399 research outputs found
On the MISO Channel with Feedback: Can Infinitely Massive Antennas Achieve Infinite Capacity?
We consider communication over a multiple-input single-output (MISO) block
fading channel in the presence of an independent noiseless feedback link. We
assume that the transmitter and receiver have no prior knowledge of the channel
state realizations, but the transmitter and receiver can acquire the channel
state information (CSIT/CSIR) via downlink training and feedback. For this
channel, we show that increasing the number of transmit antennas to infinity
will not achieve an infinite capacity, for a finite channel coherence length
and a finite input constraint on the second or fourth moment. This insight
follows from our new capacity bounds that hold for any linear and nonlinear
coding strategies, and any channel training schemes. In addition to the channel
capacity bounds, we also provide a characterization on the beamforming gain
that is also known as array gain or power gain, at the regime with a large
number of antennas.Comment: This work has been submitted to the IEEE Transactions on Information
Theory. It was presented in part at ISIT201
MISO Broadcast Channel with Delayed and Evolving CSIT
The work considers the two-user MISO broadcast channel with gradual and
delayed accumulation of channel state information at the transmitter (CSIT),
and addresses the question of how much feedback is necessary, and when, in
order to achieve a certain degrees-of-freedom (DoF) performance. Motivated by
limited-capacity feedback links that may not immediately convey perfect CSIT,
and focusing on the block fading scenario, we consider a progressively
increasing CSIT quality as time progresses across the coherence period (T
channel uses - evolving current CSIT), or at any time after (delayed CSIT).
Specifically, for any set of feedback quality exponents a_t, t=1,...,T,
describing the high-SNR rates-of-decay of the mean square error of the current
CSIT estimates at time t<=T (during the coherence period), the work describes
the optimal DOF region in several different evolving CSIT settings, including
the setting with perfect delayed CSIT, the asymmetric setting where the quality
of feedback differs from user to user, as well as considers the DoF region in
the presence of a imperfect delayed CSIT corresponding to having a limited
number of overall feedback bits. These results are supported by novel
multi-phase precoding schemes that utilize gradually improving CSIT.
The approach here naturally incorporates different settings such as the
perfect-delayed CSIT setting of Maddah-Ali and Tse, the imperfect current CSIT
setting of Yang et al. and of Gou and Jafar, the asymmetric setting of Maleki
et al., as well as the not-so-delayed CSIT setting of Lee and Heath.Comment: Submitted to Transactions on Information Theory - November 2012 18
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Optimal DoF Region of the Two-User MISO-BC with General Alternating CSIT
In the setting of the time-selective two-user multiple-input single-output
(MISO) broadcast channel (BC), recent work by Tandon et al. considered the case
where - in the presence of error-free delayed channel state information at the
transmitter (delayed CSIT) - the current CSIT for the channel of user 1 and of
user 2, alternate between the two extreme states of perfect current CSIT and of
no current CSIT.
Motivated by the problem of having limited-capacity feedback links which may
not allow for perfect CSIT, as well as by the need to utilize any available
partial CSIT, we here deviate from this `all-or-nothing' approach and proceed -
again in the presence of error-free delayed CSIT - to consider the general
setting where current CSIT now alternates between any two qualities.
Specifically for and denoting the high-SNR asymptotic
rates-of-decay of the mean-square error of the CSIT estimates for the channel
of user~1 and of user~2 respectively, we consider the case where for any two positive current-CSIT quality exponents
. In a fast-fading setting where we consider communication over
any number of coherence periods, and where each CSIT state is present
for a fraction of this total duration, we focus on the
symmetric case of , and derive
the optimal degrees-of-freedom (DoF) region. The result, which is supported by
novel communication protocols, naturally incorporates the aforementioned
`Perfect current' vs. `No current' setting by limiting .
Finally, motivated by recent interest in frequency correlated channels with
unmatched CSIT, we also analyze the setting where there is no delayed CSIT
High dimensional generalized empirical likelihood for moment restrictions with dependent data
This paper considers the maximum generalized empirical likelihood (GEL)
estimation and inference on parameters identified by high dimensional moment
restrictions with weakly dependent data when the dimensions of the moment
restrictions and the parameters diverge along with the sample size. The
consistency with rates and the asymptotic normality of the GEL estimator are
obtained by properly restricting the growth rates of the dimensions of the
parameters and the moment restrictions, as well as the degree of data
dependence. It is shown that even in the high dimensional time series setting,
the GEL ratio can still behave like a chi-square random variable
asymptotically. A consistent test for the over-identification is proposed. A
penalized GEL method is also provided for estimation under sparsity setting
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