In this paper, we present a comprehensive performance evaluation of TCP NewReno and TCP Vegas with and without ACK thinning for static multihop wireless IEEE 802.11 networks. Opposed to previous studies, we consider not only IEEE 802.11 operating in ad hoc mode with 2 Mbit/s bandwidth, but also with 5.5 Mbit/s and 11 Mbit/s bandwidths. Simulation results using ns-2 show that TCP Vegas achieves between 15% and 83% more goodput and between 57% and 99% fewer packet retransmissions than TCP NewReno. Considering fairness among multiple TCP flows, we show that using TCP Vegas results in between 21% and 95% fairness improvement compared to TCP NewReno. The reduced amount of packet retransmissions of TCP Vegas also leads to significant savings of energy consumption. The paper gives insight on the particular reasons for such performance advantages of TCP Vegas in comparison to TCP NewReno.

隨著IEEE 802.11無線傳輸頻率的快速發展，而傳輸距離卻隨著縮短，使得我們考慮多跳接的傳輸方式來擴展通訊的範圍。但是在IEEE 802.11 的多跳接無線網路中並沒有服務品質的保證，而且在傳輸上的效能不高，因此我們希望在IEEE 802.11 多跳接的無線網路中改善傳輸效能且提供服務品質保證。在這篇論文中，我們提出了一個安排MAC存取的方法，來達到服務品質保證。我們使用一個樹狀架構來建構這個無線網路並且運作訊標繞樹的動作來建立我們的分離集合，而分離集合提供我們安排無衝突傳輸。當訊務流在這個網路中產生，我們的方法能夠有效的安排MAC存取並且保證不同類型訊務之品質。我們同時也提供一種適應性安排機制，來有效利用整個網路的效能，並且避免重新安排整個網路的MAC存取規畫，來維持網路品質在適當的滿意度。實驗結果顯示我們在多跳接的無線網路中有效的達到服務品質保證。 / With fast development of radio frequency, the wireless communication in IEEE 802.11 is growing up to high transmission rate (802.11g). However the distance of transmission decreases when wave frequency increases. Thus there is growing need to extend communication distance through multihop transmissions. But there is no QoS in IEEE 802.11 Multihop Wireless Networks; it has poor performance on transmission. Thus we are motivated to provide QoS in IEEE 802.11 Multihop Wireless Networks. In This Thesis, we propose a MAC Access Scheduling Scheme to support guaranteed QoS in IEEE 802.11 Multihop Wireless Networks. We use a tree-based architecture to construct the network and form the operation of token traversal. Token traversal operation builds the Disjoint Set to support scheduling collision-free transmission. When traffic is generated to the network, our scheme provides efficient schedule of MAC access and guarantee the QoS of different types of traffic. We also provide a adaptive scheduling to utilize the network performance and avoid the overhead of re-schedule to maintain the network quality at a satisfied level. The simulation results show we achieve the network QoS efficiently and provide guaranteed QoS.

This thesis is split into two parts: first a statistical analysis of multi-hop MIMO relay networks, followed by a simulation of the perfomance of a P25 SISO multi-hop relay network. The basis of the MIMO section is the developement of an end to end statistical model of the multiple relay channel. This end to end model simplifies the statistics involved, making the analysis of systems with large numbers of relays and antennas more practical. A partial system model is obtained. This is exact for a multiple input single output network and can be used to describe the received signal at a single antenna in a multiple output system. We go on to look at the relationship between end to end system parameters and the paramters of individual inter-relay channels. The SISO section contains a characterisation of BER for P25 relay chains. The effect of the SNR at each relay node, the nature of the channel and the number of relay hops on the BER is determined. Furthermore, the performance trends are compared for a range of common relaying protocols, including amplify and forward and two types of decode and forward.

High performance real-time applications have become and will continue to be anintegral part of today’s world. With this comes the requirement to provide reliablecommunication networks for these applications requiring real-time guarantees.Depending on the specific application the requirements vary and adapting to allthese requirements is important. Ethernet is a commonly used communication medium in these real-time applicationnetworks because of the advantages it provides with its simplicity, which comesalong with lower cost and higher bit rates. However since Ethernet was notspecifically designed for real-time applications, it has been under constant study inorder provide the required QoS (Quality of Service) requirements for theapplication. In this thesis our aim is to provide a less pessimistic approach to the real-timeanalysis of packet switched networks by the use of knowledge about the offsetintroduced to the packets travelling in the network. Therefore we have taken aspecific application with high real-time requirements, namely a radar application.We are using the available data to simulate and analyze the network’s performanceunder the use of offsets. The analysis is done by calculating some of the commonlyused QoS requirements such as end to end delay, deadline miss ratio and link utilization.

We question about multihop gets better performance than single hop in wireless networks. In this paper we design a new and simple multihop transmission model called PESR, performance enhancement of IEEE 802.11 by spatial reuse. We elect an intermediate node which between a source-destination pair for forwarding packets to become multihop instead of directly transmission from the source to the destination. By this way, we will have more links at the one time, the channel utilization should be grown and we will get better system performance. However, there is much overhead we have not considered. We will discuss the detail about overhead in coming sections. In fact, the results of simulation show that the performance is not present very well. And we wonder if the multihop in wireless networks is a pretty good idea.

We present a new Channel State Information (CSI) signalling strategy for single- branch Mobile Multihop Relay (MMR) systems. This novel signalling strategy reduces the signalling overhead at each relay by at least 50%, and eliminates the need for channel estimation at the relays. We prove that this significant overhead reduction comes at the expense of no performance loss at all when hard Maximum Likelihood detection is carried out at the destination. Furthermore, we consider the use of our system with concatenated channel codes to carry out soft Maximum a Posteriori (MAP) detection, and show that with channel codes employed the optimum detection rule becomes prohibitively complex to implement. We propose two approximate soft MAP detection schemes to make the detection feasible for our system, and demonstrate that the performance is either almost identical or slightly degraded from the ideal case with full CSI at the destination. We demonstrate the validity of our analysis through performance simulation plots. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-08-08 19:27:48.283

The exploding growth of wireless devices like smartphones and tablets has driven the emergence of various applications, which has exacerbated the congestion over current wireless networks. Noticing the limitation of current wireless network architectures and the static spectrum policy, in this dissertation, we study a novel hybrid network architecture, called multihop cognitive cellular network (MC2N), taking good advantage of both local available channels and frequency spatial reuse to increase the throughput of the network, enlarge the coverage area of the base station, and increase the network scalability. Although offering significant benefits, the MC2N also brings unique research challenges over other wireless networks. Of note are the problems associated with the architecture, modeling, cross-layer design, privacy, and security issues. In this dissertation, we aim to address these challenging and fundamental issues in MC2Ns. Our contributions in this dissertation are multifold. First, we consider multiradio multi-channel in MC2Ns and propose a multi-radio multi-channel multi-hop cognitive cellular network (M3C2N). Under the proposed architecture, we then investigate the minimum length scheduling problem by exploring joint frequency allocation, link scheduling, and routing. Second, energy consumption minimization problem is further studied for MC2N under physical model. Third, we introduce device-to-device (D2D) communications among cellular users in MC2Ns by bypassing the base stations (BSs) and utilizing local available spectrums, and hence potentially further alleviate network congestion. A secondary spectrum auction market is constructed to dynamically allocate the available licensed spectrums. Fourth, we propose realtime detection, defense, and penalty schemes to identify, defend against, and punish MAC layer selfish misbehavior, respectively, in multihop I 802.11 networks, noticing that most traditional detection approaches are for wireless local area networks only, and rely on a large amount of historical data to perform statistical detection. Last, a new location-based rewarding system, called LocaWard is proposed, where mobile users can collect location-based tokens from token distributors, and then redeem their gathered tokens at token collectors for beneficial rewards. Besides, we also develop a security and privacy aware location-based rewarding protocol for the LocaWard system.

Multihop Cellular Networks (MCNs) form combined wireless paradigm that carries the advantages of both traditional cellular networks and wireless multihop relay. Cellular networks depend on a fixed infrastructure to provide wide area coverage for users with high mobility profile. Multihop relay networks depend on wireless devices inside the network to relay signals through multiple hops from source to destination. MCNs were proposed to overcome inherent drawbacks in cellular networks like congestion and dead spots. These gains build on the characteristics of multihop relay that result in increased capacity, decrease energy depletion and virtually extended coverage. But while these gains have been widely accepted and advocated, they have not been verified in rigor. A realistic need therefore exists to quantify these gains in order to realize more capable network management functionalities for this new paradigm. In this thesis, we present an analytical framework for MCNs. We quantify the capacity and energy consumption in MCNs, while considering various call distributions, network loads and transmission power. We apply our framework to Code Division Multiple Access (CDMA) cellular networks, which are very dependent on interference levels in their performance. Our results show that capacity can be increased in CDMA cellular networks using multihop relay by increasing either the number of simultaneous calls or data rates. We also demonstrate that consumed energy is decreased in MCNs, especially in environments with high path loss. We validate that multihop relay is most rewarding when calls tend to originate near cell borders. Beyond verifying basic claims, we explore other potential gains of MCNs. We investigate the viability of congestion relief and load balancing and substantiate the benefits for congested cells neighbored by lightly loaded cells. Load balancing has also been shown to increase data rates and fairness in user allocations. Lastly, we explore enabling multimedia applications in MCNs and study the application of data rate adaptations given multiple classes of service. A key advantage of our work is that, while applied to CDMA in this thesis, the presented analytical framework can be extended to other technologies. The framework also accommodates both mobile and fixed network relay elements, expanding its applicability to next generation cellular networks. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2009-01-30 09:34:39.735

在無線區域網路的範疇，IEEE 802.11是一個主要的媒介存取控制協定。然而在隨意式多跳接的網路中，IEEE 802.11面臨更嚴重的hidden terminal和exposed terminal problems，而這些問題主因都源自於過大的訊號干擾範圍與過大的訊號感應範圍。在這篇論文裡，我們提出一個可調式的媒介存取控制協定，針對IEEE 802.11 RTS/CTS handshake機制做簡單地修改，使得IEEE 802.11 devices可以依據週遭的傳收狀態動態調整自身的傳送和接收行為。實驗結果顯示我們的方法使原來的 802.11 減少了互相干擾的情形並且提升了系統的效能。 / The IEEE 802.11 standard is the most popular Medium Access Control (MAC) protocol for wireless local area networks. However, in multihop wireless ad hoc networks, the IEEE 802.11 MAC protocol will suffer from more serious hidden terminal and exposed terminal problems than those in single hop WLANs. More specifically, it is due to the large interference range and the large carrier sensing range. In this thesis, we propose an adaptive IEEE 802.11 MAC (AMAC) that makes two simple modifications of IEEE 802.11 RTS/CTS handshake to dynamically adjust the transmission and reception according to the shared medium status near transmitter and receiver, respectively. Simulation results show that our method can lessen interferences and increase system throughput as compared with IEEE 802.11 MAC.

A significant challenge for fourth generation cellular systems is the reliable delivery of high speed (up to 1 gigabit per second) data to mobile or nomadic users throughout a cluttered urban environment. The wireless channel is a difficult channel over which to achieve high rate reliable communications. The wireless channel suffers many impairments such as small-scale multipath fading, shadowing, high path loss, co-channel interference, and Doppler shift due to mobility of the terminals and mobility in the propagation environment. Since radio spectrum is a scarce resource it is necessary to build cellular networks with high spectral efficiency. Two promising methods to solve this problem are multihop (MH) relaying and multiple-input multiple-output (MIMO) antenna techniques. The most difficult mobile users to serve reliably are those close to cell edges and those shadowed by large objects such as buildings. With MH relaying, a number of simple and inexpensive wireless relays are deployed throughout the cell to relay transmissions around obstacles and to reduce the path loss to distant mobile users. Also, MH relaying enables the deployment of small subcells throughout the cell, increasing the system's area averaged spectral efficiency. Various MIMO techniques can be used in scattering channels to increase capacity and reliability of data links in a wireless network. MH relaying and MIMO are key inclusions in emerging cellular standards such as IEEE 802.16 and LTE-Advanced, so it is necessary to study how these may be used jointly in a cellular environment. We look at various techniques available in MH relaying and MIMO, and assess the benefits and difficulties of these techniques when used in cellular systems. We put together a realistic cellular system model, with typical cellular topologies and well-accepted propagation models, and assess the performance of a multihop MIMO system. We find that there are tradeoffs in using these techniques jointly since they provide gains by somewhat conflicting methods. MH relaying lowers path loss and mitigates scattering in the channel, while MIMO benefits from significant scattering. As a result, it is necessary to understand how to design a MH-MIMO network carefully in order to maximize the net benefit. / Communications