Efficient massively parallel simulation of dynamic channel assignment schemes for wireless cellular communications

Fast, efficient parallel algorithms are presented for discrete event simulations of dynamic channel assignment schemes for wireless cellular communication networks. The driving events are call arrivals and departures, in continuous time, to cells geographically distributed across the service area. A dynamic channel assignment scheme decides which call arrivals to accept, and which channels to allocate to the accepted calls, attempting to minimize call blocking while ensuring co-channel interference is tolerably low. Specifically, the scheme ensures that the same channel is used concurrently at different cells only if the pairwise distances between those cells are sufficiently large. Much of the complexity of the system comes from ensuring this separation. The network is modeled as a system of interacting continuous time automata, each corresponding to a cell. To simulate the model, conservative methods are used; i.e., methods in which no errors occur in the course of the simulation and so no rollback or relaxation is needed. Implemented on a 16K processor MasPar MP-1, an elegant and simple technique provides speedups of about 15 times over an optimized serial simulation running on a high speed workstation. A drawback of this technique, typical of conservative methods, is that processor utilization is rather low. To overcome this, new methods were developed that exploit slackness in event dependencies over short intervals of time, thereby raising the utilization to above 50 percent and the speedup over the optimized serial code to about 120 times

Coordination and Antenna Domain Formation in Cloud-RAN systems

We study here the problem of Antenna Domain Formation (ADF) in cloud RAN systems, whereby multiple remote radio-heads (RRHs) are each to be assigned to a set of antenna domains (ADs), such that the total interference between the ADs is minimized. We formulate the corresponding optimization problem, by introducing the concept of \emph{interference coupling coefficients} among pairs of radio-heads. We then propose a low-overhead algorithm that allows the problem to be solved in a distributed fashion, among the aggregation nodes (ANs), and establish basic convergence results. Moreover, we also propose a simple relaxation to the problem, thus enabling us to characterize its maximum performance. We follow a layered coordination structure: after the ADs are formed, radio-heads are clustered to perform coordinated beamforming using the well known Weighted-MMSE algorithm. Finally, our simulations show that using the proposed ADF mechanism would significantly increase the sum-rate of the system (with respect to random assignment of radio-heads).Comment: 7 pages, IEEE International Conference on Communications 2016 (ICC 2016

Accelerating the simulation of wireless cellular systems

The simulation of comprehensive models for cellular wireless systems poses a computational burden of great proportions. When a sub-model for transmitter power level control is included in the simulation, a continuous process in discrete-time is introduced, requiring traditional execution to advance in small, regular time-steps. to accelerate these simulations, we propose the use of interval jumping, a novel technique which allows time to progress in adaptive, irregularly-sized jumps in time. The foundations for this mechanism are laid out in the light of the simulation of a complex simulation model which includes teletraffic, radio propagation, channel allocation, transmitter power control, and user mobility. We demonstrate the performance of this method through the use of sequential and parallel simulation.;Approaching the problem of accelerating the simulation of wireless systems from a different angle, we also identify a second important performance bottleneck. Calculations for interference computation, which may be carried out hundreds of times for each second of simulated time, require the evaluation of O(N2) interactions, for a system with N transmitter/receiver pairs. In order to provide a computationally cheaper and more scalable alternative to these operations, we study the applicability of an N-body algorithm, which brings time complexity down to O(N log N)