KR100254804B1 - Method for controlling call admission and call handoff in cdma cellular systems - Google Patents

Abstract

PURPOSE: A CDMA call admission and handoff method considering a forward power consumption is provided to make the admission of a call, accessing around a base station consuming large power, processed by a base station having enough power by varying and operating a forward power reference value according to the current traffic of a base station in a CDMA cellular system. CONSTITUTION: An MSC(Mobile Switching System) judges power consumption for each base station(200). If a base station i is dense, the MSC sets up a new reference value T_ADM_i = adm_d (202). If the base station i is sparse, the MSC sets up a new reference value T_ADM_i = adm_s (204). In other cases, the MSC sets up a new reference value T_ADM_i = adm_o (206). The MSC detects the pilot strength of the base station from a mobile station(208). The MSC defines Q_i = (Ec/Io)_i - T_ADD_i as a new reference value(Q_i) to indicate the pilot strength of a base station measured at a mobile station(210). The MSC judges whether the largest Q_i value among the calculated Q_i values has a negative value(212). If the largest Q_i value has a negative value, the MSC blocks a new call(214). In case that the largest Q_i value is not a negative value, the MSC connects a new call to the base station of the largest Q_i value(214).

Description

Method for controlling call admission and call handoff in CDMA cellular systems

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system of a code division multiple access method (hereinafter, referred to as CDMA). In particular, the present invention relates not only to a reverse link (from a mobile station to a base station) but also to a forward link (from a base station to a mobile station). Call) Accept and handoff to distribute the load of the power-intensive base station, i.e., by connecting the call that occurred near the base station to the base station with enough power remaining, it can handle more calls and The present invention relates to a method of rock-locking and handoff of a code division multiple access method in consideration of a forward power consumption to reduce the burden.

In general, reverse link power control is considered to overcome the battery capacity limit of a mobile station that a user carries as the most important operating factor affecting the system capacity of a CDMA cellular system, while power control of the forward link is also considered. It is being tested as an important factor in system capacity.

Meanwhile, in the CDMA cellular system, sufficient power for communication in power control of the forward link should be supplied to each user. On the other hand, the transmission power to the user should be minimized for the following reasons.

First, because all users of a CDMA cellular system share the same frequency spectrum, the carrier signal to the user also interferes with all other users.

Therefore, if we increase the power of the forward link traffic from one cell to one user, then another user also needs to increase the power to overcome the increased interference.

Second, because the total traffic power capacity in one cell is limited to maintain adequate cell area, increasing forward traffic power to one user reduces power resources for another user, which in turn reduces system capacity.

On the other hand, two important factors indicating the quality of service in a wireless communication network are Call Blocking Probability and Call Dropping Probability.

When the forward link power resources are exhausted at the base station, a call block occurs that makes the access inaccessible when a new call accesses the wireless network, and an ongoing call requiring forward power is incremented at the base station or when all the active calls are handed off. Call truncation occurs, which is lost and loses communication.

On the other hand, conventionally, the lake lock was determined in consideration of only the reverse link. That is, in the existing new call acceptance defined in IS-95, the base station with the strongest pilot strength received by the mobile station of the new call becomes the base station in charge of the new call if the strength of the pilot is larger than a predetermined reference value.

In addition, in the soft handoff method defined in IS-95, if the strength of a pilot of a base station measured by a mobile station exceeds a predetermined reference value, the pilot is included in a candidate set for handoff of the mobile station. If the strength of the pilot is greater than a predetermined threshold above the minimum intensity pilot in the current active set (the pilot set of the base station sending forward traffic power to the actual mobile station), it is included as an active set.

However, as described above, if only the reverse direction is considered and the forward direction is not considered at the same time, the acceptance of a new call by this has a problem that adversely affects the forward link and thus, many calls may be blocked or disconnected.

An important limiting factor of the forward link of a CDMA system is the limited power that a base station can send in the forward direction, and if the mobile station needs to increase the power to improve sound quality, it will hang up if it cannot send the required power. . Therefore, by connecting a call generated near a base station that uses a lot of power to a base station with a sufficient amount of power remaining in the vicinity, it has been sought to relieve the burden on the base station that processes a lot of calls.

It is an object of the present invention to operate a mobile station by varying a reference value that requires the forward power of a base station according to the base station's current call volume in a CDMA cellular system, thereby providing sufficient power remaining to accept a call accessed near a base station that is using a lot of power. Forward power consumption that allows the base station to handle and connects calls made near the base stations with high power consumption to base stations with sufficient remaining power to distribute the call processing burden of the base station to minimize call blocking and call disconnection. It is to provide a rock lock and a handoff method of the code division multiple access method in consideration of the following.

According to the present invention, a method of accepting a new call in a CDMA cellular system is a method of accepting a new call in a CDMA cellular system, comprising: setting an adjustment value for each base station that is proportional to the currently used forward traffic power of the base station; Detecting a signal strength of the pilot channel, subtracting a set adjustment value from the detected signal strength corresponding to each base station, and calculating a subtraction value; if the largest subtraction value is negative, the new call is blocked and the largest subtraction value is If it is not a negative value, it comprises the step of accepting a new call to the base station corresponding to the largest subtraction value.

A CDMA call handoff method considering forward power consumption according to the present invention is a method of handing off an ongoing call in a CDMA cellular system, comprising: setting an adjustment value for each base station that is proportional to the currently used forward traffic power of the base station; Detecting a signal strength of a pilot channel for each base station, subtracting a set adjustment value from the detected signal strength corresponding to each base station, calculating a subtraction value, and including the base station whose subtraction value is a positive value in the candidate set and actually And performing a handoff by including, in the active set, a base station having a subtracted value greater than or equal to a predetermined reference value from a minimum subtracted value among the base stations included in the active set, which is a set of base stations sending forward traffic power to the mobile station. .

1 is a schematic block diagram of a CDMA cellular system employed in accordance with the present invention.

2 is a flow chart illustrating a call acceptance process in accordance with the present invention.

3 is a flowchart illustrating a handoff process according to the present invention.

<Explanation of symbols for main parts of drawing>

10: mobile station 20: base station

30: Mobile Switching Center (MSC)

40: Visitor Register

The above objects and various advantages of the present invention will become more apparent from the preferred embodiments of the invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic block diagram of a CDMA cellular system employed in accordance with the present invention, which includes a mobile station (10), a base station (20), a mobile switching center (MSC) 30, and a visitor register ( Visitor Location Register (VLR, 40), which depicts the signaling of each component.

In this configuration, the mobile station 10 transmits a radio network channel assignment completion signal to the base station 20 when the mobile station 10 requests channel assignment to the base station 20 and receives a radio network channel from the base station 20.

When the base station 20 receives a channel assignment request from the mobile station 10, the base station 20 requests a channel assignment from the switch 30, receives a channel assignment from the switch 30, and allocates a wireless network channel to the mobile station 10. The radio network channel allocation completion signal from 10 is transmitted to the exchange 30.

On the other hand, the exchange 30 is a subject in charge of channel assignment. If there is a channel assignment request from the base station 20, the exchanger 30 inquires the subscriber data from the visitor register 40, and if the subscriber data is received from the visitor register 40, each cell is currently present. The channel usage situation and power usage status of each base station 20 are directly reported from the base station 20, and the strength values of the pilots measured by the respective mobile stations 10 are received and described later. Manage and decide off.

In addition, when the exchanger 30 requests the subscriber data inquiry, the visitor registrar 40 transmits the requested subscriber data to the exchange 30 using an internal database.

Next, a flowchart illustrating a call acceptance process according to the present invention of FIG. 2 with a CDMA lock and handoff process considering forward power consumption according to the present invention in the CDMA cellular system having the above-described configuration, and FIG. A handoff process according to the present invention will be described in detail with reference to a flowchart.

First, referring to FIG. 2, a call acceptance process is performed so that a call generated around a base station that is busy with a lot of traffic is saved by a base station that is busy with less traffic instead of the base station. will be. This also has the effect of dividing the traffic burden among base stations. However, if the newly created call is very close to the base station and the call can be made with less power, the call is handled by the base station if possible. This process is made possible by adjusting the reference value for determining the base station allocation of the new call.

Each base station has limited available forward traffic power. If this power is depleted, new calls will not be accepted and current calls will not be able to respond even if they require an increase in power. In general, if a base station is in charge of a large number of calls, a lot of power must be used, so observing how much power a given base station uses can measure the current burden of the base station.

Reference values are set to classify the state of the base station. If the value is t_d, t_s (t_d> t_s), when a base station consumes more than t_d% of the total traffic power, the cell in charge of that base station denses, and another base station t_s% The cell that the base station is responsible for is said to be sparse when it consumes less power.

In the existing new call acceptance defined in IS-95, the base station with the strongest pilot strength (Ec / IO) received by the mobile station of the new call is the base station in charge of the new call if the strength of the pilot is larger than the threshold T_ADD. do. In the present invention, T_ADM_i (i is the base station number) is newly introduced instead of T_ADD, and the value of T_ADM_i is adjusted as follows.

First, the power consumption that is the load of each base station is determined (step 200), when base station i dense sets a new reference value T_ADM_i = adm_d (step 202), and when base station i sparse sets T_ADM_i = adm_s (step 204), otherwise T_ADM_i = adm_o (step 206), and generally adm_d &gt; adm_o &gt; adm_s.

Next, the mobile station detects the pilot strength of the base station (step 208).

Then, a new reference value Q_i is introduced as a value representing the strength of the pilot of the base station measured by one mobile station. Q_i = (Ec / Io) _i-T_ADD_i ((Ec / Io_i is an Ec / Io value of pilot i).

Then, it is determined whether the largest Q_i value among the calculated Q_i values has a negative value (step 212), and if the largest Q_i value has a negative value, a new call is blocked (step 214).

On the other hand, if the largest Q_i value does not have a negative value, a new call is connected to the base station of the pilot having the largest Q_i value (step 216) and ends.

As a result, since the base station of the dense cell has a relatively small Q_i value, it is difficult to accept a new call if the strength of the pilot is not very strong. On the contrary, the base station of the sparse cell can easily accept a new call. As a result, a base station having a relatively large amount of forward power can reduce the traffic burden of a small base station to increase the traffic digestibility of the overall system.

On the other hand, if only the above-described improved rockacing method is introduced, even if the generated call is preferentially connected with a base station of a relatively far sparse cell instead of a close dense base station, it may be handed off again to the dense cell with a slight movement. If such a reverse phenomenon occurs, the base station of the dense cell has to be allocated back power by handoff. Therefore, there is a need to modify the handoff method.

Accordingly, referring to the handoff process according to the present invention with reference to FIG. 3, in the handoff according to the present invention, a handoff to a dense cell which is a problem is prevented. In the soft handoff method defined in the conventional IS-95, if the strength of a pilot of a base station measured by a mobile station exceeds T_ADD, the pilot is included in a candidate set for handoff of the mobile station, and the strength of the pilot is now present. If the T_COMP is larger than the minimum-strength pilot in the active set (pilot set of the base station sending forward traffic power to the actual mobile station), it is included as the active set.

While maintaining the framework of the existing handoff method, the reference value is adjusted to T_ADD_i (i is the base station number) instead of T_ADD and adjusted as follows.

First, the load of each base station is determined (step 300), and each base station I of the dense cell increases T_ADD_i by setting T_ADD_i = add_d (step 302). Other base stations set T_ADD_i = add_o (step 304) and generally add_d &gt; add_o.

Next, the mobile station detects the pilot strength ((Ec / IO) _i) of the base station (step 306).

Then, for handoff, a new reference value H_i is introduced as a value representing the strength of the pilot of the base station, calculated by defining H_i = (Ec / Io) _i-T_ADD_i (step 308), and the call currently in progress is set to this value. To perform a handoff.

That is, it is determined whether the calculated H_i value has a positive value (step 310), and if the calculated H_i value has a positive value, the base station is included in the candidate set (step 312).

Next, if the H_i value of the pilot is larger than the minimum H_i value of the base stations included in the currently active set (actually, the set of pilots of the base station sending the forward traffic power to the mobile station), the T_COMP which is a predetermined reference value (step 314), handing off to the active set (step 316) and ending.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

As described above, according to the present invention, even if the occurrence of a new call in a CDMA cellular system is very non-uniform per cell, each cell can eventually extinguish a similar number of calls, so that a particular cell is currently in a saturated state. At this time, the surrounding cells extinguish the call generated in the area of the cell, thereby reducing the call blocking rate and the cutting rate of the entire system.

Claims (4)

A method of accepting a new call in a code division multiple access method (CDMA) cellular system, Setting an adjustment value for each base station in proportion to the base station's current forward traffic power; Detecting signal strength of a pilot channel for each base station; Calculating a subtracted value by subtracting the set adjustment value from the detected signal strength corresponding to each base station; A call division multiple access method considering forward power consumption including the step of blocking a new call if the largest subtracted value is negative and accepting the new call to the base station corresponding to the largest subtracted value if the largest subtracted value is not negative. Acceptance method. 2. The code division according to claim 1, wherein the adjustment value proportional to the forward traffic power is set in three stages of high load, heavy load, and low load corresponding to the current total power used by the base station. Lake lak method of plural connection method. A method for handing off an ongoing call in a code division multiple access method (CDMA) cellular system, Setting an adjustment value for each base station in proportion to the base station's current forward traffic power; Detecting signal strength of a pilot channel for each base station; Calculating a subtracted value by subtracting the set adjustment value from the detected signal strength corresponding to each base station; In the active set, the base station includes a base station having a positive subtraction value in the candidate set, and the base station includes a base station having a subtracted value that is greater than or equal to a predetermined reference value than the minimum subtracted value among the base stations included in the active set, which is a set of base stations that are actually forwarding power to the mobile station. A call handoff method of a code division multiple access method considering forward power consumption, comprising performing a handoff. 4. The code division multiplex according to claim 3, wherein the adjustment value proportional to the forward traffic power is set in two stages of high load, medium load, and low load corresponding to the current total power used by the base station. Call handoff method of connection method.