In order to construct optical access networks economically for fiber to the home (FTTH), it is important to reduce the cost of optical fiber cable installation. Optical fiber and cable costs have been reduced over the past ten years, however there have been few reports describing installation cost reduction. In this paper, we describe the design of high-density optical fiber cable that reduces the required installation time. To achieve this we have reduced the optical fiber cable weight and the friction coefficient of the cable sheath. We reduced the cable weight by using polyethylene foam and a non-metallic tensile strength member made of a new material, PBO. These two approaches reduce the cable weight by a total of about 30%. We also added a lubricant to the polyethylene sheath of this cable and this reduced the pulling force required for the additional cable by 30%-50%.

Low cost optical subscriber systems and effective operation are indispensable to the construction and maintenance of greatly expanded optical fiber networks. An optical fiber line monitoring system is essential for reducing maintenance costs and improving service reliability in optical access networks. To promote cost-effective optical fiber line operation, we propose an extended automatic optical fiber operations support system (AURORA) with a remotely installed fiber selector. We suggest a configuration for extended AURORA and design the dynamic range of the system. We confirmed that testing could be carried out on an extended optical network section of 10 km in length by using extended AURORA when the optical trunk line was less than 15 km. We also discuss the effect on the maintenance cost of optical fiber cables in access networks. We calculated the annual maintenance cost for periodic tests in actual operation areas, and confirmed that this cost could be reduced by 30% compared with that for a conventional system.

Existing MultiCode-CDMA MAC protocols perform only single dimensional access control either in the code or time domain. In this paper, we propose a MAC protocol, called SCTAC which can perform simultaneous code-time access control to achieve better system utilization. Also, SCTAC intends to provide service differentiation among different traffic classes. In order to simultaneously control access in both the code and time domain, SCTAC decouples the function of transmission ordering from the function of packing the scheduled transmissions in the resource space. As such, different transmission scheduling algorithms can be adopted without altering the MAC protocol. A water filling approach is used for efficient transmission packing where each of the scheduled transmissions is treated as a rectangular capsule with an arbitrary size and the resource space is viewed as a water container. In addition, SCTAC uses different request sending probabilities with an improved probability update algorithm to achieve service differentiation. Simulation results indicate that SCTAC is capable of providing different performances to different traffic classes. The results also confirm that SCTAC can achieve higher throughput compared to single dimensional access control protocols. Therefore, SCTAC is a better MAC protocol.

Iterative schemes for demodulating M-ary orthogonal signaling formats in direct-sequence code-division multiple access (DS-CDMA) systems are proposed and compared with the standard noncoherent matched filter receiver. Interference cancellation, i.e., (approximative) removal of the multiple access interference (MAI) by means of subtraction is studied. The considered system is similar to the uplink (reverse link) of an IS-95 system. Hence, the received signals from the concurrent users are asynchronous, and no pilot signals are available for channel estimation. A decision-directed algorithm is proposed for estimating the time-varying complex channel gains of a multipath channel. The receivers are evaluated on Rayleigh-fading channels and are shown to provide large capacity gains compared with the conventional receiver.

In 1998, Jan and Tseng proposed two integrated schemes of user authentication and access control which can be used to implement a protection system in distributed computer systems. This paper will analyze the security of both schemes and show that an intruder can easily forge a login, be accepted and logged in as a legal user, and access system resources. We will then propose a modified scheme to withstand our proposed attacks.

In this paper, the sequence interference suppression characteristics of code-diversity DS/CDMA over multipath fading channels are presented. In a code-diversity system, the data signal is modulated with several PN sequences, and using these sequences at the receiver, diversity reception of the signal is carried out to suppress the influence of multiple access interference (MAI) or sequence interference (SI) especially under a near-far problem. First, in a sequence interference and AWGN environment, the basic performance of code-diversity system is presented. Next, in single-path (flat-fading) and multipath fading channels, the average BER performance of the code-diversity system is shown and the observation that the performance of code-diversity system (combined with RAKE reception) is more effective over a multipath fading channel is clarified. Finally, it is presented that by implementing adaptive weight control (AWC) for the code-diversity system over fading channels, the BER performance can further be improved.

In this paper a different view on Viterbi's method for the estimation of the reverse link capacity of a single cell of CDMA based mobile communications systems is given. Viterbi's approach is well-known and of great importance for the capacity estimation. However, the interpretation of Viterbi's result on the system capacity is not that clear. Thus, we introduce a new approach giving accurate reasons for Viterbi's capacity estimation. When neglecting the noise power, both methods provide nearly the same result. We conclude that Viterbi's finding relates to the average capacity, which is an important statistical parameter. However, we should note that this average capacity will be not available all the time. The improvements discussed in this paper focus on the specification of a certain reliability about the availability of the average capacity.

External pins for tests are precious hardware resources because this number is strongly restricted. Cores are tested via test access mechanisms (TAMs) such as a test bus architecture. When cores are tested via test buses which have constant bit widths, test stimuli and test responses for a particular core have to be transported over these test buses. The core might require more widths for input and output than test buses, and hence, for some part of the test, the TAMs are idle; this is a wasteful usage of the TAMs. In this paper, an optimization method of test accesses with a combined BIST and external test (CBET) scheme is proposed for eliminating the wasteful usage of test buses. This method can minimize the test time and eliminate the wasteful usage of external pins by considering the trade-off between test time and the number of external pins. Our idea consists of two parts. One is to determine the optimum groups, each of which consists of cores, to simultaneously share mechanisms for the external test. The other is to determine the optimum bandwidth of the external input and output for the external test. Our idea is basically formulated for the purpose of eliminating the wasteful external pin usage. We make the external test part to be under the full bandwidth of external pins by considering the trade-off between the test time and the number of external pins. This is achieved only with the CBET scheme because it permits test sets for both the BIST and the external test to be elastic. Taking test bus architecture as an example, a formulation for test access optimization and experimental results are shown. Experimental results reveal that our optimization can achieve a 51.9% reduction in the test time of conventional test scheduling and our proposals are confirmed to be effective in reducing the test time of system-on-a-chip.

We present a new technique for hierarchical intellectual property (IP) protection using partially-mergeable cores. The proposed core partitioning technique guarantees 100% protection of critical-IP, while simplifying test generation for the logic that is merged with the system. Since critical-IP is tested using BIST, the controllability and observability of internal lines in the core are enhanced, and test application time is reduced. Case studies using the ISIT-DLX and Picojava processor cores demonstrate the applicability of our technique.

A quality-of-service based link control scheme to counteract correlated channel errors for wireless multimedia communications is proposed in this paper. Both the medium access (MAC) and data link control (DLC) layers are treated. The performance of the proposed scheme is evaluated using both analysis and simulation. The delay and jitter behaviors are examined for both the constant bit rate (CBR) traffic and variable bit rate (VBR) traffic. The throughput performance is also obtained for the available bit rate (ABR) traffic. Through numerical experiments, the proposed scheme is demonstrated to be not only robust against channel impairments but also capable of providing the desired QoS for wireless multimedia communications.

This paper proposes a bandwidth division type parallel combinatory (PC) spread spectrum (SS) modulation scheme. In the proposed system, a given system bandwidth for the conventional single-carrier PC-SS system is divided into H subbands, and H PC-SS signals are transmitted in parallel. We evaluate the frame error rate (FER) of the proposed system under the asynchronous CDMA environment. We show that the proposed scheme provides a smaller FER than the single-carrier PC-SS system for a given information bit rate. We also show that the proposed scheme attains a higher information bit rate than the single-carrier PC-SS system for a given FER.

Broadband fixed wireless access (FWA) systems offer significantly higher bit rates than current cellular systems to which adaptive arrays are partly applied. Digital beam forming is being eagerly explored on account of its flexibility, but it will be difficult to apply to the high-speed systems, because its digital signal processing requires huge resources and power consumption. Conventional phased arrays, on the other hand, utilize phase shifters through RF or IF signal lines, but the phase shifters are usually both bulky and expensive. The authors propose an adaptive array steered by IF local signal phase shifters in this paper. The phase shift and the frequency shift of the signal from each antenna element can be simultaneously accomplished at the down conversion stage by the phase-controlled local signal. A prototype receiver operated in the K-band with the proposed configuration and its beam pattern measurement results are also described.

This paper evaluates high-speed broadband packet wireless access in the forward link using coherent Time Division-Orthogonal Frequency and Code Division Multiplexing (TD-OFCDM) by applying time-multiplexed pilot symbol assisted channel estimation and integrating efficient multi-level modulation, hybrid automatic repeat request (ARQ), and code-multiplexing over a 50-100 MHz bandwidth. Computer simulation results first clarify that the common time-multiplexed pilot symbols with the transmit power of 6 dB higher than that of data symbols should be placed at both the beginning and end of a packet, and that the optimum averaging interval of channel estimates in the frequency domain is different according to the delay spread of a channel. Based on these optimized parameters for packet transmission, we show that the orthogonality among the code-multiplexed channels is destroyed due to severe frequency selective (multipath) fading and the accumulation of spread signals using equal gain combining (EGC) in the frequency domain. This degrades the achievable throughput performance especially when employing multi-level modulation and a high coding rate. Consequently, coherent TD-OFCDM with 8PSK data modulation and the convolutional coding of rate R = 2/3 employing sixteen-code multiplexing (spreading factor (SF) is 16) achieves the highest throughput of approximately 105 Mbps at the average received Eb/N0 (signal energy per bit-to-noise power spectrum density ratio) of approximately 24 dB in a 3-path Rayleigh fading channel (rms delay spread, σ= 0.1 µsec). Furthermore, in coherent TD-OFCDM with QPSK and R = 4/5 or 8PSK and R = 1/2, throughput performance greater than 80 Mbps is achieved at the average received Eb/N0 of approximately 20 dB even in a 24-path Rayleigh fading channel (σ= 0.2 µsec).

This paper elucidates the most appropriate hybrid automatic-repeat-request (ARQ) scheme, i.e., which can achieve the highest throughput, for high-speed packet transmission in the W-CDMA forward link by comparing the throughput performance of three types of hybrid ARQ schemes: type-I hybrid ARQ with packet combining (PC), type-II hybrid ARQ, and basic type-I hybrid ARQ as a reference. Moreover, from the viewpoint of maximum throughput, the respective optimum roles of ARQ and channel coding in hybrid ARQ are also clarified, such as the optimum coding rate and the packet length related to the interleaving effect. The simulation results reveal that the type-II scheme exhibits the best throughput performance, and the required received signal energy per chip-to-background noise spectral density ratio (Ec/N0) at the throughput efficiency of 0.2/0.4/0.6 is improved by 0.7/0.3/0.1 dB and 3.9/1.8/0.5 dB, respectively, compared to the type-I scheme with and without PC in a 2-path Rayleigh fading channel with the average equal power at the maximum Doppler frequency of 5 Hz and the packet length of 4 slots (= 0.667 4 = 2.667 msec). However, the improvement of the type-II scheme compared to the type-I scheme with PC is small or the achievable throughput is almost identical in the high-received Ec/N0 region. On the other hand, the type-I scheme with PC is much less complex and thus preferable, while maintaining almost the same throughput performance or allowing very minor degradation compared to that with type-II. The results also elucidate that, while the optimum coding rate depends on the required throughput in the basic type-I and type-I with PC schemes, it is around between 3/4 and 8/9 in type-II, resulting in a higher throughput efficiency. In addition, for high-speed packet transmission employing a hybrid ARQ scheme, a shorter retransmission unit size is preferable such as 1 slot, and the fast transmit power control is effective only under conditions such as a low maximum Doppler frequency and a high transmit Ec/N0 region.

This paper investigates the improvement of the radiation pattern design of transmitting array antenna beamforming and transmission power control (TPC) for forward link of DS-CDMA/FDD system. Optimum transmission beamforming and TPC can be derived from the information of the propagation channel for the forward link, in terms of outage probability minimization. It is assumed that the channel is static and then all mobile stations (MS's) report channel characteristics measured in the forward link to a base station (BS) that can control signal to interference plus noise ratios (SINR's) received by individual MS's using that measured information. Then, for the multi-user environment of a single cell, goal programming (GP) is applied to derive an optimum weight vector of the transmitting array antenna and optimum TPC such that outage probability can be minimized.

In code division multiple access (CDMA) systems with adaptive antennas, the direction of terminals must be considered when controlling new call admission. This paper proposes a data access control algorithm based on estimated signal-to-interference-plus-noise ratio (SINR) at the output of adaptive antennas. The algorithm estimates SINR for new data call using a response vector of the request packet to determine acceptance or blocking of the new data call. Numerical results show that the combination of transmission technology of adaptive antennas and proposed data access control can effectively increase the capacity of CDMA systems.

Magnetic random access memory (MRAM) possesses the attractive properties of non-volatility, radiation hardness, nondestructive readout, low voltage, high access speed, unlimited read and write endurance and high density. MRAM technology is described for the devices using giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) materials in this paper. The TMR type MRAM architectures using ferromagnetic tunneling junctions (MTJ) are more attractive for mainstream RAM applications than the GMR type, because the signal of the TMR type is larger than that of the GMR type. A MRAM device with an MTJ plus MOS transistor switch architecture, which can provide large signal-to noise ratio, is detailed. A design of the MTJ element is discussed and the requirements for the junction resistance and the TMR needed for the memory device are demonstrated based on the simple signal voltage calculations. The TMR significantly decreases with increasing bias voltage, which leads to the reduction of the signal voltage for the actual MRAM. A ferromagnetic double tunneling junction is proposed for the high density MRAM application demanding large signal voltage, because of the smaller degradation of the TMR for the bias voltage, compared with that of the conventional single junctions. Recent trials of MRAM fabrication are introduced, which demonstrates high-speed access time. Finally, challenges for the higher bit density MRAM above Gb are discussed, and it is noticed that higher signal voltage, lower power consumption for writing and novel cell designs are needed for the achievement.

Access control plays an important role in the area of information security, which guarantees that any access to data is authorized. Hierarchical access control is a special access control model in distributed environment, in which each user protects his local data using a secret key; moreover, for any two related users ui and uj, ui can access uj's data if, and only if, ui's priority is higher than uj. Therefore, there should be a way for ui to obtain the secret key of uj if ui's priority is higher than uj. This paper presents an efficient solution to the problem. A special kind of function called secure filter is used as the building block of the proposed solution. In the solution, an authorized user can acquire correct keys efficiently and securely via secure filters. The proposed solution is also well-performed while inserting/deleting users, injecting/removing relations, and changing secret keys. Especially, only deleting users and removing relations will change some keys in the system, other operations can be performed freely without affecting other keys in the system; only secure filters need to be modified in these cases.

We have developed a new scheme to provide Diffserv-based QoS over ATM access networks. Well-known Diffserv over ATM scheme requires some extension for conventional routers with ATM interfaces. The routers must map their Diffserv classes of services into ATM QoS classes and forward IP packets into prioritized VCs based on DSCP (DiffServ Code Point). The purpose of this work is to provide Diffserv-based QoS over ATM network using conventional IP over ATM interfaces on routers. We propose DSCP snooping at ATM edge nodes, which differentiates services over a single VC between two IP domains. A prototype circuit was used to evaluate this scheme.

This paper conducts performance evaluation and performs simulation for a code division multiple access (CDMA) system when channel bands of multiple neighboring CDMA/DSSS are overlapped in time domain. It is assumed that all systems adopt direct-sequence spread-spectrum (DSSS) technique and are BPSK modulated by the different carrier frequencies. Automatic power control (APC) is also applied in the interfered system such that the receiver gets the same power from all users. Without loss generality, an additive white Gaussian noise (AWGN) channel is also assumed during analysis. In this paper, the analytic solution of the signal to noise ratio (SNR) is first derived in which both CDMA systems are modulated by different carrier frequencies. We have the results by simulation with Δ f = 0 and Δ f = 1 MHz, respectively. This analysis is good for general cases; and the results show an excellent computational performance. In particular, the result is very close to Pursley's result, when the systems have the same code length with no carrier difference.