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One of the recent trends in mobile communication industry is the use of multiple antennas in transmitter and at the receiver in order to gain diversity and achieve high bit rates. At the same time, as the mobile terminals are getting smaller, the number of electronic elements squeezed inside of them increases. Inside this hostile environment the coupling, which can considerably alter the overall system performance, is bound to emerge.To combat the multi antenna RF front-end coupling a DSP software module, positioned between the output of AD converter and any further digital signal processing is proposed. The coupling is modelled with polynomials limited to third order nonlinear behaviour. The inverse nonlinear coupling function of the 9 th degree is solved using simulated annealing (SA) approximation method. The proposed coupling cancellation algorithm is analyzed under different system conditions with different processing power requirements. A trade off between the guaranteed precision and speed is made, and the simplified algorithm version, showing good coupling cancellation characteristics, is presented.

In order to achieve higher bit rates and gain diversity, trends in mobile communication industry include the use of recent trends in communication industry include the use of multiple antennas in transmitter and at the receiver [3,4,5]. multiple antennas in transmitter and at the receiver. At the At the same time, the mobile terminals minimization is being same time the terminals are getting smaller incrementing the emphasized leaving less space to increased number of level of electronic interferences in their interior. In this electronic elements. The closeness of data metallic wires and contribution, the signal distortion known as RF front-end antenna coupling is analyzed. The coupling between antennas is m anylecroice c ts leatoiferen distortincs ta n modeled with polynomials limited to third order nonlinear significantly reduce the entire system performances [6].behavior. Nonlinear software decoupling module, located at the Nevertheless these imperfections are still not analyzed output of analog-to-digital (AD) converter, is proposed for thoroughly by scientific research community. coupling cancellation. Inside the module, signal enhancement is In this contribution a proposal how to model and overcome achieved with the approximation of inverse nonlinear coupling the multi antenna RF front end coupling distortions is function with the polynomial of gth degree. The inverse function presented and analyzed. The coupling is modeled with is obtained using guided multilevel search approximation polynomials limited to third order nonlinear behavior.method. The proposed coupling cancellation algorithm is

2. System description 2.1. Non-linear coupling model Coupling is commonly defined as undesirable transfer of energy between physical mediums (like metallic wires or optical fibers) or circuit segments. Inside multi-antennas mobile terminal the data received at the antennas is affected on its path both by direct distortion imperfections and coupling as modeled in Figure 1.

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