In this paper we propose a total quality evaluation method in an ATM network-type remote conference system, and describe the results of evaluations of a proving system. The quality of a remote conference system depends on such various elements as video images, voice signals, and cost; but a total quality index may be regarded as the cost of a remote conference system compared with that of a conventional face-to-face conference. Here, however, the decline in communication quality arising from the remote locations of participants must be included in the evaluation. Moreover, the relative weightings of voice signals, video images of participants, and shared data will vary depending on the type of conference, and these factors must also be taken into account in evaluations. An actual conference systems were constructed for evaluation, and based on a MOS (Mean Opinion Score) of the quality elements, the total system quality was evaluated with reference to the proposed concepts. These results are also described in this paper.

In the IETF, discussions on the authentication method of the Dynamic Host Configuration Protocol (DHCP) message are active and several methods have been proposed. These related specifications were published and circulated as the IETF Internet-Drafts. However, they still have several drawbacks. One of the major drawbacks is that any user can reuse addresses illegally. A user can use an expired address that was allocated to a host. This kind of "illegal use" of the addresses managed by the DHCP server may cause serious security problems. In order to solve them, we propose a new access control method to be used as the DHCP message authentication mechanism. Furthermore, we have designed and developed the DAG (DHCP Access Control Gateway) according to our method. The DAG serves as a gateway that allows only network accesses from clients with the address legally allocated by the DHCP server. This provides secure DHCP service if DHCP servers do not have an authentication mechanism, which is most likely to occur. If a DHCP server has such an authentication scheme as being proposed in IETF Internet-Draft, the DAG can offer a way to enable only a specific client to access the network.

The second generation of mobile communications is growing rapidly to the third generation due to various communication techniques and the increasing number of users. PCS, the communication method of the third generation, should be able to provide users with various services, independently of the current location. To PCS, the mobility management of users is essential. The mobility management method which has been used has a structural drawback: as the number of users increase, HLR becomes the bottleneck. Everyone is expected to have one terminal in the third generation mobile communications age. Therefore, an enhanced mobility management scheme to reduce the bottleneck of the HLR, should be used in the third generation mobile communications. In this paper, we propose a new mobility management method where the trace of terminals is left in the VLRs, so that a call can be connected by querying only to the VLRs rather than to the HLR when the terminal-terminated-call occurs. The proposed method distributes messages to VLRs and effectively reduce mobility management cost. To estimate overall mobility management cost, we simulated the new method of PCS network. The simulation model is based on the Jackson's network, and makes it possible to estimate mobility management cost of PCS networks. IS-41 and proposed scheme are compared based on the computer simulation. Considering the delay times both in HLR and VLR, and considering both location registration cost and call delivery cost, the proposed modeling method shows the improvement.

This paper describes a real-time connection admission control scheme for supporting multiple service categories. The scheme is based on a real-time cell-loss ratio evaluation algorithm for VBR based on peak/sustainable cell rates and maximum burst size. The algorithm is based on a notion of Allan variance of VP utilization. The most remarkable characteristics of the admission control scheme are that it terminates within constant time, a few milliseconds, and that its time is independent of both the number of VCs and the capacity of a cell buffer.

In this paper, we propose a multiple access technique using a simple interference canceller for common code transmission. In the proposed system, we adopt a common code for a receiver oriented system. All the transmitters utilize the same pseudo noise (PN) code to communicate with a receiver. Here the receiver structure becomes very simple with only one matched filter (MF). The proposed system has two very important merits. One is to avoid packet collisions by means of an interference cancellation method based on a common code chip shift transmission technique. That is, in order to avoid interference, which occurs because all the received signals have the same PN code, the same data with different timing are transmitted in two channels. In this study, we define and evaluate three types of packet collision which can be reduced by the canceller. The other merit is to reduce the system degradation due to the correlation side-lobes by means of a side-lobe canceller. In spread spectrum (SS) communication systems with PN codes like M-sequences, the correlation side-lobes appear at the detector in the case of the polarity data changing from 1 to 1 . The side-lobes degrade the system quality. Therefore in this system a interference canceller operates to cancel the correlation side-lobes and attempts to reduce the system degradation. Finally, by our cancellation method it becomes possible to realize a simple multiple access using only one PN code under the condition of a receiver oriented system without a base station.

Optical frequency division multiplexing (FDM) technique has the advantage of fully orthogonal transmissions. However, FDM system permits only a small number of FDM channels despite of a great effort, such as frequency stabilization. On the other hand, frequency-domain encoding code-division multiple-access (FE-CDMA) has been widely studied as a type of optical CDMA. In this system, encoding is done in the frequency domain of an ultrashort light pulse spread by optically Fourier transform. However, FE-CDMA accommodates very limited number of simultaneous users, though this scheme uses a vast optical bandwidth. It is attractive to consider the combination of both advantages of FDM and FE-CDMA. We propose FE-CDMA enhancement of FDM (FDM/FE-CDMA). Since in FDM/FE-CDMA the total bandwidth is partitioned into M optical bands and each band is encoded by the code with code length of N_c, we expect nearly perfect orthogonal transmissions. In addition, since the creation of FDM bands is realized by a passive filter, the optical frequency is precisely controlled and the optical frequency allocation is flexible. We derive the bit error rate (BER) as a function of the number of simultaneous users, bit rate, and the utilization efficiency of total bandwidth. We compare the performance of FDM/FE-CDMA with that of the conventional FE-CDMA in terms of the number of simultaneous users on condition that each chip width is constant. As a result, we show that FDM/FE-CDMA can support the larger number of simultaneous users than the conventional FE-CDMA at a given bit error rate under the same total bandwidth.

As a data transmission rate must be increased as required to support the future high-speed wireless communication systems under multipath fading, the conventional DS-CDMA scheme suffers considerably from an intensive processing requirement for the increased spreading rate to combat the inter-chip interference (ICI) and furthermore, from the intersymbol interference (ISI) as the symbol duration becomes less than the channel delay spread. In this paper, a multi-carrier parallel combinatory DS-CDMA (MC-PC-CDMA) scheme is considered as one possible variant access scheme to realize a bandwidth efficient transmission for high transmission rate while maintaining the beneficial features of the DS-CDMA scheme. This scheme combines the parallel combinatory signaling feature of the existing parallel combinatory CDMA (PC-CDMA) scheme with the orthogonal carrier multiplexing feature of multi-carrier modulation so as to improve the bandwidth efficiency and to reduce the self-interference among the parallel spreading sequences of each user, respectively. This particular system configuration also treats the previously proposed multi-carrier DS-CDMA systems as a special case. Our analysis of the bit error rate for the asynchronous CDMA system investigates the performance characteristics of the proposed system on varying design parameters, and shows the performance comparison with other types of multi-carrier DS-CDMA systems.

Two families of rapidly synchronizable spreading codes are compared using the same component codes. The influence of component code choice is also discussed. It is concluded that correlation, code-division multiple-access (CDMA) and information security (measured by the value of linear complexity) properties of Kronecker sequences are considerably better than those of Combination sequences. Combination sequences cannot be recommended for CDMA use unless the number of active users is few. CDMA performance of Kronecker sequences is almost comparable with that of linear pseudonoise (PN) code families of equal length when a Gold or Kasami code is used as the innermost code and the Barker code is used as the outermost code to guarantee satisfactory correlation and CDMA properties. Kronecker sequences possess a considerably higher value of linear complexity than those of the corresponding non-linear Geffe and majority logic type combination sequences. This implies they are highly non-linear codes due to the Kronecker product construction method. It is also observed that the Geffe type Boolean combiner resulted in better correlation and CDMA performance than with majority logic. The use of the purely linear exclusive-or combiner for considerable reduction of code synchronization time is not found recommendable although it results in good CDMA performance.

The proposed method tracks the user location in a hierarchically distributed fashion. Call patterns in personal communications services (PCS) have the locality. The virtually hierarchical link (VHL) is used to support the call locality and makes the fast call set up possible. The locality consideration effectively reduces the query traffic compared with non-locality consideration.

This comment rectifies the auto-correlation function of the raised-cosine pulse shaping filter response derived in the above paper, giving its exact expression. We give, not only the exact solution for the auto-correlation taken at multiples of the chip period, Φ(rT_c), but also for its entire domain, Φ(τ). Nevertheless, due to an approximation made in [1], the conclusions reached therein remain valid.