# Performance Analysis of a 3D Wireless Massively Parallel Computer
## 1 Introduction  
In an HPC system there is a constant need for increasing the density of processors within a given volume. However, there are limitations that occur when wired interconnects and traditional 2D Printed Circuit-Board (PCB) modules are stacked. Also, the thermal issues become more serious in a system that achieves higher density and ever faster CPU cores, leading to the need for liquid cooling. Both issues indicate that a high-density system should attempt to eliminate traditional 2D PCB planes and avoid hard-wired interconnects if realistic alternatives can be employed. The purpose of our evaluations, in this paper, is to determine if the performance constraints for such a system are within the range that makes them competitive with existing systems, and ultimately more capable, as scaling reduces the size of nodes and increases the number of nodes in an array. Wireless technologies have not been regarded as serious options for an interconnect network in high-performance computing thus far. This is mainly because of their size, energy demands and transfer rates. Considering new developments in on-chip high-speed wireless devices, we are now close to a viable wireless interconnect network for a massively parallel computer. These technologies have narrowed the gap between wireline and wireless devices. One reason why wireline data rates do not increase as fast as wireless devices is that wireline transceivers are close to reaching their performance limits [1]. There is a separate (yet closely related) field of research in which independent agents collaborate with each other to perform a computationally heavy task. Generally referred to as Swarm Computation, it can be regarded as a variation on swarm robotics. The key issue in swarm computing (and swarm robotics in general) is to take advantage of the flexibility of the agents in configuring and re-configuring and re-configuring themselves to tackle different tasks depending on changes in circumstances (e.g., [2]). Among applications for such a concept is computation in hazardous or remote environments like spacecrafts [3]. Another characteristic of such platforms is the higher level of intelligence or computation power emergent from collaboration of agents with lower intelligence. Swarm computing does have some overlap with the work presented here and offers significant potential for future avenues of work; however, the differences between these two fields should be noted. This paper presents a novel interconnect network for a massively parallel computer. Although the interconnect network we proposed can be regarded as reconfigurable in the sense that new nodes can be added to it, the topology of the network is fixed during normal operation. Moreover, the dynamic reorganization of nodes has not been considered in our work to date. In our previous papers [4; 5] a 3D wireless grid was introduced for a novel parallel platform called A Ball Computer (ABC). It can scale easily since there is no wiring limitation. Other advantages of such a platform are significant reduction in network cost and complexity. However, there are some critical issues, such as wireless power delivery and heat dissipation. [PERSON] [6] and [PERSON] [7] have investigated several options for those issues. [PERSON] [6] has shown that there are some promising options for wireless power delivery; however, they still need to be more mature for a viable solution. This paper focuses on connectivity in the ABC and its impact on the nodes' and links' performances. This research considers the impact of a novel combination of two concepts: wireless interconnect technology and a 3D structure with hexagonal lattice topology. However, to the best of our knowledge those concepts have been combined for such an application for the first time in our evaluations. The ABC envisages a computer system made of balls (1-2 cm in diameter) each containing computing and communicating elements that can be rapidly and cheaply assembled.