Philippe Godlewski

An Auction Framework for Spectrum Allocation with Interference Constraint in Cognitive Radio Networks

Extensive research in recent years has shown the benefits of \textit{cognitive radio} technologies to improve the flexibility and efficiency of spectrum utilization. This new communication paradigm, however, requires a well-designed spectrum allocation mechanism. In this paper, we propose an auction framework for cognitive radio networks to allow unlicensed secondary users (SUs) to share the available spectrum of licensed primary users (PUs) fairly and efficiently, subject to the interference temperature constraint at each PU. To study the competition among SUs, we formulate a non-cooperative multiple-PU multiple-SU auction game and study the structure of the resulting equilibrium by solving a non-continuous two-dimensional optimization problem. A distributed algorithm is developed in which each SU updates its strategy based on local information to converge to the equilibrium. We then extend the proposed auction framework to the more challenging scenario with free spectrum bands. We develop an algorithm based on the no-regret learning to reach a correlated equilibrium of the auction game. The proposed algorithm, which can be implemented distributedly based on local observation, is especially suited in decentralized adaptive learning environments as cognitive radio networks. Finally, through numerical experiments, we demonstrate the effectiveness of the proposed auction framework in achieving high efficiency and fairness in spectrum allocation.

A fluid model for performance analysis in cellular networks

We propose a new framework to study the performance of cellular networks using a fluid model and we derive from this model analytical formulas for interference, outage probability, and spatial outage probability. The key idea of the fluid model is to consider the discrete base station (BS) entities as a continuum of transmitters that are spatially distributed in the network. This model allows us to obtain simple analytical expressions to reveal main characteristics of the network. In this paper, we focus on the downlink other-cell interference factor (OCIF), which is defined for a given user as the ratio of its outer cell received power to its inner cell received power. A closed-form formula of the OCIF is provided in this paper. From this formula, we are able to obtain the global outage probability as well as the spatial outage probability, which depends on the location of a mobile station (MS) initiating a new call. Our analytical results are compared to Monte Carlo simulations performed in a traditional hexagonal network. Furthermore, we demonstrate an application of the outage probability related to cell breathing and densification of cellular networks.

Analytical evaluation of various frequency reuse schemes in cellular OFDMA networks

In this paper, we present an analytical solution to carry out performance analysis of various frequency reuse schemes in an OFDMA based cellular network. We study the performance in downlink in terms of signal to interference (SIR) ratio and cellular capacity. Analytical models are proposed for integer frequency reuse (IFR), fractional frequency reuse (FFR) and two level power control (TLPC) schemes. These models are based on a fluid model originally proposed for CDMA networks. The modeling key of this approach is to consider the discrete base stations entities as a continuum. To validate our approach, Monte Carlo simulations are carried out. Results of validation study show that results obtained through our analytical method are in conformity with those obtained through simulations. However, compared to time consuming simulations, our model is very time efficient. We also present a comparison between above three frequency reuse scheme.

Spatial Outage Probability for Cellular Networks

In this paper, we propose a new framework for the study of cellular networks called the fluid model and we derive from this model analytical formulas for interference, outage probability, and spatial outage probability. The key idea of the fluid model is to consider the discrete base stations (BS) entities as a continuum of transmitters which are spatially distributed in the network. This allows us to obtain simple analytical expressions of the main characteristics of the network. In this paper, we focus on the downlink other-cell interference factor, f, which is defined here as the ratio of outer cell received power to the inner cell received power. Although this factor has been firstly defined for CDMA networks (in particular UMTS and HSDPA), the analysis presented hereafter is still valid for other systems using frequency reuse 1, like OFDMA (WiMAX), TDMA (GSM with frequency hopping), or even ad hoc networks. A closed- form formula of f is provided in this paper. From f, we are able to derive the global outage probability and the spatial outage probability, which depends on the location of a mobile station (MS) initiating a new call. All results are compared to Monte Carlo simulations performed in a traditional hexagonal network.

Performance evaluation of the R-BTMA protocol in a distributed mobile radio network context

A reservation multiple-access protocol for mobile communication in a decentralized environment is proposed and investigated both analytically and by simulation. The reservation-busy-tone multiple access (R-BTMA) is a fully distributed and reservation-based protocol. It is a medium access control (MAC) protocol designed for short-range communications between vehicles in a decentralized context (i.e., without a base station). The specificity of this protocol relies on the utilization of two different characteristic channels. Information is transmitted on the data channel (DC), whereas the busy-tone channel (BTC) is used for signalling traffic. The range of the BTC is typically longer than the DC one. The throughput and access delay performance are studied in the particular context of two cells sharing a common BTC. The traffic between the vehicles is supposed to be regular and is parameter sharing. The comparison of the model analysis results to those obtained by the simulative approach shows a satisfactory matching. >

On the dimensioning of cellular OFDMA networks

In this paper, we address the issue of cellular OFDMA networks dimensioning. Network design consists of evaluating cell coverage and capacity and may involve many parameters related to environment, system configuration, and quality of service (QoS) requirements. In order to quickly study the impact of each of these parameters, analytical formulas are needed. The key function for network dimensioning is the Signal to Interference Ratio (SIR) distribution. We thus analyze in an original way the traditional issue of deriving outage probabilities in OFDMA cellular networks. Our study takes into account the joint effect of path-loss, shadowing, and fast fading effects. Starting from the Mean Instantaneous Capacity (MIC), we derive the effective SIR distribution as a function of the number of sub-carriers per subchannel. Our formula, based on a fluid model approach, is easily computable and can be obtained for a mobile station (MS) located at any distance from its serving base station (BS). We validate our approach by comparing all results to Monte Carlo simulations performed in a hexagonal network, and

Analytical performance evaluation of various frequency reuse and scheduling schemes in cellular OFDMA networks

In this paper, we present an analytical solution to carry out performance analysis of various frequency reuse schemes in an OFDMA based cellular network. We study the performance in downlink in terms of signal to interference (SIR) ratio and total cell data rate. The latter is analyzed while keeping in view three different scheduling schemes: equal data rate, equal bandwidth and opportunist. Analytical models are proposed for integer frequency reuse (IFR), fractional frequency reuse (FFR) and two level power control (TLPC) schemes. These models are based on a fluid model that was originally being proposed for CDMA networks. The modeling key of this approach is to consider the discrete base station entities as a continuum. To validate our approach, Monte Carlo simulations are carried out. Validation study shows that results obtained through our analytical method are in conformity with those obtained through simulations. A comparison between the above-mentioned frequency reuse schemes and scheduling policies is also presented. We also propose an optimal tuning of involved parameters (inner cell radius and power ratios).

Admission control strategy and scheduling algorithms for downlink packet transmission in WCDMA

In this paper we investigate the performance of an admission control strategy and two scheduling algorithms for downlink packet transmission in WCDMA. The model incorporates two traffic classes: real-time and non real-time. The admission control strategy is based on mean power and mean traffic load in the target base station. Both scheduling schemes give higher priority to real-time packets. Within a traffic class, one algorithm gives priority to a user having the smallest queue whereas second algorithm prioritizes a user with the largest queue. The performance of the two scheduling algorithms is compared with and without admission control. The performance is evaluated using dynamic simulations. Results are manifested in terms of grade of service, delay, delay-jitter and packet loss rate. The results depict that the smallest queue priority scheduling has a better performance compared to the second algorithm. It is also observed that when input load is high, admission control improves the system performance.

Network Controlled Joint Radio Resource Management for Heterogeneous Networks

In this paper, we propose a way of achieving optimally in radio resource management (RRM) for heterogeneous networks. We consider a micro or femto cell with two co-localized radio access technologies (RAT), e.g. WLAN and HSDPA. RAT are mainly characterized by the data rates they offer at a given distance of the access point. Dual-technology mobile stations (MS) are initiating downlink sessions in the considered cell. A network controlled joint RRM algorithm is responsible to assign MS to a RAT, while taking into account the joint spatial distribution of already accepted MS, the current load of each RAT, the location of the newly accepted session and its influence on the global performance. In a study based on the Semi Markov Decision Process (SMDP) theory, we show how to obtain an optimal policy. Optimality is here defined through a utility function accounting for user satisfaction.

Radio resource management for packet transmission in UMTS WCDMA system

In this work the trade-off between throughput maximization and power allocation is studied in the case of non-real time data in a downlink WCDMA multi-cell environment. Two policies are compared. The first is equal rate per user and minimal power assignment with constrained transmitted power per channel. The second is a scheduled allocation with constrained total transmitted power. This latter maximizes the total throughput and tends to assign minimal rates to mobiles situated far from the serving base station and high rates to mobiles near the base station.