POSTCELL aims at laying the foundation for future generations of wireless networks as they move past the current cell-centric paradigm and enter the post-cellular era.
Cellular systems have undergone four generational transitions, stretching from the 1st Generation (1G) of analog telephony in the 1980s to the advanced and fully digital 5th Generation (5G). Despite their major differences, subsequent generations have all conformed to the same architecture that underpinned 1G, namely the cellular architecture (See Fig. 1). A cellular network tessellates a territory into cells, each centered on a site where a so-called base station houses all the necessary equipment to radio-communicate with users.
The cellular architecture has served us well and has remained unchallenged, to the point that base stations have witnessed generational transitions as hardware upgrades. However, the time is approaching when this architecture will have become exhausted and, unlike in previous transitions, a more transformational change that transcends the cellular architecture will be required. There is broad consensus on two ways to tackle this transformation:
- A dramatic scaling of the number of antennas per base station.
- Extreme densification.
While seemingly exclusive, we posit that the two ideas above are complementary, and a driver of POSTCELL was that, with a proper architecture, these can become two sides of a coin we term massification:
- Scaling the number of antennas per base station amounts to localized massification.
- Extreme densification can be regarded as distributed massification.
Reconciling these ideas and enabling a truly phenomenal degree of massification calls for an entirely new architecture where cells are transcended and base stations are deconstructed. Precisely, some of the base station functionalities should be pushed towards the antennas while others should be pulled away from them. On one hand, as antennas multiply, radios need to also multiply, and each should attach to one antenna yielding antenna-radio units that become the basic building blocks of the infrastructure. On the other hand, the signal processing needs to move up to a higher plane such that all these units can work together and the network can be smarter.
This deconstruction of the base station, hitherto the cornerstone of cellular networks, is the starting point for POSTCELL.
The research conducted under the umbrella of the action has led to a number of powerful conclusions:
1) Future wireless networks will necessitate a variable degree of massification, taking the form of dense distributed antenna-radio units in urban areas while taking the form of localized antenna-radio units in suburban and rural areas.
2) In post-cellular wireless networks, every user is to be served by a subset of antenna-radio units, and results have been derived on how to determine these subsets depending on the type of deployment. Concepts aligned with this idea are already discussed for 6G networks, as the improvements in coverage, capacity, and power efficiency, are major.
3) Power control functionalities, relevant in cellular networks, acquire even higher importance in post-cellular networks. A specific form of power control has been propounded and is getting considerable traction.
4) For the downlink, linear transmission schemes are preferred as their nonlinear brethren become rather unwieldy.
5) For the uplink, the classical nonlinear approach of successive interference cancellation is unfeasible, but a parallel interference cancellation scheme has been proposed that outperforms linear solutions.
6) Pilot contamination, a long-standing concern in cellular networks, has been shown not to be a significant impediment in postcellular networks.
