WO2002035720A1

WO2002035720A1 - A method of framing pilot and traffic signals in the cdma system and data frame thereof

Info

Publication number: WO2002035720A1
Application number: PCT/CN2000/000359
Authority: WO
Inventors: Cosmos Zhang; Daoben Li
Original assignee: Linkair Communications. Inc.
Priority date: 2000-10-24
Filing date: 2000-10-24
Publication date: 2002-05-02
Also published as: HK1052416A1; AU2001211262A1; CN1421070A; WO2002035720A8

Abstract

The present invention discloses a method of framing pilot and traffic signals in the Code Division Multiple Access (CDMA) mobile communication system, and the data frame structure on the basis of the method, which utilizes time division multiplex in the framing pilot and traffic signals, so as to reduce Multiply Access Interference (MAI) therein, and interposes a plurality of idle time slots between the time division multiplexed pilot and traffic signals to decrease Adjacent Cell Interference (ACI) therein. The performance of the system can be improved and thus the capacity of the CDMA system can be increased with the method disclosed by the present invention.

Description

Pilot and service signal framing method for CDMA system and data frame

Technical field

The present invention relates to the field of digital mobile communication systems, and in particular, to a method for framing a pilot and a service signal applied in a code division multiple access (CDMA) communication system and a data frame thereof. Background of the invention

The introduction of code division multiple access (CDMA) technology can effectively alleviate the contradiction between the limited frequency band and the needs of unlimited users, so the code division multiple access (CDMA) mobile communication system has increasingly become the mainstream of mobile communications. In a CDMA cellular mobile communication system, since users in a cell and users in different cells obtain different code division channels by using different spreading address codes, for an N-cell cellular mobile communication system, Its frequency reuse factor is reduced from N in a frequency division multiple access communication system or a time division multiple access communication system to 1, that is, all cells can share the entire bandwidth. At the same time, in a CDMA communication system, since the bandwidth of the spread spectrum signal is wider than that of other systems, the multipath signal can be separated, thereby obtaining a diversity effect. CDMA communication systems are more convenient and make fuller use of technologies such as voice activation and directional antennas. All of these make the spectrum efficiency of CDMA system much higher than other systems, about 20 times that of frequency division multiple access mobile communication systems and 10 times that of time division multiple access mobile communication systems.

In CDMA mobile communication systems, pilot signals are essential as the main basis for channel estimation, synchronization, and soft handover. Because of the existence of the pilot signal, the receiver can effectively estimate the characteristics of the channel, and thus be applied to the demodulation of the signal. The existence of pilot signals also helps complete the synchronization of the system, and provides the necessary basis for key technologies in CDMA systems such as power control and handover. Therefore, the design of pilot signals in CDMA systems is very important. There are already various methods of framing pilot signals. For example, IS95 and CDMA2000 in the third generation mobile communication system use the pilot channel method, that is, the pilot signal By occupying an address code different from the service signal, the number achieves code division multiplexing with the service signal. Because the pilot signal must occupy a larger transmit power to obtain better signal reception quality, such as

IS95 is 20% of the total transmit power of the base station, so the existence of the pilot channel has multiple MAI (Multiply Access Interference) for traffic signals and ACI (Adjacent Cell Interference) for neighboring cells. On the other hand, the signal power of the traffic channel also brings a large MAI to the pilot channel of the cell and an ACI to the pilot channel of the neighboring cell. The presence of these interferences ultimately reduces the capacity of a CDMA system. In the WCDMA standard, a method called a dedicated time-division pilot channel is used, which is a time-division multiplexing of pilot signals and service signals. This is avoided to a certain extent for synchronous CDMA mobile communications. The MAI between the pilot signal and the service signal is improved, but the ACI between the pilot signal and the service signal is still not reduced. Therefore, its performance will still be affected considerably, especially when the mobile user is at the cell boundary. Summary of the Invention

An object of the present invention is to provide a new method for framing pilot signals and service signals in a code division multiple access CDMA mobile communication system and a data frame formed according to the method, so as to solve the problems existing in the prior art. Technical issues and flaws.

The present invention is a method for framing a pilot signal and a service signal in a code division multiple access mobile communication system. According to the present invention, the MAI and ACI between the pilot signal and the service signal can be reduced or eliminated. In order to reduce the MAI between the pilot and the service signal, the present invention uses a time division multiplexing method to design the pilot signal. In order to reduce or eliminate ACI, the present invention introduces the concept of empty time slots. A plurality of empty time slots are inserted between the pilot symbol and the service signal, so as to reduce the ACI between the pilot and the service between different cells.

The framing method of the pilot signal and the service signal in the CDMA mobile communication system of the present invention can be applied to the frame structure design of the pilot and the service signal of most CDMA systems In this way, the MAI and ACI between the pilot signal and the service signal can be effectively reduced, thereby improving the performance of the system. Moreover, the method according to the present invention can save the transmission power of the base station and the mobile station, and finally increase the capacity of the system. Brief description of the drawings

Figure 1 is a schematic diagram of a preferred embodiment of the method according to the invention. Mode of Carrying Out the Invention

The present invention is described in detail below with reference to the drawings. The invention discloses a method for framing a pilot signal and a service signal applied in a code division multiple access mobile communication system. The method is to process the pilot signal and the service signal in a time division multiplexing manner in a frame, and A certain number of empty time slots are added between the time division multiplexed pilot signal and the service signal.

In more detail, in order to reduce the MAI between the pilot and the service signal, the present invention uses a time division multiplexing method to design the pilot signal. This part of the time division multiplexing method inside the code division multiple access system is quite effective for reducing the MAI of pilot and service signals. Because of time division multiplexing, for a synchronous CDMA system, the pilot signal and the service signal are distinguished not by an address code but by a time slot, thereby avoiding mutual interference between the pilot and the service signal. However, this is still fundamentally different from a communication system that fully adopts time division multiplexing, because for pilot signals and service signals alone, the frequency extension between pilot signals or between service signals is still achieved through spreading and depends on the address Code to distinguish.

Through the above methods, the purpose of reducing or even eliminating the MAI between the pilot and the service signal is achieved. However, this does not fundamentally solve the problem of ACI between pilots and service signals, because signals of different cells cannot reach receivers at any position at the same time due to different transmission delays, resulting in different inter-cell pilots and services. The signals overlap each other in time, from This leads to mutual ACI. Especially at the cell boundary, the inter-cell ACI becomes the main source of interference. In the present invention, the concept of empty slots is introduced to reduce the ACI between pilots and services in different cells. That is, in the design of the signal frame structure, a certain number of empty time slots are inserted between the time division multiplexed pilot signal and the service signal, and no signal power is transmitted in the empty time slots. The number of empty slots depends on the size of the cell, the chip rate of the system, and so on. With such a simple design, the impact on the complexity of the system is minimal. However, due to the existence of empty time slots, it is avoided that near the cell boundary, between adjacent cell pilots and service signals, due to different transmission delays. The time overlap causes ACI. And when the mobile station is far from the cell boundary, so that the difference between the transmission delays of the signals of different cells exceeds the inserted empty time slot, then ACI will occur. However, it is not difficult to understand that, as the path loss rapidly decays with increasing distance, the interference between pilots and services in neighboring cells is also reduced to a small extent. Therefore, by using the method provided by the present invention, the ACI between the pilot and the service signal is greatly suppressed, and it can be easily known that the present invention provides a simple method to control the acceptable signals from neighboring cells. Method of interference level between pilot and service signals. That is, by increasing the number of inserted empty slots, interference can be suppressed more effectively. The degree of ACI inhibition can be calculated by the following formula (1):

In formula (1), PVP represents the ratio of the ACI value after adding the empty time slot and when not adding the empty time slot, R is the cell radius, c is the speed of light, t is the duration of the empty time slot, and α is the path loss factor. Values are between 2-6. It can be clearly seen from the formula (1) that by increasing the number of empty time slots and thereby increasing t, the ratio F / P will decrease, thereby achieving the effect of more effectively suppressing ACI. The determination of the number of specific empty time slots requires a compromise between the occupancy of time resources by the empty time slots and its degree of suppression of the ACI between the pilot and the service signal according to the size of the cell radius. The present invention is applicable to the design of forward and reverse channels in a CDMA system, and the method provided by the present invention is equally applicable to a dedicated pilot signal or a common pilot signal. This is because the difference between the dedicated pilot signal and the common pilot signal is that, for each service channel, the dedicated pilot signal uses a different spreading address code and the common pilot signal uses the same spreading address code. Both of them use the time division multiplexing mode with the service signal, so the present invention has no significant difference with respect to the dedicated pilot signal or the common pilot signal.

Referring to FIG. 1, a specific implementation example of the present invention. The figure shows a pilot and service signal frame structure designed according to the method provided by the present invention. In the figure, P represents the time slot transmission pilot signal, V represents the time slot is an empty time slot, and T represents the time slot to send a service signal. More specifically, in this embodiment, the pilot occupies 128 Tc, the empty time slot occupies 30 Tc, and the service signal occupies 1024 Tc. It can be seen from this embodiment that the proportion of resources occupied by empty slots is only 2.5% of all resources. Compared with the IS95 pilot channel, the framing method provided by the present invention reduces the MAI of the service signal to the pilot signal which accounts for 80% of the total signal energy, and the pilot signal pair which accounts for 20% of the total signal energy. MAI for business signals. When the system chip rate is 1.2288 MHz and the cell radius is 2KM, the reduction in ACI between the pilot and the service can be calculated. That is, the transmission delay of the signals transmitted by the users or base stations in the neighboring cells and the local users or base stations will not exceed the inserted empty time slot, so there will be no ACI between the pilot and the service signals. Only the outer users or base stations in a cellular system can cause ACI to local users. However, due to the path loss, the power of the interference signal has been reduced by at least 20dB at this time, which can actually be ignored.

According to the method described in the present invention, there may be many embodiments for those skilled in the art. The general principles defined here can be applied to other embodiments without creativity. Therefore, the present invention is not limited to the embodiments shown here, but the widest range consistent with the principles and novel features disclosed herein.

Claims

Claim

1. A method of framing a pilot and a service signal applied in a code division multiple access (CDMA) communication system is to use a time division multiplexing method between the pilot symbol and the service signal within a frame to reduce its Multiple access interference (MAI, Multiply Access Interference); its characteristics are:

A plurality of empty time slots are inserted between the time division multiplexed pilot symbol and the service signal, so as to reduce interval interference (ACI, Adjacent Cell Interference) between them.

2. The framing method according to claim 1, characterized in that: the number of said empty time slots is determined by the size of the cell radius, the chip rate of the system, the occupancy rate of empty time slots to time resources and the empty The degree of time slot suppression to the Interference Interference (ACI) between the pilot and the service signal.

3. The framing method according to claim 1, characterized in that: no signal power is transmitted in the space time slot.

4. The framing method according to claim 1, characterized in that: by increasing the number of empty slots, it is possible to more effectively suppress interval interference (ACI).

5. The framing method according to claim 1, wherein the pilot symbols are dedicated pilot symbols.

6. The framing method according to claim 1, wherein the pilot symbols are common pilot symbols.

7. A data frame for pilot and service signals applied in a code division multiple access (CDMA) communication system, in which a pilot symbol and a service signal are time-multiplexed in a frame to reduce the Multiple access interference (MAI, Multiply Access Interference); its characteristics are:

Between the time-division multiplexed pilot symbol and the service signal, there are a plurality of empty slots inserted to reduce interval interference (ACI, Adjacent Cell Interference).

8. The pilot and service signal data frame according to claim 7, characterized in that: the number of said empty slots is determined by the size of the cell radius, the chip rate of the system, and the time slot versus time resources The occupancy rate and the degree of suppression of the interval interference (ACI) between the pilot and the service signal by the empty time slot.

9. The data frame of the pilot and service signals according to claim 7, wherein the pilot symbols are dedicated pilot symbols.

10. The pilot and service signal data frame according to claim 7, wherein the pilot symbols are common pilot symbols.