Equal-Gain Precoders for Closed Loop MIMO Transmission
Document Number: S802.16m-08/309r2
Date Submitted: 2008-05-13
Source:
Yu-Tao Hsieh, Cheng-Ming Chen, Chien-Yu Kao,
Chao-Wang Huang, Pang-An Ting, Richard Li
ITRI
Email: ythsieh@itri.org.tw
Shang-Ho Tsai
NCTU
Venue:
IEEE 802.16m-08/005 “Call for Contributions on Project 802.16m System Description Document (SDD)”, In response to the following
topics: “DL MIMO”
Purpose:
To be discussed and adopted by TGm for the 802.16m SDD.
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1
Equal-gain precoders
 This contribution presents an equal-gain precoder for DL
MIMO
 Conventional MIMO feedback mechanism
 UL sounding
 Quantized channel
 Precoding matrix index
j
1
-1
 Equal-gain precoder
 Feedback with matrix index
 Much less codebook storage than existing codebook
 Phase rotation operation is easier than complex-valued operations
-j
Block diagram of DL MIMO
 f is the precoder with g the matching post-coder
• f is Nt x Ns with elements be the constellation points
on the unit circle
 Feedback of the first element can be saved due to
normalization
Simulation results
• Compared precoders
– STBC without precoding, EG, Grassmannian [1], and SVD
• Nt=2, Ns=1. Nr=1 or 2
• Total feedback numbers are the same (2 bits)
[1] http://cobweb.ecn.purdue.edu/djlove/grass
Simulation results
• Compared precoders
– AS, EG, Grassmannian [1], and SVD
• Nt=4, Ns=1. Nr=1 or 2
• Total feedback numbers are the same (6 bits)
Summary
• EG precoder provides comparable performance to
Grassmannian precoder under equal quantization bit
numbers (2 and 6 bits)
• Elements in EG precoder is easier to be stored and
manipulated
Proposed texts
11.x DL MIMO schemes
11.x.y DL MIMO Precoding
In the precoding MIMO schemes, the equal-gain precoder with
equi-spaced constellations can be taken into consideration for
improving the system performance while decreasing the
feedback overhead.