1. S.A. Rein and F.H.P. Fitzek and C. Gühmann and T. Sikora. Evaluation of the wavelet image two-line coder: A low complexity scheme for image compression. 2015. Signal Processing: Image Communication, 37:58--74.

2. H. Nestor and J. Heide and D. Lucani and F.H.P. Fitzek. Throughput, Energy and Overhead of Multicast Device-to-Device Communications with Network Coded Cooperation. 2016. Transactions on Emerging Telecommunications Technologies (Online).

3. A. Sipos and J. Heide and D. Lucani and M.V. Pedersen and F.H.P. Fitzek and H. Charaf. Adaptive Network Coded Clouds: High Speed Downloads and Cost-Effective Version Control. 2015. IEEE Transactions on Cloud Computing.

4. J. Hansen and D. Lucani and J. Krigslund and M. Médard and F.H.P. Fitzek. Network Coded Software Defined Networking: Enabling 5G Transmission and Storage Networks. 2015. I E E E Communications Magazine, 53(9):100--107.

5. P. Torres and F.H.P. Fitzek and D. Lucani. Network Coding is the 5G Key Enabling Technology: Effects and Strategies to Manage Heterogeneous Packet Lengths. 2015. Transactions on Emerging Telecommunications Technologies (Online), 26(1):46--55.

6. A. Paramanathan and S. Thorsteinsson and D. Lucani and F.H.P. Fitzek. On bridging theory and practice of inter-session network coding for CSMA/CA based wireless multi-hop networks. 2015. Ad Hoc Networks, 24(Part B):148--160.

7. V. Talooki and R. Bassoli and D. Lucani and J. Rodriguez and F.H.P. Fitzek and H. Marques and R. Tafazolli. Security Concerns and Countermeasures in Network Coding Based Communications Systems: A Survey. 2015. Computer Networks, 83:422--445.

8. S. Mumtaz and A. Radwan and J. Rodriguez and A. Nascimento and D. Yang and F.H.P. Fitzek and T. Dagiuklas. 5G networks and smart video transmission 2014. 2014. I E E E International Symposium on Computers and Communications, vol Workshops.

9. M. Medard and F.H.P. Fitzekand M.J. Montpetit and C. Rosenberg. Network coding mythbusting: why it is not about butterflies anymore. 2014. IEEE Communications Magazine, 52(7):177-183.

10. M. Katz and F.H.P. Fitzek and D.E. Lucani and P. Seeling. Mobile Clouds as the Building Blocks of Shareconomy: Sharing Resources Locally and Widely. 2014. IEEE Vehicular Technology Magazine, 9(3):63-71.

11. A. Paramanathan and S. Thorsteinsson and D.E. Lucani and F.H.P. Fitzek. On bridging theory and practice of inter-session network coding for CSMA/CA based wireless multi-hop networks. 2014. Ad Hoc Networks.

12. P. Torres and F. H. P. Fitzek and D. E. Lucani. On the effects of heterogeneous packet lengths on network coding. 2014. Transactions on Emerging Telecommunications Technologies.

13. P. Pahlevani and M. Hundeboll and M.V. Pedersen and D.E. Lucani and H. Charaf and F.H.P. Fitzek and and H. Bagheri and M. Katz. Device to Device Communication using Network Coding. 2014. IEEE Wireless Communication Magazine.

14. A. Paramanathan and M.V. Pedersen and D.E. Lucani and F.H.P. Fitzek and M. Katz. Lean and Mean: Network Coding for Commercial Devices. 2013. IEEE Wireless Communication Magazine.

15. F.H.P. Fitzek and J. Heide and M.V. Pedersen and M. Katz. Implementation of Network Coding for Social Mobile Clouds. 2013. IEEE Signal Processing Magazine, 30(1):159-164.

16. M.V. Pedersen and F.H.P. Fitzek. Mobile Clouds the New Content Distribution Platform. 2012. IEEE Transaction on Entertainment Technologies, 100:1400-1403.

17. P. Vingelmann and F.H.P. Fitzek and M.V. Pedersen and J. Heide and H. Charaf. Synchronized Multimedia Streaming on the iPhone Platform with Network Coding. 2011. IEEE Communications Magazine - Consumer Communications and Networking Series, 49(6):126-132.

18. G.P. Perrucci and P. Anggraeni and S. Wardana and F.H.P. Fitzek and M. Katz. Bio-Inspired Energy Aware Protocol Design for Cooperative Wireless Networks. 2011. International Journal of Autonomous and Adaptive Communications Systems (IJAACS), Special issue on Bio-inspired Wireless Networks, vol 4.

19. T. Balke and M. De Vos and J. Padget and F.H.P. Fitzek. Using A Normative Framework to Explore the Prototyping of Wireless Grids. 2011. Springer, Lecture Notes on Articial Intelligence, Coordination, Organizations, Institutions, And Norms In Agent Systems VI, 6541:95-113.

20. L. Blazovics and C. Varga and W. Bammford and P. Zanaty and F.H.P. Fitzek. Future Cooperative Communication Systems Driven by Social Mobile Networks. 2010. Wireless Personal Communications - Special Issue: 5G Workshop on Networks, Services and Applications, 57(3):377-391.

21. M.V. Pedersen and J. Heide and F.H.P. Fitzek and T. Larsen. A Mobile Application Prototype using Network Coding. 2010. European Transactions on Telecommunications (ETT), 21(8):738-749.

22. L. Militano and F.H.P. Fitzek and A. Iera and A. Molinaro. Network coding and evolutionary theory for performance enhancement in wireless cooperative clusters. 2010. European Transactions on Telecommunications (ETT), 21(8):725-737.

23. C. Lu and F.H.P. Fitzek and P.C. Eggers. Cooperative Spatial Reuse with Transmit Beamforming in Multi-Rate Wireless Networks. 2009. Journal of Communications, 4(1):26-33.

We present a cooperative spatial reuse (CSR) scheme as a cooperative extension of the current TDMA-based MAC to enable spatial reuse in multi-rate wireless networks. We model spatial reuse as a cooperation problem on utilizing the time slots obtained from the TDMA-based MAC. In CSR, there are two operation modes. One is TDMA mode while the other is spatial reuse mode in which links transmit simultaneously. Links contribute their own time slots to form a cooperative group to do spatial reuse. Each link joins the group only if it can benefit in capacity or energy efficiency. Otherwise, the link will leave spatial reuse mode and switch back to TDMA. In this work, we focus on the transmit beamforming techniques to enable CSR by interference cancellation on MISO (Multiple Input Single Output) links. We compare the CSR scheme using zero-forcing (ZF) transmit beamforming, namely ZF-CSR, to the TDMA-based MAC using maximum ratio combining (MRC) transmit beamforming, namely MRC-TDMA. The numerical results of a simulated two 2

24. G.P. Perrucci and F.H.P. Fitzek and Q. Zhang and M. Katz. Cooperative Mobile Web Browsing. 2009. EURASIP Journal on Wireless Communications and Networking.

25. Janus Heide and Morten V. Pedersen and Frank H.P. Fitzek and Torben Larsen. Cautious View on Network Coding - From Theory to Practice. 2009. Journal of Communications and Networks (JCN).

26. G.P. Perrucci and F.H.P. Fitzek and M.Katz. Using Wake-up Signals for Energy Savings in Mobile Devices. 2008. iC@ST magazine.

27. F.H.P. Fitzek and M. Katz and Q. Zhang. Cellular Controlled Short-Range Communication for Cooperative P2P Networking. 2008. Wireless Personal Communications.

28. Chenguang Lu and Frank H.P. Fitzek and Patrick C.F. Eggers and Ole Kiel Jensen and Gert F. Pedersen and Torben Larsen. Terminal-Embedded Beamforming for Wireless Local Area Networks. 2007. IEEE Wireless Communications.

In dense traffic areas, wireless local area networks (WLANs) suffer from interference problems due to congestion of the open and unlicensed ISM band. To mitigate these problems, a terminal-embedded beamforming framework is proposed --- this beamforming is capable of focusing the transmission and the reception in the direction of the relevant access point. At the same time the framework is backward compatible with existing WLAN networks. The beamforming enabled terminal benefits in terms of capacity, security, and energy efficiency while not requiring any changes on the network side costing network providers new investments. The beamforming solution is seen as an attractive value-added feature as well as low cost solution for the future WLAN terminal design. This opens the door for mobile device manufacturers to include the proposed solution into their product line. In this work, the backwards compatibility challenges are addressed and some possible solutions and the limitations are discussed. Also shown is a prototype design built on a laptop computer. The experimental results show a significant capacity increase in both an interference free scenario and an interference limited scenario.

29. C. Lu and F.H.P. Fitzek and P.C.F. Eggers. Capacity Enhancement by Terminal Originated Beamforming for Wireless Local Area Networks. 2007. Wireless Personal Communications.

In dense traffic areas, wireless local area networks (WLANs) suffer from interference problems due to the usage of the crowded unlicensed ISM band and the lack of available spectrum. To mitigate these problems, a terminal side beamforming framework is proposed --- this beamforming is capable of focusing the transmission and the reception in the relevant direction of the access point to exploit the directivity of the indoor propagation channel. It provides network transparency to achieve the backward compatibility to the existing WLAN networks, and vendor transparency to ease the system design process and thereby achieve low complexity and costs. The beamforming enabled terminal benefits in terms of capacity, power efficiency and security while it does not require any change on the network side costing network providers new investments. It will be an attractive value-added feature as well as low cost solution for the future WLAN terminal design opening the door for WLAN terminal manufacturers to include the proposed solution into their product line. In this work, a WLAN terminal beamforming demonstrator has been developed to demonstrate the capacity enhancement in real environments. Signal to interference ratio (SIR) improvement as well as array gain were investigated by simulations with IEEE 802.11n cluster channel models and by experiments with the demonstrator in a typical office environment. The comparable results of simulations and experiments show significant array gain and SIR improvement. The significant capacity increase has been demonstrated in the experiments in both an interference free scenario and an interference limited scenario.

30. M. Stini and M. Mauve and F.H.P. Fitzek. Digital Ownership: From Content Consumers to Owners and Traders. 2006. IEEE Multimedia-IEEE Computer Society, 13(5):4-6.

31. S. Rein and C. Guehmann and F.H.P. Fitzek. Compression of Short Text on Embedded Systems. 2006. Journal of Computers (JCP).
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The paper details a scheme for lossless compression of short data series larger than 50 Bytes. The method uses arithmetic coding and context modeling with a low-complexity data model. A data model that takes 32 kBytes of RAM already cuts the data size in half. The compression scheme just takes a few pages of source code, is scalable in memory size, and may be useful in sensor or cellular networks to spare bandwidth. As we demonstrate the method allows for battery savings when applied to mobile phones.

32. P. Seeling and M. Reisslein and F.H.P. Fitzek. Offset Trace-Based Video Quality Evaluation Network Transport. 2006. Journal of Multimedia (JMM), vol 1.

Video traces contain information about encoded video frames, such as frame sizes and qualities, and provide a convenient method to conduct multimedia networking research. Although widely used in networking research, these traces do not allow to determine the video quality in an accurate manner after networking transport that includes losses and delays. In this work, we provide (i) an overview of frame dependencies that have to be taken into consideration when working with video traces, (ii) an algorithmic approach to combine traditional video traces and offset distortion traces to determine the video quality or distortion after lossy network transport, (iii) offset distortion and quality characteristics and (iv) the offset distortion trace format and tools to create offset distortion traces.

33. S. Frattasi and F.H.P. Fitzek and R. Prasad. A Look Into the 4G Crystal Ball. 2006. IFIP International Federation for Information Processing, 190:281 - 290.
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34. P. Seeling and M. Reisslein and T.K. Madsen and F.H.P. Fitzek. Performance Analysis of Header Compression Schemes in Heterogeneous Wireless Multi--Hop Networks. 2006. Springer - Wireless Personal Communications.

35. S. Frattasi and H. Fathi and F.H.P. Fitzek. 4G: A User-Centric System . 2006. Kluwer - Wireless Personal Communications Journal (WPC) - Special Issue on Advances in Wireless Communications: Enabling Technologies for 4G.

36. S. Frattasi and H. Fathi and A. Gimmler and F.H.P. Fitzek and R. Prasad. Designing Socially Robust 4G Wireless Services. 2006. IEEE Technology and Society Magazine, 25(2):51 - 64.

37. S. Frattasi and H. Fathi and F.H.P. Fitzek and M. Katz and R. Prasad. Defining 4G Technology from the User Perspective. 2006. IEEE Network Magazine, 20(1):35-41.
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The ever-increasing growth of user demand, the limitations of the third generation of wireless mobile communication systems, and the emergence of new mobile broadband technologies on the market have brought researchers and industries to a thorough reflection on the fourth generation. Many prophetic visions have appeared in the literature presenting 4G as the ultimate boundary of wireless mobile communication without any limit to its potential, but in practical terms not giving any design rules and thus any definition of it. In this article we give a pragmatic definition of 4G derived from a new user-centric methodology that considers the user as the cornerstone of the design. In this way, we devise fundamental user scenarios that implicitly reveal the key features of 4G, which are then expressed explicitly in a new framework the user-centric system that describes the various level of interdependency among them. This approach consequently contributes to the identification of the real technical step-up of 4G with respect to 3G. Finally, an example of a potential 4G application is also given in order to demonstrate the validity of the overall methodology.

38. F.H.P. Fitzek and M. Zorzi and P. Popovski. A Symbotic Perspective on Low--Cost Cellular and Multi--Hop WLAN Interworking Solutions. 2005. IEEE Wireless Communication, 12(6):4-10.

Interworking between wireless local area networks (WLANs) and cellular networks (such as 2G and 3G) is expected to break new ground for sophisticated business models. Omnipresent cellular networks have a well-defined infrastructure, but lack capability to provide broadband and/or real-time services (e.g., streaming video and gaming). Conversely, WLANs supports high data rates, while the infrastructure for service provision is vague. Therefore, the combination of the cellular core network infrastructure with its service centers and accounting capabilities with the achievable data rate of WLANs can provide the possibility of offering new services to the customer. This interworking is being considered in different standardization and operational activities. WLAN hotspots are already on the way, but the high installation costs of WLANs, especially for larger hotspots, is repressing a faster evolution. The installation costs are mainly driven by the cabling infrastructure. To reduce these costs and to gain flexibility, we advocate exploiting multihop capability for WLAN coverage extension by introducing the concept of virtual access points. However, the high data rates of WLAN solutions are hindered by the standard IEEE8O2. 11 MAC protocol, which has been shown to be inappropriate for multihop operation. In this article we consider an improved version of the IEEE8O2. 11 MAC that involves only minor changes to the existing standard, which allows for a faster deployment and the usability of the approach in existing interworking scenarios. The specific contribution of this article is a thorough exploration, by means of simulation, of the performance of such an approach. In particular, we demonstrate that the enhanced MAC is capable of offering high data rates in multihop WLAN extensions to the cellular network. Besides the networking structure, a pertinent issue in the WLAN cellular symbiosis is security. In this respect we discuss multihop operation in light of current interworking (security) activities.

39. P. Popovski and F. Fitzek and R. Prasad. A Class of Algorithms for Batch Conflict Resolution Algorithms with Multiplicity Estimation. 2005. Algorithmica, Springer-Verlag.

The wireless connectivity, essential for pervasive computing, has ephemeral character and can be used for creating ad hoc networks, sensor networks, connection with RFID tags etc. The communication tasks in such wireless networks often involve an inquiry over a shared channel, which can be invoked for: discovery of neighboring devices in ad hoc networks, counting the number of active sensors in sensor networks, estimating the mean value contained in a group of sensors etc. Such inquiry solicits replies from possibly large number of terminals n. This necessitates the usage of algorithms for resolving batch conflicts with unknown conflict multiplicity n. In this paper we present a novel approach to the batch conflict resolution. We show how the conventional tree algorithms for conflict resolution can be used to obtain progressively accurate estimation of the multiplicity. We use the estimation to propose a more efficient binary tree algorithm, termed Estimating Binary Tree (EBT) algorithm. We extend the approach to design the Interval Estimation Conflict Resolution (IECR) algorithm. For n ! 1 we prove that the efficiency achieved by IECR for batch arrivals is identical with the efficiency that Gallager’s FCFS algorithm achieves for Poisson packet arrivals. For finite n, the simulation results show that IECR is, to the best of our knowledge, the most efficient batch resolution algorithm reported to date.

40. F.H.P. Fitzek and S. Rein and P. Seeling and M. Reisslein. RObust Header Compression (ROHC) Performance for Multimedia Transmission over 3G/4G Wireless Networks. 2005. Wireless Personal Communications -- Springer Science+Business Media B.V., Formerly Kluwer Academic Publishers B.V., 32(1):23 - 41. (Article)
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RObust Header Compression (ROHC) has recently been proposed to reduce the large protocol header overhead when transmitting voice and other continuous media over IP based protocol stacks in wireless networks. In this paper we evaluate the real-time transmission of GSM encoded voice and H.26L encoded video with ROHC over a wireless link. For the voice transmission we examine the impact of ROHC on the consumed bandwidth, the voice quality, and the delay jitter in the voice signal. We find that for a wide range of error probabilities on the wireless link, ROHC roughly cuts the bandwidth required for the transmission of GSM encoded voice in half. In addition, ROHC improves the voice quality compared to transmissions without ROHC, especially for large bit error probabilities on the wireless link. The improvement reaches 0.26 on the 5-point Mean Opinion Score for a bit error probability of 10 percent. For the video transmission we examine the impact of ROHC on the consumed bandwidth. We find that the bandwidth savings with ROHC depend on the quantization scale used for the video encoding and the video content and ranges between 5 percent for typical scenarios.

41. S. Rein and F.H.P. Fitzek and M. Reisslein. Voice Quality Evaluation in Wireless Packet Communication System: A Tutorial and Performance Results for ROHC. 2005. IEEE Wireless Communication, 12(1):60-67.
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As wireless systems are evolving towards supporting a wide array of services, including the traditional voice service, using packet-switched transport, it becomes increasingly important to assess the impact of packet-switched transport protocols on the voice quality. In this article, we present a tutorial on voice quality evaluation for wireless packet-switched systems. We introduce an evaluation methodology that combines elementary objective voice quality metrics with a frame synchronization mechanism. The methodology allows networking researchers to conduct effective and accurate quality evaluation of packet voice. To illustrate the use of the described evaluation methodology and the interpretation of the results, we conduct a case study of the impact of Robust Header Compression (ROHC) on the voice quality achieved with real-time transmission of GSM encoded voice over a wireless link.

42. S. Frattasi and H. Fathi and F.H.P. Fitzek and R. Prasad. A Pragmatic Methodology to Design 4G: From the User to the Technology. 2005. Springer:Lecture Notes in Computer Science, 3420:366-373. (Article)

The ever-increasing growth of user demands, the limitations of the Third Generation of Mobile Communication Systems (3G) and the emergence of new mobile broadband technologies on the market have brought researchers and industries to a throughout reflection on the Fourth Generation (4G). Many prophetic visions have appeared in literature presenting the future generation as the ultimate boundary of the wireless mobile communication without any limit in its potential, but practically not giving any designing rules and thus any definition of it. In this paper we hence propose a new user-oriented methodology that considers the user as the angular stone in the design of 4G and identifies his functional needs and expectations, reflecting and illustrating them in everyday life situations. In this way, we devise fundamental user scenarios where new services are significant assets for the user. The latter implicitly reveal the key features of 4G, which are then explicated in a new framework, the user-centric system, that, through a satellite hierarchical vision, describes the various level of interdependency among them. This approach consequently brings to the identification of the designing rules and therefore to a more pragmatic definition of 4G. Finally, an example of a new 4G application is also given in order to demonstrate the validity of the overall methodology.

43. F.H.P. Fitzek and B. Can and R. Prasad and M. Katz. Traffic Analysis and Video Quality Evaluation of Multiple Description Coded Video Services for Fourth Generation Wireless IP Networks. 2005. Special Issue of the International Journal on Wireless Personal Communications.
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For the performance evaluation of future wireless communication systems, such as the fourth generation wireless networks, traffic traces of realistic services are needed. Multiple description coding (MDC) is gaining a lot of interest lately and is a viable solution to provide robust video services over single or multi hop wireless networks and MDC introduces more flexibility for network coding. Furthermore it has the capability to support heterogeneous terminals as they are accepted to be used in 4G wireless networks. By means of twelve well known video sequences, in different video formats, we generate the frame size traces and evaluate the multiple description coding characteristics. In addition to that we highlight the expected overhead due to the underlying RTP/UDP/IP protocol suite. As an objective quality measurement at the application layer, we investigate the video quality in dependency of lost and error-prone descriptors. This allows researcher to convert the network losses of their network models directly into video quality values. This step makes the work unique as single layer coded video streams would always need further postprocessing to retrieve the video quality.

44. Y. Takatori and K. Tsuneksawa and F.H.P. Fitzek and R. Prasad. On The Exploitation of Multiple Access Points in a Wireless SFN Using TDD-OFDM-MIMO Techniques. 2005. Special Issue of the International Journal on Wireless Personal Communications.
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The multiple input multiple output (MIMO) technique is the most attractive candidate to improve the spectrum efficiency in the next generation wireless communication systems. However, the efficiency of MIMO techniques reduces in the line of sight (LOS) environments. In this paper, we propose a new MIMO data transmission scheme, which combines Single Frequency Network (SFN) with TDD OFDM MIMO applied for wireless LAN networks. In our proposal, we advocate to use SFN for multiple access points (MAP) MIMO data transmission. The goal of this approach is to achieve very high channel capacity in both LOS and non line of sight (NLOS) environments. The channel capacity of the proposed method is derived for the direct path environments and it confirms the e®ectiveness of the proposed scheme in the LOS scenario. Moreover, solid computer simulation results con¯rm the e®ectiveness of the proposed method in both, single user and multiuser scenarios.

45. K. Madsen and F.H.P. Fitzek and G. Schulte and R. Prasad. Connectivity Probability of Wireless Ad Hoc Networks: Definition, Evaluation, Comparison. 2005. Special Issue of the International Journal on Wireless Personal Communications.
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The paper presents a new approach investigating mobile ad hoc network connectivity. It is shown how to dene and evaluate the connectivity probability of a mobile network where the position of the nodes and the link quality changes over time. The connectivity probability is a measure that can capture the impact of the node movement on the network connectivity. A number of mobility models is considered ranging from the classical Random Direction model to the Virtual World model based on the mobility measurements of a multi-player game. We introduce an Attractor model as a simple way to model non homogeneous node distribution by incorporating viscosity regions in the simulation area. Methods of ergodic theory are used to show the correctness of the approach and to reduce the computational time. Simulation results show how the node density distribution aspects the network connectivity.

46. M. Rossi and F.H.P. Fitzek and M. Zorzi. Error Control Techniques for Efficient Multicast Streaming in UMTS Networks: Proposals and Performance Evaluation. 2004. Journal on Systemics, Cybernetics and Informatics, vol 2.
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In this paper we introduce techniques for efficient multicast video streaming in UMTS networks where a video content has to be conveyed to multiple users in the same cell. Efficient multicast data delivery in UMTS is still an open issue. In particular, suitable solutions have to be found to cope with wireless channel errors, while maintaining both an acceptable channel utilization and a controlled delivery delay over the wireless link between the serving base station and the mobile terminals. Here, we first highlight that standard solutions such as unequal error protection (UEP) of the video flow are ineffective in the UMTS systems due to its inherent large feedback delay at the link layer (Radio Link Control, RLC). Subsequently, we propose a local approach to solve errors directly at the UMTS link layer while keeping a reasonably high channel efficiency and saving, as much as possible, system resources. The solution that we propose in this paper is based on the usage of the common channel to serve all the interested users in a cell. In this way, we can save resources with respect to the case where multiple dedicated channels are allocated for every user. In addition to that, we present a hybrid ARQ (HARQ) proactive protocol that, at the cost of some redundancy (added to the link layer flow), is able to consistently improve the channel efficiency with respect to the plain ARQ case, by therefore making the use of a single common channel for multicast data delivery feasible. In the last part of the paper we give some hints for future research, by envisioning the usage of the aforementioned error control protocols with suitably encoded video streams.

47. F.H.P. Fitzek and M. Reisslein. Wireless video streaming with TCP and simultaneous MAC packet transmission (SMPT). 2004. International journal of communication systems (Wiley Interscience), 17(5):421-435.
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Video streaming is expected to account for a large portion of the tra.c in future networks, including wireless networks. It is widely accepted that the user datagram protocol (UDP) is the preferred transport protocol for video streaming and that the transmission control protocol (TCP) is unsuitable for streaming. The widespread use of UDP, however, has a number of drawbacks, such as unfairness and possible congestion collapse, which are avoided by TCP. In this paper we investigate the use of TCP as the transport layer protocol for streaming video in a multi-code CDMA cellular wireless system. Our approach is to stabilize the TCP throughput over the wireless links by employing a recently developed simultaneous MAC packet transmission (SMPT) approach at the link layer. We study the capacity, i.e. the number of customers per cell, and the quality of service for streaming video in the uplink direction. Our extensive simulations indicate that streaming over TCP in conjunction with SMPT gives good performance for video encoded in a closed loop, i.e. with rate control. We have also found that TCP is unsuitable (even in conjunction with SMPT) for streaming the more variable open-loop encoded video.

48. M. Krishnam and M. Reisslein and F.H.P. Fitzek. An Analytical Framework for Simultaneous MAC Packet Transmission (SMPT) in a Multi-Code CDMA Wireless System. 2004. IEEE Transactions on Vehicular Technology, 53(1):223-242.
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Stabilizing the throughput over wireless links is one of the key challenges in providing high-quality wireless multimedia services. Wireless links are typically stabilized by a combination of link-layer automatic repeat request (ARQ) mechanisms in conjunction with forward error correction and other physical layer techniques. In this paper, we focus on the ARQ component and study a novel class of ARQ mechanisms, referred to as simultaneous MAC packet transmission (SMPT). In contrast to the conventional ARQ mechanisms that transmit one packet at a time over the wireless air interface, SMPT exploits the parallel code channels provided by multicode code-division multiple access. SMPT stabilizes the wireless link by transmitting multiple packets in parallel in response to packet drops due to wireless link errors. While these parallel packet transmissions stabilize the link layer throughput, they also increase the interference level in a given cell of a cellular network or cluster of an ad hoc network. This increased interference reduces the number of traffic flows that can be simultaneously supported in a cell/cluster. We develop an analytical framework for the class of SMPT mechanisms and analyze the link-layer buffer occupancy and the code usage in a wireless system running some form of SMPT. Our analysis quantifies the tradeoff between increased link-layer quality of service and reduced number of supported flows in SMPT with good accuracy, as verified by simulations. In a typical scenario, SMPT reduces the probability of link-layer buffer overflow by over two orders of magnitude (thus enabling high-quality multimedia services, such as real-time video streaming) while supporting roughly 20 percent fewer flows than conventional ARQ. Our analytical framework provides a basis for resource management in wireless systems running some form of SMPT and optimizing SMPT mechanisms.

49. F.H.P. Fitzek and D. Angelini and G. Mazzini and M. Zorzi. Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Ad Hoc Networks and Coverage Extension for Wireless Networks. 2003. IEEE Wireless Communications, Special issue on the evolution of wireless LANs and PANs, 10(6):30-39.
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Ad hoc communication is gaining popularity in recent times, not only for pure ad hoc communication networks but also as a viable solution for coverage extension in wireless networks. Especially for upcoming WLAN hotspots this is an interesting option to decrease installation costs. In this paper we introduce a new MAC protocol that needs only marginal changes to the standard and enables efficient multi-hop networking. We advocate the use of multiple IEEE802.11 channels, where one channel is reserved as a common signaling channel for the task of assigning the others data channels among wireless terminals. The proposed MAC protocol is based on a four way handshake over the common signaling channel, while data transmission occurs on a dedicated channel. We propose a further optimization applying multiple wireless network interface cards. This improvement in performance comes at the price of a slightly more complex hardware. Two different simulation models are implemented to investigate our approach. The first model investigates the MAC protocol and its improvements while the second model analyzes the multi-hop performance in terms of delivery ratio and transmission delay. By means of numerous simulations we present the performance of our MAC approach in comparison with two standard approaches in terms of bandwidth, packet delivery, and transmission delay. For our performance evaluation we apply the IEEE802.11a technology, but we note that our approach can also be used for IEEE802.11b.

50. F.H.P. Fitzek and P. Seeling and M. Reisslein and M. Zorzi. ViTAN - Visualisation Tool for Ad hoc Networks. 2003. IEEE Network, 17(1):5.
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The Visualization Tool for Ad Hoc Networks ViTAN is a tool for visualizing the connectivities and link qualities (capacities) between the terminals in wireless ad hoc networks. The tool takes the location of the terminals (specified by (x, y) coordinates) and the link qualities between the terminals (specified by positive integers) as input. The tool produces a visualization of the graph of the terminals’ connectivities in the fig format, which in turn can be converted to any common graphic format. ViTAN does not evaluate the connectivities and link qualities in ad hoc networks. Instead, ViTAN takes the link qualities obtained from other tools, simulations, or analytical evaluations as input and graphically visualizes these link qualities and the resulting connectivities in the network. ViTAN facilitates the visual study of complex ad hoc networks by depicting higher link qualities with thicker edges and in darker grey shades. In addition, ViTAN draws the edges at different depth levels of the fig format depending on the corresponding link quality. This feature enables the selective display and visual study of the connectivities provided by links with a specific quality range.

51. P. Seeling and F.H.P. Fitzek and M. Reisslein. VideoMeter. 2003. IEEE Network, 17(1):5.
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VideoMeter is a software tool for the comparative evaluation of the quality of raw video data in the YUV format. The tool gives the differences in PSNR quality between two or three YUV video sequences and includes also a player for YUV video streams. In a typical application scenario, the tool is used for the quality assessment of videos that have been encoded with some lossy compression scheme and transported over a lossy network. The tool can be used to simultaneously play (1) the original YUV video sequence, (2) the encoded (and subsequently decoded) video sequence, and (3) the video sequence obtained after encoding, network transport, and subsequent decoding. The tool gives the quality di erences in PSNR (in dB) between the original video sequence and the video sequences obtained after encoding and network transport. The VideoMeter also displays the difference pictures for the Y (luminance) component to visualize the errors. The quality di erences for the current frame and the average over the past 20 frames are provided. VideoMeter takes YUV video in the 4:2:0 format as input. Both the CIF (352x288 pixels) and the QCIF (176x144 pixels) video frame format are supported. Synchronization in the case of frame drops (either in a rate-adaptive encoder or in the network) is achieved by supplying the VideoMeter with a freeze file. This file gives the frames that are to be held for comparison since the following frame(s) have been dropped. The VideoMeter has been tested on Linux (SuSe 7.x, 8, Mandrake 8/9, and RedHat 7.3) and requires an X11 terminal with 16, 24, or 32 bit display depth.

52. F.H.P. Fitzek and A. Wolisz and M. Reisslein. Uncoordinated Real-Time Video Transmission in Wireless Multi-Code CDMA Systems: An SMPT-Based Approach. 2002. IEEE Wireless Communications,Special issue on IP multimedia in next generation mobile networks, 9(5):100-110.
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We consider the real-time transmission of encoded video from distributed, uncoordinated wireless terminals to a central base station in a multi-code CDMA system. Our approach is to employ the recently proposed simultaneous MAC packet transmission (SMPT) approach at the data link layer (in conjunction with UDP at the transport layer). We consider the real-time transmission of both video encoded in an open loop (i.e., without rate control) and video encoded in a closed loop (i.e., with rate control). We conduct extensive simulations and study quantitatively the trade-off between video quality, transmission delay (and jitter), and number of supported video streams (capacity). We find that the simple-to deploy SMPT approach achieves significantly higher video quality and smaller delays than the conventional sequential transmission approach, while ensuring high capacity. In typical scenarios, with SMPT the probability of in-time video frame delivery is more than twice as large as with sequential transmission (for given delay bounds). Our results provide guidelines for the design and dimensioning of cellular wireless systems as well as ad hoc wireless systems.

53. F.H.P. Fitzek and A. Koepsel and A. Wolisz and M. Krishnam and M. Reisslein. Providing Application-Level QoS in 3G/4G Wireless Systems: A Comprehensive Framework Based on Multi-Rate CDMA. 2002. IEEE Personal Communications - Special issue on 4G Technologies and Applications, 9(2):42-47.
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The emerging applications for 3G and 4G wireless systems typically require highly heterogeneous and time-varying quality of service from the underlying protocol layers. The wireless links, however, provide only an unreliable communication channel that suffers from temporal outages. As a consequence, protocol mechanisms are needed that, based on the unreliable wireless links, provide the different service qualities required by the emerging applications. We identify the emerging IP-based applications for 3G and 4G wireless systems and categorize their QoS requirements. We discuss the wireless access mechanisms that show promise as the basis for supporting these applications. We then propose a set of protocol mechanisms that, based on the discussed wireless access mechanisms, provide the required QoS for the different application categories.

54. F.H.P. Fitzek and M. Reisslein. MPEG-4 and H.263 Video Traces for Network Performance Evaluation. 2001. IEEE Network, 15(6):40-54.
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MPEG-4 and H.263 encoded video is expected to account for a large portion of the traffic in future wireline and wireless networks. However, due to a lack of sufficiently long frame size traces of MPEG-4 and H.263 encoded videos, most network performance evaluations currently use MPEG-1 encodings. We present and study a publicly available library of frame size traces of long MPEG-4 and H.263 encoded videos, which we have generated at the Technical University Berlin. The frame size traces have been generated from MPEG-4 and H.263 encodings of over 10 video sequences each 60 minutes long. We conduct a thorough statistical analysis of the traces.

55. F.H.P. Fitzek and M. Reisslein. A Prefetching Protocol for Continuous Media Streaming in Wireless Environments. 2001. IEEE Journal on Selected Areas in Communications (special issue), Mobility and Resource Management in Next Generation Wireless Systems, 19(6):2015-2028.
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Streaming of continuous media over wireless links is a notoriously difficult problem. This is due to the stringent Quality of Service requirements of continuous media and the unreliability of wireless links. We develop a streaming protocol for the real--time delivery of prerecorded continuous media from (to) a central base station to (from) multiple wireless clients within a wireless cell. Our protocol prefetches parts of the ongoing continuous media streams into prefetch buffers in the clients (base station). Our protocol prefetches according to a Join-- the--Shortest--Queue policy. By exploiting rate adaptation techniques of wireless data packet protocols, the Join-- the--Shortest--Queue policy dynamically allocates more transmission capacity to streams with small prefetched reserves. Our protocol uses channel probing to handle the location--dependent, time--varying, and bursty errors of wireless links. We evaluate our prefetching protocol through extensive simulations with VBR MPEG and H.263 encoded video traces. Our simulations indicate that for bursty VBR video with an average rate of 64 kbit/sec and typical wireless communication conditions our prefetching protocol achieves client starvation probabilities on the order of 10e-4 and a bandwidth efficiency of 90 per cent with prefetch buffers of 128 kBytes.

56. F.H.P. Fitzek and R. Morich and A. Wolisz . Comparison of Multi-Code Link-Layer Transmission Strategies in 3G wireless CDMA. 2000. IEEE Communication Magazine - Technologies on Broadband Wireless Mobile: 3Gwireless and Beyond, 38(10):58-64.
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Within this article we investigate the possibility of using multiple codes within a code-division multiple access system to reduce the losses in a delay bounded transmission for 3G multimedia applications over wireless links with fading. Multiple codes are used to recover from gaps on the wireless link after a fading period by means of ARQtype retransmissions. One key feature of our work is that even a small number of multiple codes leads to a dramatic reduction of losses regarding delay bounds of multimedia applications.