CN1972178A - A method for increasing multicast broadcasting service - Google Patents

Abstract

A method for enhancing multicast/broadcast services in a mobile communication system. The network controller selects a suitable transmit diversity scheme, and then divides the cells into multiple groups according to the geographic location of each cell in the network; the network controller divides the cells into multiple groups through signaling Parameters such as the signal pattern change cycle and pattern change rules are sent to each cell. At the same time, the network controller broadcasts the adopted transmit diversity scheme and signal pattern update cycle parameters to the UE through downlink signaling; each cell receives the network controller configuration through signaling. The pattern update cycle parameters and the corresponding signal pattern change rules, and select a signal pattern to transmit multicast/broadcast service signals according to the parameters configured by the network controller; UE receives the transmit diversity scheme and signal pattern adopted by the current system through downlink signaling Update the parameters of the period and receive multicast/broadcast signals according to the transmit diversity technology adopted by the network.

Description

Method for Enhancing Multicast Broadcasting Service

technical field

The invention relates to a mobile communication system, in particular, the invention relates to a method for enhancing multicast/broadcast service in the mobile communication system.

Background technique

At present, the 3GPP standardization organization has begun to carry out long-term evolution (LTE) of its existing system specifications. Among many physical layer transmission technologies, Orthogonal Frequency Division Multiplexing (OFDM) technology has become a promising one among all downlink schemes because of its high spectrum utilization rate and low processing complexity.

OFDM technology is essentially a multi-carrier modulation communication technology. Its basic principle is to decompose a high-rate data stream into several low-rate data streams and transmit them simultaneously on a group of mutually orthogonal sub-carriers. OFDM technology has performance advantages in many aspects due to its multi-carrier nature. (1) A significant advantage of OFDM technology is that due to the parallel transmission of data on multiple subcarriers, the length of symbols on each subcarrier increases accordingly, which is not sensitive to channel delay; by further adding a guard interval to each symbol , that is, the introduction of a cyclic prefix (CP), when the channel delay is less than the length of the cyclic prefix, the inter-symbol interference (ISI) can be completely eliminated. In this way, each subcarrier experiences a flat fading channel. Fig. 1 is a schematic diagram of adding a cyclic prefix to an OFDM symbol. An entire OFDM symbol (100) is composed of an available OFDM signal (101) plus a cyclic prefix (103). Wherein the cyclic prefix (103) is realized by directly copying and adding some later samples (102) of the available OFDM signal (101) to the front of the available OFDM signal (101). (2) The spectrum utilization rate of OFDM technology is high, and OFDM signals actually overlap in the frequency domain, which greatly improves the spectrum utilization rate. (3) OFDM technology has a strong ability to resist narrow-band interference and frequency selective fading. Through channel coding and interleaving, OFDM can have frequency diversity and time diversity functions, thus effectively combating narrowband interference and frequency selective fading. (4) OFDM technology modulation can be realized through baseband IFFT transformation, and IFFT/FFT has a mature and fast calculation method, which can be easily realized in DSP chip and hardware structure.

Multicast/Broadcast is a technique for transmitting datagrams from one data source to multiple destinations. In the traditional mobile network, the cell broadcast service allows low bit rate data to be sent to all users through the cell shared broadcast channel, which belongs to the message service. Now, people's demand for mobile communication is no longer satisfied with telephone and message services. With the rapid development of the Internet, a large number of multimedia services have emerged, some of which require multiple users to receive the same data at the same time, such as video on demand, TV, etc. Broadcasting, video conferencing, online education, interactive games, etc. Compared with general data, these mobile multimedia services have the characteristics of large data volume, long duration, and delay sensitivity. In order to support new requirements and effectively utilize mobile network resources, the existing 3GPP specifications standardize multicast/broadcast services, and provide a point-to-multipoint service in which a data source sends data to multiple users in a mobile network, realizing network resources Sharing to improve the utilization of network resources, especially air interface resources.

In the LTE system, due to the change of the physical layer transmission technology, new requirements are put forward for the network to support multicast/broadcast services. In the case of meeting certain synchronization requirements, OFDM technology can support multicast/broadcast services more conveniently. At this time, each cell transmits the same signal according to the network configuration. FIG. 2 is a schematic diagram of the UE merging the multipath signals of each cell. The multipath signal (201) is the first arriving path, and the multipath signal (203) is the last arriving path. Under the condition that the delay between the first arriving path and the last arriving path of the multipath signals (201, 202, 203) of each cell is less than the length of the CP, each multipath signal (200) within the available OFDM signal (200) time period The signals on the path are continuous, so there is no interference between sub-carriers and inter-symbol interference when UE receives through FFT. As long as the time delay range of the signal from each cell to the UE does not exceed the length of the cyclic prefix, the UE can simply combine and receive the signals from each cell. At this time, the signals of each cell are nothing but multipath signals of the same signal to the UE. Considering the relative position of the UE to each cell, the propagation delay of each cell signal, and the impact of the timing deviation of each cell, in order to realize the combined reception of each cell by the UE, the system needs to configure a relatively long cyclic prefix (CP).

In a system configured with multiple antennas, the technology of transmit diversity can be used to make full use of the effect of space diversity. The basic principle of transmit diversity is that multiple antennas at the transmitting end use different signal forms to transmit the same data, and the receiving end can use this difference to achieve performance equivalent to maximum ratio combining (MRC). An example of transmit diversity is space-time encoding of data at the transmitter and space-time decoding at the receiver.

According to the existing discussion results of 3GPP, the encoding of multicast/broadcast service data by the network is divided into inner and outer encoding. Inner coding is coding within a transmission time interval (TTI); outer coding can span multiple TTIs, so as to make full use of time diversity to improve the performance of multicast/broadcast services. The inner code can be convolutional code, turbo code, LDPC code, etc., and the outer code is generally RS code. In the LTE system, such a structure of inner and outer coding is also a promising technology, and because the length of TTI in LTE is relatively short, the gain brought by using outer coding will be more obvious.

In the case that each multicast/broadcast cell sends the same data in the same signal form, the UE realizes the soft combination of the signals of each cell through the role of the CP. This soft combination is essentially a simple addition of the signals of each cell. Such a combination method can improve system performance by using space diversity characteristics to a certain extent, but its performance improvement is limited because it cannot fully utilize the space characteristics of each cell. By making full use of the spatial distribution characteristics of each cell, and jointly adopting the transmit diversity method in each cell sending multicast/broadcast services, the performance of the system can be further improved.

According to the characteristics of multicast/broadcast services, each cell needs to care about the coverage of the network to ensure that the UE(s) in the most disadvantaged position in the network can still receive signals with a certain probability, and will not change the transmitted signal according to the location of a certain UE Signal. In the case that each cell jointly adopts transmit diversity, the channel attenuation from different locations in the network coverage area to the antennas of each cell is different, and the received signal strength of each cell is different, and the obtained diversity gain is also unequal. By taking certain measures, the transmit diversity gain can be obtained evenly in the entire network coverage area.

Contents of the invention

The purpose of the present invention is to make full use of the spatial distribution characteristics of multiple cells sending multicast/broadcast services to maximize the gain of space diversity, and at the same time ensure that the gain of diversity can be obtained relatively uniformly in all areas covered by the network.

In order to achieve the above object, a method for enhancing multicast/broadcast services in a mobile communication system comprises the following steps:

a) The network controller selects an appropriate transmit diversity scheme, and then divides the cells into multiple groups according to the geographic location of each cell in the network;

b) The network controller sends parameters such as the signal pattern change cycle and pattern change rules to each cell through signaling, and at the same time, the network controller broadcasts the adopted transmit diversity scheme and signal pattern update cycle parameters to the UE through downlink signaling;

c) Each cell receives the pattern update period parameter configured by the network controller and the corresponding signal pattern change rule through signaling, and selects a certain signal pattern to transmit a multicast/broadcast service signal according to the parameter configured by the network controller;

d) The UE receives parameters of the transmit diversity scheme and signal pattern update cycle adopted by the current system through downlink signaling, and receives multicast/broadcast signals according to the transmit diversity technology adopted by the network.

According to the present invention, each sub-district coordinates and implements transmit diversity for multicast/broadcast service signals according to the instruction of the network controller, and can fully utilize the spatial distribution characteristics of each sub-district to obtain antenna diversity gain to the greatest extent. By periodically changing the pattern of signals sent by each group of cells, the average transmit diversity gain obtained by UEs at each point in the network coverage area is basically equal during the multicast/broadcast service outer coding time period, thereby providing the network with the largest possible Cover multicast/broadcast services and enhance the performance of multicast/broadcast services.

Description of drawings

FIG. 1 is a schematic diagram of adding a cyclic prefix to an OFDM symbol;

FIG. 2 is a schematic diagram of UE merging multipath signals of various cells;

FIG. 3 is a schematic diagram of processing of UE receiving a multicast/broadcast signal;

FIG. 4 is a pattern distribution diagram of signals transmitted by each cell when dual-antenna transmit diversity is adopted;

FIG. 5 is a pattern distribution diagram of signals transmitted by each cell when four-antenna transmit diversity is adopted.

Detailed ways

Aiming at the problem that the existing multicast/broadcast service signal transmission and soft combined reception methods cannot make full use of the spatial distribution characteristics of each cell, the present invention proposes a method for supporting multicast/broadcast service in a mobile communication network.

In the present invention, the network controller coordinates and controls the processing and sending of multicast/broadcast service signals by each cell in the network. The network controller selects the appropriate transmit diversity scheme, and then divides the cells into multiple groups according to their geographic location. Each group of cells transmits multicast/broadcast signals in the same signal form, and configures the same pilot frequency at the same time. style. Because it is a multicast/broadcast service, the network cannot care about the characteristics of each UE, and this grouping method has nothing to do with the location of a specific UE.

The network controller configures the cycle of signal pattern change and the rule of pattern change for each group of cells. The network controller sends parameters such as signal pattern change period and pattern change rule to each cell through signaling. At the same time, the network controller broadcasts the adopted transmit diversity scheme and signal pattern update cycle parameters to the UE through downlink signaling. The period of pattern change is related to the time of internal and external coding of multicast/broadcast services, system frame length, subframe length and TTI length, and this period is shorter than the time length of external coding of multicast/broadcast services.

Each cell receives the pattern update cycle parameters configured by the network controller and the corresponding signal pattern change rules through signaling, and selects a certain signal pattern to transmit multicast/broadcast service signals according to the parameters configured by the network controller. According to the number of transmitting antennas equipped in a specific cell, this cell can transmit one signal, multiple signals or all signals of the selected transmit diversity technology; each cell sets a timer whose period is equal to the pattern update period, when the timer expires , each cell transforms the pattern of the transmitted signal and the pilot pattern according to the rules configured by the network controller.

The UE receives the parameters of the transmit diversity scheme and signal pattern update cycle adopted by the current system through downlink signaling, and receives multicast/broadcast signals according to the transmit diversity technology adopted by the network, so as to achieve performance equivalent to maximum ratio combining. As shown in Figure 3, when the UE is receiving multicast/broadcast service signals, the UE first needs to detect whether the strength of each signal in transmit diversity can meet the requirements for reception (301); , the UE uses all signals to demodulate data (302), and at this time the gain of transmit diversity is the largest; when a certain path or several paths of signals cannot meet the reception requirements, UE uses the remaining signals to demodulate data (303), at this time The gain of transmit diversity is reduced, but the performance is still better than that without transmit diversity. According to the network configuration, the UE may need to set a timer whose timing period is equal to the update period configured by the network controller. When the timer arrives, the UE needs to perform corresponding operations, such as channel estimation and interpolation. In a system where multicast/broadcast services and unicast services are time-division multiplexed, this impact can be minimized by properly selecting update cycle parameters.

According to the actual network configuration, the parameters used in the present invention, such as the selected transmit diversity scheme, cell grouping information, signal pattern change cycle, signal pattern change rules, etc., can be fixed in the network planning stage, so that there is no need to Additional broadcast signaling; or these parameters can be changed semi-statically, bringing certain flexibility.

FIG. 4 is a pattern distribution diagram of signals transmitted by each cell when dual-antenna transmit diversity is adopted. It is assumed here that each cell is configured with one antenna, and adjacent cells cooperate to implement dual-antenna transmit diversity. It is assumed here that the network configures two pattern distributions (400, 410) of transmitted signals, and when the pattern update counter expires, the system switches between the pattern distribution (400) and the pattern distribution (410). In the pattern distribution (400), for the UE in the position (401), the signal strengths of the two channels of transmit diversity are equal or not much different, so the diversity gain is relatively large; correspondingly, in the pattern distribution (410), For UEs at the same location (411), the signal strength difference between the two channels of transmit diversity is relatively large, and the gain of transmit diversity is relatively small. In the pattern distribution (400), for the UE in the position (402), the difference in signal strength between the two paths of transmit diversity is relatively large, and the gain of transmit diversity is relatively small; correspondingly, in the pattern distribution (410), the For UEs at the same location (412), the signal strengths of the two channels of transmit diversity are equal or not much different, so the diversity gain is relatively large. In this way, by switching between the pattern distribution (400) and the pattern distribution (410) in the cycle of inner coding or outer coding, the gains of transmit diversity obtained at different positions in the network can be basically equal or relatively close.

FIG. 5 is a pattern distribution diagram of signals transmitted by each cell when four-antenna transmit diversity is adopted. It is assumed here that each cell is configured with two antennas, and adjacent cells cooperate to implement four-antenna transmit diversity. It is assumed here that the network configures three pattern distributions (500, 510, 520) of transmitted signals, and when the pattern update counter expires, the system switches among pattern distribution (500), pattern distribution (510) and pattern distribution (520). In the pattern distribution (500), for the UE in the position (501), the signal strength of the three paths of transmit diversity is relatively strong, and the signal strength of the other path is relatively weak, so the diversity gain is limited; correspondingly, in the pattern distribution ( 510), for the UEs in the same position (511), the signal strength of the three paths of transmit diversity is relatively strong, and the signal of the other path is relatively weak, so the diversity gain is still limited; in the pattern distribution (520), the For UEs at the same location (521), the signal strengths of the four channels of transmit diversity are relatively strong, so that a relatively large diversity gain can be obtained. A similar situation exists at other points in the network. In this way, by switching between the pattern distribution (500), the pattern distribution (510) and the pattern distribution (520) within the cycle of inner coding or outer coding, the gains of transmit diversity obtained at different positions in the network can be basically equal or comparable near.

Claims (10)

1. a method that strengthens multicast/broadcast business in mobile communication system comprises the steps:

A) network controller is selected suitable emission diversity scheme, then according in the network each

The geographical position of sub-district will be distinguished into a plurality of groups for a short time;

B) network controller by signaling signal modal shift cycle and modal shift rule etc.

Parameter sends to each sub-district, and simultaneously, network controller is broadcast to UE to the emission diversity scheme and the signal pattern update cycle parameter that adopt by downlink signaling;

C) each sub-district receives the pattern update cycle parameter of network controller configuration by signaling

With corresponding signal modal shift rule, and select certain signal pattern emission multicast/broadcast business signal according to the parameter of network controller configuration;

D) UE receives emission diversity scheme and the signal sample that current system adopts by downlink signaling

The parameter of formula update cycle, and according to the transmit diversity techniques receiving multicast/broadcast signal of network using.

2. method according to claim 1 is characterized in that also comprising step:

Each sub-district is provided with timer, and its cycle equals the pattern update cycle, and when timer expired, each sub-district sent the pattern and the pilot pattern of signal according to the rule transformation of network controller configuration.

3. method according to claim 1 is characterized in that described step a) comprises: every group of sub-district disposes identical pilot pattern simultaneously according to identical signal form emission multicast/broadcast signal.

4. method according to claim 1 is characterized in that described step a) comprises: the mode of described grouping and the location independent of particular UE.

5. method according to claim 1 is characterized in that mode, the signal modal shift cycle of scheme, the cell group of described transmit diversity, rule change of signal pattern etc. can be fixed up in the network planning stage.

6. method according to claim 5 is characterized in that the change that mode, the signal modal shift cycle of scheme, the cell group of described transmit diversity, rule change of signal pattern etc. can be semi-static.

7. method according to claim 1, it is characterized in that described step b) comprises: the cycle of modal shift is relevant with TTI length with time, system-frame length, the subframe lengths of the inside and outside coding of multicast/broadcast business, and this cycle is less than the time span of the outer coding of multicast/broadcast business.

8. method according to claim 1 is characterized in that described step c) comprises: according to specific cell number of transmit antennas purpose difference, the sub-district can send one road signal, multiple signals or whole signal of selected transmit diversity techniques.

9. method according to claim 1 is characterized in that described step d) comprises:

Whether the intensity of each road signal of UE detection transmit diversity can both satisfy the requirement of reception;

Receive when requiring when each road signal can both satisfy, UE utilizes all signal demodulating datas;

Receive when requiring when a certain road or a few roads signal can not satisfy, UE utilizes remaining each road signal demodulating data.

10. method according to claim 1 is characterized in that also comprising: according to system configuration, UE need be provided with timer, equal the signal pattern update cycle of network controller configuration its time-count cycle, when timer arrived, UE need do corresponding operation, processing channel estimation and interpolation etc.

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