This paper proposes applying fast transmit power control (TPC) to the forward link of a direct sequence-code division multi-access (DS-CDMA) cellular system. Orthogonal spreading is assumed at a base station transmitter and coherent RAKE combining is assumed at a mobile station receiver. In DS-CDMA cellular mobile radio, the multiple access interference (MAI) from other cells and background noise limit the forward link capacity. Therefore, to increase the link capacity, fast transmit power control (TPC) can be introduced, which is similar to that developed for the reverse link, i. e. , the transmit powers of forward link channels are independently raised or lowered according to the instantaneous signal-to-background noise plus interference ratios (SIR's) measured at mobile stations. Fast TPC is fast enough to track the multipath fading as well as slow variations in the distance-dependence path loss and shadowing. On the average, the transmit power is increased to a user closer to the cell edge so that the effects of both other-cell MAI and background noise can be reduced while it is decreased to a user closer to the cell center. The effect of the TPC parameters (TPC interval, TPC target value, TPC step size, etc) on the forward link capacity in single- and multi-cell environments is evaluated by computer simulation. It is shown that fast TPC can almost double the forward link capacity in a multi-cell environment.

The outage probability of a forward link DS-CDMA cellular system with fast transmit power control (TPC) based on signal-to-interference ratio (SIR) is investigated. The expression for SIR at the output of RAKE receiver is developed, and the outage probability is evaluated by using Monte Carlo simulation. We consider two kinds of channel models: random delay resolvable path model and tapped delay line model which are suitable models for a few distinct paths channel and highly frequency-selective-channel model, respectively. The outage probability of a system with fast TPC based on SIR is compared to that without fast TPC. The use of orthogonal spreading codes is compared to that of the random spreading codes in terms of outage probability. The effects of the maximum and minimum transmit powers and the dispersive loss of signal power on the outage probability are also investigated.

This paper addresses an important issue on the spreading bandwidth of direct sequence code division multiple access (DS-CDMA) cellular mobile radio systems: does wider spreading bandwidth provide larger capacity? And if so, to what extent? The capacity of the perfect power controlled reverse link is evaluated by computer simulation for 1.25 MHz and 5 MHz spreading bandwidths under various sets of propagation channel parameters (path loss decay factor, shadowing standard deviation, shadowing correlation, number of resolved propagation paths) and antenna diversity reception.

In this paper, system capacity of the reverse link of a wireless multimedia CDMA system with transmission power control is analysed for receivers with and without CCI cancellers. For N classes of users, system capacity is represented by a point in an N-dimensional space. It is shown that system capacity is improved considerably with CCI cancellers, that system capacity region is non-convex in general, and that its boundary is well approximated with a unique hyper plane when CCI cancellers are fully employed.

We have two goals in this paper. One is the comparison of Spread Spectrum (SS) CDMA and Spread Time (ST) CDMA. The other is to propose a new SS-ST CDMA system, which is an adaptive CDMA with both merits of SS and ST CDMA. SS and ST CDMA are compared from the view point of two dimensional space "frequency (B Hz)-time (T Sec)" together with their communication capacity. A primary modulation is assumed to be PPM in ST CDMA, and FSK in SS CDMA which is regarded as PPM in frequency axis. Both SS and ST CDMA are combined to give the proposed SS-ST CDMA, where transmitted signals are spread both in time and frequency domain. In order to realize the proposed system, a transmitter model is presented, and two receiver structures are discussed. The discrete Fourier transform (DFT) is employed for the system flexibility. Although SS, ST and SS-ST CDMA are shown to have the same capacity of 0.7213, the combined SS-ST CDMA has a merit of adaptability to adjust spreading gain of ST and SS according to property of channels, an impulsive noise dominated or a CW interference dominated channel. Numerical results of DFT are also shown to illustrate the waveform and spectrum of the proposed SS-ST CDMA system. Finally the symbol error probability performance of ST PPM, SS FSK and combined SS-ST systems in CW and impulsive environment is presented.

In this paper, we study the link capacity assignment problem in packet-switched networks (CA problem) focusing on the case where link cost function is a piecewise linear concave function. This type of cost function arises in many communication network design problems such as those arising from developments in communication transmission technologies. It is already known that the method of link set assignment is applicable for solving the CA problem with piecewise linear convex cost function. That is, each link in the network is assigned to one of a group of specific sets, and checked for link set contradiction. By extending the method of link set assignment to the case of piecewise linear concave cost function, an important characteristic of the optimal solution of the CA problem is derived. Based on this characteristic, the non-differentiable link cost function can be treated as a differentiable function, and a heuristic algorithm derived from the Lagrange multiplier method is then proposed. Although it is difficult to determine the global optimum of the CA problem due to its non-convexity, it is shown by numerical results that the solution obtained from the proposed algorithm is very close to the global optimum. Moreover, the computation time is linearly dependent on the number of links in the problem. These performances show that the proposed algorithm is very efficient in solving the CA problem, even in the case of large-scale networks.

Recently, the quantum information theory attracts much attention. In quantum information theory, the existence of superadditivity in capacity of a quantum channel was foreseen conventionally. So far, some examples of codes which show the superadditivity in capacity have been clarified. However in present stage, characteristics of superadditivity are not still clear up enough. The reason is as follows. All examples were shown by calculating the mutual information by quantum combined measurement, so that one had to solve the eigenvalue and the eigenvector problems. In this paper, we construct a simplification algorithm to calculate the mutual information by using square-root measurement as decoding process of quantum combined measurement. The eigenvalue and the eigenvector problems are avoided in the algorithm by using group covariancy of binary linear codes. Moreover, we derive the analytical solution of the mutual information for parity check codes with any length as an example of applying the simplification algorithm.

As a means of CDMA network evolution toward future wireless services, a spectral overlay of narrowband CDMA (N-CDMA) and wideband CDMA (W-CDMA) systems is proposed in [8]. In order to justify the overlaying strategy, the reverse link capacity is examined in the same work. Although the capacity of conventional CDMA cellular systems is usually limited by the reverse link, the limit could occur at the forward link depending on the transmission technologies adopted by specific CDMA proposals. Especially, the number of users that can be simultaneously accommodated in the system would be limited by the forward link in future mobile service environments where unequal traffic is offered between two links. In this paper, we first examine the forward link capacity of the spectrally overlaid narrowband and wideband CDMA (N/W CDMA) system. And we compare it with the reverse link capacity to obtain the overall performance. The effects of various parameters on the capacity of N/W CDMA system are numerically evaluated for different mobile environments.

This paper describes the error probability of the second order BAM estimated by a computer simulation and an analytical calculation method. The computer simulation suggests that the iterations to retrieve a library pattern almost converge within four times and the difference between once and twice is much larger than that between twice and four times. The error probability at the output of the second iteration is estimated by the analytical method. The effect of the noise bits is also estimated using the analytical method. The BAM with larger n is more robust for the noise. For example, the noise bits of 0.15n cause almost no degradation of the error probability when n is larger than 100. If the error probability of 10-4 is allowable, the capacity of the second order BAM can be increased by about 40% in the presence of 0.15n noise bits when n is larger than 500.

In this paper, we focus on the evaluation of the Erlang capacity for multimedia DS-CDMA systems supporting the multi-class services with different transmission rates, bit error rates, traffic activity factors in the reverse link. The number of concurrent users of the corresponding service group is modeled as a K-dimension Markov chain. Then, the Erlang capacity for the multimedia system can be found based on a K-dimension M/M/m loss system. For an IS-95 type DS-CDMA system, supporting voice/data services, the capacity bounds are depicted in conjunction with the 2-dimensional Markov chain. Furthermore, it is observed that the Erlang capacity with respect to the each service group should be balanced to enhance the total system Erlang capacity. Finally, the channel reservation scheme is considered to increase the total system Erlang capacity.

The self-healing capability against network failure is one of indispensable features for the B-ISDN infrastructure. One problem in realizing such self-healing backbone network is the inefficient utilization of the large spare capacity designed for the failure-restoration purpose since it will be used only in the failure time that does not occur frequently. "Pool-capacity" is the concept that allows some VPs (virtual paths) to efficiently utilize this spare capacity part. Although the total capacity can be saved by using the "Pool Capacity," it is paid by less reliability of VPs caused by the emerging influence of indirect-failure. Thus, this influence of indirect-failure has to be considered in the capacity designing process so that network-designers can trade off the saving of capacity with the reliability level of VPs in their self-healing networks. In this paper, Damage Rate:DR which is the index to indicate the level of the influence caused by indirect-failure is defined and the pool-capacity design scheme with DR consideration is proposed. By the proposed scheme, the self-healing network with different cost (pool-capacity) can be designed according to the reliability level of VPs.

This paper is concerned with radio resource allocation in multiple-chip-rate (MCR) DS/CDMA systems accommodating multimedia services with different information rates and quality requirements. Considering both power spectral density (PSD) over a radio frequency (RF) band and the effect of RF input filtering on the receiver in MCR-DS/CDMA systems, criteria for capacity estimation are presented and the characteristics of co-channel interference between subsystems are investigated. System performance in MCR-DS/CDMA systems is strongly affected by radio resource assignment. A minimum power-increment-based resource assignment scheme for an efficient resource assignment scheme is proposed herein. The performance of this scheme is compared with that of a random-based resource assignment scheme in terms of blocking probability and normalized throughput. The minimum power-increment-based resource assignment scheme yields a better performance than the random-based resource assignment scheme for multimedia services.

We apply evolutionary algorithms to neural network model of associative memory. In the model, some of the appropriate configurations of the synaptic weights allow the network to store a number of patterns as an associative memory. For example, the so-called Hebbian rule prescribes one such configuration. However, if the number of patterns to be stored exceeds a critical amount (over-loaded), the ability to store patterns collapses more or less. Or, synaptic weights chosen at random do not have such an ability. In this paper, we describe a genetic algorithm which successfully evolves both the random synapses and over-loaded Hebbian synapses to function as associative memory by adaptively pruning some of the synaptic connections. Although many authors have shown that the model is robust against pruning a fraction of synaptic connections, improvement of performance by pruning has not been explored, as far as we know.

An associative memory model with a forgetting process a la Mezard et al. is investigated for a piecewise nonmonotonic output function by the SCSNA proposed by Shiino and Fukai. Similar to the formal monotonic two-state model analyzed by Mezard et al. , the discussed nonmonotonic model is also free from a catastrophic deterioration of memory due to overloading. We theoretically obtain a relationship between the storage capacity and the forgetting rate, and find that there is an optimal value of forgetting rate, at which the storage capacity is maximized for the given nonmonotonicity. The maximal storage capacity and capacity ratio (a ratio of the storage capacity for the conventional correlation learning rule to the maximal storage capacity) increase with nonmonotonicity, whereas the optimal forgetting rate decreases with nonmonotonicity.

We consider a finite-capacity single-server queue with constant service and vacation times, which is seen in the time division multiple access (TDMA) scheme. First we derive the probability that j customers remain in the queue when a test customer arrives. Using this probability we then evaluate the probability that the test customer who arrives during the vacation or service time has to wait in the queue for longer than a given time. From these results, we obtain the waiting time distribution for the customer arriving at an arbitrary time. We also show a practical application to wireless TDMA communications systems.

CDMA unslotted ALOHA system with finite size of queueing buffers is discussed in this paper. We introduce an analytical model in which the system is divided into two Markov chains; one is in the user part, and the other is in the channel part. In the user part, we can model the queueing behavior of the user station as an M/G/1/B queue. In the channel part, we can consider the number of simultaneously transmitted packets as an M1 + M2/D///K queue. We analyze the queueing system by using this analytical model, and evaluate the effect of buffer capacity in terms of the throughput, the rejection probability and the average delay. As a result, increase in the buffer size brings about an improvement in the grade of service in terms of higher throughput and lower rejection probability.

To expand signal wavelength bandwidth in long-haul, large-capacity WDM transmission systems, we investigated gain-equalizers (GEQs) for Erbium doped fiber amplifiers (EDFAs). We applied GEQs using Mach-Zehnder type filters with two different free-spectral-ranges (FSRs) to accurately compensate for the EDFAs gain-wavelength characteristics. The 1st GEQ with a longer FSR was the main GEQ to compensate for the overall gain-wavelength characteristics, and the 2nd GEQ with a shorter FSR was the secondary GEQ to compensate for the resultant gain undulation after the 1st GEQ. The 2nd GEQ had low maximum loss and long period of equalization-spacing compared to the 1st GEQ. We designed that the FSR for the 1st GEQ was twice the signal wavelength bandwidth, and the FSR for the 2nd GEQ was two thirds of the signal wavelength bandwidth. To compensate for the asymmetry in the EDFAs gain-wavelength characteristics, we designed that the 2nd GEQ minimum-loss wavelength was shorter than the 1st GEQ maximum-loss wavelength. Using a circulating loop with a 21-EDFA chain, we confirmed the signal wavelength bandwidth expanded by the above GEQs. We also investigated the trade-off relationship between the signal wavelength bandwidth and the optical signal-to-noise ratio, as the parameter of the number of the 1st GEQ inserted in the EDFAs chain. The achieved signal wavelength bandwidth after 10,000-km transmission was 12 nm. We successfully transmitted 170 Gbit/s (325. 332 Gbit/s) WDM signals over 9,879 km employing high alumina codoped EDFAs and Mach-Zehnder type filters with long FSRs.

In this paper, dependence of storage capacity of an analogue associative memory model using nonmonotonic neurons on static synaptic noise and static threshold noise is shown. This dependence is analytically calculated by means of the self-consistent signal-to-noise analysis (SCSNA) proposed by Shiino and Fukai. It is known that the storage capacity of an associative memory model can be improved markedly by replacing the usual sigmoid neurons with nonmonotonic ones, and the Hopfield model has theoretically been shown to be fairly robust against introducing the static synaptic noise. In this paper, it is shown that when the monotonicity of neuron is high, the storage capacity decreases rapidly according to an increase of the static synaptic noise. It is also shown that the reduction of the storage capacity is more sensitive to an increase in the static threshold noise than to the increase in the static synaptic noise.

In this paper, CDMA slotted ALOHA system with finite size of buffers is proposed. To analyze the system performance, we use the linear approximate solution based on restricted occupancy urn models. We evaluate the system performance in terms of throughput, average delay, and rejection probability and clarify the effect of buffer capacity.

The Future Public Land Mobile Telecommunication Systems (FPLMTS) standards have made it quite clear that in the near future, the capability in doing wireless data transmission will become necessary in order to make the tether-free use of multimedia applications possible. CDMA is considered the most appropriate and probable radio access method of FPLMTS for its high capacity and flexibility in accommodation of multimedia and variable rate users. In order to further increase the capacity of CDMA system, several techniques have been studied and proposed such as an interference canceller and adaptive array antenna. We propose the novel multi-user detection type interference cancellation technique named SRIC (Symbol Ranking type IC) in this paper. SRIC is very feasible for its small amount of operation compared with other multi-user detection type ICs and can be added to a base station with slight alteration according to the requirement of higher capacity. The performance of SRIC depends on the method of calculating the likelihood. We studied three methods. In order to reduce the operations, we tried to propose two more methods. We confirmed that SRIC can make the system capacity about three times greater than that of a conventional RAKE receiver. We also confirmed that SRIC can be reduce its operations very much at some sacrifice of their performance. There are nine variants of SRIC, which have a trade off between performance and amount of operation. We can choose one of them which is most fit to our requirement. The first operation of SRIC is common with that of a conventional RAKE receiver. Therefore, SRIC can be introduced to conventional systems afterwards by inserting the interference canceller block which functions replica generation, removal, and ranking between output of a RAKE receiver and FEC decoder.