FIELD

The present disclosure relates generally to wireless communication and, in particular embodiments, to methods and systems for non-orthogonal multiple access communication.

BACKGROUND

A number of transmitters may be associated with one receiver in a multiple access communication system. Some transmitters may simultaneously transmit different signals on the same radio resources, thereby resulting in a collision at the receiver. Simultaneously transmitting different signals on the same radio resources would enhance overall system capacity if the receiver manages to achieve a similar receiving performance with a collision as without the collision. System capacity enhancement is relevant on both downlink and reverse link (i.e., uplink including radio transmissions from a number of terminals to a base-station).

An outcome of the collision is largely related to the methods or topologies by which the multiple simultaneous transmitters transmit on the same resource. In wireless radio communication systems, the definition, specification, or mechanism of these methods or topologies is known as non-orthogonal multiple access (NoMA) technology.

To help a receiver resolve the collision, a NoMA technology seeks to minimize the resultant interference at the receiver. Although NoMA technology typically improves the spectrum efficiency of a communication system, the non-orthogonality inherent in the NoMA technology may also create challenges in terms of transmitter and receiver implementation. It is desirable to design a non-orthogonal multiple access transmission mechanism that simplifies or facilitates transmitter and receiver implementation.

SUMMARY

Technical advantages are generally achieved, by embodiments of this disclosure which describe methods and systems for non-orthogonal multiple access communication. Some embodiments of the present disclosure provide a flexible signaling capability between network side and UE side while catering many different use scenarios to meet multiple performance metrics/system parameters.

According to an aspect of the present disclosure there is provided a method that involves obtaining, by a transmitter, an indication of a group of spreading sequences, the spreading sequences in the group being from a pool of spreading sequences in which at least two spreading sequences in the pool are non-orthogonal, and each of the spreading sequences in the group are orthogonal to one another. The method further involves spreading, by the transmitter, a sequence of modulated symbols using a spreading sequence from the group of spreading sequences to generate a sequence of spread symbols; mapping, by the transmitter, the sequence of spread symbols to a set of resource elements, to generate a set of resource-mapped symbols; and transmitting, by the transmitter to a receiver, a non-orthogonal multiple access (NoMA) signal generated from the set of resource-mapped symbols.

According to some embodiments, spreading, by the transmitter, the sequence of modulated symbols using the spreading sequence corresponding to the obtained indication, to generate the sequence of spread symbols involves: spreading, by the transmitter, a first sequence of modulated symbols using a first spreading sequence of the group of spreading sequences corresponding to the obtained indication, to generate a first sequence of spread symbols; and spreading, by the transmitter, a second sequence of modulated symbols using a second spreading sequence of the group of spreading sequences corresponding to the obtained indication, to generate a second sequence of spread symbols.

According to some embodiments, the method further involves, prior to mapping the sequence of spread symbols to a set of resource elements, combining the first sequence of spread symbols and the second sequence of spread symbols.

According to some embodiments, in the group of spreading sequences, the spreading sequences are ordered in a direction of increasing or decreasing value of a transmission metric associated with the respective spreading sequence.

According to some embodiments, the transmission metric is a performance metric that is at least one of: cubic metric (CM); peak to average power ratio (PAPR); reliability including block error rate (BLER); transmission block size (TBS); modulation and coding scheme (MCS); overloading capability; receiver capability; allocated bandwidth; maximum coupling loss (MCL) range; and number of active user equipments (UEs).

According to some embodiments, the group of spreading sequences and respective spreading sequences in the groups are each identified by a respective index value.

According to some embodiments, the method further involves, receiving, by the transmitter, a starting index for the first spreading sequence; and at least one of: a direction of increasing index or decreasing index to identify the second spreading sequence; and a hopping pattern of spreading sequence indices.

According to some embodiments, the indication further includes an indication of at least one of: a type of spreading sequence to be used by the transmitter; a number of spreading sequences per group; a number of groups of spreading sequences; a performance metric; and a user equipment identifier.

According to some embodiments, obtaining the indication comprises selecting, by the transmitter, a spreading sequence or a group of spreading sequences from the pool of spreading sequences.

According to some embodiments, selecting the spreading sequence is based on at least one of: a network access device receiving type and/or capability; traffic load; traffic characteristics; signal to interference and noise ratio; interference to noise ratio; and signal to interference ratio.

According to some embodiments, the first spreading sequence and the second spreading sequence have at least one of the following characteristics: are both associated with a same spreading factor; are associated with different spreading factors; are both associated with a same sparsity ratio; and are both associated with different sparsity ratios.

According to some embodiments, each spreading sequence in the pool of spreading sequences has a corresponding association with a user equipment identifier (UE id) and obtaining the indication of a spreading sequence from a pool of spreading sequences comprises selecting the spreading sequence based the UE id.

According to some embodiments, the group of spreading sequences is grouped based on a type of spreading sequence, wherein the type of spreading sequence is at least one of: a spreading sequence having only one non-zero element; a spreading sequence having at least two non-zero elements and at least one zero element; or a spreading sequence having no zero elements.

According to some embodiments, the method further involves, generating a pool of discrete Fourier transform (DFT) spreading sequences using a fast Fourier transform (FFT) algorithm, the pool of spreading sequences including at least one group and each group including at least one spreading sequence; wherein the generating further comprises grouping spreading sequences based on at least one of: characteristics of the spreading sequences; and based on spreading sequences in the at least one group are non-orthogonal with respect to at least one other spreading sequence in the pool, and each of the spreading sequences in the at least one group are orthogonal to one another.

According to an aspect of the present disclosure there is provided an apparatus including a processor and a non-transitory computer readable storage medium. The non-transitory computer readable storage medium stores programming for execution by the processor, the programming including instructions to: obtain, by the apparatus, an indication of a group of spreading sequence, the spreading sequences in the group being from a pool of spreading sequences in which at least two spreading sequences in the pool are non-orthogonal, and each of the spreading sequences in the group are orthogonal to one another; spread, by the apparatus, a sequence of modulated symbols using the spreading sequence from the group of spreading sequences to generate a sequence of spread symbols; map, by the apparatus, the sequence of spread symbols to a set of resource elements, to generate a set of resource-mapped symbols; and transmit, by the apparatus to a receiver, a non-orthogonal multiple access (NoMA) signal generated from the set of resource-mapped symbols.

According to some embodiments, the programming including instructions to spread, by the apparatus, the sequence of modulated symbols using the spreading sequence corresponding to the obtained indication, to generate the sequence of spread symbols comprises programming including instructions to: spread, by the apparatus, a first sequence of modulated symbols using a first spreading sequence of the group of spreading sequences corresponding to the obtained indication, to generate a first sequence of spread symbols; and spread, by the apparatus, a second sequence of modulated symbols using a second spreading sequence of the group of spreading sequences corresponding to the obtained indication, to generate a second sequence of spread symbols.

According to some embodiments, programming includes instructions to combine the first sequence of spread symbols and the second sequence of spread symbols prior to mapping the sequence of spread symbols to a set of resource elements.

According to some embodiments, in the group of spreading sequences, the spreading sequences are ordered in a direction of increasing or decreasing value of a transmission metric associated with the respective spreading sequence.

According to some embodiments the transmission metric is a performance metric that is at least one of: cubic metric (CM); peak to average power ratio (PAPR); reliability including block error rate (BLER); transmission block size (TBS); modulation and coding scheme (MCS); overloading capability; receiver capability; allocated bandwidth; maximum coupling loss (MCL) range; and number of active user equipments (UEs).

According to some embodiments the group of spreading sequences is grouped based on a type of spreading sequence, wherein the type of spreading sequence is at least one of: a spreading sequence having only one non-zero element; a spreading sequence having at least two non-zero elements and at least one zero element; or a spreading sequence having no zero elements.

