Doru Calin

On femto deployment architectures and macrocell offloading benefits in joint macro-femto deployments

This article provides an overview of opportunities and challenges related to joint deployments of macro and femtocells. It provides insights on possible deployment architectures for femtocells along with an analysis framework for quantifying macro offloading benefits in realistic network deployment scenarios by means of advanced performance analysis techniques. Such benefits include potential enhancement in quality of radio signals for users served by the macro network in joint macro-femto deployments. This in turn translates into potentially better data rates (throughput) for macrocell users and may offer the possibility of adding more users to the macro network while preserving the network configuration -- resulting in direct capital expenditure savings. The approach taken in this article consists of creating a framework for quantifying macro offloading benefits in joint macro-femto deployments. A baseline configuration where all users (indoor and outdoor) are served by a traditional macro network (state-of-the-art macro only network) is considered first. The analysis is followed through joint macro-femto deployments, where femtocells serve indoor users. Through comparison of the baseline configuration and the joint macro-femto analysis, we quantify the benefits of the joint macro-femto deployment.

A Bayesian method to improve mobile geolocation accuracy

We present a geolocation method for GSM/CDMA/UMTS networks. A cell area is partitioned into a grid, and a sequential Bayesian updating scheme is proposed to identify the grid point within the circular belt, defined by the one-way delay between the mobile and the base station, that is the most likely position of the user. Using GSM as case study, we employ an RF simulation model to study the accuracy of the algorithm compared to existing methods. We show that the accuracy of the Bayesian update method is relatively insensitive to cell size and robust to parameter settings.

Design and analysis of an IEEE 802.16e-based OFDMA communication system

IEEE 802.16e has emerged as a strong candidate standard for future wireless systems primarily because it offers the potential for high spectral efficiency, flexible spectrum options (e.g., 2–6 GHz), scalable carrier bandwidth options (e.g., from 1.25 MHz to 20 MHz), multiple duplexing options (time and frequency division duplex), various subchannelization options, and, unlike its IEEE 802.16 predecessors, mobility. Because of the recent emergence of IEEE 802.16e and the complexity it poses in system analysis, there is little published work in the literature regarding the actual system capacity/throughput performance of IEEE 802.16e for high data rate services. In this paper, we investigate the link and system level performance on the downlink of an IEEE 802.16e-based orthogonal frequency division multiple access (OFDMA) communication system and provide recommendations on high performance IEEE 802.16e system design and deployment configurations. We also propose dynamic resource allocation methods that may be used in OFDMA systems and investigate their performance.

A Quality-Driven Cross-Layer Solution for MPEG Video Streaming Over WiMAX Networks

Extensive efforts have been focused on deploying broadband wireless networks. Providing mobile users with high speed network connectivity will let them run various multimedia applications on their wireless devices. Satisfying users with different quality-of-service requirements while optimizing resource allocation is a challenging problem. In this paper, we discuss the challenges and possible solutions for transmitting MPEG video streams over WiMAX networks. We will briefly describe the MPEG traffic model suggested by the WiMAX Forum. A cross-layer solution for enhancing the performance of WiMAX networks with respect to MPEG video streaming applications is explained. Our solution uses the characteristics of MPEG traffic to give priority to the more important frames and protect them against dropping. Besides, it is simple and compatible with the IEEE 802.16 standards and thus easily deployable. It is shown that the proposed solutions will improve the video quality over WiMAX networks.

Impact of radio resource allocation policies on the TD-CDMA system performance: evaluation of major critical parameters

This paper investigates the impact of major critical parameters and the effect of some radio resource allocation policies on the TD-CDMA system performance. Critical parameters are related either to the user behavior (e.g., user mobility, activity factors) or to processing techniques and algorithms implemented to control network performance and individual radio link quality (e.g., joint detection imperfection, handover margin, timeout for maintaining alive bad radio links). Network topology (e.g., distance between neighboring base stations) also undoubtedly influences capacity results. Analysis is carried out through accurate modeling of user behavior, interference scenarios, and power budget limitations at both terminals and infrastructure, allowing for proper implementation of radio resource allocation algorithms. Among these algorithms, power management (both at the initial channel assignment and during communication), dynamic channel allocation (DCA), and ongoing calls management are explored. An event-driven simulation approach was considered to model realistic system behavior and address system stability under various events generating traffic/interference fluctuations (e.g., call arrivals and departures, handovers, steps of power control loops). Such an approach is expected to offer a good estimate of the real conditions provided the propagation models are close to real life. As a consequence, measures to be taken to avoid/control overloading in a TD-CDMA (CDMA in general) environment can be naturally derived and tested with this methodology.

Macrocell offloading benefits in joint macro-and femtocell deployments

Femtocells are low-cost, low-power cellular base stations that are designed to provide high quality cellular service in residential or enterprise environments and operate in licensed spectrum to connect conventional, unmodified mobile terminals to a mobile operators network. The deployment of femtocells will reduce the number of indoor users that need to be served by the macrocellular network. Moreover, since indoor users usually have poorer radio channel conditions to the macrocell compared to outdoor users, for each indoor user that is served by a femtocell, the equivalent system resources of the macrocellular network might be able to serve more than one outdoor user, resulting in a potential macrocell offloading gain. The macrocell offloading benefits achievable in joint macro-femtocell deployments are investigated using system level simulations. It is shown that the potential increase in the number of supported users per macrocell in joint macro- and femtocell deployments depends on the macrocellular network configuration and can range from no gain for a system which is only interference limited to more than 30% in cases where noise is the limiting factor for indoor users at the macrocell edge.

Intelligent content delivery over wireless via SDN

On the Internet, most traffic is generated by content delivery applications such as video streaming, P2P and web surfing. With the proliferation of mobile applications that offer on-demand access to services, the ability to track end-users perceived service quality has become a pivotal aspect for future networks such as 5G. Software-defined networking (SDN) and network functions virtualization (NFV) in the mobile core offer unprecedented flexibility for opportunistic traffic steering, leading to advanced levels of quality-of-service (QoS) control. We leverage the SDN concept to dynamically control network traffic over wide area networks (WANs) from edge nodes of wireless networks (e.g., a packet data network gateway in LTE), depending on changing network conditions and application types. Our SDN-based application-aware routing system allows mobile network operators to achieve better utilization of their networks, service providers to improve customer satisfaction, and end-users to experience desirable service quality for various network applications. As for a prototype, we attach 802.11g to Mininets virtual networks in order to show the feasibility of our approach.

YouSlow: a performance analysis tool for adaptive bitrate video streaming

Adaptive bitrate (ABR) technologies are being widely used in todays popular HTTP-based video streaming such as YouTube and Netflix. Such a rate-switching algorithm embedded in a video player is designed to improve video quality-of-experience (QoE) by selecting an appropriate resolution based on the analysis of network conditions while the video is playing. However, a bad viewing experience is often caused by the video player having difficulty estimating transit or client-side network conditions accurately. In order to analyze the ABR streaming performance, we developed YouSlow, a web browser plug-in that can detect and report live buffer stalling events to our analysis tool. Currently, YouSlow has collected more than 20,000 of YouTube video stalling events over 40 countries.

Uncoordinated Beamforming for Cognitive Networks

In this paper, we propose jointly-optimized beam-forming algorithms for cognitive networks to maximize the achievable rates assuming single information stream in both primary and secondary links. The primary and cognitive users share the same spectrum and are equipped with multiple antennas. No coordination is required between the primary and cognitive users and the interference cancellation is done at the cognitive user. Specifically, the beamforming vectors of the cognitive link are designed to maximize the achievable rate under the condition that the interference both at the primary and cognitive receivers is completely nullified. The sum rate performance of the proposed algorithms is evaluated by Monte Carlo simulations.

Performance analysis of high speed circuit switched data (HSCSD) over GSM

The paper presents a nonpreemptive priority queueing system model for voice and HSCSD service integration in GSM. The study is conducted using a multidimensional Markov chain. An HSCSD connection can be established if the number of available channels is between a minimum acceptable capacity, b, and a maximum required capacity, B. This leads to an effective service time for HSCSD calls, proportional to the bandwidth negotiated with the base station. Finite buffers are used for new and handoff requests to increase the total carried traffic, while maintaining the quality-of-service (QoS) requirements. The analysis can be applied when mean service times for voice and HSCSD calls are different. The key parameters which control the new data service performance are identified and adequate formulas are obtained. Especially, delays experienced by HSCSD calls are evaluated and compared to an optimal transmission operating at the maximum capacity.