DCA Algorithms and MAC Protocols for COFDM Based Cellular and Ad hoc Systems Using Carrier Sensing Time Division Multiple Access (CSTDMA)

• Applicant: Professor Dr. Harald Haas
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2004 to 2008
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5425901

• Final Report Year: 2007

Final Report Abstract

The TDD underlay concept, which can be considered as a cognitive radio system, has been comprehensively studied in this project. The fundamental issues and limitations regarding the concept have been highlighted. An initial system-level study has then been carried out by applying the TDD underlay concept to a WCDMA system in which the users are distributed in clusters. The issues of inter-cluster interference and more importantly, the bottleneck present on the BS-GM link have not been considered in this study. Also, the FDD-TDD SP was fixed in this study therefore allowing the system to support a static asymmetry. Next, the problem of finding the optimum position of the FDD-TDD SP is looked into, and a respective model has been developed assuming different traffic asymmetry distributions. Since the GM-BS link has been identified as the bottleneck for achieving higher throughput, a further investigation aimed at characterizing and identifying such GMs has been conducted. In this context, the probability is determined of a node being connected to k other nodes (such a node is known as a star-node) which are uniformly distributed in a circle with path losses that fall below a threshold, with the level of which being set as a parameter. In order to find such a probability, the pdf of path loss distribution for uniformly distributed nodes in a circle must be known. This has been derived and confirmed through simulations. The theory of random graphs is used to find the desired probabilities. This has also been done and confirmed through simulations. Using this theory, the probability of detecting N clusters (the presence of a star-node denotes the presence of a cluster) from n uniformly distributed users in a circle has also been derived. The obtained result can further be useful if one wishes to study the probability of a completely autonomous network forming clusters. Finally, a full system-level simulation of an OFDMA-TDD system using the TDD underlay concept is carried out. This is done based on the WINNER air interface in keeping with the envisaged heavy traffic demands of users in future generation systems. Realistic, frequency-selective channels are simulated. In this case, inter-cluster interference has been considered and it has been found to be extremely harmful given that the frequency reuse factor for intra-cluster communication is one and that cluster-merging is not done. This simulation has opened up several possible avenues of research. On the one hand, it is envisaged that the gain in capacity over the benchmark can be further enhanced. This can be done by modifying the frame structure such that in the DL band, communication between the BS and the individual MSs and part of the UL band is also used for DL communication between the GM and its MSs (the GM transmits buffered data to the MS in this part of the frame) and the rest of the frame is used for UL traffic between the MSs and the BS through the GM. On the other hand, if intra cluster traffic is exploited, which can typically be the case in indoor scenarios such as ”Home NodeB” deployments, the gain in spectral efficiency is up to a factor 7 due to the high frequency reuse. Another area of research must be devoted to reducing inter-cluster interference. Clearly introducing orthogonality between the clusters either by introducing orthogonal codes or powerful interference cancelation techniques (when the interferer is strong) or by using FDMA will reduce inter-cluster interference. Another method to reduce this form of interference is to merge clusters that are very close to one another. However, this adaptation will require changes in the frame structure to support cluster with varying numbers of users.

Publications

• “Effects of user distributions on CDMA system performance,”. In: 16th International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2005. vol. 3, pp. 1652 - 1656, September 2005
  P. K. Jain and H. Haas
  
• “Performance analysis for hybrid wireless networks,”. In: 16th International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2005. vol. 3, pp. 1742 - 1746, September 2005
  H. Venkataraman, H. Haas, Y. Lee, S. Yun and S. McLaughlin
  
• “Capacity Enhancement Using Ad Hoc Pico-Cells and TDD Underlay,”. In: Proceedings of the 17th International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2006. Helsinki, Finland: IEEE, 5 pages on CD ROM, September 2006
  P. Jain, H. Haas, and S. McLaughlin
  
• “Throughput Capacity for 2-Hop Hybrid Cellular Networks,”. In: Proceedings of 6th Scandinavian Workshop on Wireless Ad-hoc Networks (ADHOC ’06), 2006. Stockholm, Sweden: May 2006
  H. Venkataraman and H. Haas
  
• “Performance Analysis of Multihop Ad hoc and Hybrid Wireless Networks,”. Dissertation, September 2007
  H. Venkataraman
  
• “Time Slot Partitioning and Random Data Hopping for Multihop Wireless Networks,”. In: IEEE 65th Vehicular Technology Conference (VTC2007-Spring). Dublin, Ireland: IEEE, vol. 3, pp. 1742 - 1746, April 2007
  H. Venkataraman, A. Mudesir, S. Sinanovic and H. Haas
  
• “Variation of Spatial Protection Margins on Multihop Wireless Networks,”. In: 18th International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2007. Athens, Greece: IEEE, September 2007
  H. Venkataraman, S. Sinanovic, and H. Haas