Background & Objectives: Spectrum sensing is a feature of cognitive radio (CR) systems which is proposed to improve spectral utilization of wireless signals. One of the sensing methods is the non-coherent energy detector, and even though it is computationally more effective than coherent methods, it has critical drawbacks, e.g. requirement of certain signal-to-noise ratio and number of samples. Moreover, type of digital modulation employed also affects the performance of the energy detectors. Therefore, the performance of the energy detectors is investigated for phase shift keying (PSK) and quadrature amplitude modulated (QAM) signals. Such an analysis is essential, because once the performance of the different modulated signals are understood; next generation wireless networks (NGWNs) and CRs can be designed in such a way that the arduous and expensive planning stage is omitted. This way, a higher data rate can be achieved by using the proper modulation type and/or order for indoor CRs and NGWNs. Methods: Instead of false alarm and missed detection analysis, probability mass function vs. energy detection statistics are introduced to better understand the effect of modulation type, order and wireless channel. A measurement setup is developed to consider line-of-sight and non-line-of-sight conditions. Signals are constructed, transmitted and recorded based on the signal model provided. All experiments took place in the Wireless Research Laboratory of the department of ECEN at Texas A&M University at Qatar. Results: The results show that performance of the energy detector changes drastically with the digital modulation scheme employed at the transmitter side. Another interesting point is the impact of the used energy detector samples (N). As expected, with the increase in N, the impact of central limit theorem (CLT) can be felt in a clearer way as well. Conclusions: By using the experimental results, the design and deployment of future cellular mobile radio systems such as femtocells in Qatar could be optimized. This is crucial, since most communications such as voice/internet/text traffic occur inside buildings especially for rapidly changing network topographies as is the case with the city of Doha. This way, data rate and speed can be optimized for the indoor environments.