KR20010103047A - Cdma signal transmission using ratios of in-band and out-of-band signals - Google Patents

Abstract

The present invention is a CDMA signal transmission control technique 316. The transmitted CDMA 307 signal has an in-band component and an out-of-band component. The transmit control logic 316 automatically generates a ratio of the strength of the out-of-band component to the in-band component. In some embodiments of the invention, control logic 436 generates a transmit power metric signal based on this ratio. In another embodiment of the present invention, control logic 436 determines the excess forward link capacity based on this ratio. CDMA signal transmission control technique 166 may be implemented in CDMA base station 312.

Description

CDMA signal transmission using ratio of in-band and out-of-band signal {CDMA SIGNAL TRANSMISSION USING RATIOS OF IN-BAND AND OUT-OF-BAND SIGNALS}

Code Division Multiple Access (CDMA) technology is commonly used in communication systems. In a typical CDMA system, a CDMA base station transmits a CDMA signal to many CDMA communication devices, such as a wireless telephone. CDMA signals include the signals of multiple individual users. The CDMA base station generates a CDMA signal by encoding each individual user signal into a unique spreading sequence, such as a pseudo random sequence. The CDMA base station then combines the encoded user signals together to form a CDMA signal.

In a CDMA system, individual user signals are not separated based on frequency or time, but spread over the entire frequency band. Each CDMA communication device finds a particular user signal based on a unique spreading sequence. Due to the combination of multiple signals encoded with a random sequence, the CDMA signal has random signal characteristics that cause special power control problems.

The CDMA base station generates undesirable noise in the form of signal power outside 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 adjacent frequency bands. These other signals are interrupted by interference. Government agencies, such as the US Federal Communications Commission, strictly regulate interference caused by out-of-band signal power.

The existing solution to this problem is implemented in base station testing. The test equipment is used to calculate the ratio for the test CDMA signal transmitted from the base station. This ratio represents the ratio of in-band signal power to out-of-band signal power. The base station transmit power is adjusted during the test so that the ratio is less than the maximum and has a margin for some rise in the ratio below the maximum. Unfortunately, the ratio is not calculated in this field and is not used during normal base station operation. Test equipment is used to calculate the ratio, and base stations in this field are not equipped to calculate the ratio. Thus, the ratio is not automatically generated, and changes in temperature and load are used to control the operation in the field of changing the operation of the base station.

Another existing solution to this problem is to operate a CDMA base station so that the ratio of power out to pilot signal does not exceed a value equal to five. Since the maximum power level based on the pilot signal is not an optimal measure of the point where out-of-band signal power is a problem, this solution is lacking. As a result, the range and capacity of the base station is not optimized.

CDMA systems are improved by transmitting at power levels slightly below the point where out-of-band signal power is a concern. Transmission at this power level optimizes the range and capacity of the base station.

The present invention relates to a code division multiple access (CDMA) system. In particular, the present invention includes, but is not limited to, a new and improved CDMA base station that produces a ratio of the in-band signal strength to in-band signal used for base station transmission control.

The features, objects and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals indicate correspondingly corresponding throughout the figures.

1 is a block diagram of a CDMA system with transmission control logic.

2 is a diagram illustrating a frequency spectrum of a CDMA signal.

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

4 is a block diagram of a CDMA base station with transmission control logic.

5 is a diagram illustrating the frequency spectrum of portions of a CDMA signal used for transmission control.

6 is a diagram illustrating a logic table used for transmission control.

The problem described above is solved as a CDMA transmission control technique. CDMA transmission control techniques allow a CDMA base station to operate at an optimized power level without generating an inappropriate amount of out-of-band noise. This optimized power level extends the range and capacity of the base station. Increased range and capacity are delivered to end users in the form of reduced cost and increased performance.

The transmitted CDMA signal has an in-band component and an out-of-band component. The transformation logic automatically generates the ratio of the signal strength of the in-band component to the signal strength of the out-of-band component. In some embodiments of the invention, the control logic uses the ratio to generate metric signals that indicate whether transmit power should be limited and excessive forward link capacity. The present invention eliminates the need to leave margin during testing for future rain increases. Elimination of this margin allows operation at high power levels.

CDMA Transmission Control Techniques-Figure 1-2

1 shows a CDMA signal 100, a CDMA transmitter 101, an RF CDMA signal 102 and a CDMA receiver 103. CDMA is a spread spectrum communication technology. Some versions of CDMA are specified by standards such as IS-95, approved by the Telecommunications Industry Association (TIA). The CDMA signal 100 may be any CDMA signal, such as a signal generated at a cell site modem of a CDMA base station. CDMA receiver 103 may be any device capable of receiving CDMA signals, such as a wireless CDMA telephone.

CDMA transmitter 101 transmits CDMA signal 102 to CDMA receiver 103. CDMA transmitter 101 may be any CDMA transmission device that includes transmission control logic 116. One example of a CDMA transmitter 101 is a CDMA base station.

The transmission control logic 116 of the CDMA transmitter 101 generates a ratio based on the in-band signal to out-of-band signal strength of the CDMA signal 102 portion. Signal strength can be measured in a variety of ways, such as power, voltage, or energy. In some embodiments of the invention, the transmit control logic 116 generates a metric signal that indicates whether transmit power should be limited and excessive forward link capacity.

2 shows the frequency spectrum of a CDMA signal. The vertical axis represents signal power and the horizontal axis represents frequency. Preferred in-band signal power is included in the bandwidth defined by the corner frequencies around the center frequency. A typical example is the frequency band of 1.25 MHz with a corner frequency of (1.96 GHz + 625 KHz) and (1.96 GHz-625 KHz) at the center frequency of 1.96 GHz. Signal power is drastically reduced outside the frequency band, but some out-of-band signal power still remains and is shaded in FIG. Out-of-band signal power is undesirable because it represents wasted power that interferes with other signals in adjacent frequency bands.

CDMA System with Transmission Control Technology—Figure 3-5.

3-5 illustrate specific examples of a CDMA system utilizing the transmission control technique of the present invention, those skilled in the art will recognize various types of CDMA systems applicable to the present invention described above.

3 illustrates a communication system 304 coupled to a CDMA communication system 306. CDMA communication system 306 communicates with CDMA communication device 308. CDMA communication system 306 includes a switching center 310 and a base station 312. The communication system 304 exchanges communication signals 305 with the switching center 310. The switching center 310 exchanges a communication signal 311 with the base station 312. Base station 312 exchanges a wireless CDMA communication signal 307 with a CDMA communication device 308 via an air interface. Although the present invention uses an air interface, other transmission media such as RF cables, power lines, and telephone lines may also be used.

Communication system 304 is any communication system capable of exchanging communication signals 305 with CDMA communication system 306. Communication system 304 is typically a conventional public telephone network, but may be any other network, such as a local area network (LAN), wide area network (WAN), or the Internet.

The switching center 310 may be any device that provides an interface between the base station 312 and the communication system 304. Typically, several base stations are connected to the communication system 304 through the switching center 310, but the number of base stations has been limited for clarity of explanation.

Base station 312 exchanges a wireless CDMA signal 307 with a CDMA communication device 308. Base station 312 includes transmit control logic 316 that generates power and capacity metric signals based on the ratio of in-band to out-band power of CDMA signal 307. Those skilled in the art will be able to adapt the base station 312 from known systems, such as the base station provided by Qualcomm Incorporated, San Diego, California.

CDMA communication device 308 exchanges CDMA signal 307 with base station 312. Typically, many CDMA communication devices exchange signals with a base station 312, but the number of communication devices is limited for clarity. Typical CDMA communication devices are mobile phones, but other CDMA communication devices are also possible, such as fixed wireless devices, data terminals, set-top boxes, or computers.

In operation, CDMA communication devices 308 communicate with communication system 304 or with each other via CDMA communication system 306. In the forward link communication path from communication system 304 to CDMA communication device 308, transmission control logic 316 generates various ratios based on the in-band to out-of-band power of CDMA signal 307. The transmit control logic 316 compares the ratio with predetermined values that indicate the point at which the out-of-band signal power is inappropriate.

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 an associated predetermined value, the power metric signal indicates that the transmit power of the base station 312 should be limited. The capacity metric signal represents an estimate of the excess forward link capacity of the base station 312. Estimates are typically given to a number of additional simultaneous calls that can be processed without exceeding any value associated with any of the calculated specific gravity.

4 shows the base station 312 of FIG. 3 receiving a communication signal 311 and a transmit CDMA communication signal 307. The base station 312 is configured by connecting the following elements in series: a cell site modem 421, a D / A conversion and filter 422, an up-converter 423, a 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 CDMA signal 307 transmitted. The transmit control logic 316 includes a down-converter 432, a transform logic 434, and a control logic 436. Apart from the transmit control logic 316, those skilled in the art will be familiar with these elements and their operation.

The cell site modem 421 generates a baseband CDMA signal and provides it to the D / A conversion and filter 422. D / A conversion and filter 422 converts the CDMA signal to analog and filters components outside the desired bandwidth. D / A conversion and filter 422 provides the CDMA signal to upconverter 423. Up-converter 423 modulates the CDMA signal to intermediate and radio frequencies to form a radio frequency (RF) CDMA signal, and typically generates undesirable out-of-band signal power. Upconverter 423 provides an RF CDMA signal to gain limiter 424. Gain limiter 424 limits the power level of the RF CDMA signal based on power metric signal 437. Gain limiter 424 provides an RF CDMA signal to power amplifier 425. 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 of the RF CDMA signal 307.

Downconverter 432 of transmit control logic 316 monitors CDMA signal 307. The down converter 432 demodulates the RF CDMA signal 307 to form a baseband CDMA signal. Down converter 432 provides the baseband CDMA signal to transform logic 434.

5 shows the frequency spectrum of the baseband CDMA signal received by transform logic 434. Those skilled in the art will appreciate that Figure 5 is an ideal representation of the signal. The vertical axis represents signal power and the horizontal axis represents frequency. Preferred in-band signal power is included in the bandwidth defined by the corner frequency around the 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 shown in FIG. 5 in shades. The segments shown in FIG. 5 are shown for illustrative purposes, and the actual segments used may vary in number or bandwidth. Segments can also be determined according to industry standards.

Transform logic 434 performs a Fast-Fourier transform to generate values indicative of the power of each bandwidth segment 551-557. Those skilled in the art will be familiar with the logic required to perform this fast-Fourier transform. Transform logic 434 generates non-values depending on the segment 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;

Non 6-bandwidth segment 551 power / bandwidth segment 557 power;

Transform logic 434 generates a ratio signal 435 representing the ratio value, and passes ratio signal 435 to control logic 436. Control logic 436 compares each of the ratio values with a predetermined maximum associated with a particular ratio. Control logic 436 determines whether any one of the calculated specific gravity exceeds their respective maximum value.

FIG. 6 shows a logic table containing ratios 1-6, each maximum value, an indication of whether the ratio has exceeded the maximum value, and the difference between the ratio value and the maximum value. Those skilled in the art will appreciate that a table is a logical representation of which many implementations are possible using conventional techniques. The letters A-G of the power ratio items listed in the table represent actual power measurements. The letter H-M of the maximum value entry listed in the table represents the actual maximums that can be easily obtained from standard industry publications such as IS-97 published by the Telecommunications Industry Association (TIA). The Federal Communications Commission also publishes maximum non-valued values.

Control logic 436 of base station 312 generates power metric signal 437 and passes it to gain limiter 424. The power metric signal 437 sets the flag of the gain limiter 424 if either specific gravity exceeds the maximum. The flag causes the gain limiter 424 to limit the transmit power of the base station 312. If neither specific gravity exceeds the maximum, the power metric signal 437 releases the flag. In this way, the transmit power of the base station 312 is optimized to the point set by the maximum ratio values.

Control logic 436 of base station 312 generates capacity metric signal 438 and sends it to a base station control system (not shown). The capacity metric signal 438 represents an estimate of the excess forward link capacity of the base station 312. To generate an estimate, control logic 436 determines an average difference between the measured ratio and the maximum values, and the base station 312 can process the difference without any of the calculated weights exceeding a predetermined value. Translate into multiple additional concurrent calls. The base station control system determines whether to block call handoff or new calls based on the capacity metric signal 438. In this way, the number of concurrent calls handled by the base station 312 is optimized to the point set by the maximum ratio values.

Another application of the ratio is described in the U.S. patent application assigned to the applicant of the present invention. The use of the ratio to control the pre-distortion of the power amplifier is described in "Predistortion Technique For High Power Amplifiers", filed June 26, 1998 and incorporated herein by reference. The use of the ratio to control deresting is described in "CDMA Signal Transmission Control", filed June 26, 1998 and incorporated herein by reference.

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

Claims (48)

A method of processing a code division multiple access (CDMA) signal, Transmitting a CDMA signal having an in-band component and an out-of-band component; Automatically generating a ratio of the strength of at least a portion of the out of band component to the strength of the at least a portion of the in-band component; And Automatically limiting transmission power based on the ratio. The method of claim 1, Comparing the ratio with a predetermined value to automatically generate a power metric signal, And automatically limiting the transmission power based on the ratio comprises automatically limiting the transmission power based on the power metric signal. The method of claim 1, Automatically generating additional ratios using other portions of the out of band components; And Automatically limiting the transmit power based on the additional ratio. The method of claim 1, And said intensity is based on power. The method of claim 1, And said intensity is based on voltage. The method of claim 1, And said intensity is based on energy. The method of claim 1, Generating the CDMA signal. The method of claim 1, The method being performed at a CDMA base station. The method of claim 1, Generating a capacity metric signal based on the ratio. A method of processing a code division multiple access (CDMA) signal, Transmitting a CDMA signal comprising an in-band component and an out-of-band component; Automatically generating a ratio of intensities of at least a portion of the out of band component to at least a portion of the in-band component; And Automatically generating a metric signal based on the ratio. The method of claim 10, The metric signal is a power metric signal. The method of claim 11, And automatically limiting transmit power based on the power metric signal. The method of claim 10, The metric signal is a capacitive metric signal; The method of claim 10, The metric signal indicates whether the ratio has exceeded a predetermined value. The method of claim 10, Automatically generating additional ratios using other portions of the out-of-band component; And And automatically generating the metric signal based on the additional ratio. The method of claim 10, And said intensity is based on power. The method of claim 10, And said intensity is based on a power source. The method of claim 10, And said intensity is based on energy. The method of claim 10, Generating the CDMA signal. The method of claim 10, The method being performed at a CDMA base station. A code division multiple access (CDMA) apparatus for processing a CDMA signal having in-band components and out-of-band components, Transform logic that automatically operable to generate a ratio of the strength of at least a portion of the out-of-band component to the strength of the at least portion of the in-band component; And And control logic operable to automatically generate a power metric signal based on the ratio. The method of claim 21, And a gain limiter operable to limit transmission power based on the power metric signal. The method of claim 21, And the CDMA device is a CDMA base station. The method of claim 21, The transform logic operates to automatically generate additional ratios using other portions of the out of band component, The control logic is further operable to automatically generate the power metric signal based on the additional ratio. The method of claim 21, And said intensity is based on power. The method of claim 21, And said intensity is based on a power source. The method of claim 21, And said intensity is based on energy. The method of claim 21, And the control logic is operable to automatically generate a capacitive metric signal based on the ratio. The method of claim 21, And a cell site modem operable to generate the CDMA signal. The method of claim 21, And a D / A converter operable to convert the CDMA signal from digital to analog. The method of claim 21, And a low-pass filter operable to attenuate portions of the CDMA signal out of bandwidth. The method of claim 21, And an up-converter operable to convert the CDMA signal into a radio frequency CDMA signal. The method of claim 21, And a power amplifier operable to amplify the CDMA signal. The method of claim 21, And an antenna operable to transmit the CDMA signal. A code division multiple access (CDMA) apparatus for processing a CDMA signal having in-band components and out-of-band components, Transform logic operable to automatically generate a ratio of the intensity of at least a portion of the out-of-band component to the intensity of the at least portion of the in-band component; And And control logic to automatically generate a capacitive metric signal in operation based on the ratio. 36. The method of claim 35 wherein The transmission metric signal is indicative of excess forward link capacity. The method of claim 36, Wherein the excess forward link capacity is a plurality of simultaneous calls. 36. The method of claim 35 wherein The transform logic operates to automatically generate additional ratios using other portions of the out of band component, And the control logic operates to automatically generate the capacitive metric signal based on the additional ratio. 36. The method of claim 35 wherein And said intensity is based on power. 36. The method of claim 35 wherein And said intensity is based on a power source. 36. The method of claim 35 wherein And said intensity is based on energy. 36. The method of claim 35 wherein And a cell site modem operable to generate the CDMA signal. 36. The method of claim 35 wherein And a D / A converter operable to convert the CDMA signal from digital to analog. 36. The method of claim 35 wherein And a low-pass filter operable to attenuate the portion of the CDMA signal out of bandwidth. 36. The method of claim 35 wherein And an upconverter operable to convert the CDMA signal into a radio frequency CDMA signal. 36. The method of claim 35 wherein And a power amplifier operable to amplify the CDMA signal. 36. The method of claim 35 wherein And an antenna operable to transmit the CDMA signal. 36. The method of claim 35 wherein And the CDMA device is a CDMA base station.