In recent years there have been many researches and trials to combine many heterogeneous wireless works, and tried to integrate them into one network by establishing standard like IEEE 802.16. Above of all, integrated network should not degrade QoS(quality of service). For the purpose, BS(base station) should allocate appropriate bandwidth to each traffic by using good scheduler. In wireless networks, SNR is changing with time due to many reasons like fading. If users use fixed modulation for time varying SNR, then for low SNR large amount of error can occur, so QoS may not be guaranteed. But exact estimation of SNR is difficult and estimating method is complex and expensive. So we proposed SNR estimation algorithm using previous error rate, and by using the algorithm we propose time slot allocation algorithm. The proposed algorithm guarantee minimum throughput and delay requirement not only in single hop network, but also in multi-hop network.