That's 50 bits per second per Hertz of radio spectrum.
Under the title NTT DoCoMo Achieves World's First 5Gbps Packet Transmission in 4G Field Experiment DoCoMo announced a new level of modulation efficiency. Their title is flashy, but they were using 100MHz of spectrum. To find that much spectrum you have to look to very high frequencies and thus short ranges with poor penetration of buildings (or trees and shrubs).
The benchmark to follow is modulation efficiency — how many bps can you cram through a limited amount of spectrum. Today commercially deployed systems tend to achieve less than 10 bps. Here's an excerpt from a picture of their setup.
The full image with explanation is in this pdf file.
In some sense, this is a brute force expansion of earlier work with an increased number of antennas at slightly different positions being used to send different information on the same frequency simultaneously and multiple receiving antennas used to resolve the individual transmitted signals, i.e. multiple inputs and multiple outputs (MIMO). It also builds on the most current modulation scheme which is orthogonal frequency division multiplexing (OFDM), the modulation used in WiMAX. None-the-less, it's an impressive achievement. Thank you DoCoMo.
Everyone has heard of Moore's law describing the decades-long continuous exponential increase in performance of integrated circuit technology. Fewer people comment on the continuous exponential increase in radio spectrum utilization that's been in progress for more than 100 years, i.e. since Marconi patented "resonant tuning" in 1900, showing how he could send multiple signals over the air at the same time (versus a single transmission in his initial system of 1896).