We investigated a simple Adaptive selection/maximal-ratio(ASM) combining cooperative system with output threshold over independent nonidentical composite Nakagami-lognormal fading channels using Mixture gamma(MG) distribution. Some novel closed-form expressions for the probability density function, the cumulative distribution function and the momentgeneration function of the output Signal-to-noise ratio(SNR) for the ASM system are derived, respectively. The average symbol error rate, outage probability and the diversity order for the ASM system are given based on the above expressions. For the purpose of comparison, we also derive the statistical characterizations of the conventional selection combining and maximal-ratio combining cooperative systems using MG distribution. Numerical and simulation results are shown to verify the accuracy of the analytical results under different scenarios, such as varying average SNR, fading parameters per hop, and the location of relaying nodes. These results show that ASM is a simple and flexible cooperative system, and can be useful in future practical deployment. We investigated a simple Adaptive Selection / maximal-ratio (ASM) combining system with output threshold over independent nonidentical composite Nakagami-lognormal fading channels using Mixture gamma (MG) distribution. Some novel closed-form expressions for the probability density function, the cumulative distribution function and the momentgeneration function of the output Signal-to-noise ratio (SNR) for the ASM system are derived, respectively. The average symbol error rate, outage probability and the diversity order for the ASM system are given based on the above expressions For the purpose of comparison, we also derive the statistical characterizations of the conventional selection combining and maximal-ratio combining cooperative systems using MG distribution. Numerical and simulation results are shown to verify the accuracy of the analytical results under different scenarios, such as varying average SNR, fading parameters per hop, and the location of relaying nodes. These results show that ASM is a simple and flexible cooperative system, and can be useful in future practical deployment.