KR100820798B1 - Walsh Code Resource Allocation Method in Communication System - Google Patents

Abstract

The present invention relates to a mobile communication system, and more particularly, to a method for allocating Walsh code resources. The Walsh code allocation according to the present invention may include: determining a maximum data rate that can be transmitted using received channel information in a mobile communication system in which a time division scheme and a code division scheme are mixed; Determining a payload size and a transmission data rate according to the data to be transmitted; Calculating the number of Walsh codes required for the data transmission when the transmission data rate according to the data to be transmitted is smaller than the maximum data rate that can be transmitted; And determining the remaining number except the required Walsh code from the predetermined total Walsh code and allocating Walsh codes for other terminals.

Data rate, Walsh code

Description

Method for allocating walsh code resource in communication system

1 is a diagram illustrating an example of data transmission by a general TDM scheme.

2 is a diagram illustrating an example of data transmission by a general CDM / TDM scheme.

3 is a view showing a comparison of TDM system and CDM / TDM Walsh code utilization efficiency.

4 is a diagram showing the number of slots per service packet according to the data rate according to the present invention.

FIG. 5 shows a procedure for selecting the data rate shown in FIG. 4 and the number of Walsh codes according to this data rate. FIG.

6 illustrates another example of a terminal selection, a data rate of a selected terminal, and a Walsh code number determination procedure according to the present invention;

7 illustrates an example of a method for equally allocating remaining Walsh codes to CDM terminals according to the present invention.

The present invention relates to a mobile communication system, and more particularly, to a Walsh code resource allocation method.

In general, the wireless communication environment is a channel that changes according to the location and mobility of the terminal, so a method that can adapt to a changing channel is required. As a method of enabling high-speed data transmission while efficiently using a wireless channel in a wireless channel environment that changes with time, a method of adaptively changing a modulation scheme by changing a channel and a method of changing a channel coding are provided. have.

In order to reduce the error rate by adding redundancy of information data using channel coding, an increase in the amount of data transmitted on an actual wireless channel is essential. Since the wireless communication environment is a channel that changes according to the location and mobility of the terminal, the communication environment may be good or bad.

Therefore, when the wireless communication environment is good, the transmission speed can be increased by sending a lot of actual information data by using high code rate coding, which reduces the redundancy. In addition, when the wireless communication environment is bad, the low code rate coding that gives a lot of redundancy to the error should be used to be strong in noise and low in transmission speed.

On the other hand, in the case of a modulation scheme, when the wireless communication environment is good, transmission capable of high-speed data transmission such as quadrature amplitude modulation (QAM) or phase shift keying (PSK), which transmits multiple information bits in one transmission symbol If the wireless communication environment is bad, a transmission method such as BPSK, which is resistant to interference noise but has a slow transmission speed, is selected.

The modulation method as described above needs to send information about the channel environment from the receiver for estimating the channel environment in order to adaptively change the modulation method and the coding method according to the change of the channel environment.

In addition, the mobile communication system for packet transmission uses a hybrid automatic repeat request (HARQ) scheme.

HARQ is a method of combining ARQ and Forward Error Correction (FEC) to improve reliability and throughput in data transmission in a communication system.

ARQ aims to improve reliability by requiring the retransmission of the same information until it is received without error when an error occurs due to the channel environment in the transmitted information, and FEC uses an error correcting code. The purpose is to correct errors caused by the channel environment. If the channel environment is always good and there is a low frequency of errors in the information sent, using ARQ alone will suffice. However, when the channel environment becomes bad, the frequency of errors occurring in the transmitted information increases, and accordingly, the number of times of requesting retransmission increases. This lowers the throughput of the system. It is therefore proposed to use FEC with ARQ and this is HARQ.

One type of HARQ is Incremental Redundancy (IR), which initially adds redundant bits after encoding at a higher coding rate and lowering the coding rate whenever it is required to retransmit. It sends only bits and combines with already sent information to decode. The retransmitted bits are the bits that make up the previously sent packet. In this way, the gain of the combination can be obtained, and the coding rate is gradually reduced with each retransmission, thereby reducing the adaptive redundancy according to the channel environment.

In a system requiring high-speed data transmission, a time division multiplexing (TDM) scheme is used to schedule a terminal to transmit data every frame period in consideration of the channel environment and the amount of data to be transmitted. However, if only one terminal is selected in every frame section and data is transmitted, the amount of data to be sent is small but the Walsh code space is left when the channel environment is good, resulting in an inefficient system. Here, the Walsh code space refers to a collection of Walsh codes.

Thus, if a Walsh code is allocated to one terminal in each frame period, the system uses a TDM / CDM (Code Division Multiplexing / Time Division Multiplexing) method that transmits data to another terminal using the remaining Walsh code. The efficiency can be improved.

1 is a diagram illustrating an example of data transmission by a general TDM scheme.

2 is a diagram illustrating an example of data transmission by a general CDM / TDM scheme.

Figure 3 shows a comparison of the TDM system and CDM / TDM Walsh code utilization efficiency.

As shown in FIG. 3, the TDM system is more likely to waste Walsh codes than the CDM / TDM system.                         

Therefore, a method of selecting a terminal to transmit data in a CDM / TDM system having higher resource utilization efficiency than a TDM scheme, optimally determining the number of Walsh codes used by the terminal, and using the optimally determined Walsh code It is necessary to determine the data rate of the.

Accordingly, an object of the present invention is to provide a Walsh code resource allocation method in a communication system that allows Walsh codes to be efficiently used.

According to an aspect of the present invention for achieving the above object, in a mobile communication system in which a time division scheme and a code division scheme are mixed, determining a maximum data rate that can be transmitted using received channel information; Determining a payload size and a transmission data rate according to the data to be transmitted; Calculating the number of Walsh codes required for the data transmission when the transmission data rate according to the data to be transmitted is smaller than the maximum data rate that can be transmitted; And determining the remaining number except the required Walsh code from the predetermined total Walsh code and allocating Walsh codes for other terminals.

Advantageously, the required Walsh code number is calculated using the maximum data that can be transmitted, the data rate according to the data to be sent, the number of Walsh codes available, and the code rates. Here, the required Walsh code number is calculated by applying the ratio of the transmit data rate and the transmittable data rate according to the data to be sent to the available Walsh code number.

Preferably, in the allocating step, the remaining number is compared with a threshold, and if the value is greater than or equal to, a further Walsh code for another terminal is allocated, and if less, the remaining number is converted into an available Walsh code number. It further comprises the step of.

According to another aspect of the present invention for achieving the above object, in a mobile communication system where a time division scheme and a code division scheme are mixed, the channel information and power received from each terminal and the number of available Walsh codes are used. Selecting a data rate of the terminals; Assigning priority to each terminal according to the determined data rate; Selecting a terminal having a relatively high priority; And comparing a threshold value with channel information of the selected terminal and assigning a Walsh code to the selected terminal according to the comparison result.

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 present invention proposes a method of selecting a data rate using feedback information from a receiver and a method of determining the number of Walsh codes in a CDM / TDM system in order to use a mobile communication system efficiently.

In addition, the present invention proposes a method for selecting a terminal according to priority and determining the number of Walsh codes to be allocated to the selected terminal.                     

It is assumed that there are six payload sizes of data bits to be transmitted: 384 bits, 768 bits, 1536 bits, 2304 bits, 3072 bits, and 3840 bits. In FIG. 4, the payload size is represented by EP.

At this time, the available data rate according to each payload size (EP) is shown in FIG. In FIG. 4, N.A indicates that it is not defined. In the above IR scheme, one packet is composed of sub-packets of fixed length or variable length, and these subpackets are composed of repeated encoded sequences of a predetermined length in order to apply the HARQ scheme.

First embodiment

FIG. 5 is a diagram illustrating an example of a procedure of selecting a data rate shown in FIG. 4 and a number of Walsh codes according to the data rate.

First, the scheduler of the base station selects a terminal to transmit data every frame using information such as channel environment feedback information (C / I) from the terminal and the amount of data to be sent (S10).

When the terminal to transmit data is selected, the maximum data rate DR _A is selected in FIG. 4 using the channel environment feedback information transmitted from the terminal. (S11) At this time, a threshold to be compared to determine the maximum data rate There are 24 types of 'number of slots per packet (4 types) x payload size (6 types)'. As shown in Fig. 4, among these 24, the same data rate exists. Those having the same data rate may have similar thresholds, and thus, those having the same data rate may be bundled together. In our current system, there are 15 data rates, so there are 15 thresholds.

Accordingly, the base station compares the received channel environment information C / I with 15 thresholds to determine the maximum possible data rate DR _A (S12).

When the maximum data rate DR _A is determined as described above, the base station determines the payload size by checking the amount of data to be sent, and determines the corresponding data rate DR _B.

It is determined whether the data rate DR _B according to the determined payload size is smaller than the maximum data rate DR _A according to channel information from the terminal (S13).

If, DR, if _B is smaller than the DR _A, determines the number of Walsh codes are actually needed (W _B) by using the DR _A, DR _B and the available Walsh code number _{(W A). (S14)} DR B the DR _A because the data rate is less than that if you want to send a good channel environment than the current channel environment, it is necessary to require the state it is less than the number of Walsh codes available Walsh code (W _a) can be used. In this case, the required number of cache codes W _B is obtained by considering parameters such as DR _A , DR _B , W _A , and code rate.

As one embodiment, the following Equation 1 may be used.                     

또는

or

,

는 상수이고,

는 x보다 크거나 같은 최소 정수이고,

는 x보다 작거나 같은 최대 정수이다.

을 사용하는 경우는 사용하는 왈쉬 코드 수를 충분히 단말기들에게 할당해주는 방법이고,

를 사용하는 경우는 사용하는 왈쉬 코드 수를 최소로 하는 방법이다. here,

,

Is a constant,

Is the smallest integer greater than or equal to x,

Is the largest integer less than or equal to x.

In case of using, the number of Walsh codes to be used is sufficiently allocated to the terminals.

Is used to minimize the number of Walsh codes used.

Also, for operational convenience, W _B can be limited to multiples of 2, multiples of 3, multiples of 4, multiples of 5, multiples of 6, and so on.

If the number of Walsh codes (W _C = W _A -W _B ) is greater than or equal to a threshold value according to the necessary Walsh code number determination in step S14, the number of available Walsh codes W _A is determined by the number of Walsh codes remaining. (W _C ). (S17)

After substituting the available Walsh code number (W _A) to the number of remaining Walsh codes (W _C), the scheduler of the base station using the information such as the amount of data to be sent and the channel condition information from the terminal, the remaining Walsh codes can Select a new data terminal to transmit with the remaining number of Walsh codes (S18).

If, in step S14, the number of Walsh codes remaining is smaller than the threshold according to the required Walsh code number determination, however, if the number of Walsh codes remaining (W _C = W _A -W _B ) is smaller than the threshold, the number of Walsh codes required Substitute (W _B ) by the number of Walsh codes available (W _A ) (S16).

Similarly, in step S13, if DR _B is not less than DR _A , ie, greater than or equal to, the required Walsh code number W _B is replaced with the available Walsh code number W _A (S16).

Then, the newly determined data terminal is repeated until the condition is satisfied from step S11.

By doing so, the present invention can efficiently use the remaining Walsh codes.

Second embodiment

6 illustrates another example of a terminal selection, a data rate of a selected terminal, and a Walsh code number determination procedure according to the present invention.

Referring to FIG. 6, first, an I value indicating a sequence of terminals (hereinafter, referred to as a CDM terminal) is set to 1 (S21), where I is a variable for counting the number of terminals that can simultaneously transmit data at the same time. Is used.

The data rate for all terminals is determined using the PWR, NW, and CQI information (S22). At this time, it is assumed that all Walsh codes are assigned to any one terminal.

Where PWR represents the amount of power available in the Forward Packet Data CHannel (F-PDCH), NW represents the number of 32-chips Walsh codes available for the F-PDCH, and CQI represents channel quality. Indicates an indicator (Channel Quality Indicator).                     

The scheduler allocates a priority value to each terminal by reflecting the data rate obtained in step S22.

That is, the higher the data rate obtained, the higher the priority, and the lower the lower the priority.

If the I value is less than or equal to the number of CDM terminals MAX_NUM_CDM capable of transmitting data at the same time set in the system (S24), it is again determined whether NW and PWR are not zero (S25). If I is greater than MAX_NUM_CDM in step S24, if NW is greater than 0 (S38), the remaining NW Walsh codes are allocated to the scheduled CDM terminals (S39), and all procedures are terminated.

If NW and PWR are not 0, it is again determined whether the assigned priority value is not 0 (S26). However, if NW or PWR is zero, all procedures are terminated.

In step S26, if the priority value of the at least one terminal is not 0, the terminal having the highest priority is selected (S27). However, if the priority value of all terminals is 0, all procedures are terminated.

The priority of the selected terminal is set to 0. (S28)

)로 설정하고, 최소 인코더 패킷 크기((MIN_EP_SIZE))는 표준에 정해져 있는 최소 인코더 패킷 크기로 설정한다.(S31) In step S27, it is determined whether a packet to be transmitted to a selected terminal having the highest priority is a retransmission packet (S29). In the case of a retransmission packet, a maximum encoder packet size (MAX_EP_SIZE) and a minimum encoder packet size (MIN_EP_SIZE) are first transmitted. The size of the encoder packet used for the packet (EP_SIZE) is set (S30). However, for the first packet transmitted, the maximum encoder packet size ((MAX_EP_SIZE)) is the maximum integer (not exceeding the buffer size).

(MIN_EP_SIZE) is set to the minimum encoder packet size specified in the standard.

The maximum or minimum encoder packet size is synonymous with the payload size in FIG.

After the encoder packet sizes are determined as in S30 or S31, it is determined whether I is 1 (S32), and when I is 1, the length of the slot using channel environment information (C / I) received from each terminal. (Slot Length; hereinafter SL) is selected (S33). If it is the first transport packet, the encoder packet size (EP_SIZE) should also be selected. In this case, it is assumed that all Walsh codes are assigned to one terminal. The larger the received C / I, the shorter the transmission interval of the SL, and the smaller the longer the transmission interval.

In step S32, if I is not 1, it is determined whether the channel environment information (C / I) value received from each terminal is greater than or equal to a threshold value (this threshold value is changed according to NW, SL, and EP_SIZE). Determine (S37), if greater than or equal to the minimum Walsh code number required for the I-th CDM terminal using the slot length (SL), encoder packet size (EP_SIZE), channel environment information (C / I) received from each terminal ( NB_WALSH_CODES) is determined (S34). However, if it is not equal to or greater than one, it is again determined whether the priority value is not 0, and the subsequent steps are repeated.

The slot length of each terminal code-multiplexed in one transmission unit section by the process of step S33 and S34 is the same.                     

The NB_WALSH_CODES represents the minimum number of Walsh codes required for any Frame Error Rate (FER).

The strength of the power used by the I-th CDM terminal using the Walsh code number (NB_WALSH_CODES), PWR, and NW determined in step S34 is obtained by using Equation 2 below (S35).

P (I) = PWR * NB_WALSH_CODES / NW

Referring to the result of Equation 2, the strength of the remaining power that can be used in the F-FDCH is calculated using Equation 3 and Equation 4 (S36).

PWR = PWR-P (I)

NW = NW-NB_WALSH_CODES

After calculating the strength of the remaining power that can be used for the F-FDCH as above, the value of I is increased by 1, and it is determined whether this I is less than or equal to the maximum number of CDM terminals (MAX_NUM_CDM) (S24). Repeat the process.

As in step S39, there are three cases of assigning the remaining NW Walsh codes to the scheduled CDM terminals.

First, the same Walsh codes are allocated to all CDM terminals. For example, if the number of remaining Walsh codes is greater than or equal to the CDM terminal, a procedure of additional allocation to all CDM terminals is performed one by one. This procedure is repeated until the number of Walsh codes is smaller than the CDM terminal.

If the number of remaining Walsh codes is smaller than the CDM terminal, Walsh codes are additionally allocated one by one from the CDM terminal having the highest priority.

This first example is shown in FIG.

7 illustrates an example of a method of equally allocating remaining Walsh codes to CDM terminals according to the present invention.

That is, it is determined whether the NW is smaller than the number of CDM terminals (NUM_CDM) (S41), and if it is small, Walsh codes are additionally allocated to NW CDM terminals having a high priority (S42). However, if the NW is greater than or equal to the number of CDM terminals NUM_CDM, Walsh codes are additionally allocated to all CDM terminals one by one (S43). Then, the NW value is subtracted by NUM_CDM, updated (S44), and again, it is determined whether the updated NW is smaller than NUM_CDM (S41).

Second, all remaining Walsh codes are allocated to the CDM terminal having the highest priority.

Third, a method of allocating the remaining Walsh codes in proportion to the number of Walsh codes allocated to each CDM terminal (NB_WALHS_CODES). For example, if the number of Walsh codes remaining is NW, the number of CDM terminals is n, and the number of Walsh codes allocated to each CDM terminal (NB_WALSH_CODES) is NB_WALSH_CODES1, NB_WALSH_CODES2, ..., NB_WALSH_CODESn, the number of Walsh codes to be allocated is further calculated. . If the number of Walsh codes additionally allocated to each CDM terminal is AW1, AW2, ..., AWn, AW1 is 'NW * round {NB_WALSH_CODES1 / (NB_WALSH_CODES1 + NB_WALSH_CODES2 + ... + NB_WALSH_CODESn)}', and AW2 is It is calculated as '(NW-AW1) * round {NB_WALSH_CODES2 / (NB_WALSH_CODES2 + ... + NB_WALSH_CODESn)}'. And AWn-1 is' (NW-AW1-AW2-...-AWn-2) * round {NB_WALSH_CODESn-1 / (NB_WALSH_CODESn-1 + NB_WALSH_CODESn)} ', and AWn is' (NW-NW1-NW2- ...-AWn-1) '. 'Round' in the above means rounding.

In the third embodiment, 'round', 'ceil', 'floor', etc. may be used, and the order of calculation for each CDM terminal is prioritized or the number of Walsh codes allocated (NB_WALSH_CODES). You can do

As described above, the present invention determines a data rate using feedback information from a receiver, selects a terminal to be transmitted at each transmission unit interval in a CDM / TDM system, and selects a data rate of the selected terminal and the selected terminal. Optimizing the number of Walsh codes and transmitting the data to other terminals using the remaining number of Walsh codes improves system efficiency.

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 (26)

In the method of assigning Walsh codes, A first step of determining a maximum data rate usable by comparing the channel information value of the forward link with a first threshold value; A second step of determining one data rate based on the amount of data to be transmitted; According to a result of comparing the data rates including the data rate according to the first step and the data rate according to the second step, finishing the allocation of the Walsh code or determining the number of Walsh codes required for the data. Three steps; And A fourth step of determining the number of Walsh codes for other terminals by checking the number of remaining Walsh codes other than the required Walsh codes in the available Walsh codes How to assign a Walsh code comprising a. The method of claim 1, The number of Walsh codes required is determined according to the data rates and the number of available Walsh codes. How to assign Walsh code. The method of claim 2, The required number of Walsh codes is determined by substituting the available Walsh codes for the ratio between the data rates. How to assign Walsh code. The method of claim 1, The first threshold value is, According to the channel information value of the forward link, the size of the payload and the number of slots per subpacket for determining the maximum data rate Characterized in that it is determined differently How to assign Walsh code. The method of claim 1, The first threshold value is, If the data rate is the same, the payload size is different, and the number of slots per subpacket for determining the maximum data rate is different Characterized in that the same, How to assign Walsh code. The method of claim 1, The fourth step, If the number of remaining Walsh codes is greater than or equal to a second threshold, Replacing the new number of available Walsh codes with the number of remaining Walsh codes Repeating the first to third steps; And Determining the number of Walsh codes for another terminal by using the replaced number of available Walsh codes Containing How to assign Walsh code.  The method of claim 1, The fourth step, If the number of remaining Walsh codes is less than a second threshold, Replacing the new number of available Walsh codes with the number of remaining Walsh codes Repeating the first to third steps; And Replacing the required number of Walsh codes with the number of available Walsh codes Terminating the allocation of the Walsh code Containing How to assign Walsh code. A method for allocating Walsh codes in a communication system using a time multiplexing method and a code multiplexing method, Determining a data rate for each terminal using the channel quality indicator, the power level available for transmission, and the number of Walsh codes available; A second step of allocating priority of each terminal according to the determined data rate; Determining at least one of a transmission slot and an encoder packet size for a first selected terminal according to the priority; And The number of Walsh codes required for the selected terminal is determined based on one of a predetermined number of the transmission slots and the determined transmission slots, forward link channel information from the selected terminal, and the determined encoder packet size. 4th step Containing How to assign Walsh code. The method of claim 8, The third step, Determining whether data for the selected terminal is retransmitted Determining a minimum or maximum encoder packet size according to the determination of whether to retransmit; Transmitting the number of transmission slots when the selected terminal is the first selected terminal Containing How to assign Walsh code.  The method of claim 9, If the data for the selected terminal is retransmitted data, The size of the minimum or maximum encoder packet for the retransmitted data, characterized in that determined by the size of the encoder packet of the original transmission data, How to assign Walsh code. The method of claim 9, If the data for the selected terminal is the first transmitted data, The size of the minimum or maximum encoder packet is determined by the size of the preset minimum or maximum encoder packet, How to assign Walsh code. The method of claim 9, If the data for the selected terminal is the first transmitted data, The number of the transmission slots, characterized in that the number of transmission slots of a predetermined number is used, How to assign Walsh code. The method of claim 8, The fourth step, Comparing a threshold with the forward link channel information Containing more How to assign Walsh code. The method of claim 13, The threshold varies with the number of available Walsh codes, the number of determined transmission slots, and the determined encoder packet size. How to assign Walsh code. The method of claim 8, The second step, The number of code-division-multiplexed (CDM) terminals including the selected terminal is determined. Maximum number of code multiplexing terminals that can transmit data at the same time Comparing with; Selecting a terminal according to the priority when the comparison result is less than the maximum number of code multiplex terminals and the available Walsh code and the available power level exist; Distributing the usable Walsh code to all terminals if the number of maximum code multiplexing terminals exceeds the maximum number of available Walsh codes as a result of the comparison; Containing How to assign Walsh code. The method of claim 15, Distributing the available Walsh codes uniformly to all terminals and then distributing the remaining Walsh codes according to the priorities Containing more How to assign Walsh code. The method of claim 15, Distributing the remaining Walsh codes to the UEs of higher priority after uniformly distributing the available Walsh codes to all terminals. Containing more How to assign Walsh code. The method of claim 15, Distributing the usable Walsh codes in proportion to the number of Walsh codes already assigned to each terminal; Containing more How to assign Walsh code. The method of claim 8, The method may further include a fifth step of repeatedly performing the third and fourth steps. Calculating a power level for data transmission based on the number of Walsh codes required for the terminal, the power level available for the transmission, and the number of Walsh codes available; Updating the usable power level using the calculated power level; And And updating the number of available Walsh codes by using the number of Walsh codes required for the terminal. How to assign Walsh code. In the method of assigning Walsh codes, Determining the number of Walsh codes required for data transmission using the available Walsh codes, the data rate determined using the amount of transmitted data, and the maximum data rate determined by the channel information from the scheduled terminal. Containing How to assign Walsh code The method of claim 20, Determining the number of Walsh codes required for at least one terminal by using the remaining Walsh codes except for the required Walsh codes from the available Walsh codes. Include more, The at least one terminal is scheduled to transmit data simultaneously with another terminal. How to assign Walsh code The method of claim 20, The data transmission is performed over a packet sharing channel How to assign Walsh code The method of claim 20, A data rate determined by using the maximum possible data rate and the amount of transmitted data Comparing steps Containing more How to assign Walsh code In the method of assigning Walsh codes, Determining a data rate for each of the at least one terminal; Allocating a priority of each terminal according to the determined data rate; And Determining the number of Walsh codes required for data transmission based on the forward link channel information, the length of the transmission slot, and the encoder packet size for data transmitted to the terminal selected according to the priority. Containing How to assign Walsh code. The method of claim 24, Determining a power level for the data transmission according to the number of Walsh codes required for the data transmission, the number of available Walsh codes, and the available power level for the terminal selected according to the priority. Containing more How to assign Walsh code. The method of claim 24, The data rate is determined according to the forward link channel information, the number of Walsh codes available and the available power level. Characterized by How to assign Walsh code.

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