MXPA00009412A - System and method for aggregate overload control - Google Patents

Abstract

The present disclose a wireless communications system and method controls network load by selectively scaling aggregate base station transmit signals. In one implementation, aggregate in-phase (I) and quadrature (Q) channel transmit signals are multiplied by a scaling coefficient output by an aggregate overload controller based on load levels relative to a threshold. By scaling aggregate I- and Q-channel transmit signals when load level measurements indicate a high load situation, handoff control measurements made at mobile subscriber terminals, such as received signal strength from the base station, bit/frame error rates, and signal-to-noise ratio, will be affected, thereby prompting mobile subscriber terminals at the cell/sector boundaries to request handoff to an adjacent cell/sector. Thus, load is balanced between a number of cells/sector to increase network capacity and prevent overload without relying on a call admission/blocking scheme.

Description

SYSTEM AND METHOD FOR AGGREGATED OVERLOAD CONTROL FIELD OF THE INVENTION The present invention is concerned with the field of wireless communications.

DESCRIPTION OF RELATED TECHNIQUE In wireless communication networks based on spread spectrum technology, such as a code division multiple access network (CDMA), a plurality of mobile subscriber terminals ("mobile devices") share the same radio frequency bandwidth (RF) and are separated by using different Walsh codes and other orthogonal functions. Compared to communication systems that create multiple channels from a single RF band by assigning different time segments to users, that is, time division multiple access (TDMA) or by subdividing an RF band into a plurality of subbands, that is, frequency division multiple access (FDMA), orthogonal code sequences are used to form separate channels that allow a CDMA system to display a "flexible" network capability. In other words, the number of mobile devices that can share a given RF bandwidth at a time is not fixed and instead they are commonly limited only by the degradation of Ref: 123271 the quality of service caused by interference from other users of the same and adjacent cells / sectors. The resulting exchange between network capacity and quality of service in a CDMA system is commonly solved by reverse link power control techniques (mobile device to the base station) that adaptively adjusts the transmit power of the mobile device to the minimum level necessary to maintain proper performance. Despite the use of reverse link power control techniques to reduce co-channel interference and increase capacity, overloading in cells / network sectors can occur when the number of mobile devices that are serviced exceeds the number maximum at which the target call quality (commonly represented as the ratio of energy per bit, Ep, to noise and No interference, in a given bandwidth) can be maintained, for example when a large number of mobile devices are trying to communicate with only one base station at a time. A technique previously implemented to avoid overloading depends on a call admission / blocking scheme to ensure proper communication quality by blocking the service to additional subscribers when the load levels exceed a certain threshold. Such call-in schemes, however, can result in unacceptable service interruptions.

BRIEF DESCRIPTION OF THE INVENTION The present invention consists of a system and method that scales the transmission signals of the base station in a wireless communication network in response to high load levels, thereby affecting the transfer control values measured in mobile devices that will be serviced to "push" mobile devices to adjacent cells / sectors and avoid overload conditions. In one implementation, an overload controller of the base station scales the amplitude of the forward link (base station to mobile device) transmission signals aggregated as a function of the difference between the magnitudes of the aggregate transmission signal and a threshold level . By scaling the aggregated base station transmission signals including control signal components (eg, a pilot signal component in a CDMA system), transfer control values including reception signal strength, error proportions bit / frames and signal-to-noise ratio, measured on mobile devices within the network service area are affected. Depending on the location of the mobile devices and the degree to which the added base station transmit signals are scaled, a percentage of mobile devices that are particularly serviced at the borders of the cells / sector, will require the transfer to an adjacent cell / sector. As the load level increases in relation to the threshold level, the degree of scaling also increases, thereby affecting more significantly the transfer control values measured in the mobile devices within the service area of the network and causing an increased number of transfers to balance the load among a plurality of cells / sectors. Thus, the present invention increases network capacity and prevents overload without relying exclusively on a call admission scheme. In one embodiment, the present invention is an aggregate overload controller that samples and adds the aggregate phase (I) and quadrature (Q) channel transmission signal quantities in a load measurement period to obtain a value of load measurement and emits a scaling coefficient as a function of the difference between the load measurement and a threshold. The aggregate overload controller initially adjusts the scaling coefficient to one and maintains the scaling coefficient to one as long as the load measurement value remains below the threshold. When the load measurement exceeds the threshold first, the scaling coefficient of the preceding load measurement period (that is, 1) is decreased by a displacement value that is calculated as a function of the difference between the load measurement value and the load measurement value. threshold. In one implementation, the updated scaling coefficient is calculated as: SM = min. { l, SM-? + μ (Eth-MS)} Where SM-? is the scaling coefficient of the preload measurement period, Eth is the threshold, EM is the load measurement for the current load measurement period and μ is a constant. The constant μ can be adjusted to a small value, for example, 0.01, to prevent substantial fluctuations in the scaling coefficient SM and thereby avoid the instability of the network. The channel multipliers U and Q multiply the scaling coefficient SM received from the aggregate overload controller by the aggregated I and Q channel transmission signals received from a baseband processor. The resulting scaled I and Q channel transmission signals are received by an RF processor, which performs digital-to-analog conversion, low-pass filtering, modulates the scaled I and Q channel transmission signals on RF carriers. separate, it combines the modulated I and Q channel carriers and emits the combined RF transmission signal to the base station antenna for transmission.

BRIEF DESCRIPTION OF THE DRAWINGS Other aspects and advantages of the present invention will become apparent upon reading the following detailed description and with reference to the drawings in which: Figure 1 illustrates an exemplary wireless network configuration appropriate for implementing the modalities of the present invention; Figure 2 is a general block diagram illustrating certain components of a base station transmitter according to embodiments of the present invention; Figure 3 is a block diagram illustrating an exemplary baseband processor of a transmitter of • base station that generates channel I transmission signals and Q aggregates that are scaled by a scaled coefficient of an aggregate overload controller according to an embodiment of the present invention; . Figure 4 is a flow diagram illustrating an exemplary operation carried out by the aggregate overload controller to calculate a scaling coefficient according to a mode of the. present invention and Fig. 5 is a block diagram of an exemplary RF processor of the base station transmitter according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention consists of a system and method that scales the transmission signals of the base station in a wireless communication network, such as a CDMA network, to affect the transfer control values measured in the devices in the network area under high load conditions and thereby prevent overload conditions. An illustrative embodiment of an overload control system and method according to the present invention is described hereinafter. With reference to Figure 1, an appropriate wireless network configuration 10 is shown for implementing embodiments of the present invention. The wireless network 10 includes a plurality of geographical subareas ("cells") 12-1 ..., 12-i. Each cell 12-1, ..., 12-i has a corresponding base station 14-1, ..., 14-i to provide communication service to mobile devices located therein, such as mobile devices 20-1 , ..., 20-j located in cell 12-1. Each of the base stations 14-1, ..., 14-i is connected (for example, via a main line) to a switching office or telephone exchange 16 of mobile telephones (MTSO). The MTSO 16 manages or manages communication within the network and serves as an interface or interconnection between the wireless network and a public switched telephone network (PSTN) 40. As will be apparent to those skilled in the art, numerous variations of the network 10 wireless illustrated in Figure 1 are possible. For example, each of the cells 12-1, ..., 12-i can be divided into a variety of sectors. In addition, although cells 12-1, ..., 12-i are shown as hexagonal shaped areas, different cell shapes are possible. Figure 2 is a general block diagram illustrating selected components of a base station transmitter 100 in accordance with an exemplary implementation of the present invention. As shown in Figure 2, the base station transmitter 100 includes a baseband processor 110 that receives a polarity of baseband communication signals inputs i, ... N input. These baseband communication signals input, ..., inputN may include voice / data traffic received from the MTSO 16, • also as control information, for example pilot signals, radiolocation signals and synchronization signals to be transmitted. For the exemplary implementation illustrated in FIG. 2, the baseband processor 110 uses a spectrally efficient modulation scheme such as quadrature phase shift manipulation (QPSK) to output separate aggregated I and Q channel transmission signals. Nevertheless, it should be noted that the principles of the present invention can be applied to base station transmitters that do not form separate transmission signals of I and Q channels. A multiplier 130 of channel I receives the aggregate channel I transmit signal from the baseband processor 110 and multiplies the aggregate channel I transmit signal received by a scaling coefficient SM received from an aggregate overload controller 140. Similarly, a Q channel multiplier 132 receives an aggregated Q channel transmission signal emitted by the baseband processor 110 and multiplies the Q channel transmission signal received by the received SM scaling coefficient from the aggregate overload controller 140. An RF processor 160 receives the scaled aggregate I and Q channel transmission signals from I and Q channel multipliers 130 and 132. As described. in more detail later herein, the RF processor 160 performs well-known processing on the scaled aggregate I and Q channel transmission signals received from the multipliers 130 and 132, such as digital to analog conversion, step filtration. band and modulation of RF carrier signal, before emitting a combined RF signal to an antenna 170. The aggregate overload controller 140 also receives the outputs of the I and Q channel scaling multipliers 130 and 132 to calculate scaling coefficients updated SMs in a manner described in more detail later herein. The aggregate overload controller 140 may be implemented for example as an application-specific integrated circuit (ASIC) or as computer-executed programming elements. Figure 3 is a block diagram illustrating selected components of an exemplary baseband processor 110 for use in the configuration 100 of the base station transmitter in accordance with an implementation of the present invention. As illustrated in Figure 3, the baseband processor 110 includes a variety of baseband processing units 111-1, ..., 111-N, corresponding respectively to the input input communication signals, ... entranceN. Each baseband processing unit 111-1, ..., 111-N emits a channel signal I IKI, ..., IKN and a channel signal Q Q ??, ..., QKN. The baseband processor 110 further includes a channel summation unit 128 I that generates an aggregated channel I transmission signal from the channel signals I IK ?, ..., IKN, received from the processing units of broad band 111-1, ..., 111-N and a Q channel summation unit 129 to generate a Q channel transmission signal added from the QQ channel signals. ••• / QKN received from the individual baseband processing units 111-1, ..., 111-N. As will be apparent to those skilled in the art, each baseband processing unit 111-1, ..., 111-N includes conventional components for CDMA communication, such as is specified in the CDMA-2000 standard proposed by the Association. of the Telecommunications Industry of the United States of • America (TIA) to the International Telecommunication Union (ITO). Although a configuration of the specific baseband processing unit is shown in Figure 3, it should be noted that the principles of the present. invention are not limited to a particular baseband processing configuration. Referring again to the exemplary configuration of Figure 3, each baseband processing unit 111-1, ..., 111-N includes a channel coder 112-1, ..., 112-N, for example a convolution encoder, which generates coded blocks of predetermined length from the corresponding input communication signals input i, ..., input N, to protect the bits of information therein with error correction codes. A first multiplier 113-1, ..., 113-N multiplies the coded blocks emitted by the channel coder 112-1, -, 112-N with a designated PN code sequence, assigned to the proposed mobile device to receive the signal input, issued by a sequence generator PN 114-1, ..., 114-N. A second multiplier 115-1, ..., 115-N multiplies the output of the first multiplier 113-1, ..., 113-N by a sequence of Walsh codes, for example containing values of a row of a matrix function of Walsh, generated by a Walsh sequence generator 116-1, ..., 116-N. As is well known, the combination of a communication signal with an orthogonal Walsh code sequence disperses the input data signal over the bandwidth spectrum to prevent the co-channel interference signal. To obtain the QPSK modulation, a separator unit 117-1, ..., 117-N divides the output of the second multiplier 115-1, ..., 115-N into even and odd bits. As is well known, the QPSK modulation allows 2 bits of information to be transmitted simultaneously in orthogonal carriers. A third multiplier 118-1, ..., 118-N multiplies the even bits of the separator unit 117-1, ..., 117-N by a PN sequence of channel I emitted by a PN sequence generator. of channel I 119-1, ..., 119-N. Similarly, a fourth multiplier 120-1, ..., 120-25 N multiplies the odd number bits of the unit of % _, ..._% & & amp; separator 117-1, ..., 117-N for a PN sequence of Q channel emitted by a PM sequence generator of Q channel 121-1, ..., 121-N. The channel summation units I and Q 128 and 129 respectively receive the I and Q channel outputs of the individual baseband processing units 111-1, ..., 111-N to generate transmission signals of channel I and Q added IEN and QEN- Figure 4 is a flow diagram illustrating an exemplary calculation carried out by the aggregate overload controller 140 to generate and update the scaling coefficient SM. As illustrated in FIG. 4, aggregate overload controller 140 initially sets SM = 1 (step 201) and samples the scaled I and channel Q transmission signals I) _SAL and QICSAL received from multipliers 130 and 312 , at a sampling rate ts (step 202). Next, the aggregate overload controller 140 calculates (I) .SAL2 + Q) CSA_2) for each sample (step 204) and obtains the sum of (IksAL2 + QksAL2) in a load measurement period T (eg, 20 milliseconds) to calculate a load measurement, EM (step 206). In this period of charge measurement several thousand samples of IksAL and QSAL can be taken. Although the calculation of step 206 provides an appropriate load measurement to control scaling, it should be noted that other techniques for obtaining a load measurement can be used. For example, it may be dependent on a value of the total receive signal strength indicator (RSSI) at the base station or the number of users serviced by the base station to represent the load. Next, the aggregate load controller 140 determines an updated scaling coefficient SM when calculating: SM = min. { l, SM-? + μ (Eth-MS)} (1) where SM ~ 1 is the scaling coefficient of the preceding charge measurement period, Eth is a threshold level and μ is a constant (step 208). The constant μ can be adjusted to a relatively small value, for example, 0.01, to limit fluctuations in the scaling coefficient SM and thereby avoid network instability. This operation is carried out repeatedly to successively update the scaling factor SM. It should be recognized that equation (1) represents an exemplary calculation for updating the scaling factor SM and can be modified in various ways without deviating from the spirit and scope of the present invention. Figure 5 is a block diagram illustrating selected components of an exemplary RF processor 160 used in the base station transmitter 100 shown in Figure 2. As shown in Figure 5, the RF processor 160 includes a converter 162. digital to analog channel I and a digital converter 170 to analog channel Q to convert respectively IsAL and QkSAL to analogous form. The channel I and channel Q filters 164 and 172 respectively filter through the low pass the analog I and Q channel signals received from the digital to analog converters 162 and 170. A first multiplier 166 multiplies the channel I signal emitted by the filter 164 with an RF carrier signal of I-channel Cos (τ) and a second multiplier 174 multiplies the Q-channel signal emitted by the filter 172 with a Q-channel RF carrier signal Sen (Δt). A combiner 178 combines the RF signals emitted by the first and second multipliers 166 and 176 and outputs a composite RF transmission signal to the antenna 170 for transmission. By scaling the transfer control values of the I and Q channel transmission signals measured in the mobile devices, such as the receive signal strength of the base station, bit / frame error ratio and signal-to-noise ratio will be affected to alter cell / sector boundaries under high load conditions. Depending on the location of mobile devices in relation to cell / sector boundaries and the degree of scaling, a percentage of mobile devices will require transfer to adjacent cells / sectors, thereby balancing the load to improve network capacity and avoid overload. Also, when using a relatively small μ constant, the fluctuations in the scaling factor S? they are limited to avoid the instability of the network. Although the present invention has been described in considerable detail with reference to certain embodiments, it should be apparent to those skilled in the art that various modifications and applications of the present invention can be made without departing from the spirit and scope of the invention. For example, although the implementation illustrated in Figure 2 scales Q and I channel transmission signals before such signals reach the RF processor 100, the scaling can alternatively be carried out as part of RF processing, for example, after from digital to analog conversion. It is noted that, in relation to this date, the best method known by the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention.

Claims (18)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A method for controlling the load in a wireless communications network, characterized in that it comprises: obtaining a load measurement; calculate a scaling factor based on the load measurement and scale an aggregate base station transmission signal according to the scaling factor. The method according to claim 1, characterized in that the calculation step recursively calculates the scaling coefficient as a function of the difference between the load measurement and a threshold. 3. The method of compliance with the claim 1, characterized in that the scaling step scales each of the aggregate phase I channel transmission signals and an aggregate quadrature Q channel transmission signal according to the scaling factor. 4. The method of compliance with the claim 2, characterized in that the calculation step calculates the scaling factor when solving: SM = min. { l, SM-? + μ (Eth-MS)} where SM-1 is the scaling coefficient of a previous load measurement period, Eth is the threshold, EM is the load measurement for a current load measurement period and μ is a constant. 5. The method of compliance with the claim 4, characterized in that the constant μ limits the fluctuations in the scaling coefficient SM. 6. The method according to claim 3, characterized in that the obtaining stage obtains a load measurement when calculating (IksAi / 2 and QksAL2) where ISAL is a scaled aggregate I channel transmission signal and QksAL is a signal of Added channel Q transmission scaling and add a polarity of values of (IsAL2 and QksA2) calculated during a load measurement period. 7. The method of compliance with the claim 1, characterized in that the wireless telecommunications network is a code division multiple access network (CDMA). The method according to claim 1, characterized in that it further comprises: transmitting the scaled aggregate base station transmission signal. The method according to claim 8, characterized in that the scaling and transmission steps alter the cell / sector service boundaries for a corresponding network base station to balance the load between a cell / sector polarity. 10. A system for controlling the load in a wireless communications network, characterized in that it comprises: load measuring means for obtaining a load measurement; calculation means for calculating a scaling factor based on the load measurement and scaling means for scaling an aggregated base station transmission signal according to the scaling factor. The system according to claim 10, characterized in that the calculating means recursively calculates the scaling coefficient as a function of the difference between the load measurement and a threshold. The system according to claim 10, characterized in that the scaling means scaled each of the transmission signal of channel I in aggregate phase and an aggregate quadrature channel transmission signal according to the scaling factor. 13. The system according to claim 11, characterized in that the calculation means calculate the scaling factor, SM when solving: SM = min. { l, SM-? + μ (Eth-MS)} where SM-1 is the scaling coefficient of a previous load measurement period, Eth is the threshold, EM is the load measurement for a current load measurement period and μ is a constant. The system according to claim 13, characterized in that the constant μ limits the fluctuations in the scaling coefficient SM. 15. The system according to claim 12, characterized in that the load measuring means obtain a load measurement when calculating (IsAL2 + QsAL) wherein IksAL is a scaled aggregate I channel transmission signal and QsAL is a signal of Added Q channel transmission scaling and adding a plurality of values of (IsAL2 + QksAL2) calculated during a load measurement period. 16. The system according to claim 10, characterized in that the wireless communication network is a code division multiple access network (CDMA). The system according to claim 10, characterized in that it further comprises: transmission means for transmitting the transmission signal of the scaled aggregate base station. The system according to claim 17, characterized in that the scaling means and the transmission means alter the service boundaries of the cell / sector for a corresponding network base station to balance a load between a plurality of cells / sectors .