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The mobile environment introduces unique design challenges to the communications system engineer. The most prominent of such challenges is the time-varying characteristics of the communication channel due to fading, multipath, shadowing and path loss. In communication theory, traditionally the channel fading is viewed as a source of unreliability that has to be mitigated. This is because, inherent in the design parameters of most of the communication systems of the past and present is the goal of providing circuit-switched voice service.

Circuit-switched digital voice communication in wireless systems requires the transmission of a pre-defined, constant data rate at all times, regardless of the state of the wireless channel. The data rate is dictated by the vocoder in use. Moreover, for acceptable voice quality, such systems are designed to maintain a desired signal-to-noise ratio (SNR) level at all fading states of the channel. This SNR level corresponds to a tolerable error probability for the vocoder in use.

Today, voice communication remains to be the dominant application in wireless systems. Its status as a premier application is expected to continue for several years to come. However, it has also become evident that the explosive growths of the Internet and the wireless communications will very likely create new opportunities for new all-IP wireless networks to support various multimedia applications. This points to the need for a new, and optimized, set of techniques unique to packet data transmission.

We envision that wireless systems of the future will indeed provide a multitude of multimedia services, each with a unique set of quality-of-service (QoS) requirements over an all-IP platform. QoS covers a wide array of service attributes, including data-rate, delay, and packet delivery guarantees. Services such as streaming video, live broadcast video, voice over IP, circuit switched voice, data, peer-to-peer file sharing all have different QoS requirements. QoS provisioning in a wireless network is a particularly difficult problem even for a single application due to the time-varying nature and unreliable physical channel. The design of a unique wireless air interface that would yield satisfactory performance for all envisioned services is not likely. Therefore, our vision for the future compromises numerous air interfaces, each optimized for a unique application, or a set of applications, and a wireless resources manager that oversees the dynamic division of wireless resources across these air interfaces.

Therefore, the focus of our current research is the development of air interfaces optimized for a number of specific multimedia services over wireless networks. As such, we conduct research on the provisioning of streaming video [1], live broadcast video [2], data with statistical QoS guarantees [3-4]. and best effort data [5] over all-IP wireless cellular networks. Two research grants have been awarded for these studies; one for wireless streaming-video provisioning (T\”{u}bitak, the NSF equivalent entity for Turkey) and another on best effort data (Nokia Headquarters). Future research will add voice over IP service to this group. We will also investigate the provisioning of such services in wireless ad-hoc networks. The work on ad-hoc networks will also enable the introduction of wireless peer-to-peer networking and design of efficient protocols for this purpose. Here, cooperation between nodes will have impact on the design of source compression and transmission strategies. The interaction between cellular and ad-hoc networks towards satisfying the QoS is also an active area of research [6]. Furthermore, we propose to conduct research on spectrally efficient design of the wireless resources manager so that different QoS requirements may be met over the wireless medium simultaneously.

References

[1]Tanır Özçelebi, M. Oğuz Sunay, A. Murat Tekalp and M. Reha Civanlar, “Cross-Layer Optimized Rate Adaptation and Scheduling for Multiple-User Wireless Video Streaming,” IEEE Journal on Selected Areas in Communications, vol. 25, no.4, pp. 760-769, May 2007.
[2] Çağdaş Atıcı and M. Oğuz Sunay, “High Data-Rate Video Broadcasting over 3G Wireless Systems,” IEEE Transactions on Broadcasting, vol. 53, no. 1, pp. 212-223, March 2007.
[3] Ulaş Kozat and M. Oğuz Sunay, “On The Achievable Gains of Coding and Opportunistic Scheduling for Wireless Multicast,” in preparation for submission to IEEE Transactions on Mobile Computing, 2010.
[4] Ferit O. Akgül and M. Oğuz Sunay, “Statistical QoS Assurances for High Speed Wireless Communication Systems,” Springer Lecture Notes in Computer Science, vol. 3970, pp. 287-298, 2006.
[5] Ferit O. Akgül and M. Oğuz Sunay, “QoS-Aware Scheduling for 3G Wireless Packet Data Systems,” Journal of Internet Engineering, Klidarithmos, vol. 1, no. 1, pp. 24-30, January 2007.
[6] M. Oğuz Sunay and Ali Ekşim, “Fair Scheduling for Spectrally Efficient Multi-Service Data Provisioning,” International Journal of Communication Systems, Wiley, vol. 17, pp. 615-642, August 2004.
[7] Çağdaş Atıcı, M. Oğuz Sunay, “Improving Broadcasting Performance for Wireless Ad-Hoc Networks,” {\em submitted to IEEE Transactions on Mobile Computing,} 2010.
[8] Tuğba Özbilgin, M. Oğuz Sunay, “On the Capacity of Wireless Peer-to-Peer Networks with Transmitter and Receiver Cooperation,” Proceedings of the IEEE PIMRC’07 Conference, Athens, Greece, September 3-6, 2007.
[9] Ferit O. Akgül and M. Oğuz Sunay, “Enhancing 3G High Speed Wireless Data Performance Through Utilization of 3G-WLAN System Integration: A Cross-Network, Cross-Layer Approach,” Personal Wireless Communications Journal, Springer, vol. 43, pp. 89-106, October 2007.
[10] Çağdaş Atıcı and M. Oğuz Sunay, “Cross-Layer Design for Wireless Video Broadcasting using H.264/AVC,” submitted to Signal Processing: Image Communication, 2010.

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