As the popularity of wireless communication increases rapidly, the unlicensed Industrial Scientific and Medical (ISM) band becomes crowded. Interference avoidance thus becomes an important issue when designing wireless communication in the unlicensed ISM band. As shown in related works, channel hopping with blacklisting is a promising mechanism addressing interference in 802.15.4e time slotted channel hopping (TSCH) networks. However, the blacklisting mechanism changes the number of channels used, and thus requiring the frequency hopping sequence (FHS) be regenerated. A time-random channel selection mechanism avoids regeneration overhead; however, it breaks close-to-optimality property of the default FHSs, which in turns leads to high probability of interference. In this paper, we propose a new algorithm that generates FHSs in presence of interference without regeneration overhead, and at the same time maintains the optimality property. With the new proposed mechanism, we can generate FHSs with one designed original sequence. Analysis and simulation results show that optimal/near optimal properties are achieved by these new FHSs.

We present a novel scanning algorithm to enable mobile units to obtain measurements from surrounding access points for indoor positioning using the wireless local area network (WLAN) infrastructure. Our scanning algorithm adapts to minimize its impact on network throughput and battery power consumption while meeting a target positioning accuracy. This is achieved by using a learning procedure that dynamically adapts the parameters of the WLAN scanning procedure. Further, we show static algorithms that do not consider high-traffic scenarios will not only fail to meet positioning accuracy targets, but they also severely degrade network throughput.

We study the non-cooperative game when many WLAN stations compete for responses from WLAN access points in order to find their positions. The main objective of the WLAN stations, which are the players in our game, is to minimize the positioning error under various constraints on power consumption and network throughput. We provide a rigorous and general formulation of the game model where we use the Cramer-Rao bound of the WLAN positioning error so that the analysis is independent of the underlying positioning algorithm. The strategies for each player are combinations of the frequency of probe requests within the network and the corresponding listening time. We compute the Nash Equilibrium for the game under different practical network scenarios.

In this paper, we investigate the issue of 20/40 MHz coexistence in next generation wireless local area networks (WLAN). To that end, we present simulation results of overlapping basic service sets (BSSs) an 802.11n BSS operating in 20/40 MHz mode and a legacy BSS operating in 20 MHz channel. Our results show that if clear channel assessment (CCA) is not used in the overlapping channel; i.e., the 20 MHz channel used by both BSSs, the throughput in legacy BSS falls to zero, while the throughput of 802.11n BSS decreases dramatically. If CCA is used in the overlapping channel, the throughput of both, legacy and 802.11n BSS increases compared to the earlier case. When devices operating in 20/40 MHz BSS are able to dynamically switch between 20 and 40 MHz transmissions and in addition, CCA is used in the overlapping channel, the throughput of both BSSs further increases. Reducing transmission opportunity (TXOP) interval for 40 MHz transmissions also improves fairness and throughput for legacy BSSs.

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.

In this paper, we present a performance analysis for different implementations of handover in indoor wireless networks (IWN) that use heating, ventilation, and air conditioning (HVAC) ducts as communication channels. If FDMA/TDMA technology is used, our results show that the handover performance, i.e., new call blocking and handover dropping probabilities, of an IWN that uses HVAC ducts are up to 6.6 times better for practical scenarios compared to those of traditional IWN (i.e., IWN that do not use HVAC ducts). Our results also indicate that for scenarios under investigation, using a single access point to serve one floor and its staircase region achieves the best handover performance for IWN that use HVAC ducts. The solution to the handover problem in HVAC-IWN is tightly coupled with the coverage, capacity, and load balancing issues in indoor wireless networks. We show, for the first time, that the proposed solution to the handover problem in HVAC-IWN results in an increase in capacity per coverage area, an increase in the radius of coverage for an access point, and can be used to achieve load balancing in WLAN that use IEEE 802.11 technology.

Multi-element antenna arrays at both transmitter and receiver systems have emerged as a new technique for wireless communication systems in rich multipath environments. HVAC ducts, viewed as over-moded waveguide network systems at RF frequencies, have the multipath richness through various propagating modes and reflections within the system. This paper studies multiple-input multiple-output (MIMO) systems for HVAC ducts. Computations based on measured channel responses of a 6/spl times/6 MIMO system in 0.3 m diameter HVAC ducts in the 2.4 GHz ISM band demonstrate a five-fold increase in mean capacity over single antenna systems for an SNR of 30 dB.

In this paper, we present an analytical framework for dynamic priority queueing of handover calls in wireless networks. The framework employs a queueing discipline with two classes of priority for handover calls. Two queues, first priority and second priority, are employed for the two priority classes of handover calls. The priority of queued handover calls is not based only on the received signal strength, but also on the remaining time in the overlap region between two cells. We also incorporate a priority transition between handover calls in the queue; specifically, a second-priority handover call in the second-priority queue, based on certain criteria, can become a first-priority handover call and join the first-priority handover queue. In addition, the event that a handover call could finish its call while waiting in the queue is taken into account in the analysis. This event was not taken into consideration in previous related studies and, as a result, these previous studies overestimate handover failure probability. Our results also show that the predictions of the analytical framework developed in this paper are in very good agreement with simulation results. The developed analytical framework is comprehensive and can also cope with several priority schemes proposed by other researchers in the literature. For example, it is shown that, under certain conditions, the proposed framework converges to first-in-first-out queueing of handover calls. One can easily modify the proposed framework to incorporate priority schemes that use guard channels for handover calls. It is also shown that one could potentially use the framework developed in this paper in integrated voice/data networks, as well as for handover between different network types. The proposed analytical framework is anticipated to be a very useful tool in evaluating performance of present and future wireless networks employing dynamic priority queueing for handovers and in designing more efficient handover algorithms.

In this paper, we present an innovative solution to the handover problem in multi-story buildings using HVAC ducts for wireless communications. The proposed solution is based on a new system architecture design of the indoor wireless networks that use the heating, ventilation, and air conditioning (HVAC) ducts as a communication channel. Exploiting the system architecture design and the time diversity at the mobile terminal, we show that intra-floor handover can be eliminated, while inter-floor handover can be substantially reduced due to the fact that multiple floors can be served via the same access point. Our results indicate that the mean number of handovers per call achieved in the indoor wireless networks that use HVAC ducts reduces; e.g., by up to a factor of nine for the illustrative example considered in this paper compared to that of indoor wireless networks that do not use HVAC ducts. The improvement; i.e., reduction in the mean number of handovers in multi-story building, depends on the number of access points used.

While most analytical studies on handover performance assume exponential channel holding times, recent field measurements have shown that channel holding time follows a mixed lognormal distribution. In this paper, the impact of mixed lognormal channel holding time on the handover performance of guard channel scheme with first-in first-out (GCM-FIFO) queuing examined. Our results show that the handover performance of GCM-FIFO is almost the same as the one when the channel holding time follows an exponential distribution. Hence, to evaluate the handover performance of PCS networks where the channel holding time follows a mixed lognormal distribution, one could use the analytical framework developed for the case of exponential channel holding time distributions.

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.

We present a simple path loss prediction model for link budget analysis in indoor wireless local area networks (LANs) that use heating, ventilation, and air conditioning (HVAC) ducts. The model we propose predicts the average power at each location in an HVAC duct network. This prediction model greatly simplifies the analysis for a complex duct network, making it a convenient and simple tool for system design. Our prediction model Is verified by experimental measurements.

We report theoretical channel capacity estimates of heating, ventilation, and air-conditioning (HVAC) ducts based on multi-carrier transmission that uses M-QAM modulation and measured channel responses at 2.4 GHz Industrial, Scientific, and Medical (ISM) band. It is shown that, data rates in excess of 1 Gbps are possible over distances up to 500 m in "matched" ducts (one can think of "matched" ducts as user-friendly ducts, since "matching" can, in principle, eliminate all the multipath reflections in HVAC ducts). Our work also shows that data rates in excess of 300 Mbps are possible over distances up to 500 m even in the presence of significant multipath reflections.

In this paper, an analytical framework which employs a delay-dependent queue discipline with two classes of priority for handoff calls is considered. Results obtained with the analytical framework are compared with the simulation results of Ebersman and Tonguz (1999) and it is shown that the accuracy of the analytical approximation is better than 95% for traffic loads of practical interest. The benefit of delay-dependent queueing compared to FIFO queueing increases as the handoff traffic increases.

An analytical framework which employs a multiple queuing scheme (MQS) for handoff calls in wireless networks is considered. Results show that, MQS and delay-dependent priority queuing (DDPQ) reported in Xhafa and Tonguz (2001) reduce handoff dropping probability by 40% when compared to the first-in-first-out (FIFO) scheme. It is also shown that, if one compares the MQS and DDPQ schemes, MQS achieves lower handoff dropping probability when the percentage of high-mobility handoff call users is greater than 38%.