KR100270578B1 - Method of controlling a call connection in cdma-based mobile system - Google Patents

Abstract

The present invention relates to a call connection control method in a CDMA mobile communication system.

According to the present invention, a waiting queue for handoff is provided for each frequency band, the lowest occupied frequency band is selected according to a new call connection request, and the channel is allocated or disconnected according to the existence of an idle channel. In addition, if the request for the maximum occupied frequency band is not requested according to the handoff call connection request, the soft handoff is executed; if the request for the maximum frequency band is used, the use of the idle queue is checked depending on the existence of an idle channel or the hard hand is performed. If you use the wait queue, compare the size of the hard handoff threshold with the difference in the number of calls in service in the maximum occupied and minimum occupied frequency bands, including handoff calls waiting in the wait queue. Perform a soft handoff or hard handoff.

According to the present invention, traffic occupancy between each frequency band can be allocated in a balanced manner, artificially controlling the incidence of soft handoff and hard handoff, and reducing the truncation rate for an ongoing handoff call.

Description

Call connection control method in code division multiple access mobile communication system

The present invention relates to a call connection control method in a code division multiple access (hereinafter referred to as CDMA) mobile communication system, and in particular, to handoff in a CDMA mobile communication system using a plurality of frequency bands (FA). The present invention relates to a call connection control method for handoff more efficiently using a waiting queue and a hard handoff threshold.

The biggest advantage of using CDMA as a wireless access method is that soft handoff is possible. Soft handoff not only provides excellent call quality without interruption, but also performs better than hard handoff in cell area and link capacity. However, soft handoff is only possible when diversity is made in the same frequency band. That is, soft handoff is possible only when the frequency band used in the existing cell and the frequency band to be allocated from the neighboring cell are the same at the time of handoff of the mobile station. Otherwise, the hard handoff process occurs. Therefore, when a plurality of frequency bands are allocated to a base station to increase capacity, hard handoff may be inevitable to use frequency resources more efficiently.

Currently, CDMA mobile communication systems such as CDMA Mobile System (hereinafter referred to as CMS) or Personal Communication System (hereinafter referred to as PCS) have multiple frequency bands depending on traffic conditions in the region. There is a cell that serves. In such a cell, a control method for requesting connection of a new call or a handoff call takes a method of first allocating a channel of a fixed frequency band determined for each mobile station without assigning a channel considering the balance between frequency bands. In other words, the frequency band that is basically operated when the mobile terminal is manufactured is determined, and a channel allocation of the predetermined frequency band is requested. There is also no function to control the incidence of soft handoff and hard handoff.

When using multiple frequency bands in the CDMA scheme, it is necessary to balance channels in each frequency band for efficient use of resources. However, in the conventional system, since the frequency band is fixedly allocated to the mobile terminal, it cannot be regarded as an efficient use of resources, and there is no function of adjusting the incidence rate of soft handoff and hard handoff.

Accordingly, the present invention provides a call connection control method that can adjust the soft handoff incidence rate and the hard handoff incidence rate in a CDMA mobile communication system, and solves the above problems by giving priority to the handoff call. There is a purpose.

According to an aspect of the present invention, a base station receiving a new call connection request from a mobile station selects a lowest occupied frequency band among service frequency bands, and whether or not an idle channel exists in the selected lowest occupied frequency band. Allocating a traffic channel of the corresponding frequency band or truncating the call; and at a base station receiving a handoff call connection request from the mobile station, the same frequency band as the frequency band being used in the adjacent cell is the maximum occupied frequency in the current cell. Performing a soft handoff if the maximum occupied frequency band is not the maximum occupied frequency band, and checking whether an idle channel exists in the corresponding frequency band if the maximum occupied frequency band is found; If it does not exist, run a hard handoff If there is an idle channel, checking whether to use a standby queue, and if the result of the check does not use the queue, comparing the difference between the number of calls being serviced in the maximum occupied frequency band and the lowest occupied frequency band to the hard handoff threshold. And comparing the difference between the number of calls serviced in the maximum occupied frequency band and the lowest occupied frequency band including the handoff call waiting in the wait queue and the hard handoff threshold when using the waiting result queue. And performing a soft handoff when the hard handoff threshold is large and performing a hard handoff when the hard handoff threshold is small as a result of the two comparisons.

1 is a block diagram of a CDMA mobile communication system to which the present invention is applied.

2 is a diagram illustrating cell arrangement when multiple frequency bands are used in a CDMA mobile communication system to which the present invention is applied.

3 is an exemplary diagram of a forward CDMA channel structure in a CDMA mobile communication system to which the present invention is applied.

4 is a model diagram of traffic generated in one frequency band in a CDMA mobile communication system to which the present invention is applied.

5 is a model diagram of traffic generated in a plurality of frequency bands in a CDMA mobile communication system to which the present invention is applied.

6 is a flowchart illustrating a call connection control method according to the present invention.

<Description of the code | symbol about the principal part of drawing>

100: mobile station 101: base station

102 control station 103 mobile switching center

The present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a CDMA mobile communication system to which the present invention is applied. The CDMA mobile communication system in the present invention means all mobile communication systems based on the CDMA wireless access method, including the CMS and PCS currently being serviced. This configuration diagram is a general configuration diagram of such a CDMA-based mobile communication system.

The mobile station (MS) 100 is a mobile subscriber station and has a wireless connection with the base station 101 and has mobility. A base transceiver system (BTS) 101 performs a wired / wireless connection function between the mobile station 100 and the control station 102, CDMA signal processing, a wireless connection function with the mobile station 100, and the like. The base station controller (BSC) 102 performs mobile call control, handoff control, channel allocation and power control functions for packetized CDMA voice data processing. The Mobile Switching Center (MSC) 103 performs functions such as handoff, paging, roaming, and subscriber authentication based on circuit switching and incoming and outgoing call processing functions between mobile subscribers.

2 is an exemplary cell arrangement according to traffic characteristics when a plurality of frequency bands are used in a CDMA mobile communication system to which the present invention is applied. In a commonly used CDMA mobile communication system, a frequency allocation method allocates only one frequency band (1 FA) to one cell 200, but in a high traffic area such as a city center, a plurality of frequency bands are allocated according to its characteristics. It can also be allocated to accommodate large amounts of traffic. In such a CDMA cell environment, a handoff occurs when a mobile station serving a cell crosses a cell boundary, and smooth handoff support is essential to provide an efficient service in a mobile network.

Handoffs are classified into soft handoffs and hard handoffs according to resource usage relations between their own and adjacent areas, system configurations of adjacent areas, and handoff points. Soft handoff is a method in which a mobile station initiates communication with a new base station between adjacent base stations using the same frequency band without disconnection with the previous base station. Hard handoff, on the other hand, occurs when a mobile station crosses boundaries between base stations using different frequency bands. Soft handoff has the advantages over hard handoff such as improved quality of service, control of mobile station interference, reduction of service disconnection probability, and the like. However, when using multiple frequency bands, providing only soft handoffs without providing hard handoffs results in traffic concentrating on channels in a particular frequency band, resulting in reduced overall resource efficiency. Done.

3 is an exemplary diagram of a forward CDMA channel structure used in a CDMA mobile communication system to which the present invention is applied. In the CDMA-based mobile communication system, the detailed structure of the radio channel of the forward link and the reverse link may be different for each system (for example, CMS, PCS, and IMT-2000), but basically consists of a control channel and a traffic channel. do. In order to illustrate the structure of a general CDMA radio channel, this example shows the structure of a forward CDMA channel of a CMS. The forward CDMA channel 300 for one frequency band (1 FA) includes a pilot and sink channel and a plurality of paging and traffic channels separated by Walsh codes having a bandwidth of 1.23 MHz and having orthogonality. Have.

The pilot channel 301 provides a reference phase as a direct sequence spread spectrum signal continuously transmitted from a base station and is used as a reference for handoff determination. The sink channel 302 is a channel used for time and frame synchronization, and the paging channels 303 and 304 are used for transmitting control information from a base station to a mobile station without a traffic channel being allocated. Traffic channels 305 and 306 are channels used when communicating traffic information from a base station to a mobile station.

As shown, a plurality of traffic channels exist in one frequency band. In order to enable soft handoff when there are multiple frequency bands, traffic channels of the same frequency band as the one currently in use are allocated from a neighboring base station where handoff operation occurs due to movement of the mobile station. Hard handoff occurs with different service frequency bands. The present invention provides a method for balancing soft handoff and hard handoff according to the characteristics of a network in a base station or a control station which allocates a traffic channel when requesting a handoff connection or a new call connection of a mobile station in such a CDMA environment. It is about.

4 is a modeling of the traffic generated in any frequency band serviced by any base station with a queuing system. The queuing system consists of one wait queue 402 and a plurality of servers 403, the number of servers being equal to the number of traffic channels. Where [lambda] 400 is the rate of new calls and [gamma] 401 is the rate of handoff call from adjacent cells. Μ (403) is the sum of the probability of ending an ongoing call and the probability of handing off to an adjacent cell as the termination rate of the call. That is, λ and γ are input parameters of the modeled queuing system, and μ are output parameters. In general, λ and γ can be modeled by the Poisson process, and μ can be modeled by the exponential distribution.

In general, it is necessary to reduce the probability of an in-progress call being disconnected because it can be seen that an in-progress call truncation in the telephone system results in a decrease in the overall quality of service compared to the initiation of a new call. The present invention uses a waiting queue for handoff calls to reduce the probability of truncation of an ongoing call, i.e., a handoff call. The processing scenario is briefly described as follows.

As shown in this model, the handoff call is input through the waiting queue. However, if all servers are in service, the handoff call will wait in the wait queue until an empty server is created. In other words, handoff calls increase the likelihood of call connectivity by immediately queuing the call without cutting the call immediately, even if all traffic channels are occupied and in service to reduce the possibility of truncation. Cut immediately.

5 is a traffic model diagram including hard handoff processing when using a plurality of frequency bands. Here, the incidence rate lambda 500 of the new call, the incidence rate γ 501 of the handoff call, the termination rate mu 503 of the call, and the handoff wait queue 502 are the same as those in FIG. The hard handoff is performed as follows.

For a handoff call requesting a traffic channel allocation of the largest occupied frequency band 505 having the highest traffic channel occupancy rate among a plurality of frequency bands, the number of calls currently being serviced and the number of calls being serviced in the lowest occupied frequency band 506. If the difference is equal to or greater than a certain threshold (hereinafter referred to as a "hard handoff threshold"), the traffic channel of the lowest occupied frequency band is allocated (that is, hard handoff is performed) without allocating a traffic channel of the requested frequency band (504). . This can improve call quality, taking into account the balance between soft handoffs that reduce resource efficiency when using multiple frequency bands and hard handoffs that can cause instantaneous disconnection but increase resource efficiency. Can be run in combination. In addition, if the hard handoff threshold is changed according to the traffic characteristics of the service area, the execution ratio of soft handoff and hard handoff can be adjusted.

6 is a flowchart illustrating a call connection control method according to the present invention. The base station (or control station) that controls the allocation of traffic channels receives a call connection request from the mobile station (600).

When the received call connection request is a new call connection request (601), the lowest occupied frequency band having the lowest service occupancy among the frequency bands being serviced is selected (602). It checks whether there is an idle channel that can be serviced in the selected lowest occupied frequency band (603), disconnects the call if there is no idle channel (604), and allocates a traffic channel of the corresponding frequency band if there is an idle channel. (605).

If the call connection request received from the mobile station is a handoff call connection request (601), since the call is already in progress, it is checked whether the same frequency band as the frequency band already in use in the adjacent cell is the maximum occupied frequency band in the current cell (606). . If the result of the check is not the maximum occupied frequency band, a soft handoff is performed by allocating a traffic channel having the same frequency band as the frequency band in use (607). Otherwise, if it is the maximum occupied frequency band, it is checked whether an idle channel exists in the corresponding frequency band (608). If the idle channel does not exist, the hard handoff is performed to the lowest occupied frequency band (609). If the idle channel exists, it is checked whether the idle queue is used (610). In other words, it checks if it is waiting in the waiting queue.

Until now, only the case of using the wait queue for the handoff call has been described, but if the priority is not given to the handoff call, the wait queue for the handoff call may not be used. Therefore, the present invention considers both cases.

The size of the difference between the number of calls in service in the maximum occupied frequency band (that is, the frequency band already in use) and the number of calls in service in the lowest occupied frequency band and the size of the hard handoff threshold when not using the wait queue for handoff. Is compared (611). As a result of the comparison, if the hard handoff threshold is large, a soft handoff is performed by allocating a traffic channel having the same frequency band as the frequency band already in use (613), and if the hard handoff threshold is small, the hard handoff threshold is hard to the lowest occupied frequency band. Handoff is executed (614).

If you are using a wait queue for handoff, the lowest number, including the number of calls in service in the occupied frequency band (that is, the frequency band already in use) and the handoff calls waiting in the wait queue. The difference between the number of calls in service in the occupied frequency band and the size of the hard handoff threshold is compared (612). As a result of the comparison, if the hard handoff threshold is large, a soft handoff is performed by allocating a traffic channel of the same frequency band as the frequency band already in use (613), and if the hard handoff threshold is small, the hard handoff threshold is hard to the lowest occupied frequency band. Handoff is executed (614).

The method proposed in the present invention may vary depending on the traffic characteristics of each region, but the following operation method may be suggested as a general simulation result.

1. If you do not use the wait queue, the hard handoff threshold directly affects the probability of hard handoff. In this case, it is better to suppress the hard handoff by increasing the threshold.

2. When using the wait queue, the hard handoff threshold affects both the probability of handoff blocking and the probability of hard handoff. Therefore, it is necessary to select an appropriate hard handoff threshold according to the traffic characteristics of each region.

By controlling the call connection using the handoff wait queue and the hard handoff threshold according to the present invention, the rate of occurrence of soft handoff and hard handoff can be adjusted according to the characteristics of the region, and the probability of disconnection of the handoff call can be reduced. The radio resource of the mobile communication system can be utilized more efficiently. In addition, the present invention can be used not only for CMS and PCS but also for all CDMA mobile communication systems such as IMT-2000 in the future.

Claims (3)

Selecting a lowest occupied frequency band of the serviced frequency bands at the base station receiving the new call connection request from the mobile station; Allocating a traffic channel of the corresponding frequency band or truncating the call according to whether an idle channel of the selected lowest occupied frequency band exists; Checking, by the base station receiving the handoff call connection request from the mobile station, whether the same frequency band as the frequency band being used in the neighboring cell is the maximum occupied frequency band in the current cell; Performing soft handoff when the test result is not the maximum occupied frequency band, and checking whether an idle channel exists in the frequency band when the maximum occupied frequency band is obtained; Performing a hard handoff if the idle channel does not exist, and checking whether a standby queue is used if the idle channel exists; Comparing the difference between the number of calls being serviced in the maximum occupied frequency band and the lowest occupied frequency band and the hard handoff threshold when the test result does not use the wait queue; Comparing the difference between the number of calls in service in the maximum occupied frequency band and the lowest occupied frequency band including the handoff call waiting in the wait queue and the hard handoff threshold when the check result is used. In the mobile communication system of the code division multiple access method, the soft handoff is executed when the hard handoff threshold is large, and the hard handoff is executed when the hard handoff threshold is small. Method of controlling call connection. 2. The method of claim 1, wherein the soft handoff is performed by allocating a traffic channel having the same frequency band as the frequency band being used. The method of claim 1, wherein the hard handoff is performed in a lowest occupied frequency band.