KR20020092747A - Method for Transmission Antenna Diversity - Google Patents

Abstract

PURPOSE: A transmission antenna diversity method is provided to increase the transmission quality of an F-PDCH(Forward-Packet Data CHannel) according to the transmission diversity selection of a mobile communication system. CONSTITUTION: One or more pilot signals are received from one or more BTSs(Base Transceiver Systems). An optimum BTS is selected according to the signal strength of the pilot signals. A determined diversity mode is reported to the selected BTS. A feedback signal including information for supporting the diversity mode is generated according to the diversity mode. The feedback signal is transmitted to the BTS. A terminal's own moving state is grasped using doppler information with the base station. The diversity mode is determined according to the grasped state.

Description

Transmission antenna diversity method {Method for Transmission Antenna Diversity}

The present invention relates to a mobile communication system, and more particularly, to a transmission antenna diversity method.

As is known, the existing 1x cdma2000 system is designed to support voice services in circuit switched mode and medium and low speed data services.

In addition, as the desire for services such as wireless Internet has increased, a system for high-speed packet data communication has been proposed, excluding voice service, which is called HDR (High Data Rate) or 1x-EV DO (1x-Evolution Data Only). do. The integrated version of these two systems is called 1x-EV DV (1x-Evolution Data and Voice).

The 1x-EV DV system refers to a system capable of simultaneously performing a voice mode and data service in a circuit mode with a high speed packet data service.

Therefore, the 1x-EV DV system should be compatible with the lower layer of 1x of the existing cdma2000. Accordingly, all currently considered 1x-EV DV specifications are abbreviated to the radio configuration of the existing cdma2000. ), And additionally, a shared channel for packet data service is configured in an independent RC form.

Basically, the shared channel for forward packet data service (F-PDCH: F-PDCH) may accommodate multiple users by using time division multiplexing (TDM), such as HDR, and also includes code division multiplexing (CDM) and A mixed form of TDM can also be used to accommodate multiple users.

In the 1x-EV DV system, there is a method of dynamically allocating extra base station power and Walsh code to the F-PDCH in the presence of existing line mode voice users and data users.

In addition, the data throughput of the base station is increased by using the method of allocating such redundant base station power and Walsh code to a specific user having a good link quality.

At this time, for the operation of the F-PDCH, each user needs some feedback channel for transmitting the link quality between itself and the base station to the base station.

The base station selects a modulation scheme and channel coding rate suitable for the current link quality and transmits it to the planned target user based on the link quality reported by the users.

At this time, the method of measuring the quality of the link between the user and the base station is as follows.

First, the C / I value of the common pilot of the existing 1x system is measured at the terminal. And this method uses a method of quantizing the value and transmitting it to the base station through the reverse channel.

In this case, a channel used to transmit the quality of the link is referred to as a reverse channel quality indication channel (R-CQICH) in the future.

Through this process, the terminal selects a base station or sector that provides the best performance and reports the result to the base station. After octal Walsh covering is performed, the resulting 96-bit symbols are spread by the hexadecimal Walsh code and transmitted for a slot time of 1.25 ms. This process continues for every 1.25ms slot time.

Through this process, channel quality information between the base station (or sector) and the user is transmitted to the base station (or sector) through the R-CQICH channel, and only the selected base station (or sector) transmits data to the user based on the R-CQICH information. Done.

In the forward link of the existing cdma2000 1x system, there is a transmission diversity mode. The transmit diversity mode is a technique used to improve the performance of the 1x forward link of the cdma2000 system. In this case, the base station uses two antennas of the transmitting end.

Since the mobile communication system has a very poor channel environment, two transmission antennas are applied to increase the probability of improving the channel environment. Since each transmit antenna is installed at a considerable distance away from each other, each transmit antenna has an independent channel environment.

This means that even if the performance of one antenna is not good, the other antenna may not be so that more stable transmission can be achieved. This improves the channel environment and ultimately increases the probability of transmission success.

1 is a block diagram illustrating a fast antenna selective transmit diversity according to the prior art.

As can be seen in Figure 1, the transmission signal of the base station is transmitted through two antennas far apart.

At this time, the channels between the two antennas and the terminal can be seen as independent channels.

The terminal needs to estimate the channel condition for each path. After this operation, the terminal performs combining and channel decoding by using the estimated channel information.

In this case, two techniques, OTD (Orthogonal Transmission Diversity) and STS (Space Time Spreading), are used according to a method of generating diversity gain through transmission diversity of a base station from a terminal.

In OTD, a technique of improving performance after channel decoding by using a kind of time diversity, and STS is considered as a method of increasing the diversity order of a received symbol before channel decoding by using a space time coding technique. Can be.

In general, in order to use transmit diversity, antenna A and antenna B having the same power are used. In this case, assume that antenna A is a main antenna and antenna B is a transmit diversity antenna.

At this time, each antenna A and B requires a pilot. This pilot channel is used for the purpose of estimating the channel paths between each transmit antenna and the receive antenna of the terminal as described above.

In this case, the pilot transmit power of the transmit diversity antenna B may be defined as part of the pilot transmit power of the main antenna A (for example, 0 dB, 3 dB, -6 dB, -9 dB).

Next, the transmission power for the data is divided into 1/2 each antenna A and antenna B.

Currently, the F-PDCH of the 1x-EV DV system is considered to apply the above-described transmission diversity scheme such as OTD and STS.

As described above, the transmission diversity scheme can be considered as a method of improving the transmission channel environment through two different antenna paths.

In other words, even if the environment of one antenna path is bad, the environment of the other antenna may be good.

However, it is not a good idea to apply only transmission diversity techniques such as OTD or STS to the F-PDCH of the 1x-EV DV system.

This is a channel that requires feedback of the reverse link because the F-PDCH transmits based on the channel quality of the user. If the feedback information is used, the maximum transmit power available for the antenna providing a good reception environment is used. It is possible to transmit.

Of course, if the channel change state between the user and the base station is so fast that the terminal cannot accurately estimate and predict the channel condition, a transmission diversity scheme such as STS or OTD may gain.

However, fundamentally, the transmit diversity scheme such as STS and OTD is an approach to improve the diversity gain in the long term when there is no feedback on the channel quality information, and thus, based on the channel quality information between the base station and the user. Therefore, it is not preferable to use only the existing STS or OTD in the F-PDCH of 1x-EV DV that selects and uses a case where the channel quality is good.

That is, if the channel between the base station and the user changes slowly (medium, low speed user), if the quality information of the channel can be accurately estimated and predicted, the existing OTD or STS transmission diversity would not be desirable.

Accordingly, an object of the present invention has been made in view of the above-mentioned problems of the prior art, and according to the transmission diversity selection of the mobile communication system, a transmission antenna diversity method that can further increase the transmission quality of the F-PDCH. It is to provide.

According to an aspect of the present invention for achieving the above object, the step of receiving at least one pilot signal from at least one or more base stations; Selecting an optimal base station according to the signal strength of the pilot signals; Reporting the diversity mode determined to the selected base station; Generating a feedback signal including information for supporting the mode according to the diversity mode; And transmitting the feedback signal to the base station.

1 is a block diagram illustrating fast antenna selective transmit diversity according to the prior art;

2 is a block diagram of an R-CQICH for supporting fast diversity in accordance with the present invention.

3 is a block diagram for (12,5) code of an R-CQICH according to the first embodiment of the present invention.

4 is a block diagram for a (12,6) code of an R-CQICH according to a second embodiment of the present invention.

5 is a flowchart illustrating a process of generating a feedback signal of a terminal according to a transmit diversity scheme according to the present invention.

In the present invention, for the sake of convenience, the F-PDCH of the TDM structure is assumed and described.

According to the present invention, when a base station supporting 1x-EV DV (1x-Evolution Data and Voice) uses a transmit diversity mode, that is, when an antenna for transmit diversity is used in a base station, a forward for packet transmission is performed. When transmitting a Forward Packet Data Channel (F-PDCH), instead of using conventional Orthogonal Transmission Diversity (OTD), Space Time Spreading (STS) and Transmit Diversity, a better reception environment is achieved. A method of applying transmit diversity for selecting and transmitting antennas is proposed.

Also, a method of applying such selective transmission diversity at a high speed is proposed, and a method of configuring a reverse feedback channel for antenna selection is proposed.

The selective transmit diversity scheme proposed in the present invention assumes that the user is moving at a medium speed or a low speed, and thus the user can accurately estimate and predict quality information about a channel formed between the base station and the user.

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

The operation of the present invention can be described as follows.

In transmission of the F-PDCH, it is assumed that the base station uses a transmit diversity antenna.

That is, it is assumed that the main antenna A and the transmit diversity antenna B exist in the base station.

At this time, the terminal measures the pilot of each antenna A and antenna B. From the result of this measurement, the UE selects an antenna that provides a better reception environment among the two antennas. The result is then transmitted to the base station using the reverse feedback channel. This process will be described in detail.

(1) pilot transmission method

Each antenna A and antenna B use a pilot channel. The strength of the pilot of antenna A, which is the main antenna, and the strength of the pilot of antenna B are determined according to a predetermined rule.

That is, the power of? (? ≦ 1) times the pilot power of the main antenna is used for the pilot channel of the antenna B.

(2) antenna selection

The pilot signal transmitted from the antennas of all base stations (or sectors) in the active set is received at the terminal and used to select the best antenna of the base station (or sector) having the best channel condition.

Basically, the principle is to select the one with the best reception strength of the pilot from all antennas of all base stations (or sectors) in the active set.

However, as mentioned above, since the power of the pilot transmitted from each antenna may be different, the received strength should be compared by correcting it.

Assume that the power of the pilot of the main antenna A is P.

Then, the power of the pilot of the transmit diversity antenna B will be αP.

At this time, the strength of the pilot received from each antenna can be corrected through the following process.

When the strength of the pilot signal is expressed in CIR (Carrier to Interference Ratio), it is assumed that the CIR measurement value of the pure meaning without considering the transmission power difference is the antenna A is CIR_ (A) and the antenna B is CIR_ (B).

Then, the CIR measurement values of the antenna A and the antenna B in consideration of the power difference of the transmission pilot between the antennas may be expressed as CIR_ (A) and CIR (B) / αP, respectively. By comparing these two values, an antenna that provides better CIR measurements is selected and notified to the base station, and the base station allocates and transmits the maximum power that can be allocated for transmission of the F-PDCH to the selected antenna. Will be used.

(3) Report method of selected antenna

Basically, in the 1x-EV DV system, the reverse channel for transmitting channel quality between the base station (or sector) and the user is used for the operation of the F-PDCH. This reverse feedback channel structure is designed to have low latency.

2 is a block diagram of an R-CQICH for supporting fast diversity according to the present invention.

As shown in Fig. 2, the present invention contemplates a structure for reporting channel quality information (CQI symbol) every 800 Hz, i.e., 1.25 ms. In addition, the R-CQICH structure has a structure of quantizing a 6-bit symbol including quality information of the measured channel, block coding the same, taking Walsh covering, and spreading the data.

At this time, one of the 6 bits of information includes a bit for indicating the selected antenna. Therefore, 6 bits of information are required. Therefore, it can be seen that 6 bits of information are input to every 1.25ms slot.

If 5 bits of (a ₀ Λ a ₄ ) are bits indicating quality information of the channel, additionally, a ₅ bits may be used to express selected antenna information of the fast diversity mode.

That is, when a ₅ bit is '0', this means that the terminal selects the A antenna because channel quality from the antenna A, which is the main antenna, is better, and conversely, when the a ₅ bit is '1', the terminal is the B antenna. Means to select.

At this time, the structure of the R-CQICH is preferably designed with the following in mind.

If the base station is a base station using transmission diversity such as the existing STS or OTD, and the user is moving at medium speed or low speed, the base station transmits using the fast antenna selection transmit diversity proposed in the present invention when transmitting the F-PDCH. You will be able to improve the quality.

However, since the transmit diversity mode itself is an option of the base station, if the base station does not use transmit diversity, the existing R-CQICH transmission structure should be used as it is.

That is, the channel structure of the R-CQICH should not be changed. At this time, the mode using or not using the transmission diversity will be determined at the negotiation stage between the UE and the base station, and the transmission mode of the R-CQICH should be determined according to this determination.

The preferred method is to use an R-CQICH structure that represents both the case of transmit diversity mode and the mode that does not use transmit diversity using a common one structure. For this purpose, the following structure can be considered.

Figure 3 shows a block diagram for the (12,5) code of the R-CQICH according to the first embodiment of the present invention.

As shown in FIG. 3, five bits of a ₀ to a ₄ are each multiplied by a mask function Mi (i = 0, 1, 4) having a length of 16, and the result values are bits. An exclusive or operation of units forms the result sign of length 16. Four of these are punctured to form the resulting (12, 5) code.

In the present invention, when the fast antenna selective transmit diversity scheme is not used, the code of FIG. 3 is used as it is, and when the fast antenna selective transmit diversity scheme is applied, it is extended from the code of FIG. 6) Suggest ways to use the code.

4 shows a block diagram of a (12,6) code of an R-CQICH according to a second embodiment of the present invention.

As shown in FIG. 4, in case of using the fast antenna selective transmit diversity scheme, whether the selected antenna is the main antenna A or the transmit diversity antenna B through the sixth bit a ₅ bits is indicated.

At this time, if a ₅ = 0, it indicates that the selected antenna is A as the main antenna, and when a ₅ = 1, it is promised that the selected antenna is B, which is a transmit diversity antenna.

Comparing FIG. 3 with FIG. 4, it can be seen that the product of the mask code M ₅ having a ₅ bit and the length of 16 has the same structure except that the product is additionally used in the exclusive sum operation process.

Therefore, after using the same coding structure as shown in FIG. 4 in the R-CQICH, if the information is transmitted to a base station that does not support transmission diversity, a method of always selecting a ₅ bits as 0 may be used. .

In addition, after making common use in the R-CQICH of the base station supporting the transmission diversity, when transmitting information to the base station not supporting the transmission diversity, a method of always selecting a ₅ bits as 0 can be used. have.

When transmitting an R-CQICH to a base station supporting transmission diversity, a ₅ bit is selected as 0 or 1 according to the selected antenna.

In FIG. 3 or FIG. 4, the position of the specific mask function and the puncturing of 4 bits should be optimized to maximize coding performance.

The base station (or sector) establishes a transmission plan for the target user according to the received R-CQICH, determines the transmission data rate and the modulation & coding scheme (MCS) level to be used for the current transmission, and then selects the transmission antenna selected by the target user. Through the data transmission to the maximum power allocated to the F-PDCH.

(4) Selection method of transmission diversity scheme

As described above, the fast diversity technique used in the present invention can be considered as a useful method when the user's moving speed is medium speed or low speed. However, if the change rate of the channel between the user and the base station is fast, the antenna A may have a better reception quality when the terminal measures the channel quality, but when the base station is scheduled to transmit The reception quality from antenna B may be better.

Therefore, it is desirable for a high speed user to use OTD or STS, which is an existing transmit diversity mode.

5 illustrates a process of generating a feedback signal of a terminal according to a transmit diversity scheme according to the present invention.

Referring to FIG. 5, if a base station supports a transmission diversity scheme, it may negotiate which transmission diversity scheme to apply in the negotiation stage of a call setup stage.

The terminal may estimate the Doppler information of the channel using channel variation information between the base station and itself, and thus negotiate using a transmission diversity scheme such as an existing OTD or STS in a high speed channel environment.

In this case, the UE reports the diversity selection mode to the base station (BTS). (O1) Then, observe the pilot signals of the antennas A and B (O2), combine these pilot signals appropriately (O3), and then R-CQICH. Is generated by setting a ₅ bit to 0 (O4).

At this time, the quality information of the channel transmitted by the terminal to the base station should be obtained by combining the pilot C / I of the two antennas in an appropriate method.

Conversely, in a medium or low speed channel environment, a fast diversity scheme can be selected.

If it is promised to use the fast diversity scheme in the negotiation phase, report the diversity selection mode to the base station (BTS) (F1), observe the pilot signals of antenna A or antenna B (F2), and then select the optimal antenna. To select (F3). Then, in Fig. 4 in the R-CQICH used to add a ₅ bit by using the indication of the selected antenna, and report the best antenna at the base station by using this channel (F4).

On the other hand, when the base station does not support the transmission diversity mode, the UE reports a ₅ to 0 in the three R-CQICH (T1), by observing only the main antenna a pilot signal.

As described above, the present invention has the advantage that the existing base station antenna structure does not need to be changed, and since the existing reverse channel can be used as a feedback channel by using additional information of 1 bit, the present invention can be easily implemented. Have

In addition, the configuration of the feedback channel, it has the advantage that can implement a channel having a structure in common with the existing feedback channel.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the examples, but should be defined by the claims.

Claims (11)

Receiving at least one pilot signal from at least one base station; Selecting an optimal base station according to the signal strength of the pilot signals; Reporting the diversity mode determined to the selected base station; Generating a feedback signal including information for supporting the mode according to the diversity mode; And transmitting the feedback signal to the base station. The method of claim 1, further comprising: determining a state of movement of the mobile station using Doppler information with a base station; And determining a diversity mode according to the state. 3. The antenna selection transmission according to claim 2, wherein the state is divided into high, medium, and low speed stages, and when the medium and low speeds correspond, the base station selects one of a plurality of antennas to transmit a signal using a feedback signal. Transmit antenna diversity method, characterized in that the diversity mode. 4. The method of claim 3, wherein a feedback signal is generated along with antenna selection information in the antenna selection transmission diversity mode. 5. The method of claim 4, wherein in the antenna selection diversity mode, the base station selects a transmit antenna according to a specific bit value of an input bit sequence of a feedback signal. The transmission antenna diver according to claim 2, wherein the state is divided into high, medium, and low speed stages, and a high speed, high speed, medium speed, and low speed transmission mode is determined as an orthogonal transmit diversity (OTD) or a space time spread transmit diversity (STS) mode. City way. 7. The method of claim 6, wherein in the OTD and STS modes, antenna selection information is not transmitted because a specific bit of an input sequence of a feedback signal is not transmitted. The method of claim 1, wherein the feedback signal is generated by encoding an input bit sequence at a coding rate of 6/12. 10. The method of claim 8, wherein the input bit sequence is multiplied by a 16-length mask code, and the resulting bit sequence is punctured by 4 bits to generate an encoded bit. 10. The method of claim 9 wherein each bit of the input bit sequence and the mask code are generated by an exclusive sum. The method of claim 1, wherein the feedback signal further includes channel quality information in addition to information for supporting a diversity mode.