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Novlan T.D.,University of Texas at Austin | Ganti R.K.,Indian Institute of Technology Madras | Ghosh A.,AT and T Laboratories | Andrews J.G.,University of Texas at Austin
IEEE Transactions on Wireless Communications

Fractional frequency reuse (FFR) is an interference management technique well-suited to OFDMA-based cellular networks wherein the bandwidth of the cells is partitioned into regions with different frequency reuse factors. To date, FFR techniques have been typically been evaluated through system-level simulations using a hexagonal grid for the base station locations. This paper instead focuses on analytically evaluating the two main types of FFR deployments-Strict FFR and Soft Frequency Reuse (SFR)-using a Poisson point process to model the base station locations. The results are compared with the standard grid model and an actual urban deployment. Under reasonable special cases for modern cellular networks, our results reduce to simple closed-form expressions, which provide insight into system design guidelines and the relative merits of Strict FFR, SFR, universal reuse, and fixed frequency reuse. Finally, a SINR-proportional resource allocation strategy is proposed based on the analytical expressions and we observe that FFR provides an increase in the sum-rate as well as the well-known benefit of improved coverage for cell-edge users. © 2011 IEEE. Source

Liou J.-C.,AT and T Laboratories
Proceedings of the 6th IASTED International Conference on Software Engineering and Applications, SEA 2002

During the last decade, software engineering researchers have tried to identify the success and obstacle factors to the software development. Conclusions from most of the researches related to the issue show that software process is one of the most important subjects contributing into the success or failure to the software development. The Capability Maturity Model (CMM), the ISO9000 series, and best practices are some well known parts of the process management and improvement standards or guidelines. Among them, the CMM is the one specially focusing on the software development. In this paper, we demonstrate that leadership and other human factors can negatively affect the process maturity of software development organizations. Even for those organizations that are assessed for certain levels of process maturity, with no periodical audit from CMM assessors, their process maturity still under influence of these factors. These human factors, based on the industry experience, are identified and possible resolutions are discussed. Source

Novlan T.D.,University of Texas at Austin | Ganti R.K.,Indian Institute of Technology Madras | Ghosh A.,AT and T Laboratories | Andrews J.G.,University of Texas at Austin
IEEE Transactions on Communications

Interference management techniques are critical to the performance of heterogeneous cellular networks, which will have dense and overlapping coverage areas, and experience high levels of interference. Fractional frequency reuse (FFR) is an attractive interference management technique due to its low complexity and overhead, and significant coverage improvement for low-percentile (cell-edge) users. Instead of relying on system simulations based on deterministic access point locations, this paper instead proposes an analytical model for evaluating Strict FFR and Soft Frequency Reuse (SFR) deployments based on the spatial Poisson point process. Our results both capture the non-uniformity of heterogeneous deployments and produce tractable expressions which can be used for system design with Strict FFR and SFR. We observe that the use of Strict FFR bands reserved for the users of each tier with the lowest average \sinr provides the highest gains in terms of coverage and rate, while the use of SFR allows for more efficient use of shared spectrum between the tiers, while still mitigating much of the interference. Additionally, in the context of multi-tier networks with closed access in some tiers, the proposed framework shows the impact of cross-tier interference on closed access FFR, and informs the selection of key FFR parameters in open access. © 1972-2012 IEEE. Source

Novlan T.,University of Texas at Austin | Andrews J.G.,University of Texas at Austin | Sohn I.,University of Texas at Austin | Ganti R.K.,University of Texas at Austin | Ghosh A.,AT and T Laboratories
GLOBECOM - IEEE Global Telecommunications Conference

Fractional frequency reuse (FFR) is an interference coordination technique well-suited to OFDMA based wireless networks wherein cells are partitioned into spatial regions with different frequency reuse factors. This work focuses on evaluating the two main types of FFR deployments: Strict FFR and Soft Frequency Reuse (SFR). Relevant metrics are discussed, including outage probability, network throughput, spectral efficiency, and average cell-edge user SINR. In addition to analytical expressions for outage probability, system simulations are used to compare Strict FFR and SFR with universal frequency reuse based on a typical OFDMA deployment and uniformly distributed users. Based on the analysis and numerical results, system design guidelines and a detailed picture of the tradeoffs associated with the FFR systems are presented, showing that Strict FFR provides the greatest overall network throughput and highest cell-edge user SINR, while SFR balances the requirements of interference reduction and resource efficiency. ©2010 IEEE. Source

Quackenbush S.R.,AT and T Laboratories
143rd Technical Conference and Exhibition

MPEG-4 standardizes natural audio coding at bitrates ranging from 2 kbit/s, suitable for intelligible speech coding, to 64 kbit/s per channel, suitable for high-quality audio coding. Within this range, three categories of coding are defined: parametric coding, Code Excited Linear Predictive coding (CELP) and time/frequency (T/F) coding. The unique contribution of MPEG-4 audio is that not only does it scale across a wide range of bitrates, but it also scales across a broad set of other parameters, such as sampling rate, bandwidth, voice pitch and complexity. This paper presents an overview of the MPEG-4 natural audio coding framework and each of its component coding techniques. © 2001 Society of Motion Picture and Television Engineers, Inc. Source

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