A New Way Based on Relative Forward Delay to Improve TCP Performance Over Heterogeneous Networks

Modern network technologies first evolved in wired networks and subsequently entered the wireless network field. Applications may work in pure wired network, pure wireless network or hybrid network. Improving performance in these network infrastructures has been a continuous effort for decades. In this dissertation, we tackle two important challenges: (1) improving handover performance in heterogeneous wireless network, and (2) improving TCP performance in multi-hop wireless network. In heterogeneous network, users expect uninterrupted services moving from one network to another. IEEE proposed Media Independent Handover (MIH) to make it possible to achieve better handover performance. Currently, Mobile IPv4 (MIP) is the dominant mechanism for mobility management and is expected to persist into the future. However, when multiple interfaces of a mobile client are connected to a Foreign Agent (FA), MIP and its existing improvements do not perform well when the active interface fails unexpectedly. In this dissertation, we propose novel mechanism and MIP extension with MIH support. We prove experimentally that the new approach eliminates the FA-HA latency and achieves much faster handover, compared with existing mechanism. Our method also allows FA-bicasting, which can improve transmission reliability by combining traffic from different links, through the same FA. In multi-hop wireless networks, the main network factor that affects TCP performance is the medium-access contention, complicated by other factors like hidden terminal. We analyze the TCP congestion window and provide a more accurate estimate of its optimal value than those reported in the prior work. We also show that the much shorter TCP-ACK packets consume comparable channel capacity as the much longer data packets. We therefore propose two methods to improve TCP throughput, as follows. (1) Segregate the flows of data and ACK using static routing in grid wireless network, (2) Develop an improved variant of delayed TCP ACK by minimizing the number of ACK packets. Our evaluation validates the effectiveness of the proposed method, which can enhance TCP performance significantly. In terms of throughput, it achieves up to 204% improvement over the regular TCP in chain-topology wireless networks, and about 35% improvement in a complex grid wireless network. We also propose a new architecture to achieve higher throughput when multiple TCP connections exist.

The advancement of computing capabilities and increase of available network bandwidths have resulted in an emergency telemedicine services which can provide high quality medical services. However, existing telemedicine systems mainly have offered a one to one communication configuration instead of a multi-connection configuration. Therefore, we suggested a hybrid multimedia telemedicine system to support the multi-patients services in wired and wireless (heterogeneous) network environments. Methods: We designed the hybrid multimedia telemedicine system consisting of 4 sub-systems, a patient system, a doctor system, a emergency monitoring system, and a multi-control server system. The patient system could deliver multimedia data of a patient to the emergency monitoring system or to the doctor system according to link configuration. The link configuration was decided as 'Flowing', or 'By-passing' in accordance the connection type of patient systems or doctor systems. At this time, as the multi-control server system considers the hybrid network, it monitored the patient's multimedia data and the state of emergency telemedicine services. Results: The hybrid multimedia telemedicine system including the multi-control server system performed the best communication configuration over heterogeneous networks. This system achieved high quality emergency telemedicine services through dynamic wired and wireless networks at real-time. Conclusion: This study represented a hybrid multimedia telemedicine system over heterogeneous networks in emergency cases. We expected that the designed system could provide not only the high quality services, tele-diagnosis and tele-consultation, but also the effective emergency telemedicine services to multi-patients in the heterogeneous network environments.239

TCP is suboptimal in heterogeneous wired/wireless networks because it reacts in the same way to losses due to congestion and losses due to link errors. In this paper, we propose to improve TCP performance in wired/wireless networks by endowing it with a classifier that can distinguish packet loss causes. In contrast to other proposals we do not change TCP’s congestion control nor TCP’s error recovery. A packet loss whose cause is classified as link error will simply be ignored by TCP’s congestion control and recovered as usual, while a packet loss classified as congestion loss will trigger both mechanisms as usual. To build our classification algorithm, a database of pre-classified losses is gathered by simulating a large set of random network conditions, and classification models are automatically built from this database by using supervised learning methods. Several learning algorithms are compared for this task. Our simulations of different scenarios show that adding such a classifier to TCP can improve the throughput of TCP substantially in wired/wireless networks without compromizing TCP-friendliness in both wired and wireless environments.

This paper provides a congestion control mechanism under heterogeneous network and analyze the TCP’s represented research achievements and current situation problems under heterogeneous environment. According to the shortage of the TCP under heterogeneous network, we design TCP congestion control algorithm based on model bandwidth estimation to solve the problem of heterogeneous network switching. The results validate the effectiveness of this mechanism under simulation analysis, which effectively achieve the fair competition of resource and can improve the utilization of network resources

Many studies have shown that Vegas TCP has a better throughput and stability than Reno TCP in homogeneous networks with a single TCP flavor, but performs less well in heterogeneous networks in which two TCP flavors coexist. The progressive behavior of Reno TCP and the conservative behavior of Vegas TCP cause a bias when they are used simultaneously, and thus Vegas TCP fails to obtain a fair share of the bandwidth. This paper examines the origins of this bias and proposes a threshold-based congestion control mechanism designed to alleviate the resulting unfairness problem. The simulation results show that the proposed scheme achieves a higher throughput than the conventional Vegas TCP scheme and preserves the stability of the conventional scheme when used in heterogeneous wired and wireless networks.

Quality of experience (QoE) has been a user-centric performance metric for multimedia communications. Existing communication protocols over heterogeneous networks are mostly based on quality of service, which ignores the user satisfaction and subjective evaluation. In this paper, the authors propose a novel QoE-aware multimedia communication framework for heterogeneous wireless networks. Specifically, the authors make three main contributions in this paper: (i) a general QoE model has been established by jointly characterising the multimedia applications and heterogeneous networks, (ii) the issue of multimedia communications over heterogeneous networks has been transformed as a stochastic optimisation problem, and (iii) the optimal solution is provided by designing a QoE-aware multimedia scheduling scheme. Importantly, the proposed scheme is simply enough for online implementation. Numerical simulations have demonstrated the efficiency and robustness of the proposed scheme.

Mobile communication plays an important role in the future of communication systems. To meet personalized and intelligent requirements, mobile communication has evolved from single wireless cellular network to heterogeneous mobile communication network, including wireless cellular network, wireless local network, and wireless personal network. In the heterogeneous communication system, to entirely fulfill the spectrum resource complementary advantages of such a heterogeneous wireless network, the spectrum resource trade algorithm has attracted tremendous research efforts. In this paper, the advantages and disadvantages of dynamic spectrum allocation and load balancing are discussed and spectrum auction takes the place of spectrum allocation to maximize the operation revenue. The authors design a joint spectrum auction and load balancing algorithm (SALB) based on heterogeneous network environment to develop a more flexible and efficient spectrum management. The simulation result shows that SALB increases the operation profit significantly.

The wireless network environment in the future is going to include various heterogeneous wireless networks. In a heterogeneous wireless network environment, vertical handoff processes caused by the movement of users are inevitable. However, the research related to how to achieve seamless vertical handoff and improve QoS guarantees in today's heterogeneous wireless networks is still something to work on. Therefore, this paper proposed the Advanced Vertical Handoff Translation Center (Advanced VHTC) architecture for Wi-Fi/WiMAX heterogeneous wireless networks, aiming to improve the quality of services in heterogeneous wireless networks by means of packet formats translation between heterogeneous wireless networks and the MIH-based seamless vertical handoff mechanism, which cut down the time for vertical handoff and obtain high quality and persistent connection service. Lastly, with the brilliant results of a complete simulation, this paper will show the performance in terms of delay, jitter, packets loss and throughput to prove that the Advanced VHTC for next generation heterogeneous wireless networks can provide good QoS guarantees and obtain persistent transmission with high performance while performing seamless vertical handoff.

Decision making is the hot topic in business management. Recently, there have been investigations in Call Admission Control (CAC) to handle the handover events in wireless network environments. Wireless networks have been seen to support different handoff mechanisms, in which the user can switch from one wireless network to another such as from IEEE 802.11 to IEEE 802.16. Many wireless standards, such as IEEE 802.16e and IEEE 802.11, have been proposed to satisfy diverse requirements for mobile users.. Several strategies have been proposed to realize seamless handoff in the heterogeneous networks; in this paper, we analyze the performance of some novel intelligent handoff mechanisms with multiple attributes. The mobile set dynamically selects the optimal network and provides the user with high throughput of Quality of Service (QoS) as to minimize the blocking probability of the system in heterogeneous networks. We evaluate some intelligent handoff mechanisms such as Technique for Order Preference by Similarity to Ideal Solutions (TOPOSIS), Simple Additive Weight (SAW), Analytic Hierarchy Process (AHP) and Fuzzy Logic and Grey Relational Analysis (GRA). From the results, blocking probability and dropping rate can be referenced to support better QoS.

In virtual power plants (VPPs), distributed devices (such as residential appliances, energy storage, and electric vehicles) communicate with control centers via wireless access points (APs). Nevertheless, with a massive number of devices connected to APs, VPPs would be adversely affected by packet loss and consequently suffer from revenue reduction. Therefore, devices’ access connections need to be delicately designated to mitigate these negative impacts. This paper studies the device access optimization problem from the perspective of VPP operations. An optimization model to minimize the revenue reduction induced by packet loss is first formulated to designate APs for devices in heterogeneous communication networks. The significance of various device data is determined by revenue reduction as a result of packet loss. Additionally, the heterogeneous access network model is established to characterize different types of APs. To make the model implementable, this paper further proposes a layered decomposition solution algorithm, which decomposes optimization tasks into small-scale sub-problems and successively assigns them to different layers of APs. Sub-problems are further decomposed for APs to greedily cut revenue reduction by evaluating devices’ marginal contributions to revenue reduction. Numerical case studies are also conducted to verify the benefits of device access optimization.

SUMMARY With the rapid development of wireless network technologies, heterogeneous networks with wired and wireless links are becoming common. However, the performance of TCP data transmission deteriorates significantly when a TCP connection traverses such networks, mainly because of packet losses caused by the high bit error rate of wireless links. Many solutions for this problem have been proposed in the past literature. However, most of them have various drawbacks, such as difficulties in their deployment by the wireless access network provider and end users, violation of TCP’s end-to-end principle by splitting the TCP connection, or inapplicability to IP-level encrypted traffic because the base station needs to access the TCP header. In this paper, we propose a new mechanism without such drawbacks to improve the performance of TCP over wired and wireless heterogeneous networks. Our mechanism employs a receiver-based approach, which does not need modifications to be made to the sender TCP or the base station. It uses the ACK-splitting method for increasing the congestion window size quickly in order to restrain the throughput degradation caused by packet losses due to the high bit error rate of wireless links. We evaluate the performance of our mechanism and show that our mechanism can increase throughput by up to 94% in a UMTS network. The simulation results also show that our mechanism does not significantly deteriorate

In this paper we investigate the impact of a Relay Node (RN) placement plan on a heterogeneous wireless network called Hybrid Wireless Network with dedicated delay nodes (HWN*) in terms of system capacity, transmission delay and Quality of Service (QoS). A novel HWN* Heuristic RN Placement (HHRP) algorithm, which considers RN assistance & support for radio resource sharing such as inter-network traffic balancing, TD/CDMA soft handover, routing and user mobility has been implemented. A system level simulation is used to quantify the benefits of HWN* using HHRP algorithm over HWN* with other RN placement plans and multi-hop cellular networks. I. INTRODUCTION A heterogeneous wireless network refers to a wireless net- work that is comprised of wireless nodes with different radio access technologies or equipment with different operating systems. For example, it can be a wireless sensor network including bluetooth based radio access and zigbee 802.15.4 based radio access or a hybrid wireless network including cellular access and 802.11b/g based radio access. Specifi- cally for a hybrid wireless network, the increase of cellular communication intensity results in a reduction in cell size, thus much denser clusters are required resulting in increased infrastructure cost and system complexity. Meanwhile, the bursty nature of communication traffic and path loss results in traffic prediction difficulty. A solution must be found to provide effective resource management, congestion control and routing. The hybrid wireless network which incorporates cellular and MANET interfaced RELAY nodes, provides a practical approach for this. Nevertheless, the dedicated relay infrastructure approach can be also be adapted to the emerging wireless sensor network in order to maintain node connectivity, support sensor data aggregation and optimise power consump- tion.

How many small cell (SC) access points (APs) are required to guarantee a chosen quality of service in a heterogeneous network? In this chapter, we answer this question considering two different network models. The first is the downlink of a finite-area SC network where the locations of APs within the chosen area are uniformly distributed. A key step in obtaining the closed-form expressions is to generalize the well-accepted moment matching approximation for the linear combination of lognormal random variables. For the second model, we focus on a two-layer downlink heterogeneous network with frequency reuse-1 hexagonal macro cells (MCs), and SC APs that are placed at locations that do not meet a chosen quality of service from macro base stations (BSs). An important property of this model is that the SC AP locations are coupled with the MC coverage. Here, simple bounds for the average total interference within an MC makes the formulation possible for the percentage of MC area in outage, as well as the required average number of SCs (per MC) to overcome outage, assuming isolated SCs. Introduction Heterogeneous cellular networks (HCNs) are being considered as an efficient way to improve system capacity as well as effectively enhance network coverage [1, 2]. Comprising multiple layers of access points (APs), HCNs encompass a conventional macro cellular network (first layer) overlaid with a diverse set of small cells (SCs) (higher layers). Cell deployment is an important problem in heterogeneous networks, both in terms of the number and positioning of the SCs. Traditional network models are either impractically simple (such as the Wyner model [3]) or excessively complex (e.g., the general case of random user locations in a hexagonal lattice network [4]) to accurately model SC networks. A useful mathematical model that accounts for the randomness in SC locations and irregularity in the cells uses spatial point processes, such as Poisson point process (PPP), to model the location of SCs in the network [5–10]. The independent placement of SCs from the MC layer, has the advantage of analytical tractability and leads to many useful SINR and/or rate expressions. However, even assuming that wireless providers would deploy SCs to support mobile broadband services, the dominant assumption remains that SCs are deployed randomly and independent of the MC layer [11].

The TCP performance degradation over heterogeneous networks is caused by not only network congestion, but also random errors of wireless links. We propose an end-to-end stable accurate rapid bandwidth estimate (SARBE) algorithm reacting appropriately to the end-to-end loss differentiation estimate algorithm (LDED), which can improve the TCP performance over heterogeneous networks without the incipient congestion notifications of the intermediate routers. LDED detects the signal of incipient congestion to lead the sender to enter the congestion avoidance phase opportunely before router’s queue overflows. As well as relying distinguishing ability the causes of loss, our algorithm adjusts the packet transmission rate precisely according to the estimated bandwidth after new ACK receiving, fast retransmit or transmission timeout events.

The challenge for applied TCP over heterogeneous networks is the performance degradation caused by not only network congestion, but also random errors of wireless links. We propose a stable accurate rapid bandwidth estimate (SARBE) algorithm reacting appropriately to explicit congestion notification (ECN), which improves the TCP performance over heterogeneous networks. Our SARBE algorithm takes advantage of estimating the forward bandwidth of connection to improve the estimated bandwidth more accurate than TCP Westwood. By incorporating the estimated bandwidth of SARBE and the incipient congestion notifications of the intermediate routers, our proposal adjusts the packet transmission rate precisely, according to the causes of packet loss