A Channel Estimation Method for MIMO-OFDM Systems
Jiun Siew, Robert Piechocki, Andrew Nix, and Simon Armour
Centre for Communications Research, University of Bristol
Abstract: This paper proposes a simple and efficient method for MIMO-OFDM channel
estimation using parameters similar to HIPERLAN/2. Both preamble and pilot structures
are compared in a 2 transmit-2 receive Space Frequency Trellis Coded system and the Mean
Squared Error is used as a metric for comparing the results. It is shown, via simulation, that
the proposed methods incur a maximum loss of approximately 1 to 1.5dB as compared to
perfect channel knowledge.
1 Introduction
Channel estimates for Multiple Input Multiple Ouput-Orthogonal Frequency Division Multiplexing (MIMO-
OFDM) systems can be obtained by transmitting a training sequence from one antenna at a time while
the remaining transmit antennas are idle. This method, however, becomes inefficient when the number
of transmit antennas are large.
In this paper, we extend the channel estimation technique proposed in [1] to a MIMO system. Firstly,
a brief description of the method used in [1] is provided in Section 2. Section 3 extends this technique
to a MIMO system and proposes two specific methods for channel estimation. A 2 transmit-2 receive
antenna system is examined as an example in Section 4. Simulation results for channel estimates, the
Mean Squared Error (MSE), and the system performance of this technique when combined with trellis
codes are shown in Section 5. Finally, Section 6 draws several conclusions from these results.
2 Iterative Channel Estimation Algorithm
In [1] a hardware efficient algorithm shows how the frequency response of null subcarriers can be inter-
polated by exploiting the frequency correlation of limited time excess delay channels. The algorithm is
briefly described as follows:
1. Obtain initial channel estimate (typically performed using the Least Squares (LS) method).
2. Convert channel estimate to the Time Domain (TD) and window significant taps.
3. Convert this TD signal back to the frequency domain.
4. Replace the values of the known subcarriers with the initial estimate in step 1 (ignore this step for
the last iteration).
5. Repeat steps 2-4.
Although the original application for this technique was single antenna IEEE 802.11a systems, it can
be easily extended to MIMO systems. Consider a MIMO-OFDM system with M transmit, N receive
antennas, and K subcarriers. Let c
m,k
be a pilot symbol transmitted from antenna m for subcarrier k.
The received signal at receive antenna n canbemodelledas:
r
n,k
=
m
i=1
h
n,m,k
c
m,k
+ η
n,k
(1)
where h
n,m,k
is the frequency response of subcarrier k between transmit antenna m and receive antenna
n,andη
n,k
represents additive white Gaussian noise with zero mean and variance
σ
2
n
2
per dimension.
Hence, the received symbol at each receive antenna is a linear combination of transmitted symbols that
are modified by channel gains and noise.
1
资源评论
