CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 109111918, filed on Apr. 9, 2020. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electronic device and a method, and in particular, to a base station and a modulation method supporting lattice-partition (LP)-based downlink non-orthogonal multiple access (NOMA).

2. Description of Related Art

Most existing wireless communication systems adopt orthogonal multiple access (OMA) techniques, which may perform user multiplexing orthogonally in a time domain, a frequency domain, or a code domain to avoid inter-user interference.

With the continuous growth of mobile devices and network activities, the amount of data and the corresponding transmission rates required for wireless communications are getting higher. In order to meet such stringent transmission requirements, NOMA has been considered a promising solution for future wireless communications. As compared with OMA, NOMA allows multiple users to share the same channel resources, and can provide higher system capacity or sum capacity. Specifically, in a downlink power-domain NOMA system, message signals intended for different pieces of user equipment (UE) are superposed in the power domain at the base station for transmission on the same frequency band at the same time slot. For such a NOMA system, the message signals for different pieces of UE would interfere with each other, and successive interference cancellation (SIC) is often applied at UE receivers before detection of the desired message signals.

The theoretical capacity region of a downlink power-domain NOMA system can be achieved by employing continuous Gaussian input signals at the base station and using SIC at the UE receivers. However, using continuous Gaussian input signals at the base station is impractical, and using SIC also increases the decoding complexity and delay on the UE receivers.

In recent years, there has been a growing interest in investigating lattice-partition-based (LP-based) NOMA in which NOMA transmission is performed with practical discrete input signals at the base station and without using SIC at the UE receivers. Since LP-based NOMA involves lower decoding complexity and delay on the UE receivers, it is important to develop techniques for improving sum capacity performance of an LP-based NOMA system.

SUMMARY OF THE INVENTION

The invention is directed to a base station and a modulation method supporting lattice partition (LP)-based downlink non-orthogonal multiple access (NOMA), through which the sum capacity performance of an LP-based NOMA system is improved.

A base station supporting LP-based downlink NOMA provided by the invention is configured to communicate with strong user equipment (UE) (i.e., UE with a high channel gain) and weak UE (i.e., UE with a low channel gain), where the base station includes a processor and a transceiver. The processor is coupled to the transceiver, and is configured to modulate at least one most significant bit (MSB) of the weak UE into a first signal with first transmission power. The processor modulates at least one least significant bit (LSB) of the weak UE into a second signal with second transmission power, where the second transmission power is less than the first transmission power. The processor modulates at least one second MSB of the strong UE into a third signal with third transmission power, where the third transmission power is between the first transmission power and the second transmission power.

In an embodiment of the invention, the processor is further configured to determine the third transmission power according to the number of the at least one LSB.

In an embodiment of the invention, the processor is further configured to determine the first transmission power according to the number of the at least one second MSB.

In an embodiment of the invention, the processor is further configured to modulate at least one second LSB of the strong UE into a fourth signal with fourth transmission power, where the fourth transmission power is less than the third transmission power.

In an embodiment of the invention, the fourth transmission power is less than the second transmission power.

In an embodiment of the invention, the processor is further configured to determine the second transmission power according to the number of the at least one second LSB.

In an embodiment of the invention, the fourth transmission power is greater than the second transmission power.

In an embodiment of the invention, the processor is further configured to determine the fourth transmission power according to the number of the at least one LSB.

A modulation method for communicating with strong UE and weak UE provided by the invention is applied to a base station supporting LP-based downlink NOMA. The modulation method includes the following steps. At least one MSB of the weak UE is modulated into a first signal with first transmission power. At least one LSB of the weak UE is modulated into a second signal with second transmission power, where the second transmission power is less than the first transmission power. At least one second MSB of the strong UE is modulated into a third signal with third transmission power, where the third transmission power is between the first transmission power and the second transmission power.

In an embodiment of the invention, the step of modulating the at least one second MSB of the strong UE into the third signal with the third transmission power includes the following step. The third transmission power is determined according to the number of the at least one LSB.

In an embodiment of the invention, the step of modulating the at least one MSB of the weak UE into the first signal with the first transmission power includes the following step. The first transmission power is determined according to the number of the at least one second MSB.

In an embodiment of the invention, the modulation method further includes the following step. At least one second LSB of the strong UE is modulated into a fourth signal with fourth transmission power, where the fourth transmission power is less than the third transmission power.

In an embodiment of the invention, the fourth transmission power is less than the second transmission power.

In an embodiment of the invention, the step of modulating the at least one LSB of the weak UE into the second signal with the second transmission power includes the following step. The second transmission power is determined according to the number of the at least one second LSB.

In an embodiment of the invention, the fourth transmission power is greater than the second transmission power.

In an embodiment of the invention, the step of modulating the at least one second LSB of the strong UE into the fourth signal with fourth transmission power includes the following step. The fourth transmission power is determined according to the number of the at least one LSB.

Based on the above, the base station and the modulation method supporting LP-based downlink NOMA provided by the invention may be used to increase a sum capacity of an LP-based downlink NOMA system. The base station may distribute transmission power to a plurality of bits of the strong UE and a plurality of bits of the weak UE, so that all the bits of the strong UE obtain a higher sum of transmission power than all the bits of the weak UE. In this way, a greater sum capacity compared to that of a conventional LP-based downlink NOMA system is provided.

