@article{
  author = {M. Petermann and M. Stefer and F. Ludwig and D. W\"{u}bben and M. Schneider and S. Paul and K.-D. Kammeyer},
  year = {2013},
  month = {Sep},
  title = {Multi-User Pre-Processing in Multi-Antenna OFDM TDD Systems with Non-Reciprocal Transceivers},
  volume = {61},
  number = {9},
  pages = {3781-3793},
  URL = {http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6573241&queryText%3DMulti-User+Pre-Processing+in+Multi-Antenna+OFDM+TDD+Systems+with+Non-Reciprocal+Transceivers},
  abstract={The    combination    of    OFDM    with    joint    pre-processing  in  adaptive  multi-antenna  systems  offers  both  an ease of equalization in frequency-selective channels and keepingthe  signal  processing  at  the  mobile  stations  simple.  In  addition, the   spatial   dimension   can   be   efficiently   exploited   to   ensure high  system  throughput.  With  the  utilization  of  higher-order modulation  the performance  of  the system  is  highly sensitive to multiple access interference and nonorthogonal subchannels due to hardware impairments or insufficient adaptation to the current channel  conditions.  A  further  source  of  error  in  TDD  systems are  the  non-reciprocal  transceivers  inhibiting  the  baseband-to-baseband channel reciprocity required for accurate channel state acquisition based on  the uplink channel estimate. In  this paper, measurement  results  of  a  low-cost  hardware-based  calibration are  presented  and  the  drawbacks  are  discussed  leading  to  the utilization  of   a  recently   introduced  relative   calibration.   The latter  is  applied  to  an  OFDM  system  and  achieves  or  at  leastapproximates   the   baseband-to-baseband   reciprocity.   Thus,   it enables  the  link  adaptation  using  the  uplink  channel  state  in-formation. Furthermore, preliminary hardware implementations of  the  relative  calibration  running  on  a  real-time  system  show accurate  results.
},
  journal={IEEE Transactions on Communications}
}