386 research outputs found
Sum-Rate Maximization for Linearly Precoded Downlink Multiuser MISO Systems with Partial CSIT: A Rate-Splitting Approach
This paper considers the Sum-Rate (SR) maximization problem in downlink
MU-MISO systems under imperfect Channel State Information at the Transmitter
(CSIT). Contrary to existing works, we consider a rather unorthodox
transmission scheme. In particular, the message intended to one of the users is
split into two parts: a common part which can be recovered by all users, and a
private part recovered by the corresponding user. On the other hand, the rest
of users receive their information through private messages. This
Rate-Splitting (RS) approach was shown to boost the achievable Degrees of
Freedom (DoF) when CSIT errors decay with increased SNR. In this work, the RS
strategy is married with linear precoder design and optimization techniques to
achieve a maximized Ergodic SR (ESR) performance over the entire range of SNRs.
Precoders are designed based on partial CSIT knowledge by solving a stochastic
rate optimization problem using means of Sample Average Approximation (SAA)
coupled with the Weighted Minimum Mean Square Error (WMMSE) approach. Numerical
results show that in addition to the ESR gains, the benefits of RS also include
relaxed CSIT quality requirements and enhanced achievable rate regions compared
to conventional transmission with NoRS.Comment: accepted to IEEE Transactions on Communication
Outage Probability of Multiple-Input Single-Output (MISO) Systems with Delayed Feedback
We investigate the effect of feedback delay on the outage probability of
multiple-input single-output (MISO) fading channels. Channel state information
at the transmitter (CSIT) is a delayed version of the channel state information
available at the receiver (CSIR). We consider two cases of CSIR: (a) perfect
CSIR and (b) CSI estimated at the receiver using training symbols. With perfect
CSIR, under a short-term power constraint, we determine: (a) the outage
probability for beamforming with imperfect CSIT (BF-IC) analytically, and (b)
the optimal spatial power allocation (OSPA) scheme that minimizes outage
numerically. Results show that, for delayed CSIT, BF-IC is close to optimal for
low SNR and uniform spatial power allocation (USPA) is close to optimal at high
SNR. Similarly, under a long-term power constraint, we show that BF-IC is close
to optimal for low SNR and USPA is close to optimal at high SNR. With imperfect
CSIR, we obtain an upper bound on the outage probability with USPA and BF-IC.
Results show that the loss in performance due to imperfection in CSIR is not
significant, if the training power is chosen appropriately.Comment: Submitted to IEEE Transactions on Communications Jan 2007, Revised
Jun 2007, Revised Nov 200
Rate Splitting for MIMO Wireless Networks: A Promising PHY-Layer Strategy for LTE Evolution
MIMO processing plays a central part towards the recent increase in spectral
and energy efficiencies of wireless networks. MIMO has grown beyond the
original point-to-point channel and nowadays refers to a diverse range of
centralized and distributed deployments. The fundamental bottleneck towards
enormous spectral and energy efficiency benefits in multiuser MIMO networks
lies in a huge demand for accurate channel state information at the transmitter
(CSIT). This has become increasingly difficult to satisfy due to the increasing
number of antennas and access points in next generation wireless networks
relying on dense heterogeneous networks and transmitters equipped with a large
number of antennas. CSIT inaccuracy results in a multi-user interference
problem that is the primary bottleneck of MIMO wireless networks. Looking
backward, the problem has been to strive to apply techniques designed for
perfect CSIT to scenarios with imperfect CSIT. In this paper, we depart from
this conventional approach and introduce the readers to a promising strategy
based on rate-splitting. Rate-splitting relies on the transmission of common
and private messages and is shown to provide significant benefits in terms of
spectral and energy efficiencies, reliability and CSI feedback overhead
reduction over conventional strategies used in LTE-A and exclusively relying on
private message transmissions. Open problems, impact on standard specifications
and operational challenges are also discussed.Comment: accepted to IEEE Communication Magazine, special issue on LTE
Evolutio
Cross-layer design for single-cell OFDMA systems with heterogeneous QoS and partial CSIT
Abstract— This paper proposes a novel cross-layer scheduling scheme for a single-cell orthogonal frequency division multiple access (OFDMA) wireless system with partial channel state information (CSI) at transmitter (CSIT) and heterogeneous user delay requirements. Previous research efforts on OFDMA resource allocation are typically based on the availability of perfect CSI or imperfect CSI but with small error variance. Either case consists to typify a non tangible system as the potential facts of channel feedback delay or large channel estimation errors have not been considered. Thus, to attain a more realistic resolution our cross-layer design determines optimal subcarrier and power allocation policies based on partial CSIT and individual user’s quality of service (QoS) requirements. The simulation results show that the proposed cross-layer scheduler can maximize the system’s throughput and at the same time satisfy heterogeneous delay requirements of various users with significant low power consumption
MISO Networks with Imperfect CSIT: A Topological Rate-Splitting Approach
Recently, the Degrees-of-Freedom (DoF) region of multiple-input-single-output
(MISO) networks with imperfect channel state information at the transmitter
(CSIT) has attracted significant attentions. An achievable scheme is known as
rate-splitting (RS) that integrates common-message-multicasting and
private-message-unicasting. In this paper, focusing on the general -cell
MISO IC where the CSIT of each interference link has an arbitrary quality of
imperfectness, we firstly identify the DoF region achieved by RS. Secondly, we
introduce a novel scheme, so called Topological RS (TRS), whose novelties
compared to RS lie in a multi-layer structure and transmitting multiple common
messages to be decoded by groups of users rather than all users. The design of
TRS is motivated by a novel interpretation of the -cell IC with imperfect
CSIT as a weighted-sum of a series of partially connected networks. We show
that the DoF region achieved by TRS covers that achieved by RS. Also, we find
the maximal sum DoF achieved by TRS via hypergraph fractional packing, which
yields the best sum DoF so far. Lastly, for a realistic scenario where each
user is connected to three dominant transmitters, we identify the sufficient
condition where TRS strictly outperforms conventional schemes.Comment: submitted for publicatio
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