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In this paper, we study the performance of three handover priority schemes--the pure guard channel method (GCM), GCM with first-in-first-out (GCM-FIFO), and dynamic priority queuing (DPQ)--and, for the first time, compare them for different scenarios and provide guidelines as to which scheme to use under which scenario. In the first scenario, the channel holding time is assumed to follow an exponential distribution. For this scenario, we derive new accurate formulas to evaluate the performance of GCM and GCM-FIFO schemes. Our results show that existing analytical frameworks for GCM and GCM-FIFO overestimate the handover failure probability. Recent field measurements have shown that the best fits to measured data for channel holding time are lognormal and mixed lognormal distributions rather than an exponential distribution. We quantify and compare the handover performance of GCM, GCM-FIFO, and DPQ for ideal (i.e., exponential channel holding time distribution) and for practical (i.e., lognormal and mixed lognormal channel holding time distributions) scenarios. Our results show that, depending on the cell type, the number of channels per cell, and the traffic load, the operator should use either DPQ or GCM. For example, for high handover traffic and high traffic load, the operator should use GCM-FIFO; for light-to-moderate traffic load and a high number of channels per cell (40 or more), DPQ seems to be the best option. To make the handover scheme adaptive, a switching mechanism can be used such that, depending on the time of the day, traffic load, number of channels per cell, and cell type, the handover scheme that provides the best performance is selected. The guidelines provided in our paper are, in most cases, valid for both exponential and pure/mixed lognormal distributions. Index Terms--Cellular networks, dynamic priority queuing (DPQ), guard channel method (GCM), handover.

In this paper, the authors quantify the impact of mobility on the bit error rate (BER) performance of ad hoc wireless networks. Analytical expressions, relating the BER at the end of a multihop route with the mobility characteristics of the nodes and the switching strategy, are derived on the basis of a rigorous detection-theoretic approach. In particular, two network switching scenarios are considered: 1) opportunistic nonreservation-based switching (ONRBS), where a message flows from source to destination by opportunistically choosing the available shortest consecutive links and 2) reservation-based switching (RBS), where, after the creation of a multihop route from source to destination, the message is 'forced' to flow over the reserved links, regardless of their actual lengths. The network performance is evaluated for both an ideal case (without interference) and a realistic case (with interference). The improved robustness against mobility offered by ONRBS, with respect to RBS, is analyzed and quantified. In particular, two node mobility models, known as direction-persistent (DP) and direction-non-persistent (DNP), are considered, and it is shown that DP mobility causes a much more profound degradation in the end-to-end route BER than DNP mobility. This conclusion is more pronounced in ad hoc wireless networks employing RBS. Overall, the results show that if the medium access control (MAC) protocol is not efficient in canceling or mitigating the interference, then the role of the switching/ routing strategy in network performance is quite minor. Index Terms--Ad hoc wireless networks, internode interference (INI), mobility, nonreservation-based switching (NRBS), RBS.

In this paper, we report theoretical and experimental channel-capacity estimates of heating, ventilation, and air conditioning (HVAC) ducts based on multicarrier transmission that uses M-ary quadrature amplitude modulation and measured channel responses at the 2.4-GHz industrial, scientific, and medical band. It is shown theoretically that data rates in excess of 1 Gb/s are possible over distances up to 500 m in straight ducts in which reflections have been suppressed. Our experimental results also show that even in the case of more complex HVAC duct networks (i.e., HVAC duct networks that include bends, tees, etc.) data rates over 2 Gb/s are possible. Our estimations in this case are valid for distances of up to 22 m, which was the maximum distance of our experimental setup. These experimental results, measured with a large-scale testbed set up at Carnegie Mellon University, Pittsburgh, PA, albeit limited in terms of transmitter-receiver separation distance, provide further evidence on the potential of HVAC systems as an attractive solution for providing communications in indoor wireless networks. Index Terms--Heating, ventilation, and air conditioning (HVAC) systems for wireless transmission, indoor propagation, internet access, multicarrier transmission, orthogonal frequency-division multiplexing (OFDM).

In this paper, we present a simple path-loss prediction model for link budget analysis in indoor wireless local area networks that use heating, ventilation, and air conditioning (HVAC) cylindrical ducts in the 2.4-2.5-GHz industrial, scientific, and medical band. The model we propose predicts the average power loss between a transmitter-receiver pair in an HVAC duct network. This prediction model greatly simplifies the link budget analysis for a complex duct network, making it a convenient and simple tool for system design. The accuracy of our prediction model is verified by an extensive set of experimental measurements. Index Terms--Heating, ventilation, and air conditioning (HVAC) systems, indoor wireless local area networks (WLANs), Internet access, path-loss prediction model.

This paper presents a novel technique for analyzing the mode content excited by antennas placed in multimode waveguides. The technique is based on measuring the frequency response between the two antennas coupled into a waveguide and using that information to extract the mode content generated by the transmitting antenna. The technique is applicable to cases in which the mode amplitudes are approximately constant over the frequency range of interest. This method is valuable for determining the mode mix generated by arbitrary transmitting antennas in a multimode waveguide propagation environment. An example of such an environment is heating, ventilation, and air-conditioning (HVAC) ducts used for indoor communications, where an important antenna characteristic is the mode sensitivity (analogous to the antenna directive gain in free space). We validate our technique with the example of a monopole probe antenna coupled into a multimode cylindrical HVAC duct. Index Terms--Antennas, indoor radio communication, microwave measurements, multimode waveguides.

Heating, ventilation, and air conditioning (HVAC) ducts in buildings behave as multimode waveguides when excited at radio frequencies and thus, can be used to distribute radio signals. The channel properties of the ducts are different from the properties of a usual indoor propagation channel. In this paper, we describe physical mechanisms which affect the HVAC channel impulse response and analyze their influence on the delay spread. Those mechanisms include antenna coupling, attenuation, and three types of dispersion: intramodal, intermodal, and multipath. We analyze each type separately and explore the behavior of the delay spread as a function of distance in straight ducts. Experimental channel measurements taken on real ducts confirm the validity of our model. Index Terms--Dispersive channels, indoor radio communication, multimode waveguides, wireless local-area network (LAN).

Heating, ventilation, and air conditioning (HVAC) ducts in buildings are typically hollow metal pipes which can be used as waveguides to carry signals and provide the network access to offices. Knowledge of channel properties is crucial to designing such a communication system. This paper presents a propagation model for a straight HVAC duct terminated at both ends. At high frequencies this duct behaves as a multimode waveguide with a transmitting antenna coupling in and a receiving antenna coupling out. We derive a simple analytical expression for the frequency response of this channel using conventional techniques. Experimental data taken on real circular ducts excited by monopole probe antennas confirm theoretical results. This model represents an initial step toward the development of a tool for planning a wireless distribution system using building HVAC ducts. Index Terms--Indoor radio communication, monopole antennas, multimode waveguides, radio propagation, wireless LAN.

In this paper an approximate analysis is presented which can be used to predict the performance of power and signal-to-noise ratio (SNR) equalization schemes when applied to dense wavelength-division multiplexing (DWDM) lightwave systems employing erbium-doped fiber amplifier (EDFA) cascades. Expressions are provided which relate the maximum number of amplifiers, EDFA gain imbalance, bit rate ([R.sub.b]), transmitter power, receiver dynamic range and number of channels. The relative advantages of these two equalization strategies are quantified by comparing the maximum number of amplifiers allowed by each scheme. It is shown that, while SNR equalization represents, on balance, the more desirable equalization strategy for future EDFA-based DWDM lightwave transmission systems, under certain conditions power equalization may be a better choice. When employing an APD receiver, for instance, power equalization can support 1.9 times more amplifiers than SNR equalization. However, when employing the more conventional preamplified PIN/FET receiver, SNR equalization can support 1.7 times more amplifiers than power equalization. Index Terms--EDFA-based DWDM lightwave transmission systems, gain imbalance of EDFAs, power and SNR equalization.

Four-wave mixing (FWM) in dispersion-shifted optical fiber is a major problem associated with low optical input power levels in optical wavelength-division multiplexed (WDM) systems. To reduce the crosstalk caused by FWM, a generalized suboptimum unequally spaced channel allocation (S-USCA) technique has been proposed in [1]. While the S-USCA technique reduces FWM power substantially, it also reduces the minimum channel spacing compared to conventional equal channel spacing (ECS) systems when the same number of carrier channels are accommodated in a fixed optical bandwidth. This results in more interchannel interference (ICI) when employing the S-USCA scheme. The power penalty of the ECS and the S-USCA systems caused by crosstalk and frequency drift are investigated and compared in this paper. The superior system performance region, where S-USCA systems out perform ECS systems, is also quantified. For 20-channel systems using amplitude-shift keying (ASK) heterodyne detection scheme, for instance, results show that the S-USCA technique pays less power penalty up to bit rates of 5.5, 7.5, and 9.5 Gb/s, when all channels have identical states of polarization and the launched input power per channel [P.sub.in] equals to -6, -3, and 0 dBm, respectively. Index Terms - Coherent receivers, four-wave mixing, unequally spaced allocation technique, WDM systems.

Four-wave mixing (FWM) is the most serious fiber nonlinearity associated with low-input optical power levels in long-haul multichannel optical systems employing dispersion-shifted fiber. To reduce the crosstalk due to FWM, a generalized suboptimum unequally spaced channel allocation (S-USCA) technique is proposed and investigated in this paper. Even though the developed technique is useful in combating FWM crosstalk in wavelength division multiplexing (WDM) lightwave systems up to 12 channels, its main virtue is in designing multichannel WDM lightwave systems with more than 12 channels. Comparisons of power penalty due to FWM between equal channel spacing (ECS) systems and the S-USCA systems are presented. It is shown that for an intensity modulation/direct detection (IM/D) transmission system operating in an optical bandwidth of 16 nm with 0 dBm (1 mW) peak optical input power per channel, while a conventional ECS WDM system with 0.84-nm channel spacing cannot even achieve bit-error rate (BE) = [10.sup.-9], the suboptimum technique developed in this paper, for the same minimum channel spacing, can achieve BER = [10.sup.-9] with an FWM crosstalk power of less than 1 dB at the worst channel in a 20-channel WDM system. Index Terms - Four-wave mixing, unequally spaced channel allocation technique, wavelength-division multiplexing systems.

Efficient mobility management for portable stations (PS's) - handoff, channel assignment, and locating - will play an important role in future personal communication systems (PCS's). Among these tasks, location management plays a critical role for wide-area roaming. The key elements of locating are location registration/updating and paging. Due to the smaller cell size in PCS, the high boundary crossing rate of PS will result in more frequent location area (LA) updating. This, in turn, will result in more interrogations with location registers, which will generate a higher volume of access and signaling traffic (SS7 traffic). One solution to this problem is to increase the size of LA, which, unfortunately, also increases paging traffic. Efficient paging algorithms may generate relatively less paging traffic such that larger LA's may become plausible. Depending on the call-arrival rate to the cell, boundary crossing rate, optimum size of LA, and paging technique used, the overall cost could vary substantially. The paging techniques considered in this paper are simultaneous paging and sequential paging. The two schemes are studied in detail in order to understand the problems associated with location management in the PCS environment. In the authors' opinion, this paper provides, for the first time, a simple yet powerful analytical framework which can be used to analyze 'intelligent' paging schemes as well as simultaneous and sequential paging. Index Terms - Location management, mobility, paging techniques, personal communication systems.

In this paper the impact of finite intermediate frequency (IF) on the performance of heterodyne ASK lightwave systems is examined and quantified in the presence of laser phase noise and shot noise. For negligible linewidths, it is shown that certain finite choices of IF ([R.sub.b], 3[R.sub.b]/2, 2[R.sub.b], 5[R.sub.b]/2, etc.) lead to the same ideal bit-error-rate (BER) performance as infinite choices of IF. Results indicate that for negligible linewidths the worst case sensitivity penalty is 0.9 dB for proper heterodyne detection and occurs when [f.sub.IF] = 1.25[R.sub.b]. For nonnegligible linewidths (e.g., when [Delta]vT [greater than or equal to] 0.04) the sensitivity penalty is always less than 0.9 dB for finite choices of IF. The analysis presented does lead to a closed-form signal-to-noise ratio (SNR) expression at the decision gate of the receiver which can readily be used for BER and sensitivity penalty computations. The SNR expression provided includes all the key system parameters of interest such as system bit rate ([R.sub.b]), the peak IF SNR ([Xi]), laser linewidth ([Delta]v), and the IF filter expansion factor ([Alpha]). The findings of this work suggest that the number of channels in a multichannel heterodyne ASK lightwave system can be increased substantially by properly choosing a small value for the IF at the expense of a small penalty (< 1 dB). On the negative side, IF frequency stabilization becomes a more critical requirement in multichannel systems employing small values of IF. Index Terms - Coherent ASK, finite intermediate frequency, lightwave systems, phase noise.

The effect of power control on the performance of cellular code division multiple access (CDMA) networks is investigated. The bit error rate (BER) of a mobile unit at any given distance from the base station is obtained for both the forward link and the reverse link, taking into account Rayleigh fading and UHF propagation attenuation. To this end, a simple multiple-cell-system model is developed. Our work shows the dependence of performance gain on the different user spatial distributions under power control. Also, it is shown that power control in the forward link of CDMA networks may lead to a dismal performance degradation for close-in users. To alleviate this problem, the adjusted power control scheme is revisited. Two different performance criteria are proposed for this purpose, and the optimal threshold values corresponding to these criteria are computed. Results indicate that, although both threshold criteria are acceptable, the second criterion is more recommendable from a BER performance point of view, because it circumvents the socalled service 'hole' problem which may occur when one uses the first criterion. The analysis for both the forward and reverse links leads to closed-form signal-to-interference ratio (SIR) results, which not only facilitate physical insight into the impact of key system parameters on the system performance of CDMA networks with power control, but may also eliminate the need for cumbersome Monte-Carlo-type simulations. It is shown that fourth-order power control (n = 4) leads to at least a threefold enhancement in capacity for BER = [10.sup.-3].