CSIApx: A Fast and
Lightweight CSI Compression Algorithm |
We propose CSIApx, a
very fast and lightweight method to compress the CSI of Wi-Fi networks. CSIApx is based on our finding that any sinusoid can be
approximated very well by a set of base sinusoids on constant frequencies.
In
Wi-Fi, the CSI for an antenna pair is a vector of complex numbers, representing
the channel coefficients of the OFDM subcarriers. The CSI is needed to
calculate the modulation parameters for techniques such as Multi-User
Multiple-Input-Multiple-Output (MU-MIMO). In Wi-Fi, the CSI is typically
measured at the receiver and is transmitted back to the sender, which requires
significant overhead. For example, on a 20 MHz channel with 64 subcarriers, the
full CSI for a single antenna pair has 64 complex numbers, and for 9 antenna
pairs, 576. Although Wi-Fi does not use all subcarriers, the feedback for 9
antenna pairs still may exceed 1000 bytes. The Wi-Fi standard defines options
to compress the CSI, such as reducing the quantization accuracy or the number
of subcarriers in the feedback, or using the Given's rotation on the V matrix
after the Singular Value Decomposition (SVD) of the CSI matrix. However, these
methods either reduce the accuracy of the CSI, or only achieve modest
compression ratios. For example, a 3 by 3 complex V matrix can only be
compressed into 6 real numbers, at a compression ratio of 3.
CSIApx approximates the CSI vector as
the linear combination of a small number of base sinusoids on constant frequencies, and uses the complex
coefficients of the base sinusoids as the compressed CSI. While it is
well-known that the CSI vector can be represented as the linear combination of
sinusoids, fixing the frequencies of the sinusoids is the key novelty of
CSIApx, which is guided by our mathematical finding that almost any sinusoid
can be approximated by a set of base sinusoids on constant frequencies. CSIApx
enjoys very low computation complexity, because key steps in the compression
can be pre-computed due to the constant frequencies of the base sinusoids. We
extensively test CSIApx with both experimental and synthesized Wi-Fi channel
data, and the results confirm that CSIApx can achieve very good compression
ratio with little loss of accuracy.
Publication:
Patent:
·
USPN Patent 9,838,104,
“System and method
for fast compression of OFDM channel state information (CSI) based on constant
frequency sinusoidal approximation,” issued on December 5, 2017.