This paper develops an efficient mechanism for extracting primary information requests from 'Seek-Object' type query messages. The mechanism consists of three steps. The first step extracts sentences which signal that the query is 'Seek-Object' type by recognizing distinctive surface expressions. The second step, biased by the expression patterns, analyzes their internal structures. The third step integrates these fragments by a partial discourse processing and represents writers' goal-directed information request; as these sentences often include referential expressions and the referred expressions are in background goal descriptions. We claim the mechanism can extract information requests fairly accurately, by showing evaluation results.

The performance of an M-ary spread-spectrum multiple-access (M-ary/SSMA) scheme in the presence of carrier frequency offset is discussed in this paper. The influence of carrier frequency offset on the non-coherent reception of M-ary/SSMA signals is examined and it is shown that the carrier frequency offset degrades the performance remarkably, yet. this influence has a distinctive property. Making use of this property, we propose a new M-ary/SSMA scheme that can mitigate the influence of the carrier frequency offset. The scheme is based on the assignment of two distinctive Hadamard codes to in-phase and quadrature components of the transmitted signal. The effect of simultaneous transmission is evaluated in terms of bit-error-rate performance with the carrier frequency offset. As the result, it is observed that the satisfactory bit-error-rate performance can be achieved in the presence of carrier frequendy offset.

The reverse link performance of coherent multicode DS-CDMA [4], [5] under multipath Rayleigh fading environments is evaluated by computer simulation. It is demonstrated that the combined use of pilot symbol assisted (PSA)-coherent RAKE, channel coding, antenna diversity, and transmit power control is powerful in lowering the required signal energy per information bit-to-interference plus additive white Gaussian nose (AWGN) power spectrum density ratio (Eb/Io) which is an important parameter in determining the link capacity. It is also demonstrated that with slight performance degradation, high rate data transmission is realized by using multiple orthogonal spreading codes in parallel (orthogonal multicode transmission). Based on the simulated link performance, the reverse link cell capacity and link budget are also evaluated. It is found that parameter η=Io/No plays an important role in controlling the cell capacity and the maximum allowable path loss, where No is the AWGN power spectrum density.

This paper considers the evaluation of the acquisition performance for an access channel preamble based on the random access procedure of direct sequence code division multiple access (DS/CDMA) reverse link. The parallel acquisition technique that employs the single-dwell and multiple-dwell (double-dwell) detection schemes is investigated. The acquisition performance for two detection schemes is compared in terms of the acquisition probablity and the mean acquisition time. The parallel acquisition is done by a bank of N parallel I/Q noncoherent correlators. Expressions on the detection, false alarm, and miss probabilities of the single-dwell and multiple-dwell (double-dwell) detection schemes are derived for the multiple H1 cells and multipath Rayleigh fading channel. Comparing the single-dwell detection scheme with the multiple-dwell (double-dwell) detection scheme in the case of employing the parallel acquisition technique in the reverse link, the numerical results show that the single-dwell detection scheme provides a better performance.

A new ATM switch architecture, named shared multibuffering, features great advantages on memory access speed for a large switch, and overall size of buffer memories to achieve excellent cell-loss performance. We have developed a 622-Mb/s 88 shared multibuffer ATM switch with multicast functions and hierarchical queueing functions to accommodate 156-Mb/s, 622-Mb/s and 2.4-Gb/s interfaces. Implementation of the shared multibuffer ATM switch is described with respect to the four sorts of 0.8-µm BiCMOS LSIs and ATM switch boards. The switch board/type-1, with C1-LSI, allows to accommodate effectively 156-Mb/s and 622-Mb/s interfaces, which is suitable for an ATM access system. The switch board/type-2, with C2-LSI, can provide multicast functions and accommodate a 2.4-Gb/s interface. By using four switch boards, it is possible to apply them to a 2.4-Gb/s ATM loop system.

The evolution of access networks towards Fiber-To-The-Home (FTTH) receives much attention throughout the world because FTTH has a big potential for providing future attractive services. To provide such services in terms of transmission rate, the cable network transition scenario from conventional copper cable network to optical fiber cable one in access field should be clarified. Since network transition scenario deeply depends on the service evolution scenarios (what type of service would appear at a certain time and how many customers move to the other services, for example), this paper firstly categorizes telecommunication services into four kinds of services, i.e. Basic Service (e.g. POTS), Narrowband Symmetrical Service (e.g. NISDN), Broadband Asymmetrical Services (e.g. Video-On-Demand) and Broadband Symmetrical Services (e.g. BISDN) in terms of up-and down-stream transmission rates. Based on this service categorization, it is proposed to formalize service evolution scenarios by a transition pattern of the initial demands and the penetration rates of these services. Then, the evaluation method of network transition scenarios is also proposed in terms of NPV by the service evolution scenarios. It is conclude that the network transition scenarios are deeply related to the amount and behavior of the demands moving to the other services as follows.-The scenario where the new system configuration partly replaces the old one whenever the demands appear for providing higher transmission rate services is applicable, when the demands move little or constantly move to the higher transmission rate services,-The scenario where the new system configuration totally replaces the old one at the early stage for providing all services is applicable, when the demands drastically move to the higher transmission rate services during short period.

A hybrid network architecture using subcarrier multiplexed optical fiber (SCMOL) and coaxial cable is proposed in this paper for the access link of future personal communication systems (PCS) between tiny passive radio base stations in microcells and remote central base stations. Results indicate that the required number of laser diodes, photodetectors and amount of fiber could be reduced by more than 4 times with the proposed hybrid access link compared to the point-to-point SCMOL link and the network cost would decrease proportionally.

In this paper, a feasible optical code-division multiple-access (CDMA) technique is proposed for high-speed computer networks using prime codes and optical signal processing to guarantee real-time data communications. All-optical architectures for fastly tunable CDMA encoders and decoders are presented, which can be feasibly implemented in the optical domain by using electrooptic switches and optical delay lines. This can support an ultrahigh throughput and a very fast reconfiguration time. Furthermore, we present a self-synchronized sample technique to ensure the correct phase synchronization between optical clock stream and asynchronous electronic data at each electrooptic modulator of an optical CDMA transmitter.

This paper describes the concept of the regional community network system. The system provides PC connectionless communication services to residential customers and a platform on which customers can construct closed user groups. The proposed system is superior to conventional dial-up PC communications from the viewpoint of quick response and communication charge. A new mechanism of group management using the MAC addresses of the interface cards embedded in the ONU and PC terminals is proposed. Conventional telecommunication services, multi-channel video distribution services, and connectionless computer communication services can be provided simultaneously by utilizing the fiber-optic access system. The regional community network system is promising for the construction of a regional information platform and would be one of the forces driving FTTH.

Video services such as video-on-demand are expected to be a motivation for deploying multimedia services in residential areas. These services should increase customer demand for video channels as customer demands become more sophisticated and diverse in the future. Therefore, it is important to determine how network configurations (i.e. network transition scenarios) should evolve in response to changes in access network demand. This paper proposes economical deployment of access networks based on transition scenarios. We conclude that transition scenarios offer more economical deployment than single-network configurations. Two transition scenarios, from passive double-star to fiber single-star, and from hybrid fiber-coax to fiber single-star, are evaluated as examples. These transition scenarios are economical even when customer demand changes. The transition starting time affects the present worth of annual charges (PWAC) of access networks more than the transition period does.

Precise direct mounting of laser diode (LD) and photodiode (PD) chips on silica planar lightwave circuits (PLCs) has been investigated for application to transceiver modules. To achieve submicron optical alignment, self-aligned index marks on the PLCs and LDs were directly detected by transmission infrared light. The repeatability of the positioning was measured to be within 0.125 µm. The output power of the resultant module was 0.2 mW at 80 mA. A waveguide-type PD was also mounted in the same way, and module sensitivity of 0.25 A/W was demonstrated.

For the successful realization of the multimedia information environment, it is strongly required to develop very cost effective optical access networks. Accordingly, ways of reducing system cost are described. At the same time, the development of attractive new services is indispensable to drive network modernization. The connectionless networking service for community user groups is proposed together with the new concept of group communication.

In this letter, we propose an adaptive multiuser receiver using a Hopfield network for code-division multiple-access communications and its performance is compared with that of the other types of multiuser receiver via computer simulation. The proposed adaptive receiver estimates both the signal amplitudes and spreading sequences for all the users using training data.

A uniquely decodable code pair (C, S) is considered for the two-user binary adder channel. When the first code C is linear, a lower bound of |S| is formulated and a uniquely decodable code pair (C, S) is presented. When a rate R1 of C is less than 1/3, a rate R2of S is greater than the best rate known previously.

In ths letter, we suggest a collision resolution algorithm when the packet length is random, and analyze its throughput and delay performance. Here, three different packet length distributions and two feedback schemes (ternary and binary success/failure feedback) are considered.

This paper presents a method of employing a priority scheme in a random access environment. A prioritized nonblocked stack collision resolution algorithm with binary feedback is developed and tested using simulations. The algorithm accommodates an n-level priority scheme which makes it attractive in mobile data systems. The effectiveness of the algorithm is described on its ability to first, reject the lowest priority class when the system load is near or on the maximum value and second, minimize the delay spread of the higher class users. The performance of the algorithm is characterized using the throughput/delay and cumulative delay for each class of users.

Air interfaces of the future mobile communication are widely spreading, because of the multimedia service demands, technology trends and radio propagation conditions. Radio-Highway Networks are expected to realize the universal, seamless and multi-air-interface capability for mobile access networks, and play an important role in the future multimedia radio communications. For the radio-highway networks, this paper newly proposes natural bandpass sampling - asynchronous time division multiple access (NBS-ATDMA) method, where radio signals are natural bandpass sampled at the radio base station and are asynchronously multiplexed on the optic fiber bus link and intelligently transmitted to its desired radio control station. We theoretically analyze the loss probability of the radio signal due to collision in the network and the carrier-to-noise power ratio of received radio signals at the radio control station. Moreover, in order to reduce the loss probability, two access control methods, carrier sense and pulse width control, are proposed, and it is clarified that these improve the number of base station connected to radio highway networks.

This letter describes an efficient and economical method for dropping optical fiber to residential premises in which several fiber ribbons in a distribution cable are assigned to one dropping point. The optical fiber cables for dropping, which contain mono-coated fibers, are then aerially installed between several poles from this point during initial construction. One or two fibers in a cable are then branched and dropped to a subscriber when the demand arises. When an optical drop wire stranded cable is used as the optical fiber cable for dropping, the above method can be employed without the need for a fiber joint in the dropping portion. The tube stranding pitch of this cable is investigated theoretically and experimentally, and the cable is manufactured based on the results. The transmission characteristics of the cable are confirmed to be stable.

Shortened prime codes (SPR-codes) are presented, which can maintain the fixed code weight for any arbitrary number of codewords while still preserve the same cross and auto-correlation constraints as original prime codes. The use of SPR-codes can reduce both cost and power loss of optical encoders/decoders. Tunable all-optical SPR-code encoders are also designed, which are based on rapidly tunable optical delay lines. It is shown that using this type of encoders not only can further reduce the coding power loss, but also can achieve a very cost-effective fashion.

We propose a novel architecture (Switched Access Star: SAS) using an optical switch for access networks and prove its operating principle experimentally. In this architecture, the multiple optical network units (ONUs) in subscriber premises are connected to one optical subscriber unit (OSU) in a central office through an optical switch. SAS can increase the number of accommodated ONUs, the transmission line length, and the capacity per ONU. Moreover, this architecture does not need encryption or ID/passwords. SAS can reduce system cost and yield flexible transmission capacities and realize easy management and maintenance of optical transmission lines.