Over the years, BlackBerry has amassed a giant portfolio of patents, but it hasn't used them to sue others—until now.

BlackBerry has filed three patent infringement lawsuits in as many weeks. The struggling phone company's offensive barrage began with a case filed against IP telephony company Avaya on July 27. Last week, BlackBerry filed two lawsuits against budget cell phone maker BLU's products, alleging that BLU infringes a whopping 15 patents.

The dual lawsuits against BLU suggest that BlackBerry's new turn toward patent licensing isn't going to be a one-off event, but rather a more extended campaign. In a May earnings call, BlackBerry CEO John Chen told investors he's in a "patent licensing mode" and is hoping to monetize his company's 38,000 patents.

The new lawsuits also suggest that BlackBerry has patents it believes describe Android features, so don't be surprised if more Android phones are in the crosshairs soon. One of the two cases filed last week accuses user-interface features that are more about Android than they are about BLU. A small manufacturer like BLU could make for a good "test case" against a maker of Android phones.

In the first lawsuit against BLU (PDF), BlackBerry says BLU infringes seven patents:

8,489,868, a software code-signing system

8,402,384, a "dynamic bar" display

8,411,845, a phone log display

6,271,605, a battery disconnection system

8,745,149, describing a way of time-stamping messages

and 8,169,449, a system for making composite images from multiple applications.

In the second lawsuit (PDF), Blackberry alleges infringement of eight US patents, mostly related to transmitting signals. They are:

7,969,924, "Method and apparatus for state/mode transitioning"

8,483,060, "Method for configuring a telecommunication system"

8,406,118, "Scattered pilot pattern and channel estimation method for MIMO-OFDM systems"

8,472,567, "Detecting the number of transmit antennas in a base station"

8,265,034, "Method and system for a signaling connection release indication"

8,625,506, "System and method for determining establishment causes"

7,933,355, "Systems, devices, and methods for training sequence, transmission and reception"

7,050,413, "Information transmission method, mobile communications system, base station and mobile station in which data size of identification data is reduced"

Both suits were filed last Tuesday in the Southern District of Florida. That's the district including BLU's headquarters, located in the Miami suburb of Doral.

The second complaint notes that on November 21, 2015, BlackBerry sent BLU a list of patents "required to practice, inter alia, the 2G, 3G, and LTE standards." At that time, BlackBerry offered to license the patents on "fair, reasonable, and nondiscriminatory terms." The first complaint, with the more user interface-oriented allegations, doesn't mention the November notice.

Neither BlackBerry nor BLU responded to requests for comment for this story.