KR20080054987A - Apparatus and method for ranging in wireless communication system - Google Patents

Abstract

A ranging device in a wireless access communication system and a method therefor are provided to allocate ranging resources variably according to ranging loads, thereby increasing a probability of ranging success. A controller(310) decides on retransmission frequency of a random access code. A code generator selects a code set in accordance with the retransmission frequency, and selects one random code within the selected code set to output the selected code. A transmitter(314) transmits the random access code of the code generator through previously allocated resources. The random access code is a code for ranging. The controller obtains window size for backoff and a resource area for transmitting the random access code from a predetermined message received from a base station.

Description

Ranging apparatus and method in a wireless access communication system {APPARATUS AND METHOD FOR RANGING IN WIRELESS COMMUNICATION SYSTEM}

1 is a view for explaining a method of selecting a ranging code.

2 is a diagram illustrating a configuration of a terminal in a broadband wireless communication system according to an embodiment of the present invention.

3 is a diagram illustrating a configuration of a base station in a broadband wireless communication system according to an embodiment of the present invention.

4 is a diagram illustrating an operation procedure of a terminal in a broadband wireless communication system according to an embodiment of the present invention.

5 is a diagram illustrating an operation procedure of a base station in a broadband wireless communication system according to an embodiment of the present invention.

The present invention relates to a random access device and method in a wireless communication system, and more particularly to a ranging device and method in a broadband wireless communication system.

In general, communication systems have been developed mainly for voice services, and are gradually developing into communication systems capable of not only voice but also data services and various multimedia services. However, the voice-oriented communication system has not satisfied the rapidly increasing user's service needs due to the relatively small transmission bandwidth and high usage fee. In addition, due to the development of the communication industry and increasing user demand for Internet services, there is an increasing need for a communication system that can efficiently provide Internet services. Accordingly, it has been introduced into a broadband wireless communication system for efficiently providing Internet services.

Since the broadband wireless communication system uses Orthogonal Frequency Division Multiplexing / Orthogonal Frequency Division Multiple Access (OFDMA), high-speed data transmission is achieved by transmitting a physical channel signal using a plurality of sub-carriers. It is possible. The wireless access method of the broadband wireless communication system is being standardized by the IEEE 802.16 standardization group of the Institute of Electrical and Electronics Engineers, one of the international standardization organizations.

Ranging, a type of random access procedure in the broadband wireless communication system, is a process for correcting a correct time and frequency offset between a base station and a terminal and correcting a transmission power of the terminal. It may be classified into initial ranging, periodic ranging, bandwidth request ranging, and handover ranging.

First, the terminal obtains information necessary for ranging such as ranging opportunity interval and ranging window size from the base station. The base station determines the ranging opportunity period, ranging window size, and the like at the time of initial setting of the system. However, when the ranging opportunity period or the ranging window size is set to a fixed value, performance may be degraded due to excessive access attempts by the terminal or increase in terminal user in the cell. In addition, there is a drastic difference in communication performance when the connection load degree of the terminal is appropriate or not. However, according to the prior art, since there is no way for the base station to know the connection load of the terminal attempting ranging, it is difficult to properly adjust the parameters necessary for the ranging.

For example, when the size of the ranging opportunity period is small, when the number of terminals attempting ranging increases rapidly and the connection load increases, the terminal frequently attempts to access due to collision between terminals attempting ranging. The number decreases. Or, if the size of the ranging opportunity interval is too large for the number of terminals attempting ranging, a problem of wasting ranging channel resources occurs.

Similarly, when the window size provided for the backoff operation is small, the collision probability increases when the number of terminals attempting to connect is large. In this case, therefore, a large window size is advantageous. Alternatively, if the number of terminals attempting to connect is small, if the window size is large, the connection delay may be increased due to the backoff since the connection attempt may be made after waiting for the window size. Thus, in this case, a small window size is advantageous.

Therefore, there is a need for a method of appropriately allocating a ranging opportunity period and a window size by determining the access load of a terminal to which the base station attempts to access.

Accordingly, an object of the present invention is to provide an apparatus and method for determining an access load in a wireless communication system.

Another object of the present invention is to provide an apparatus and method for adjusting a resource size for a random access and a window size for a backoff in a wireless communication system according to an access load.

Another object of the present invention is to provide an apparatus and method for reporting a reconnection number of terminals to a base station in a wireless communication system.

Another object of the present invention is to provide an apparatus and method for determining an access load according to the number of reconnections of terminals in a wireless communication system.

It is another object of the present invention to provide an apparatus and method for increasing the access success rate of a terminal in a wireless communication system.

Another object of the present invention is to provide an apparatus and method for adjusting a ranging opportunity interval and a window size according to an access load in a broadband wireless communication system.

Another object of the present invention is to provide an apparatus and method for reporting a ranging retransmission number of a terminal to a base station in a broadband wireless communication system.

According to an aspect of the present invention for achieving the above object, a terminal device in a wireless communication system, the controller for determining the number of retransmission of a random access code, and selects a code set according to the retransmission number, and the selected code set And a transmitter for selecting and outputting any one code within the transmitter and a transmitter for transmitting a random access code from the code generator through a pre-allocated resource.

According to another aspect of the present invention, in a base station apparatus in a wireless communication system, a receiver for extracting and outputting data corresponding to a pre-allocated resource from received data, and data from the receiver and each of the predefined random access codes And a code demodulator for outputting the code number from which the correlation peak is detected, managing different code sets for each retransmission number, and determining the number of retransmissions by examining a code set to which a code number from the code demodulator belongs, And a controller for determining a system connection load according to the number of codes detected for each retransmission number.

According to still another aspect of the present invention, in a communication method of a terminal in a wireless communication system, determining a number of retransmissions of a random access code, selecting a code set according to the number of retransmissions, and in the selected code set And selecting a random code and transmitting the selected random access code through a pre-allocated resource.

According to still another aspect of the present invention, in a communication method of a base station in a wireless communication system, extracting data corresponding to a pre-allocated resource from the received data, and each of the extracted data and the predefined random access codes Obtaining a code number from which the correlation peak is detected; managing different code sets for each retransmission number; determining a number of retransmissions by examining a code set to which the obtained code number belongs; And determining a system connection load according to the number of codes detected for each retransmission number.

Hereinafter, the operating principle of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

Hereinafter, an embodiment of the present invention will be described a method for determining an access load in a broadband wireless communication system and adjusting a resource for random access and a window size for backoff according to the access load. . The present invention divides a ranging code into a plurality of groups according to the number of retransmissions, and the terminal attempts ranging by randomly selecting a code from a group according to the number of retransmissions. The present invention can be applied to both cases in which a code is transmitted, such as initial ranging and band request ranging, and the following description will be given with reference to band request ranging.

Meanwhile, in the following description, the broadband wireless communication system is a communication system using an Orthogonal Frequency Division Multiplexing (OFDM) scheme or an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.

1 is a diagram illustrating a method of selecting a ranging code. In particular, (a) shows a method for selecting a code during initial ranging or band request ranging in an existing system, and (b) shows a code selection method proposed in the present invention.

First, referring to FIG. 1A, it is assumed that a total of 18 codes are used for initial ranging or band request ranging. When ranging, the UE selects and transmits any one code among all 18 codes whenever retransmission is performed. Assuming the maximum number of retransmissions to be 16, one code is randomly selected from the total of 18 codes for 16 attempts and then transmitted.

Next, referring to (b) of FIG. 1, it is assumed that a total of 18 codes are used for initial ranging or band request ranging. However, the present invention is limited to a code that can be selected according to the number of retransmissions. As shown, in the first transmission (0 retransmission) attempt, the terminal selects and transmits any one code from 1 to 8 codes. When the first transmission fails, the terminal selects any one code among the 9th to 12th codes and attempts the second transmission (once retransmission). In case of failure, the UE selects one code from 13 to 15 codes and attempts a third transmission (2 retransmissions). On the other hand, if it fails more than that, the terminal selects and transmits one code from 16 to 18 codes. As such, the present invention divides the available ranging codes into a plurality of groups according to the number of retransmissions, and the terminal attempts ranging by randomly selecting a code from the group according to the number of retransmissions. The code set by the number of retransmissions (8 in the first attempt, 4 in the second attempt, 3 in the third attempt, and 3 in the fourth or more attempts) proposed in FIG. 1 (b) is one for explanation. It is only an example and may be variously applied when applied to an actual system.

2 illustrates a configuration of a terminal in a broadband wireless communication system according to an embodiment of the present invention.

As shown, the terminal includes a controller 200, ranging code generator 202, ranging subchannel mapper 204, OFDM modulator 206, digital to analog (D / A) converter 208, RF (Radio Frequency) processor 210, receiver 212 and the message analyzer 214 is configured.

Referring to FIG. 2, first, the receiver 212 is a physical layer decoder, which physically decodes a signal received through an antenna and provides the message to the message analyzer 214. For example, the receiver 212 may be configured to include an RF receiving block, a demodulation block, a channel decoding block, and the like.

The message analyzer 214 is a block for decoding a Media Access Control (MAC) message. The message analyzer 214 interprets a received message from the receiver 212 and provides the result to the controller 200. According to the present invention, the message analyzer 214 analyzes the MAP message received from the base station, obtains ranging opportunity section information, and provides the ranging opportunity section information to the controller 200. In addition, the message analyzer 214 analyzes an uplink channel descriptor (UCD) message received from a base station, obtains backoff window size information, and provides the backoff window size information to the controller 200.

The controller 200 controls the overall operation of the terminal. According to the present invention, the controller 200 obtains the ranging opportunity section information and the backoff window size information, and instructs the ranging code generator 202 to generate a code when ranging is necessary. In addition, the controller 200 checks whether a response is received after transmitting the ranging code, and if the response is not received, increases the number of retransmissions by '1' and attempts to transmit the ranging code again. The following description will look at the band request ranging as an example. When the band request ranging, the controller 200 checks the number of retransmissions of the band request ranging code, and the number of retransmissions and the type of the ranging (eg, band request ranging, initial ranging, periodic ranging, etc.) To the ranging code generator 202.

The ranging code generator 202 manages a plurality of code sets for each ranging type (eg, initial ranging, band request ranging, etc.). The ranging code generator 202 determines a code set according to the number of retransmissions among the code sets according to the ranging type (band request ranging), and selects any one code among the codes in the determined set. Output

The ranging subchannel mapper 204 maps the ranging code from the ranging code generator 202 to a ranging slot (or resource) according to the window size. For example, in the IEEE 802.16 system, a plurality of ranging slots may exist in a ranging opportunity interval allocated to each frame. The terminal selects a random number within a window size (eg, 16) obtained from the UCD, and counts a ranging slot by the selected number to transmit a ranging code in the corresponding slot.

The OFDM modulator 206 performs an Inverse Fast Fourier Transform (IFFT) operation on the resource-mapped ranging code from the ranging subchannel mapper 204, inserts a guard interval into the sample data after the IFFT operation, and performs an OFDM symbol. Create The D / A converter 208 converts the baseband sample data from the OFDM modulator 206 into an analog signal and outputs the analog signal. The RF processor 210 converts the baseband analog signal from the D / A converter 208 into a signal of an RF band that can be actually transmitted and transmits the signal through an antenna.

3 illustrates a configuration of a base station in a broadband wireless communication system according to an embodiment of the present invention.

As shown, the base station includes an RF processor 300, an analog to digital (A / D) converter 302, an OFDM demodulator 304, a ranging subchannel extractor 306, a code demodulator 308, and a controller 310. ), A message generator 312, and a transmitter 314.

Referring to FIG. 3, the RF processor 300 includes a filter, a frequency converter, and the like, and converts a signal of an RF band received through an antenna into a baseband signal and outputs the signal. The A / D converter 302 converts the analog baseband signal from the RF processor 300 into a digital signal (sample data) and outputs it.

The OFDM demodulator 304 removes the guard interval from the sample data from the A / D converter 302 and then performs a fast fourier transform (FFT) operation to output each subcarrier value (receive value). The ranging subchannel extractor 206 extracts and outputs subcarrier values to which a ranging signal is mapped from subcarrier values from the OFDM demodulator 304. Hereinafter, an example of receiving a band request ranging code will be described.

The code demodulator 308 multiplies the subcarrier values from the ranging subchannel extractor 206 by a predefined band request ranging codes to perform code demodulation. That is, the code demodulator 308 correlates each of the band request codes with the signal received in each ranging slot and provides the controller 310 with the number of the code from which the correlation peak was detected.

The controller 310 classifies the code numbers from the code demodulator 308 according to the number of code retransmissions, and determines the intra-cell connection load in consideration of the number of detection codes according to the number of retransmissions. For example, when a number of codes corresponding to two or more transmissions than one transmission is detected, it may be determined that many terminals attempting intra-cell access. On the contrary, when a relatively small code corresponding to two or more transmissions is detected, it may be determined that the connection load is small. The controller 310 determines the ranging opportunity interval and the backoff window size based on the determined load, and provides the result to the message generator 312. Herein, when the controller 310 determines that the connection load (or collision probability) is large, the controller 310 sets the ranging opportunity interval and the backoff window size to be large, and when the controller load is determined to be small, the ranging opportunity interval and the backoff window size are determined. Can be set small.

The message generator 312 is a block for encoding a MAC message, and generates a transmission message using various control information from the controller 310. According to the present invention, the message generator 312 generates and provides a MAP message including the ranging opportunity section information to the transmitter 314, and generates a UCD message including the backoff window size information to generate the MAP message. 314). Here, the MAP message may be generated and transmitted, for example, at a frame period (eg, 5 msec), and the UCD message including system information may be generated and transmitted at a longer period (eg, 2 sec).

The transmitter 314 is a physical layer encoder, which physically encodes a transmission message from the message generator 312 and transmits the same through an antenna. For example, the transmitter 314 may include a channel code block, a modulation block, an RF transmission block, and the like.

4 is a flowchart illustrating an operation procedure of a terminal in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 4, when ranging from a bandwidth request, the terminal selects any one of slots in the ranging opportunity interval allocated from the base station in step 401. If retransmission, the terminal selects a random number within the backoff window size obtained from the UCD message, and selects a slot to transmit a ranging code by counting slots by the selected number. Here, slot counting may be performed not only in one frame but continuously in successive frames.

After determining the slot to transmit the ranging code, the terminal selects a code set according to the retransmission number of the band request ranging code in step 403, and selects any one code from the selected code set. The present invention can manage a plurality of code sets according to the types of ranging codes (eg, initial ranging, band request ranging, etc.). For example, as shown in (b) of FIG. 1, the plurality of code sets includes a code set for zero retransmission (initial transmission), a code set for two retransmissions, a code set for three retransmissions, It can be classified as a code set for more than 4 retransmissions.

In step 405, the terminal maps the selected ranging code to the determined slot and transmits the determined ranging code to the base station. After transmitting the ranging code, the terminal proceeds to step 407 and checks whether a resource allocation message (MAP message) for band request is received in response to the ranging code. If the resource allocation message is received within a predetermined time, the terminal proceeds to step 417 and transmits a band request message (or band request header) to an area (resource) designated by the resource allocation message.

If the resource allocation message is not received within the predetermined time, the terminal proceeds to step 409 and performs a truncated binary exponential backoff algorithm to determine a transmission interval, and waits for the determined transmission interval. . In step 411, the terminal determines whether the number of retransmissions of the ranging code reaches the maximum number of times. If the maximum number of times is reached, the terminal proceeds to step 415 and fails processing of the bandwidth request ranging.

If the number of retransmissions does not reach the maximum number of times, the terminal proceeds to step 413 and increases the number of retransmissions by '1', and returns to step 401 to perform the following steps again.

5 illustrates an operation procedure of a base station in a broadband wireless communication system according to an embodiment of the present invention.

Referring to FIG. 5, the base station first extracts a received signal from the ranging opportunity interval region in step 501. The base station performs OFDM demodulation on the received signal to obtain data in a frequency domain, and extracts data to which a ranging signal (or ranging code) is mapped from the data in the frequency domain.

In step 503, the base station correlates the extracted data with a predefined band request ranging codes to perform code demodulation. In other words, the base station correlates each of the band request codes with the signal received in each ranging slot and obtains the number of the code from which the correlation peak was detected.

In step 505, the base station classifies the obtained code numbers according to the number of code retransmissions and analyzes the intra-cell connection load in consideration of the number of detection codes corresponding to the number of transmissions. For example, the base station can calculate the connection load by calculating the connection success rate (or collision probability) for N frames.

In step 507, the base station determines the ranging opportunity interval region and the backoff window size based on the access load of the terminal. The base station broadcasts the ranging opportunity interval region information and the backoff window size information determined in step 511 to terminals. Herein, the ranging opportunity region information may be included in MAP information and transmitted, and the backoff window size information may be included in a UCD message and transmitted. Meanwhile, the updating of the ranging opportunity interval information and the backoff window size information may be performed at predetermined intervals in consideration of the transmission period of the two pieces of information.

In the detailed description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the present invention has an advantage of increasing the ranging success probability by variably allocating ranging resources according to ranging loads in a wireless communication system. That is, the present invention provides a base station to determine the ranging load by the terminal attempting the ranging to provide the access attempt information to the base station has the advantage that can dynamically control the ranging resources based on this. That is, when the ranging load is small, resource waste may be reduced by reducing the ranging resource, and when the ranging load is large, the connection collision of the terminal may be reduced by increasing the ranging resource.

Claims (26)

A terminal device in a wireless communication system, A controller for determining the number of retransmissions of the random access code; A code generator for selecting a code set according to the number of retransmissions and selecting and outputting any one code in the selected code set; And a transmitter for transmitting a random access code from the code generator on a pre-allocated resource. The method of claim 1, The random access code is a device for ranging. The method of claim 1, And the random access code is a code for initial ranging or band request ranging. The method of claim 1, The controller waits for a response after transmitting the random access code, and if the response is not received, increases the number of retransmissions and controls retransmission of the random access code. The method of claim 1, Wherein the controller obtains a resource area for the random access code transmission and a window size for backoff from a predetermined message received from a base station. The method of claim 1, The resource area for the random access code transmission and the window size for the backoff is variable according to the system connection load. The method of claim 1, wherein the transmitter, A modulator for modulating orthogonal frequency division multiplexing (OFDM) by mapping a random access code from the code generator to a pre-allocated resource; A digital / analog converter for converting sample data from the modulator into an analog signal; And an RF processor for converting the baseband signal from the digital-to-analog converter into a radio frequency (RF) band signal for transmission. A base station apparatus in a wireless communication system, A receiver for extracting and outputting data corresponding to a pre-allocated resource from the received data; A code demodulator that correlates each of the predefined random access codes with data from the receiver and outputs a code number from which the correlation peak is detected; And a controller for managing different code sets for each retransmission number, determining the number of retransmissions by examining a code set to which a code number from the code demodulator belongs, and determining a system connection load according to the number of codes detected for each retransmission number. Device characterized in that. The method of claim 8, And the controller varies a resource area for the random access code transmission and a window size for backoff according to the determined system connection load. The method of claim 9, A message generator for generating a message including resource region information for the random access code transmission and a message including window size information for the backoff; And a transmitter for processing and transmitting a message from the message generator according to a predetermined standard. The method of claim 8, The random access code is a device for ranging. The method of claim 8, And the random access code is a code for initial ranging or band request ranging. The method of claim 8, wherein the receiver, An RF processor for converting a received RF band signal into a baseband signal; An analog / digital converter for converting an analog signal from the RF processor into sample data; A demodulator for OFDM demodulating sample data from the analog / digital converter; And an extractor for extracting and outputting data corresponding to a pre-allocated resource from data in the frequency domain from the demodulator. In a communication method of a terminal in a wireless communication system, Determining the number of retransmissions of the random access code; Selecting a code set according to the number of retransmissions; Selecting any one code in the selected code set, Transmitting the selected random access code through a pre-allocated resource. The method of claim 14, The random access code is a method for ranging. The method of claim 14, The random access code is a code for initial ranging or band request ranging. The method of claim 14, Waiting for a response after transmitting the random access code; And if the response is not received, retransmitting a random access code after increasing the number of retransmissions. The method of claim 14, Obtaining a resource area for the random access code transmission and a window size for backoff from a predetermined message received from a base station. The method of claim 18, The resource area for the random access code transmission and the window size for the backoff is variable according to the system connection load. The method of claim 14, wherein the transmission process, Mapping the selected random access code to a pre-allocated resource to perform orthogonal frequency division multiplexing (OFDM) modulation; Converting the OFDM modulated data into an analog signal; And converting the analog signal into a signal in a radio frequency (RF) band and transmitting the same. In a communication method of a base station in a wireless communication system, Extracting data corresponding to a pre-allocated resource from the received data; Correlating the extracted data with each of the predefined random access codes, and obtaining a code number from which the correlation peak is detected; Managing different code sets for each retransmission number, determining a number of retransmissions by examining a code set to which the obtained code number belongs; And determining a system connection load according to the number of codes detected by the number of retransmissions. The method of claim 21, And varying a resource area for the random access code transmission and a window size for backoff according to the determined system access load. The method of claim 22, Generating a message including resource region information for the random access code transmission and a message including window size information for the backoff; And processing the generated message according to a predetermined standard and transmitting the same. The method of claim 21, The random access code is a method for ranging. The method of claim 21, The random access code is a code for initial ranging or band request ranging. The method of claim 21, wherein the extraction process, Converting the received RF band signal into a baseband signal; Converting the baseband signal into sample data; OFDM demodulating the sample data to generate data in a frequency domain; And extracting data corresponding to a pre-allocated resource from the data of the frequency domain.

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