NTT Corp, Japan's incumbent telco, claims to have raised the ceiling on wireless bandwidth, after achieving a peak data transfer rate of 2.5Gbps in laboratory trials. The previous highest wireless transfer rate was 1Gbps, but NTT's researchers believe they can ultimately take wireless communications up to 10Gbps.
Given that wireless equipment manufacturers are struggling to build equipment that can realize 2.5Mbps, and fixed-wire equipment makers are struggling to sell switches that already support 10Gbps of sustained capacity, pushing wireless to these dizzy heights might seem a little superfluous.
However, even if there is no immediate need for gigabit wireless links, NTT's researchers are at least exploring technology that uses spectrum that has so far not been utilized by anything else. In a world where radio spectrum is becoming increasingly congested, that alone might be a reason why NTT's efforts could well pay dividends in future.
For instance, the 2.4GHz and 5GHz radio bands, spectrum previously used largely for background telemetry and monitoring tasks is quickly being occupied by IEEE 802.11x WLANs and Bluetooth interconnect links. Further up the scale, wireless local loop technology is colonizing the 20GHz and 40GHz bands, the new Wireless 1394 home multi-media standard will operate at 60GHz, and automotive navigation and in-motion information systems are targeting the 76GHz band. Probably the only reason higher bandwidths have not been exploited is that until now electronic gear hasn't been up to driving signals at frequencies that are starting to approach the optical spectrum.
NTT's solution has been to harness new electronic and optical technologies to access the empty 120GHz radio band. Optical systems are used to generate the original signal which is passed, using amplitude modulation to a 300GHz photodiode, which creates an electrical signal that is passed to a direct slot antenna. The key to the whole process is the 300GHz photodiode, which harnesses optical technology, in this case the Lithium Niobate substrate originally designed for light switching, to the business of generating an electrical signal.
Inevitably, there is great deal to do before NTT's 120GHz wireless technology becomes commercially viable. At the moment, for instance, the sustained 1.25Gbps signal generated in the laboratory has a range of just 50cm. But as spectrum becomes ever scarcer over the next several decades, the motivation to refine this technology will undoubtedly intensify.