Given the various questions that keep coming from readers I want to briefly summarize where we are on the xMax issue from a technical standpoint.
xMax is a new modulation technique using a particular type of waveform. It’s performance is comparable to that of conventional techniques. As a physical layer it does not offer any advantage over the physical layers used in existing systems. Statements made on the xG ompany webpage such as “… xG Flash Signal will offer significant improvements in speed, range, and power savings over existing technologies.” and “xG Flash Signal is a breakthrough system design that improves RF signal performance at its most elemental level – the physical layer. Flash Signal uses revolutionary single cycle modulation to deliver longer range and lower power communications.” are not supported by any data and are in direct contradiction of well established principles of communication theory, as well as xG Technology’s own BER curve. All of the claimed advantages of xMax derive from the one basic claim of power efficiency which is simply false. Given xG Technology’s publication of the BER vs. Eb/N0 curve I hope that we can put to rest these claims and move on to other more interesting topics.
The fact that xMax offers no advantages as a physical layer does not mean that it can not work. Technical analysis of xMax shows that in principle it can be used as the physical layer of a wireless network, provided that xG Technology addresses the myriad of other issues involved in building such a network. It should be clearly understood, however, that the xMax based network can not perform better than a network built using conventional communication technology. While I find it puzzling that someone will go to so much trouble to re-invent the wheel, when perfectly good (or better) wheels are readily available, this is a business decision which is beyond the scope of what I want to discuss in this blog. There may well be valid non-technical reasons for this approach.
As far as I am concerned we seem to have exhausted the issue of the xMax modulation technique – there is simply nothing very interesting there. Now a complete working system involves many issues beyond the choice of the modulation technique which has been the focus of the discussion so far. There are physical layer issues such as the multi-access method (FDMA, TDMA, etc.), handling of fading, rate adaptation, choice of coding, power control, use of multiple antennas, and so on. Then there is the MAC layer and its various protocols, scheduling of users, Quality of Service, mobility, handoff, and the list goes on. Very little information seems to be available at this time on how these topics are being addressed in the overall xMax system. The information provided by xG Technology, its patents and the media, focuses almost entirely on the modulation technique and its non-existent advantages. This is rather peculiar and potentially worrisome. I hope to discuss some of these issues if and when some meaningful technical information about them becomes available.