Communication theory is one of the few in engineering that actually has a set of known, computable boundaries for optimum system performance, which boundaries serve as guides as to what can be achieved by design, quite apart from the technology implemented. In fact, comm systems are usually evaluated in terms of “implementation loss” compared to theory. Research in comm theory for the last 60 years has been dominated by the search for ways for systems to achieve capacity.

In this regard, around 1993 I had a very odd conversation with a friend who had already been an IEEE Fellow for many years. He was a major force in coding theory and had made serious money in a startup that went IPO. He had also written a few books on communications theory, including a giant tome on spread spectrrum. He said he thought most research topics in comm theory were at their limits. The only real problems, he continued, were implementation. (Of course, he failed to predict Turbo Codes, or even MIMO…but who’s counting?)

I was very surprised to hear this from such a creative guy. And I even thought about how it was once said (around 1900) that the patent office wasn’t needed anymore. So consider me a total optimist about creative research. My optimism has just been boosted by a recent paper discussing the death of PHY research!

The article reviews the state of comm theory and shows how in almost every aspect, the theoretical limits defined by Shannon have been achieved, at least for single cell systems. The authors (see IEEE reference below), claim only these fields need more single cell PHY research:

• Design of Short Codes
• New Coding Paradigms (beyond LDPC and turbo….e.g., fountain codes)
• Implementation Impairments (e.g., nonlinearities in power amplifiers, phase noise,…)

The authors go on to list important system problems clearly needing basic PHY research, especially for multi-cell systems. For example, Relaying and Femtocell architectures. But now, they say, it seems clear that research about single cell PHY layer behavior is so well understood that research may be un-needed, except in certain narrow areas as named above.

However, to add to the research potential of the PHY, consider this theoretical problem for single cell PHYs that has never been formally solved:

Find the optimum Bayes receiver to minimize BER, subject to an implementation complexity constraint. (Recall that the optimum Bayes maximum likelihood receiver minimizes BER without constraints).

So, maybe there is still some theoretical life left in the PHY!

REFERENCE:

M. Dohler, R. W. Heath, A. Lozano, C. B. Papadias, R. A. Valenzuela, “Is the PHY Layer Dead?”, IEEE Communications Magazine, APRIL 2011, v.49, no.4, pp159-165