Verizon Wireless has taken the top spot for U.S. wireless performance in the second-half of 2014, according to RootMetrics by showing excellent performance against the three other major carriers.

It means Verizon maintains the top spot, which it won in the first-half of 2014. Verizon's performance numbers increased dramatically in the second-half due to new wireless investments.

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Verizon's overall performance hit 93.9 percent, two percent higher than AT&T and nine percent higher than the lowest, T-Mobile USA. The only place Verizon slipped-up was on text performance, where AT&T managed to overtake them by 0.8 percent.

The two major carriers -- AT&T and Verizon Wireless -- both seem to be further ahead than the two smaller carriers -- Sprint and T-Mobile USA -- in the rankings. The two minor carriers scored between 70 and 90 at most, with T-Mobile USA not surpassing 85.4 percent.

There are big reasons why AT&T and Verizon still hold the power in the U.S. wireless market. This is due to the spectrum investments both completed over the past decade, dwarfing the investments made by both Sprint and T-Mobile.

Just recently, AT&T spent $13.3 billion in an airwaves spectrum that ended with $44.9 billion in bids. Dish Network was the only company to come close to AT&T's spending with $12 billion. Verizon and T-Mobile spent less than $5 billion.

In 2016, the Federal Communications Commission (FCC) will open up the spectrum auction on various airwaves and all four carriers need to be ready to spend big. The recent net neutrality laws being pushed by the FCC might dampen some of the carrier's investment spirits, however.

TagsVerizon wireless, AT&T, T-Mobile, Sprint, U.S. carriers, RootMetrics, carrier performance