RESEARCH PROJECTS
Future generation mobile radio systems must support a great variety of services including those applications requiring high data rates. One of the difficulties in achieving higher data rates is excessive inter-symbol interference (ISI) introduced by the multipath wireless communications channel. One possible solution is Orthogonal Frequency Division Multiplexing (OFDM). In OFDM serial data with a high rate is first converted to many parallel streams each of which operates at a much lower rate. By inserting a guard time in each channel, OFDM can support high data rates with little or no ISI. The spectra of the subcarriers are allowed to overlap each other to maximize spectral efficiency.
The objective of this study is to implement a high data rate (54 Mb/s) OFDM wireless LAN transceiver using Field Programmable Gate Array (FPGA) technology. Practical performance capabilities and limitations will be determined. Analytical and computer simulation studies will be conducted to determine Bit Error Rate performance.
The 802.11a OFDM wireless transmitter baseband processor has been designed. The VHDL code has been written, and the simulation is now complete. It consists of 48 subcarriers each modulated with 64 QAM to achieve a data rate of 54 Mb/s.
The baseband processor was implemented using an FPGA from Xilinx using the Very High Speed Integrated Circuit (VHSIC) Hardware Description Language (VHDL). The baseband receiver module VHDL code is also complete.
Simulation is in progress. After the simulation is verified, the RF front end design will begin.
Key-words: Orthogonal Frequency Division Multiplexing (OFDM), Field Programmable Gate Array (FPGA), inter-symbol interference.
Participating Faculty: Frank Cassara (cassara@rama.poly.edu)
[1] Y-S Choi, P. Voltz, F. Cassara, On Channel Estimation and Detection for Multicarrier Signals in Fast and Selective Rayleigh Fading Channels, IEEE Transactions on Communications, Vol. 49, No. 8, August 2001.
[2] Y-S Choi, P. Voltz, F. Cassara, ML Estimation of Carrier Frequency Offset for Multicarrier Signals in Rayleigh Fading Channels, Vol. 50, No. 2, March 2001.
Cyber Security Processor (CYSEP)
As the need for cost-effective, ubiquitous secure communications continue to rise, corporations are turning to virtual private networks (VPNs) to eliminate expensive leased lines to provide secure access of sensitive data for both intra and inter-organization communications. As these institutions increasingly rely on web-based applications to interface with customers, clients and business partners alike, they also place their sensitive information and databases at greater risk of attack at the web application level. Conventional solutions such as firewalls, VPN gateways and intrusion detection systems do not completely solve the problem. They only analyze packet headers and cannot detect threats embedded in network content, because they lack the processing power necessary to analyze content in real time to detect viruses, worms, or inappropriate content – and therefore leave the network edge open to a wide range of costly, content-borne threats.
We plan to enhance the network security in four aspects by implementing a Cyber-Security Processor (CYSEP) to perform the functions of firewall/intrusion detection, encryption/decryption, authentication, and distributed denial of service (DDoS) attack protection, as shown in the Figure 1. The CYSEP, consisting of four engines, will be implemented on application-specific integrated circuits (ASIC) with the state-of-art CMOS 0.18-mircron technology and expected to operate at 10 Gbps or higher.
· The firewall and intrusion detection engine (FIDE) detects and prevents possible attacks from outside or inside of an enterprise network. The FIDE implements the functions of finite automata based signature detection and packet classification at 10 Gbps.
· The encryption/decryption engine implements the message confidentiality primitives necessary to establish VPN over the public Internet. Our preliminary field-programmable-gate-array (FPGA) implementation of the optimized Advanced Encryption Standard (AES) block and stream cipher operates at about 5 Gbps. We expect to achieve 10 Gbps or higher throughput with ASIC implementation.
· The authentication and authorization engine implements the message integrity primitive necessary to establish VPNs. The engine will implement a universal hash function based Message Authentication Code with extremely small collision probability. Based on the throughput estimates obtained from our synthesis experiments, we expect the throughput for the ASIC implementation to be >70 Gbps.
· The DDoS protection engine uses our proposed PacketScore scheme, which determines the legitimacy of a suspicious packet according to the score assigned to the packet. By taking a score-based filtering approach, we avoid the problems of conventional binary rule-based filtering and achieve great scalability in speed (e.g., 10 Gbps or higher) and the number of potential victims.
Massive parallelism and pipelining technique is to be employed in the ASIC to achieve the 10 Gbps wire-speed operation. The CYSEP can be deployed at various places in the network, e.g., at high-performance end-systems, data centers, enterprise networks, and the Internet service provider’s backbone network to enhance cyber security and to increase bandwidth efficiency of the network, as shown in Figure 2.
Key-words: Network Security, Cryptograph, Intrusion Detection, Denial of Service.
Participating Faculty: H. Jonathan Chao (chao@poly.edu) and Ramesh Karri (ramesh@india.poly.edu)
Website: http://eeweb.poly.edu/~chao/research/cysep.html
[1] M. C. Chuah, W. Lau, Y. Kim, and H. J. Chao, Transient Performance of PacketScore for blocking DDoS attack, IEEE ICC 2004, Paris, June 2004.
[2] W. Lau, M. C. Chuah, Y. Kim, and H. J. Chao, Distributed architecture for statistical overload control against distributed denial of service attacks, patent application filed on Nov. 26, 2003.
[3] Y. Kim, W. Lau, M. C. Chuah, and H. J. Chao, PacketScore: statistical-based overload control against distributed denial-of-service, IEEE Proc. INFOCOM, Hong Kong, March 2004.
[4] Y. Kim, J.-Y. Jo, H. J. Chao, and F. L. Merat, High-speed router filter for blocking TCP flooding under distributed denial of service attack, International Performance, Computing and Communications Conference, Phoenix, Arizona, April 2003.
The Internet has become a fundamental driving force for a variety of information technologies due to its ever-growing ability to handle traffic, its ubiquitousness, and the services. New applications, such as sensor fusion, bio-informatics, grid computation, global data storage, and on-line video applications, are emerging. Common among these applications is their demand for a huge amount of bandwidth and a global packet switching infrastructure. In contrast to the success in increasing the raw bandwidth for terabit transmission capability using dense wavelength division multiplexing (DWDM) technology toward the end of last century, today’s electronic router technology may soon exhaust its capacity of a few terabit/s. To find a cost-effective way to build a router with a few tens of terabit or even petabit capacity will be the key to the continuing success of the next-generation Internet.
Many researchers have attempted to build high-speed large-capacity packet switches, which are often categorized into different architectures based on the placement of buffers, e.g., input-buffered, output-buffered, crosspoint-buffered, internal buffered, and combined input-output buffered. Reference [1] addresses the basics, theories, architectures, and technologies to implement ATM switches, IP routers, and optical packet switches. One of promising architectures is a multi-stage buffered switch as shown in the figure below. It is very scalable and doesn’t require any arbitration if a flow control scheme is implemented between the stages.
One of the challenges for the multi-stage buffered switches is to resolve packet out-of-sequence problem because packets sent to different paths may experience different queuing delays. One way to avoid the packet out-of-sequence problem in the buffered multi-path switch fabric is to re-sequence packets at the output port. This re-sequencing scheme has been studied in many literatures. Another way to avoid the out-of-sequence problem is to send all packets belong to the same flow to the same path. This idea is attractive in the sense that the out-of-sequence problem is only counted for the packets belong to the same flow.
One problem of the static hashing scheme is the load imbalance. Since each flow may have different bandwidth, it is possible that one path is more congested than the other path. This creates the complexity of choosing proper paths to route packets from an input port to an output port. If paths are not properly chosen, the probability of internal block in the middle stage increases, adversely impacting switch performance. In order to make the loads of all paths comparable, we propose to use a dynamic hashing. In dynamic hashing, the input port maintains outstanding number of packets in the switch fabric for each flow. If there is an outstanding packet in the switch fabric, all the following packets belonging to the flow must be sent to the same path with the previous packet. Otherwise, they can be sent to any other path. Therefore, there is no need for packet re-sequencing circuitry at the output port. This scheme is more attractive than the re-sequencing scheme because the high-speed input port may have hundreds of thousands flows and the number of paths is only a few hundreds.
We have prototyped a 16x16 multi-stage buffered switch with line rate of 10 Gbit/s, as shown below. We are experimenting different load-balancing schemes by using the FGPA-based reconfigurable switch fabric.
Key-words: packet switches, Clos network, packet scheduling.
Participating Faculty: H. Jonathan Chao (chao@poly.edu)
Website: http://eeweb.poly.edu/~chao/research/
[1] Broadband Packet Switching Technologies – A Practical Guide to ATM Switches and IP Routers, H. J. Chao, C. Lam, and E. Oki, John Wiley & Sons, Inc, Sep. 2001.
[2] H. J. Chao, Z. Jing, and K. Deng, PetaStar: A petabit photonic packet switch, in IEEE Journal on Selected Areas in Communications (JSAC), Special Issue on High-Performance Optical/Electronic Switches/Routers for High-Speed Internet, vol. 21, no. 7, pp. 1096-1112, Sep. 2003.
[3] R. Rojas-Cessa, E. Oki, and H. J. Chao, Concurrent fault detection for a multiple-plane packet switch, in IEEE/ACM Trans. on Networking, vol. 11, no. 4, pp. 616-627, Aug. 2003.
[4] E. Oki, Z. Jing, R. Rojas-Cessa, and H J. Chao, Concurrent round-robin-based dispatching schemes for Clos-network switches, in IEEE/ACM Trans. on Networking, vol. 10, no. 6, pp. 830-844, Dec. 2002.
[5] H. J. Chao, Next generation routers, invited paper, IEEE Proceeding, vol. 90, no. 9, pp. 1518-1558, Sep. 2002.
[6] E. Oki, R. Rojas-Cessa, and H J. Chao, A pipeline-based maximal-sized matching scheme for high-speed input-buffered switches, in IEICE Trans. Commun, vol. E85-B, no. 7, pp. 1302-1311, July 2002.
[7] J. S. Park and H. J. Chao, Design and analysis of enhanced Abacus switch, Computer Communications, vol. 25, no. 6, pp. 577 – 589, April 2002.
[8] H. J. Chao and T. S. Wang, An optical interconnection network for terabit IP routers, IEEE Journal of Lightwave Technology, vol. 18, no. 12, pp. 2095-2112, Dec. 2000.
Most existing wireless systems, such as 802.11 or 3G cellular, comprise a number of independent nodes or users that are in contact with an access point (base station). Ad-hoc (multihop) networks, on the other hand, transmit information from the source node to the destination via relaying nodes. The standard technique is for the nodes to only process signals coming from the previous node in the route. Cooperative networking presents a different approach, where two or more active users in the network share their information to jointly transmit their messages, either at different times or simultaneously, with the objective of gaining greater reliability and efficiency than they could obtain individually.
The idea behind cooperative communication rests on the observation that in a wireless environment, the signal transmitted by the source node is “overheard" by other nodes, which we call partners. The partners process and re-transmit the signals they receive. The destination combines the signals coming from the source and the partners, thereby creating spatial diversity. This user cooperation diversity (a term coined by our group [1], [2]) or cooperative diversity, can be used on top of existing diversity schemes already present in the nodes. We note that the spatial diversity arising from cooperation is not exploited in the current implementation of cellular, wireless LAN or ad-hoc systems; only one copy of the signal, whether it comes from the mobile directly or from a relay, is processed at the destination. In addition, we envision a situation in which all partners take turns in creating spatial diversity for each other, turning the cooperative scheme into a virtual transmit antenna array. Further benefits of this virtual array include higher throughput and extended battery life for nodes, leading to a higher network life in the case of ad-hoc networks. However, the elements of this array are not co-located, they belong to different terminals which are connected via noisy channels. Hence one has to carefully study the conditions under which cooperation is useful and investigate practical schemes to get the desired benefits.
This project considers an information theoretic study of cooperative communication systems. Our capacity and outage analysis illustrates benefits of cooperation in terms of both data rates and robustness to channel variations [1], [2]. The research plan includes a study of cooperative techniques when multiple terminals are involved. We study the diversity gains of using multiple relays with various processing capabilities [3]. We illustrate how the overall robustness of the system can be maximized by forming a virtual transmit and receive antenna array [4]. We also consider cooperative relaying strategies for multiple transmitters (multiple access channel with relays) or multiple receivers (broadcast channel with relays).
Participating Faculty: Elza Erkip (elza@poly.edu)
Website: http://eeweb.poly.edu/~elza/
Funding Sources: NSF, CATT, WICAT
[1] A. Sendonaris, E. Erkip, and B. Aazhang. User cooperation diversity–Part I: System description. IEEE Transactions on Communications, 51(11):1927–1938, Nov. 2003.
[2] A. Sendonaris, E. Erkip, and B. Aazhang. User cooperation diversity–Part II: Implementation aspects and performance analysis. IEEE Transactions on Communications, 51(11):1939–1948, Nov. 2003.
[3] M. Yuksel and E. Erkip. Diversity in relaying protocols with amplify and forward. In Proceedings of 2003 GLOBECOM Communication Theory Symposium, San Francisco, December 2003.
[4] M. Yuksel and E. Erkip. Diversity gains and clustering in wireless relaying. In Proceedings of 2004 International Symposium on Information Theory, Chicago, June 2004.
User cooperation represents an effective way of introducing diversity in wireless networks. Spatial diversity gains are obtained through the cooperative use of antennas belonging to several nodes. We design and analyze the performance of channel codes that are capable of achieving the full diversity provided by user cooperation. The codes provide substantial diversity and coding gains over the non-cooperative case, even when the inter-user channel is faded and noisy. The work extends to cooperative space-time codes designed to achieve cooperation among nodes with different number of antennas. The codes use the principle of overlays in time and space, and ensure that cooperation takes place as often as possible. We illustrate that cooperative coding greatly reduces the error rates of all nodes involved, in a variety of cooperation scenarios.
Key-words: diversity methods, error-correction coding, fading channels, multiple-input/multiple-output (MIMO) systems.
Participating Faculty: Andrej Stefanov (stefanov@poly.edu), Elza Erkip (elza@poly.edu)
Websites: http://eeweb1.poly.edu/stefanov/, http://eeweb.poly.edu/~elza/
[1] A. Stefanov and E. Erkip, Cooperative Coding for Wireless Networks, IEEE Transactions on Communications, vol. 52, No. 9, pp. 147—1476, September 2004.
[2] A. Stefanov and E. Erkip, Cooperative Space-Time Coding for Wireless Networks, Proceedings of IEEE Information Theory Workshop, pp. 50-53, La Sorbonne, Paris, France, April 2003.
[3] A. Stefanov and E. Erkip, On the Performance Analysis of Cooperative Space-Time Coded Systems, Proceedings of IEEE Wireless Communications and Networking Conference (WCNC), pp. 729-734, New Orleans, Louisiana, March 2003.
[4] A. Stefanov and E. Erkip, Cooperative Coding Theory and Applications, 32nd Annual IEEE Communication Theory Workshop, Mesa, Arizona, April 2003.
[5] A. Stefanov and E. Erkip, Cooperative Information Transmission in Wireless Networks, Proceedings of 2nd IEEE Asian-European Workshop on Concepts in Information Theory, pp. 90-93, Breisach, Germany, June 2002.
Cooperative Source and Channel Coding
Current and next generations of wireless devices and services are substantially different than the original cellular phones which could only carry voice signals. Third/fourth generation cellular and wireless local area networks are designed to support data services, image and video communications as well as voice. Multimedia signals require higher data rates and larger bandwidths than their voice counterparts. This necessitates a more efficient use of already scarce radio resources. Furthermore, guaranteeing a desired level of signal quality for image and video is especially difficult given that the wireless channel is unreliable and compressed audio and video streams are very sensitive to transmission errors.
In order to provide robust wireless multimedia communications, this research uses cooperative communication techniques along with jointly optimized source compression and channel coding strategies. Cooperation of wireless terminals is achieved by overhearing other terminal's signals and retransmitting towards the desired destination. This provides signal diversity and enables robust source-to-destination routes which can adapt to changes in the wireless environment. In order to establish the theory and practice of cooperative source and channel coding, the research plan consists of three interrelated components: Information theory of source channel cooperation; design of cooperative source and channel coding techniques with numerical/simulation studies to jointly optimize the parameters; and application of these techniques to wireless video transmission. Our initial results illustrate the benefits of layered cooperation both for idealized and practical channel codes. Layered cooperation improves the overall source distortion by providing higher reliability for important source bits via cooperation [1], [2], [3].
Participating Faculty: Elza Erkip (elza@poly.edu), Yao Wang (yao@vision.poly.edu)
Website: http://eeweb.poly.edu/~elza/, http://eeweb.poly.edu/~yao/
Funding Sources: NSF, Philips Research, CATT, WICAT
[1] D. Gunduz and E. Erkip. Joint source-channel cooperation: Diversity versus spectral efficiency. In Proceedings of 2004 International Symposium on Information Theory, Chicago, June 2004.
[2] X. Xu, Y. Wang and E. Erkip. Layered cooperation for wireless multimedia communications. To appear, Proceedings of 2004 Picture Coding Symposium, San Francisco, December 2004.
[3] X. Xu, D. Gunduz, E. Erkip and Y. Wang. Layered cooperative source and channel coding. Submitted, 2005 ICC Multimedia Communication and Home Networking Symposium, Seoul, Korea, May 2005.
Cooperation of mobiles provides signal diversity in wireless networks. See project “Cooperative Wireless Communications: Fundamental Principles” for a detailed description of the cooperation principle. Most work in the literature of cooperative systems assumes that a cooperating partner is already chosen and investigates the details of how cooperation should be carried out. However, it is also important to be able to choose a partner among available candidates to maximize cooperation benefits for the user or the whole system. Therefore, for a given cooperative protocol, it is desirable to know exact conditions under which cooperation is useful, how much benefits can be brought by cooperation and how the channel qualities of user-to-user and user-to-destination links affect these benefits of cooperation.
In this project we consider a coded cooperative system as described in the project “Cooperative Coding for Wireless Networks” and investigate the choice of partners to minimize the error rates. We study the partner choice problem both in an asymptotic regime when the received signal to noise ratios are high, and as a function of the locations of users [1], [2]. Our results provide simple analytical tools that identify locations of partner terminals, which we call “cooperative region,” such that if a source terminal cooperates with someone in the cooperative region, it will observe a reduction in the frame error rate with respect to no cooperation. Formulation of the cooperative region enables us to limit the search region of good partners. We also develop analytical tools that indicate the best partner from a set of available nodes that are all inside the cooperative region. Using these results, cooperation decisions can be made online without need of simulations or large look-up tables.
Participating Faculty: Elza Erkip (elza@poly.edu), Andrej Stefanov (stefanov@poly.edu)
Website: http://eeweb.poly.edu/~elza/, http://eeweb1.poly.edu/stefanov/
Funding Sources: NSF, Philips Research, CATT, WICAT
[1] Z. Lin, E. Erkip and A. Stefanov, An asymptotic analysis on the performance of coded cooperation systems. In Proceedings of 2004 Fall Vehicular Technology Conference, Los Angeles, September 2004.
[2] Z. Lin, E. Erkip and A. Stefanov, Cooperative regions for coded cooperative systems. To appear, Proceedings of 2004 GLOBECOM Communication Theory Symposium, Dallas, December 2004.
Most practical systems provide channel estimation at the receiver through preambles. Furthermore, this information can be partially relayed to the transmitter through some kind of feedback, in the form of ARQ or power control. However, it is not clear how effective these ad-hoc channel estimation and feedback methods are in utilizing network resources, what losses are incurred by imperfect or finite rate estimation and feedback strategies and how the transmitter and receiver should be designed based on partial channel estimation and feedback. These issues are especially relevant for multiple-antenna systems where considerable gains can be achieved via feedback.
In this project we study achievable communication rates for some practical multi-antenna preamble and feedback strategies. We provide analytical bounds on the outage probability, the probability that communication at a particular information rate cannot be supported, for finite rate feedback. We also illustrate how one can design good beamformers for multiple transmit antennas based on this finite rate feedback.
Participating Faculty: Elza Erkip (elza@poly.edu)
Website: http://eeweb.poly.edu/~elza/
Funding Sources: NSF
[1] K. K. Mukkavilli, Sabharwal, E. Erkip and B. Aazhang. On beamforming with finite rate feedback in multiple antenna systems. IEEE Transactions on Information Theory, Special Issue on Space-Time Transmission, Reception, Coding and Signal Design, vol. 49, no.10, pp. 2562-2579, October 2003.
[2] K. K. Mukkavilli, A. Sabharwal, E. Erkip and B. Aazhang. Beamformer design with feedback rate constraints: Criteria and constructions. In Proceedings of 2003 International Symposium on Information Theory, Yokohoma, Japan, July 2003.
[3] K. K. Mukkavilli, A. Sabharwal, E. Erkip and B. Aazhang. Performance limits on beamforming with finite rate feedback for multiple antenna systems. In Proceedings of Thirty Sixth Annual Asilomar Conference on Signals, Systems and Computers, Pacific Grove, California, November 2002.
[4] A. Sabharwal, E. Erkip and B. Aazhang. On channel state information in multiple antenna block fading channels. In Proceedings of 2000 International Symposium on Information Theory and its Applications, pp. 116-119, Honolulu, Hawaii, November 2000.
Radio Resource Management in Cellular Communications
The quality and efficiency of Wireless Internet communications depend on a large number of design parameters and operational variables. In the 1990s, researchers and system designers produced new theories and practical algorithms that maximize the capacity of cellular systems carrying telephone conversations. Anticipating rapid growth in the volume and diversity of data traffic in a Wireless Internet, this project research focuses on issues directly related to efficient multimedia wireless communications.
Emerging wireless communications systems adapt their operating parameters to changing channel conditions. This cluster of projects derives principles for designing wireless systems and adapting them to provide optimum performance as conditions change. The overall theme is allocating scarce radio resources by adjusting the transmission rates and radiated power levels of terminals sharing the same radio channels.
Because the issues are complex we pursue a “divide-and-conquer” approach, with separate studies looking at pieces of the overall problem. One study began with a noise-limited system and considered the effect on throughput of three design parameters: binary transmission rate, packet size, and the amount of forward error correction coding.
Later work provides guidance on how to adapt a wireless communications system to a wide range of transmission conditions. When conditions are very good throughput is optimum with multi-level modulation and no forward error correction. As the conditions deteriorate, the number of modulation levels should decrease. Under poor conditions it is best to use binary modulation and error correcting codes. The quantitative results of the study can be used to match transmission conditions to changing locations of wireless terminals.
Other research focuses on data transmission from a collection of CDMA terminals to a single base station. The CDMA studies address two different optimization criteria: aggregate weighted throughput of the base station and the battery life of the terminals. They include several different optimization studies distinguished by the constraints on the transmission rate and transmission power of each terminal.
Key-words: Cellular Communications; Power Control; Rate Adaptation: CDMA
Participating Faculty: David Goodman (goodman@duke.poly.edu)
Funding Sources: NSF and WICAT
Website: http://eeweb.poly.edu/dgoodman/
[1] Rodriguez, V. An Analytical Foundation for Resource Management in Wireless Communications, IEEE Globecom, Vol. 2, pp. 898-902, San Francisco, December, 2003.
[2] Rodriguez, V., Resource Management for Scalably Encoded Information: The Case of Image Transmission Over Wireless Networks, IEEE ICME, Vol. 1, pp. 813-6, Baltimore, July 7-09, 2003
[3] Rodriguez, V., D.J. Goodman, and Y. Wang, Optimal Coding Rate and Power Allocation for the Streaming of Scalably Encoded Video Over a Wireless Link, IEEE ICASSP, Montreal, May 17-21, 2004.
[4] Rodriguez, V., and D.J. Goodman, Power and Data Rate Assignment for Maximal Weighted Throughput in 3G CDMA, IEEE WCNC, Vol.1, pp. 525-31, New Orleans, March 16-20, 2003.
[5] P. Orenstein, D. J. Goodman, Z. Marantz, and V. Rodriguez, Effects of Additive Noise on The Throughput of CDMA Data Communications, IEEE International Conference on Communications (ICC) 2004, Paris, 2004.
[6] V. Rodriguez, D. J. Goodman, and Z. Marantz, Power and Data Rate Assignment for Maximal Weighted Throughput in 3G CDMA: A Global Solution with Two Classes of Users, IEEE Wireless Communications & Networking Conference (WCNC), Atlanta, Georgia, March 21-25, 2004
[7] P. Orenstein, D. J. Goodman, and Z. Marantz, Maximizing the throughput of CDMA Data Communications through joint admission and power control, 38th Conference on Information Sciences and Systems (CISS) 2004, Princeton, NJ, March 16th-18th, 2004.
[8] D. J. Goodman, Z. Marantz, P. Orenstein, and V. Rodriguez, Maximizing The Throughput of CDMA Data Communications, IEEE 58th Vehicular Technology Conference (VTC), Orlando, FL, October 6-9, 2003.
In a single cell of a CDMA system, some terminals transmit real-time media signals, such as voice or video, and other terminals transmit data signals to the same base station. Each media terminal has a fixed bit rate and needs to be received without delay and with a signal-to-interference ratio that exceeds a given minimum. The data terminals accept more delay than media terminals in exchange for error free information transfer. They retransmit packets received in error and adapt their transmission rates and transmitter power levels to maximize the aggregate throughput of the base station.
Theoretical work simultaneously optimizes the packet size, binary transmission rates and transmitter power levels of the data terminals. The results include performance bounds of the system indicating the tradeoff between number of media terminals, media signal-to-interference ratio, number of data terminals, and data transmission rates. The work also indicates the conditions in which it is better for the data terminals to transmit simultaneously and the conditions that call for time-division scheduling of data transmissions.
Key-words: Cellular communications, multimedia, power control, rate adaptation
Participating Faculty: David Goodman (goodman@duke.poly.edu)
Funding Sources: NSF and WICAT
Website: http://eeweb.poly.edu/dgoodman/
Sangwook Suh, Resource Allocation and Hybrid TDMA/CDMA Scheme for the Uplink Of Media/Data Wireless Systems, Master of Science Thesis, Polytechnic University, November, 2004.
Power Efficient Multimedia Wireless Communications
An important lesson of cellular telephone communications is that effective management of radio resources, including transmitter power and channel bandwidth, is essential to the quality and efficiency of a network and to the utility of subscriber equipment. The theory and algorithms for radio resource management were first confined to telephone communications. Later work showed that efficient power control algorithms for cellular data transmission differ from those devised for telephony. The radio resource management problem becomes even more complex when we anticipate networks that simultaneously carry a variety of information types. Our research focuses on managing radio resources in multimedia wireless networks with an emphasis on power efficiency.
As video transmission is integrated into wireless communication systems, the theory of power control should be expanded to consider both signal processing power and transmission power when designing new algorithms, since video coding can be a significant drain on the battery of a portable wireless terminal.
This project examines the interaction of signal processing and radio transmission in the design of algorithms for managing power and bandwidth utilization in multimedia wireless networks. Initial research focused on a single portable terminal transmitting video signals to a cellular base station. The research combines theory of source coding and radio transmission, models of distortion due to source coding and channel errors in H.263 video coders, and measurements of power dissipation in equipment performing video coding. Initial results show that the optimum amount of video compression depends on the distance between the terminal and the base station. To avoid using excessive transmitter power, terminals far from a base station should employ more video compression (at the expense of additional signal processing power consumption) than terminals near a base station.
Subsequent work expands the studies of a single terminal to consider the mutual interference of several terminals, all transmitting video signals to the same CDMA base station. Work in progress considers a network in which some terminals are transmitting video signals and others are transmitting data to the base station.
Key-words: Cellular communications, power control, video compression
Participating Faculty: Elza Erip (erkip@poly.edu), David Goodman (goodman@duke.poly.edu) and Yao Wang (yao@vision.poly.edu)
Funding Sources: NSF and WICAT
Website: http://eeweb.poly.edu/dream-it/
[1] Xiaoan Lu, Yao Wang, Elza Erkip and David Goodman, Minimize the Total Power Consumption for Multiuser Video Transmission over CDMA Wireless Network: a Two-step Approach, to be presented at 2005 International Conference on Acoustics Speech and Signal Processing (ICASSP2005).
[2] Xiaoan Lu, David Goodman, Yao Wang and Elza Erkip, Complexity-bounded Power Control in Video Transmission over a CDMA Wireless Network, To be presented at IEEE Globecom 2004 Conference.
[3] Xiaoan Lu, Yao Wang, Elza Erkip and David Goodman, Power Optimization of Source Encoding and Radio Transmission in Multiuser CDMA Systems, in Proceedings of 2004 International Conference on Communications (ICC), Vol. 5, pp. 3106-3110, June, 2004.
[4] Xiaoan Lu, Thierry Fernaine, Yao Wang, Modelling Power Consumption for H.263 Video Coding, in Proceedings of IEEE International Symposium on Circuits and Systems (ISCAS), Vol. 2, pp. 77-80, 2004.
[5] Xiaoan Lu, Elza Erkip, Yao Wang and David Goodman, Power efficient multimedia communication over wireless channels, IEEE Journal on Selected Areas on Communications, Special Issue on Recent Advances in Wireless Multimedia, Vol. 21, No. 10, pp. 1738-1751, Dec., 2003.
[6] Xiaoan Lu, Yao Wang and Elza Erkip, Power efficient H.263 video transmission over wireless channels, in Proceedings of 2002 International Conference on Image Processing (ICIP), Vol. 1, pp. 533-536, September 2002.
[7] Elza Erkip, Xiaoan Lu, Yao Wang, David Goodman, Total power optimization for wireless multimedia communication, in System Level Power Optimization for Wireless Multimedia Communication: Power Aware Computing, edited by R. Karri and D. Goodman, Chapter 1, Kluwer Academic Publishers, 2002.
[8] Elza Erkip, Yao Wang, David Goodman, Yuantao Wu and Xiaoan Lu, Energy efficient coding and transmission, in Proceedings of IEEE Vehicular Technology Conference (VTC), Vol. 2, pp. 1444-1448, Spring 2001, May 2001.
Network X-ities: Foundations and Applications
Given society's increasing reliance on communication networks such as the Internet, it is becoming increasingly important that these networks not only provide good performance, but do so in the face of a complex, uncertain, error-prone, and ever-changing environment. The need for such robust network operation leads to a set of design considerations that we refer to as the network X-ities (since they all end in ``ity''): non-fragility, manageability, diagnosability, optimizability, scalability, and evolvability. Although these X-ities are crucially important in designing and analyzing robust networks and protocols, they often lack theoretical foundations, quantitative frameworks, or even well-defined metrics and meaning. The goal of this research project is to begin to build a solid, quantitative foundation for explicitly considering the X-ities in the design and analysis of network architectures and protocols. We do so by considering a number of specific problems, broadly in the area of routing protocols, that allow us to concretely address several of the X-ities and to begin to draw larger lessons from commonalities among the problems studied. We also plan to apply our results in the context of two ongoing system-building projects to demonstrate the value of our research in guiding design decisions in a practical setting.
In studying non-fragility---the goal of operating a network under a wide range of conditions---we quantify this X-ity in the routing context in terms of routing stability, and the trade-off in data-plane performance between the case in which routing is narrowly optimized (but may provide catastrophically bad performance when operating outside of normal operating conditions) and the case in which it is optimized to perform well over a wide range of operating conditions. We focus on specific problems posed by various interacting layers of control (e.g., overlay/underlay routing, transport/network layer, intra/inter-domain routing) and uncertainty (whether in traffic demands or as a result of element failure) in the operating environment. In studying manageability---the ability for network operators to easily configure routing protocols, diagnose (and fix) persistent problems, and control the evolution of the network infrastructure---we consider challenges posed by couplings between intra-domain routing and egress-point selection, root cause identification for routing changes and the trade-off between routing protocol overhead and diagnostic precision, and optimally deploying a network's physical infrastructure over a multi-step time horizon. Finally, in the area of scalability, we consider the trade-offs between a routing protocol's scalability and the resulting data-plane performance, as well as techniques that can improve scalability with a minimal effect on performance.
Participating Faculty: Yong Liu (yongliu@duke.poly.edu)
Funding Sources: National Science Foundation
Website: http://eeweb.poly.edu/faculty/yongliu
[1] Chun Zhang, Zihui Ge, Jim Kurose, Yong Liu, and Don Towsley, "Optimal Routing with Multiple Traffic Matrices: Tradeoff between Average Case and Worst Case Performance", in the 13th IEEE International Conference on Network Protocols (ICNP'2005)
[2] Chun Zhang, Yong Liu, Weibo Gong, Jim Kurose, Robert Moll and Don Towsley, "On Optimal Routing with Multiple Traffic Matrices", in the Proceedings of IEEE Conference on Computer and Communications (INFOCOM) 2005。
Analysis and Design of Overlay and Peer-Peer Networks
Application-level networks, such as overlay and peer-peer networks, have recently emerged as a new paradigm for building distributed networked applications. Application-level control can be used to overcome deficiencies or improve the performance of existing underlay networks. For example, traditional network congestion control and routing schemes are generally unable to fully utilize available network resources for high-bandwidth data transport. In [1], we explored the flexibility of control at the application layer and proposed various application-level data relay schemes to significantly improve network users' throughput by optimally integrating application-level routing and transport-layer control. The proposed algorithms can be easily adopted by data intensive applications, such as grid-computing and content distribution, to achieve high speed data transport over wide area networks. We are also investigating how to design a relay network to efficiently support new end-end applications, such as voice-over-IP and video conferencing.
While overlay networks improve the performance perceived by overlay users, a fundamentally important question is to understand how overlay networks might affect the operation of underlay networks. In [2, 3], we systematically studied the interac |
