15 research outputs found
Signature Quantization in Fading CDMA With Limited Feedback
In this work, we analyze the performance of a signature quantization scheme
for reverse-link Direct Sequence (DS)- Code Division Multiple Access (CDMA).
Assuming perfect estimates of the channel and interference covariance, the
receiver selects the signature that minimizes interference power or maximizes
signal-to-interference plus noise ratio (SINR) for a desired user from a
signature codebook. The codebook index corresponding to the optimal signature
is then relayed to the user with a finite number of bits via a feedback
channel. Here we are interested in the performance of a Random Vector
Quantization (RVQ) codebook, which contains independent isotropically
distributed vectors. Assuming arbitrary transmit power allocation, we consider
additive white Gaussian noise (AWGN) channel first with no fading and
subsequently, with multipath fading. We derive the corresponding SINR in a
large system limit at the output of matched filter and linear minimum mean
squared error (MMSE) receiver. Numerical examples show that the derived large
system results give a good approximation to the performance of finite-size
system and that the MMSE receiver achieves close to a single-user performance
with only one feedback bit per signature element
Joint Wireless Information and Energy Transfer with Reduced Feedback in MIMO Interference Channels
To determine the transmission strategy for joint wireless information and
energy transfer (JWIET) in the MIMO interference channel (IFC), the information
access point (IAP) and energy access point (EAP) require the channel state
information (CSI) of their associated links to both the information-decoding
(ID) mobile stations (MSs) and energy-harvesting (EH) MSs (so-called local
CSI). In this paper, to reduce th e feedback overhead of MSs for the JWIET in
two-user MIMO IFC, we propose a Geodesic energy beamforming scheme that
requires partial CSI at the EAP. Furthermore, in the two-user MIMO IFC, it is
proved that the Geodesic energy beamforming is the optimal strategy. By adding
a rank-one constraint on the transmit signal covariance of IAP, we can further
reduce the feedback overhead to IAP by exploiting Geodesic information
beamforming. Under the rank-one constraint of IAP's transmit signal, we prove
that Geodesic information/energy beamforming approach is the optimal strategy
for JWIET in the two-user MIMO IFC. We also discuss the extension of the
proposed rank-one Geodesic information/energy beamforming strategies to general
K-user MIMO IFC. Finally, by analyzing the achievable rate-energy performance
statistically under imperfect partial CSIT, we propose an adaptive bit
allocation strategy for both EH MS and ID MS.Comment: accepted to IEEE Journal of Selected Areas in Communications (IEEE
JSAC), Special Issue on Wireless Communications Powered by Energy Harvesting
and Wireless Energy Transfe
Using Channel Output Feedback to Increase Throughput in Hybrid-ARQ
Hybrid-ARQ protocols have become common in many packet transmission systems
due to their incorporation in various standards. Hybrid-ARQ combines the normal
automatic repeat request (ARQ) method with error correction codes to increase
reliability and throughput. In this paper, we look at improving upon this
performance using feedback information from the receiver, in particular, using
a powerful forward error correction (FEC) code in conjunction with a proposed
linear feedback code for the Rayleigh block fading channels. The new hybrid-ARQ
scheme is initially developed for full received packet feedback in a
point-to-point link. It is then extended to various different multiple-antenna
scenarios (MISO/MIMO) with varying amounts of packet feedback information.
Simulations illustrate gains in throughput.Comment: 30 page