The capacity of quantum channel with product input states was formulated by the quantum coding theorem. However, whether entangled input states can enhance the quantum channel is still open. It turns out that this problem is reduced to a special case of the more general problem whether the capacity of product quantum channel exhibits additivity. In the present study, we apply one of the quantum Arimoto-Blahut type algorithms to the latter problem. The results suggest that the additivity of product quantum channel capacity always holds and that entangled input states cannot enhance the quantum channel capacity.

The European Commission, through RACE, ACTS and now the IST programmes, has funded numerous consortium based research projects addressing capacity enhancement by means of Smart or Adaptive Antenna Technology. In addition to capacity enhancement, these projects have also considered the additional operational benefits, such as multipath mitigation and range extension, that this technology can offer to wireless network deployments. This paper provides an overview of the results obtained from the test-bed and field trial evaluations conducted under the ACTS TSUNAMI project. Here, a test-bed facility was developed by the project partners in order to appraise the potential merits of a Smart antenna facet deployment at the base-station cell site of a DCS1800 network. Details of the test-bed hardware and adaptive control algorithms are given, as well as results from the user tracking, traffic bearer quality assessments and range extension experiments. These results help substantiate many of the claims put forward by the proponents of Smart antenna technology, as well as ranking the relative performance of the family of adaptive control algorithms evaluated here. Further, new research activities, which embody Smart Antenna Technology, now supported under IST funding are also introduced.

The capacity analysis of CDMA forward link is required to allocate high data-rate users. To solve this problem, we analyze the capacity of the CDMA forward link based on optimum power control. In a multi-cell environment, the intracell interference and intercell interference are derived. To show the capacity impact of high data-rate users, we introduce a location dependent factor, which is the ratio of intercell interference to intracell interference. Considering the location dependent factor, we propose a coordinated allocation scheme that can be used to allocate high data-rate users in sectorized cells. As a result, we show the capacity impact of high data-rate users according to location variations. The outage probability can be decreased when the coordinated allocation scheme is applied.

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.

Optimum antenna sub-set selection in MIMO systems is an attractive cost reducing technique. In this paper we develop an optimal antenna sub-set selection technique to be used in conjunction with space-time block codes over a MIMO link to optimize link error performance over a fading channel. We study the case when antenna sub-set selection is applied either at the transmitter or the receiver. We provide analytical results for substantial improvement in average SNR and outage capacity when antenna sub-set selection is used. Simulation results that verify our analytical prediction are also presented.

In future mobile communication systems, forward link may be a limiting one because emerging data services are likely to require higher data rates in the forward link than in the reverse link. In this paper, we derive joint Erlang capacity of a DS/CDMA forward link in terms of both outage probability and blocking probability for each type of traffic in a mixed traffic environment. Resource sharing algorithm and generalized Erlang model are employed to derive joint Erlang capacity of the DS/CDMA system with various types of traffics. The joint Erlang capacity reflecting both outage probability and blocking probability of each type of traffic is obtained by an approach based on virtual circuit switching perspective. We take into account effect of closed loop power control in the analysis. From numerical results, it is confirmed that blocking probability as a QoS (quality of service) parameter has a significant impact on the forward link capacity. The results of this paper can be applied to design of the DS/CDMA systems supporting wireless multimedia traffics.

In this paper, we propose a Call Admission Control (CAC) scheme for the Direct Sequence-Code Division Multiple Access (DS-CDMA) systems supporting voice and data services and analyze the Erlang capacity under the proposed CAC scheme. Service groups are classified by Quality of Service (QoS) requirements such as the required Bit Error Rate (BER) and information bit rate, and Grade of Service (GoS) requirement such as required call blocking probability. Different traffics require different system resources based on their QoS requirements. In the proposed CAC scheme, some system resources are reserved exclusively for handoff calls to have high priority over new calls. Additionally, the queueing is allowed for both new and handoff data traffics that are not sensitive to delay. As a performance measure of the suggested CAC scheme, Erlang capacity is introduced. For the performance analysis, a four-dimensional Markov chain model is developed. As a numerical example, Erlang capacity of an IS-95B type system is depicted, and optimum values of system parameters such as the number of reservation channels and queue lengths are found. Finally, it is observed that Erlang capacity is improved more than 2 times by properly selecting the system parameters with the proposed CAC scheme. Also, the effect of handoff parameters on the Erlang capacity is observed.

The performance of a twisted-pair channel under ADSL environment is assumed to be dominated by far end crosstalk (FEXT) and additive white Gaussian noise (AWGN). In this paper, we study the channel capacity of the copper twisted pair and the optimum input power spectral density distribution at this channel capacity in the presence of ADSL environment. The channel capacity under different loop length and different input power will also be given. The simulation results show that the distribution of the optimum input power spectral density in the presence of AWGN and FEXT is not uniform. This is different from the situation where AWGN is the only interference, where the input power distribution is approximately uniform.

In cellular networks, the system performance can be degraded because of the inefficient use of channels with the two types of traffic, that is, the new call traffic and handover call traffic. This problem can be alleviated if the channels are used efficiently for new call traffic and handover call traffic. In this paper, we consider the proper ratio of the number of channels for new calls to the number of total channels denoted as α. We introduce the new call channel limiting technique incorporating velocity of mobile user. We model one-dimensional cellular networks and evaluate the performance in terms of the blocking probabilities, the probability of call dropping and the probability of incomplete call. We show with numerical examples that the system performance can be improved by selecting the appropriate α for various velocities of mobile users.

In this paper, we propose an analytical procedure for the Erlang capacity in the reverse link of the DS-CDMA systems supporting voice and data services with the limited number of channel elements. Especially, we focus on IS-95B type systems with sectorized directional antenna that support the medium data rates for data traffic by aggregating multiple codes in both directions, to and from the mobile device. For the performance analysis, a 6-dimensional Markov chain model is developed, and the Erlang capacity is depicted as a function of the offered traffic loads of voice and data. The call blocking is caused not only by the scarcity of channel elements that perform the baseband spread spectrum signal processing for the given channel in the base station, but also by insufficient available channels per sector. The effect of the different Grade of Service (GoS) requirements on the Erlang capacity is observed, and the optimum values of the system parameters such as channel elements are selected with respect to the Erlang capacity. Furthermore, we expand our approach to the multi-FA systems that support multiple CDMA carriers more than one. It is observed that Erlang capacity for a high FA can be well estimated through the linear regression with the Erlang capacity results of low FAs.

The reverse-link of the DS-CDMA cellular system requires transmit power control (TPC) and diversity reception. This paper develops the expression of the received signal-to-interference ratio (SIR), and evaluates the outage probability using the Monte Carlo simulation to obtain the link capacity. The link capacities with received signal strength (SS)-based TPC and SIR-based TPC are compared. This paper investigates the required maximum and minimum transmit powers and the capacity gain of the SIR-based TPC over SS-based TPC as well as the effect of the diversity reception on the link capacity and transmit power. The reverse-link capacity is compared with the forward-link capacity to check the balance of capacities between both links.

We consider a dynamically reconfigureable network where dynamically changing traffic is offered. Rearrangement and adjustment of network capacity can be performed to maintain Quality of Service (QoS) requirements for different traffic classes in the dynamic traffic environment. In this work, we consider the case of a single, dynamic traffic class scenario in a loss mode environment. We have developed a numerical, analytical tool which models the dynamically changing network traffic environment using a time-varying, fluid-flow, differential equation; of which we can use to study the impact of adaptive capacity adjustment control schemes. We present several capacity adjustment control schemes including schemes which use blocking and system utilization as means to calculate when and how much adjustment should be made. Through numerical studies, we show that a purely blocking-based capacity adjustment control scheme with a preset adjustment value can be very sensitive to capacity changes and can lead to network instability. We also show that schemes, that uses system utilization as a means to calculate the amount of capacity adjustment needed, is consistently stable for the load scenarios considered. Finally, we introduce a minimum time interval threshold between adjustments, which can avoid network instability, in the cases where the results showed that capacity adjustment had been performed too often.

This paper presents efficient time slot assignment algorithms applicable to the uplink of SDMA system. A frame consists of one control time slot and multiple communication time slots where terminals in different angular positions share the same time slot. In the proposed algorithms, a time slot is assigned to a new terminal considering not only the signal quality of the new terminal but also the signal quality of active terminals. Simple calculation method for estimated signal-to-interference plus noise ratio (SINR) is employed to decrease the computational complexity. The performance of the proposed algorithms is evaluated by computer simulation and compared with sectorized systems to show the validity of the proposed algorithms.

System capacity of a system consisting of N classes of users is characterized by N-vectors representing the number of users that can be accommodated under a specified BER (bit error rate) constraint in each class. In this paper, system capacity of the reverse link of a wireless multimedia CDMA system with processing gain control is analyzed in the asymptotic regime, when the processing gain G, for receivers with and without CCI cancellers. A new scheme for processing gain control with an optimized power allocation is proposed and its system capacity is compared with the conventional processing gain control scheme as well as the previously discussed power control scheme. It is shown that the proposed scheme has a certain advantage over other schemes.

In practice, the DS-CDMA system is equipped with a finite number of Channel Element (CE)s that performs the baseband spread signal processing for a given channel in the base station. In this situation, the call blocking can be caused not only by the insufficient number of channel elements but also by the limit of available traffic channels. In this paper, we focus on analyzing the effect of the limited number of CEs on the Erlang capacity of multimedia DS-CDMA systems in the reverse link when the CDMA cells are sectorized with 3 sectors. For the performance analysis, a multi-dimensional Markov chain model is developed. As a result, the more CE results in the larger Erlang capacity. However, the Erlang capacity is saturated after a certain value of CEs where the call blocking is mainly caused by the insufficient channels per sector.

The call processing capacity of a base station in CDMA cellular network can be changeable due to the additive loads from handoff, paging and location registration as well as call setup/release. In general, the load box test is widely used for measuring the call processing capacity of a exchange in the fixed network. But, it is difficult to estimate the processing capacity accurately because system load includes hand-off, paging in a mobile network. In this paper, we propose a new methodology for the calculation of call processing capacity to investigate the effect of traffic parameters on the system capacity, through the traffic modeling of call flow in base station. This result shows that the traffic load of hand-off limits the system capacity largely and is more severe than has been expected. Regression analysis will be also derived for the investigation of unit load and linear relation between CPU load and traffic load. This analysis using the field data from an operating site indicates that the call processing capacity in the wireless network must be specified with the rates of hand-off, paging and location registration, in contrast with the fixed network.

There has been a rapid advance in wavelength-division multiplexing (WDM) and high bit-rate time-division multiplexing (TDM) as techniques for coping with burgeoning demand for transmission capacity. In the past this expansion of capacity has been achieved by 2.5-Gbit/s and 10-Gbit/s WDM using the C-band (around 1550 nm), but research on the 1600-nm L-band (around 1600 nm) is being stepped up to obtain further expansion. With the achievement of 40-Gbit/s speeds, which mark the limit of electrical signal processing, optical TDM, with speeds of 100 Gbit/s, is coming into use. In this kind of high-density, high bit-rate WDM transmission, the occurrence of non-linear phenomena within optical fibers reduces transmission quality, and this raises the importance of technology for suppressing non-linearity and specifically, in the case of WDM transmission systems, of four-wave mixing (FWM). Obviously there is also the problem of signal distortion due to dispersion, so that technology for suppressing cumulative dispersion is also essential. There is also a need for transmission lines with sophisticated dispersion management over a wide band of wavelengths, and it may be consisted of novel fibers.

Reverse link performance analysis in single-code and multi-code CDMA systems is presented. Results show that the single-code system yields better performance than does the multi-code system in terms of link capacity and signal power. This improvement increases as spreading bandwidth is reduced and the number of spreading codes assigned to a user is increased.

Closed-loop power control providing maximum capacity of the multicarrier channel with frequency selective Nakagami fading is investigated. Use of the famous Gallager channel capacity (water-filling) theorem with the assumption of limited transmitter power and independent fading in partial channels leads to the algorithm for their optimal power loading. Analytical expressions for the capacity of the multicarrier channel as a function of the number of its subchannels and the fading parameters are derived for the cases of Optimal Power Distribution (OPD) and Equal Power Distribution (EPD). The dependence of the capacity gain on the OPD system order, the fading depth and the average SNR due the optimal power control is obtained. Comparison of the power efficiencies of the systems with OPD and EPD is presented.

One of the most important capacity parameters in the DS-CDMA cellular systems is the system reliability on which the reverse link capacity is usually limited by a prescribed lower bound. In this letter, the effect of the system reliability as well as imperfection of the power control on the system capacity is quantitatively considered using sensitivity analysis in a multimedia DS-CDMA cellular system. As a result, an analytical close-form formula is presented in terms of the standard deviation of the received SIR and the system reliability. In a numerical example, sensitivity with respect to the system reliability on the system capacity has the value ranging from 5 to 50 between 95% and 99% the range in we are interested.