Qualcomm (NASDAQ:QCOM) is a company that is, perhaps more-so than any other, at the center of the mobile revolution. It has one of the richest portfolios of mobile-oriented chips, as well as arguably the most valuable -- figuratively and literally -- wireless patent portfolio in existence today. 

Though Qualcomm's core businesses are supported by robust secular trends and protected by wide and deep technological and economic moats, it's important for all investors -- bullish and bearish -- to understand both sides of the argument. Without further ado, here are three potential reasons to be bearish on Qualcomm's stock.

Qualcomm could lose cellular baseband share
According to Strategy Analytics, Qualcomm accounted for approximately 66% of worldwide cellular baseband -- the chips that allow devices to connect to cellular networks -- revenue share in the first quarter of this year. Additionally, Qualcomm reportedly took no less than 91% of LTE baseband revenue share, down from 95% in the prior-year period. However, recent developments suggest that Qualcomm may see this share number erode.

Intel, for example, finally has a competitive LTE-Advanced modem with its XMM 7260, which Samsung has chosen for the international variant of its Galaxy Alpha smartphone. Intel has also won a number of lower-key sockets at Samsung with its prior generation XMM 7160 LTE modem such as the Galaxy K Zoom, and the international version of the Galaxy S5 mini.

At the low-end of the market, Qualcomm's integrated baseband and applications processor products are seeing competitive pressures from companies such as Marvell and MediaTek. Samsung, too, recently announced an integrated apps processor and cellular baseband intended for lower-cost smartphones. These developments could potentially serve to slow Qualcomm's chip growth during the coming quarters.

Applications processors share at risk, too
According to Strategy Analytics, Qualcomm enjoyed 54% revenue share of the mobile applications processor market during 2013. One driving factor behind Qualcomm's high applications processor share has been Qualcomm's integrated baseband leadership, in addition to solutions that are well-rounded and power and performance competitive.

Though Qualcomm's products are generally regarded as best-in-class, one of the company's largest customers, Samsung, has continued to develop and deploy its in-house Exynos processors in some versions -- usually those intended for international distribution -- of its smartphones. One risk is that Samsung begins to utilize its Exynos processors, paired with non-Qualcomm baseband chips, more broadly, perhaps, even in the domestic versions of its smartphones. In fact, in a recent interview published in EETimes, wireless chip expert Will Strauss remarked, "I fully expect that Qualcomm and others will be eliminated from future Samsung smartphones." 

Samsung accounted for approximately 25% of all smartphones sold during the second quarter of 2014 according to IDC,, so losing share at Samsung could be a not-so-insignificant negative for Qualcomm.

The China licensing problem
Finally, Qualcomm's patent licensing business has seen some difficulties lately. The good news is that the issues are unrelated to demand; but the bad news is that Qualcomm alleges that it is not being paid what it is owed. 

"[W]e believe that some of our Chinese licensees are under-reporting and may continue to under-report a portion of their 3G/4G device sales," Qualcomm's Derek Aberle noted on the company's most recent earnings call. Aberle also noted that some handset vendors may be selling 3G/4G devices without a license.

Though management seemed confident on the call that it would be able to resolve these patent disputes, the process could potentially drag out over multiple quarters, leading to weakness in the company's licensing division during that time. This could continue to pressure the stock, though investors with long-enough time horizons may view this as an opportunity to capitalize on short-term weakness.

Foolish bottom line
Qualcomm is a great business. However, given that it is set to face heightened competitive pressures in its chip unit during the coming quarters, and given that the licensing situation in China may take some time to resolve, the stock could continue to decline from current levels.