A bump from one model to another would usually entail a lot of changes but as far as the Sony Xperia Z3 and Xperia Z4 are concerned, the improvements may not be as emphatic as one would expect.

Given that the market of mobile phones nowadays would normally include large improvements, worth noting are the expected improvements for Sony's next device. And that includes a slightly bigger display, an improved front-facing camera and of course a higher processor to carry out the phone's functionalities.

The Xperia Z4 is expected to be unveiled at the 2015 Mobile World Congress which will be held from March 2 to 5 in Barcelona. However, the presentation will not be as fancy like previous Sony launches. Reports have it that Sony will not hold a big press conference and that the device will come out modestly.

With regards to comparing the Z4 to the Z3, one may find minimal changes.

The display will be the only significant change the Z4 will be carrying. Compared to the Z3's 5.2-inch full HD (1920x1080) display, the Z4 will be toting a larger 5.5-inch Quad HD (2560x1440) display. With that bump, the Z4 should have a vastly improved screen display.

There is an expected hardware bump as well. Compared to the Xperia Z3's existing specs (2.5 GHz Qualcomm Snapdragon), the Z4 will reportedly boast of a 64-bit Qualcomm Snapdragon 810 octa-core processor.

For the OS, the Z3 initially came out with Android Kitkat. For the Z4, it will expectedly come with the Android Lollipop.

With regards to the camera, Sony has applied improvements to the already existing 20.7 MP rear camera meaning it could still be the same for the Z4. The only improvement comes on the front end where the Z3 will have a 5MP front shooter compared to the Z3's 2.2 MP.

It should be noted as well that the Z4 may come in two variants if rumors are true. A dual-SIM version and a music variant may come out, justifying a rumored S-Force PRO Front Surround speaker that the Z4 will come out with.

It would be best to note again that these specs are rumored and remain unofficial. Though rumors have a knack of eventually being official, it would be best to wait for the actual and official launch of the Sony Xperia Z4 which is just a couple of weeks away.