Modeling and Performance of Uplink Cache-Enabled Massive MIMO Heterogeneous Networks

A significant burden on wireless networks is brought by the uploading of user-generated contents to the Internet by means of applications such as social media. To cope with this mobile data tsunami, we develop a novel multiple-input multiple-output (MIMO) network architecture with randomly located base stations (BSs) a large number of antennas employing cache-enabled uplink transmission. In particular, we formulate a scenario, where the users upload their content to their strongest BSs, which are Poisson point process distributed. In addition, the BSs, exploiting the benefits of massive MIMO, upload their contents to the core network by means of a finite-rate backhaul. After proposing the caching policies, where we propose the modified von Mises distribution as the popularity distribution function, we derive the outage probability and the average delivery rate by taking advantage of tools from the deterministic equivalent and stochastic geometry analyses. Numerical results investigate the realistic performance gains of the proposed heterogeneous cache-enabled uplink on the network in terms of cardinal operating parameters. For example, insights regarding the BSs storage size are exposed. Moreover, the impacts of the key parameters such as the file popularity distribution and the target bitrate are investigated. Specifically, the outage probability decreases if the storage size is increased, while the average delivery rate increases. In addition, the concentration parameter, defining the number of files stored at the intermediate nodes (popularity), affects the proposed metrics directly. Furthermore, a higher target rate results in higher outage because fewer users obey this constraint. Also, we demonstrate that a denser network decreases the outage and increases the delivery rate. Hence, the introduction of caching at the uplink of the system design ameliorates the network performance.Peer reviewe

Aminoacylation kinetics of <i>B. bacteriovorus</i> AspRS and AsnRS at 37°C.

<p>^*L  =  Specificity relative to the catalytic efficiency of AspRS with tRNA^Asn as a substrate, (<i>k</i>_cat/<i>K</i>_M)/(<i>k</i>_cat/<i>K</i>_M) of AspRS for tRNA^Asn. Experiments were repeated three to four times and standard deviations are reported.</p><p>Aminoacylation kinetics of <i>B. bacteriovorus</i> AspRS and AsnRS at 37°C.</p

The <i>B. bacteriovorus aspS</i> rescues the Trp auxotrophy of <i>E. coli trpA34</i>.

<p><i>E. coli trpA34</i> was grown with pCBS2 containing either 1) the <i>ND-aspS</i> from <i>D. radiodurans</i> as a positive control, 2) the <i>discriminating(D)-aspS</i> from <i>D. radiodurans</i> as a negative control, or 3) the <i>B. bacteriovorus aspS</i>. The cultures were grown in triplicate on M9 minimal media agar plates with 100 µg/ml of ampicillin in the presence (+ Trp, 20 µg/ml) or absence (- Trp) of Trp at 37°C for three days. Representative results are shown from three separate trials.</p

Presence of Asn, Asn-tRNA^Asn, and Gln-tRNA^Gln biosynthetic pathways in bacteria.¹

1<p>Representative genomes from 547 different bacterial genera were analyzed for the presence of genes coding for AsnA, AsnB, AsnRS, GlnRS, and GatCAB. The results are detailed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110842#pone.0110842.s001" target="_blank">Table S1</a>. In parentheses is the number of bacterial genera with a tRNA^Asn isoacceptor containing a U1-A72 base pair.</p><p>Presence of Asn, Asn-tRNA^Asn, and Gln-tRNA^Gln biosynthetic pathways in bacteria.^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110842#nt102" target="_blank">1</a>}</p

<i>B. bacteriovorus</i> AspRS aspartylates tRNA^Asn.

<p>Aminoacylation of <i>in vitro</i> transcribed tRNA^Asp (○) and tRNA^Asn (▵) by either (A) <i>B. bacteriovorus</i> AspRS or (B) <i>B. bacteriovorus</i> AsnRS. Reactions were carried out at 37°C with 1.0 µM ³²P-labeled tRNA^{Asp or Asn}, 11.0 µM tRNA^{Asp or Asn}, 4.0 mM ATP, 4.0 mM relevant amino acid (L-Asp or L-Asn) and 3.0 µM enzyme. Experiments were repeated three times and error bars represent standard deviations.</p

The <i>L. pneumophila</i> AspRS aspartylates tRNA^Asn.

<p>(A) <i>E. coli trpA34</i> was grown with pCBS2 containing either 1) the <i>ND-aspS</i> from <i>D. radiodurans</i> as a positive control, 2) the <i>discriminating(D)-aspS</i> from <i>D. radiodurans</i> as a negative control, or 3) the <i>L. penumophila aspS</i>. The cultures were grown in triplicate on M9 minimal media agar plates with 100 µg/ml of ampicillin in the presence (+ Trp, 20 µg/ml) or absence (- Trp) of Trp at 37°C for three days. Representative results are shown from three separate trials. (B) Asparylation of <i>in vitro</i> transcribed tRNA^Asp, tRNA^Asn, and tRNA^Gln by the <i>L. pneumophila</i> AspRS. Reactions were carried out at 37°C with 0.1 µM ³²P-labeled tRNA^{Asp, Asn, or Gln}, 4.0 mM ATP, 4.0 mM L-Asp and 10 nM AspRS. Experiments were repeated three times and error bars represent standard deviations.</p