4 research outputs found
Feedback-Aided Coded Caching for the MISO BC with Small Caches
This work explores coded caching in the symmetric -user cache-aided MISO
BC with imperfect CSIT-type feedback, for the specific case where the cache
size is much smaller than the library size. Building on the recently explored
synergy between caching and delayed-CSIT, and building on the tradeoff between
caching and CSIT quality, the work proposes new schemes that boost the impact
of small caches, focusing on the case where the cumulative cache size is
smaller than the library size. For this small-cache setting, based on the
proposed near-optimal schemes, the work identifies the optimal cache-aided
degrees-of-freedom (DoF) performance within a factor of 4.Comment: 8 pages, 1 figure. arXiv admin note: substantial text overlap with
arXiv:1511.0396
Fundamental Limits of Cache-Aided Wireless BC: Interplay of Coded-Caching and CSIT Feedback
Building on the recent coded-caching breakthrough by Maddah-Ali and Niesen,
the work here considers the -user cache-aided wireless multi-antenna (MISO)
symmetric broadcast channel (BC) with random fading and imperfect feedback, and
analyzes the throughput performance as a function of feedback statistics and
cache size. In this setting, our work identifies the optimal cache-aided
degrees-of-freedom (DoF) within a factor of 4, by identifying near-optimal
schemes that exploit the new synergy between coded caching and delayed CSIT, as
well as by exploiting the unexplored interplay between caching and
feedback-quality. The derived limits interestingly reveal that --- the
combination of imperfect quality current CSIT, delayed CSIT, and coded caching,
guarantees that --- the DoF gains have an initial offset defined by the quality
of current CSIT, and then that the additional gains attributed to coded caching
are exponential, in the sense that any linear decrease in the required DoF
performance, allows for an exponential reduction in the required cache size.Comment: 14 pages, 2 figures, submission Trans IT, V
Throughput Region of Spatially Correlated Interference Packet Networks
In multi-user wireless packet networks interference, typically modeled as
packet collision, is the throughput bottleneck. Users become aware of the
interference pattern via feedback and use this information for contention
resolution and for packet retransmission. Conventional random access protocols
interrupt communication to resolve contention which reduces network throughput
and increases latency and power consumption. In this work we take a different
approach and we develop opportunistic random access protocols rather than
pursuing conventional methods. We allow wireless nodes to communicate without
interruption and to observe the interference pattern. We then use this
interference pattern knowledge and channel statistics to counter the negative
impact of interference. We prove the optimality of our protocols using an
extremal rank-ratio inequality. An important part of our contributions is the
integration of spatial correlation in our assumptions and results. We identify
spatial correlation regimes in which inherently outdated feedback becomes as
good as idealized instantaneous feedback, and correlation regimes in which
feedback does not provide any throughput gain. To better illustrate the
results, and as an intermediate step, we characterize the capacity region of
finite-field spatially correlated interference channels with delayed channel
state information at the transmitters.Comment: Accepted for publication in IEEE Transactions on Information Theor
Cache-Assisted Broadcast-Relay Wireless Networks: A Delivery-Time Cache-Memory Tradeoff
An emerging trend of next generation communication systems is to provide
network edges with additional capabilities such as storage resources in the
form of caches to reduce file delivery latency. To investigate this aspect, we
study the fundamental limits of a cache-aided broadcast-relay wireless network
consisting of one central base station, cache-equipped transceivers and
receivers from a latency-centric perspective. We use the normalized delivery
time (NDT) to capture the per-bit latency for the worst-case file request
pattern, normalized with respect to a reference interference-free system with
unlimited transceiver cache capabilities. The objective is to design the
schemes for cache placement and file delivery in order to minimize the NDT. To
this end, we establish a novel converse and two types of achievability schemes
applicable to both time-variant and invariant channels. The first scheme is a
general one-shot scheme for any and that synergistically exploits both
multicasting (coded) caching and distributed zero-forcing opportunities. We
show that the proposed one-shot scheme (i) attains gains attributed to both
individual and collective transceiver caches (ii) is NDT-optimal for various
parameter settings, particularly at higher cache sizes. The second scheme, on
the other hand, designs beamformers to facilitate both subspace interference
alignment and zero-forcing at lower cache sizes. Exploiting both schemes, we
are able to characterize for various special cases of and which satisfy
the optimal tradeoff between cache storage and latency. The
tradeoff illustrates that the NDT is the preferred choice to capture the
latency of a system rather than the commonly used sum degrees-of-freedom (DoF).
In fact, our optimal tradeoff refutes the popular belief that increasing cache
sizes translates to increasing the achievable sum DoF