258 research outputs found
Bit Allocation Law for Multi-Antenna Channel Feedback Quantization: Single-User Case
This paper studies the design and optimization of a limited feedback
single-user system with multiple-antenna transmitter and single-antenna
receiver. The design problem is cast in form of the minimizing the average
transmission power at the base station subject to the user's outage probability
constraint. The optimization is over the user's channel quantization codebook
and the transmission power control function at the base station. Our approach
is based on fixing the outage scenarios in advance and transforming the design
problem into a robust system design problem. We start by showing that uniformly
quantizing the channel magnitude in dB scale is asymptotically optimal,
regardless of the magnitude distribution function. We derive the optimal
uniform (in dB) channel magnitude codebook and combine it with a spatially
uniform channel direction codebook to arrive at a product channel quantization
codebook. We then optimize such a product structure in the asymptotic regime of
, where is the total number of quantization feedback
bits. The paper shows that for channels in the real space, the asymptotically
optimal number of direction quantization bits should be times
the number of magnitude quantization bits, where is the number of base
station antennas. We also show that the performance of the designed system
approaches the performance of the perfect channel state information system as
. For complex channels, the number of magnitude and
direction quantization bits are related by a factor of and the system
performance scales as as .Comment: Submitted to IEEE Transactions on Signal Processing, March 201
Interleaving Channel Estimation and Limited Feedback for Point-to-Point Systems with a Large Number of Transmit Antennas
We introduce and investigate the opportunities of multi-antenna communication
schemes whose training and feedback stages are interleaved and mutually
interacting. Specifically, unlike the traditional schemes where the transmitter
first trains all of its antennas at once and then receives a single feedback
message, we consider a scenario where the transmitter instead trains its
antennas one by one and receives feedback information immediately after
training each one of its antennas. The feedback message may ask the transmitter
to train another antenna; or, it may terminate the feedback/training phase and
provide the quantized codeword (e.g., a beamforming vector) to be utilized for
data transmission. As a specific application, we consider a multiple-input
single-output system with transmit antennas, a short-term power constraint
, and target data rate . We show that for any , the same outage
probability as a system with perfect transmitter and receiver channel state
information can be achieved with a feedback rate of bits per channel
state and via training transmit antennas on average, where and
are independent of , and depend only on and . In addition,
we design variable-rate quantizers for channel coefficients to further minimize
the feedback rate of our scheme.Comment: To appear in IEEE Transactions on Wireless Communication
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