an alternative solution for OVSF code assignment in order to mitigate so-called code blocking in OVSF-CDMA and to correspond to each service equally. We present the performance evaluation of HCA by computer simulations.

Cell loss properties for multiplexing of MPEG video sources considering picture coding types in ATM networks

In MPEG coding, there are three types of encoded pictures. Since these picture coding types have different importance of data content, the cell loss of each picture coding type affects the video quality differently in MPEG video transmission through ATM networks. This paper analyzed the per-session cell loss properties of MPEG video traffic in an ATM switching node in both the steady-state case and the transient case considering each picture type. In the analysis, a 3-state Markov modulated Bernoulli process (MMBP) is proposed as a traffic model for MPEG video which is tractable analytically. Numerical results revealed the influence of the picture transmission pattern on the cell loss properties of each picture coding type.

Performance evaluation of power level division multiple access (PDMA) scheme

The authors present a new multiple access method, PDMA (power level division multiple access), for sharing a common channel among stations by dividing the channel into several power levels. By this method, the capture effect among packets sent at different power levels can be exploited. The authors propose two access schemes employing PDMA and show that the schemes improve the throughput-delay characteristics of the conventional schemes. An approximate analysis of the performance of each scheme is presented. The analytical results are in agreement with the simulation results.<<ETX>>

Data rate improvement with dynamic reassignment of spreading codes for DS-CDMA

We investigate a dynamic reassignment of spreading codes for DS-CDMA systems by reconstructing the code tree, according to the number of users in the system. The system may provide the maximum transmission rate in the homogeneous communication situation, where only delay-tolerant services are supported. The improvement on average data rate when using the reassignment scheme compared to the system without applying it is calculated. The simulation results are also given to demonstrate the effectiveness of the proposed scheme.

Performance evaluation of orthogonal variable-spreading-factor code assignment schemes in W-CDMA

This paper compares the performance of the orthogonal-variable-spreading-factor (OVSF) code assignment among three proposed schemes so far, i.e., the conventional OVSF-code assignment scheme (CONV), the dynamic OVSF-code assignment scheme (DCA), and region division assignment scheme (RDA). In OVSF-CDMA, the maintenance of orthogonality among the assigned OVSF codes causes the code blocking problem which increases the high blocking rate for high-rate requests. DCA is aimed at eliminating the code blocking problem in order to reduce the high blocking rate for high-rate requests, whereas RDA has been proposed to mitigate the code blocking problem in order to efficiently provide services for all supported rates. The computer simulation results show that the blocking probability of RDA is lower than that of DCA under heavy traffic conditions. The simulation results also show that the calculation time of DCA is significantly larger than that of RDA. Furthermore, RDA is shown to be able to simultaneously handle many more voice sources than DCA.

Effects of cell distance on capacity of two-tier cellular networks

Two well known methods to increase the capacity in a cellular network, TDMA and CDMA, are evaluated on a two-tier cellular structure. In order to use the network resources preciously, we consider sharing the available spectrum effectively between these tiers. We investigate two models, called System I and System II. In System I, CDMA access methods are employed in both layers. In System II, TDMA is deployed for users in the microcell tier and CDMA for macrocell users. The results of numerical calculations are presented. The impact of interference caused by different distances among the related cells is assessed. It is shown that the capacity of the above systems is decreased as the distance of related cells becomes closer. The characteristics showing that System I is better than System II in terms of user capacity, can be recognized for various values of cell distances.

Simulation-Based Optimization on MPEG-4 over SCTP Multi-streaming with Differentiated Retransmission Policy in Lossy Link

The stream control transmission protocol (SCTP) is a reliable transport layer protocol standardized by IETF as RFC 2960 in 2000. Because of its attractive features such as multi-homing and multi-streaming, SCTP has received much attention from researchers in worldwide with an expectation that would address limitations of TCP performance encountered in wired-cum-wireless networks. In this paper, we focus on the multi-streaming feature of SCTP. Making use of the partial reliability extension in SCTP, we compare performance of MPEG-4 video quality under the policy with/without differentiated retransmission among streams. Differentiated policy allows packets belonging to a specific stream to be retransmitted, while packets are transmitted exactly one time (no retransmissions) in homogeneous policy. We show by simulation, that video object traffic streams encoded by MPEG-4 can be efficiently conveyed under lossy link by SCTP with differentiated policy among streams than with homogeneous policy. We further analyze and show, also by simulation, that SCTP with optimally tuned retransmission policy can minimize the play- out delay time as well as keep high quality video decoding of MPEG-4 traffic stream.