Telecom Providers and the Quest for Full-Duplex - Stanford University Drumline

Speak thy speech, I pray you, as I pronounce it to you, trippingly on the tongue

Shakespeare, Hamlet, III, 2

This Sunday, a friend of mine from New York, whom I have not seen for quite a while, spoke via Google Voice with regards to the design of a simple microwave link. A trifling thing any Telecoms Technician would say.

But my female friend, a former colleague of mine from C&W and devout Christian, found out that she had to seriously put her innovation cap on. Note Innovation, not thinking, as designing a Microwave Link using Motorola Motorola PTP 500 Series Point-to-Point Microwave Link  requires little thinking as everything is plug-and-play.

Rather, most of the thinking was reserved for the planning: get that wrong and you costs double when you realize that you equipment is incompatible. K.I.S.S (Keep it simple, Stupid)!

It was during the planning and discussion phase that I began to explain to my white colleague, who is more into the Bible than Engineering, between much cussin’, the nuances of Half-Duple and Full-Duplex. Rightly so, as many times while I worked at Telecom Provider C&W (2001 to 2004) as a Network Maintenance Technician that I discovered that Managers are completely clueless.

In Jamaica, most people in management positions are basically in the position via “frien’ and company” or “links” as we Jamaicans call it or “contacts” as our American counterparts enunciate.

Thus, I was quite shocked when I was once told by a manager at Telecom Provider C&W in 2003 that all communications are Full-Duplex! Full-Duplex communications do not exist, whether in Wired, Wireless or Waveguide. Fact!

Needless to say, I developed a dislike for Management, as to me Engineering and Science are my forte, not politics, debates of which are for the social climbers in society with apparently little in the way of creativity or innovation.

But the why is important. Like a CPU (Computer Processing Unit) in a computer, a communication link can only handle one thing at a time: Transmit or Receive, no matter how complex the Communication System. The oft cited example of CDMA (Code Division Multiple Access) and WCDMA Networks as being Full-duplex is misguided.

The modulation schema is transmission from Tower to UE (User Equipment) and is what makes CDMA and WCDMA spectrally efficient. However, Transmit and Receive side are still encoded as separate frequencies within the CDMA envelope and are decoded by the communication chipset as separate frequencies for DSP processing inside the customer UE (User Equipment)  and as such, Full-Duplex is still not achieved.

Even some more exotic Fiber Optic Systems, which some foreign contractors used to boast of being able to do multiple transmission and receptions, is actually Half-Duplex, as the Transmit Signal is on a different IR frequency than the Receive Signal.

The nuance of the communication occurring over the same physical link does not make it Full-Duplex, which strictly peaking is simultaneous communications over the same physical link, same channels at exactly the same time!

Self-interference have plagued previous attempts at Full-Duplex, as the Transmitter and Receiver, in any Full-Duplex attempt, have to be physically the same electronics, hence the self interference.

So I was pleasantly surprised to discover that a group of researchers Jung Il Choi, Kannan Srinivasan, Mayank Jain, Philip Levis, and Sachin Katti from Stanford University had apparently made a major breakthrough on this front.

According to the article “Stanford Technology Can Double Wi-Fi Speeds”, published February 17, 2011 1:55PM by Mark Long, NewsFactor, they achieved this feat despite the obvious problem of self interference.

This problem, again is best expressed in a paraphrased quote, this time from Stanford Assistant Professor Philip Levis, one of them members of the research team: “When a radio is transmitting, its signal is millions or even billions of times stronger than anything else it might hear - it's [like] trying to hear a whisper while you yourself are shouting. However, a radio Receiver can now be built that can filter out the substantial noise generated by its associated Transmitter, so you don't hear your own shout and you can hear someone else's whisper”

So what the clever devils did? Solutions which should be familiar to any Telecoms Technician and is elegantly simple save for the requirement of DSP (Digital Signal Processing). Basically, their research, based on Wi-Fi (IEEE 802.11n), a simple IEEE (Institute of Electronics and Electrical Engineers), but applicable to Mobile Telecoms, involves, amusingly using off-the-shelf equipment.

They basically sampled the Transmit Signal in real-time and using DSP, subtracted if from the inherently noisy weaker Receive signal. The remaining signal from the subtraction process is then resampled, again in real-time and decoded using standard decoding techniques. Thus the same channel can be reused to both Transmit and Receive on the same antenna. Full-Duplex at last!

So if this was so simple, why was it not done before?

Possibly the inclusion of the additional electronics was expensive and added to the cost of the equipment. Or possibly DSP Processors did not exist that could do the subtraction in real time. Or even better, the Management of most of these Telecoms Providers thought they had Full-Duplex all along, a kind of its-not-broke-so-don’t-fix-it kind of mentality.

Thus, so no-one bothered to do the research and make it possible, muchless make a request for University sponsored research to be done into the issue. Curiously enough, I had long suspected this was possibly a mean or removing noise from a noisy channel.

My solution was to use a summing junction with an inverted sample of the Transmit Signal to squelch out the noise. This DSP based solution is my idea, but with DSP Communication Processors.

But the Telecoms Operators should be interested. Full-Duplex on one single physical link and channel means cost savings on spectrum of 50%, with a 100% increase in efficiency, as only one channel is needed, Drumline (2002).

Coupled with the ongoing development of smaller Node B’s by Alcatel-Lucent as in my blog article entitled “Telecom Providers, Alternative Energy and ISO9001 - Alcatel-Lucent, I shrunk the Node B Kids”.

An additional bonus is that this kind of research encourages innovative thinking and partnerships between Telecoms Providers and Local Universities, such as the suggestion by research students at Rice University Researchers Ardalan Amiri Sani, Lin Zhong, and Ashutosh Sabharwal in a paper published in 2010 to use an Omni directional antenna for reception and a directional antenna for transmission as a means of improving antenna efficiency.

Their design, when tested, achieved 85% increase in Receiver Gain, meanwhile reducing the Transmitter power consumption by 51%, which in turn reduces the battery usage as stated in the article “Maybe all the iPhone needs is more Antennas”, published August 13, 2010 06:31 PM ET by John P. Mello Jr., PC World.

This worthy of a separate article and should be of especial interest to Apple Inc, who are looking to making a cheaper Apple iPhone competitive enough to beat Google Android’s pricing as concluded my blog article entitled “Apple and the Cloud Phone - Cheaper by the Dozen and Up in the Air”!

This type of relationship that is sadly lacking in Jamaica between the Telecom Providers LIME, Digicel and CLARO and suggested in my blog article entitled “How UWI can save Money in a Recession”.

Telecom Provider in Jamaica, where are on this point of argument?