Enhanced HARQ based on full-duplex and device-to-device communication in non-orthogonal multiple access

Abstract

It is expected that in the new radio communication system, there will be various types of different application services. Therefore, the traffic of the cellular network would be increased dramatically which requires much more resource than existing cellular network system. However, since the resource in the cellular network is limited, the effective usage of these resource system is demanded. Multiple access with non-orthogonality transmission has been highlighted as communication strategy since it improves spectral efficiency in cellular communication. On the other hand, a full-duplex communication and device-to-device (D2D) communication have also been viewed as promising technologies from advantages they have. The full-duplex communication is capable of transmission and reception at the same time which leads to enhanced system throughput, and D2D communication has benefit since it does not require signaling to the base station (BS) which results in fast signal process. With these technologies, in this dissertation paper, we suggest the combined technology of non-orthogonal multiple access, full-duplex communication, and D2D communication to improve hybrid automatic repeat request (HARQ) in the cellular network.

The non-orthogonal multiple access (NOMA) exploits non-orthogonality by allocating different power fractions among paired users in downlink transmission. The user who has better channel condition than others receives with lower power allocation coefficients, then the user decodes signals from the other user at first during successive interference cancellation (SIC) process.

In the case of the user in a bad channel condition, since it receives higher power allocation coefficients, it is possible to decode its own signal without SIC process. Both users should send retransmission request if they could not decode their own signal. Suppose that the user in a good channel condition can decode successfully whereas the user in a bad channel condition are not, then it is possible to make additional service from the better channel user to the worse channel gain user if the user memorizes SIC signals. Unfortunately, there are no researches about this effective re-usage of interference cancelled signal from the SIC process. In this thesis paper, we proposed effective HARQ process by exploiting interference cancelled signal. We also supposed that the user in a bad channel condition transmits an acknowledgement feedback information to the BS and the nearest user to inform the feedback information on both nodes. If the user in a good channel condition can successfully decode the signal of the bad channel gain user by SIC, the good channel user can support the bad channel user at the next time slot. Therefore, we can utilize SIC data by additional transmission from near user to far user. We generalized this process to K users case, and we analyzed the outage probability, symbol error rate (SER), and the expected number of transmission. We compared this proposed system to conventional system by simulations. Keywords Non-orthogonal multiple access, device-to-device communication, full-duplex communica- tion, hybrid automatic repeat request