Trade‐off analysis of forward link capacity in IS‐95‐based CDMA cellular systems

This paper provides an analytic method to determine how many paging channels can be simultaneously used with traffic channels in the same CDMA forward link. So far, since one or two paging channels are enough to convey control messages from bases to mobiles, little considerations have been given to the paging channel configuration. CDMA network operators, however, recently plan to provide optional services which highly utilize the paging channel. Thus, more paging channels are required for the latest situation. Since the total number of channels that can be used in the forward link is limited by the interfering cellular environments, less traffic channels should be used if additional paging channels are required. It is the objective of this paper to examine the capacity of forward link in terms of paging and traffic channels so as to determine the impact of introducing value‐added services via paging channels. Different capacity regions are presented for various cellular environments. This revised version was published online in August 2006 with corrections to the Cover Date.     

Handover and new call blocking performance with dynamic single‐channel assignment in linear cellular arrays

We consider dynamic assignment of a single channel in a linear cellular array, and derive closed‐form expressions for the blocking probability of handover calls and new calls in terms of the array size and traffic load assuming a Markov traffic model. Handover and new call blocking performance in the limit of large arrays and extreme traffic loads is also determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Performance evaluation of optimum combining and maximal ratio combining in the presence of co‐channel interference and channel correlation for wireless communication systems

Antenna diversity is an important technique to combat fading and reduce cochannel interference (CCI). In this paper, we present an analytical approach to derive bit error rate (BER) for Optimum Combining (OC) and Maximal Ratio Combining (MRC) in the presence of CCI. The paper has two parts. In the first part, the analysis of BER for OC with two cochannel interferers and MRC with an arbitrary number of interferers is presented for Marray antenna systems under the assumption that the channels of users are independent of each other. In the second part, the analysis of BER for OC and MRC in the presence of one dominant cochannel interferer is presented for dual antenna systems by assuming that the channels of the desired user or cochannel interferer are correlated. For DPSK signal, an exact BER expression is derived. The work presented here also yields an upper bound for BPSK or QAM signal based on the results of Foschini and Salz (1983).     

A simplified approach to the performance evaluation of FDMA‐CDMA systems

This work shows it is possible to apply for the performance evaluation of FDMA‐CDMA cellular mobile systems a simple analytical approximated method, previously successfully proposed by two of the authors with reference to FDMA‐TDMA systems. The distinctive feature of the methodology we describe is that it allows for an immediate determination of both the indexes traditionally employed to define system performance, i.e., average bit error probability _e and outage probability P _out at a very low computational cost. The hypothesis required to apply the proposed approximation is that the examined spread spectrum system be characterized by a bandwidth occupancy lower than the coherence bandwidth of the transmission channel. This could be the case of a wireless DS‐CDMA system envisioned to provide voice service and exploiting a processing gain of the order of a hundred. We apply our methodology to determine the performance improvements in both _e and P _out introduced increasing the protection of the transmitted information through error correcting codes and interleaving, in different operating conditions as regards the functioning of the power control loops. A comparison is also satisfyingly carried out with some other approximated analytical methods found in literature. We strongly point out that the corresponding results are achieved at a much more modest computational cost than in traditional approaches. This revised version was published online in July 2006 with corrections to the Cover Date.     

Scheduling of real‐time traffic in IEEE 802.11 wireless LANs

The desire to provide universal connectivity for mobile computers and communication devices is fueling a growing interest in wireless packet networks. To satisfy the needs of wireless data networking, study group 802.11 was formed under IEEE project 802 to recommend an international standard for Wireless Local Area Networks (WLANs). A key part of the standard are the Medium Access Control (MAC) protocols. Given the growing popularity of real‐time services and multimedia based applications it is critical that the 802.11 MAC protocols be tailored to meet their requirements. The 802.11 MAC layer protocol provides asynchronous, time‐bounded, and contention free access control on a variety of physical layers. In this paper we examine the ability of the point coordination function to support time bounded services. We present our proposal to support real‐time services within the framework of the point coordination function and discuss the specifics of the connection establishment procedure. We conduct performance evaluation and present numerical results to help understand the issues involved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Issues of Modeling Fading Dispersive Channels in DS／CDMA Communications

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Mobility model and performance analysis for zone‐based registration in CDMA mobile communication system

In this paper, we describe a mobility model and analysis for zone-based registration in the CDMA mobile communication system. We first propose a simple and proper mobility function for single zone-based registration. We establish the circumstances of multiple zone-based registration, which is based on the mobility function of single zone-based registration, and perform computer simulations for the circumstances. Using the simulation results, we obtain the optimal number of zones, N, that minimizes signaling traffic on radio channels. Results show that, in most cases, N is 2. We also show that multiple zone-based registration has lower signaling traffic on radio channels than single zone-based registration, and zone‐based registration must be implemented as multiple zone‐based registration. This revised version was published online in August 2006 with corrections to the Cover Date.     

A comparative study of bandwidth reservation and admission control schemes in QoS‐sensitive cellular networks

This paper compares five different schemes – called CHOI, NAG, AG, BHARG, and NCBF – for reserving bandwidths for handoffs and admission control for new connection requests in QoS‐sensitive cellular networks. CHOI and NAG are to keep the handoff dropping probability below a target value, AG is to guarantee no handoff drops through per‐connection bandwidth reservation, and BHARG and NCBF use another type of per‐connection bandwidth reservation. CHOI predicts the bandwidth required to handle handoffs by estimating possible handoffs from adjacent cells, then performs admission control for each newly‐requested connection. On the other hand, NAG predicts the total required bandwidth in the current cell by estimating both incoming and outgoing handoffs at each cell. AG requires the set of cells to be traversed by the mobile with a newly‐requested connection, and reserves bandwidth for each connection in each of these cells. The last two schemes reserve bandwidth for each connection in the predicted next cell of a mobile where the two schemes use different admission control policies. We adopt the history‐based mobility estimation for the first two schemes. Using extensive simulations, the five schemes are compared quantitatively in terms of (1) handoff dropping probability, connection‐blocking probability, and bandwidth utilization; (2) dependence on the design parameters; (3) dependence on the accuracy of mobility estimation; and (4) complexity. The simulation results indicate that CHOI is the most desirable in that it achieves good performance while requiring much less memory and computation than the other four schemes. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Applicative Investigation of Adaptive BP Networks for Multi-user Detection in Asynchronous DS-CDMA Mobile Communications

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Low complexity joint estimation of synchronization impairments in sparse channel for MIMO–OFDM system

Low complexity joint estimation of synchronization impairments and channel in a single-user MIMO–OFDM system is presented in this paper. Based on a system model that takes into account the effects of synchronization impairments such as carrier frequency offset, sampling frequency offset, and symbol timing error, and channel, a Maximum Likelihood (ML) algorithm for the joint estimation is proposed. To reduce the complexity of ML grid search, the number of received signal samples used for estimation need to be reduced. The conventional channel estimation techniques using Least-Squares (LS) or Maximum a posteriori (MAP) methods fail for the reduced sample under-determined system, which results in poor performance of the joint estimator. The proposed ML algorithm uses Compressed Sensing (CS) based channel estimation method in a sparse fading scenario, where the received samples used for estimation are less than that required for an LS or MAP based estimation. The performance of the estimation method is studied through numerical simulations, and it is observed that CS based joint estimator performs better than LS and MAP based joint estimator.     

Generalized carrier to interference ratio analysis for shotgun cellular systems in multiple dimensions over composite Rayleigh–Lognormal (Suzuki) fading

Telecommunication Systems - This paper analyzes the carrier-to-interference ratio (CIR) of the so-called shotgun cellular systems (SCSs) in $$\tau $$ dimensions ( $$\tau =1, 2,$$ and 3). SCSs are...     

Performance evaluation of path optimization schemes for inter‐switch handoff in wireless ATM networks

One of the major design issues in wireless ATM is the support of inter‐switch handoff. An inter‐switch handoff occurs when a mobile terminal moves to a new base station connecting to a different switch. Recently, a two‐phase handoff protocol has been proposed to support inter‐switch handoff in wireless ATM networks. With the aim of shortening handoff delay while using the network resources efficiently, the two‐phase handoff protocol employs path extension for each inter‐switch handoff, followed by path optimization if necessary. To implement the two‐phase handoff protocol efficiently, we need to determine when to trigger path optimization. In this paper, we propose and analyze three path optimization schemes, namely: periodic, exponential, and Bernoulli, for the two‐phase handoff protocol. The design objective is to determine the time to invoke path optimization such that the average cost per connection is minimized. We develop a discrete time analytical model and a discrete‐event simulation model for comparing the performance of the three path optimization schemes. Results indicate that the Bernoulli path optimization scheme outperforms the other two schemes by providing a lower average cost per connection. The proposed models can also be adapted to analyze other path optimization schemes in general. This revised version was published online in July 2006 with corrections to the Cover Date.     

Design and analysis of an algorithm for fair service in error‐prone wireless channels

In order to support diverse communication‐intensive real‐time and non‐real‐time data flows over a scarce, varying and shared wireless channel with location‐dependent and bursty errors, we define a service model that has the following characteristics: short‐term fairness among flows which perceive a clean channel, long‐term fairness for flows with bounded channel error, worst‐case delay bounds for packets, short‐term throughput bounds for flows with clean channels and long‐term throughput bounds for all flows with bounded channel error, expanded schedulable region, and support for both delay sensitive and error sensitive data flows. We present the wireless fair service algorithm, and show through both analysis and simulation that it achieves the requirements of the service model in typical wireless network environments. The key aspects of the algorithm are the following: (a) an enhanced fair queueing based service scheme that supports decoupling of delay and bandwidth, (b) graceful service compensation for lagging flows and graceful service degradation for leading flows, (c) support for real‐time delay sensitive flows as well as non‐real‐time error sensitive flows, and (d) an implementation within the framework of the simple and robust CSMA/CA wireless medium access protocol. This revised version was published online in July 2006 with corrections to the Cover Date.     

A call admission and control scheme for quality‐of‐service (QoS) provisioning in next generation wireless networks

We propose a framework for quality‐of‐service (QoS) provisioning for multimedia services in next generation wireless access networks. This framework aims at providing a differentiated treatment to multimedia traffic flows at the link layer, which can be broadly classified as real‐time (or delay‐sensitive) and non‐real‐time (or delay‐tolerant). Various novel schemes are proposed to support the differential treatment and guarantee QoS. These schemes include bandwidth compaction, channel reservation and degradation, with the help of which a call admission and control algorithm is developed. The performance of the proposed framework is captured through analytical modeling and simulation experiments. Analytically, the average carried traffic and the worst case buffer requirements for real‐time and non‐real‐time calls are estimated. Simulation results show up to 21% improvement in the admission probability of real‐time calls and up to 17% improvement in the admission probability of non‐real‐time calls, when various call control techniques like bandwidth compaction are employed. Using our channel reservation technique, we observe a 12% improvement in the call admission probability compared to another scheme proposed in the literature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Assessment of the potential risk for humans exposed to millimeter‐wave wireless LANs: the power absorbed in the eye

This paper deals with the interaction between a millimeterwavelength plane wave and the human eye. The study has been conducted utilizing the finite difference time domain (FDTD) numerical technique, and an accurate eye model obtained through photographic images of the human head. A partly automatic procedure has been developed to obtain the FDTDcompatible eye model. The dielectric properties of the human tissues at millimeter wavelengths have been extrapolated from experimental data available at lower frequencies and by using Debyes dispersion equation. The power distribution in the exposed eye has been calculated in both conditions of closed and open eye, and the results have been compared with the limits settled by some of the most recognized safety standards for human exposure.     

Effect of linker used in D–A–π–A metal free dyes with different π-spacers for dye sensitized solar cells

Two novel D–A–π–A metal free dyes with triphenylamine as donor, dithiophene-diketo-pyrrolo-pyrrole as acceptor unit, thiophene and phenyl π-conjugated bridges and a cyanoacetic acid as electron acceptor (TDPP1 and TDPP2 were denoted for thiophene and phenyl π-conjugated bridge, respectively) have been designed and used as sensitizers for DSSCs. Incorporation of dithiophene-diketo-pyrrolo-pyrrole, reduces the band gap significantly. The influence of π-conjugated bridge on optical and electrochemical properties were investigated. Results demonstrated that the absorption band of TDPP with thiophene π-conjugated bridge has red shifted due to the enhancement of electron donating ability of π-conjugated bridge. The DSSC based on TDPP1 shows prominent power conversion efficiency about 4.81%, which is higher that for TDPP2 (3.42%). The electrochemical impedance spectroscopy analysis reveal that the charge recombination resistance at the TiO₂/dye/electrolyte interface for the DSSC based on TDPP1 is higher than that for TDPP2, which improves both J_sc and V_oc. The PCE of the DSSC based on TDPP1 is further improved up to 6.34%, when deoxycholic acid (DCA) was employed as coadsorbant.     

Localization of the two constitutively expressed nitric oxide synthase isoforms (nNOS and eNOS) in the same cell types in the saccule maculae of the frog Rana pipiens by immunoelectron microscopy: evidence for a back-up system?

There is growing evidence for a nitric oxide/cyclic GMP pathway of signal transduction in the vestibular system. Recently, two isoforms of nitric oxide (NO) synthase (nNOS and eNOS) and NO itself have been identified at the light microscopic level in the vestibulocochlear system of mice using specific antibodies and a new fluorescence indicator. In order to acquire more information about signal transduction and tissue modulation in this neuroepithelium at the cellular and subcellular levels, ultrathin sections of London Resin White-embedded saccule maculae of the frog Rana pipiens were incubated with various concentrations of commercially available antibodies to nNOS and eNOS. The immunoreactivity was visualized by a gold-labelled secondary antibody and the amount of the immunoreactions per microm2 was quantified for the different cell types and subcellular regions. Significant eNOS immunoreactivity was identified in the hair bundles, cuticular plates and the rest of the cytoplasm of the hair cells as well as in different subcellular regions of the supporting cells. Gold-labelled anti-nNOS antibodies stained mainly stereovilli and cuticular structures of hair cells and supporting cells, whereas the number of the immunoreactions in the remaining cytoplasm of both cell types was near the background level. The spatial co-localization of the two NOS isotypes in the same cell regions of hair cells and supporting cells was confirmed in double-labelling experiments. The immunocytochemical findings are suggestive of a redundant system in which one NOS isoform can (partially) replace the other. The different subcellular localization of the NOS isoforms may allow for isoform specific regulation of NOS activity by different Ca2+ currents at the subcellular level, underlining the importance of NO-regulated processes in neuroepithelia of the inner ear.