Self-organizing ad hoc femtocells for cell outage compensation using random frequency hopping

This paper analyzes self-organization of ad hoc femtocells within a macrocell infrastructure by using random frequency hopping. Femtocell users select their frequency subbands randomly, so that corresponding femtocells are capable of integrating themselves into macrocells without any exchange of information. No sensing equipment is required in femtocell devices and no time is consumed for self-organization. This makes random frequency hopping highly attractive as a self-organization policy in outage situations, i.e. where macrocell base stations fail and immediate coverage has to be provided by femtocells. We present an exact analytical model for the Bit Error Rate (BER) of femtocell users and access points using random frequency hopping, based on Signal to Interference and Noise Ratio (SINR) and Laplace transform techniques. Moreover, for performance evaluation, the model is applied to frequency-nonselective and frequency-selective channels and is verified by simulations implemented in MATLAB. The results of random frequency hopping are compared to classical resource planning with orthogonal patterns and to systems without resource planning. It is shown that random frequency hopping introduces a reduction of the BER up to a factor of 7 compared to systems where the interferer is transmitting in the same subband as the femtocell user.