As we transition from the 5G epoch, a new horizon beckons with the
advent of 6G, seeking a profound fusion with novel communication
paradigms and emerging technological trends, bringing once-futuristic
visions to life along with added technical intricacies. Although
analytical models lay the foundations and offer systematic insights, we
have recently witnessed a noticeable surge in research suggesting
machine learning (ML) and artificial intelligence (AI) can efficiently
deal with complex problems by complementing or replacing model-based
approaches. The majority of data-driven wireless research leans heavily
on discriminative AI (DAI) that requires vast real-world datasets.
Unlike the DAI, Generative AI (GenAI) pertains to generative models
(GMs) capable of discerning the underlying data distribution, patterns,
and features of the input data. This makes GenAI a crucial asset in
wireless domain wherein real-world data is often scarce, incomplete,
costly to acquire, and hard to model or comprehend. With these appealing
attributes, GenAI can replace or supplement DAI methods in various
capacities. Accordingly, this combined tutorial-survey paper commences
with preliminaries of 6G and wireless intelligence by outlining
candidate 6G applications and services, presenting a taxonomy of
state-of-the-art DAI models, exemplifying prominent DAI use cases, and
elucidating the multifaceted ways through which GenAI enhances DAI.
Subsequently, we present a tutorial on GMs by spotlighting seminal
examples such as generative adversarial networks, variational
autoencoders, flow-based GMs, diffusion-based GMs, generative
transformers, large language models, autoregressive GMs, to name a few.
Contrary to the prevailing belief that GenAI is a nascent trend, our
exhaustive review of approximately 120 technical papers demonstrates the
scope of research across core wireless research areas, including 1)
physical layer design; 2) network optimization, organization, and
management; 3) network traffic analytics; 4) cross-layer network
security; and 5) localization & positioning. Furthermore, we outline
the central role of GMs in pioneering areas of 6G network research,
including semantic communications, integrated sensing and
communications, THz communications, extremely large antenna arrays,
near-field communications, digital twins, AI-generated content services,
mobile edge computing and edge AI, adversarial ML, and trustworthy AI.
Lastly, we shed light on the multifarious challenges ahead, suggesting
potential strategies and promising remedies. Given its depth and
breadth, we are confident that this tutorial-cum-survey will serve as a
pivotal reference for researchers and professionals delving into this
dynamic and promising domain.