The development of 5G wireless technology is what underpins mobile phone makers' hopes that they can boost sales which have recently flagged

Phone makers will focus on foldable screens and the introduction of blazing fast 5G wireless networks at the world's biggest mobile fair starting Monday in Spain as they try to reverse a decline in sales of smartphones.

Huawei will also be in the spotlight at the four-day Mobile World Congress (MWC) in Barcelona as the Chinese telecom giant fights US efforts to persuade its allies not to use the company's technology to build their 5G networks due to concerns that its gear could facilitate Chinese spying.

The firm is the leading manufacturer of equipment for the fifth-generation cellular networks which operators are starting to install. The technology—known as 5G— will bring near-instantaneous connectivity for smartphones and devices from automobiles to robots.

"This year we are going to see real 5G ready launches happening in different countries and the focus will be on where, when, how and what are the consumer benefits going to be of 5G in 2019," said Ian Fogg, a mobile industry analyst at OpenSignal, which collects and analyses data from .

Huawei and other firms are scheduled to carry out 5G smartphone demos at the fair even though the next generation wireless network will not be widely available for several more years.

Samsung, the world's biggest seller of smartphones, unveiled a handset that folds open to be a tablet on Wednesday in San Francisco, becoming the first major manufacturer to offer the long-awaited feature.

China's Xiaomi and several other firms are expected to follow Samsung's lead and present foldable devices of their own in Barcelona although it was not clear if they would be prototypes or commercially available devices such as Samsung's.

'Consumer frustration'

Foldable phones come as handset makers are scrambling to introduce new features to attract customers.

Global smartphone sales fell 4.1 percent in 2018 to a total of 1.4 billion units due to an economic slowdown in China, which consumes about one-third of the world's phones, and a lack of major innovations that encourage people to upgrade their devices, according to research firm IDC.

Huawei is reserving its next moves for an event in Paris in March while Apple is also not going to be present in Barcelona

Sales fell by 0.5 percent in 2017 for a first annual decline.

"People have been holding on to their phones longer. A lot of it is consumer frustration that devices aren't changing a tonne and prices keep going up," said senior IDC research analyst Ryan Reith.

Apple as usual will not be present at the show and Huawei this year will present its new flagship at an event in Paris in March instead of at the fair.

With the three biggest smartphone makers not unveiling new devices in Barcelona, the rest of the industry will have a rare opportunity to grab the spotlight at the fair.

Huawei opportunity?

Huawei received a boost in its battle to ease concerns over its technology in the lead up to the congress after the Financial Times reported on Monday that British intelligence has concluded posed by using equipment made by the firm can be managed.

And mobile communications industry body GSMA, which organises the fair, urged European governments not to ban Huawei from helping to build their 5G networks.

Australia, New Zealand and Japan have followed Washington's call for a Huawei ban, but the picture in Europe is more nuanced, not least because Huawei's 5G capabilities are ahead of those of its rivals, analysts say.

Major countries such as Germany fear banning the Chinese firm would cause a considerable setback in Europe's efforts to deploy 5G and stay competitive in communications.

The fair will be an opportunity for the Chinese firm "to show that it is continuing to do their work, that it's still innovating, and that it does things well differently from its competitors," said Dexter Thillien, an analyst at Fitch Solutions.