An Uplink Non-Orthogonal Multiple Access Method Based on Frozen Bit Patterns of Polar Codes

An Uplink Non-Orthogonal Multiple Access Method Based on Frozen Bit Patterns of Polar Codes

Abstract: In this work, we propose a low-complexity uplink non-orthogonal multiple access (NOMA) scheme based on polar codes. The proposed scheme, called Polar Coding Based Non- Orthogonal Multiple Access (PC-NOMA), relies on separation of user signals transmitted in the same physical resources using binary-valued patterns embedded in the frozen bit locations of polar codes. By means of frozen bit patterns unique to each user, the superimposed user signals are separated at the receiver by an interference-cancellation algorithm and a polar decoder. We demonstrate that the proposed scheme performs well even when the received powers of the multiplexed users are not significantly distinct.

Existing system: NOMA for uplink transmissions was first studied in, where a Minimum Mean Squared Error (MMSE)-based Successive Interference Cancellation (SIC) decoding was used to separate superimposed user signals. Similar to the downlink case, the performance of uplink NOMA heavily depends on the difference in received user powers at the receiver. The performance of uplink NOMA degrades

significantly when the channel conditions, such as path loss or small scale fading, among the multiplexed users are not significantly different. Power allocation schemes for uplink transmissions in a NOMA cluster was studied. Another method to create received power difference at the receiver is power back off applied at the transmitters. The user and power allocation schemes proposed for uplink NOMA rely on the assumption that the channel conditions are known precisely to achieve sufficient received signal power difference between superimposed user signals.

Proposed system: However, such an assumption may not be satisfied in real-life scenarios. Moreover, the back-off scheme proposed in relies on the assumption that the user with longer transmit distance has smaller received power, which is not guaranteed to hold in practice either. Furthermore, creating significant received power difference is difficult in communications scenarios such as satellite communications, in which users may not be able to perform significant back-off or power control due to large communication distances and variations in the user channels are also limited. In this work, we propose a novel user separation method, named PC-NOMA, based on the frozen bits of polar codes that enhance the error performance of NOMA even though the received powers of the multiplexed users are similar.

Advantages: In this work, we propose a novel user separation method, named PC-NOMA, based on the frozen bits of polar codes that enhance the error performance of NOMA even though the received powers of the multiplexed users are similar. In PCNOMA, user specific binary-valued patterns are embedded in the frozen bit locations of polar codes used for Forward Error Correction (FEC) by the transmitter devices.

The receiver identifies and decodes the data of each user by using the corresponding pattern in the frozen bit locations during the decoding procedure.

We show that by employing unique frozen bit patterns for each user and interference cancellation algorithms at the receiver, the code words of the different users can be recovered despite multiuser interference. Therefore, PC-NOMA is robust to imperfect power control unlike classical uplink NOMA.

Disadvantages: NOMA for uplink transmissions was first studied in, where a Minimum Mean Squared Error (MMSE)-based Successive Interference Cancellation (SIC) decoding was used to separate superimposed user signals. Similar to the downlink case, the performance of uplink NOMA heavily depends on the difference in received user powers at the receiver.

The performance of uplink NOMA degrades significantly when the channel conditions, such as path loss or small scale fading, among the multiplexed users are not significantly different. Power allocation schemes for uplink transmissions in a NOMA cluster was studied. Another method to create received power difference at the receiver is power back off applied at the transmitters.

Modules: Successive Interference Cancellation: INITIALLY proposed in for downlink transmissions, NOMA has attracted great attention due to its potential to provide higher spectral efficiency. NOMA is based on superposition of multiple user signals during transmission and their separation by an interference-canceler at the receiver. As NOMA is based on the detection of user signals with different received powers, user and power allocation methods are the main study topics. NOMA for uplink transmissions was first studied in, where a Minimum Mean Squared Error (MMSE)-based Successive Interference Cancellation (SIC) decoding was used to separate superimposed user signals.

Similar to the downlink case, the performance of uplink NOMA heavily depends on the difference in received user powers at the receiver. The performance of uplink NOMA degrades significantly when the channel conditions, such as path loss or small scale fading, among the multiplexed users are not significantly different.

Real –life: However, such an assumption may not be satisfied in real-life scenarios. Moreover, the back-off scheme proposed in relies on the assumption that the user with longer transmit distance has smaller received power, which is not guaranteed to hold in practice either. Furthermore, creating significant received power difference is

difficult in communications scenarios such as satellite communications, in which users may not be able to perform significant back-off or power control due to large communication distances and variations in the user channels are also limited. In this work, we propose a novel user separation method, named PC-NOMA, based on the frozen bits of polar codes that enhance the error performance of NOMA even though the received powers of the multiplexed users are similar.

Forward error correction: In PC-NOMA, user specific binary-valued patterns are embedded in the frozen bit locations of polar codes used for Forward Error Correction (FEC) by the transmitter devices. The receiver identifies and decodes the data of each user by using the corresponding pattern in the frozen bit locations during the decoding procedure. We show that by employing unique frozen bit patterns for each user and interference cancellation algorithms at the receiver, the code words of the different users can be recovered despite multiuser interference. Therefore, PC-NOMA is robust to imperfect power control unlike classical uplink NOMA. The rest of the work is organized as follows: Section II gives background information. The proposed method and analyses on the frozen bit patterns are given in Section III. Section IV gives the performance results of the proposed scheme. Section V concludes the paper.