Esa Piri

3G/HSPA Performance in Live Networks from the End User Perspective

Operators around the world are improving their 3G/UMTS networks by introducing HSPA (High Speed Packet Access) that includes both, enhanced uplink and downlink. The HSPA is expected to finally provide the mobile broadband access that is able to compete with the fixed connections in performance regarding popular applications such as web browsing, VoIP, and video. However, it has remained unclear how well the live networks fulfill the promises of performance. We contribute in filling this void by providing measurements in live 3G/HSPA networks. We compare TCP and UDP goodput performance in basic WCDMA, HSDPA-only, and HSPA. Moreover, one-way delay and jitter measurement results are presented in a stationary as well as in a mobile scenario. The results show that the enhanced network outperforms clearly its predecessor by offering considerably higher data rates, lower delay, and lower jitter. Also, because of the HARQ (Hybrid Automatic Repeat request), there are notably less delay spikes observed with HSPA than with WCDMA. However, the drive tests show that handovers result in high jitter and interruptions to the communications, which causes, e.g., decreased VoIP call quality. The uplink enhancement (HSUPA) improves the TCP performance beyond the HSDPA-only access, but it is still behind that of the fixed connections. In addition, the properties of the channel allocation mechanism still considerably deteriorate the data rates seen by the user. Nevertheless, the HSPA is an enabler for true mobile broadband internet access.

An experimental investigation of VoIP and video streaming over fixed WiMAX

Despite the significant interest in WiMAX technology and deployment, there are very few publicly reported measurements from testbeds and field trials. As such, most WiMAX studies employ simulation and modeling. This paper contributes to our understanding of what is realistically possible using off-the-shelf fixed WiMAX equipment today. We employ multiple competing traffic sources over a point-to-multipoint WiMAX topology and measure the capacity of the WiMAX equipment to handle a multitude of VoIP flows between subscriber stations while delivering a variable number of video streams. We measure throughput, packet loss, and one-way delay for both line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. For the one-way delay measurements we synchronize the clocks of all testbed hosts with a software-only, open source implementation of the IEEE 1588 Precision Time Protocol. We compare these one-way delay measurements with those obtained when GPS-based synchronization is used.

Towards a GNU/Linux IEEE 802.21 Implementation

Multiaccess mobile devices and overlapping wireless network deployments have emerged as a next generation network fixture. To make the most of all available networks, mobile devices should be capable of handing over between heterogeneous networks seamlessly and automatically. At the same time, operators should be able to steer network attachment based on their criteria. Although several cross layer mechanisms have been proposed in recent years, only the Media Independent Handover (MIH) Services framework has advanced in any of the established standardization bodies. This paper presents a blueprint for a GNU/Linux implementation of IEEE 802.21. We review the salient points of the standard, introduce our software implementation architecture, detail information gathering in GNU/Linux, and show how our prototype implementation can be used in practice. In contrast with prior published work, this paper presents a real IEEE 802.21 implementation, not an abstracted or reduced MIH-like framework, tested and empirically evaluated over real heterogeneous networks.

Dynamic Cross-Layer Adaptation of Scalable Video in Wireless Networking

The recent trend in Internet traffic indicates the proliferation of usage of multimedia services where a substantial part is related to some sort of video transmission. Moreover, an increasing number of Internet users employ wireless access technologies. High-quality video streaming over wireless access in unison with great mobility brings challenges to sustain the mobile user perceived video quality high. Capacities of wireless links vary due to, for instance, coverage area limitations, multipath propagation, and fading. However, novel video codecs utilize a layered encoding/decoding mechanism, which conveniently allows adapting the video quality, and thus the bitrate, by adjusting the number of layers transmitted. In this study, we exploit an extensive cross-layer signaling framework for a dynamic scalable video adaptation in varying network capacity. We focus on comparing a fast and fair MAC-layer packet scheduling with a relatively slow and long-term adaptivity taken place already at the application layer using a real H.264/SVC video. Our results attest the advantages of adaptation through the use of feedback signaling, which enables continuing the use of the current network access despite its capacity variation.

Cross-layer architecture for adaptive real-time multimedia in heterogeneous network environment

Despite the interest, the utilization of todays networking environment including a variety of access technologies and various services and capabilities is still minimal. Multiaccess mobile devices already on the market provide a capability to hand over the heterogeneous networks but so far there has not been any commonly approved way to efficiently capitalize on this feature. Media Independent Handover Services standard specified by the IEEE 802.21 working group is expected to establish the basis for heterogeneous handovers. Although IEEE 802.21 has usage also beyond heterogeneous handovers, its capabilities do not fulfill all the requirements of adaptive multimedia transmission. For example, upper layer events and end-to-end traffic control communication are outside the scope of IEEE 802.21. In this study, we introduce an information service architecture for adaptive multimedia which enables to collect and disseminate events and information from the different layers of the protocol stack locally and also between network entities regardless of their location in the network. Our architecture presents a Triggering Engine on top of the IEEE 802.21 services in order to introduce upper layer events, flexibility to event distribution, and end-to-end event based signaling to adaptive multimedia transmission.

ROHC and aggregated VoIP over fixed WiMAX: An empirical evaluation

WiMAX has been at the center of attention in wireless communications during the last years. Nonetheless, very few testbed or field trial measurement accounts have been reported in the peer-reviewed literature. We fill this gap by exploring scenarios where fixed WiMAX is employed for VoIP traffic. VoIP packets typically exhibit large header overheads and small total packet sizes. The actual codec payload per packet is very small compared to the total length of headers appended to each voice frame. Robust header compression (ROHC) can significantly decrease header size by capitalizing on static or rarely changing header fields. Aggregating multiple voice frames into one packet is another attractive and effective way to increase application goodput and overall bandwidth utilization. We study the effect of ROHC and application layer aggregation on VoIP performance in a fixed WiMAX testbed consisting of one base station and two subscriber stations. We find that ROHC increases the number of simultaneous bidirectional emulated VoIP flows by 6% when compared to plain VoIP. When aggregation and ROHC are employed in unison, they allow for 86% more flows than standard VoIP to be sustained in our testbed.

Scaling network information services to support HetNets and dynamic spectrum access

Wireless network information services allow end systems to discover heterogeneous networks and spectrum available for secondary use at or near their current location, helping them to cope with increasing traffic and finite spectrum resources. We propose a unified architecture that allows end systems to find nearby base stations that are using either licensed, shared or unlicensed spectrum across multiple network operators. Our study evaluates the performance and scalability of spatial databases storing base station coverage area geometries. The measurement results indicate that the current spatial databases perform well even when the number of coverage areas is very large. A single logical spatial database would likely be able to satisfy the query load for a large national cellular network. We also observe that coarse geographic divisions can significantly improve query performance.

Towards ubiquitous video services through scalable video coding and cross-layer optimization

Video content as one of the key features of future Internet services should be made ubiquitously available to users. Moreover, this should be done in a timely fashion and with adequate support for Quality of Service (QoS). Although providing the required coverage for ubiquitous video services, wireless networks, however, pose many challenges especially for QoS-sensitive video streaming due to their inadequate or varying capacity. In this article, we propose a cross-layer video adaptation solution, which may be used for optimizing network resource consumption and user experienced quality of video streaming in wireless networks; thus improving the availability of video services to mobile users. Our solution utilizes the flexibility of the Scalable Video Coding (SVC) technology and combines fast and fair Medium Access Control (MAC) layer packet scheduling with long-term application layer adaptation. The proposed solution both improves the usage of network resources by dropping video data based on its priority when the network is congested but also reduces efficiently the number of useless packet transfers in a congested network. We evaluate our solution with a simulation study under varying network congestion conditions. We find that already application layer adaptation gains over 60% less base layer losses, momentous for SVC video decodability and quality, than in the case without any adaptation. When our MAC layer scheduling is enabled, nearly a zero loss situation with respect to packet losses carrying base layers can be attained, resulting in peak-signal-to-noise ratio values very close to the original.

Mobility management for NGN WiMAX: Specification and implementation

The anticipated deployment of IEEE 802.16-based wireless metropolitan area networks (WMANs) will usher a new era in broadband wireless communications. The adoption of the WiMAX technology for remote areas, for example, can address challenging scenarios in a cost-effective manner. While WiMAX Forum documents describe an architecture that inherently supports Quality of Service and mobility, several areas are left uncovered. We present an architecture which integrates WiMAX, Quality of Service and mobility management frameworks over heterogeneous networks, developing mechanisms for seamless handovers. Our approach takes into consideration the expected deployment of, on the one hand, the IEEE 802.21 (Media Independent Handover) proposed standard and, on the other, the IETFstandardized Next Steps in Signalling framework. The first contributions of this paper comprise a specification of the mechanisms for make-before-break vertical handovers taking Quality of Service signalling into account and the integration in a heterogeneous environment. The latter contribution is an empirical evaluation of the proposed architecture using a testbed demonstrator. We quantify the processing delays of the main components in our prototype implementation when a terminal hands over between different access technologies, demonstrating the potential of the proposed architecture.

On the Performance Gains of VoIP Aggregation and ROHC over a WirelessMAN-OFDMA Air Interface

A growing number of mobile WiMAX deployments are in progress world-wide and the technology is anticipated to play a key role in next generation mobile broadband wireless networks. However, although the theoretical potential of WiMAX technologies is already well established, independent, publicly released, thorough evaluations of WiMAX network performance in the real world are yet to become available. In this study, we consider synthetic Voice over IP (VoIP) performance over the WirelessMAN-OFDMA air interface of a state of the art mobile WiMAX testbed operating at the 3.5 GHz frequency band and quantify the benefits of employing VoIP aggregation and Robust Header Compression (ROHC). Although VoIP aggregation and ROHC have been proposed and thoroughly evaluated through simulation and modeling, this is the first study to present empirical results from employing them over the Wireless MANOFDMA air interface of a real-world WiMAX system. Our results indicate that the combined use of VoIP aggregation and ROHC can increase the number of flows sustained without loss by approximately a factor of three.