Non-Modulation-Based Capacity Improvement Techniques

Abstract

In Chap. 4, it was shown that for a given bandwidth radio link capacity can be improved by increasing the modulation order applied. This improvement is achieved, however, at the expense of reduced receiver sensitivity and increased complexity. From a practical point of view, therefore, there is a limit to how much modulation-based capacity improvement is appropriate if alternative improvement methods are available. In Chap. 5, it was shown that with forward error correction coding (FEC) receiver sensitivity can be increased. This increase is achieved, however, at the expense of useful capacity as redundant information is transmitted. In this chapter, we describe additional techniques employed in point-to-point links in order to enhance capacity which, when used along with modulation-based capacity improvement, can lead to extremely high-capacity capability. There techniques are (a) co-channel dual polarization (CCDP) transmission accompanied by cross-polarization interference cancellation (XPIC) in the receiver, (b) line-of-sight multiple-input multiple-output (LoS MIMO) transmission, (c) orbital angular momentum (OAM) multiplexing, and (d) band and carrier aggregation (BCA).