Multi-cell coordination system and channel calibration method thereof

#The disclosure relates to a multi-cell coordination technology, and more particularly to a multi-cell coordination system and a channel calibration method thereof.

#As compared to the traditional Fourth Generation (4D) Long Term Evolution (LTE) system, more antennas will be implemented in the Fifth Generation (5G) New Radio (NR) system to increase the transmission efficiency. Theoretically and practically, multi-antenna systems have been proved to be able to make use of technologies such as precoding and/or beamforming to allow multiple User Equipment (UE) to access wireless resources simultaneously, thereby enhancing the spectrum usage efficiency. In addition, researches in recent years have indicated that if the number of antennas carried by a base station is more than four times of the number of users, the spectral usage efficiency will be able to grow linearly as the number of users increases.

#However, due to physical limitations, it is difficult for conventional base stations to be equipped with massive antennas. Therefore, relevant research has proposed that through coordinating multiple base stations to jointly perform data transmission to UE, the efficiency equivalent to that of massive antennas can be achieved. Such a structure is known as a Multi-Cell Coordination (MCC) system. In the MCC system, all base stations are controlled by a coordination server, and the coordination server can select the best transmission mode according to the user's condition. Since the clock source of each of the base stations in the MCC system is independent, Carrier Frequency Offset (CFO) between the base stations may exist, which is the largest difference as compared to a massive antenna system. In addition, other imperfect factors (for example, Sampling Clock Offset (SCO) generated due to CFO, timing offset caused by transmission delay, CFO causing downlink and uplink channels to have opposite linear phases, time-varying effect of Radio Frequency (RF) response, etc.) may also cause channel estimation to be inaccurate. Also, after precoding, Inter-Cell Interference (ICI) and Inter-User Interference (IUI) are more likely to be generated, thereby reducing the system capacity. This shows that the existing MCC systems still need to be improved.

#FIG. 1 is a schematic view of a multi-cell coordination system according to an embodiment of the disclosure.

#FIG. 2 is a flowchart of a channel calibration method according to an embodiment of the disclosure.

#FIG. 3 is a transmission model between a base station and a reference apparatus according to an embodiment of the disclosure.

#FIG. 1 is a schematic view of a multi-cell coordination system 1 according to an embodiment of the disclosure. Referring to FIG. 1, the multi-cell coordination system 1 includes at least but not limited to one or more base stations BS1˜BSj, one or more reference apparatuses RA1˜RAr, a server CS, and one or more user equipment UE1˜UEn. j, r, and n are positive integers.

#The base station BS1˜BSj may have various embodiments, such as (but not limited to) Home Evolved Node B (HeNB), eNB, Advanced Base Station (ABS), Base Transceiver System (BTS), relay, repeater, and/or satellite-based communication base station. In the embodiment, each of the base stations BS1˜BSj has one or more antennas, and the antennas can provide multiple directional beams b1˜bh, which are directed in a specific direction. For example, a base station BSb (b is a positive integer between 1 and j) transmits wireless signals using different directional beams b1˜bh in sequence through a beam sweeping technique. h and j are positive integers.

#The reference apparatuses RA1˜RAr may have various embodiments, such as (but not limited to) mobile app, personal computer, or idle base station. The so-called idle base station refers to a base station judged by the server CS as not providing any service currently or with loading lower than a specific threshold value. The server CS may also schedule the base stations BS1˜BSj and alternately use any idle one of the base stations BS1˜BSj as the reference apparatuses RA1˜RAr. In the embodiment, each of the reference apparatuses RA1˜RAr has one or more antennas. r is a positive integer.