QoS-controlling soft handoff based on simple step control and a fuzzy inference system with the gradient descent method

Quality of service (QoS) is an important criterion considered in mobile communication systems since it directly affects system users in terms of both call blocking and call quality. This paper aims to control the QoS in code-division multiple-access mobile communication systems by proposing two new practical methods applied to the conventional soft handoff (SHO) process based on a simple step-control method and a human-oriented information method of fuzzy inference system with classical mathematics of the gradient descent method. The output parameters selected to be controlled by adapting SHO thresholds are the trunk-resource efficiency (TRE), the forward link´s average energy per bit to the interference plus noise power spectral density ratio (E_b/I₀), and the outage probability (P_out). TRE is concerned with call blocking while E_b/I₀ is an indicator of the call quality. The number of the remaining channels of serving base station (CH_rm), the moving average number of pilots in active set of any mobile station (no_BS), and E_b/I₀ is or are selected to be one, two, or three of the control plant inputs, depending on the method applied. QoS-controlling SHO (TRE- and E_b/I₀-controlling SHO) can improve the system performance. However, which method that will be selected for use is according to the environment and the requirement of the system operator and/or users.