A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Baseline non-orthogonal medium access <s> Compressed sensing based multiuser detection is a novel research field in massive machine to machine communication. Mainly focusing at decreasing signaling overhead, this approach implements sophisticated detection algorithms at the physical layer that jointly estimate activity and data. As a consequence, the reliability of the activity detection is crucial for the system performance as data is lost if users are erroneously classified as inactive. This paper introduces a novel approach to estimate node activity on a per frame basis by Multiple Measurement Vector Compressed Sensing approaches. This approach allows for reliable activity detection with complexity invariant of the length of the transmitted frame. Moreover, we are able to show that this approach works with only a few measurements available to the detector. In particular we demonstrate that reliable activity detection is possible if the number of observations is larger than the square root of the number of nodes in the system. <s> BIB001 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Baseline non-orthogonal medium access <s> Massive Machine Type Communication is seen as one major driver for the research of new physical layer technologies for future communication systems. To handle massive access, the main challenges are avoiding control signaling overhead, low complexity data processing per sensor, supporting of diverse but rather low data rates and a flexible and scalable access. To address all these challenges, we propose a combination of compressed sensing based detection known as Compressed Sensing based Multi User Detection (CS-MUD) with multicarrier access schemes. We name this novel combination Multicarrier CS-MUD (MCSM). Previous investigations on CS-MUD facilitates massive direct random access by exploiting the signal sparsity caused by sporadic sensor activity. The new combined scheme MCSM with its flexibility in accessing time frequency resources additionally allows for either reducing the number of subcarriers or shortening the multicarrier symbol duration, i.e., we gain a high spectral efficiency. Simulation results are given to show the performance of the proposed scheme. <s> BIB002 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Baseline non-orthogonal medium access <s> Compressed Sensing Multi-User Detection is a recently developed physical layer method to decrease signaling in massive Machine communications by using means from the field of Compressed Sensing and sparse signal processing. Within this work we use the advances of recent research and present a non-coherent CS-MUD system concept basing on a combination of multi-carrier modulation and CDMA. This so called Multi- Carrier Compressed Sensing Multi-User Detection (MCSM) concept aims at multiplexing machine-to-machine traffic in narrow band transmissions over the radio resources. Using non-coherent modulation schemes further decreases the needs for pilot symbols and increases robustness with respect to carrier frequency offsets. <s> BIB003
Most of the current research considers the conventional CDMA-like medium access in the physical layer, where a dedicated spreading code is assigned to each node in time domain. These code sequences act as signatures to distinguish the active nodes. The data frame of the node consists of only the payload and no extra control signaling is needed for medium access. As every node has dedicated sequence, there is no collision in accessing the medium access, however, the sequences are non-orthogonal and have some correlation. Authors in BIB002 BIB003  improved the medium access scheme by introducing the CS-MUD in multicarrier CDMA which is named as multicarrier compressed sensing based multiuser detection (MCSM). The proposed scheme improves the scalability and flexibility of accessing both the time and frequency resources. The spectral efficiency of the system can be improved by reducing the number of subcarriers per node. To gain frequency diversity in MCSM, a scheduling technique for allocating the subcarriers is introduced in BIB003 . In the proposed scheduling scheme, the set of allocated subcarriers changes after a predefined number of symbols. Furthermore, the subcarriers are allocated such that they lie within the coherence bandwidth of the channel, which facilitates the use of non-coherent modulation and avoids pilot transmissions for channel estimation. A hardware implementation is also demonstrated in  . Although, the non-orthogonal medium access scheme with CS-MUD facilitates the grant free medium access and increases the spectral efficiency, the main challenge is the activity detection in massive mMTC. In CS-MUD, the activity detection is dependent on the correlation between the spreading sequences. For a fixed length of the spreading sequence, increasing the number of sequences increases the correlation between sequences. Therefore, in case of massive mMTC where the number of devices is higher, allocating low correlated sequences to each node will be a challenging task. -Complexity is independent of Frame length -Robust to asynchronous transmissions -Additional data estimation step -Simulation parameters are not realistic for mMTC BIB001 