Uppsala universitet

Robust Linear Precoder for Coordinated Multipoint Joint Transmission Under Limited Backhaul With Imperfect Channel State Information.

Rikke Apelfröjd and Mikael Sternad , Uppsala University.

IEEE Eleventh International Symposium on Wireless Communication Systems, Barcelona, August 26-29, 2014,
© 2014 IEEE

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Coordinated Multipoint (CoMP) transmission provides high theoretic gains in spectral efficiency, in particular with coherent linear Joint Transmission (JT) to multiple users. However, this requires high backhaul capacity. If the backhaul requirement cannot be met by the system, then CoMP gains decrease as the linear precoder matrix must be adjusted to include zeros.

To minimize the loss of CoMP gains, all elements in the precoder should be adjusted as zeros are added to the precoder. We here propose a low complexity method for adjusting a precoder matrix when some elements are required to be zero, with respect to a robust MSE criterion. This is done by introducing penalties on specific precoder matrix elements. This generalized MSE criterion can then be used as a low complexity tool for optimizing e.g. with respect to sum-rate.

Results show that this does indeed provide a better solution than if zeros are added separately. It is especially beneficial for cell edge users, i.e. for the same users that can gain the most from JT CoMP.

Related publications:
PhD Thesis by Rikke Apelfröjd, April 2018
(of which this is the third contribution paper).

EURASIP JWCN paper 2014 that evaluates on measured channels, without backhaul constraints, and improves performance by using a very simple and appropriate user grouping strategy.

User-centric pre-selection and scheduling for CoMP. (IEEE ISWCS 2014).

Performance Evaluation of Coordinated Multi-Point Transmission Schemes with Predicted CSI (IEEE PIMRC 2012).

Report by Rikke Apelfröjd on Kalman prediction for multipoint OFDM downlink channels, May 2014.

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