KR100240103B1 - Rake receiver of mobile communication system and method of controlling tab delay - Google Patents

Abstract

Disclosed are a rake receiver and a method for adjusting a tap delay, which can prevent a decoding error of a received signal in a mobile communication system. The disclosed method is characterized in that the tap delay time is variably adjusted in accordance with the level of the level by periodically checking the level of the received signal strength information every predetermined time.

Description

Rake receiver of mobile communication system and adjusting method of tap delay

1 is a block diagram of a receiver applied to a conventional mobile communication system.

2 is a detailed block diagram of a rake receiver in FIG.

3 shows sampling of an intermediate frequency signal in an analog-to-digital converter in FIG.

4 is a detailed block diagram of a rake receiver in accordance with the present invention.

5 is a view showing a comparison between the conventional tap delay fixed method and the tap delay adjustment method of the present invention.

6 is an operation control flowchart for adjusting tap delay of the fourth controller.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system that provides high frequency wireless communication between a base station and a base station such as a cellular phone. In particular, the present invention relates to a rake receiver and a method of adjusting a tap delay, thereby preventing a decoding error of a received signal.

Typically, portable communication terminals, such as cellular phones, provide the user with the performance of two-way mobile wireless communications. In order to enable the portable communication terminal to communicate with the called party, the mobile communication base station uses the cell site through a cell site using a code division multiple access (CDMA) spread spectrum communication signal. Performs radio frequency (RF) wireless communication with a communication terminal. The base station is also connected to a public switched telephone network (PSTN) for a telephone connection between a user of a later communication terminal and a wired subscriber. For example, when a user of the portable communication terminal attempts to make a call with a called party in a certain office, if the user digits a telephone number installed in the called party's office through a keypad present in the portable communication terminal, the portable communication terminal is used. Dialing is performed by a set operation between the base station and the base station. When the called person is not in a call, when the user hooks off, the call is formed and the call is performed by both parties.

On the other hand, a receiver for receiving a high frequency radio signal in a mobile communication system is employed in not only the base station but also the terminal. The receiver employed in the base station decodes the high frequency radio signal transmitted from the terminal to perform demodulation, and the receiver employed in the terminal decodes the high frequency radio signal transmitted from the base station and performs demodulation. It is shown in FIG. Referring to FIG. 1, the IF processor 2 down converts a high frequency radio signal provided from an input terminal IN into an intermediate frequency IF signal. LPF 4 receives the intermediate frequency signal and performs a low pass filtering operation. The analog-to-digital converter ADC 6 receives the output of the LPF 4, converts it into 4-bit digital data, and then provides the converted data to the RAKE receiver 10. Received Signal Strength Information (RSSI) detector 8 functions to detect the strength of the output of the LPF 4.

The RAKE receiver 10 shown in detail in the embodiment of FIG. 2 has a plurality of fingers consisting of delays 20, 21, 2n and a multiplier 30, 31, 3n, and a combiner 40 which combines the output symbols of the fingers. The Viterbi decoding unit, which is installed at a later stage, decodes and demodulates the digital data, thereby synchronizing the delay of the digital data generated due to a fading environment using diversity. That is, in the CDMA scheme, the RAKE receiver 10 is generally adopted because a signal delayed by a building, a terrain, etc. as well as a main signal is included when transmitting and receiving between a base station and a terminal. Therefore, the receiving end (terminal or base station) receiving these signals has a delay process as much as the time delay by fading using the RAKE receiver 10 before decoding (Viterbi decoding), and then the main signal sample and the delay signal sample. The correlation process is performed for at least two time shifts. The correlation is then combined at symbol combiner 40 to determine the content of the signal. Since the RAKE receiver 10 performs a correlation process by a plurality of delays, the RAKE receiver 10 is called a TDL (Tab Delayed Line) structure. Here, the delay amount of the delay is fixed.

In the conventional RAKE receiver as shown in FIG. 2, the delay of each tap is fixed as described above, assuming that the delay is always the same, for example, in the unit of a hand. It is often triggered. The reason for such a decoding error is that the delay time of the signal varies according to the fading channel environment.

As described above, the conventional RAKE receiver has a problem of causing a decoding error at a later stage because it fails to properly synchronize the received signals through various paths by fixing the tap delay. Accordingly, if the demodulation operation is not performed properly, a problem of deterioration of service quality of the call may be caused.

Accordingly, it is an object of the present invention to provide a rake receiver and a tap delay adjustment method according to the conventional problem described above.

Another object of the present invention is to provide a structure of a rake receiver and a delay adjusting method for preventing a decoding error of a received signal.

It is still another object of the present invention to provide an improved rake receiver capable of adjusting the delay time of a tap delay according to a fading channel environment.

According to an aspect of the present invention, there is provided a method of adjusting a tap delay, the method including: checking a level of received signal strength information periodically at predetermined time intervals; And adjusting a delay time of the rake receiver by selecting any one of the plurality of tap delays according to the level of the checked level of the received signal strength information. The rake receiver of the mobile communication system may further include a first finger for receiving an input signal and outputting the delayed signal without delay, and a second and N-finger for respectively delaying the input signal with a plurality of delays and outputting the input signal. A symbol combiner which combines all of the outputs of the fingers and provides the decoding unit; and a signal for adjusting delay times of the plurality of delays when the average intensity of the input signal is periodically detected and below a specific level. A controller is applied to the finger to adjust the delay time.

Hereinafter, a rake receiver and a tap delay adjustment method according to a preferred embodiment of the present invention will be described with the accompanying drawings. In the following description, specific details are set forth in detail, for example, in order to provide a more thorough understanding of the present invention. However, for those skilled in the art, the present invention may be practiced by the above description without these details. In addition, the basic functions and operations of detailed call conduction of mobile communication systems well known in the art are not described in detail in order not to obscure the gist of the present invention.

In the following description, a preferred embodiment of the present invention will be described by way of example only, with reference to the accompanying drawings.

First, a description for a schematic understanding before the detailed description of the present invention. Since the RAKE receiver according to the conventional sampling method uses diversity by fixing the delay of each tap, it is difficult to improve performance in a mobile communication environment in which chip delay due to a fading channel does not occur in units of one chip. However, in the present invention, the tap delay of the RAKE receiver is variably changed according to the fading channel environment by the RSSI controller to obtain a correlation value in an optimal state. That is, in the TDL structure, the TAB delay for the RAKE receiver must have a delay such as chip delay due to a fading channel. However, the chip delay due to the fading channel depends on the channel environment and the number of paths depends on the channel environment. Therefore, in the present invention, the TAB delay of the RAKE receiver is controlled to achieve an optimal correlation in the RAKE receiver. This will be described in detail with reference to the accompanying drawings.

FIG. 3 shows that the IF signal (reference numeral O.S in FIG. 3) of FIG. 1 is sampled K (8 times) per chip in ADC 6 after passing through low pass filter 4. FIG. This is because the analog value is not integrated when the correlation value is obtained from the RAKE receiver.

4, consisting of three fingers 50, 51, 53, delay 52, 54, an RSSI controller 55, and a combiner 40, illustrates the RAKE receiver architecture of the present invention capable of tap delay adjustment. The RSSI controller 55 obtains an average intensity of the sampled input signal, and adjusts a delay time of the delay through the control lines L1 and L2 when it is below a certain level. The output of each finger is summed by the number of PNs of one bit in the symbol combiner 40, which is provided to the input of the Viterbi decoder which decodes the bit value. Each finger has a time delay through each delay, and the delay of each finger is controlled by the RSSI controller 55. However, since the finger 1 50 detects a wave directly, delay control is not necessary.

5 shows a comparison between a conventional method and a method for obtaining correlation values by the method of the present invention. In the conventional method 5a, the delay is fixed, and in the method 5b of the present invention, delays of D2 and D3 are respectively given. (5c) shows the position where each sampling point starts by the delay. In other words, when detecting a signal using diversity through three paths due to fading, an optimal performance is obtained by delaying a correlation between a direct wave and a signal coming through each path by the same time at the tap of the RAKE receiver. . At this time, since the time delay cannot be given precisely, the RSSI of the incoming signal is detected so that the delay can be adjusted if it is below a certain level.

FIG. 6 is an operation control flowchart of adjusting delay through RSSI detection at each finger, which is shown in steps 100-110. The variable org_delay means originally set delay and is set as it is because it is an initial step in step 100. After step 102, the delay is changed at a specific time (determined by a timer) in step 103. If the RSSI is above a certain level, the previous delay is used as it is. For example, if you adjust the tap delay once every 10ms, if the RSSI is below a certain level after 10ms, adjust the TAB delay to one of eight, and if the RSSI is above the level, repeat the next 10ms. If the RSSI is less than or equal to the set level in step 103, the loop continues until step 110 so as to find a delay having the RSSI level or higher among the K delay positions. If K samples are obtained per chip, there are K delay point positions. When the current delay position is X, the delay is increased to K, then the delay is reduced until 1 to detect RSSI. If a RSSI that is above the level is detected during this process, the delay is used, and the timer is reset and org_delay = delay. The variable org_delay is a variable for increasing or decreasing the original position when controlling the delay. Therefore, as described above, the present invention improves the performance of the RAKE receiver by appropriately adjusting the tap delay of the RAKE receiver having a TDL structure through analog RSSI detection.

According to the present invention as described above, the use of the rake receiver to adjust the tap delay can be completely correlated, thereby preventing the decoding error during decoding at the later stage. In addition, there is an advantage in improving the call quality service by increasing the reliability of the demodulation operation.

Although the above-described invention has been described and limited by way of example with reference to the drawings, the same will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. .

Claims (5)

A delay time adjusting method of a rake receiver having a plurality of tap delays, the method comprising: checking a level of received signal strength information periodically at a predetermined time; And adjusting the delay time of the rake receiver by selecting any one of the plurality of tap delays according to the magnitude of the checked level of the received signal strength information. The method of claim 1, wherein the adjusting process uses a previous delay as it is if the received signal strength information is above a certain set level, and finds a delay that is above a set level among a plurality of delay positions after the set delay level. To adjust the delay time. A rake receiver of a mobile communication system, comprising: a first finger for receiving an input signal and outputting it without delay; a second and an N-finger for respectively delaying and outputting the input signal with a plurality of delays; A symbol combiner which combines all of the outputs of the fingers and provides the decoding unit; and a signal for adjusting delay times of the plurality of delays when the average intensity of the input signal is periodically detected and below a specific level. And a controller for applying a finger to adjust the delay time. 4. The rake receiver of claim 3, wherein the N-th finger is a third finger. 4. The rake receiver of claim 3, wherein the input signal is a signal sampled eight times per chip.