7 research outputs found
Multiuser Millimeter Wave Beamforming Strategies with Quantized and Statistical CSIT
To alleviate the high cost of hardware in mmWave systems, hybrid
analog/digital precoding is typically employed. In the conventional two-stage
feedback scheme, the analog beamformer is determined by beam search and
feedback to maximize the desired signal power of each user. The digital
precoder is designed based on quantization and feedback of effective channel to
mitigate multiuser interference. Alternatively, we propose a one-stage feedback
scheme which effectively reduces the complexity of the signalling and feedback
procedure. Specifically, the second-order channel statistics are leveraged to
design digital precoder for interference mitigation while all feedback overhead
is reserved for precise analog beamforming. Under a fixed total feedback
constraint, we investigate the conditions under which the one-stage feedback
scheme outperforms the conventional two-stage counterpart. Moreover, a rate
splitting (RS) transmission strategy is introduced to further tackle the
multiuser interference and enhance the rate performance. Consider (1) RS
precoded by the one-stage feedback scheme and (2) conventional transmission
strategy precoded by the two-stage scheme with the same first-stage feedback as
(1) and also certain amount of extra second-stage feedback. We show that (1)
can achieve a sum rate comparable to that of (2). Hence, RS enables remarkable
saving in the second-stage training and feedback overhead.Comment: submitted to TW
Enforcing Statistical Orthogonality in Massive MIMO Systems via Covariance Shaping
This paper tackles the problem of downlink transmission in massive
multiple-input multiple-output(MIMO) systems where the equipments (UEs) exhibit
high spatial correlation and the channel estimation is limited by strong pilot
contamination. Signal subspace separation among the UEs is, in fact, rarely
realized in practice and is generally beyond the control of the network
designer (as it is dictated by the physical scattering environment). In this
context, we propose a novel statistical beamforming technique, referred to
asMIMO covariance shaping, that exploits multiple antennas at the UEs and
leverages the realistic non-Kronecker structure of massive MIMO channels to
target a suitable shaping of the channel statistics performed at the UE-side.
To optimize the covariance shaping strategies, we propose a low-complexity
block coordinate descent algorithm that is proved to converge to a limit point
of the original nonconvex problem. For the two-UE case, this is shown to
converge to a stationary point of the original problem. Numerical results
illustrate the sum-rate performance gains of the proposed method with respect
to reference scenarios employing the multiple antennas at the UE for spatial
multiplexing.Comment: Submitted for journal publicatio
Achievable Sum DoF of the K-User MIMO Interference Channel with Delayed CSIT
This paper considers a -user multiple-input-multiple-output (MIMO)
interference channel (IC) where 1) the channel state information obtained by
the transmitters (CSIT) is completely outdated, and 2) the number of transmit
antennas at each transmitter, i.e., , is greater than the number of receive
antennas at each user, i.e., . The usefulness of the delayed CSIT was
firstly identified in a -phase Retrospective Interference Alignment (RIA)
scheme proposed by Maddah-Ali et al for the Multiple-Input-Single-Output
Broadcast Channel, but the extension to the MIMO IC is a non-trivial step as
each transmitter only has the message intended for the corresponding user.
Recently, Abdoli et al focused on a Single-Input-Single-Output IC and solved
such bottleneck by inventing a -phase RIA with distributed overheard
interference retransmission. In this paper, we propose two -phase RIA
schemes suitable for the MIMO IC by generalizing and integrating some key
features of both Abdoli's and Maddah-Ali's works. The two schemes jointly yield
the best known sum Degrees-of-Freedom (DoF) performance so far. For the case
, the achieved sum DoF is asymptotically given by
when
Space-Time Encoded MISO Broadcast Channel with Outdated CSIT: An Error Rate and Diversity Performance Analysis
Studies of the MISO Broadcast Channel (BC) with delayed Channel State
Information at the Transmitter (CSIT) have so far focused on the sum-rate and
Degrees-of-Freedom (DoF) region analysis. In this paper, we investigate for the
first time the error rate performance at finite SNR and the
diversity-multiplexing tradeoff (DMT) at infinite SNR of a space-time encoded
transmission over a two-user MISO BC with delayed CSIT. We consider the
so-called MAT protocol obtained by Maddah-Ali and Tse, which was shown to
provide 33% DoF enhancement over TDMA. While the asymptotic DMT analysis shows
that MAT is always preferable to TDMA, the Pairwise Error Probability analysis
at finite SNR shows that MAT is in fact not always a better alternative to
TDMA. Benefits can be obtained over TDMA only at very high rate or once
concatenated with a full-rate full-diversity space-time code. The analysis is
also extended to spatially correlated channels and the influence of transmit
correlation matrices and user pairing strategies on the performance are
discussed. Relying on statistical CSIT, signal constellations are further
optimized to improve the error rate performance of MAT and make it insensitive
to user orthogonality. Finally, other transmission strategies relying on
delayed CSIT are discussed
Achievable sum DoF of the K-user MIMO interference channel with delayed CSIT
This paper considers a K-user multiple-inputmultiple-output (MIMO) interference channel (IC) where 1) the channel state information obtained by the transmitters (CSIT) is completely outdated, and 2) the number of transmit antennas at each transmitter, i.e., M, is greater than the number of receive antennas at each user, i.e., N. The usefulness of the delayed CSIT was firstly identified in a K-phase Retrospective Interference Alignment (RIA) scheme proposed by Maddah-Ali et al for the Multiple-Input-Single-Output Broadcast Channel, but the extension to the MIMO IC is a non-trivial step as each transmitter only has the message intended for the corresponding user. Recently, Abdoli et al focused on a Single-Input-SingleOutput IC and solved such bottleneck by inventing a K-phase RIA with distributed overheard interference retransmission. In this paper, we propose two K-phase RIA schemes suitable for the MIMO IC by generalizing and integrating some key features of both Abdoli’s and Maddah-Ali’s works. The two schemes jointly yield the best known sum Degrees-of-Freedom (DoF) performance so far. For the case M N ≥K, the achieved sum DoF is asymptotically given by 64 15N when K→∞