Uppsala universitet

Reuse Within a Cell - Interference Rejection or Multiuser Detection?

Claes Tidestav , Mikael Sternad and Anders Ahlén

IEEE Vehicular Technology Conference (VTC'99)
Houston, TX, May 16-20, 1999, pp 1618-1622. © 1999 IEEE

In a cellular communication system, multi-element antennas, also known as antenna arrays, can be used at the receiver to increase the capacity. It may even be possible to employ reuse within a cell, i.e. to let several users share each channel in one cell. In this paper, we illustrate, compare and explore two ways of using an antenna array at the receiver to accomplish channel reuse within a cell:
  • Detect data from one user at a time while treating the other users as interference. This approach is denoted interference rejection or interference cancellation .
  • Detect the data from several of all users simultaneously. We call this method multiuser detection.

The performance of (nonlinear) multiuser detectors mostly turns out to be superior to that of interference cancellers, for two reasons:

  • They can suppress interference more efficiently than non-linear interference cancellers.
  • The channel estimation is improved, which leads to more precise tuning of the detector.

We illustrate the influence of these two factors by comparing two types of minimum mean square error-optimal decision feedback equalizers (MMSE DFE:s) in FDMA/TDMA systems.

We investigate the use of an antenna array at the receiver in FDMA/TDMA systems, to let several users share one communication channel within a cell. A decision feedback equalizer which simultaneously detects all incoming signals (multiuser detection) is compared to a set of decision feedback equalizers, each detecting one signal and rejecting the remaining as interference.

We also introduce the existence of a zero-forcing solution to the equalization problem as an indicator of near-far resistance of different detector structures.

Simulations indicate that multiuser detection in general provides better performance than interference rejection. We have applied the proposed algorithms to experimental measurements from a DCS-1800 antenna array testbed. The results from these experiments confirm that reuse within a cell is indeed possible using an eight-element array antenna at the receiver.

Related publications:
PhD Thesis by Claes Tidestav.
IEEE-COM paper and report version, with derivations and measurements.
ICASSP'99 paper on MIMO IIR DFE's.
ICUPC'98 paper on bootstrap equalization.
ICUPC'96 paper on MIMO DFE's as CDMA multiuser detectors.

Paper in Pdf, 415K.
Presentation slides in Pdf.

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