KR20020076501A - Method of handoff using NAK rate - Google Patents

Abstract

PURPOSE: A handoff method using NAK(Not Acknowledgement) rates is provided to decide a handoff time of an SCH(Supplemental Channel) by an NAK rate requesting a retransmission of a transmission signal to a base station from a mobile station, thereby improving transmitting/receiving ratios of data. CONSTITUTION: A BSC(Base Station Controller) initializes parameter values necessary for an NAK_Rate(701). The BSC updates the NAK-Rate according to a frame type transceived between a mobile station and a base station(702,703). The BSC decides whether an active pilot is more than 1, and compares whether the NAK-Rate is bigger than an NAK_Threshold value. If so, the BSC decides an SCH handoff to proceed a next order(704,705). The base station transmits a pilot measurement request order message to the mobile station(706). The mobile station requests a pilot strength measurement message necessary for handoff decision to the base station(707). An SCH assign request message is transmitted to a CCP of the BSC with the strength measurement message(708). The CCP analyzes the received pilot strength measurement message, and transmits an SCH assign message to an HSVC of the BSC(709). The HSVC transmits an extended supplemental channel assign message to the mobile station by inserting a PN code, to complete a handoff procedure(710).

Description

Method of handoff using NAK rate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handoff control method in a mobile communication system. In particular, the present invention relates to a handoff control method. The present invention relates to a handoff method using a Not Acknowledgment (NAK) ratio for improving a transmission / reception ratio of data due to handoff by determining a handoff time of a supplemental channel.

More specifically, the present invention is to determine how much the amount of NAK sent to the base station by the mobile station in the handoff of the mobile communication system by comparing with a reference value, the parameter of the signal (NAK) requesting the retransmission of the received signal Initialize these data to transmit and receive data between the mobile station and the base station. In addition, NAK rate is calculated by adding or subtracting the NAK rate requesting retransmission according to the type of frames transmitted and received between the mobile station and the base station, and the weight value defined in the NAK Weight Table for the frame type transmitted to the mobile station. Update the value, determine whether the updated NAK rate is greater than the NAK reference value, and transmit and receive information for measuring the pilot strength between the mobile station and the base station, and the base station analyzes the transmitted and received information, and the mobile station analyzes the PN to identify each base station. A coded Extended Supplemental Channel Assign Message is sent to the mobile station to perform a handoff process for high speed data transmission and reception.

Hereinafter, a general description of the general handoff mentioned in the present invention.

1) Softer Handoff

It is a handoff that occurs when moving between sectors within the same base station service area. When a mobile station moves from the current sector to a new sector, the method keeps the call in the new sector without interruption of the call.

In this case, a sector is an area obtained by dividing a service area into smaller ones and is generally divided into alpha, beta, and gamma.

2) Soft Handoff

It is a handoff that occurs when moving between adjacent base stations using the same frequency.

When a mobile station in a call moves from one service area to another adjacent service area, the mobile station maintains the call in the new service area without interruption.

3) Hard Handoff

This is a handoff that occurs when moving between base stations using different frequencies or when moving between base stations belonging to different switching stations.

In a hard handoff, a call is sometimes disconnected because the mobile station and the call line are momentarily disconnected and a call channel is allocated in a new service area.

A general handoff procedure will be described with reference to the drawings.

1 is a view illustrating a soft handoff method, and a call of low speed (IS95A) and medium speed (IS95B) data using a fundamental channel (FCH) and a supplemental code channel (SCCH). In case of handoff, soft handoff and softer handoff are completed by connecting FCH and SCCH of target base station before disconnecting FCH and SCCH of serving base station. As a result, handoff is performed in a soft manner in which FCH and SCCH are passed.

FIG. 2 illustrates hard handoff. In case of a high speed (IS95C) data call using an FCH and a supplemental channel (SCH), a call resource occupancy is much higher than that of a low speed IS95A and a medium speed IS95B. As a result, 17 call resources are used for the 144Kbps service. However, if the handoff is performed in a soft manner, 34 resources are occupied for handoff between two base stations, and 51 call resources are occupied for handoff between three base stations. impossible. Therefore, the handoff is performed in a hard manner by disconnecting the serving base station SCH and attaching the target base station SCH.

Hereinafter, a conventional handoff will be described referring to an example.

3 illustrates a schematic configuration of a mobile communication system for explaining a conventional soft handoff between two base stations in a reverse link, and includes a base station controller (MSC / or Radio Network) including a selector 101a. Controller (RNC) 101 and mobile station 102 and base stations 103 and 104 of cells A and B are shown.

As shown in FIG. 3, the transmission signal of the mobile station 102 on the reverse link is simultaneously received by two base stations, namely, the current base station 103 of cell A and the target base station 104 of cell B. The two base stations 103 and 104 each demodulate the received signal from the mobile station 102 and send the demodulated frame to the base station controller (MSC or RNC) 101, and the base station controller 101 based on the received frame. The best frame among the three frames is selected by the selector 101a.

On the other hand, in soft handoff, when the mobile station 102 moves between different sectors in the same cell, the handoff is performed by the same operation as the soft handoff described above, and two signals received from the mobile station are demodulated in the cell. And only one frame is transmitted to the base station controller 101.

4 is a flowchart showing a conventional handoff operation (IS-95), in which the mobile station 102 moves from the current base station 103 of cell A to the target base station B 104 of cell B in FIG. The handoff control procedure is shown.

When the mobile station enters the handoff area (step 201), the mobile station 102, which is only served by the current base station 103 of cell A, is actually talking to pilot A only. At this time, the mobile station 102 measures the signal strength (Ec / IO) of the pilot B, checks whether the value exceeds the pilot reference value, sends a pilot strength measurement message, and puts the pilot B on the handoff candidate list. That is, the mobile station 102 measures the strength of the pilot of the current base station (cell A) 103 and the target base station (cell B) 104 (step 202), and measures the measured target base station (cell B) 104. It is determined whether the pilot strength is sufficient (a predetermined reference value is exceeded) (step 203).

As a result of the determination in this step, if the measured pilot strength of the target base station (cell B) 104 is not sufficient, the pilot strengths of the current base station (cell A) 103 and the target base station (cell B) 104 are measured and the target is measured. The process of determining whether the pilot strength of the base station (Cell B) 104 is sufficient is repeated.

As a result of the determination, if the pilot strength of the target base station (cell B) 104 is sufficient, a handoff instruction message is received from the current base station (cell A) 103 to perform the current handoff process (steps 204 and 205). .

That is, mobile station 102 receives a handoff indication message from cell A's current base station 103, which causes mobile station 102 to start talking to cell B's target base station 104 over a new traffic channel. In addition, the message also includes a PN offset of the cell B and a newly assigned Walsh code. Accordingly, mobile station 102 puts pilot B on the candidate's actual call list and sends a handoff complete message after acquiring synchronization of the forward traffic channel specified in the handoff indication message. Therefore, from this point on, the pilot currently talking to the mobile station 102 becomes two signals: the base station (cell A) 103 and the target base station (cell B) 104.

In a next step 206 the mobile station 102 measures the strength of the pilot A of the current base station (cell A) 103 and determines whether this measured value is sufficient (step 207). That is, the mobile station 102 detects whether the pilot A falls below the reference value of pilot eviction, at which time the mobile station 102 immediately starts to measure the time (handoff eviction timer). The mobile station 102 sends a pilot strength measurement message when the measured time reaches the handoff eviction timer limit, and the mobile station 102 receives a handoff indication from the base station (step 208).

The handoff indication message received by the mobile station 102 only includes the PN offset of the target base station (cell B) 104, and the offset of the current base station (cell A) 103 is not included in this message. The mobile station 102 terminates the handoff process by sending the handoff end message, excluding pilot A from the actual call list (step 209).

However, conventional handoff schemes and other handoff schemes as described above

Not only is the operation implementation method complicated, but it does not provide an appropriate solution for when to change the SCH to be implemented in the present invention.

Accordingly, the present invention proposes an algorithm for finding a time point for switching the SCH of the serving base station and the target base station at the time of performing the handoff of the mobile communication system, and transmits the signal from the mobile station to the base station in the high speed data call transmitted from the base station to the base station. The handoff point of a supplemental channel (SCH) is determined by a NAK rate, which is a signal for requesting retransmission.

1 is a diagram for explaining a soft handoff method.

2 is a diagram for explaining a hard handoff.

3 is a diagram illustrating a schematic configuration of a mobile communication system for explaining handoff between two base stations;

4 is a flowchart illustrating a conventional handoff method.

5 illustrates an algorithm data structure for performing handoff using the NAK ratio of the present invention.

6 is a NAK Weight Table

7 is a flowchart for transmitting and receiving related information between a mobile station and a base station for handoff using NAK information of the present invention.

A handoff method in a mobile communication system of the present invention comprises the steps of: initializing parameters of a signal NAK requesting retransmission of a received signal; Updating a NAK rate (degree) requesting retransmission according to the type of frames transmitted and received between the mobile station and the base station; Determining whether the updated NAK rate is greater than a NAK reference value, and transmitting and receiving information for measuring pilot strength between a mobile station and a base station; And using the pilot strength size message to transmit a supplemental channel (SCH) allocation message to a block (HSVC) that generates a traffic frame and processes a signal message for the traffic channel.

In addition, in the present invention, the data structure for performing each step comprises a NAK ratio database for managing the ratio of the signal (NAK) requesting the retransmission of the received signal; A NAK rate update block for updating a NAK rate according to a predetermined value of the NAK rate management database; A handoff decision block for determining a handoff using the NAK rate value; And a call message control block for controlling transmission and reception of information between the mobile station and the base station according to the handoff decision.

In the present invention, the HSVC further comprises the step of transmitting a supplementary channel assignment message extended by the mobile station by inserting a PN code for identifying each base station to the mobile station.

In addition, in the step of updating the NAK rate of the present invention, the positive weight indicates that the state of the wireless section is not good by increasing the NAK rate, and the negative weight indicates that the state of the wireless section is good by lowering the NAK rate. It is done.

In addition, the handoff decision using the NAK rate value of the present invention is characterized in that the supplementary channel (SCH) handoff for the high-speed data call.

Other objects and features of the present invention will become apparent from the detailed description of the embodiments with reference to the accompanying drawings.

Hereinafter, a procedure of handoff control according to the present invention will be described with reference to the accompanying drawings.

5 is a diagram illustrating an algorithm data structure for performing a handoff using the NAK ratio of the present invention, wherein the algorithm is operated in HSVC, which is a software block for controlling hardware in a base station controller (BSC).

As shown in the figure, the algorithm comprises: a NAK Rate Database (NAK Rate DB) for managing the rate (degree) of the signal (NAK) requesting retransmission of the received signal; A NAK Rate Update Block (NAK Rate Update Block) for updating the NAK rate every 20 ms according to a predetermined value of the NAK Rate Management Database; A handoff decision block for determining SCH handoff according to the NAK rate value and the handoff situation; According to the handoff decision, a call message control block is configured to control message processing for transmitting and receiving with a mobile station and a higher processor in the base station, CCP.

The NAK Rate DB is composed of NAK_Rate, NAK_Threashold and NAK Weight Table.

In addition, the NAK Weight Table is used to determine whether to handoff by increasing or decreasing NAK_Rate according to a retransmission request signal NAK of data transmitted and received as shown in FIG. 6.

More specifically, the NAK Weight Table of FIG. 6 is a table in which a value added to the NAK Rate is determined according to the type of traffic frames currently being transmitted / received, and the positive weight increases the NAK rate. The Negative Weight indicates that the wireless section is in good condition by lowering the NAK ratio. The Negative Weight is used to update the NAK Rate based on the above state, and to determine the handoff by comparing the updated value with the NAK reference value.

7 is a flowchart for transmitting and receiving related information between a mobile station and a base station for handoff using the NAK information of the present invention.

First, a general description relating to handoff by the NAK amount of the present invention will be described.

As the mobile station moves from the serving base station to the target base station in the handoff process, the wireless environment with the existing serving base station gradually worsens and the wireless environment between the target base stations gradually improves on the mobile station side.

Therefore, when the SCH (Supplementary Channel) is moved from the serving base station to the target base station at an appropriate time according to the state of the wireless environment, the data transmission rate can not be significantly degraded and handoff can be made.

As described above, in the algorithm of the present invention, the NAK amount (retransmission request) is used as an indicator of the quality of the wireless environment for determining the handoff, and when the NAK rate is higher than or equal to a certain level, it is used for high-speed data transmission. Channel) to perform a handoff.

As described above, NAK is a type of RLP (Radio Link Protocol) frame requesting to resend a frame that was not normally transmitted.

Hereinafter, the control procedure of the flowchart of FIG. 7 will be described.

Parameter values required for the NAK_Rate (ratio) calculation, which is a handoff index of the present invention, are initialized. (Step 701).

That is, NAK_Rate in FIG. 5 is set to 0, and the NAK Threshold value and the NAK Weight Table value in FIG. 6 are initialized.

After step 701, NAK_Rate is updated according to the frame type transmitted and received between the mobile station and the base station in a 20 ms period. (Step 702,703).

That is, the weight value defined in the NAK_Weight Table of FIG. 6 is increased or decreased to NAK_Rate according to the frame type transmitted to the mobile station.

In addition, the weight value defined in the NAK_Weight Table of FIG. 6 is increased or decreased to NAK_Rate for the frame type received from the mobile station.

After determining in step 702,703 and whether the active pilot is 1 or more, and comparing NAK_Rate is greater than the NAK_Threashold value, if it is large, it is determined that the situation of the current radio section is not suitable for the data call to determine the SCH handoff. Proceed with the procedure. (Step 704,705).

The base station transmits a pilot measurement request order message to the mobile station. (Step 706)

In response, the mobile station requests a pilot strength measurement message from the base station for handoff determination. (Step 707).

In step 707, when the base station receives a pilot strength measurement message from the mobile station, the base station controller (BSC) in the base station controller (BSC) in the base station to request a SCH allocation request with the strength measurement message Send an Assign Request Message. (Step 708).

Receiving an SCH allocation request message together with the strength measurement message, the CCP analyzes a pilot strength measurement message, selects a pilot having a higher intensity, and sends the SCH allocation message to the HSVC in the BSC. send. (Step 709).

In the HSVC, the mobile station inserts a PN code for identifying each base station and transmits an extended supplemental channel assign message to the mobile station to complete the handoff (step 710).

As described above, the handoff in the present invention is to determine how much the amount of NAK sent by the mobile station to the base station is compared with a reference value, and initializes the parameters of the signal (NAK) requesting retransmission of the received signal to initialize the mobile station and the base station. Send and receive data between In addition, NAK rate is calculated by adding or subtracting the NAK rate requesting retransmission according to the type of frames transmitted and received between the mobile station and the base station, and the weight value defined in the NAK Weight Table for the frame type transmitted to the mobile station. Update the value, determine whether the updated NAK rate is greater than the NAK reference value, and transmit and receive information for measuring the pilot strength between the mobile station and the base station, and the base station analyzes the transmitted and received information, and the mobile station analyzes the PN to identify each base station. A coded Extended Supplemental Channel Assign Message is sent to the mobile station to perform a handoff process for fast data transmission and reception.

Although the preferred embodiment of the present invention has been described above, the present invention may use various changes, modifications, and equivalents. It is clear that the present invention can be applied in the same manner by appropriately modifying the above embodiments.

Accordingly, the above description does not limit the scope of the invention as defined by the limitations of the following claims.

The present invention uses the ratio of the NAK signal in the handoff method of the mobile communication system, and the occurrence of many NAKs indicates that the quality of the wireless environment is rapidly deteriorated. Therefore, by determining the SCH handoff using the NAK rate, the data rate can be maintained at the maximum by receiving data transmission from a better base station in response to the quality of the wireless environment.

Claims (6)

In the handoff of the mobile communication system, Transmitting, by the receiver, a NAK signal requesting retransmission of the received signal; Comparing the transmitted NAK signal with a NAK reference value already set in the transmitter; Determining whether to handoff based on the comparison result; And controlling the call after performing the handoff. In the handoff of the mobile communication system, Initializing parameters of a signal NAK requesting retransmission of the received signal; Updating a NAK rate (degree) requesting retransmission according to the type of frames transmitted and received between the mobile station and the base station; Determining whether the updated NAK rate is greater than a NAK reference value, and transmitting and receiving information for measuring pilot strength between a mobile station and a base station; Using the pilot strength size message, the supplementary channel (SCH) allocation message is generated using a NAK ratio, comprising generating a traffic frame and transmitting a signal message for the traffic channel (HSVC) block. Handoff method. 3. The data structure of claim 1 or 2, further comprising: a NAK ratio database for managing a ratio of signals NAK requiring retransmission of received signals; A NAK rate update block for updating a NAK rate according to a predetermined value of the NAK rate management database; A handoff decision block for determining a handoff using the NAK rate value; And a call message control block for controlling transmission and reception of information between a mobile station and a base station according to the handoff decision. 3. The handoff method according to claim 2, wherein the HSVC further includes the mobile station transmitting an extended supplemental channel assignment message to the mobile station by inserting a PN code for identifying each base station. 3. The method of claim 2, wherein in the updating of the NAK rate, the positive weight indicates that the radio section is not in good condition by increasing the NAK rate, and the negative weight indicates that the radio section is in good condition by lowering the NAK rate. Handoff method using the NAK ratio, characterized in that. 3. The method of claim 2, wherein performing the handoff using the NAK rate value is a supplemental channel (SCH) handoff for a high speed data call.