164 research outputs found
On the Fundamental Feedback-vs-Performance Tradeoff over the MISO-BC with Imperfect and Delayed CSIT
This work considers the multiuser multiple-input single-output (MISO)
broadcast channel (BC), where a transmitter with M antennas transmits
information to K single-antenna users, and where - as expected - the quality
and timeliness of channel state information at the transmitter (CSIT) is
imperfect. Motivated by the fundamental question of how much feedback is
necessary to achieve a certain performance, this work seeks to establish bounds
on the tradeoff between degrees-of-freedom (DoF) performance and CSIT feedback
quality. Specifically, this work provides a novel DoF region outer bound for
the general K-user MISO BC with partial current CSIT, which naturally bridges
the gap between the case of having no current CSIT (only delayed CSIT, or no
CSIT) and the case with full CSIT. The work then characterizes the minimum CSIT
feedback that is necessary for any point of the sum DoF, which is optimal for
the case with M >= K, and the case with M=2, K=3.Comment: An initial version of this paper has been reported as Research Report
No. RR-12-275 at EURECOM, December 7, 2012. This paper was submitted in part
to the ISIT 201
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
GDoF of the MISO BC: Bridging the gap between finite precision CSIT and perfect CSIT
This work bridges the gap between sharply contrasting results on the degrees of freedom of the K user broadcast channel where the transmitter is equipped with K transmit antennas and each of the K receivers is equipped with a single antenna. This channel has K DoF when channel state information at the transmitter (CSIT) is perfect, but as shown recently, it has only 1 DoF when the CSIT is limited to finite precision. By considering the full range of partial CSIT assumptions parameterized by β ⋯ [0,1], such that the strength of the channel estimation error terms scales as ∼ SNR-β relative to the channel strengths which scale as ∼ SNR, it is shown that this channel has 1 - β + Kβ DoF. For K = 2 users with arbitrary βij parameters, the DoF are shown to be 1 + mini,j βij. To explore diversity of channel strengths, the results are further extended to the symmetric Generalized Degrees of Freedom setting where the direct channel strengths scale as ∼ SNR and the cross channel strengths scale as ∼ SNRα, α ⋯ [0,1], β ⋯ [0,α]. Here, the roles of α and β are shown to counter each other on equal terms, so that the sum GDoF value in the K user setting is (α - β) + K(1 - (α-β )) and for the 2 user setting with arbitrary βij, is 2 - α + mini,j βij
Generalized Degrees of Freedom of the Symmetric Cache-Aided MISO Broadcast Channel with Partial CSIT
We consider the cache-aided MISO broadcast channel (BC) in which a
multi-antenna transmitter serves single-antenna receivers, each equipped
with a cache memory. The transmitter has access to partial knowledge of the
channel state information. For a symmetric setting, in terms of channel
strength levels, partial channel knowledge levels and cache sizes, we
characterize the generalized degrees of freedom (GDoF) up to a constant
multiplicative factor. The achievability scheme exploits the interplay between
spatial multiplexing gains and coded-multicasting gain. On the other hand, a
cut-set-based argument in conjunction with a GDoF outer bound for a parallel
MISO BC under channel uncertainty are used for the converse. We further show
that the characterized order-optimal GDoF is also attained in a decentralized
setting, where no coordination is required for content placement in the caches.Comment: first revisio
Retroactive Anti-Jamming for MISO Broadcast Channels
Jamming attacks can significantly impact the performance of wireless
communication systems. In addition to reducing the capacity, such attacks may
lead to insurmountable overhead in terms of re-transmissions and increased
power consumption. In this paper, we consider the multiple-input single-output
(MISO) broadcast channel (BC) in the presence of a jamming attack in which a
subset of the receivers can be jammed at any given time. Further,
countermeasures for mitigating the effects of such jamming attacks are
presented. The effectiveness of these anti-jamming countermeasures is
quantified in terms of the degrees-of-freedom (DoF) of the MISO BC under
various assumptions regarding the availability of the channel state information
(CSIT) and the jammer state information at the transmitter (JSIT). The main
contribution of this paper is the characterization of the DoF region of the two
user MISO BC under various assumptions on the availability of CSIT and JSIT.
Partial extensions to the multi-user broadcast channels are also presented.Comment: submitted to IEEE Transactions on Information Theor
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