JP2003500978A - Improved reverse path automatic gain control - Google Patents

Abstract

(57) Abstract: In a wireless microcell distribution system, a method is provided for adjusting the level of a signal from a microcell, which uses a shortened gain tone to minimize interference with telephone calls. Is becoming Further, the gain tones for the primary and diversity receive paths from the microcell are generated independently, not simultaneously, to minimize interference with the call. In one embodiment, each gain tone is limited to 120 milliseconds, thereby limiting the overall duration of one gain tone in the primary or diversity path to 120 milliseconds. The measurement of the gain tones is likewise made independently, and rather than turning on both gain tones simultaneously over the entire measurement period, each gain tone is a measure of the gain tone relative to the primary or diversity receive path. Only needs to be on for a part of the measurement period corresponding to. Further, the absolute amplitude of the gain tone is reduced to minimize the impact of automatic gain control on the system, and the shortened gain tone is injected after the first down conversion stage. , The power level at which the gain tone is injected can be increased, thus improving vulnerability to noise.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION

FIELD OF THE INVENTION The present invention relates to wireless microcell distribution systems, and more particularly to reverse path automatic gain control systems for producing shortened reduced-amplitude gain tones.

[0002]

[Prior art]

In a wireless microcell distribution system that includes receiving signals from multiple microcells that are simultaneously transmitted to summing points in simulcast mode, the level adjustments should be made so that the reverse path signals from the microcells are at the same level There exists the condition that the areas covered by the various microcells must not disappear when a non-equilibrium occurs due to. This occurs when the signal from one microcell is significantly higher than the signal from another microcell. In such a case, a situation arises in which the wireless handset at the fringe of the coverage area for a given microcell must approach that microcell in order for its signal to be detected. Sometimes.

The reason for the disappearance of the coverage area of a microcell with low power is that the system detects a high level signal from an unregulated microcell and at the same time signals below that level from the microcell. Is rejected. The net result is a call break in the perimeter region. Therefore, wireless microcell signal distribution systems require that the signals from the microcells on the reverse path are all at the same level.

In a typical wireless microcell distribution system, each microcell has a transceiver and other circuitry referred to as a cable microcell integrator. The signal from the cable microcell integrator is
Added and coupled to the headend interface converter. The headend interface converter processes the return path signal and sends it to the base station.

Conventionally, as described in US patent application Ser. No. 08 / 998,874 filed by John Sabat, Jr. on Dec. 24, 1997 (this US patent application was assigned The gain tones generated by the cable microcell integrator, which is assigned to a person and incorporated by reference in the present application.
Automatic level adjustment is achieved by transmitting the tones to the headend interface converter and measuring the amplitude at the headend interface converter. After measuring the amplitude for a given gain tone, the headend interface converter sends a message to the cable microcell integrator, adjusting the attenuator in the cable microcell integrator, The signal arriving at this cable microcell integrator is at a standard level.

Each cable microcell integrator has a primary antenna and a diversity antenna. The reason is to compensate for the effects of fading or phase cancellation in the microcell. Conventionally, a gain tone generator is used to inject a gain control signal in front of the first down conversion stage of each receiver to provide gain gain along the primary and diversity paths to the headend interface converter. It was made to inject the tone. Tones injected before the first down conversion stage have proven difficult to control.

The system described above works reasonably well, but the duration of the gain tone is longer than 800 ms, which causes interference with the telephony signal transmitted to the headend interface converter. there is a possibility. In some cases, the gain tone duration will be in conflict with the telephone signal. The longer the duration of the gain tone, the more likely it is to interfere with the telephone signal.

Furthermore, higher gain tone amplitudes are also more likely to cause interference with telephone signals, so a system with small gain tone amplitudes is desired.

Further, in the system described above, each cable microcell integrator is instructed by the headend interface converter to simultaneously turn on its corresponding gain tone generator. Once a sufficient amount of gain tones are received, the headend interface converter will
Instruct the Cable Microcell Integrator to stop transmitting gain tones. As a result, all timing for the generation of gain tones is achieved in the headend interface converter, rather than in the cable microcell integrator, thereby increasing the duration of the gain tones. The effect occurs and reduces the overall efficiency of the system somewhat.

[0010]

[Outline of the Invention]

Unlike the system described above, the system according to the invention generates gain tones independently for each of the primary and diversity paths, which causes the gain tones for the primary path to turn on and then off. , And then the gain tone for the diversity path is turned on and off. It has been found that in such a scheme, the gain tone need not be on continuously throughout the measurement period. Importantly, the gain tone duration is dramatically reduced to reduce interference, but still provide a robust system. In one embodiment, the duration of each gain tone is reduced to 100 ms instead of 400 ms. This has multiple gain tones
It is meant to be independently on for only 120 ms for each path, rather than being on for a total of over 800 ms at the same time, thereby allowing microcell to headend interface converters. The interference with the telephone signal returning to is minimized.

Further, the amplitude of the gain tone is preset to be lower than the cumulative level for the reverse path signal from the cable microcell integrator. This is in contrast to setting the gain tone amplitude to the maximum cumulative amplitude allowed for the carrier. In the case of the 6 cable microcell integrator, the cumulative acceptable level is at -93 dBm level. For this purpose, the signals from six cable microcell integrators are listed, but the number of reverse path signals is the number of cable microcell integrators added at a given point. Dependent.

As will be appreciated, the amplitude of the gain tones can be reduced to minimize interference. Also, the duration of the gain tone can be shortened to minimize interference.

In addition, each cable microcell integrator is provided with a timer to clock the start and stop of each gain tone, and the headend interface converter starts and stops each tone. Providing a message to Cable Microcell Integrators about the fire that will stop. Therefore, the timing for the gain control tones is controlled by the cable microcell integrator upon receiving the message from the headend interface converter, which constitutes a more efficient automatic gain control system.

Furthermore, an algorithm is provided in the headend interface converter. This algorithm sets a window for the measurement of the gain tone amplitude, thereby delaying the measurement window from the expected onset of the gain tone sufficiently to avoid false measurements.

As a result, a robust and automatic reverse path gain control system is provided,
The level of reverse path transmission from the microcell integrator can be adjusted to avoid shrinking the coverage area of a given microcell due to signal imbalance in the headend interface converter.

Furthermore, rather than injecting gain control tones in the primary and diversity circulators coupled to the primary and diversity receive antennas, the reduced gain tones after the first down conversion stage for the primary and diversity paths are Is inserted, which allows more control over the gain tone amplitude.

In summary, in a wireless microcell distribution system, there is provided a method for leveling signals from microcells, which uses shortened gain tones to minimize interference with telephone calls. It has become. Furthermore, the gain tones for the primary and diversity receive paths from the microcells occur independently rather than simultaneously to minimize call interference. In one embodiment,
Each gain tone is limited to 120 ms, which limits the overall duration of one gain tone in the primary or diversity path to 120 ms. Gain tone measurements are likewise made independently, with each gain tone measuring the gain tone relative to the primary or diversity receive path, rather than turning both gain tones on simultaneously throughout the measurement period. Need only be on for a portion of the measurement period corresponding to. In addition, gain
The absolute amplitude of the tone is shortened to minimize the impact of automatic gain control on the system, and this shortened gain tone is injected after the first down conversion stage to provide the gain tone. Can increase the injected power level and thus improve vulnerability to noise.

[0018]

DETAILED DESCRIPTION OF THE INVENTION

The above and other features of the present invention can be better understood with reference to the following detailed description and the accompanying drawings.

Referring to FIG. 1, in a typical wireless microcell distribution system, a number of microcells 10, 12, 14 that function as cell sites are coupled to a headend interface converter 18 and a handset 20 to a base. The signal is provided via the reverse path to a summing unit 16 which provides the telephone signal received to the station.

In this case, the signals from the microcells are provided through the network, in which the amplitude of the signals from the respective microcells along the paths 22, 24, 26 is mainly Fluctuates due to temperature differences in multiple microcells.

As already mentioned, each microcell contains one cable microcell integrator. For each cable microcell integrator, the temperature inside the device in a plurality of microcells will be significantly different depending on conditions such as how sunlight shines and changes in wind. As a result, the signal from some cable microcell integrators is considered "hot" in the sense that it is about 10 dB above the preset maximum level at the summing point. Thus, for example, the signals on paths 24 and 26 are 10 dB above this level.
If high, the signals along path 22 will be nearly overwhelmed by these signals. The net result is that the coverage area of the microcell 10 is
This imbalance, illustrated by the dotted circles 30, 32, 34, causes a reduction. If this imbalance continues to exist, many calls are expected to break.

Referring now to FIG. 2, a wireless microcell distribution system is shown, in this case a number of cable microcell integrators 40, 42, 44 ,.
46 each have a primary antenna 48 and a diversity antenna 50, providing signals along the reverse path to a summing point 52.

The result of the signal from the handset 53 being received at the primary and diversity antennas is the carrier from each of these cable microcell integrators. The primary and diversity signals on this carrier are
2 to the headend interface converter 54, and thus
It is transmitted to the base station 56.

Cable microcell integrator 40, as illustrated in FIG.
Includes a gain tone generator 6 in each of the primary and diversity reverse paths.
0 and 62 are provided. The respective outputs of these gain control generators are provided to transceivers 64 and 66, which in one embodiment are CDMA receivers, and are further provided to headend interface converter 54 via adjustable attenuators 68 and 70. Sent. This results in a gain tone whose amplitude is measured by the headend interface converter.

As illustrated by waveform 72, primary and diversity path carriers 74 and 76 each carry an appropriate gain tone 78 and 80. In one embodiment, these gain tones are offset by 400 KHz from the center frequencies of the primary and diversity channels, each having a duration of 400 milliseconds.

Referring now to FIG. 4, the gain tones for the primary and diversity paths are shaded, and shaded portions 82 and 84 have an overall gain tone duration of 800 mm. It illustrates having the order of seconds. This is because the gain tones continuously turn on during the measurement period, regardless of the time window in which these gain tones are sampled as illustrated by waveforms 86 and 88. In conventional systems, the gain tones were on for the entire 800 ms, independent of the measurement window at the headend interface converter.

Referring now to FIG. 5, as can be seen from waveforms 90 and 92, the amplitudes of the associated gain tones in the primary and diversity reverse paths are 94 and 9, respectively.
6 is shown. The primary reverse path is sampled at the time indicated by arrow 98, while the diversity path is sampled at the time illustrated by arrow 100. Therefore, as shown in FIG. 4, sampling is done sequentially and the gain tone generation is both turned on at all times during the sampling window in which was synthesized.

Referring to FIG. 6, in the system according to the present invention, the gain tones for the primary reverse path 102 are limited to 100 ms in one embodiment, rather than the gain tones being on all the time. , The gain tones for diversity path 104 are similarly limited to 100 ms. Obviously, in the system according to the invention, the two gain tones are turned on sequentially rather than on at the same time. In this way, tones are generated independently.

Further, as illustrated in FIG. 7, the corresponding gain tone amplitudes 106 and 108 are designed so that their amplitudes are smaller than those associated with envelopes 110 and 112.

More specifically, referring to FIG. 8, assuming that the signals from six different cable microcell integrators are coupled to the summing point, then as illustrated by carrier level 120, the overall Amplitude is only -93 dBm
Is set to.

It has been found using the system according to the invention that the gain tone 122
Can be robust with respect to reception and measurement while being set 10 dB below the carrier level 120.

The problem of gain tones interfering with telephone signals in the reverse path can be largely eliminated as a result of the reduced amplitude and reduced duration of the gain tones.

More specifically, referring to FIG. 9, in the system according to the present invention, the headend interface converter 54 has a message that controls the gain tone generator in the cable microcell integrator for the primary and diversity paths. Generators 124 and 126 are provided. In this case, the cable microcell integrator 40 has a headend interface
A decoder is provided for decoding the message from the converter, and the decoder 128 decodes the message for the primary path gain tone and the diversity path gain tone at 130. The decoded message is provided to units 132 and 134 to activate their respective gain tones for the required time. A clock signal from clock 136 is provided to each of these units.

In operation, the headend interface converter sends a message to the cable microcell integrator, turning on the corresponding gain tone. Units 132 and 134 then energize the gain tone generators to provide start and stop of the respective gain tones at the appropriate times. In this way, the generation of gain tones is timed in the cable microcell integrator in response to the message from the headend interface converter.

Referring to FIG. 10, in the headend interface converter, the window for the detection and measurement of the gain tone amplitude is set as illustrated in waveforms 140 and 142. Although it should be discontinued, in one embodiment the gain generated by the cable microcell integrator is
The tone is nominally set to 120 microseconds and the headend interface converter measurement window is nominally set to 88 milliseconds. Headend
The interface converter is provided with a programmable delay 144 that can be set to never miss a gain tone. In this way, the delay associated with the distance from the cable microcell integrator to the headend interface converter can be obtained. Delays or losses due to distance as well as temperature fluctuations can be compensated directly in the headend interface converter, thereby ensuring the reception of gain tones.

Referring now to FIG. 11, in one embodiment the temperature sensor 150 is
Provided in the microcell integrator 40, it senses temperature on a real-time basis and provides that temperature to the temperature compensation table 152 inside the headend interface converter 54 via the reverse channel 151. Here, the gain tones are illustrated as being transmitted via the reverse path 154 to the measurement unit 155 inside the headend interface converter. The measurement unit measures the absolute amplitude and generates a message at 156. This message is then sent to the attenuator 158 inside the cable microcell integrator.

The message sent has been modified from that established by the absolute amplitude measured at 155 and the temperature compensation table is used to fine tune the point at which the attenuator 158 is set. In this way, a very precise control is performed on the output from each cable microcell integrator, whereby a precise balance can be achieved.

Referring to FIG. 12, in one embodiment, the circuitry within the cable microcell integrator is illustrated. The signals from the primary and diversity antennas are coupled to circulators 160 and 162, which circulator 160
And 162 are connected to appropriate bandpass filters and amplifiers 164 and 166. Local oscillator 168 is coupled to splitter 170, which provides signals to mixers 172 and 174 in corresponding channels. The purpose of this mixing operation is to downconvert the signals from the primary and diversity antennas. In the preferred embodiment, the outputs of these mixers are connected to couplers 176 and 178, which are provided with the gain tones generated at 180 and 182. Not an antenna
The mixing of gain tones in this down conversion stage allows gain tones with high amplitude to be easily generated. If the gain tones are typically injected at 2 GHz before down conversion, it is difficult to obtain the proper gain tone amplitude because of the high frequencies involved. Injecting after the first down conversion stage solves this problem.

The outputs of couplers 176 and 178 are sawtooth filters and amplifiers 180 and 18
2 and is further coupled to attenuators 184 and 186 having attenuation adjusted according to the message sent from the headend interface converter. The output of the attenuator is then down converted by mixers 190 and 192. The mixers 190 and 192 are provided with the outputs of local oscillators 194 and 196. The down-converted result is provided to power divider 198, the output of which is then passed to handpass filter / amplifier 200 and further to attenuator 2.
02, and also splitter 204, amplifier and bandpass filter 2
Coupled to transformer coupler 208 via 06.

Attenuators 184 and 186 for each path control the attenuation and thus the magnitude of the signal provided to the power divider. Additional damping control is provided by attenuator 2
Provided by 02.

A program listing written in C for gain tone generation and attenuator control is attached as Table 1. While some embodiments of the present invention have been described above, including the accompanying computer programs, and some modifications and alterations of these embodiments have been described, those skilled in the art will appreciate that the present examples It should be clear that what is mentioned with reference to is merely exemplary and not intended to be limiting. Many modifications and other embodiments will occur to those skilled in the art, which are deemed to be within the scope of the invention which is defined solely by the appended claims and their equivalents. To be

[Brief description of drawings]

FIG. 1 is an overview of the coverage area of multiple microcells and the reduction of the coverage area, where an imbalance exists between the microcells.

FIG. 2 is a block diagram of a wireless microcell distribution system in which signals from multiple cable microcell integrators are summed and provided to a headend interface converter coupled to a base station.

FIG. 3 is a block diagram illustrating the injection of gain tones into the signals from the primary and diversity antennas of the cable microcell integrator, which gain tones are detected at the headend interface converter. And measured. The headend interface converter sends a message back to the cable microcell integrator to adjust the attenuators in the primary and diversity paths, thereby causing the cable at the summing point in FIG.
The amplitude of the reverse path signal from the microcell integrator can be adjusted to be equal.

FIG. 4 is a waveform diagram showing the generation of gain tones in a conventional system, where the duration of the gain tones for the primary and diversity paths totals 800 ms.

5 is a waveform diagram in the frequency domain for the carrier and gain tones of the system of FIG. 4, showing the gain and gain in the band set for each reverse path carrier.
Figure 7 illustrates tone positioning, where the headend interface converter is sampling gain tones at a first frequency corresponding to the primary path and a second frequency corresponding to the diversity path.

FIG. 6 is a waveform diagram of the generation of gain tones in the system of the present invention, showing how the gain tones are generated independently and sequentially, with a limited duration of the gain tones.

FIG. 7 is a waveform diagram in the frequency spectrum of the occurrence of gain tones for the primary and diversity paths, showing independent measurements of each tone, where the tone is the maximum amplitude allowed for the corresponding carrier. Has an amplitude set to.

FIG. 8 is a schematic diagram in which carrier amplitudes from six cable microcell integrators are combined, one for the embodiment with gain tones in the present invention.
As low as 0 dB below the maximum level is shown reducing potential interference with the associated telephone signal.

FIG. 9 is a block diagram of a system according to the present invention that provides a message to a given cable microcell integrator to turn on gain tones for the corresponding primary and diversity paths. It is an interface converter, and shows that the start and stop timings of the gain tones are inside the cable microcell integrator.

FIG. 10 is a waveform diagram illustrating a measurement window for detecting shortened gain tones in a headend interface converter. Here, a known fixed delay is provided, ensuring that the gain tones of the cable microcell integrator are lowered to a position where accurate amplitude measurements can be made.

FIG. 11 is a block diagram illustrating the use of temperature sensors in each cable microcell integrator. This output is transmitted to the headend interface converter on the reverse path, which has a temperature compensation table to modify the message sent to the attenuator in the cable microcell integrator. The attenuator can be set in consideration of the temperature sensed in the micro cell.

FIG. 12 is a block diagram of a circuit used in a cable microcell integrator to generate a gain tone and provide the generated gain tone to a headend interface converter.

[Table 1]

[Procedure for Amendment] Submission for translation of Article 34 Amendment of Patent Cooperation Treaty

[Submission date] August 8, 2001 (2001.8.8)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Contents of correction]

[Claims]

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), OA (BF, BJ , CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, K E, LS, MW, MZ, SD, SL, SZ, TZ, UG , ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, C H, CN, CR, CU, CZ, DE, DK, DM, DZ , EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, K G, KP, KR, KZ, LC, LK, LR, LS, LT , LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, RO, RU, S D, SE, SG, SI, SK, SL, TJ, TM, TR , TT, TZ, UA, UG, UZ, VN, YU, ZA, ZW (72) Inventor Ro Verme, Clifford Em             New Hampshire, United States             03054, Merrimack, Bates Road 23 (72) Inventor Gravelline, Stephen Jay             New Hampshire, United States             03052, Litchfield, Chat fee             Ludo Drive 14 (72) Inventor Frevotte, Glenn Tee             New Hampshire, United States             03054, Merrimack, Pratt Rain             Two F term (reference) 5K067 AA03 AA33 DD13 DD16 EE02                       EE10 EE43 GG08 HH21 [Continued summary] Power level can be increased, Thus, the vulnerability to noise can be improved.

Claims (10)

[Claims] 1. A wireless microcell distribution system in which gain tones are transmitted from a microcell to a gain tone amplitude measurement unit via primary and diversity paths that carry telephone signals and are embedded through summing points. In, the system comprising means for limiting the duration of the gain tones to the point where interference of the gain tones with the telephone signal in which they are embedded is minimized. 2. The system according to claim 2, wherein the cumulative amplitude of the telephone signal at the addition points from a plurality of microcells is set to a predetermined maximum value,
A system wherein the amplitude of one gain tone is set to a predetermined distance from which the amplitude has decreased in amplitude. 3. The system of claim 2, wherein the distance is set to minimize interference between the gain tone and the telephone signal. 4. The system of claim 3, wherein the amplitude of the gain tone is at least 10 dB less than the maximum value. 5. A system for providing level adjustment of a telephone signal from a microcell to a summing point in a wireless microcell distribution system, wherein a message is transmitted to each of the microcells to obtain a gain control from each of the microcells. A head-end interface converter that requires the generation of tones, a means to establish primary and diversity paths to each microcell, and a gain tone that is in each microcell and that has a limited duration to the primary and diversity. Means for independently generating for injection into the path, wherein the duration of the gain tone is short enough to minimize interference with the telephone signal; Means for injecting tones into the primary and diversity paths, the headend In the interface converter, the amplitude of the gain tone is measured and the message is transmitted to the corresponding microcell to adjust the level of the telephone signal therefrom, whereby the signal from the microcell is added to the sum. And a means for making the amplitudes equal at the points. 6. The system of claim 5, wherein the cumulative level of the telephone signal from the microcell to the summing point has a predetermined maximum value and the gain
A system wherein the tone amplitude is set below the maximum value by a predetermined amount. 7. The system according to claim 5, wherein a temperature sensor in each of the cable microcell integrators and a temperature in one microcell in the cable microcell integrator up to the headend interface converter. Further comprising means for transmitting, a temperature lookup table at the headend interface converter, and means for modifying a level adjustment signal transmitted to the microcell to account for temperature at the microcell. Characterized system. 8. The system of claim 5, wherein the amplitude measuring means includes means for establishing separate measurement windows for gain tones in the primary and diversity paths. 9. The system of claim 5, wherein the start of the measurement window is delayed by a predetermined amount to ensure detection of the gain tone. 10. The system of claim 5, wherein the microcell is
Each includes a primary and diversity antenna and a down converter coupled thereto, wherein the injection means is provided after the down conversion to stably control the amplitude of the injected gain tone. , Injecting the gain tone into the primary and diversity paths.