Lindy Effect in Wireless Communications
How long a concept, a technology or an idea sticks around and keeps to have an impact? The Lindy effect refers to the hypothesis that the life expectancy of non-perishable entities, such as a model or an idea, is proportional to its current age. That is, the longer an idea has been around, the longer it is likely to stick around in the future. The Lindy effect and its statistical properties have been discussed by luminaries such as Benoit Mandelbrot and Nassim Nicholas Taleb.
In some way, the Lindy effect is a statistical description of the phenomenon of applying the old-school tricks and proven recipes from grandparents. Its name comes from the Lindy's diner in New York, where the effect was discussed by the comedians and the historian Albert Goldman introduced it as “life expectancy of a television comedian is proportional to the total amount of his exposure on the medium.”
Let us then look what Lindy effect has to say about the life expectancy of some of the most important ideas that are underpinning today's wireless communication systems.
Spectrum allocation
A key asset in wireless communication is the right to transmit within a given frequency band. In the case of licensed spectrum, wireless mobile operators pay a large sum of money to acquire exclusive access to some frequency bands and get the right to control the interference that occurs in those bands. The need for centrally managed spectrum allocation and licensing became apparent after the sinking of RMS Titanic in 1912, where radio interference prohibited a prompt rescue operation. With the Radio Act of 1912, the government for the first time seized control of the wireless spectrum. This has continued in various forms until today, including the expensive auctions for cellular mobile frequency bands that ensure interference guarantees to the mobile connections. This is in contrast to open, unlicensed bands, such as the ones used by Wi-Fi and Bluetooth, where interference is unpredictable and, in principle, can be uncontrollably large in terms of intensity and duration.
Any alternative to the spectrum allocation should be able to provide a robust, resilient, and distributed interference management. Despite a plethora of ideas in the form of cognitive radio and dynamic spectrum usage, the task of finding such an alternative turns out to be immensely difficult, both in terms of design and in terms of potential for large deployment. Ideally, we should be able to find "the best" spectrum regulation and allocation in which we can apply the most up-to-date technology we have about wireless systems. However, that technology should operate in a wireless ecosystem populated by legacy devices and systems. This is one of the strong arguments to trust the estimate of the Lindy effect, according to which spectrum allocation with some exclusivity in time and space is likely to be around for more than 100 years from now.
Satellites
In 1945, the science fiction writer Sir Arthur C. Clarke introduced the idea of satellites as extraterrestrial relays used for wireless communication; the article was published in a magazine with an appropriate name, Wireless World. Since then, satellite communication has become indispensable for a large number of applications, most famously for TV distribution, but also for vital functions such as GPS, airlines, maritime, etc. With the emergence of mobile cellular communication systems from the 1990s, the role of satellite communication for personal communication devices decreased markedly. This led to a gradually diminishing role of satellites in communication engineering research throughout the years. This started to change significantly in the recent years, with the emergence of small satellites, NewSpace and, since very recently, the efforts to integrate terrestrial wireless networks with LEO satellite constellations and other non-terrestrial networks. The Lindy effect predicts around 80 years for this idea, but this is very likely going to be exceeded. This is because it is hard to think of alternatives that can replace all communication uses of the satellites, but also due to their ability to revive and find new uses.
Multicarrier modulation
One of the dominant ideas used in wireless systems is the one of transmission of data on multiple parallel channels or carriers. Wi-Fi, 4G and 5G use a transmission technique that that is some form of Orthogonal Frequency Division Multiplexing (OFDM), which is a multicarrier modulation suited to deal with wireless propagation through multiple paths. Multicarrier modulation and OFDM rely on the degrees of freedom that are available in a time-frequency grid. The usefulness of this representation was noticed already by Dennis Gabor, the inventor of holography and a Nobel prize winner, in his paper on communication theory published in 1946. The more concrete idea of OFDM was presented already in 1966 but it got traction in the early 1990s and is ubiquitously used today. Alternatives can be sought in communication waveforms that use different signal representations, such as impulses or perhaps quantum communication. Whatever they are, the Lindy effect expects that multicarrier/OFDMA will likely be around for 80 more years.
Shannon's communication model
In 1948 Claude E. Shannon published the paper that established the mathematical theory of communication. One of the several seminal contributions of this paper was to introduce a communication model that solves the technical problem of communication, which is how to transfer reliably data from a sender to a receiver over a noisy channel. Here "technical" means that the problem deals with the mere transfer of data, neither taking into account what is the meaning of that data for the receiver or for the sender-receiver pair, nor considering what is the usage/value of the data. Thus, besides the (1) technical problem, Shannon and Weaver defined two other types of problems not of direct interest for communication engineering: (2) Semantic problem, the meaning conveyed by the transmitted symbols should accurately reflect the intentions of the sender; and (3) Effectiveness problem, the conduct or action of the system in response to communications should be effective in accomplishing a desired task. Since its introduction, the Shannon model was a basis for extensive study and innovative communication schemes. Shannon's model is very general and is very likely to exceed the prediction of the Lindy that it will be present for around 80 years more.
Nevertheless, it should be noted that Shannon's communciation model is just one of the models used in the communication theory within the domain of the humanities. Furthermore, as the wireless systems move beyond 5G and potentially towards 6G, there are attempts to expand the problem domain of communication engineering towards inclusion of semantic and effectiveness. This has created a lot of excitement about semantic communications and goal-oriented communications, but these are still built upon Shannon's model. An alternative beyond Shannon's model would be a different set of communication models that account, for example, for the growing intelligence of the communication nodes or the need for data trustworthiness.
Multi-antenna systems and MIMO communications
The use of multiple antennas at the transmitter and/or the receiver brings the opportunity for better spatial control over the propagated signals and the use of additional, spatial degrees of freedom for communications. The ideas shaping multi-antenna systems and Multiple Input Multiple Output (MIMO) communications started to appear in 1970s and 1980s, but got a significant momentum with the ideas of space-time codes and spatial multiplexing that appeared in the 1990s. MIMO technology quickly foud the way to wireless system standardization and is now an integral part of 4G, 5G and Wi-Fi. The use of multiple antennas for communication is a general and very vital idea that continuously evolves. For example, the antennas can be distributed to multiple nodes that participate in the communication, rather than being put only on a single receiver and single transmitter; this leads to the concept of distributed MIMO. Since the 2010s the Massive MIMO technology holds the spotlight, in which a large number of antennas at the base station are capable to offer unprecedented levels of multiplexing users in space as well as making the wireless channel immune to fading. Most recently, the concept of Reconfigurable Intelligent Surfaces (RIS), also called Intelligent Reflective Surfaces (IRS), is seen as the new kid on the block, where surfaces that are neither transmitting nor receiving are (partially) controlling the propagation environment. RIS can be seen as an extension of the ideas of multi-antenna systems and distributed MIMO to a new setting; however, it still bears large similarity with the communication models with relays and distributed MIMO. Having seen its innovative transformations since the 1990s, I am curious to see how this general multi-antenna technology will evolve beyond 2050s, as predicted by the Lindy effect.
