31-01-2013, 09:41 AM
SINR Degradation in MIMO-OFDM Systems with Channel Estimation Errors and Partial Phase Noise Compensation
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Abstract
The phase noise effect in multiple-input-multipleoutput
systems employing orthogonal frequency division multiplexing
is considered in a realistic scenario where the estimated
channel matrix is affected by an error. The analytical SINR
degradation due to phase noise and channel estimation is
obtained for linear receivers (ZF and MMSE).
INTRODUCTION
ORTHOGONAL Frequency Division Multiplexing
(OFDM) is becoming the most frequently used
technique for wireless systems, such as Long Term Evolution
(LTE), and enhanced standards are contemplating its
combination with multiple input-multiple output (MIMO).
These systems suffer from inter-channel interference (ICI)
introduced by phase noise and channel estimation errors. In
most of the works these impairments are treated separately
[1]–[4]: with ICI reduction schemes assuming perfect channel
knowledge or analyzing the channel estimation error without
phase noise. In [1] a scheme is proposed to remove the
common phase error (CPE) and in [3] an iterative technique
is presented to cancel successively the ICI terms, both
assuming ideal channel estimation. In [2] the ICI power is
obtained for zero-forcing (ZF) with ideal channel estimation
by a first-order approximation of the phase noise term.
The channel estimation error is analyzed in [4] for ZF, in
flat fading, without phase noise. In [5]–[7] the effects are
considered jointly for SISO-OFDM. The combination of
MIMO with OFDM introduces the spatial dimension that
causes additional interference.
PERFORMANCE RESULTS
To validate the above expressions, we show some results
with N = 64 sub-carriers and, without loss of generality, the
same variance of the estimation error on the channel and on the
CPE. First, we present the case of independent
fading among the sub-carriers and Wiener phase noise, to
compare our analytic approach with simulations and with [2].
The curves of the ICI power vs. Bθ of Fig. 2 show a very
good matching, although the first order approximation of [2]
is slightly optimistic. Note that the assumption of independent
fading in sub-carriers is an idealization analyzed here just to
compare with [2].
CONCLUSIONS
We derived the expression of the SINR degradation in linear
receivers for MIMO-OFDM, considering both the channel
estimation error and the phase noise, with partial CPE compensation.
The accuracy of the expressions has been compared
to previously published works and verified with simulation
results.