###### Abstract
All the bursts detected in such an interval are sorted according to the descending values of their received power and demodulated accordingly. Each correctly demodulated burst is then locally regenerated, corrected by the received timing offset, frequency and channel gain values, and subtracted from the stored samples in the memory window. The iterative SIC process improves the signal to noise plus interference value (SNIR) after each stage of interference removal, thus increasing the chance of correctly detecting and demodulating additional bursts within locally stored samples of the received signals. This process continues for a given number of SIC iterations, or until the point that no additional bursts are demodulated. Then, the sliding window is advanced forward and the process starts from the beginning on the new memory window. It is worth noting that the E-SSA scheme does not affect the transmit waveform from the user terminal, hence no additional complexity is imposed at the transmitter. The iterative cancellation process that is more computationally intensive affects mainly the receiver that is shared among a large number of users. Despite the significant throughput enhancement offered by the E-SSA scheme (compared to the SSA), there is a theoretical performance gap between the throughput offered by the E-SSA scheme and the achievable aggregate capacity of the corresponding multiple access channel. While the E-SSA receiver uses a single user matched filter (SUMF), it is known that the use of a linear minimum mean square error (MMSE) detector can improve the aggregate throughput, or achievable capacity of spread-spectrum schemes [7,8]. This concept was further investigated in [9] and a receiver architecture based on the approximation of the linear MMSE detector at the receiver prior to successive interference cancellation was proposed. The new receiver architecture is referred to as MMSE Enhanced Spread-Spectrum Aloha (ME-SSA) [9]. Following the initial concept introduced in [9], this paper describes the outcomes of a recently completed R&D project on \"Satellite Gateway Development for Massive Uncoordinated Access Networks\", referred to as the MASSIVE project [10], where the ME-SSA scheme was implemented and its performance was demonstrated in a lab environment, representing realistic satellite IoT system scenarios. While a preliminary set of results of the MASSIVE project was already reported in [2], in this paper we provide more details regarding the project objectives, key features and main outcomes, complementing previously reported results. In particular, in the MASSIVE project the following aspects were investigated and compared to the standardized E-SSA protocol [4; 5] using a lab test-bed environment:  
* Increased flexibility of the air-interface, by supporting quadrature phase shift keying (QPSK) modulation and time domain pilot insertion, as opposed to the overlaid BPSK data and signaling channels as used in E-SSA,
* Reduction of the signal envelope peak-to-average ratio by implementing a quasi-constant envelope (CE) spread-spectrum waveform [11]. This feature enables a cost reduction of the transmitters by improving the power efficiency. In particular, it allows the non-linear power amplifiers to operate closer to the saturation point without distorting the transmitted signal. This scheme also provides a sharper power spectrum in the presence of non-linearity at the transmitter, hence much lower spectral side lobes, in order to better exploit the available bandwidth especially in the case of narrowband channels,
* Implementation of the MMSE receiver based on the multi-stage detector/despreader (MSD) approximation [9], which ensures a better performance when coupled with the QPSK modulation at the transmitter,
* Implementation of a more robust preamble searching and detection algorithm, in order to deal with harsher channel conditions (e.g., larger frequency offsets and Doppler rate values, typical of Low Earth Orbit (LEO) or Medium Earth Orbit (MEO) satellites scenarios).