PHY-MAC Optimization for Beyond LTE Systems


Consider the downlink of cellular multi-user MIMO OFDM systems, users may be scheduled to the transmission resources defined over time, frequency and space. Targeting a practical solution, we assume the use of fixed DFT-based pre-coding beams at the base stations and linear receivers at the multi-antenna terminals. After having received feedback on the frequency-selective interference conditions from all terminals, each base station schedules the terminals to their resources of highest quality while following a fair scheduling policy. It is shown that this rather simple practical concept enables spatial multiplexing transmission for all users in the system, in particular even for users at cell edge. This results in a capacity scaling of MIMO systems, similar to the one known for isolated point-to-point links.

Key relations for efficient transmission in practice

  • MU-MIMO using static DFT-based beamforming, which ensures predictable interference
  • Synchronized downlink from all BSs, w.r.t. carrier frequency and frame start, to enable sufficiently precise channel estimation (serving and interfering BSs)
  • MMSE equalization at mobile terminals for interference suppression
  • Interference-aware scheduling with fairness constraints

⇒ multi-user selection diversity allows to flatten the effective point-to-multi-point channel with a relatively high SINR level

Multi-Cell Performance Evaluation


  • L. Thiele, M. Schellmann, T. Wirth, and V. Jungnickel, "Interference-Aware Scheduling in the Synchronous Cellular Multi-Antenna Downlink", IEEE 69th Vehicular Technology Conference VTC2009-Spring, Barcelona, Spain, Apr. 2009, invited.
  • M. Schellmann, L. Thiele, T. Haustein, and V. Jungnickel, "Spatial transmission mode switching in multi-user MIMO-OFDM systems with user fairness", IEEE Transactions on Vehicular Technology, 2009, accepted.
  • L. Thiele, M. Schellmann, S. Schiffermüller, V. Jungnickel, and W. Zirwas, "Multi-Cell Channel Estimation using Virtual Pilots", IEEE 67th Vehicular Technology Conference VTC2008-Spring, Singapore, May 2008.
  • V. Jungnickel and T. Wirth and M. Schellmann and T. Haustein and W. Zirwas, "Synchronization of Cooperative Base Stations", IEEE International Symposium on Wireless Communication Systems 2008 (ISWCS2008), 2008