Pablo Serrano

Device-to-device communications with Wi-Fi Direct: overview and experimentation

Wi-Fi Direct is a new technology defined by the Wi-Fi Alliance aimed at enhancing direct device to device communications in Wi-Fi. Thus, given the wide base of devices with Wi-Fi capabilities, and the fact that it can be entirely implemented in software over traditional Wi-Fi radios, this technology is expected to have a significant impact. In this article we provide a thorough overview of the novel functionalities defined in Wi-Fi Direct, and present an experimental evaluation that portrays the performance to be expected in real scenarios. In particular, our results quantify the delays to be expected in practice when Wi-Fi Direct devices discover each other and establish a connection, and the performance of its novel power saving protocols. To the best of the authors¿ knowledge this is the first article in the state of the art that provides a wide overview and experimental evaluation of Wi-Fi Direct.

An architecture for software defined wireless networking

Software defined networking, characterized by a clear separation of the control and data planes, is being adopted as a novel paradigm for wired networking. With SDN, network operators can run their infrastructure more efficiently, supporting faster deployment of new services while enabling key features such as virtualization. In this article, we adopt an SDN-like approach applied to wireless mobile networks that will not only benefit from the same features as in the wired case, but will also leverage on the distinct features of mobile deployments to push improvements even further. We illustrate with a number of representative use cases the benefits of the adoption of the proposed architecture, which is detailed in terms of modules, interfaces, and high-level signaling. We also review the ongoing standardization efforts, and discuss the potential advantages and weaknesses, and the need for a coordinated approach.

Proportional fair throughput allocation in multirate IEEE 802.11e wireless LANs

Under heterogeneous radio conditions, Wireless LAN stations may use different modulation schemes, leading to a heterogeneity of bit rates. In such a situation, 802.11 DCF allocates the same throughput to all stations independently of their transmitting bit rate; as a result, the channel is used by low bit rate stations most of the time, and efficiency is low. In this paper, we propose a more efficient throughput allocation criterion based on proportional fairness. We find out that, in a proportional fair allocation, the same share of channel time is given to high and low bit rate stations, and, as a result, high bit rate stations obtain more throughput. We propose two schemes of the upcoming 802.11e standard to achieve this allocation, and compare their delay and throughput performance.

Optimal Configuration of 802.11e EDCA for Real-Time and Data Traffic

The enhanced distributed channel access (EDCA) mechanism of the IEEE 802.11e standard provides quality-of-service (QoS) support through service differentiation by using different medium-access-control (MAC) parameters for different stations. The configuration of these parameters, however, is still an open research challenge, as the standard provides only a set of fixed recommended values that do not take into account the current wireless local area network (WLAN) conditions and, therefore, lead to suboptimal performance. In this paper, we propose a novel algorithm for EDCA that, given the throughput and delay requirements of the stations that are present in the WLAN, computes the optimal configuration of the EDCA parameters. We first present a throughput and delay analysis that provides the mathematical foundation upon which our algorithm is based. This analysis is validated through simulations of different traffic sources (both data and real time) and EDCA configurations. We then propose a mechanism to derive the optimal configuration of the EDCA parameters, given a set of performance criteria for throughput and delay. We assess the effectiveness of the configuration provided by our algorithm by comparing it against 1) the recommended values by the standard, 2) the results from an exhaustive search over the parameter space, and 3) previous configuration proposals, which are both standard and nonstandard compliant. Results show that our configuration outperforms all other approaches.

Energy consumption anatomy of 802.11 devices and its implication on modeling and design

A thorough understanding of the power consumption behavior of real world wireless devices is of paramount importance to ground energy-efficient protocols and optimizations on realistic and accurate energy models. This paper provides an in-depth experimental investigation of the per-frame energy consumption components in 802.11 Wireless LAN devices. To the best of our knowledge, our measurements are the first to unveil that a substantial fraction of energy consumption, hereafter descriptively named cross-factor, may be ascribed to each individual frame while it crosses the protocol/implementation stack (OS, driver, NIC). Our findings, summarized in a convenient new energy consumption model, contrast traditional models which either neglect or amortize such energy cost component in a fixed baseline cost, and raise the alert that, in some cases, conclusions drawn using traditional energy models may be fallacious.

Greening wireless communications: Status and future directions

In recent years, concerns on energy consumption and greenhouse pollution due to the operation of wireless devices have triggered a vast amount of research work on the so called green wireless technologies, leading to new, energy-aware proposals. Even for the case of battery powered devices, where energy conservation is a key design goal, new approaches have been proposed, based on a better understanding of the cost-performance trade-offs introduced by energy efficient operation, while increasingly focusing on emerging communication technologies, e.g., body sensor networks, MIMO or LTE. This paper presents a survey of the recent proposals for green wireless communications, with a view to understanding the most relevant sources of inefficient energy consumption and how these are tackled by current solutions. We introduce a classification of the existing mechanisms based on their operational time-scale, discuss the most important techniques employed to date from this perspective, analyze the employed evaluation methodologies and undertake a quantitative comparison of their performance gains. Following this analysis, we identify the key challenges yet to be addressed by the research community, as well as several possible future directions towards greener communications.

Detecting selfish configurations in 802.11 WLANs

Lately, there has been an increase in the number of IEEE 802.11 devices that provide users with the ability to modify the MAC parameters or do not conform to the standard specification. This increases the risk of having a WLAN with selfish stations that, through the CSMA/CA parameters, obtain a larger share of the resources at the expense of well-behaved users. In this letter we propose a mechanism to detect these selfish stations that, unlike previous approaches, is not based on heuristics nor makes any assumption about radio conditions.

A Control Theoretic Approach for Throughput Optimization in IEEE 802.11e EDCA WLANs

The MAC layer of the 802.11 standard, based on the CSMA/CA mechanism, specifies a set of parameters to control the aggressiveness of stations when trying to access the channel. However, these parameters are statically set independently of the conditions of the WLAN (e.g. the number of contending stations), leading to poor performance for most scenarios. To overcome this limitation previous work proposes to adapt the value of one of those parameters, namely the CW, based on an estimation of the conditions of the WLAN. However, these approaches suffer from two major drawbacks: i) they require extending the capabilities of standard devices or ii) are based on heuristics. In this paper we propose a control theoretic approach to adapt the CW to the conditions of the WLAN, based on an analytical model of its operation, that is fully compliant with the 802.11e standard. We use a Proportional Integrator controller in order to drive the WLAN to its optimal point of operation and perform a theoretic analysis to determine its configuration. We show by means of an exhaustive performance evaluation that our algorithm maximizes the total throughput of the WLAN and substantially outperforms previous standard-compliant proposals.

End-to-end delay analysis and admission control in 802.11 DCF WLANs

In this paper, we first present an analytical model to study the distribution of the backoff delay in an 802.11 DCF WLAN under saturation conditions. We show that, with our method, the probability that the backoff delay is below a given threshold can be computed accurately and efficiently. Then, we extend our backoff delay distribution model to analyze the end-to-end delay, and propose an admission control algorithm based on this analysis. The proposed algorithm is evaluated in a mixed environment with voice and data stations, and simulation results confirm that it effectively provides voice stations with end-to-end delay guarantees. The algorithm is also evaluated in terms of computational cost and shown to be efficient enough for run-time usage.

srsLTE: an open-source platform for LTE evolution and experimentation

Testbeds are essential for experimental evaluation as well as for product development. In the context of LTE networks, existing testbed platforms are limited either in functionality and/or extensibility or are too complex to modify and customise. In this work we present srsLTE, an open-source platform for LTE experimentation designed for maximum modularity and code reuse and fully compliant with LTE Release 8. We show the potential of the srsLTE library by extending the baseline code to allow LTE transmissions in the unlicensed bands and coexistence with WiFi. We also expand previous results on this emerging research area by showing how different vendor-specific mechanisms in WiFi cards might affect coexistence.