Consider a reference FAP at distance D from a central MBS, and its home users (or neighboring cellular users) at distance R and D c from the FAP and the MBS, respectively.
Note that when there are more than one cellular users to be served by a base station, the base station just chooses one cellular user to serve at each time slot through the time-division multiple access (TDMA) scheme2.
From Equation (21), increasing λ c reduces ρ b CA. Intuitively, this means that an MBS load is higher at more cellular user deployment and thereby fewer time slots are allocated home user served by the MBS.
This is because a cellular user or a D2D receiver at the cell edge will see much more interference from D2D transmitters than from the BS in a neighboring cell, simply because the D2Ds are much closer (e.g., at the other side of the cell edge) leading to potentially huge proximity gains.
The Pareto boundary of the region of the sum rate of D2D link versus that of the cellular link was found by optimizing the transmit power at base station and cellular user, as well as, D2D users [37].
Indeed, these studies find that cellular user performance is improved with open (or shared) access at the cost of reduced home user performance.
The throughput is high at a low femtocell density and a high cellular user density, which agrees with the prediction in Remarks 2 and 3.
A suboptimal solution could be given to the original optimization problem, thus maximizing the system throughput gain can take into account the performance gain of the D2D user and at the same time the performance loss of the cellular user.
The density of the cellular user is 0.0005/m 2, i.e., λ c =0.0005/m 2. The number of antennas equipped at each base station is set to be M=10.
At the same time, the BS sends the message to the cellular user and causes interference to both UE1 and UE2.
