KR19990073939A - Optimization of Handoff Processing Delay in Code Division Multiple Access Networks - Google Patents

Abstract

A method of optimizing handoff processing delay time in a code division multiple access (CDMA) network is disclosed. The method includes a first step of selecting a section for measuring a handoff processing delay time; A second process of optimizing a propagation environment of a set section; A third step of analyzing logging data of the mobile terminal in a traffic state; And a fourth process of calculating a handoff processing delay time for the handoff processing period.

Description

Optimization of Handoff Processing Delay in Code Division Multiple Access Networks

The present invention relates to a method for optimizing a handoff processing delay time in a code division multiple access (CDMA) network, and in particular, a mobile terminal performs a pilot strength measurement message (PSMM). The present invention relates to a method for minimizing the time until the base station sends a handoff complete message (HCM) to the mobile terminal and verifying the process.

According to IS-95, an international standardization organization, a typical mobile communication system using Code Division Multiple Access (CDMA) technology includes a mobile station (MS) provided with a service and a base station transceiver that provides a service. Subsystem: BTS).

Currently, a CDMA system operating in Korea includes a base station controller (BSC) for controlling the base station, a base station manager system (BSM) for operating and managing various base station controllers, in addition to a mobile terminal and a base station. A mobile switching center (MSC) for connecting a base station to a public switched telephone network (PSTN), and a home location register (HLR) for managing a service state of a mobile terminal connected to the switching center system. .

1 is a block diagram of a conventional code division multiple access system. The base station (BTS) 6 is connected to an existing Public Switched Telephone Network (PSTN) 2. The mobile terminal in each cell forms a radio channel with the base station serving the cell and performs communication. In this case, a channel formed in the direction of the mobile station from the base station is called a forward channel, and a channel formed in the direction of the base station from the mobile station is called a reverse channel.

The mobile station and the base station transmit and receive voice information and data by using a traffic channel, and pilot, synchronous, and paging channels except for the traffic channel are transmitted and received. It is called an additional channel, ie an overhead channel. Each base station and mobile terminal determines whether it should receive the data through pilot or paging (or code) transmitted on additional channels.

Each base station is assigned several frequencies according to system capacity and uses as many frequency channels. Each frequency channel is called frequency assignment (FA). CDMA systems can include multiple access channels by varying frequency offset and sequence per frequency channel.

The main processor of the base station controller system is referred to as a call control processor (hereinafter referred to as CCP), and the main processor of the base station system is referred to as a base station transmitter control processor (hereinafter referred to as BCP). It is called.

Wireless telephony (mobile stations) aim to ensure that there are no obstacles to communication when traveling in different areas. Therefore, when the mobile station is in an idle state, it must be regularly re-registered with the system according to various parameters. When the call is in operation, the mobile station and the base station and the switching station manage communications between the base station and the mobile station to maintain good radio link efficiency.

In CDMA technology, one system can simultaneously receive mobile transmissions from two or more base stations. One terminal may simultaneously receive signals transmitted from two or more base stations. Having such a function, it is possible to handle handoffs from one base station to another, or from one antenna area to another within one base station.

The handoff here refers to a process in which a mobile station moves from one base station to a new base station or within one base station to a new antenna allowance area, i.e., to a new traffic channel. It is very important to ensure that the success of the moving call and the quality of the voice information are not degraded during the handoff.

Various types of handoffs have been provided to ensure call continuity in CDMA cellular and PCS systems. Depending on the method and implementation, the handoff may have a difference in efficiency in terms of reliability of call continuity and system load. The setting of the channel by the handoff is called ADD, and the release of the channel by the handoff is called DROP.

There are two major handoff methods: soft handoff and hard handoff. Soft handoff is a method of making a call before making a call, and hard handoff is a method of cutting an arc before creating a new call. -before-make) method. When handoff is required due to the movement of a mobile station, the CDMA system preferentially handles soft handoff. However, if it is inevitable, hard handoff ensures call continuity.

In general, the handoff process time delay is a time from when the mobile terminal uploads a pilot strength measurement message (PSMM) to the base station until the base station sends a handoff completion message (HCM) to the mobile terminal. Say

In order to maintain the best service quality, this handoff processing delay time should be minimized. Therefore, the handoff processing delay time is measured, and the measured delay time is set to satisfy the specified range. The method for measuring the handoff processing delay time according to the prior art is as follows.

First, about 10 base stations are configured in one cluster. Select a test route in which a two-way or three-way handoff occurs within the cluster. Connect service option 2 or service option 3 to the Mobile Diagnostic Moniter (MDM). The test is performed by moving the mobile diagnostic device with respect to the set path. Message parsing measures handoff processing latency and checks whether the measured time is within a specified range. However, in the case of using the prior art method performed as described above, in most cases, the handoff processing delay time is generally exceeded.

This is because the system is operated mainly on the success of the handoff rather than the reduction of the processing delay time of the handoff in the conventional system. In general, the handoff processing delay time should not exceed 200 ms in order not to affect the service of the subscriber. However, when the handoff process by the prior art as described above was often exceeded the range.

Therefore, in order to solve the problems described above, the present invention clarifies the definition of the handoff processing delay time and minimizes the handoff processing delay time in the system, thereby improving the performance of the network. An object of the present invention is to provide a method for optimizing handoff processing delay time.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention and the accompanying drawings.

1 is a block diagram of a conventional code division multiple access system.

2 is a message flow diagram generated upon the occurrence of a handoff.

3 is an exemplary diagram illustrating a process of measuring handoff processing time;

<Explanation of symbols for the main parts of the drawings>

1: Mobile switching center (MSC)

2: public switched telephone network (PSTN)

3: Home Location Registration System (HLR)

4: Voice Mailbox System (VMS)

5: base station controller (BSC)

6: base station (BTS)

7: mobile terminal (MS)

One preferred embodiment of the present invention devised to achieve the object as described above,

Selecting a section for measuring a handoff processing delay time;

Optimizing a propagation environment of a set section;

Analyzing logging data of the mobile terminal in a traffic state; And

Computing the handoff processing delay time for the handoff processing interval.

In one embodiment of the present invention, the selection process, it is preferable to select a route (Route) in which a handoff in two or three directions can occur as a measurement section,

The handoff is preferably caused by soft handoff or softer handoff,

Preferably, the selecting process includes selecting a path having the smallest cell radius for the selected section.

Preferably, the selection process includes checking a system parameter with respect to the selected section.

The system parameter checking step

Checking handoff related parameters, checking for serving in neighboring base station list and missing destination cell, and

Preferably, the step of checking the status of the target base station,

In the optimization process, it is preferable to perform an idle handoff for the selected section to adjust the transmission attenuation value of the base station and the direction and inclination of the antenna so that the corresponding service area is out of the shadow area.

The analysis process,

The mobile terminal posting a pilot strength measurement message and recognizing the system;

The system receiving and processing a pilot strength measurement message and sending down a handoff indication message; And

Preferably, the system sends a handoff indication message and the mobile terminal responds with a handoff complete message;

In the calculating process, it is preferable to calculate the time from the mobile terminal to recognize the pilot signal higher than the threshold and send a handoff strength measurement message until the system sends the handoff instruction message as the handoff processing delay time.

The present invention selects a section in which the air delay is minimized in selecting a path required for the measurement of the handoff processing delay time, and the processing delay time section in the message is the pure processing time (PSMM ~ HDM) of the system. It is done.

In order to optimize the handoff processing delay time according to the present invention, the following items are considered.

First, perform preliminary work to test the handoff processing delay time.

Second, optimize the propagation environment.

Third, the logging data of the mobile terminal is analyzed in the traffic state.

Fourth, the message interval of the handoff processing delay time is selected.

Hereinafter, the operation of the present invention will be described in detail.

First, perform preliminary work to test the handoff processing delay time.

First, a handoff generation path capable of detecting two pilot signals or three pilot signals is selected. For this task, a path in which soft handoff, an intra-frequency handoff, or softer handoff, an inter-sector handoff, can occur in two or three directions is selected. The path with the smallest cell radius is selected from the selected paths.

Check the following system parameters. To do this, check the handoff related parameters. The handoff related parameters include T_ADD, which is a threshold power strength to which a call is added, T_DROP, and T_TDROP, which are threshold power strengths to which a call is dropped. Check whether the serving of the neighbor base station list and the destination cell is missing. Then, the state of the target base station is checked through the base station management system (BSM).

Second, optimize the propagation environment. At this time, the criteria of the shadow area for the coverage area is as follows. In the forward service area, the Ec / Io of the mobile terminal is -14 dBm or less, and the received power of the mobile terminal is -95 dBm or less in the outskirts of the service area and -91 dBm or less in the city center. In the reverse service area, the transmission power of the mobile terminal is more than +10 dBm. If it belongs to the reference shaded region as described above, the transmission attenuation value Tx_Atten of the base station and the direction and tilt of the antenna are adjusted to deviate from the shaded region. Through the above operation, the propagation environment is optimized.

Third, the mobile terminal logging data in the traffic state is analyzed. Idle Handoff is performed on the set section to log data. Logging of data uses a mobile diagnostic device (MDM).

2 illustrates a message flow diagram generated when a handoff occurs. First, when the strength of the pilot included in the neighboring base station list among the pilot offset list owned by the mobile station exceeds T_ADD, the mobile station transmits and receives a transceiver selection bank of the base station controller through a current traffic channel element (TCE). Transmitter and Selector Bank (TSB) sends a pilot strength measurement message (PSMM).

The transceiver selection bank compares whether the pilot received as a candidate corresponds with each sector pilot offset of the base station currently in use. If there is a match, it is determined as soft handoff. If it is not matched, it is judged as softer handoff. The decision result is sent as a handoff request message to the call control processor (CCP) of the base station controller.

The call control processor refers to a database of which the mobile terminal has a handoff mode (ho_mode) assigned to a soft handoff (HM_SOFT) to a base station control processor (BCP) of a destination base station (Destination BTS). Send a handoff request message.

The base station control processor of the target base station determines the appropriate traffic channel element by considering the frequency, frame offset, and availability of the traffic channel element suitable for the required handoff. The handoff assignment message is then sent to the call control processor in response.

The call control processor sends a handoff assignment message to the transceiver selector bank to inform it of power control information and information to communicate with the newly allocated traffic channel element.

The transceiver selection bank requests related information from the call control processor in a Call Config Request Message when additional information is needed depending on the situation.

The call control processor receiving the call setup request message provides the information requested by the transceiver selection bank through the call setup message.

The transceiver selection bank simultaneously sends a handoff indication message to the original base station and the destination base station through the traffic channel elements of the original base station (Original BTS) and the destination base station (Destination BTS).

The mobile terminal receives the handoff indication message through the original base station where the channel is established, and recognizes the handoff procedure. The mobile terminal then forwards the handoff complete message to the transceiver selection bank through the traffic channel elements of the original base station and the target base station.

In the handoff procedure performed as described above, the handoff processing delay time may be largely divided into several steps. First, the time until the mobile station receives the pilot strength measurement message to the base station receives the signal. This is related to the delay on the radio path. And internal system processing time from receiving the pilot strength measurement message to sending down the handoff indication message. This is the pure processing time of the system and there is no way to reduce the delay time internally. Finally, it is the time until the mobile station responds with the handoff completion message after sending down the handoff indication message from the base station. This is equal to the value of the delay value on the radio path added to the processing time of the mobile terminal.

As noted above, the delay on the radio path can be an important factor in determining handoff processing delay time. Therefore, in order to minimize the delay on the radio path, it is very important to select the handoff interval having the smallest cell radius.

3 is an exemplary view illustrating a process of measuring handoff processing time. As shown, the processing time of each message measured in the common air interface (CAI) environment of the reverse and forward traffic channels (TC) is shown. The time when the base station receives the pilot strength measurement message (PSMM) is 05: 53: 35.805, and the time when the mobile terminal receives the handoff indication message (HDM) is 05: 53: 36.993. Therefore, the time from the pilot strength measurement message PSMM to the handoff indication message HDM is 188 ms. Also, after the mobile terminal receives the handoff indication message (HDM) and processes the handoff, the time when the mobile station sends the handoff completion message (HCM) to the base station is 05: 53: 36.045. Therefore, the time from the handoff indication message (HDM) to the handoff completion message (HCM) is 52 ms. Therefore, the total processing delay time for handoff processing is 240ms.

As a last item to be considered in the optimization method of the handoff processing delay time according to the present invention, a section of the handoff processing delay time is selected. As can be seen from the example of FIG. 3, the time from the pilot strength measurement message to the handoff completion message is generally more than 200 ms.

Therefore, it is better to view the range of the handoff processing delay time as the time from the pilot strength measurement message of the mobile terminal to the handoff indication message, that is, the pure processing time of the system. This is because the time from the handoff indication message to the handoff completion message is due to the delay on the radio path from the base station to the mobile terminal and the delay time of the mobile terminal.

The present invention can be variously modified and can take various forms and only the specific embodiments thereof are described in the detailed description of the invention. It is to be understood, however, that the present invention is not limited to the specific forms mentioned in the detailed description of the invention, but rather includes all modifications, equivalents, and substitutions within the spirit and scope of the invention as defined by the appended claims. It should be understood to do.

According to the present invention operating as described above, the handoff processing delay time is optimized, and the handoff processing delay time is determined by the system after the mobile terminal recognizes a pilot signal higher than a threshold and sends a handoff strength measurement message. By defining the time to send a message, a faster handoff can be achieved, which facilitates access to a threshold of handoff processing delay time.

Claims (9)

Selecting a section for measuring a handoff processing delay time; Optimizing a propagation environment of a set section; Analyzing logging data of the mobile terminal in a traffic state; And A method for optimizing handoff processing delay time in a code division multiple access system comprising calculating a handoff processing delay time for a handoff processing interval. 2. The method of claim 1, wherein the selecting process selects a route in which two or three handoffs can occur as a measurement section. 3. 3. The method of claim 2, wherein the handoff is a soft handoff or softer handoff. The method of claim 1, wherein the selecting comprises selecting a path having the smallest cell radius for the selected section. The method of claim 1, wherein the selecting comprises checking a system parameter for the selected section. The method of claim 5, wherein the checking of the system parameters Identifying handoff related parameters; Checking whether the serving of the neighbor base station list and the destination cell are missing; And A method for optimizing handoff processing delay time in a code division multiple access system, comprising the step of checking the status of a target base station. The code division multiple access of claim 1, wherein the optimization process performs idle handoff for a selected section to adjust transmission attenuation of the base station and direction and inclination of the antenna so that the corresponding service area is out of the shadow area. How to optimize handoff processing latency in the system. The method of claim 1, wherein the analyzing process, The mobile terminal posting a pilot strength measurement message and recognizing the system; The system receiving and processing a pilot strength measurement message and sending down a handoff indication message; And And the system responds with a handoff complete message by sending a handoff indication message. The method of claim 1, wherein the calculating process comprises: calculating a time for handoff processing delay time after the mobile terminal recognizes a pilot signal above a threshold and sends a handoff strength measurement message to the system to send a handoff instruction message. A method of optimizing handoff processing delay time in a code division multiple access system.