BARCELONA - With Samsung's upcoming Galaxy S7 and S7 edge smartphones, the Korean tech giant has addressed the major criticisms that were levelled against the current-generation Galaxy S6 series.

They have re-introduced expandable storage - notably missing in the Galaxy S6 and S6 edge - and they have also ramped up battery life, although the battery is still not removable.

Samsung has also announced the Gear 360, a camera which can take 360-degree pictures and videos.

All three gadgets were unveiled on Sunday (Feb 21), a day before the start of the annual Mobile World Congress in Barcelona, Spain.

The new 5.1-inch Galaxy S7 and the 5.5-inch S7 edge look broadly the same as both Galaxy S6 phones, with a sleek glass-and-metal design.

The S7 edge retains its distinctive dual-curved edges, and the back of the phone is now curved on both sides as well, making it easier to grip.

With the Galaxy S7 series, Samsung has included a hybrid SIM tray in order to provide expandable storage. The tray has two slots, and can either hold two SIM cards, or one SIM card and one microSD card that can provide up to 200GB of additional space.

The battery life of the phone has also been improved. When the current-generation Galaxy S6 was released, the 2,550 mAh battery was a reduction from the 2,800 mAh of the Galaxy S5.

This time round, the capacity of the Galaxy S7 has been shored up to 3,000 mAh, and the S7 edge's battery has increased from 2,600 mAh to 3,600 mAh.

Samsung has also brought back features such as water resistance, which was last seen on the Galaxy S5 series. The two new phones have an IP68 rating, which means that they can be submerged one metre underwater for over 30 minutes.

Both phones will be available starting in mid-March this year.

Alongside the two Galaxy phones, Samsung also announced the Gear 360, a 360-degree camera.

The camera will allow users to capture immersive images which can then be viewed on virtual reality devices such as the Samsung Gear VR and Google Cardboard.

While 360-degree cameras are not new, the Gear 360 is the first such device by a major mobile phone manufacturer.

The spherical 153g device comes with two 15-megapixel fisheye lenses placed back to back, and can shoot both stills and videos.

It has a microSD card slot for up to 128GB of storage space, and also comes with a stand that can either be used as a handle or a tripod.

The camera does not have a viewfinder, but if synced up with selected Samsung smartphones, a real-time feed from the camera can be seen on the phone's screen.

Images and videos can also be wirelessly transmitted to the phone, and directly uploaded to sites that support 360-degree videos, such as YouTube and Facebook.

The Gear 360 will be available from the second quarter of this year in selected countries.