It turns out that QAM-256, which was originally intended for small cells, delivers benefits to operators and consumers in the macro network as well. Those are the findings of a recent study by Signals Research Group.
Just what is QAM-256? It refers to Quadrature Amplitude Modulation, which is the means by which a carrier signal, such as an LTE waveform, transmits data and information. Ideally, a waveform/symbol carries as much data as possible in order to achieve higher data rates and increase spectral efficiency.
“QAM achieves this objective by increasing the number of unique waveform shapes, with each waveform shape, or constellation, representing a specific binary number,” the researchers wrote in their report. “In both wireless and wireline communications, there is 16-QAM, 64-QAM, and 256-QAM, which all pertain to LTE, as well as even higher QAM schemes, such as 1024-QAM, which are now being considered for the future evolution of LTE/LTE-Advanced Pro and 5G.”
As one might expect, 256-QAM is better than 64-QAM and 64-QAM is better than 16-QAM because the higher QAM numerology reflects the ability to represent more data with the same number of symbols. “Since with the binary notation each data bit is either a 1 or a 0, 256-QAM can theoretically support eight bits per symbol, thanks to the 256 unique constellations (2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 2⁸ = 256),” the report stated. Using the same thought process, 64-QAM supports six bits per symbol and 16-QAM supports four bits per symbol.
T-Mobile US knows the value of 256 QAM for the macro network. T-Mobile CTO Neville Ray last month boasted that T-Mobile was the first to launch 256 QAM for downloads and 64 QAM for uploads. Combined with 4x4 MIMO, 256 QAM delivers download speeds up to 400 Mbps, he said in a blog.
He reported that 256 QAM and 64 QAM are already live in half of T-Mobile’s network, and by end of October, “we’ll light up every single cell site across our nationwide network,” he said. “Customers with the Samsung Galaxy S7 and S7 Edge will be able to use this new technology with a software update in October, with more phones on the way.”
Signals Ahead, which was founded by industry analyst Michael Thelander, pointed out that the 3GPP standards body endorsed 256-QAM as an LTE-Advanced feature in late 2013 when the higher modulation scheme was included as part of the Release 12 functionality. The irony of its introduction is that, originally, 3GPP intended for 256-QAM to be focused on small cells, which the industry felt were better prepared to deliver the high Signal to Interference and Noise Radio (SINR) values that 256 QAM requires.
Australian operator Telstra, along with industry partners Ericsson (infrastructure), Netgear (810S mobile hotspot) and Qualcomm (Snapdragon X12 LTE modem), first deployed 256-QAM in macro cell sites throughout Telstra's network. SRG paid a visit to Melbourne, Australia, in early 2016 to conduct an independent evaluation of 256-QAM in an LTE network. The results showed that 256-QAM provides benefits to network performance that affect both the operator and the consumer. A mobile data user who is in an area of the network with the poorest signal quality still benefits indirectly from the benefits of 256-QAM.