# Advanced Communications

Advanced Modulation:

The most advanced modulation used in wireless is QAM-modulation. It uses two orthogonal eigen- functions (Sine and Cosine) to double the spectral efficiency. To increase throughput, one has to increase the order of QAM-Modulation (i.e. 16, 32, 64, 128, …etc.). The higher the order, the higher the data rate and spectral efficiency but it requires higher signal to noise (S/N) ratio. As the requirement for S/N goes up, it means that the distance between TX and RX is reduced for a given TX power allowed. Sine and Cosine are not the only orthogonal eigen-functions. It is indeed possible to minimize Time-Bandwidth product of a given channel achieving the highest spectral efficiencies using new orthogonal eigen-functions. These functions are derived through minimization of Time-bandwidth product through Lagrange minimization and the resulting equations are like Schrodinger equation with a harmonic oscillator potential. The solutions are very well known in quantum mechanics and they can be used as basis functions in modulation. The advantage here is that there are infinite number of these functions and each is orthogonal to any other. If one would peg the highest order of these functions to the physical bandwidth, then all lower orders that consume less bandwidth, can be overlaid on top and therefore the same physical bandwidth is reused multiple time and each represents a new channel. When these channels are aggregated, one can improve spectral efficiency. This improved spectral efficiency can be used as a currency to either increase the number of users, or the throughput, or the quality of the links, or a little bit of each.

Spatial Multiplexing:

A very well-known feature of electromagnetic waves is its polarization. This polarization can be in form of linear (vertical and Horizontal) or circular (left-hand circular and right-hand circular) or even elliptical polarizations. However, in all these cases the electric field spans on a plane perpendicular to direction of propagation (Plane and parallel wave front). All polarizations have only two states because they are the classical analog of spin in quantum mechanics that also have only two states. However, there is a new discovery that photons not only carry spin, but they can also carry Orbital Angular Momentum (OAM). This quantum property of photons also has a classical analog in electromagnetic waves which is called helicity. This property of photons is not limited to only two states, but rather infinite number of states and therefore infinite number of helicities. These helicities can be generated with holograms in photonics and patch antennas in RF. Once generated, they can be muxed together and each helicity would represent a distinct channel as all the helicities are mutually orthogonal to one another. There are multiple patents on using spatial orthogonal functions for improving spectral efficiencies, control of interference, and massive MIMO. These patents have multiple application areas in wireless backhaul, fixed wireless access, free space optics as well as fiber. There are patents on how antennas could be built to twist electromagnetic waves in conjunction with dish antennas to increase the gain and use the helicities of the wave fronts as orthogonal independent channels. There are also some patents on new elliptical core fibers that allow muxing of new orthogonal channels. New multiple access technologies are also introduced in some of these patents.