JP2000050340A - Method for controlling cell traffic load on base station in cdma cellular wireless communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CDMA system to maximize the transmission capacity. SOLUTION: In this method for controlling a traffic load of cells on base stations A, B in a CDMA cellular wireless communication system, the base station transmits a pilot signal to make a subscriber station possible to obtain a system operation code from the base station and the coverage area of the pilot signal is maintained nearly constant. The base station transmits a paging signal to make the subscriber station possible to obtain the assignment of a traffic channel. When the traffic load on the base station increases, the arrival range of a paging signal is made narrower than the arrival range of the pilot signal. In the case that the traffic load on the base station decreases, the arrival range of the paging signal is extended more than the arrival range of the pilot signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to code division multiplexed (CDMA) wireless communication systems, and more particularly, to C-based wireless communication systems.
The present invention relates to a system in which a DMA base station can adjust its own traffic load without deteriorating the performance of a user of an existing base station.

[0002]

BACKGROUND OF THE INVENTION The application of CDMA technology to cellular wireless telephone systems and data networks has certain advantages over current frequency division multiplexing (FDMA) and time division multiplexing (TDMA) technologies. There is.
With respect to the capacity of the system (ie, the number of users that a base station can support at one time in the cell of that base station), FDMA and TDMA systems are limited by the number of frequencies already allocated to the operation of the system. I have. An FDMA system employs a base station and the subscribers covered thereby (e.g., mobile) on each assigned forward (base station to subscriber) and reverse (subscriber to base station) frequency pair. Only one duplex (bidirectional) communication can be supported between stations at a time. Currently, TDMA cellular systems in the United States carry three time slots on the forward and reverse links, providing up to three times the maximum capacity of FDMA systems with the same frequency allocation. it can.

On the other hand, a CDMA system has a certain FDMA
For a / TDMA system, it is possible to operate within the same frequency allocation, but the capacity of the CDMA system is not limited by the available frequency pairs (ie a finite number of time slots). A CDMA system employs a direct sequence spread spectrum on forward / reverse frequency pairs.
m: DSSS) transmission system is used. Furthermore, in order to minimize interference between different communication links, transmissions defined by a frequency spreading code that are mutually orthogonal are set by the base station. Thus, the number of users served by one CDMA base station is limited only by the maximum amount of noise that can be tolerated on each user's link, which noise originates from the other currently active user links.

In a CDMA cellular wireless system, each base station radiates a robust pilot signal containing a cyclic pseudo-random binary code sequence over the geographic area (cell) covered by the base station. The pilot signals of each base station all have the same binary code sequence, but have a time lag with respect to the zero time reference. When a subscriber of the system (eg, a base station moving within a cell of a base station) receives the pilot signal, the pilot signal identifies the base station,
Used by the subscriber station in decoding other signals (synchronization (sync signal, paging signal, traffic signal)) from the base station transmitted on other frequency channels assigned to the system. To provide the sign.

[0005] Normally, a mobile station (MS) in a CDMA cellular system always obtains the strongest pilot signal at its current location. Thereafter, the mobile station transmits the obtained pilot signal to the base station (ba
Some information related to the se station (BS) is obtained via a synchronization signal, which is time aligned with the pilot signal from the base station. When the mobile station requests the base station to set up a two-way traffic link, the mobile station needs information about available traffic channels by a paging signal transmitted from the base station. That is, a mobile station cannot initiate a bidirectional traffic link to a base station without receiving and decoding the base station's paging signal. In this regard, the applications of VKGarg, et al
CDMA in Wireless / Personal Communications, Prentice
See Hall (1997).

[0006] When the number of users connected to and simultaneously communicating with a base station reaches a limit where its accumulated noise interferes with the reception of other users at the base station, the current traffic link may be of poor quality of service. Will decrease. Therefore, by controlling the amount of traffic loaded on the base station, the service quality for the current user is not dropped or degraded. It is desirable to maintain.

Furthermore, each base station in a CDMA cellular system typically has the maximum allowable forward (transmit)
Has a power limit. That is, all allowable power is allocated at all times among all forward traffic signals transmitted from the base station. Thus, as the number of links simultaneously communicating with the base station increases beyond the limit, the forward signal power on each link eventually weakens, making error-free reception impossible for the current user, and Quality will be degraded.

Currently, a so-called forward overload control algorithm is used to limit the total forward power required by a base station based on the power budget (transmission power capacity) of a certain station's amplifier. . This known algorithm uses blind blocking (approach). That is, once a low trigger threshold (e.g., 85%) is reached, all new user requests to set a reserve will be blocked even if sufficient power is available to accommodate one user's request. . Also, this known approach tends to operate conservatively, so that the available base station power is under-utilized by about 3 dB.

[0009]

Accordingly, it is an object of the present invention to provide a CDMA system that maximizes transmission capacity.

[0010]

According to the present invention, a method for controlling the traffic load of a cell of a base station in a CDMA cellular wireless communication system according to the present invention is provided wherein the subscriber station obtains a system operation code from the base station. In order to be able to do so, a pilot signal is transmitted from the base station, but the area covered by the pilot signal is kept almost constant, thereby defining the limit of the pilot signal of the base station. A paging signal is sent from the base station to enable the subscriber station to get the traffic channel assignment. The traffic load at the base station is monitored and the boundaries covered by the paging signal are changed to within the boundaries of the pilot signal, including (a) when the traffic load of the base station is increasing, the paging signal covers. The boundaries are narrower than the boundaries covered by the pilot signal,
And (b) when the load on the base station is reduced, the boundary covered by the paging signal is extended in the direction of the boundary of the pilot signal.

[0011]

FIG. 1 shows two base stations A, B serving users in adjacent cells of a CDMA cellular wireless communication system 12. FIG. Each of the base stations A and B transmits the above-described pilot signal, and transmits a signal to a subscriber station (eg, mobile station 1).
4, 15) can reach a code synchronization state with the base station. A coverage area of a pilot signal of the base station A;
The coverage area of the pilot signal of base station B is kept substantially constant, which is indicated by pilot signal reach 18 and 20 for base stations A and B respectively. The power level of the pilot signal transmitted from each base station is usually 1
08 digital gain unit (DGU).

Each base station A, B also transmits a synchronization signal and a paging signal so that a system user can obtain a traffic channel assignment from the base station for which a pilot signal has been reserved by the user. The coverage area of the paging signal of the base station A and the coverage area of the paging signal of the base station B are shown by the paging signal reach ranges 22 and 24 of the base stations A and B in FIG. The transmission power of the paging signal is usually set to 64 DGU.

When a user in the paging signal range 22, 24 issues a request to the associated base station to set up an initial traffic channel, the requested base station will have a maximum initial traffic signal range 26 in FIG. , 28 with a forward power sufficient to maintain the user's coverage. The power of the base station on the forward traffic link is typically set to 96 DGU. The call is sent to the paging signal reach 22, 22 in FIG.
Only after the user has entered one of the four, can the first be set. That is, the border of the paging signal determines the call setting area related to the base stations A and B.

The traffic loads at base stations A and B are: (a) the total output power on the forward traffic link (forward load) and (b) the level of interference detected on the reverse traffic link (reverse Load) or both of the conditions (a) and (b). The following description shows that the traffic load of base station B falls within the normal range, while the traffic load of base station A rises to the upper trigger threshold (FIG. 2,
Assume that FIG. 3) increases above and then lies between the upper and lower trigger thresholds (FIG. 4).

According to the present invention, the base station self-regulates (self-controls) its own traffic load and is served by the current user to whom the base station is assigned a traffic channel and by the base station. At least the lowest desired signal quality for potential users is to be maintained. Specifically,
The base station implements the following adaptive “cell breathing” load control system (eg, by using available equipment and digital signal processing hardware). 1. If (forward load> F_t OR reverse load> R_t) {N = N + 1; Paging DGU = Dp-NΔp; Initial Traffic DGU = Dt-NΔt; 2. Else if (forward load> F_L_t OR reverse load> R_L_t) {N = N-1; if N <0; N = 0; Paging DGU = Dp-NΔp; Initial traffic DGU = Dt-NΔt; Else if (forward load ≤ F_L_t AND reverse load ≤ R_L_t) {N = 0; Paging DGU = DP; Initial traffic DGU = Dt;}

Here, the instruction "Else" means that the immediately preceding condition is not satisfied. The definitions of the other instructions are 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 Δp: Delta DGU change in paging signal power Δt: Delta DGU change in initial traffic signal power

Generally, according to this system, the base station can determine whether the forward load (power budget) is equal to or less than the forward upper limit trigger threshold (F_t) and the reverse load (current active user) is the reverse upper limit. Operates in "normal mode" when the trigger threshold (R_t) is reached. When either the forward load or the reverse load at the base station exceeds a specified upper trigger threshold (F_t) or (R_t), cell breathing operation (cell breathing a).
ction) begins. Thus, the system of the present invention can provide dynamic call setup coverage by varying the power of the base station's paging signal to adjust for the potential number of new calls set up by the base station. it can. As a result, the initial traffic signal power of the newly established call is reduced accordingly. In fact, the power required for the base station's forward paging signal and the power required for the newly established call are used to increase the base station's forward link capacity.

An important feature of the system of the present invention is that the existing traffic link is maintained with all subscribers for whom the call was initially set up by the base station (ie, initial traffic coverage). For example, in FIG. 1, mobile stations 14, 16 are within the paging signal range of base station A, each requesting a call setup via base station A, and the two-way traffic link is Established between station A and each of mobile stations 14,16.

When the traffic load at the base station A exceeds the upper trigger threshold F_t or R_t as shown in FIG. 2, the signal reach of the paging signal is reduced, and the mobile station 16 transmits the paging signal of the base station A. Reach 2
2 outside. Furthermore, if the traffic load at the base station A continues to increase beyond the upper trigger threshold as shown in FIG.
Are the initial traffic signal reach 2 of the base station A.
6 will be exceeded. The initial forward traffic power of mobile stations 14, 16 was determined when each was requesting to set up a call with base station A under the conditions of FIG. Base station A
Are load conditions shown in FIGS. 2 to 4 (from mobile stations 14 and 16 to base station A
The maximum initial traffic signal coverage 26 of FIG. 1 is maintained for the current link between the mobile stations 14 and 16 (such as when a new call setup request is blocked).

The current cell breathing system (cell breathi)
ng scheme) can be performed independently of the forward and reverse links of the base station. That is, the set threshold is responsive to either or both the total forward link signal power at the base station and the total interference level on the reverse link received at the base station. Further, different step sizes (N) can be associated with the forward link and the reverse link, respectively.

Although the measurement of the forward load and the reverse load is performed in real time (for example, at intervals of one second or less), the cell breathing action (ie, expansion or contraction of the paging signal range of the base station) is performed in a prescribed manner. It is based on the average of such measurements taken over a time interval. Furthermore, the lower trigger threshold F_L_t, R_L_t
Is set within the range of 70-80% of the full limit of the base station in order to use limited resources (power) effectively.

Importantly, a constant power (ie, cell coverage) is maintained for the base station pilot signal. As a result, the coverage of so-called handoffs for system users is not affected at all and has no effect on existing calls (ie these calls were initially set up by the base station and are currently active). At some point new users may need more resources (higher forward power) than the base station,
But it is blocked.

The system of the present invention operates to control the traffic load of a base station in a CDMA cellular wireless system. That is, (1) the limited resources at the base station of the system are optimized to achieve higher capacity than without using the present invention.
(2) The base station ensures a favorable level of service quality of the currently served subscriber station (user). (3) The forward link capacity of the base station can increase due to paging channel reduction and initial forward traffic link power demand. (4) Controlling the demand for new call setup (ie, new grant) to remove only those subscribers who initially require higher resources (greater forward and reverse link power) Can be.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating two base stations in adjacent cells in a CDMA cellular wireless communication system, and illustrating coverage of signals radiated from the base stations under normal traffic load conditions.

FIG. 2 is a diagram illustrating a state in which one of the base stations in FIG. 1 has an increase in traffic load slightly exceeding an upper trigger threshold;

FIG. 3 is a diagram illustrating a state in which one of the base stations in FIG. 2 has an increase in traffic load greatly exceeding an upper trigger threshold;

FIG. 4 is a diagram illustrating a state in which the traffic load at one of the base stations in FIG. 2 or FIG. 3 is equal to or less than an upper trigger threshold and equal to or greater than a lower trigger threshold;

[Explanation of symbols]

 A, B Base station 12 CDMA cellular wireless communication system 14, 16 Mobile station 18, 20 Pilot signal reach 22, 24 Paging signal reach 26, 28 Initial traffic signal reach

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 596077259 600 Mountain Avenue, Murray Hill, New Jersey 07974-0636 U.S.A. S. A. (72) Inventor Qing Yao Han United States, 07869 New Jersey, Randolph, Hillcrest Drive 18 (72) Inventor Francis Giant United States, 07981 New Jersey, Hippany, Deerfield Road 45 (72) Inventor Yugi Yao United States, 07054 New Jersey, Parsippany, Route 46 1480, Apartment 157A (72) Inventor Lily Zoo United States, 07869 New Jersey, Randolph, Center Grove Road 46, Apartment You 510

Claims (10)

[Claims] (A) transmitting a pilot signal from a base station so that a subscriber station can obtain an operation code from the base station; and (B) substantially arranging a range of the pilot signal of the base station. (C) transmitting a paging signal from the base station so that the subscriber station that has acquired the pilot signal can secure traffic channel allocation from the base station; and (D). (E) changing the range of the paging signal within the range of the pilot signal, wherein the step (E) comprises: (Ea) the step of: When the traffic load of the base station is increasing, the step of reducing the range of the paging signal to be smaller than the range of the pilot signal. And (Eb) extending the range of the paging signal beyond the range of the pilot signal when the traffic load of the base station is reduced. A method of controlling the station's cell traffic load. (F) When the traffic load increases above a predetermined threshold, the reach of the paging signal is reduced, and when the traffic load decreases below the predetermined threshold, the paging signal is reduced. The method of claim 1, further comprising the step of extending coverage. 3. The method according to claim 1, further comprising the step of: (G) varying a level of power used by the base station with respect to the paging signal, thereby varying a range of the paging signal. . 4. The step (D) of monitoring comprises:
The method of claim 1, comprising monitoring forward link signal power demand at a base station. 5. The step (D) of monitoring comprises:
The method of claim 1, comprising monitoring the level of reverse link interference or noise received at the base station. 6. The monitoring of (D) comprises: (Da) a forward link signal power demand at the base station; and (Db) a level of reverse link interference or noise received at the base station. The method of claim 1, comprising monitoring 7. The reach of the paging signal is determined by the following algorithm: If (forward load> F_t OR reverse load> R_t) {N = N + 1; Paging DGU = Dp-NΔp; Initial Traffic DGU = Dt-NΔt ;} Else if (forward load> F_L_t OR reverse load> R_L_t) {N = N-1; if N <0; N = 0; Paging DGU = Dp-NΔp; Initial traffic DGU = Dt-NΔt;} Else if ( forward load ≤ F_L_t AND reverse load ≤ R_L_t) {N = 0; Paging DGU = DP; Initial traffic DGU = Dt;} (Here, the instruction "Else" means a case where the immediately preceding condition is not satisfied. The definition of the instruction is 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 Δp: Paging signal 3. The method according to claim 2, wherein the delta DGU change of power Δt: delta DGU change of initial traffic signal power. 8. (H) When a subscriber station secures a traffic channel assignment from a base station, an initial traffic signal reach range corresponding to a certain base station's forward link power level with respect to the subscriber station. The method of claim 1, further comprising the step of: 9. (I) When a traffic load at a base station exceeds a certain threshold value and a certain subscriber station secures a traffic channel assignment, a maximum initial traffic signal reaching the base station is obtained. 9. The method of claim 8, further comprising the step of setting an initial traffic signal coverage below the range. 10. The method further comprises the step of: (J) maintaining the set initial traffic signal reach substantially constant for the subscriber station currently linked to the base station, independently of the traffic load at the base station. The method of claim 8, wherein: