Advanced Protocols for Peer-to-Peer Data Transmission in Wireless Gigabit Networks

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

Belaidžio ryšio tinklų terpės prieigos valdymo tyrimas

Over the years, consumer requirements for Quality of Service (QoS) has been growing exponentially. Recently, the ratification process of newly IEEE 802.11ad amendment to IEEE 802.11 was finished. The IEEE 802.11ad is the newly con-sumer wireless communication approach, which will gain high spot on the 5G evolution. Major players in wireless market, such as Qualcomm already are inte-grating solutions from unlicensed band, like IEEE 802.11ac, IEEE 802.11ad into their architecture of LTE PRO (the next evolutionary step for 5G networking) (Qualcomm 2013; Parker et al. 2015). As the demand is growing both in enter-prise wireless networking and home consumer markets. Consumers started to no-tice the performance degradation due to overcrowded unlicensed bands. The un-licensed bands such as 2.4 GHz, 5 GHz are widely used for up-to-date IEEE 802.11n/ac technologies with upcoming IEEE 802.11ax. However, overusage of the available frequency leads to severe interference issue and consequences in to-tal system performance degradation, currently existing wireless medium access method can not sustain the increasing intereference and thus wireless needs a new methods of wireless medium access. The main focal point of this dissertation is to improve wireless performance in dense wireless networks. In dissertation both the conceptual and multi-band wireless medium access methods are considered both from theoretical point of view and experimental usage. The introduction chapter presents the investigated problem and it’s objects of research as well as importance of dissertation and it’s scientific novelty in the unlicensed wireless field. Chapter 1 revises used literature. Existing and up-to-date state-of-the-art so-lution are reviewed, evaluated and key point advantages and disadvantages are analyzed. Conclusions are drawn at the end of the chapter. Chapter 2 describes theoretical analysis of wireless medium access protocols and the new wireless medium access method. During analysis theoretical simula-tions are performed. Conclusions are drawn at the end of the chapter. Chapter 3 is focused on the experimental components evaluation for multi-band system, which would be in line with theoretical concept investigations. The experimental results, showed that components of multi-band system can gain sig-nificant performance increase when compared to the existing IEEE 802.11n/ac wireless systems. General conclusions are drawn after analysis of measurement results

IEEE 802.11n WLAN에서 프레임 전송 시간 조절을 통한 네트워크 성능 향상 MAC 프로토콜

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2013. 8. 최종호.최근 스마트폰, 태블릿 PC 등의 무선 네트워크를 사용하는 모바일 기기의 사용이 급증함에 따라 무선 랜 (wireless local area network (WLAN))에 대한 수요가 빠르게 증가하고 있다. 하지만, IEEE 802.11 표준에서 기본적으로 사용하는 MAC (medium access control) 프로토콜인 DCF (distributed coordination function) 는 single-cell 네트워크에서 MAC 효율 (MAC efficiency) 성능이 떨어지는 문제점과 ad-hoc 네트워크에서 노드간에 공평성 성능이 크게 저하 되는 문제점을 지니고 있다. 본 논문에서는 이러한 네트워크에서 DCF가 지니고 있는 문제점을 각각 해결할 수 있는 두 가지 다른 방식의 MAC 프로토콜들을 제안하였다. 기존의 MAC 프로토콜에서는 패킷 (packet) 이나 프레임 (frame) 의 크기가 정해지면, 각 노드 (node) 의 데이터 전송 속도에 따라 (data transmission rate) 프레임 전송 시간 (frame transmission duration) 이 정해졌다. 하지만, 본 논문에서는 IEEE 802.11n/ac/ad 표준에서 사용하는 프레임 결합 (frame aggregation) 과 block ACK 기법을 이용하여 프레임 전송 시간을 정확히 조절 할 수 있는 방법을 제안하였다. 만약 이와같이 프레임 전송 시간을 우리가 원하는 데로 정확하게 조절 할 수 있게된다면, 네트워크 상에 각 노드들은 추가적인 오버헤드 (overhead) 없이 자신이 알려주고자 하는 정보를 프레임 전송 시간을 이용하여 자신 주변의 노드들에게 간접적으로 알려줄 수 있게 된다. 즉, 프레임 전송 시간을 정확히 조절하는 것을 통해서 기존의 컨트롤 메시지 (control message) 가 수행했던 역할인 정보 전달의 역할을 수행 할 수 있게 된다. 이 아이디어는 간단하지만, 각 노드들이 네트워크 성능을 향상 시킬 수 있는 정보를 교환하는데 효과적이다. 본 논문에서 제안된 두 개의 MAC 프로토콜들은 이 아이디어를 활용하여 네트워크 성능을 향상시키고자 하였다. 우선, IEEE 802.11 single-cell 네트워크에서의 MAC 효율 성능을 향상시키기 위해 Transmission Order Deducing MAC (TOD-MAC) 프로토콜을 제안하였다. 최근 물리 계층 (physical layer) 에서의 전송 속도가 Gbps 범위까지 비약적으로 발전하고 있다. 하지만, 이러한 물리 계층 전송 속도의 증가가 MAC 계층 (MAC layer) 에서의 처리량 (throughput) 성능 향상에 효과적으로 기여하지 못하고 있는 실정이다. 왜냐하면, 물리 계층에서의 전송 속도가 올라 갈수록 PHY header와 컨텐션 시간 (contention time) 등의 MAC 계층에서 발생하는 오버헤드들이 처리량 성능 향상에 큰 걸림돌이 되기 때문이다. 이러한 문제점을 해결 하기 위해서 TOD-MAC에서 각 노드들은 자신의 전송 순서에 따라 앞서 제안된 방법을 이용하여 프레임 전송 시간을 정확히 조절하여 데이터를 전송한다. 이를 통해 네트워크 상의 각 노드들은 자신 주변 노드들의 전송 순서를 프레임 전송 시간을 통해 추정할 수 있게 되고, 자신에게 알려진 전송 순서 정보를 이용하여 순환 순서 방식 (round robin manner) 으로 데이터를 전송한다. 이를 통해 제안된 MAC 프로토콜은 전송 충돌 (transmission collision) 과 컨텐션 시간을 효율적으로 줄일 수 있게 되고, CSMA/CA (carrier sensing multiple access with collision avoidance) 기반의 single-cell 네트워크에서의 MAC 효율을 극대화 시킬 수 있게 된다. 또한, 실험을 통해 TOD-MAC이 다양한 환경에서 높은 처리량 성능과, 좋은 short/long-term 채널 점유 시간 공평성 (air-time fairness) 성능을 보여주는 것을 확인할 수 있었다. 또한, 본 논문에서는 IEEE 802.11 ad-hoc 네트워크에서의 최대-최소 채널 점유 시간 공평성 (max-min air-time fairness) 을 향상 시킬 수 있는 Max-min Air-time Fairness MAC (MAF-MAC) 프로토콜을 제안하였다. 최근 IEEE 802.11 ad-hoc 네트워크를 기반으로한 서비스에 대한 요구가 빠르게 증하하면서, ad-hoc 네트워크에서 노드들 간에 공평한 서비스를 제공하는 것이 중요한 문제가 되고 있다. 이를 위해 MAF-MAC에서는 각 노드들이 자신의 채널 점유 시간에 대한 정보를 프레임 전송 시간을 통해 주변 노드들에게 알려주고, 각 노드들은 이 정보를 이용하여 자신의 contention window (CW) 값을 적절하게 조절하여 ad-hoc 네트워크에서의 최대-최소 채널 점유 시간 공평성 성능을 향상시키고자 하였다. 이를 통해 제안된 MAC 프로토콜은 네트워크에 있는 노드들에게 보다 공평한 서비스를 제공함과 동시에 채널 점유율과 사용율을 효율적으로 향상 시킬 수 있었다. 또한, 다른 연구에서 제안된 히든 노드 감지 (hidden node detection) 방법과 히든 노드 해결 (hidden node resolving) 방법을 MAF-MAC에 적용함으로써 ad-hoc 네트워크에서 발생 할 수 있는 히든 노드 문제를 효과적으로 해결 할 수 있었다. 시뮬래이션을 통해 히든 노드의 존재 여부와 관계 없이 다양한 환경에서 MAF-MAC에 기반한 방법이 좋은 채널 점유 공평성 성능을 보여줌과 동시에 효율적으로 채널을 사용하고 있다는 것을 확인 할 수 있었다.The demand for wireless local area network (WLAN) has drastically increased due to the prevalence of the mobile devices such as smart phones and tablet PCs. However, the distributed coordination function (DCF), which is the basic MAC protocol used in IEEE 802.11 WLANs, needs to be improved on MAC efficiency in single-cell networks and fairness performance in ad-hoc networks. In this dissertation, we propose two MAC protocols that can enhance MAC efficiency in single-cell network, and max-min air-time fairness in ad-hoc network by adjusting frame transmission duration, respectively. In the traditional MAC protocol, the length of a packet or a frame is usually fixed and the transmission duration is determined by the data rate. However, we show how each node can precisely adjust the transmission duration when the frame aggregation and block ACK features are used in very high-speed IEEE 802.11n/ac/ad WLANs. If the transmission duration can be precisely controlled, it plays the role usually carried out by a control message. Therefore, a node can indirectly announce necessary information to the other nodes, which can sense the transmission of the node, without incurring any overhead. This idea is simple, but very effective to enhance the network performance by exchanging the necessary information without overheads. First, we propose the Transmission Order Deducing MAC (TOD-MAC) protocol to improve MAC layer efficiency in IEEE 802.11 single-cell network. Recently, the physical (PHY) layer transmission rate increases to Gbps range in the IEEE 802.11 WLANs. However, the increase in the PHY layer transmission rates does not necessarily translate into corresponding increase in the MAC layer throughput of IEEE 802.11 WLANs because of MAC overheads such as PHY headers and contention time. TOD-MAC precisely controls the frame length and transmission duration to indirectly provide necessary information to a node to determine the transmission order among all the nodes in a network. Each node transmits frames of different duration, and thus the other nodes can determine the time when they can transmit, which has the same effect as announcing the transmission order, without using a control message. Each node transmits a frame in a round robin manner, which minimizes the idle time between two consecutive transmissions without collisions, and significantly enhances the MAC efficiency in very high speed CSMA/CA wireless networks. The results of extensive simulations indicate that TOD-MAC achieves high throughput performance, short/long-term air-time fairness in multi-rate networks and excellent transient behavior in dynamic environments. Secondly, we propose Max-min Air-time Fairness MAC (MAF-MAC) to improve max-min air-time fairness in IEEE 802.11 ad-hoc networks. As the demand for services based on ad-hoc networks rapidly increases, enhancing fairness among nodes becomes important issue in ad-hoc networks. The concept of max-min fairness is that a node may use more channel resource as long as it does take away the channel resource from the other nodes who uses less channel resource. In MAF-MAC, the transmission duration is adjusted so that it can indirectly perform the function of a control message in announcing the state of a node, called the busy time ratio. On the basis of this information, each node adjusts its $CW$ value to improve max-min air-time fairness. Moreover, we also adopt the hidden node detection and resolving mechanism to MAF-MAC to improve the max-min air-time fairness even when there are hidden nodes in ad-hoc networks. We show through simulation that MAF-MAC incorporating hidden node detection/resolution mechanisms can provide good air-time fairness with high channel occupation and utilization ratio whether or not there are hidden nodes in the network.Docto

Enabling Technologies for Ultra-Reliable and Low Latency Communications: From PHY and MAC Layer Perspectives

© 1998-2012 IEEE. Future 5th generation networks are expected to enable three key services-enhanced mobile broadband, massive machine type communications and ultra-reliable and low latency communications (URLLC). As per the 3rd generation partnership project URLLC requirements, it is expected that the reliability of one transmission of a 32 byte packet will be at least 99.999% and the latency will be at most 1 ms. This unprecedented level of reliability and latency will yield various new applications, such as smart grids, industrial automation and intelligent transport systems. In this survey we present potential future URLLC applications, and summarize the corresponding reliability and latency requirements. We provide a comprehensive discussion on physical (PHY) and medium access control (MAC) layer techniques that enable URLLC, addressing both licensed and unlicensed bands. This paper evaluates the relevant PHY and MAC techniques for their ability to improve the reliability and reduce the latency. We identify that enabling long-term evolution to coexist in the unlicensed spectrum is also a potential enabler of URLLC in the unlicensed band, and provide numerical evaluations. Lastly, this paper discusses the potential future research directions and challenges in achieving the URLLC requirements