Ultra wide band (UWB) may offer very efficient solutions for various communication and sensing applications. Two approaches have emerged, which meet all the communication requirements: impulse and multi-band systems. The present work is concerned in the second approach. So, we propose to use orthogonal functions called Modified Gegenbauer Functions (MGF) in a multi-band UWB system occupying the 3-6 GHz frequency band. Different scenarios are studied and compared in the scope of a system offering communication and location capabilities for subway trains. In order to evaluate the performance of the proposed system, the bit error rate (BER) values for communication are calculated and analyzed in the presence of multi-user interference, assuming asynchonous users. It is shown that Gegenbauer functions offer the performance required for our multi-band UWB communication and location system.