If you would like to write for this, or any other Emerald publication, then please use our Emerald for Authors service information about how to choose which publication to write for and submission guidelines are available for all. Please visit www.emeraldinsight.com/authors for more information. About Emerald www.emeraldinsight.comEmerald is a global publisher linking research and practice to the benefit of society. The company manages a portfolio of more than 290 journals and over 2,350 books and book series volumes, as well as providing an extensive range of online products and additional customer resources and services.Emerald is both COUNTER 4 and TRANSFER compliant. The organization is a partner of the Committee on Publication Ethics (COPE) and also works with Portico and the LOCKSS initiative for digital archive preservation.

There exist various applications for indoor positioning, amongst which indoor positioning and tracking in urban environments has gained significant attention. Some user communities, like fire fighters, ideally require indoor accuracy of less than one metre, with accuracies of less than six metres acceptable by some other user communities. Achieving this level of accuracy requires a detailed profiling of error sources so that they can be better understood so that, in turn, indoor positioning accuracy in the presence of these errors can be further improved. Some well known error sources like multipath, NLOS (non line of sight), oscillator drift, dilution of precision and others have been studied and can be found in the literature. A less well known error source that can substantially affect indoor positioning accuracy are the effects of the dielectric properties of building materials on propagation delay.Various RF and non-RF based prototypes that claim to be suitable for indoor positioning can be found in the literature. Most of the existing literature discusses algorithms and summarizes the positioning results that were achieved during field tests using a prototype system or, more commonly, simulations. Little of this existing literature provides a breakdown of the total navigation system errors observed with the objective of analyzing the contribution of each error source independently.The paper will first provide a brief overview of the precision personnel locator system developed at the Worcester Polytechnic Institute. The field tests and observed indoor positioning results using this RF prototype will then be summarized and used to provide a baseline to establish a system error budget. The total observed error will be broken down and a detailed analysis of each of the error sources will be presented based on actual measured data in a variety of indoor environments. This leads to a better understanding of how each error source affects indoor positioning accuracy. Each of the error sources can then be independently optimized to minimize the observed errors. Specifically, the interplay between the dielectric properties and multipath profiles will be highlighted. This paper will conclude by presenting an error budget which can be used as a practical lower bound when designing precise indoor positioning systems.K E Y W O R D S 1. Indoor positioning.2. Dielectric properties.

Land Mobile Radio (LMR) networks have been traditionally used for transmitting voice signals. Systems like Facsimile, Radio Teletype and Distributed Digital Radios (DDR) use a conventional analog FM radio to transmit data [1], [2]. Digital Radios like Packet Radio and P-25, use complex modulation schemes like Continuous Frequency Shift keying (CFSK), Continuous Phase Modulation (CPM) to transmit voice/data information [3],[4]. The Medium Access Layer (MAC) implemented on such data networks ensures fair access to the half duplex FM channel. For voice transmission the users can themselves act as a default contention resolution mechanism. For data, some variations of channel access mechanisms like Time Division Multiple Access (TDMA) / Frequency Division Multiple Access (FDMA) / Carrier Sense Multiple Access (CSMA) are used [5]. The delays due to the Radio Hardware can significantly influence the throughput of such networks. This paper describes the effects of Push-To-Talk (PTT) delays associated with Land mobile Radios (LMR) for a CSMA based MAC layer. The results show that the PTT delays along with the number of nodes in a network can affect the throughput of a CSMA based capacity limited LMR network.

In this paper, we highlight the impact of variable Push-To-Talk (PTT) delays on performance of a heterogeneous Land Mobile Radio (LMR) network. We first present the PTT delay values and distributions observed for some commonly used LMR nodes. An analytical model is then developed to estimate the asymmetric throughput problem. The results obtained using this model and simulations show that a LMR node experiences a denial of service (DOS) due to collisions resulting from PTT delays. This leads to an asymmetry in throughput performance of individual nodes. The extent of the asymmetry is a function of total number of nodes in the system and the density of nodes with similar PTT delay profiles. These observations have implications in both, the performance and capacity planning of heterogeneous LMR network.

No abstract