Adaptive modulation and automatic modulation classification are highly demanded in software-defined radio (SDR) for both commercial and military applications. Various design options of automatic classifiers have attracted researchers in developing 3G and 4G wireless communication systems. There is an urgent need to investigate the different methods of coherent and noncoherent modulation estimations, discuss the challenges in cooperative and noncooperative communication environment, and understand the distinct requirements in real-time modulation classifications. This survey paper focuses on the automatic modulation classification methods based on likelihood functions, studies various classification solutions derived from likelihood ratio test, and discusses the detailed characteristics associated with all major algorithms.

For IEEE 802.11 wireless LANs (WLAN) with multiple access points (AP), it is critical to allocate the limited number of radio channels dynamically and efficiently. In this paper, we present a new radio channel allocation (RCA) scheme for WLANs with multiple data rates. First, we propose a new algorithm to dynamically estimate the number of active stations by using the least square estimator (LSE), which is unbiased and has minimum variance. Second, we derive an expression to evaluate the impact of the co-channel stations of an AP on the channel utilization of the AP based on the number of equivalent co-channel stations, which is the difference between the numbers of stations that are sensed by and associated with the AP. Third, we develop a new distributed RCA (DRCA) that considers the changing number of active stations, the impact of co-channel interference (CCI), and different traffic demands for different APs, which have not been considered by the existing RCA schemes. Simulation results have demonstrated that DRCA quickly finds optimal or suboptimal channel assignments and improves overall channel utilization for about 15 ~ 50% for different AP layouts, as compared to the existing schemes.

For IEEE 802.11 wireless LANs (WLAN) with multiple access points (AP), it is critical to allocate the limited number of radio channels dynamically and efficiently. This paper proposes a new framework for radio channel allocation (RCA) strategy for WLAN APs with power control capabilities. First, we formulate the RCA as a min-max optimization problem regarding channel utilization with constraints of data rate, channel quality, and transmission power. Second, we derive an expression to evaluate the channel utilization, which incorporates the condition of wireless channel, such as signal-to-noise (SNR) ratio and transmission power, in addition to the transmitting probability of a station. Third, we propose a new RCA algorithm that considers both link adaptation and power control mechanisms, in addition to the impact of co-channel interference (CCI) and multiple data rates, which have not been considered by the existing RCA schemes. Simulation results have demonstrated the effectiveness of the proposed strategy.