Uplink multi-user access in today's wireless communication systems can be performed by means of different multiple access methods. Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Domain Multiple Access (CDMA) and Orthogonal Frequency Division Multiple Access (OFDMA) have been utilized in various communication systems. The uplink multiple access methods might be orthogonal or non-orthogonal as well. The users can share the resources in an orthogonal manner in frequency, time or code domain the orthogonal multiple access (OMA) schemes; on the other hand, the non-orthogonal multiple access (NOMA) schemes are based on the idea that multiple users share the same resource blocks as time slot, subcarrier group by means of non-orthogonal resource allocation.
Modern wireless communication systems aim to provide higher spectral efficiency, increased connectivity density and lower latency compared to prior ones. OMA schemes might not be sufficient to support some of these demands, as the number of orthogonal resources might limit the number of supported users in the network. Main motivation behind non-orthogonal multiple access (NOMA) is to increase system capacity by utilizing the resources more efficiently and/or provide enhanced connectivity. In particular, NOMA schemes are considered for service scenarios such as Internet of Things (IoT) and massive Machine Type Communications (mMTC) which require the connection of massive number of low-cost and energy efficient devices sending sparse and small packets in the uplink communications, possibly in a grant-free manner.
Generally, NOMA is a technique which allows a central unit, such as a base station, to communicate with more users than the number of orthogonal resources in the uplink scenario. Many novel NOMA technologies have been proposed. Some of the example schemes are Sparse Coded Multiple Access (SCMA), Pattern Division Multiple Access (PDMA), Multi-User Shared Access (MUSA), Repetition Division Multiple Access (RDMA) and Interleave Division Multiple Access (IDMA). Said methods are based on the common idea of superposing different user signals in the same orthogonal resources in a controlled manner and then recover the signals by using advanced receiver embodiments.
To limit the multi-user interference and distinguish between users, user specific signatures or patterns are considered. The abovementioned NOMA methods can be categorized based on which type of signatures are used, which can be power-domain or in modulation and symbol level processing including spreading, repetition, interleaving and codebook mapping. For example, the users' information can be separated by distinct user-specific codebooks, spreading codes, interleavers, feature and cyclic shift repetition patterns for SCMA, MUSA, IDMA, PDMA and RDMA, respectively.
NOMA is the potential access scheme for communication scenarios in which there are many users and bandwidth is required to be used efficiently. An example is the satellite communications, in which the efficient use of bandwidth becomes more and more necessary with the increasing number of terminals and unmanned aerial vehicles (UAVs) using the satellite links. Especially, using NOMA schemes for channel requests and synchronization signaling would be a more efficient alternative to OMA and/or dynamical channel allocation methods by reducing delay and overhead. Another example is ad-hoc sensor networks, in which the sensors can be used in applications such as border safety and threat detection. In tactical area/ad-hoc communications, the increased number of connected radios in a network lead to a clustering-based network structure rather than a flat network. For the uplink communications inside the cluster, members can send packets to the cluster-head by NOMA schemes, which will potentially increase the total spectral efficiency and simplify the link scheduling algorithms. Furthermore, contention-based access methods used for channel allocation requests in tactical area/ad-hoc networks can be replaced by NOMA schemes to allow non-orthogonal access in a more controlled way, which in turn reduces the packet collisions and increases the system capacity.
In state of the art, in non-orthogonal multiple access schemes, we did not come across with a publication that discloses mapping the user specific signatures in frozen bit locations of the polar codes. The frozen bit locations of polar codes are particularly used to map device identity numbers in a communication control channel. For example; in the patent document No US2018198467A1, a wireless communication method in which user device identity number is mapped with frozen bits of the polar codes; information is carried by other bits of the polar codes, is disclosed. Said method is not an uplink multiple access method; it aims to embed the bit values based on the identity numbers of downlink and uplink units to the frozen bits in the communication control channel. In addition, this document does not disclose the usage of frozen bits for improving data transfer performance in an uplink non-orthogonal communication scenario of the units.
Similarly; in the patent document No WO2017106246A2 of the current art, a communication method, in which the frozen bits of the polar codes are mapped with wireless transmitter/receiver device (WTRU) identity number, is disclosed. Said method is not an uplink multiple access method; it only aims to embed bit values based on wireless transmitter/receiver device (WTRU) identity numbers to the frozen bits of the downlink communication units and to make separation between the control formats. In addition, this document does not disclose the usage of frozen bits for improving data transfer performance in an uplink non-orthogonal communication scenario of the units.
An uplink non-orthogonal multiple access method that has a low complexity to provide a grant-free, contention-based communications, is required. This kind of method aims to fulfill the connection requirements of multiple low cost and energy saving devices that sends sparse and small packages in uplink communications, by means of a system with low complexity.