A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> A possible future application in communications is the wireless uplink transmission in sensor networks. This application is mainly characterized by sporadic transmission over a random access channel. Since each sensor has a low activity probability, the signal for Multi-User Detection (MUD) is sparse. Compressive Sensing (CS) theory introduces detectors that are able to recover sparse signals reliably. When applied to MUD, CS detectors perform a joint detection of both data and user activity. This allows for less control signaling, since information about the activity state of each user no longer need to be signaled. Additionally, CS detectors are able to reliably detect sparse signals even in under-determined systems. In the context of transmission with Code Division Multiple Access (CDMA) this property can be exploited by reducing the length of spreading sequences, which increases the symbol-rate for a given bandwidth, and making the CDMA system overloaded. In this paper we introduce the application of greedy CS detection algorithms to detect CDMA spread multi-user data. <s> BIB001 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> This paper presents a multiuser detection technique using compressive sensing (CS) where the entries data entries of finite-alphabet signals are considered as sparse data. Thus the proposed system is underdetermined, which pave the way for the usage of lattice sphere decoding (LSD) technique. In order to demonstrate the effectiveness of the proposed method, it is tested at different sparsity levels. We show that the proposed method provides substantial performance gain over the previous work. <s> BIB002 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> One challenging future application in digital communications is the wireless uplink transmission in sensor networks. This application is characterized by sporadic transmissions by a large number of sensors over a random multiple access channel. To reduce control signaling overhead, we propose that sensors do not transmit their activity states; instead sensor activity is detected at the receiver. As sensors have low activity probabilities, the multi-user vector is in general sparse. This enables Compressive Sensing (CS) detectors to perform joint Multi-User Detection (MUD) of activity and data, by exploiting the sparsity. Since sensors are either active or inactive for several symbol durations, block-wise CS detection can be applied to improve the activity detection. In this paper, we introduce blockwise greedy CS MUD, compare it to symbol-wise greedy CS MUD, and show that statistically independent channels for each symbol further improve the activity detection for block-wise CS detection. Herein, we use Code Division Multiple Access (CDMA) as a multiple access scheme. <s> BIB003 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> In this paper, we consider a multiuser detection technique when the signal sparsity is changing over time. The key ingredient of our method is a clever switching between the CS reconstruction algorithm and classical detection depending on the sparsity level of the signals being detected. Since none of these approaches is uniformly better in a situation where the sparsity level is varying, proposed switching algorithm can effectively combine the merits of both. We show that the proposed switching algorithm provides substantial performance gain over individual algorithms in the multiuser detection of CDMA downlink. <s> BIB004 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Machine-to-Machine communication requires new physical layer concepts to meet future requirements. In previous works it has already been shown that Compressive Sensing (CS) detectors are capable of jointly detecting both activity and data in multi-user detection (MUD). For this detection we propose a new generalized Group Orthogonal Matching Pursuit algorithm that allows the use of additional side information regarding the sparsity structure. As a specific example, we exploit the information of a sparsity-aware Viterbi decoder in an iterative feedback loop to improve the activity detection. Here, a significant improvement of the activity detection is already achieved by executing only a single additional detection and decoding step. <s> BIB005 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Machine-type communications are quite often of very low data rate and of sporadic nature and therefore not well-suited for nowadays high data rate cellular communication systems. Since signaling overhead must be reasonable in relation to message size, research towards joint activity and data estimation was initiated. When the detection of sporadic multiuser signals is modeled as a sparse vector recovery problem, signaling concerning node activity can be avoided as it was demonstrated in previous works. In this paper we show how well-known K-Best detection can be modified to approximately solve this finite alphabet Compressed Sensing problem. We also demonstrate that this approach is robust against parameter variations and even works in cases where fewer measurements than unknown sources are available. <s> BIB006 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <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> BIB007 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> The emergence of Machine-to-Machine (M2M) communication requires new Medium Access Control (MAC) schemes and physical (PHY) layer concepts to support a massive number of access requests. The concept of coded random access, introduced recently, greatly outperforms other random access methods and is inherently capable to take advantage of the capture effect from the PHY layer. Furthermore, at the PHY layer, compressive sensing based multi-user detection (CS-MUD) is a novel technique that exploits sparsity in multi-user detection to achieve a joint activity and data detection. In this paper, we combine coded random access with CS-MUD on the PHY layer and show very promising results for the resulting protocol. <s> BIB008 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Rapid growth in the number of users (largely sensor nodes) of most Internet-of-Things (IoT) applications is widely expected in recent years. 3G or 4G protocols are designed for regular Human-to-Human communication purposes instead of low-rate, Machine-to-Machine (M2M) communication, which is the basis of IoT. Comparatively, traditional spread-spectrum protocols such as Code-Division Multiple Access (CDMA) are considered applicable for the majority of IoT applications. However, they are unsuitable to be utilized in the expected massive-IoT scenarios. The traditional Multi-User Detection (MUD) approach used in these protocols has poor scalability. When the number of users reaches hundreds, the complexity and hardware cost of traditional MUD become impractically high. In this paper, we employ the concept of Multiple Measurement Vector Compressive Sensing (MMV-CS) to exploit the feature of user sparsity in spread-spectrum-based IoT applications. By reformulating the CS detection model, a memory reduction of approximately 9,400 times can be achieved. Along with other hardware cost-down, the proposed simplified structure of the reconstruction model also allows a faster detection speed (∼10x to 1000x improvement) while a satisfactory level of Bit-Error-Rate (BER) is still maintained. <s> BIB009 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <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> BIB010 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <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> BIB011 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> In this paper, we present a new structure for compressive sensing(CS)-based random access (RA) scheme for machine-type communications (MTC). In the proposed scheme, we consider a one-shot transmission in which users transmit their packets right away by spreading them with multiple spreading sequences (MS) over a frame without waiting for scheduling grant from the base station. The scheme is designed for delayconstrained & sporadic traffic where a massive number of users have a very low activity factor, small packet sizes and limited power. It has been shown that by employing the proposed scheme the channel access success rate can be increased without incurring additional detection complexity. In different regions of users' activity factor, two sources of random access failure have been identified. In the design of the MS scheme, the tradeoff between these two factors can be considered to optimize the system. For strictly delay-intolerant applications where retransmission is not allowed, it is shown that about 10 times more users can be supported by employing MS in comparison with a type of random access in long term evolution (LTE) network. <s> BIB012 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> This paper presents a compressive sensing (CS)-based one-shot random access (RA) scheme for massive and delay-intolerant machine-type communication (MTC). Furthermore, an iterative order recursive least square (IORLS)-based orthogonal matching pursuit (OMP) decoding algorithm is employed for high accuracy and low decoding complexity. By employing IORLS, it has been shown that near oracle detection, i.e., detection when the activity of users is known a priori, can be achieved. <s> BIB013 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> We introduce a "one shot" random access procedure where users can send a message without a priori synchronizing with the network. In this procedure a common overloaded control channel is used to jointly detect sparse user activity and sparse channel profiles. The detected information is subsequently used to demodulate the data in dedicated frequency slots. We analyze the system theoretically and provide a link between achievable rates and standard compressing sensing estimates in terms of explicit expressions and scaling laws. Finally, we support our findings with simulations in an LTE-A-like setting allowing "one shot" sparse random access of 100 users in 1ms. <s> BIB014 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Non-orthogonal multiple access (NOMA) has become one of the promising key technologies for future 5G wireless communications to improve spectral efficiency and support massive connectivity. However, in the uplink grant-free NOMA system, the current near-optimal multi-user detection (MUD) based on message passing algorithm (MPA) assumes that the user activity information is exactly known at the receiver, which is impractical yet challenging due to anyone of massive users can randomly enter or leave the system. In this paper, inspired by the observation of user sparsity, we jointly use compressive sensing (CS) and MPA to propose a CS-MPA detector to realize both user activity and data detection for uplink grant-free NOMA. Specifically, the MUD problem is firstly formulated under CS framework by exploiting user sparsity, and then user activity can be detected by sparse signal recovery algorithms in CS. Then, MPA can be performed to reliably detect active users' data. It is shown that the proposed CS-MPA detector with affordable complexity not only outperforms the conventional MPA detector without user activity information, but also achieves very close performance to the genie- knowledge MPA detector with exact knowledge of user activity, especially when the signal-to-noise ratio (SNR) is high. <s> BIB015 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Conventional spatial modulation (SM) is typically considered for transmission in the downlink of small-scale multiple-input–multiple-output (MIMO) systems, where a single antenna element (AE) of a set of, e.g., $\mbox{2}^p$ AEs is activated for implicitly conveying $p$ bits. By contrast, inspired by the compelling benefits of large-scale MIMO (LS-MIMO) systems, here, we propose an LS-SM-MIMO scheme for the uplink (UL), where each user having multiple AEs but only a single radio frequency (RF) chain invokes SM for increasing the UL throughput. At the same time, by relying on hundreds of AEs and a small number of RF chains, the base station (BS) can simultaneously serve multiple users while reducing the power consumption. Due to the large number of AEs of the UL users and the comparably small number of RF chains at the BS, the UL multiuser signal detection becomes a challenging large-scale underdetermined problem. To solve this problem, we propose a joint SM transmission scheme and a carefully designed structured compressive sensing (SCS)-based multiuser detector (MUD) to be used at the users and the BS, respectively. Additionally, the cyclic-prefix single carrier (CPSC) is used to combat the multipath channels, and a simple receive AE selection is used for the improved performance over correlated Rayleigh-fading MIMO channels. We demonstrate that the aggregate SM signal consisting of multiple UL users' SM signals of a CPSC block exhibits distributed sparsity. Moreover, due to the joint SM transmission scheme, aggregate SM signals in the same transmission group exhibit group sparsity. By exploiting these intrinsically sparse features, the proposed SCS-based MUD can reliably detect the resultant SM signals with low complexity. Simulation results demonstrate that the proposed SCS-based MUD achieves a better signal detection performance than its counterparts even with higher UL throughput. <s> BIB016 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> In Internet of things (IoT)-oriented 5G systems, more efficient multiple access is essential to handle the massive number of sporadic traffic generating IoT users/devices, which are inactive most of the time but regularly or irregularly access or leave the wireless network without human interaction. Non-orthogonal multiple access (NOMA) is a promising solution to support massive connectivity in future IoT-oriented 5G systems, where the dynamic multi-user detection (MUD) is required. In this paper, by exploiting the structured user activity sparsity, we propose the structured matching pursuit (SMP)-based dynamic MUD to jointly realize dynamic multi-user signal detection in several continuous time slots based on structured compressive sensing (SCS). Specifically, in several continuous time slots, the set of active users usually changes slowly due to continuous data transmission. Therefore, we can divide the active user sets into two different parts, i.e., the common active user set and the dynamic active user sets. Accordingly, the proposed SMP-based dynamic MUD simultaneously detects the common active user set in all time slots at first, and then the dynamic active user sets are detected in each single time slot individually. Simulation results show that the proposed SMP-based dynamic MUD can achieve much better performance than that of the conventional compressive sensing (CS)-based MUD, while they share very similar computational complexity. <s> BIB017 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Non-orthogonal multiple access (NOMA) can support more users than OMA techniques using the same wireless resources, which is expected to support massive connectivity for Internet of Things in 5G. Furthermore, in order to reduce the transmission latency and signaling overhead, grant-free transmission is highly expected in the uplink NOMA systems, where user activity has to be detected. In this letter, by exploiting the temporal correlation of active user sets, we propose a dynamic compressive sensing (DCS)-based multi-user detection (MUD) to realize both user activity and data detection in several continuous time slots. In particular, as the temporal correlation of the active user sets between adjacent time slots exists, we can use the estimated active user set in the current time slot as the prior information to estimate the active user set in the next time slot. Simulation results show that the proposed DCS-based MUD can achieve much better performance than that of the conventional CS-based MUD in NOMA systems. <s> BIB018 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Non-orthogonal multiple access (NOMA) has been regarded as one of the promising key technologies for future 5G systems. In the uplink grant-free NOMA schemes, dynamic scheduling is not required, which can significantly reduce the signaling overhead and transmission latency. However, user activity has to be detected in grant-free NOMA systems, which is challenging in practice. In this letter, by exploiting the inherent structured sparsity of user activity naturally existing in NOMA systems, we propose a low-complexity multi-user detector based on structured compressive sensing to realize joint user activity and data detection. In particular, we propose a structured iterative support detection algorithm by exploiting such structured sparsity, which is able to jointly detect user activity and transmitted data in several continuous time slots. Simulation results show that the proposed scheme can achieve better performance than conventional solutions. <s> BIB019 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> In multiple measurement vectors (MMV) problems, the sparsity structure, i.e., the support of the measurement vectors, remains constant for multiple instants. For machine type communication (MTC) context, this sparsity structure may remain constant over all symbols in a frame, which can be termed as frame-wise sparsity. Instead of employing symbol-by-symbol detection based on algorithms such as orthogonal matching pursuit (OMP), group orthogonal matching pursuit (GOMP) can take advantage of this constant sparsity structure and decodes group of symbols together in order to improve the accuracy. Unfortunately, the exponential growth in computational complexity of the GOMP algorithm with the group size prohibits it from increasing the group size and fully exploiting the frame-wise sparsity. This letter presents an iterative order recursive least square (IORLS) algorithm, which can exploit the frame-wise sparsity and increase accuracy. IORLS iteratively employs a modified OMP operations over a frame to gather the sparsity support information with manageable complexity. IORLS substantially reduces complexity by avoiding the matrix inversions in OMP and GOMP algorithms. Furthermore, it has been shown that the proposed algorithm is robust against noise, achieving near-oracle estimation performance. <s> BIB020 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> In this paper, we propose a compressive random access scheme using multiple resource blocks (RBs) to support massive connections for machine type communications (MTC) in 5G systems. The main advantage of the proposed scheme over conventional compressive random access schemes is that there can be more devices than preambles as each active device is to randomly choose a preamble for connection to an access point (AP) at the cost of preamble collisions. To mitigate the performance degradation due to preamble collisions, a block of subcarriers is divided into multiple RBs and an active device is to randomly choose an RB and a preamble within the chosen RB. For multiple signal detection, we consider a low- complexity compressive sensing (CS) algorithm. We also demonstrate that using multiple RBs in random access can offer the benefits of reducing the computation time with a multicore processor as well as improving the throughput. <s> BIB021 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Non-Orthogonal Multiple Access (NOMA) has been considered to be one of the promising key technologies for future wireless communications and broadcasting return channels due to its high spectral efficiency under massive connectivity. The major challenge of NOMA is to realize interference cancellation and detect the optimal transmitted signals among multiple users. The message passing algorithm (MPA) based multi-user detection (MUD) has been developed to approximate optimal signals from multiple users. However, the conventional MPA always suppose that the user-activity is exactly known at the receiver, which is impractical in real systems. Thus, precise user-activity detection is significant in realizing MPA based NOMA system. In this paper, we propose a compressive sensing based time-frequency joint NOMA scheme in the uplink grant-free low density signature orthogonal frequency division multiplexing (LDS-OFDM) systems, where the priori information obtained from the timedomain m-sequence and the frequency-domain training sequence are utilized for user-activity detection under the framework of CS, while the MPA is performed for the successive user-data detection. The proposed method has a superior performance and less complexity compared to the conventional MPA detector in numerical stimulation. <s> BIB022 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> A key technology in the 5th generation (5G) wireless communications is non-orthogonal multiple access (NOMA) which can effectively support massive random access. Since in a 5G system the number of active users generally does not exceed 10% of the total number of users in practice, the main challenge for multi-user detection (MUD) is the joint detection of sparse active users and their data. To address this challenge, we propose a novel compressed sensing based NOMA (CS-NOMA) scheme which can be deployed in a CDMA or an OFDM system and does not have control signaling overhead and need no knowledge of the active state of users. In the proposed scheme, K users are multiplexed over N shared resources (K ≫ N). Then, a CS-based MUD is applied to the proposed CS-NOMA scheme. Simulation results show that, in the case that active users are sparse (e.g., 10%), the proposed scheme can achieve a superior performance even when the system loading is up to 300%. <s> BIB023 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Based on successive hypothesis testing, we propose an approach for sparse signal recovery and apply it to random access to detect multiple block-sparse signals over frequency-selective fading channels. By introducing the sparsity variable, the proposed approach decides the presence or absence of the signal in each stage. To mitigate the error propagation, adaptive ordering is also employed as a greedy algorithm. From simulation results, it is shown that the proposed approach performs better than the block orthogonal matching pursuit algorithm, which is a well-known greedy compressive sensing algorithm for compressive random access. <s> BIB024 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> In this paper, we study random access for machine-type communications based on a multiple access scheme that exploits different channel state information (CSI) from active devices under frequency-selective fading, which is called channel division multiple access (ChDMA). In ChDMA, in order to use a low-complexity compressive sensing (CS) algorithm for multiuser detection (MUD) with a high transmission rate, we propose to use index modulation. Since the CSI is used as a signature for MUD, the CSI estimation becomes crucial. For the CSI estimation, pilot transmission can be considered where each active device randomly chooses a pilot from a set of pre-determined pilots. Since the CSI estimation suffers from pilot collision in this case, we propose multiple pilot transmissions and show that a low probability of collision can be achieved. A CS-based approach is derived not only to estimate the CSI, but also to detect randomly selected multiple pilot signals by exploiting the sparsity of active devices over frequency-selective fading channels. <s> BIB025 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> In machine-type communications (MTC), a number of devices are present in a cell, but only a few of them attempt to access by sending preambles or pilots. For the sparse activity of devices, compressive sensing (CS) can be applied for joint detection of active devices and estimation of channel profiles. In this paper, a theoretical connection between pilots and the coherence of a CS measurement matrix is revealed for CS-based detection and estimation. Then, the Zadoff-Chu (ZC) and the power residue (PR) sequences are studied as potential candidates for pilot signals in CS-based random access. It is also shown that the CS measurement matrices from the ZC- and the PR-based pilots have theoretically bounded low coherence, which presents a theoretical guarantee of reliable recovery performance. Simulation results demonstrate that the proposed deterministic pilots outperform random binary and complex-valued pilots for CS-based random access in MTC. <s> BIB026 </s> A Survey: Non-Orthogonal Multiple Access with Compressed Sensing Multiuser Detection for mMTC <s> Category <s> Compressed sensing based multiuser detection is a recently developed scheme to cope with the massive machine-type communication in the fifth generation wireless system. Activity detection is one of the critical steps in compressed sensing based multiuser detection which determines the performance of system. In this paper we address this issue and propose two approaches for efficient detection and recovery of the signal. First, the diversity in the multiuser detection is increased by using a circularly right-shifted version of the sensing matrix along with the original sensing matrix for spreading the user data. Secondly, a deterministic sensing matrix based on Zadoff-Chu sequences is designed and accordingly a low complexity decoding algorithm is proposed which significantly reduces the detection error rate. It is shown that the proposed methods reduce the bit error rate by magnitude of one and two. <s> BIB027
References CS-Multiuser detection algorithms   BIB002 BIB006  BIB001 BIB003 BIB005 BIB017 BIB018 BIB019 BIB020 BIB007 BIB024 BIB009 CS-Medium access schemes BIB010 BIB011  BIB012 BIB013 BIB021 BIB025 BIB014 BIB027 BIB026 Combination of CS-MUD with other techniques BIB015 BIB022 BIB023 BIB016 BIB008 BIB004 To overcome the limitations of the code domain NOMA and to more efficiently exploit the MTC traffic pattern, recently, compressive sensing based multiuser detection (CS-MUD) techniques are used for enabling the code domain NOMA. In order to accommodate large number of nodes within the available resources, non-orthogonal spreading sequences are assigned to the nodes. At the receiver, both the activity and data are jointly detected by using CS-MUD techniques. The CS-MUD exploits the fact that the mMTC transmission is sporadic, i.e., a small number of nodes are active at a time, which allows the compressive sensing techniques to detect the activity at the receiver. The non-orthogonal spreading sequences serves as signatures for the users, which are used to distinguish the active users at the receiver. In NOMA with CS-MUD, the users transmit their data directly using the spreading sequences, thereby, avoiding the control signaling overhead to access the channel.