As the data rates supported by the physical layer increase, overheads increasingly dominate the throughput of wireless networks. A promising approach for reducing overheads is to group a number of frames together into one transmission. This can reduce the impact of overheads by sharing headers and the time spent waiting to gain access to the transmission floor. Traditional aggregation schemes require that frames that are aggregated all be destined to the same receiver. These approaches neglect the fact that transmissions are broadcast and a single transmission will potentially be received by many receivers. Thus, by taking advantage of the broadcast nature of wireless transmissions, overheads can be amortized over more data and achieve more performance gain. To show this, we design a series of MAC-based aggregation protocols that take advantage of rate adaptation and the broadcast nature of wireless transmissions. We first show the design of a system that can aggregate both unicast and broadcast frames. Further, the system can classify TCP ACK segments so that they can be aggregated with TCP data flowing in the opposite direction. Second, we develop a rate-adaptive frame aggregation scheme that allows us to find the best aggregation size by tracking the size based on received data frames and the data rate chosen by rate adaptation. Third, we develop a multi-destination frame aggregation scheme to aggregate broadcast frames and unicast frames that are destined for different receivers using delayed ACKs. Using a delayed ACK scheme allows multiple receivers to control transmission time of the ACKs. Finally, we extend multi-destination rate-adaptive frame aggregation to allow piggybacking of various types of metadata with user packets. This promises to lower the impact of metadata-based control protocols on data transport. A novel aspect of our work is that we implement and validate the designs not through simulation, but rather using our wireless node prototype, Hydra, which supports a high performance PHY based on 802.11n. To validate our designs, we conduct extensive experiments both on real and emulator-based channels and measure system performance. / text

Frame aggregation is one of the major MAC layer enhancements in the IEEE 802.11 family that boosts the network throughput performance. It aims to achieve higher throughput by transmitting huge amount of data in a single transmit oppor- tunity. With the increasing awareness of energy e ciency, it has become vital to rethink about the design of such frame aggregation protocol. Aggregation techniques help to reduce energy consumption over ideal channel conditions. However, in a noisy channel environment, a new energy-aware frame aggregation scheme is required. In this thesis, a novel Green Frame Aggregation (GFA) scheduling scheme has been proposed and evaluated. GFA optimizes the aggregate size based on channel quality in order to minimize the consumed energy. GFA selects the optimal sub-frame size that satisfies the loss constraint for real-time applications as well as the energy budget of the ideal channel situations. The design, the implementation, and evaluation of GFA using testbed deployment is done. The experimental analysis shows that GFA outperforms the conventional frame aggregation methodology in terms of energy e ciency by about 6⇥ in the presence of severe interference conditions. Moreover, GFA also outperforms the static frame sizing method in terms of network goodput and maintains almost the same end- to-end latency.

<p>The wide spread use of IEEE Wireless LAN 802.11 in battery operated mobile devices introduced the need of power consumption optimization while meeting Quality-of-Service (QoS) requirements of applications connected through the wireless network. The IEEE 802.11 standard specifies a baseline power saving mechanism, hereafter referred to as standard Power Save Mode (PSM), and the IEEE 802.11e standard specifies the Automatic Power Save Delivery (APSD) enhancement which provides support for real-time applications with QoS requirements. The latest amendment to the WLAN 802.11 standard is the IEEE 802.11n standard which enables the use of much higher data rates by including enhancements in the Physical and MAC Layer. In this thesis, different 802.11n MAC power saving and QoS optimization possibilities are analyzed comparing against existing power saving mechanisms.</p><p>Initially, the performance of the existing power saving mechanisms PSM and Unscheduled-APSD (UAPSD) are evaluated using the 802.11n process model in the OPNET simulator and the impact of frame aggregation feature introduced in the MAC layer of 802.11n was analyzed on these power saving mechanisms. From the performance analysis it can be concluded that the frame aggregation will be efficient under congested network conditions. When the network congestion level increases, the signaling load in UAPSD saturates the channel capacity and hence results in poor performance compared to PSM. Since PSM cannot guarantee the minimum QoS requirements for delay sensitive applications, a better mechanism for performance enhancement of UAPSD under dynamic network conditions is proposed.</p><p>The functionality and performance of the proposed algorithm is evaluated under different network conditions and using different contention settings. From the performance results it can be concluded that, by using the proposed algorithm the congestion level in the network is reduced dynamically thereby providing a better power saving and QoS by utilizing the frame aggregation feature efficiently.</p>

The wide spread use of IEEE Wireless LAN 802.11 in battery operated mobile devices introduced the need of power consumption optimization while meeting Quality-of-Service (QoS) requirements of applications connected through the wireless network. The IEEE 802.11 standard specifies a baseline power saving mechanism, hereafter referred to as standard Power Save Mode (PSM), and the IEEE 802.11e standard specifies the Automatic Power Save Delivery (APSD) enhancement which provides support for real-time applications with QoS requirements. The latest amendment to the WLAN 802.11 standard is the IEEE 802.11n standard which enables the use of much higher data rates by including enhancements in the Physical and MAC Layer. In this thesis, different 802.11n MAC power saving and QoS optimization possibilities are analyzed comparing against existing power saving mechanisms. Initially, the performance of the existing power saving mechanisms PSM and Unscheduled-APSD (UAPSD) are evaluated using the 802.11n process model in the OPNET simulator and the impact of frame aggregation feature introduced in the MAC layer of 802.11n was analyzed on these power saving mechanisms. From the performance analysis it can be concluded that the frame aggregation will be efficient under congested network conditions. When the network congestion level increases, the signaling load in UAPSD saturates the channel capacity and hence results in poor performance compared to PSM. Since PSM cannot guarantee the minimum QoS requirements for delay sensitive applications, a better mechanism for performance enhancement of UAPSD under dynamic network conditions is proposed. The functionality and performance of the proposed algorithm is evaluated under different network conditions and using different contention settings. From the performance results it can be concluded that, by using the proposed algorithm the congestion level in the network is reduced dynamically thereby providing a better power saving and QoS by utilizing the frame aggregation feature efficiently.

In recent years, there have been tremendous advances in wireless & mobile communications, including wireless radio techniques, networking protocols, and mobile devices. It is expected that different broadband wireless access technologies, e.g., WiFi (IEEE 802.11) and WiMAX (IEEE 802.16) will coexist in the future. In the meantime, multimedia applications have experienced an explosive growth with increasing user demands. Nowadays, people expect to receive high-speed video, audio, voice and web services even when being mobile. The key question that needs to be answered, then, is how do we ensure that users always have the "best" network performance with the "lowest" costs in such complicated situations? The latest IEEE 802.11n standards attains rates of more than 100 Mbps by introducing innovative enhancements at the PHY and MAC layer, e.g. MIMO and Frame Aggregation, respectively. However, in this thesis we demonstrate that frame aggregation's performance adheres due to the EDCA scheduler's priority mechanism and consequently resulting in the network's poor overall performance. Short waiting times for high priority flows into the aggregation queue resolves to poor channel utilization. A Delayed Channel Access algorithm was designed to intentionally postpone the channel access procedure so that the number of packets in a formed frame can be increased and so will the network's overall performance. However, in some cases, the DCA algorithm has a negative impact on the applications that utilize the TCP protocol, especially the when small TCP window sizes are engaged. So, the TCP process starts to refrain from sending data due to delayed acknowledgements and the overall throughput drops. In this thesis, we address the above issues by firstly demonstrating the potential performance benefits of frame aggregation over the next generation wireless networks. The efficiency and behaviour of frame aggregation within a single queue, are mathematically analysed with the aid of a M=G[a;b]=1=K model. Results show that a trade-off choice has to be taken into account over minimizing the waiting time or maximizing utilization. We also point out that there isn't an optimum batch collection rule which can be assumed as generally valid but individual cases have to be considered separately. Secondly, we demonstrate through extensive simulations that by introducing a method, the DCA algorithm, which dynamically determines and adapts batch collections based upon the traffic's characteristics, QoS requirements and server's maximum capacity, also improves e ciency. Thirdly, it is important to understand the behaviour of the TCP ows over the WLAN and the influence that DCA has over the degrading performance of the TCP protocol. We investigate the cause of the problem and provide the foundations of designing and implementing possible solutions. Fourthly, we introduce two innovative proposals, one amendment and one extension to the original DCA algorithm, called Adaptive DCA and Selective DCA, respectively. Both solutions have been implemented in OPNET and extensive simulation runs over a wide set of scenarios show their effectiveness over the network's overall performance, each in its own way.

This thesis tackles problems on IEEE 802.11 MAC layer, network layer and application layer, to further push the performance of wireless P2P applications in a holistic way. It contributes to the better understanding and utilization of two major IEEE 802.11 MAC features, frame aggregation and block acknowledgement, to the design and implementation of opportunistic networks on off-the-shelf hardware and proposes a document exchange protocol, including document recommendation. First, this thesis contributes a measurement study of the A-MPDU frame aggregation behavior of IEEE 802.11n in a real-world, multi-hop, indoor mesh testbed. Furthermore, this thesis presents MPDU payload adaptation (MPA) to utilize A-MPDU subframes to increase the overall throughput under bad channel conditions. MPA adapts the size of MAC protocol data units to channel conditions, to increase the throughput and lower the delay in error-prone channels. The results suggest that under erroneous conditions throughput can be maximized by limiting the MPDU size. As second major contribution, this thesis introduces Neighborhood-aware OPPortunistic networking on Smartphones (NOPPoS). NOPPoS creates an opportunistic, pocket-switched network using current generation, off-the-shelf mobile devices. As main novel feature, NOPPoS is highly responsive to node mobility due to periodic, low-energy scans of its environment, using Bluetooth Low Energy advertisements. The last major contribution is the Neighborhood Document Sharing (NDS) protocol. NDS enables users to discover and retrieve arbitrary documents shared by other users in their proximity, i.e. in the communication range of their IEEE 802.11 interface. However, IEEE 802.11 connections are only used on-demand during file transfers and indexing of files in the proximity of the user. Simulations show that NDS interconnects over 90 \% of all devices in communication range. Finally, NDS is extended by the content recommendation system User Preference-based Probability Spreading (UPPS), a graph-based approach. It integrates user-item scoring into a graph-based tag-aware item recommender system. UPPS utilizes novel formulas for affinity and similarity scoring, taking into account user-item preference in the mass diffusion of the recommender system. The presented results show that UPPS is a significant improvement to previous approaches.

[pt] Cada vez mais as redes locais sem fio conhecidas por WLAN estão presentes no meio em que vivemos, seja em nossas casas como em escritórios, aeroportos e outros locais públicos. Na busca de possibilitar que mais aplicações sejam viabilizadas pelas redes sem fio, tais como fluxos de vídeo, a qual requer uma maior largura de banda, o IEEE desenvolveu um novo padrão da família do 802.11, o IEEE 802.11n que é capaz de oferecer uma capacidade de transmissão significativamente maior que os padrões 802.11 anteriores. Em principio, o grande aumento de capacidade na camada física deveria ser suficiente para oferta de aplicações de multimídia, inclusive com vídeo em alta definição. Entretanto, a baixa eficiência da camada de controle de acesso ao meio (camada MAC) e de alguns protocolos da camada física poderiam restringir o uso de aplicações que necessitam de altas taxas de transmissão. Para resolver essa questão o padrão 802.11n contempla o recurso de agregação dos quadros que possui dois métodos distintos, A-MPDU (Aggregated MAC Protocol Data Unit) e A-MSDU (Aggregated MAC Service Data Unit). Neste trabalho foram realizadas simulações com sinais de vídeos reais e apresentados resultados que permitem comparar o desempenho destes métodos e avaliar se o uso de agregação permite efetivamente que o padrão 802.11n atenda os requisitos da transmissão de vídeo. Foram também sugeridos valores para os parâmetros da tecnologia 802.11n que permitem que um melhor desempenho seja alcançado. / [en] Wireless LANs are gradually playing an increasingly important role in our day-to-day life. It is common now to find them in airports, hotels, office buildings as well as in individual residences. Due to this success there was an effort at IEEE to develop a new standard that would allow new high data rate applications, such as video streaming, to be provided through a WiFi access point. This new standard added to the IEEE 802.11 family is known as IEEE 802.11n and it offers a significantly higher capacity physical layer. However, to derive the full benefits of this new very powerful physical layer it was necessary to improve the efficiency of the MAC layer as well as of some physical layer protocols. One of techniques included in the standard, to allow high bandwidth services with good quality, was frame aggregation. The 802.11n standard contemplates two forms of aggregation, namely: A-MPDU (Aggregated MAC Protocol Data Unit) and AMSDU (Aggregated MAC Service Data Unit). In this work, simulations were performed to evaluate the performance of both methods of aggregation when transporting real video signals. The objective was to verify whether 802.11n, with the use of aggregation, can indeed provide video and multimedia services with the required quality. We also suggest values for 802.11n system parameters that provide improved performance.