Nguyen Van Vinh, Dao Van Da, Hoang Hai Hung, Nguyen Thi Phuong Hoa, Nguyen Thi Tham, and Nguyen Thi Nhung, “OPTIMAL IPW ALGORITHM IN OFDM-BASED COGNITIVE RADIO SYSTEMS”, jst, vol. 10, pp. 45-49, Apr. 2020.