HK1024356B - Base station and method for controlling global channel power emitted to said base station - Google Patents

Description

Base station and method for controlling power of global channel transmitted by base station

Technical Field

The present invention relates generally to wireless local area loops and cellular communication systems. More particularly, the present invention relates to a wireless communication system that adjusts the power of signals transmitted from a base station over a global channel to minimize power spillover to adjacent communication cells.

Background

Wireless communication systems have rapidly become a viable alternative to wired systems due to their inherent advantages. Wireless systems enable users to move freely within the operating range provided by a service dealer and even enter the service boundaries of other service dealers while using the same communications hardware. Wireless communication systems may also be used in areas where wired systems are not efficiently implemented and have become an economically viable alternative to replacing aged telephone lines and outdated telephone equipment.

One of the deficiencies of wireless communication systems is the limited available RF bandwidth. It is always desirable to improve the efficiency of such systems in order to increase system capacity and meet the ever-increasing demands of users. One factor that causes the overall capacity of a wireless communication system to decrease is signal power spillover between adjacent cells or base stations. Signal power overflow occurs when the power of a signal transmitted by a base station in a particular cell exceeds the boundary of that cell (or called the operating range). This overflow becomes interference to adjacent cells and reduces the efficiency of the system. Therefore, minimizing overflow is one of the very important issues in the design of wireless communication systems.

Forward Power Control (FPC) is used to minimize overflow by adjusting the power level of signals transmitted from the base station to the subscriber unit on a given channel. The FPC operates in a closed loop in which each subscriber unit constantly measures the signal to noise ratio it receives and sends an indication back to the base station indicating whether the base station should increase or decrease the power transmitted to the subscriber unit. The closed loop algorithm participates in maintaining the transmit power level from the base station at a minimum acceptable level, thereby minimizing overflow to adjacent cells.

However, the FPC cannot adjust the power level for global channels such as pilot signals, broadcast channels, or paging channels. Because there is no closed loop algorithm operating in these channels, a global channel transmit power level for the worst case is typically used. This power level is typically greater than the power level required by most subscriber units, thus causing an overflow to adjacent cells.

Attempts have been made to overcome this problem of spillage. Us patent No.5,267,262 (weather, III) discloses a power control system for use by a CDMA cellular mobile telephone system which includes a network of base stations, each of which communicates with a plurality of subscriber units. Each base station transmits a pilot signal for use by the mobile unit to estimate the propagation loss of the respective pilot signal. The combined power of the signals transmitted as all base stations received at a mobile unit is also measured. This sum of power levels is used by each mobile unit to reduce the transmitter power to the minimum power required. Each base station measures the strength of the signal received from a mobile unit and compares the signal strength level to a desired signal strength level for that particular mobile unit. A power adjustment command is generated and transmitted to the mobile unit whose power is adjusted accordingly. The transmit power level of the base station may also be increased or decreased depending on the average noise situation of the cell. For example, a base station may be set at an unusual noise location and may allow higher than normal transmit power levels to be used. However, these cannot be performed dynamically, and power correction cannot be performed according to the entire transmission power of the base station.

Therefore, there is a need for an efficient method of controlling the power level of global channels transmitted from a base station.

Disclosure of Invention

The present invention comprises a system that dynamically adjusts the power of signals transmitted from a radio base station over a global channel to minimize power spillover to other communication cells. The system monitors the overall transmit power of the base station and dynamically adjusts the global channel transmit power as a function of the overall transmit power of the base station as measured at the base station.

It is therefore an object of the present invention to provide an improved method and system for dynamically controlling the power of a signal transmitted from a base station over a global channel to minimize overflow to adjacent cells.

According to an aspect of the present invention, there is provided a base station, comprising:

transmitting means for transmitting signals in a plurality of designated channels and at least one global channel at an output power level;

monitoring means for monitoring said output power level;

closed loop forward power control means for controlling the power levels of said assigned channels, respectively; and

means responsive to said power level for controlling said global channel power level; wherein the power level of the global channel is adjusted in response to changes in the total power of the designated channels.

According to an aspect of the present invention, there is also provided a method for controlling power of a global channel transmitted from a base station, comprising:

transmitting signals in a plurality of designated channels and at least one global channel at an output power level;

monitoring the output power level;

respectively controlling the power level of the appointed channel by utilizing closed loop forward power control; and

controlling a power level of the global channel in response to the power level; wherein the power level of the global channel is adjusted based on a change in the total power of the designated channels.

Other objects and advantages of the present invention will become more apparent after reading the detailed description of the preferred embodiments of the present invention.

Drawings

FIG. 1 is a communication network embodying the present invention;

FIG. 2 is a signal propagation between a base station and a plurality of subscriber units;

FIG. 3 is a base station constructed in accordance with the present invention; and

fig. 4 is a flowchart of a method of dynamically controlling the transmit power of a global channel according to the present invention.

Detailed Description

The preferred embodiments will now be described with reference to the drawings, wherein like reference numerals refer to like parts.

Fig. 1 illustrates a communication network 10 embodying the present invention. The communication network 10 generally includes one or more base stations 14, with each base station 14 communicating with a plurality of fixed or mobile subscriber units 16. Each subscriber unit 16 may communicate with both the closest base station 14 and the base station 14 providing the strongest communication signal. The base stations 14 also communicate with a base station controller 20. The base station controller 20 coordinates communications between the base stations 14 and the subscriber units 16. The communication network 10 may optionally be connected to a Public Switched Telephone Network (PSTN)22, and thus the base station controller 20 also coordinates communications between the base station 14 and the PSTN 22. Each base station 14 is preferably connected to the base station controller 20 via a wireless link, although a land line may be provided. Land lines are particularly suitable when a base station 14 is in close proximity to the base station controller 20.

The base station controller 20 performs several functions. First, base station controller 20 provides overall operations, administration, and maintenance (OA & M) associated with establishing and maintaining communications between subscriber unit 16, base station 14, and base station controller 20. The base station controller 20 also provides an interface between the wireless communication system 10 and the PSTN 22. The interface includes multiplexing and demultiplexing of communication signals into and out of the system 10 via the base station controller 20. Although the wireless communication system 10 is shown using an antenna to transmit RF signals, it will be apparent to those skilled in the art that communication may be achieved via a microwave or satellite uplink. In addition, the functionality of the base station 14 may be combined with the base station controller 20 to form a primary base station. The physical location of the base station controller 20 is not a major issue with the present invention.

Referring to fig. 2, the propagation of certain signals in a communication channel 18 established between a base station 14 and a plurality of subscriber units 16 is illustrated. A subscriber unit 16 to which the forward signal 21 is transmitted from the base station 14. A reverse signal 22 is transmitted from the subscriber unit 16 to the base station 14. All subscriber units 16 located within the maximum operating range 30 of the cell 11 are served by the base station 14.

Referring to fig. 3, there is shown a base station 100 constructed in accordance with the present invention. The base station 100 includes an RF transmitter 102, antenna 104, a baseband signal combiner 106 and a Global Channel Power Control (GCPC) algorithm processor 108. The base station 100 also includes a plurality of modems 110, one for each channel, for generating a plurality of assigned channels 112 and a plurality of global channels 114. Each modem 110 includes a corresponding code generator, spreader and other devices for determining a communication channel as is well known to those skilled in the art. Communications via the designated channel 112 and the global channel 114 are combined by the combiner 106 and up-converted by the RF transmitter for transmission. The power of each assigned channel 112 is controlled by the FPC, respectively. However, the power of the global channel 114 is simultaneously and dynamically controlled by the GCPC processor 108.

The total transmit power of all channels 112, 114 is measured at the RF transmitter 108 and the measurement is input to the GCPC processor 108. As will be described in greater detail below, the GCPC processor 108 analyzes the total transmit power of all channels 112, 114 and calculates the required transmit power level for the global channel 114. Preferably, the power level is measured before the RF signal is output to the antenna 104. Alternatively, the power level may be: 1) measured at the merger 106; 2) sampled and summed at each assigned global channel 112, 114; or 3) received as an RF signal only after transmission using a separate antenna (not shown) associated with the base station antenna 104. Those skilled in the art will recognize that any method of monitoring the overall transmit power at the base station 100 may be used without departing from the spirit and scope of the present invention.

Dynamic control of the power of the global channel 114 is performed by using several assumptions in the overall transmit power analysis. It is assumed that the FPC for the assigned channel 112 is operating ideally and that the power transmitted to each subscriber unit 16 is adjusted so that all subscriber units 16 receive their signals with a particular signal-to-noise ratio. Because varying the transmit power transmitted to a particular subscriber unit 16 affects the signal-to-noise ratio at other subscriber units 16, the analysis of the transmit power by the FPC for each designated antenna 112 is preferably performed continuously. Additionally, such analysis may be performed periodically, where appropriate, to adjust the power of each designated antenna 112.

Before analyzing the total transmit power, several factors must be defined as follows: γ represents the desired signal-to-noise ratio at a subscriber unit 16; n is a radical of₀Is white noise power density, W isThe transmission bandwidth, N, is the processing gain. The propagation loss is such that if the transmit power is P, the power level P of a subscriber unit 16 located at a distance r_rComprises the following steps:

P_rp × β (r) formula (1)

Depending on the size of the mesh, different propagation modes may be used, such as free space propagation mode, Hata mode or breakpoint mode. One skilled in the art will recognize that any empirical or theoretical propagation mode may be used in accordance with the techniques of the present invention. For example, free space propagation modes are used in small cells. The propagation loss in this mode is:formula (2) whereinFormula (3)

And λ is the wavelength of the carrier frequency. Thus, if the transmit power is P, the power seen at distance r is inversely proportional to the square of the distance. Thus, the power P seen at the distance r_rComprises the following steps:(represented by formulas 1 and 2)

When the FPC is operating on the designated channel 112, power P is transmitted from the base station 100 to a subscriber unit 16 located a distance r from the base station_iComprises the following steps:formula (4)

Wherein P is_TTotal transmit power sum:formula (5)

Because global channel 114 must be adequately received throughout the entire operating range 30 of cell 11, the required transmit power P for a global channel 114_GThe following steps are changed:formula (6)

Where R is the working range 30 of the cell 11. The value of a (r) can be easily calculated for any propagation mode. Thus, P_GTotal transmission power P equal to a constant plus a fraction_T. Because of the total transmission power P at the base station 100_TContinuous monitoring is performed so that it is different from the worst case scenario (which is the case with the maximum transmission power P that the base station 100 can transmit)_TCorresponding), global channel transmit power P_GIs dynamically updated.

For example, for the free space propagating mode mentioned laterFormula, the propagation loss is:(from the equation 2) wherein,(represented by formula 3)

And λ is the carrier frequency of the signal. In this mode, by a distance r_i：(by the formula 2) and(represented by formulas 2 and 5)

Replacing the working range 30 of the cell 11 with R:(represented by formulas 2 and 5)

We obtained:(represented by formula 6)

Thus, with free space propagation mode, the optimal global channel transmit power is given by a constant term proportional to the square of the cell radius plus a variable that is a fraction of the total transmit power P_T。

The significance of the invention can be further illustrated by the following numerical examples. Assuming that the system parameters are given as follows:

gamma 4 (desired signal to noise ratio)

130 (processing gain)

W＝10×10⁶(Transmission Bandwidth)

N₀＝4×10^-21(white noise Power Density)

R＝30×10³m (30Km mesh radius)

λ ═ 0.1667m (relative to the 1.9GHz carrier frequency). Using free space propagation mode:(represented by formula 3)

Thus, the total power P when transmitted from the base station_TAt 100W, the global channel transmission power P_GThe method comprises the following steps:

(represented by formula 6)

Referring to fig. 4, a diagram illustrating a method for dynamically controlling global channel transmit power P_GThe method of (1). Once all system parameters have been set (step 202), several constants are calculated (β (R), a (R)) (step 204), and processor 108 then calculates A and B, which are used to determine the global channel transmit power P_G(step 206). The total transmit power is measured at the base station 100 (step 208) and the required global channel transmit power P is calculated using the following equation_G(step 210):

P_G＝A+B*P_T(formula (7)

Once the required global channel transmit power P is calculated_G(step 210), all global channels 114 are set to the calculated power level (step 212). The process is then repeated (step 214), continuously monitoring the total transmit power at the base station 100 to dynamically control the power level of the global channel 114.

Depending on the traffic load of cell 11, a global channel114 may vary up to 12 dB. As a result, the global channel transmission power P is set in a method_GSuch that the global channel transmit power P is sufficiently large for applications where the highest traffic load situation is expected (i.e., worst case scenario)_GThe required power level necessary most of the time will be exceeded. The method of the invention reduces the global channel transmitting power P when the traffic load is low_GAnd increasing the global channel transmission power P when the traffic load is high_GRealizing the transmission power P of the global channel_GSo that reliable communication can be maintained at all times. In this way, overflow to adjacent cells is kept to a minimum possible level, while increasing the capacity of the overall system.

Although the invention has been described in detail with particular reference to certain specific embodiments thereof, such detail is intended to serve as a parabolic mirror and is not intended to be limiting. It will be apparent to those skilled in the art that various changes in the structure and mode of the invention can be made without departing from the spirit and scope of the invention.

Claims (20)

1. A base station, comprising:

transmitting means for transmitting signals in a plurality of designated channels and at least one global channel at an output power level;

monitoring means for monitoring said output power level;

closed loop forward power control means for controlling the power levels of said assigned channels, respectively; and

means responsive to said power level for controlling said global channel power level; wherein the power level of the global channel is adjusted in response to changes in the total power of the designated channels.

2. The base station of claim 1 wherein said means for controlling the power level of the global channel further comprises a processor responsive to said monitoring means for calculating a desired power level for said global channel and adjusting the power of said global channel based on said calculation.

3. A base station according to claim 2, wherein the distance from the base station is r_iSaid required power level P_GCalculated using the following formula:

where γ is the desired signal-to-noise ratio, N is the processing gain, and P is_TIs the total transmission power, and

wherein N is₀Is the white noise density, W is the emission bandwidth, and wherein,

where λ is the wavelength corresponding to the carrier frequency.

4. Base station according to claim 2, wherein said required power level P_GCalculated using the following formula:

wherein α ═ λ²)/(4π)²γ is the desired signal-to-noise ratio, N is the processing gain, N₀Is white noise power density, P_TFor the total transmit power, W is the transmit bandwidth, R is the maximum operating range, and λ is the wavelength of the carrier frequency.

5. A base station according to claim 2, wherein a free space propagation mode is used in the calculation of said required power level.

6. The base station of claim 2 wherein a hattach propagation mode is used in the calculation of said desired power level.

7. A base station according to claim 2, wherein a breakpoint propagation pattern is used in the calculation of said required power level.

8. The base station of claim 4, wherein said transmitting means further comprises:

combining means for combining said designated channel and said global channel to provide a transmit information signal;

means for up-converting said transmitted information signal prior to transmission; and

an antenna for transmitting the up-converted signal.

9. The base station of claim 8 wherein said output power level is monitored at said combining means.

10. The base station of claim 8 wherein the power level of each of said designated channel and said global channel is separately monitored by said monitoring means to provide said output power level.

11. The base station of claim 8, further comprising second antenna means for detecting said output power level; wherein said monitoring means is responsive to said second antenna means.

12. The base station of claim 1, wherein said means for transmitting further comprises means for transmitting signals in a plurality of global channels.

13. A method for controlling power of a global channel transmitted from a base station, comprising:

transmitting signals in a plurality of designated channels and at least one global channel at an output power level;

monitoring the output power level;

respectively controlling the power level of the appointed channel by utilizing closed loop forward power control; and

controlling a power level of the global channel in response to the power level; wherein the power level of the global channel is adjusted based on a change in the total power of the designated channels.

14. The method of claim 13, further comprising: calculating a required power level for said global channel based on said monitoring step; and adjusting the power of the global channel in response to the calculating.

15. The method of claim 14 wherein said desired power level P_GCalculated using the following formula:

wherein α ═ λ²)/(4π)²γ is the desired signal-to-noise ratio, N is the processing gain, N₀Is white noise power density, P_TFor the total transmit power, W is the transmit bandwidth, R is the maximum operating range, and λ is the wavelength of the carrier frequency.

16. The method of claim 15, wherein said transmitting step further comprises:

combining the designated channel and the global channel to provide a transmit information signal;

up-converting the transmit information signal prior to transmission; and

transmitting the up-converted signal.

17. The method of claim 16, further comprising monitoring said output power level prior to said combining step.

18. The method of claim 15, further comprising separately monitoring the power level of each of said designated channel and said global channel to provide said output power level.

19. The method of claim 15, further comprising detecting said output power level using an antenna co-located with the base station antenna.

20. The method of claim 13, further comprising transmitting signals in a plurality of global channels.