Recently several dosimetric assessment procedures have been proposed to demonstrate the compliance of handheld mobile telecommuications equipment (MTE) with safety limits. However, for none of these procedures has an estimation of the overall uncertainty in assessing the maximum exposure been provided for a reasonable cross-section of potential users. This paper presents a setup and procedure based on a high-precision dosimetric scanner combined with a new phantom derived from an anatomical study. This allows the assessment of the maximum spatial peak SAR values occurring in approximately 90% of all MTE users, including children, with a precision of better than 25%. This setup and procedure therefore satisfies the requirements of the FCC, as well as those drafted by a CENELEC working group mandated by the European Union.

High density and small diameter optical fiber cables are required in order to construct "Fiber To The Home (FTTH)" to support multi media services economically. By reducing the cable diameter and weight, it will be possible to install longer lengths of cable and use conduits more effectively. Moreover, the development of low loss multifiber connectors and joint boxes will reduce the joining time. It is expected that the achievement of the above will lead to reductions in installation and joining costs. This paper describes the design and performance of 1000-fiber single slotted core cable. Its diameter is 30 mm compared to 40 mm for currently used multi slotted core cable, and its weight is 0.85 kg/m compared to 1.4 kg/m. The reduced cable outer diameter and weight allow us to increase both the installed length from 1 to 2 km (pre-connectorized) and the maximum fiber count from 1000 to 1600 for multiple installation in a conduit. We also describe low loss 4, and 8 mechanically transferable (MT) connectors, a pulling head and a joint box. The average connection loss of those connectors is reduced from 0.35 to 0.2 dB. The cable joining time was greatly reduced from 9 to 4.5 hours by using 5 stacks of multi fiber connectors and newly developed pulling heads and a joint boxes. Finally, we describe field test results for 1000-fiber pre-connectorized cable. In field tests, this preconnectorized cable is sufficiently stable with present installation methods. These results will lead to reductions in installation and joining costs. The 1000-fiber pre-connectorized single slotted core cable is promising with regard to upgrading the access network towards FTTH.

We propose two multipriority reservation protocols for wavelength division multiplexing (WDM) networks. The network architecture is a single-hop with control channel-based passive star topology. Each station is equipped with two pairs of laser and filter. One pair of laser and filter is always tuned to wavelength λ0 for control and the other pair of laser and filter can be tuned to any of data wavelengths, λ1, λ2, ..., λN. According to the access methods of the control channel, one protocol is called slotted ALOHA-based protocol and the other protocol is called TDM-based protocol. The two protocols have the following properties. First, each of them has its own priority control scheme which easily accommodates multipriority traffics. Second, they can be employed in the network with limited channels, i.e. the number of stations in the system is not restricted by the number of data channels. Third, they are conflict-free protocols. By using a reservation scheme and a distributed arbitration algorithm, channel collision and destination conflict can be avoided. For the performance point of view, the TDM-based protocol gives an optimal solution for the priority control. However it is less scalable than the slotted ALOHA-based protocol. The slotted ALOHA-based protocol also performs good priority control even though it is not an optimal solution. We analyze their performances using a discrete time Markov model and verify the results by simulation.

This paper presents severl radio resource scheduling algorithms which aim to provide best-effort service for non-real-time unit-oriented, or message traffic. The objective of resource scheduling algorithm is to distribute radio resources between competing message traffic sources while attaining throughput as high and fair as possible for each source without any explicit quality-of-service (QoS) guarantee. Computer simulations are carried out to evaluate the performance in terms of the average of allocation plus transfer delay, the average of throughput, the variance of throughput, and the usage of resources. The message-size distributions of homepages in World-Wide-Web and e-mails obtained by actual measurement are used. Message size-based resource scheduling algorithms are found to provide high and fair throughput as well as efficient use of the resources.

Various approaches to reduce access network cost are discussed with emphasis on system and component technologies. On-going access network opticalization subjects are discussed with respect to PDS-based access systems.

This paper describes packaging techniques based on a novel passive alignment technique as key techniques for module assembly. A laser diode (LD) is passively positioned by detecting a pair of alignment marks located on the LD and Si substrate. A single-mode fiber is self aligned on a Si V groove. A simple receptacle structure for the module output port is also newly designed. This structure is more suitable for the automatic assembly line as well as the module mounting process on circuit board. In this paper, an advanced module applications such as a hybrid integrated wave guide module and a surface mountable (SMT) LD module is introduced.

As a result of increasing demand and regulatory changes, access systems are undergoing significant expansion. Although wireless and copper-based systems are being deployed, fiber access systems provide the best conduit for broadband services. Significant deployment and trials of Hybrid Fiber-Coax (HFC) and Switched Digital Video (SDV) systems are underway, and additional architectures are being considered for future upgraded networks. We review the progress in this field, and indicate where enabling device technologies can provide key functions.

This paper describes the technological issues in achieving a low-cost hybrid WDM module for access network systems. The problems which should be resolved in developing a low-cost module are clarified from the viewpoint of the module assembly in mass production. A design concept for a low-cost module suitable for mass production is indicated, which simplifies the alignment between a laser diode and a waveguide, and reduces the number of the components such as lenses and mirrors. The low-cost module is achieved by employing a flip-chip bonding method with passive alignment using a spot-size converter integrated laser diode (SS-LD) and p-i-n waveguide photodiodes (WGPDs) on a planar lightwave circuit (PLC) platform. We confirm that the SS-LD and the WGPD provide high coupling efficiency with a large tolerance for passive alignment. To achieve a high-sensitivity receiver, the module is designed to employ an asymmetric PLC Y-splitter that prefers a PD responsivity to an LD output power because of the high-coupling efficiency of the LD, and to employ a bare preamplifier mounting to reduce the parasitic capacitance into a preamplifier. We also demonstrate the dynamic performance for a 50-Mb/s burst signal, such as a high sensitivity, an instantaneous AGC response, and a small APC deviation of the transceiver.

We propose an InGaAlAs waveguide p-i-n photodiode (WG-PD) with a thick symmetric double-core for surface-hybrid integration onto optical platforms, which can be applied to low cost optical modules for access networks. The waveguide structure is designed to efficiently couple to flat-ended single mode fibers while maintaining low-voltage (less than 2 V) operation. Crystal growth conditions and a passivation technique are also investigated for obtaining high responsivity, low dark current and highly reliable operation. Fiber-coupled responsivity as high as 0.95 A/W, at a 1.3-µm wavelength, and vertical coupling tolerance as wide as 2.6 µm are demonstrated for a dispersion-shifted fiber (DSF) coupling at an operating voltage of 2 V. Dark current is as low as 300 pA at 25 and 12 nA at 100. A temperature accelerated aging test is performed to show the feasibility of using the WG-PD in long-term practical applications.

Narrow-beam and low threshold current characteristics have been realized for a 1.3 µm FS-BH (Facet Selective growth Buried Heterostructure) laser diode monolithically integrated with a tapered waveguide lens by a selective area epitaxial growth technique. The beam divergences in the perpendicular and horizontal directions have been reduced down to about 12. By the introduction of the strained quantum well structure and the optimized cavity structure, the threshold current has been kept as low as 6 mA which is comparable to the conventional Fabry-Perot laser diodes. Even at high temperature as high as 85, the threshold current and the operation current (P=10 mW) have been suppressed to as low as 23 mA and 63 mA, respectively. Furthermore error-floor-free characteristics for 622 Mbps-50 km transmission have been confirmed under severe optical feedback condition.

In this paper, we evaluate the throughput performance of CDMA Slotted ALOHA systems. To improve the throughput performance, we employ the Quasi-synchronous sequences and the Modified Channel Load Sensing Protocol as an access control procedure. As a result, we found a good throughput by the QS-sequences. By employing MCLSP, we can keep the maximum throughput even in high offered load and in the presence of a long access timing delay, which is one of the issue in satellite packet communication systems.

Periodic reservation allows periodic and random packets to share the same satellite random access channel efficiently. The periodic reservation protocol is particularly suitable for mobile satellite position reporting services, where some of the information messages, such as dispatch function, are classified as "periodic" and others, such as signaling, are classified as "random." When a new mobile terminal logs on to the system, Network Management Center (NMC) reserves subsequent time slots for transmitting periodic packets without contention. A mobile terminal recognizes each time slot as "reserved" or "unreserved (available)" according to the broadcast message received from NMC. Other random packets use the slotted ALOHA protocol to contend with other mobile terminals for an unreserved time slot. The performance results suggest that the use of the periodic reservation protocol can be regarded as a viable solution for mobile satellite position reporting services such as automatic dependent surveillance (ADS).

Optical access networks will be key infrastructures to realize the multimedia society in the near future. Usually, in the case of trunk line, optical cables are installed under the ground. But optical fiber cables approach to offices and homes for optical access networks, the cables often take forms of aerial cables. Some issues must be considered in the optical cable splicing of aerial routes. This paper discusses some subjects; for example, a spare length of the fiber in a cable closure should be short and the splicer should be light weight and compact size to ensure easy operation in the aerial site. This paper also proposes two types of fusion splicers and a useful operation table for aerial optical cable splicing.

This paper analyzed the connection points of Main Distribution Frames (MDF), which are installed between outside plants and inside plants (service nodes). This paper also proposes a connecting system for forthcoming FITL (Fiber In The Loop) networks. NTT has developed the Subscriber Line Cross-Connecting Module (LXM) for the FITL network and will continue to introduce LXMs and deploy optic subscriber networks in big cities throughout Japan.

In this paper, a multiuser receiver using a Hopfield network (Hopfield network receiver) for asynchronous codedivision multiple-access systems is proposed. We derive a novel likelihood function for the optimum demodulation of a data subsequence whose length is far shorter than that of the entire transmitted data sequence. It is shown that a novel Hopfield network receiver can be derived by exploiting the likelihood function, and the derived receiver leads to a low complexity receiver. The structure of the proposed receiver consists of a bank of correlators and a Hopfield network where the number of units is proportional to both the number of users and the length of a data sequence demodulated at a time. Computer simulation results are presented to compare the performance of the proposed receiver with those of the conventional multiuser detectors. It is shown that the proposed receiver significantly outperforms the correlation receiver, decorrelating detector and multistage detector, and provides suboptimum performnace.

The pros and cons of CDMA as a multiple access scheme for third generation cellular mobile radio systems are considered. Main criteria are spectral efficiency and capacity, but also flexibility and costs.

In this letter, we propose a blind adaptive receiver with nonlinear structure for DS/CDMA communication systems. The proposed receiver requires the signature waveform and timing for only the desired user. It is shown that the blind adaptation is equivalent to the adaptation with the training signal and the function to be minimized has no local minima.

The one of the problems in the satellite packet communication system is the existence of a long time delay, which may cause an improper packet access control resulting in a great deal of degradation of the system performance. In this paper, we clarify the effect of long time delay on the performance of CDMA ALOHA systems and then propose a new access control protocol, called Modified Channel Load Sensing Protocol (MCLSP), for the CDMA ALOHA systems. As a result, we show that a significant improvement in the throughput performance was obtained with MCLSP even in the presence of a long time delay.

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.