Saulo Queiroz

Towards an efficient header compression scheme to improve VoIP over wireless mesh networks

Header compression techniques can improve the speech quality of VoIP applications. However, its deployment over wireless mesh environments may not offer much improvement, since the wireless and multi-hop characteristics of such a network impose a high packet loss rate. In this work, we propose a new approach for header compression, using packet aggregation to cooperate with the header compression scheme. Simulation results show that the new cooperative approach can decrease significantly the packet loss, impacting positively on the speech quality.

Header compression for VoIP over multi-hop wireless mesh networks

Header compression is both an interesting and a challenging alternative to real time applications. This paper presents an evaluation of a header compression technique called CoHC - cooperative header compression - and its performance in Voice over IP within multi-hop wireless mesh networks. The CoHC technique is able to perform header compression over multiple channels in a cooperative manner in order to avoid loss of synchronism between the compressor and the decompressor. Simulation results showed that the evaluated scheme can impact positively on VoIP calls quality.

All-at-Once or Piece-by-Piece: How to Access Wide Channels in WLANs with Channel Width Diversity?

In this letter we propose the Piece-by-Piece (PbP) medium access paradigm: a novel way of getting access to the widest channel B_w of a WLAN that supports different channel widths. Adapting the IEEE 802.11 DCF access method to PbP leads B_w to be organized into primary channel, in which contention occurs, and secondary narrow orthogonal channels. Upon winning a contention in the primary channel, nodes also get access to each secondary channel but in a sequential way rather than All-at-Once (AaO). Based on infinite horizon steady-state simulations and analytic results, we show that PbP causes the IEEE 802.11 access method to put up to twice more data bits into B_w in comparison to the conventional AaO paradigm.

An Alternative Approach for Header Compression Over Wireless Mesh Networks

Header compression techniques theoretically can improve the speech quality of multimedia applications. However it introduces a new impairment directly related to the loss of packets, that can impact negatively on the quality. Its deployment over wireless mesh networks needs special treatment due to the usually high loss rates of such a network. This work shows an evaluation of an alternative approach for header compression over wireless mesh networks. Experiments by means of stochastic simulation showed that under some network characteristics the proposed approach shows significant improvements in the packet loss.

Taxonomy, flexibility, and open issues on pue attack defenses in cognitive radio networks

Primary user emulation attacks (PUEAs) are one of the most damaging threats in cognitive radio networks. Malicious or selfish secondary users pretend legitimate primary users to profit from the opportunistic use of the licensed frequency spectrum. Since cognitive radio importance has enhanced as an approach to spectral efficiency and to diminish the negative effects of wireless network scalability, approaches for PUEAs defense have arisen, evolving their architectural strategy, nodes operation and analysis design. This article overviews recent achievement in PUEA defenses and presents a classification. Persistently unsolved challenges in the field are highlighted, and a framework for tackling one of the main challenges - the lack of flexibility to address this highly compromising attack - is outlined, promoting progress in the art of PUEA defense. As proof of concept, results present improvements in attack analysis employing flexible and multidimensional techniques on a case study. Finally, open issues and future directions are emphasized.

Impact evaluation of radio propagation models on performance parameters of application layer in Wireless Mesh Backbone simulation

In this paper we propose a VoIP study case to evaluate the impact of different radio propagation models on performance parameters of application layer in simulation studies of Wireless Mesh Backbones. For each presented model, we carried out experiments taking into account the credibility aspects suggested by simulation theory of stochastic processes. Results showed that, for the same scenario, using different propagation models, voice speech quality can switch from acceptable to unacceptable.

Translating full duplexity into capacity gains for the high-priority traffic classes of IEEE 802.11

In this paper we present PbP-EDCA, a Full Duplex (FD) MAC protocol that operates according to the high-priority access rules of the standard IEEE 802.11 EDCA. With PbP-EDCA, nodes that win a contention perform a sequence of narrow-band orthogonal transmissions rather than one single wide-band. PbP-EDCA employs the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) to avoid sequences starting at the same time and takes advantage of self-interference free radios to enable multiple simultaneous orthogonal transmissions to/from a single-radio access point. By exploiting FD and the EDCA contention values standardized for high-priority traffic classes, we show that PbP-EDCA can scale the gains claimed by single-link FD proposals in a network-wide domain. Our results indicate one scenario in which PbP-EDCA can achieve about 3× the capacity of the IEEE 802.11 half duplex MAC.

Voice over Wireless Mesh Networks: A Case Study in the Brazilian Amazon Region during the Rainy Season

In this paper we present the results of an experimental analysis of the behavior and performance of VoIP calls using different codecs in a wireless mesh network (WMN) based on the IEEE 802.11g standard. Most measurements were done during the rainy season in a Brazilian Amazon region.We assessed the call quality of codecs using real measurement conditions showing the codecs coding performance over wireless mesh networks.Both between unidirectional and bidirectional transmissions were studied.

Influence of Routing Protocol on VoIP Quality Performance in Wireless Mesh Backbone

In this paper we focus on the following question: how routing protocols, working under different channel conditions, can influence the human perceived quality of VoIP calls in a wireless mesh backbone? In order to respond this question, we propose a study case where we analyze two routing approaches in a 802.11 wireless mesh backbone, namely, reactive AODV and proactive OLSR. We calculated the voice speech quality by making use of a reviewed version of ITU-T E-model proposed in previous work. Results obtained from highly credible stochastic simulation environment, also described in this paper, showed that AODV performs better in very hostile mediums while OLSR presents better results when more friendly mediums take place.

Comparative analysis of routing protocols for VoIP in a Wireless Mesh Backbone: a user perspective

In this work we select AODV, OLSR and HWMP routing protocols and focus on how they can affect the Quality of user Experience (QoE) with respect to VoIP on a wireless backbone. We calculated QoE by using a reviewed version of the E-model. Since that parameter is strongly correlated with some stochastic network variables it presents stochastic behaviour too. So, we discuss important issues needed to estimate QoE based parameters in a trusty way. Results showed that the average QoE kept acceptable only under AODV routing as the number of VoIP traffic was increased in the network.