‘Transpositional Modulation’ Could Greatly Boost Data Rates

TM Technologies, a division of Medusa Scientific, announced this week that it has successfully demonstrated a “breakthrough modulation technology” that has the potential to increase data rates between two and 33 times within a given amount of bandwidth.

The new modulation technique is called “Transpositional Modulation”(TM). Medusa Scientific's Chief Scientist Rick Gerdes said it is “the first truly new form of modulation in more than a decade, and the only form of RF modulation that has a real DC response and is completely transparent to other modulation forms.”

According to Gerdes: “TM allows transmission of much higher data rates than is possible with other forms of modulation alone; can be added to existing modulations or can operate stand-alone; is immune to Doppler effects; can combine multiple different data streams into and out of a single signal, and; generally provides the capability to meet the data rate demands of UHD and other data-intensive RF requirements.”

The news release said the company expects to complete a prototype satellite modem for testing in August that is expected to dramatically increase “bent-pipe” data rates. A demonstration of transmission of 4K UHD is planned for early September.

No details were provided on how transpositional modulation works, but the news release explanation triggered memories of an early DTV transmission technology. The news release said the patent on TM is still pending, but a search for patents with Richard Gerdes as the inventor turned up Patent #5200715 – Waveform modulation and demodulation methods and apparatus and Patent #5327237 – Transmitting data with video.

The abstract for Patent #5200715 reads: “The modulation circuit defines a non-linear voltage current transfer function wherein at low voltage levels the current voltage transfer function is substantially linear and at higher voltages, the transfer function is substantially exponential. The modulation circuit can be designed of three parallel branches…Demodulation circuitry is also disclosed that includes a circuit for determining the instantaneous phase and amplitude and then processing circuitry to decode the modulation information based upon the sampled phase and amplitude data.”

Drawings included in the Patent show the modulation results from changing the shape, but not the overall phase, frequency or amplitude, of the original RF sine wave by doing things such as adding indentations to it.

During the selection of the U.S. DTV standard, this was called the GENESYS system. It is listed in Development of HDTV Emission Systems in North America by Robert Hopkins at the Advanced Television Systems Committee and Kenneth P. Davies of Canada’s CBC. The paper describes the modulation “as a form of waveform modulation which carries the digital HDTV signal by modifying the shape--not the frequency or amplitude or phase--of the carrier making it 'invisible' to frequency or amplitude or phase demodulators.”

More information on transpositional modulation should be available after the announced demonstrations. The information provided so far mentioned an improved data rate in the same bandwidth, but I didn't see any mention of the critical third item in any modulation technology--the signal to noise (SNR) required to receive the higher data rate signal.

Doug Lung

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.