KR20000011393A - Adaptive load management control for a base station in a cdma cellular wireless communication system - Google Patents

Abstract

PURPOSE: A method is provided to control a traffic load by for a user of an existing base station. CONSTITUTION: The control method of a cell traffic load of a base station comprises steps: that a subscriber station obtains an operating code from the base station by receiving a pilot signal from the base station; of defining a pilot signal boundary about the base station; that the subscriber station obtained the pilot signal obtains a traffic channel allocation from the base station by receiving a paging signal from the base station; of monitoring a traffic load state of the base station; of changing the boundary of the valid area of the paging signal inside the pilot signal boundary.

Description

ADAPTIVE LOAD MANAGEMENT CONTROL FOR A BASE STATION IN A CDMA CELLULAR WIRELESS COMMUNICATION SYSTEM}

FIELD OF THE INVENTION The present invention relates generally to code division multiple access (CDMA) wireless communication systems, and more particularly, to the CDMA base station itself in its traffic load without sacrificing performance for existing base station users. It is about a method to be able to control with.

The application of CDMA technology in cellular wireless telephone and data networks offers clear advantages over traditional frequency division multiple access (FDMA) and time division multiple access (TDMA) systems. With regard to system capacity, i.e. number of users, any given base station can support simultaneously within the geographic “cell” of that base station, but FDMA and TDMA systems are limited by a limited number of frequencies assigned to system operation. An FDMA system is one at a time for each assigned forward (base station to subscriber) and reverse (subscriber to base station) frequency pairs between a base station and a subscriber (e.g., mobile station) in its coverage area. Only dual (two way) communication links can be supported. The capacity of a TDMA system is determined by the number of time slots in which each of the assigned forward / reverse frequency pairs can be divided. Currently, TDMA cellular systems in the United States deliver three times the slots on the forward and reverse links, providing up to three times the maximum capacity of FDMA systems with the same frequency allocation.

While a CDMA system can operate within the same frequency assignment as any given FDMA / TDMA system, the capacity of a CDMA system is not limited by a limited number of effective frequency pairs or time slots. Rather, the CDMA system advantageously employs a direct sequence spread spectrum (DSSS) transmission method for the forward / reverse frequency pair. In addition, the transmission is defined using mutually orthogonal frequency spreading codes to minimize interference between different communication links set up by the base station. Thus, the number of users that one CDMA base station can service is limited only by the maximum noise that can be tolerated on each user link, which is generated from other user links that are currently active.

In a CDMA cellular wireless system, each base station emits a robust pilot signal that includes a repeating pseudo random binary sequence code throughout its base station's geographic effective area (“cell”). The pilot signals of each base station all have the same binary sequence code, but have different time offsets for the zero reference time. When a system subscriber (e.g., a mobile station moving within any given base station cell) receives a pilot signal, it manipulates the pilot signal to identify that base station and from a base station transmitted on another frequency channel assigned to that system. Provide code suitable for use by the subscriber station in decoding other signals, viz., Sync, paging, traffic signals.

Typically, a mobile station (MS) in a CDMA cellular system always obtains the strongest pilot signal at its current location. Subsequently, the MS obtains specific information about the BS that is time-aligned with the pilot signal and generates a pilot signal obtained through the synchronization signal transmitted from the base station BS. Then, when the MS requests the BS to set up a two way traffic link, the MS gets the information required for the valid traffic channel by the paging signal sent from the BS. That is, the MS cannot initiate a two way traffic link through that base station without first acquiring and successfully decoding the paging signal of any given base station. Generally, V. K. See V. K. Garg et al., Published in Prentice Hall (1997) entitled “Applications of CDMA in Wireless / Personal Communications”.

If the number of traffic users linked concurrently with any given base station is close to the limit at which any user at the base station is disturbed by clear reception due to their cumulative noise, the existing traffic link will have corresponding quality of service correspondingly. Will be further degraded. Therefore, when user traffic increases, it would be desirable to control the traffic load at the base station to maintain the desired quality of service without disrupting or significantly reducing the quality of service being provided to existing users.

In addition, the maximum allowable forward (transmit) power of each base station in a CDMA cellular system is typically limited. That is, all allowable power must be distributed between all forward traffic signals emitted from the base station at any one time. Therefore, if the number of traffic links simultaneously connected with the base station can increase indefinitely, the power of the forward signal of each link will eventually become too low to ensure that the existing user can receive it without error, thereby resulting in a consistent signal quality. Will be degraded.

Currently, a so-called forward overload control algorithm is used to limit the overall forward power requirement at the base station based on the total amount of power of any given base station amplifier. Known algorithms use a "blind blocking" approach. That is, when a low threshold (eg, 85%) is reached, all new user's call setup requests are blocked, even if enough power is available to accommodate any given user's request. In addition, known approaches tend to operate in a limited manner, so that the available base station power is used as low as about 3 dB.

According to the present invention, a method of controlling the cell traffic load of a base station in a code division multiple access (CDMA) cellular wireless communication system comprises the steps of transmitting a pilot signal from a base station to enable a subscriber station to obtain a system operation code from the base station; And defining a boundary of the pilot signal for the base station by keeping the effective area of the pilot signal substantially constant. A paging signal is also transmitted from the base station that allows the subscriber station to obtain a traffic channel assignment. Monitor the traffic load at the base station to reduce the effective area boundary of the paging signal so as to stay away from the pilot signal boundary when the traffic load of the base station increases, and to activate the paging signal toward the pilot signal boundary when the base station traffic load decreases. By extending the boundary of the region, the boundary of the effective region of the paging signal is changed inside the pilot signal boundary.

The invention will be better understood with reference to the following detailed description taken in conjunction with the accompanying drawings and claims.

1 shows two base stations present in adjacent cells in a CDMA cellular wireless communication system and the effective area of the signal radiated from the base station under normal traffic load conditions;

2 is a diagram showing that the traffic load of one of the base stations shown in FIG. 1 is increasing just above the upper trigger threshold;

3 is a diagram showing that the traffic load of one of the base stations shown in FIG. 2 is further increased beyond the upper trigger threshold;

4 shows that the traffic load at one of the base stations shown in FIG. 2 or 3 is between an upper trigger threshold and a lower trigger threshold.

Explanation of symbols for the main parts of the drawings

12: CDMA Cellular Wireless Communication System

14, 16: mobile station

FIG. 1 shows two base stations A and B arranged to provide service to a user in an adjacent cell of a CDMA cellular wireless communication system 12. Each base station A, B transmits the pilot signal described above to synchronize the code between the subscriber station, for example, the mobile stations 14, 16 and the base station. The effective area for the pilot signal of the base station A and the effective area for the pilot signal of the base station B remain substantially constant, respectively, defining the pilot signal boundaries 18, 20 corresponding to the base stations A, B. The power level of the pilot signal transmitted from each base station is typically fixed at a value of 108 digital gain units (DGUs).

In addition, each of the base stations A and B transmits the above-described sync and paging signals so that a traffic channel can be allocated from the base station corresponding to the pilot signal acquired by the system user. The effective area for the paging signal of the base station A and the effective area for the paging signal of the base station B have boundaries 22 and 24 corresponding to the base stations A and B of FIG. The transmit power for the paging signal is typically set to 64 DGU.

If a user in the boundary 22, 24 of the base station paging signal requests the initial base station to set up an initial traffic channel, the requested base station has a user valid region whose boundary corresponds to one of the maximum initial traffic valid region boundaries 26, 28 of FIG. It will transmit with sufficient forward power to remain within. Base station power on the forward traffic link is typically set to 96 DGU. It should be noted that the initial call setup can only be made after the user enters into one of the paging signal boundaries 22, 24 of FIG. That is, the paging signal boundary defines the call setup area associated with the base stations A and B.

The traffic load at base stations A and B can be measured by monitoring one or both of the total output power (forward load) on the forward traffic link and the level of interference (reverse load) detected on the reverse traffic link. In the following description, the traffic load at base station B is within the normal range, while the traffic load at base station A has increased above the upper trigger threshold (FIGS. 2 and 3) and then the upper trigger threshold and lower trigger threshold ( Assume that it falls to any level in between.

According to the present invention, the base station itself adjusts or controls its own traffic load in order to maintain at least the minimum desired signal quality for the existing user assigned the traffic channel by the base station and for the potential user to be served by the base station. . Specifically, to implement an adaptive " cell breathing " load control method (e.g., using available equipment and digital signal processing hardware), a base station is configured as follows.

The term "Else" means that no immediately preceding state exists. Other terms are defined as follows.

F_t: forward upper trigger threshold,

R_t: reverse upper trigger threshold,

F_L_t: forward lower trigger threshold,

R_L_t: reverse lower trigger threshold,

N: trigger event counter,

Dp: default forward paging signal power,

Dt: default forward initial traffic signal power,

p and t are delta DGU changes for paging and initial traffic signal power, respectively.

In general, this method requires the base station to " normal " if the forward load (power capacity) of the base station is below the forward upper trigger threshold (F_t), and if the reverse load (currently active user) is below the reverse upper trigger threshold (R_t). Enable to operate in mode. When the forward or reverse load at the base station exceeds the defined upper trigger threshold F_t or R_t, the cell bridging operation is started. Thus, this method provides dynamic call setup coverage by allowing the power of the base station's paging signal to be changed in a manner that adjusts the number of potential new calls that the base station can set up. As a result, the initial traffic signal power for the newly set up call is correspondingly reduced. Indeed, in order to increase the forward link capacity of the base station, other methods of power saving required for the newly set up call and the forward paging signal of the base station may be used instead.

One important feature of this method is that the existing traffic link is maintained with all subscribers of the call initially set up by the base station (ie, initial traffic coverage area). For example, in FIG. 1, subscriber mobile stations 14 and 16 within the paging signal coverage area of base station A each request a call setup through base station A, and two-way traffic between base station A and each mobile station 14 and 16. FIG. Assume a link is established.

If the traffic load at base station A exceeds the upper trigger threshold F_t or R_t as in FIG. 2, the effective area of the paging signal is reduced so that the mobile station 16 is outside of the paging signal boundary 22 of base station A. do. In addition, as the traffic load at base station A continues to increase above the upper trigger threshold of FIG. 3, the mobile stations 14, 16 both cross the boundary 26 for base station A's initial traffic validity area. Under the state of FIG. 1, any new call setup from mobile station 14, 16 to base station A is determined since the initial forward traffic power for mobile station 14, 16 was determined at the time each mobile station requested base station A to call setup. Even under the load conditions of FIGS. 2-4 where the request is blocked by other methods, base station A will maintain the maximum traffic coverage area boundary 26 of FIG. 1 to proceed with the link with mobile stations 14, 16.

The cell bridging method of the present invention can also be implemented independently on the forward and reverse links of the base station. That is, the set threshold may correspond to one or both of the overall forward link signal power request at the base station and the overall interference level on the reverse link received at that base station. In addition, different step sizes N may be associated with the forward link and the reverse link.

While measurements of the forward and reverse loads can be performed in real time (eg, less than 1 second intervals), cell bridging operations (ie, extending or contracting the base station's paging signal boundaries) are defined at defined time intervals. It should be based on the average of the measurements obtained for. In addition, the lower trigger thresholds F_L_t and R_L_t may be set within a total limit of 70% to 80% of the base station in order to effectively use limited resources (power).

In particular, the power (ie, cell effective area) for the pilot signal of the base station is kept constant. As a result, the so-called "handoff" effective area for the system user is unaffected and does not affect any existing calls (i.e., calls initially set up by the base station and currently active). However, new users who require more resources (higher forward power) than any base station can provide at any given time will be blocked.

In summary, the disclosed method controls the traffic load at a base station in a CDMA cellular wireless communication system. In other words, this method

1.Observe more capacity than can be obtained by other methods by optimizing the limited resources at the system base station,

2. Maintain the desired level of quality of service for the subscriber station (user) currently served by the base station,

3. Increase the forward link capacity of the base station by reducing the paging channel and initial forward traffic link power requirements,

4. Control requests for new call setups (ie new grants) to eliminate only subscribers who initially require higher resources (higher forward link power and reverse link power).

While the foregoing detailed description shows a preferred embodiment of the present invention, it will be apparent to those skilled in the art that various changes and modifications can be made within the spirit and scope of the invention as indicated in the appended claims.

The present invention achieves higher capacity than that otherwise obtained by optimizing limited resources at the system base station, and maintains the desired level of quality of service for the subscriber station (user) currently serving by the base station, and also paging. Reduces channel and initial forward traffic link power requirements to increase the base station's forward link capacity and control requests for new call setup, eliminating only subscribers that initially require higher resources (higher forward link power and reverse link power). Has the advantage.

Claims (10)

A method of controlling the cell traffic load of a base station in a code division multiple access (CDMA) cellular wireless communication system to maintain a desired level of quality of service for a subscriber station currently serving or to serve, Transmitting a pilot signal from the base station to allow a subscriber station to obtain an operation code from the base station; Defining a pilot signal boundary for the base station by keeping the effective area of the pilot signal substantially constant; Transmitting a paging signal from the base station to cause the subscriber station acquiring the pilot signal to obtain a traffic channel assignment from the base station; Monitoring the traffic load condition of the base station; Change a boundary of an effective area of the paging signal within the pilot signal boundary, When the base station traffic load increases, the boundary of the effective area of the paging signal is reduced to be away from the pilot signal boundary, ② If the base station traffic load is reduced, the step of extending the boundary of the effective area of the paging signal toward the pilot signal boundary Cell traffic load control method comprising a. The method of claim 1, If the traffic load increases beyond a predetermined threshold, reducing the boundary of the effective area of the paging signal; Extending the boundary of the effective area of the paging signal if the traffic load decreases below a predetermined threshold; Cell traffic load control method comprising a. The method of claim 1, Changing a boundary of an effective area of the paging signal by changing a power level for the paging signal used in the base station; Cell traffic load control method comprising a. The method of claim 1, And wherein said monitoring step comprises monitoring a forward link signal power request at said base station. The method of claim 1, And wherein said monitoring step comprises monitoring interference or noise levels on a reverse link received at said base station. The method of claim 1, And wherein said monitoring step comprises monitoring both a forward link signal power request at said base station and an interference or noise level on a reverse link received at said base station. The method of claim 2, The boundary of the effective area of the paging signal is, Will change in the same way as "Else" means that the preceding state does not exist, F_t: forward upper trigger threshold, R_t: reverse upper trigger threshold, F_L_t: forward lower trigger threshold, R_L_t: reverse lower trigger threshold, N: trigger event counter, Dp: default forward paging signal power, Dt: default forward initial traffic signal power, p and t represent delta DGU changes to paging and initial traffic signal power, respectively. The method of claim 1, Establishing an initial traffic coverage area boundary corresponding to the base station forward link power level for the subscriber station when any subscriber station receives a traffic channel assignment from the base station. The method of claim 8, Setting the initial traffic coverage area boundary to be smaller than the maximum initial traffic coverage area boundary for the base station when the random subscriber station receives a traffic channel assignment when the traffic load at the base station exceeds a certain threshold. Cell traffic load control method comprising a. The method of claim 8, Irrespective of the traffic load at the base station, maintaining the established initial traffic validity area boundary substantially constant for a subscriber station currently linked with the base station.