EP1157480A1

EP1157480A1 - Cdma signal transmission using ratios of in-band and out-of-band signals

Info

Publication number: EP1157480A1
Application number: EP00913876A
Authority: EP
Inventors: Lindsay A. Weaver, Jr.; Brian K. Harms; Anthony C. K. Soong; Bruce S. Schwartz
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 1999-03-10
Filing date: 2000-03-10
Publication date: 2001-11-28
Also published as: CN1343397A; KR20010103047A; AU3523700A; HK1044084A1; WO2000054429A1; KR100649922B1; BR0008805A; CA2364397A1

Abstract

The invention is a CDMA signal transmission control technology (316). A CDMA (307) signal is transmitted that has in-band components and out-of-band components. Transmit control logic (316) automatically generates a ratio of signal strength of the in-band components versus the out-of-band components. In some embodiments of the invention, control logic (436) generates a transmit power metric signal based on the ratio. In other embodiments of the invention, control logic (436) determines excess forward link capacity based on the ratio. The CDMA signal transmission control technology (166) can be implemented in a CDMA base station (312).

Description

CDMA SIGNAL TRANSMISSION USING RATIOS OF IN-BAND AND OUT-OF-BAND SIGNALS

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to Code Division Multiple Access

(CDMA) systems. More particularly, the present invention includes, but is not limited to, a novel and improved CDMA base station that generates a ratio of in-band to out-of-band signal strength for use in base station transmission control.

II. Description of the Related Art

Code Division Multiple Access (CDMA) technology is commonly used in communications systems. In a typical CDMA system, a CDMA base station transmits a CDMA signal to numerous CDMA communications devices, such as wireless telephones. The CDMA signal is comprised of numerous individual user signals. The CDMA base station generates the CDMA signal by encoding each individual user signal with a unique spreading sequence, such as a pseudo random sequence. The CDMA base station then adds the encoded user signals together to form the CDMA signal.

In a CDMA system, individual user signals are not separated based on frequency or time, but are spread across the entire frequency band. Each CDMA communications device derives its particular user signal based on the unique spreading sequence. Due to this combination of multiple signals encoded with random sequences, the CDMA signal has random signal characteristics that create special power control concerns. CDMA base stations generate undesirable noise in the form of signal power outside of the frequency band of the CDMA signal. This undesirable power is referred to as out-of-band signal power. Out-of-band signal power is a problem because it interferes with other signals in the neighboring frequency bands. These other signals are disrupted by the interference. Government agencies, such as the Federal Communications Commission in the United States, strictly regulate the interference caused by out-of-band signal power.

An existing solution to the problem is implemented during base station testing. Test equipment is used to calculate a ratio for a test CDMA signal transmitted by the base station. The ratio represents the in-band signal power versus the out-of-band signal power. The base station transmit power is adjusted during the testing so the ratio is below a maximum value with a margin for some ratio increase under the maximum value. This usuallu Unfortunately, the ratio is not calculated and is not used during normal base station operation in the field. Test equipment is used to calculate the ratio, and base stations are not equipped to calculate the ratio in the field. Thus, the ratio is not automatically generated and used to control operation in the field where changes in temperature and load alter base station operation.

Another existing solution to this problem is to operate the CDMA base station so a ratio of the power out to the pilot signal does not exceed a value, such as five. This solution is lacking because a maximum power level based on the pilot signal is not an optimal estimate of the point where out-of-band signal power becomes a problem. As a result, the range and capacity of the base station is not optimized. CDMA systems would be improved through transmission at a power level just below the point where out-of-band signal power becomes a problem. Transmission at this power level would optimize the range and capacity of the base station.

SUMMARY OF THE INVENTION

The above-described problem is solved with CDMA transmission control technology. The CDMA transmission control technology allows a CDMA base station to operate at an optimized power level without generating improper amounts of out-of-band noise. The optimized power level extends the range and capacity of the base station. The increased range and capacity is passed on to the end-user in the form of decreased costs and increased functionality.

A transmitted CDMA signal has in-band components and out-of-band components. Transform logic automatically generates a ratio of the signal strength of the in-band components versus the out-of-band components. In some examples of the invention, control logic uses the ratios to generate metric signals that indicate if transmit power should be limited and that indicate excess forward link capacity. The invention eliminates the need to leave a margin during testing for future ratio increases. The elimination of this margin allows operation at higher power levels. BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

FIG. 1 is a block diagram of a CDMA system with transmission control logic; FIG. 2 is a graph illustrating the frequency spectrum of a CDMA signal;

FIG. 3 is a block diagram of a CDMA system with transmission control logic;

FIG. 4 is a block diagram of a CDMA base station with transmission control logic; FIG. 5 is a is a graph illustrating the frequency spectrum of portions of a

CDMA signal used for transmission control; and

FIG. 6 depicts a logical table used for transmission control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

CDMA Transmission Control Technology - FIGS. 1-2

FIG. 1 depicts a CDMA signal 100, a CDMA transmitter 101, an RF CDMA signal 102, and a CDMA receiver 103. CDMA is a spread-spectrum communications technology. Some versions of CDMA are specified by standards, such as IS-95 approved by the Telecommunications Industry Association. The CDMA signal 100 could be any CDMA signal, such as the signal produced by a cell site modem in a CDMA base station. The CDMA receiver 103 could be any CDMA device capable of receiving a CDMA signal, such as a wireless CDMA telephone.

The CDMA transmitter 101 transmits the CDMA signal 102 to the CDMA receiver 103. The CDMA transmitter 101 could be any CDMA transmission device that includes transmit control logic 116. One example of the CDMA transmitter 101 is a CDMA base station. The transmit control logic 116 in the CDMA transmitter 101 generates a ratio based on the signal strength of in-band versus out-of-band portions of the CDMA signal 102. Signal strength can be measured in various ways with examples being power, voltage, or energy. In some examples of the invention, the transmit control logic 116 generates metric signals that indicate if transmit power should be limited and that indicate excess forward link capacity.

FIG. 2 illustrates the frequency spectrum of a CDMA signal. The vertical axis represents signal power, and the horizontal axis represents frequency. The desired in-band signal power is contained within the bandwidth defined by corner frequencies around a center frequency. A typical example is a 1.25 MHz bandwidth centered about a 1.96 GHz center frequency with corner frequencies at (1.96 GHz - 625 KHz) and (1.96 GHz + 625 KHz). The signal power drops significantly outside of the bandwidth, but some undesired out-of-band signal power is still present and is shaded on FIG. 2. Out-of band signal power is undesirable because it represents wasted power that interferes with other signals in neighboring frequency bands.

CDMA System with Transmission Control Technology - FIGS. 3-5 FIGS. 3-5 depict a specific example of a CDMA system that uses the transmission control technology of the present invention, but those skilled in the art will recognize numerous other types of CDMA systems that are applicable to the invention described above.

FIG. 3 depicts a communications system 304 that is connected to the CDMA communications system 306. The CDMA communications system 306 communicates with CDMA communications devices 308. The CDMA communications system 306 is comprised of a switching center 310 and a base station 312. The communications system 304 exchanges communications signals 305 with the switching center 310. The switching center 310 exchanges communications signals 311 with the base station 312. The base station 312 exchanges wireless CDMA communications signals 307 over the air interface with the CDMA communications devices 308. Although the invention is depicted using an air interface, other transmission media could also be used, such as RF cable, power lines, or telephone lines. The communications system 304 could be any communications system capable of exchanging communications signals 305 with the CDMA communications system 306. The communications system 304 is typically a conventional public telephone network, but could also be many other networks, such as a local area network, wide area network, or internet. The switching center 310 could be any device that provides an interface between the base station 312 and the communications system 304. Typically, numerous base stations are connected to the communications system 304 through the switching center 310, but the number of base stations has been restricted for the purpose of clarity. The base station 312 exchanges wireless CDMA signals 307 with the CDMA communications devices 308. The base station 312 includes transmit control logic 316 that generates power and capacity metric signals based on ratios of the in-band versus out-of-band power in the CDMA signals 307. Those skilled in the art could adapt the base station 312 from known systems, such as the base stations provided by Qualcomm, Inc. of San Diego, California.

The CDMA communications devices 308 exchange wireless CDMA signals 307 with the base station 312. Typically, numerous CDMA communications devices exchange signals with the base station 312, but the number of communications devices has been restricted for the purpose of clarity. The typical CDMA communications device is a mobile telephone, but other CDMA communications devices are also possible, such as fixed wireless devices, data terminals, set-top boxes, or computers. In operation, the CDMA communications devices 308 communicate through the CDMA communications system 306 with the communications system 304 or with each other. On the forward link communications path from the communications system 304 to the CDMA communications devices 308, the transmit control logic 316 generates various ratios based on the in-band versus out-of-band power in portions of the CDMA signal 307. The transmit control logic 316 compares the ratios to pre-determined values that represent the point where out-of-band signal power becomes improper.

The transmit control logic 316 generates a power metric signal and a capacity metric signal based on the comparison. If one of the calculated ratios exceeds its associated pre-determined value, then the power metric signal indicates that the transmit power of the base station 312 should be limited. The capacity metric signal indicates an estimate of the excess forward link capacity of the base station 312. The estimate is typically given in a number of additional simultaneous calls that can be handled by the base station 312 without one of the calculated ratios exceeding its associated pre-determined value.

FIG. 4 depicts the base station 312 of FIG. 3 receiving the communications signals 311 and transmitting the CDMA communications signals 307. The base station 312 is comprised of the following elements connected in series: cell site modems 421, digital-to-analog conversion and filter 422, up-converter 423, gain limiter 424, power amplifier 425, and antenna 426. The transmit control logic 316 is coupled to the path between the power amplifier 425 and the antenna 426 to monitor the transmitted CDMA signal 307. The transmit control logic 316 is comprised of down-converter 432, transform logic 434, and control logic 436. Aside from the transmit control logic 316, those skilled in the art are familiar with these elements and their operation.

The cell site modems 421 produce a baseband CDMA signal and provide it to the digital-to-analog conversion and filter 422. The digital-to-analog conversion and filter 422 converts the CDMA signal to analog and filters out components outside of the desired bandwidth. The digital-to-analog conversion and filter 422 provides the CDMA signal to the up-converter 423. The up-converter 423 modulates the CDMA signal with intermediate and radio frequencies to form a Radio Frequency (RF) CDMA signal, and typically generates undesirable out-of-band signal power. The up-converter 423 provides the RF CDMA signal to gain limiter 424. The gain limiter 424 limits the power level of the RF CDMA signal based on a power metric signal 437. The gain limiter 424 provides the RF CDMA signal to the power amplifier 425. The power amplifier 425 amplifies the RF CDMA signal, and typically generates undesirable out-of-band signal power. The power amplifier 425 provides the amplified RF CDMA signal to the antenna 426 for transmission the RF CDMA signal 307.

The down-converter 432 of the transmit control logic 316 monitors the CDMA signal 307. The down-converter 432 de-modulates the RF CDMA signal 307 to form a baseband CDMA signal. The down-converter 432 provides the baseband CDMA signal to the transform logic 434.

FIG. 5 illustrates the frequency spectrum of the baseband CDMA signal received by the transform logic 434. Those skilled in the art recognize that FIG. 5 is an ideal representation of the signal. The vertical axis represents signal power, and the horizontal axis represents frequency. The desired in-band signal power is contained within the bandwidth defined by corner frequencies around a center frequency. Bandwidth segments 551-557 are shown. Bandwidth segment 551 is in-band, and bandwidth segments 552-557 are out- of-band. The power in each bandwidth segment 551-557 is shaded on FIG 5. The segments depicted on FIG. 5 are shown for illustrative purposes, and the actual segments used could vary in number or bandwidth. The segments could also be determined based on industry standards

The transform logic 434 performs Fast-Fourier transforms to generate values representing the power in each bandwidth segment 551-557. Those skilled in the art are familiar with the logic required to perform such Fast - Fourier transforms. The transform logic 434 then generates ratio values that will depend on the segments used. In this example, the following ratio values are generated: ratio 1 - bandwidth segment 551 power/bandwidth segment 552 power; ratio 2 - bandwidth segment 551 power/bandwidth segment 553 power; ratio 3 - bandwidth segment 551 power/bandwidth segment 554 power; ratio 4 - bandwidth segment 551 power/bandwidth segment 555 power; ratio 5 - bandwidth segment 551 power/bandwidth segment 556 power; ratio 6 - bandwidth segment 551 power /bandwidth segment 557 power.

The transform logic 434 generates a ratio signal 435 that indicates the ratio values and transfers the ratio signal 435 to the control logic 436. The control logic 436 compares each of the ratio values to an associated predetermined maximum value for the particular ratio. The control logic 436 determines if any of the calculated ratios exceed their respective maximum values.

FIG. 6 depicts a logical table containing the ratio values 1-6, the respective maximum values, an indication if the ratios exceed the maximum values, and the difference between the ratios and the maximum values. Those skilled in the art are aware that the table is a logical representation that is capable of numerous implementations using conventional technology. The letters A-G that are listed in the table for the power ratio entries represent actual power measurements. The letters H-M that are listed in the table for the maximum value entries represent actual maximum values that can be readily obtained in standard industry publications, such as IS-97 by the Telecommunication Industry Association. The Federal Communications Commission also publishes maximum ratio values. The control logic 436 of the base station 312 generates a power metric signal 437 and transfers it to gain limiter 424. The power metric signal 437 sets a flag in the gain limiter 424 if one of the ratios exceeds its maximum value. The flag causes the gain limiter 424 to limit the transmit power of the base station 312. The power metric signal 437 clears the flag when none of the ratios exceed their maximum values. In this fashion, the transmit power of the base station 312 is optimized to the point set by the maximum ratio values.

The control logic 436 of the base station 312 generates a capacity metric signal 438 and transfers it to a base station control system (not shown). The capacity metric signal 438 indicates an estimate of the excess forward link capacity of the base station 312. To generate the estimate, the control logic 436 determines the average difference between the measured ratios and the maximum values and translates the difference into a number of additional simultaneous calls that the base station 312 can handle without one of the calculated ratios exceeding its associated pre-determined value. The base station control system can determine whether or not to block call hand-offs or new calls based on the capacity metric signal 438. In this fashion, the number of simultaneous calls handled by the base station 312 is optimized to the point set by the maximum ratio values. Other applications of the ratio are described in United States patent applications assigned to the same entity as this application. The use of the ratio to control power amplifier pre-distortion is described in "Predistortion Technique For High Power Amplifiers", filed on June 26, 1998, and hereby incorporated by reference into this application. The use of the ratio to control decresting is described in "CDMA Signal Transmission Control", filed on the same date as this application, and hereby incorporated by reference into this application.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

WE CLAIM:

Claims

1. A method for Code Division Multiple Access (CDMA) signal processing comprising: transmitting a CDMA signal having in-band components and out-of band components; automatically generating a ratio of strength of at least a portion of the in-band components versus at least a portion of the out-of-band components; and automatically limiting transmit power based on the ratio.

2. The method of claim 1 further comprising automatically generating a power metric signal by comparing the ratio to a pre-determined value, and wherein automatically limiting the transmit power based on the ratio comprises automatically limiting the transmit power based on the power metric signal.

3. The method of claim 1 further comprising: automatically generating additional ratios using other portions of the out-of-band components; and automatically limiting the transmit power based on the additional ratios.

4. The method of claim 1 wherein the strength is based on power.

5. The method of claim 1 wherein the strength is based on voltage.

6. The method of claim 1 wherein the strength is based on energy.

7. The method of claim 1 further comprising generating the CDMA signal.

8. The method of claim 1 wherein the method is performed by a CDMA base station.

9. The method of claim 1 further comprising generating a capacity metric signal based on the ratio.

10. A method for Code Division Multiple Access (CDMA) signal processing comprising: transmitting a CDMA signal having in-band components and out-of band components; automatically generating a ratio of strength of at least a portion of the in- band components to at least a portion of the out-of-band components; and automatically generating a metric signal based on the ratio.

11. The method of claim 10 wherein the metric signal is a power metric signal.

12. The method of claim 11 further comprising automatically limiting transmit power based on the power metric signal.

13. The method of claim 10 wherein the metric signal is a capacity metric signal.

14. The method of claim 10 wherein the metric signal indicates if the ratio exceeds a pre-determined value.

15. The method of claim 10 further comprising: automatically generating additional ratios using other portions of the out-of-band components; and automatically generating the metric signal based on the additional ratios.

16. The method of claim 10 wherein the strength is based on power.

17. The method of claim 10 wherein the strength is based on voltage.

18. The method of claim 10 wherein the strength is based on energy.

19. The method of claim 10 further comprising generating the CDMA signal.

20. The method of claim 10 wherein the method is performed by a CDMA base station.

21. A Code Division Multiple Access (CDMA) device for processing a CDMA signal having in-band components and out-of band components, the device comprising: transform logic that is operational to automatically generate a ratio of strength of at least a portion of the in-band components to at least a portion of the out-of-band components; and control logic that is operational to automatically generate a power metric signal based on the ratio.

22. The CDMA device of claim 21 further comprising a gain limiter operational to limit transmit power based on the power metric signal.

23. The CDMA device of claim 21 wherein the CDMA device is a CDMA base station.

24. The CDMA device of claim 21 wherein: the transform logic is further operational to automatically generate additional ratios using other portions of the out-of-band components; and the control logic is further operational to automatically generate the power metric signal based on the additional ratios.

25. The CDMA device of claim 21 wherein the strength is based on power.

26. The CDMA device of claim 21 wherein the strength is based on voltage.

27. The CDMA device of claim 21 wherein the strength is based on energy.

28. The CDMA device of claim 21 wherein the control logic is operational to automatically generate a capacity metric signal based on the ratio.

29. The CDMA device of claim 21 further comprising a cell site modem operational to generate the CDMA signal.

30. The CDMA device of claim 21 further comprising a digital-to- analog converter operational to convert the CDMA signal from digital to analog.

31. The CDMA device of claim 21 further comprising a low-pass filter operational to attenuate portions of the CDMA signal outside of a bandwidth.

32. The CDMA device of claim 21 further comprising an up-converter operational to convert the CDMA signal to a radio frequency CDMA signal.

33. The CDMA device of claim 21 further comprising a power amplifier operational to amplify the CDMA signal.

34. The CDMA device of claim 21 further comprising an antenna operational to transmit the CDMA signal.

35. A Code Division Multiple Access (CDMA) device for processing a CDMA signal having in-band components and out-of band components, the device comprising: transform logic that is operational to automatically generate a ratio of strength of at least a portion of the in-band components to at least a portion of the out-of-band components; and control logic that is operational to automatically generate a capacity metric signal based on the ratio.

36. The CDMA device of claim 35 wherein the transmit metric signal indicates excess forward link capacity.

37. The CDMA device of claim 36 wherein the excess forward link capacity is a number of simultaneous calls.

38. The CDMA device of claim 35 wherein: the transform logic is further operational to automatically generate additional ratios using other portions of the out-of-band components; and the control logic is further operational to automatically generate the capacity metric signal based on the additional ratios.

39. The CDMA device of claim 35 wherein the strength is based on power.

40. The CDMA device of claim 35 wherein the strength is based on voltage.

41. The CDMA device of claim 35 wherein the strength is based on energy.

42. The CDMA device of claim 35 further comprising a cell site modem operational to generate the CDMA signal.

43. The CDMA device of claim 35 further comprising a digital-to- analog converter operational to convert the CDMA signal from digital to analog.

44. The CDMA device of claim 35 further comprising a low-pass filter operational to attenuate portions of the CDMA signal outside of a bandwidth.

45. The CDMA device of claim 35 further comprising an up-converter operational to convert the CDMA signal to a radio frequency CDMA signal.

46. The CDMA device of claim 35 further comprising a power amplifier operational to amplify the CDMA signal.

47. The CDMA device of claim 35 further comprising an antenna operational to transmit the CDMA signal.

48. The CDMA device of claim 35 wherein the CDMA device is a CDMA base station.