Ahead of its biggest annual trade show, the mobile industry is at something of a crossroads.

On one hand, the smartphone has firmly cemented itself as the primary computing device for a large portion of humanity. Phone makers are increasingly comfortable pricing flagship models above $800, trusting relatively affluent consumers won't object to paying such sums for devices being used for several hours per day. And genuine innovation is still happening in fields such as camera tech, 3D depth-sensing and smartphone augmented reality (AR) platforms.

On the other hand, smartphone unit sales are clearly under pressure due to high penetration rates and lengthening upgrade cycles. 4G network buildouts are largely complete in developed markets, and 5G rollouts are at least a year away from starting in earnest. And thanks in large part to the technical limitations of current hardware, the AR and VR headset markets remain in their infancy.

Here's what to keep an eye on as the Mobile World Congress (MWC) gets underway in Barcelona.

Samsung's Galaxy S9 and S9+

As is its custom, Samsung will be unveiling its latest flagship phone at a Sunday press event prior to MWC's official start. Unlike last year, when the Korean tech giant put its head-turning, edge-to-edge, Infinity displays on the Galaxy S8 and S8+, this year's Galaxy S models will look a lot like their predecessors. The most visible changes: The S9+ will (like many other high-end phones) have dual rear cameras, and the rear-panel fingerprint sensor on both models won't be as awkwardly-placed.

The S9 and S9+ are also expected to sport improved primary rear cameras with large f/1.5 apertures (good for low-light shots), along with slightly improved displays and battery life. And of course, faster processors -- some models will use Samsung's Exynos 9810 system-on-chip (SoC), and others Qualcomm's (QCOM) Snapdragon 845. Not a terrible refresh, but the lack of big hardware changes could give Alphabet/Google (GOOGL) an opening this fall.

Sony, Nokia, LG and the Rest

A slew of other Android phones are also set to be revealed at MWC. Sony  (SNE) is expected to reveal its Xperia XZ2 and XZ2 Compact phones, which respectively sport 5.8-inch and 5.2-inch displays. The Japanese conglomerate is taking a page from Samsung and putting edge-to-edge displays on the devices. Nokia (NOK)  -- or rather, Finland's HMD Global, which has the rights to sell phones under the Nokia brand -- will reportedly launch multiple phones, including one with a 5.5-inch OLED display and a Snapdragon 835 SoC.

LG is rumored to be launching a slightly updated version of its V30 flagship, one that relies on AI-powered software to produce better photos and a more useful voice assistant. Lenovo/Motorola, HTC, Asus and other Android OEMs might also launch phones.

Google's ARCore and Android Go

With the help of major Android partners, look for Google to make its presence felt at MWC. Ahead of the conference, the web giant officially launched its ARCore augmented reality platform (in beta since last fall), which serves as an Android-based rival to Apple's (AAPL) ARKit. Google claims 100 million Android phones already support ARCore, provided they're running Android O; there should be plenty of demos for ARCore-capable apps running on eligible phones.

The first phones supporting Google's trimmed-down Android Go operating system, meant for cheap smartphones aimed at emerging markets, will also be shown off at MWC. Android Go comes with lightweight versions of YouTube, Gmail, Chrome and other popular Google apps, and is pivotal to Google's efforts to further grow an Android active device base that has already topped 2 billion.

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5G Announcements

Though 5G isn't ready for primetime yet, there's a lot more substance to the technology than there was a couple of years ago, as Winter Olympics demos make clear. With the qualifier that new mobile radio technologies take time to ramp, the potential for 5G networks to deliver gigabit-plus real-life download speeds, support fixed-wireless broadband deployments and accommodate billions of low-power IoT devices is already creating plenty of buzz.

Ahead of MWC, Qualcomm has been eager to promote its Snapdragon X50 5G modem, which it aims to put into commercially-available phones and other devices next year, and has announced a partnership with Samsung to develop next-gen 5G modems relying on Samsung's 7-nanometer manufacturing process (expected to see mass-production in 2019). Intel (INTC) , meanwhile, has promised 5G-capable notebooks containing Intel modems will be launched by the likes of Dell, HP (HPQ) and Lenovo by the 2019 holiday season.

Look for additional announcements from chipmakers, OEMs and carriers during MWC. Sprint (S) and T-Mobile (TMUS)  have already promised to launch 5G mobile networks in 2019, but it remains to be seen just how widely available the networks will be at first.