Load pull compensation in multi user massive MIMO

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The purpose of this research is to determine an algorithm and/or process that lends itself to a practical solution for load pull (mutual coupling), an issue that manifests itself in 'multi user massive multiple in multiple out' (MIMO) systems. Antenna arrays used for beam forming or MIMO require the antenna elements to be physically close to each other. With this arrangement, active antenna elements affect their neighbours and visa versa; modifying the antenna impedance (at a given frequency) and electromagnetic field(s). This causes unwanted shifts in radiated power, RF beam direction and intensity. Digital pre-distortion used to compensate for the non linear nature of power amplifiers has been used extensively and can also be employed to compensate for load pull. With a uniform linear phase difference across antenna elements, such as in conventional beam steering, the digital pre-distortion coefficients can be calculated relatively easily. However, with MIMO, the antenna elements phase and amplitude configuration is irregular and hence the effects of antenna elements on one another cannot be predicted. The dynamic MIMO channel matrix, in conjunction with the power amplifier transfer function and the antenna array characteristics are thus processed by said novel algorithm that calculates the digital pre-distortion coefficients for each element, actively compensating for load pull at each element. This research details the MIMO load pull compensation algorithm and a practical real-time hardware/firmware solution. The resulting algorithm/implementation works within a large frequency range and for any PA/antenna combination. It is also inexpensive, low power and scale-able to ultra massive MIMO.