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A common strategy to utilize available resources in cellular radio systems is to control the transmitter powers. However, when applying power control to real systems, a number of challenges are prevalent. Available information in measurement reports are crude and highly quantized. This paper utilizes point-mass approximations of probability density functions to implement nonlinear estimation of relevant parameters. Most popular power control algorithms track specified target signal-to-interference ratios (SIR:s), but the challenge is to control target values in an outer control loop. Here target SIR:s are provided by utilizing models of the relation between a relevant quality measure, such as frame erasure rate (FER), and the estimated parameters. This is an interesting alternative to outer loop strategies based on relatively infrequent frame error measurements. The discussed outer loop can also include handling of different priorities. The methods proposed in this work are applicable to a general system, but FH-GSM is used as the example throughout the paper. Illuminating simulations of a FH-GSM system illustrate the behavior and performance, which are considered acceptable. By using the proposed outer loop, capacity gains of up to 30% have been observed.

Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.

Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.

Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.

A common strategy to utilize available resources in cellular radio systems is to control the transmitter powers. However, when applying power control to real systems, a number of challenges are prevalent. Available information in measurement reports are crude and highly quantized. This paper utilizes point-mass approximations of probability density functions to implement nonlinear estimation of relevant parameters. Most popular power control algorithms track specified target signal-to-interference ratios (SIR:s), but the challenge is to control target values in an outer control loop. Here target SIR:s are provided by utilizing models of the relation between a relevant quality measure, such as frame erasure rate (FER), and the estimated parameters. This is an interesting alternative to outer loop strategies based on relatively infrequent frame error measurements. The discussed outer loop can also include handling of different priorities. The methods proposed in this work are applicable to a general system, but FH-GSM is used as the example throughout the paper. Illuminating simulations of a FH-GSM system illustrate the behavior and performance, which are considered acceptable. By using the proposed outer loop, capacity gains of up to 30% have been observed.

Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.

A common strategy to utilize available resources in cellular radio systems is to control the transmitter powers. However, when applying power control to real systems, a number of challenges are prevalent. Available information in measurement reports are crude and highly quantized. This paper utilizes point-mass approximations of probability density functions to implement nonlinear estimation of relevant parameters. Most popular power control algorithms track specified target signal-to-interference ratios (SIR:s), but the challenge is to control target values in an outer control loop. Here target SIR:s are provided by utilizing models of the relation between a relevant quality measure, such as frame erasure rate (FER), and the estimated parameters. This is an interesting alternative to outer loop strategies based on relatively infrequent frame error measurements. The discussed outer loop can also include handling of different priorities. The methods proposed in this work are applicable to a general system, but FH-GSM is used as the example throughout the paper. Illuminating simulations of a FH-GSM system illustrate the behavior and performance, which are considered acceptable. By using the proposed outer loop, capacity gains of up to 30% have been observed.

Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.

Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.

A common strategy to utilize available resources in cellular radio systems is to control the transmitter powers. However, when applying power control to real systems, a number of challenges are prevalent. Available information in measurement reports are crude and highly quantized. This paper utilizes point-mass approximations of probability density functions to implement nonlinear estimation of relevant parameters. Most popular power control algorithms track specified target signal-to-interference ratios (SIR:s), but the challenge is to control target values in an outer control loop. Here target SIR:s are provided by utilizing models of the relation between a relevant quality measure, such as frame erasure rate (FER), and the estimated parameters. This is an interesting alternative to outer loop strategies based on relatively infrequent frame error measurements. The discussed outer loop can also include handling of different priorities. The methods proposed in this work are applicable to a general system, but FH-GSM is used as the example throughout the paper. Illuminating simulations of a FH-GSM system illustrate the behavior and performance, which are considered acceptable. By using the proposed outer loop, capacity gains of up to 30% have been observed.

A common strategy to utilize available resources in cellular radio systems is to control the transmitter powers. However, when applying power control to real systems, a number of challenges are prevalent. Available information in measurement reports are crude and highly quantized. This paper utilizes point-mass approximations of probability density functions to implement nonlinear estimation of relevant parameters. Most popular power control algorithms track specified target signal-to-interference ratios (SIR:s), but the challenge is to control target values in an outer control loop. Here target SIR:s are provided by utilizing models of the relation between a relevant quality measure, such as frame erasure rate (FER), and the estimated parameters. This is an interesting alternative to outer loop strategies based on relatively infrequent frame error measurements. The discussed outer loop can also include handling of different priorities. The methods proposed in this work are applicable to a general system, but FH-GSM is used as the example throughout the paper. Illuminating simulations of a FH-GSM system illustrate the behavior and performance, which are considered acceptable. By using the proposed outer loop, capacity gains of up to 30% have been observed.

Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.

When the systems evolved from analog to digital, the performance was improved by the use of power control on the one hand and different modulations and coding schemes on the other. Condensing the available information we are able to propose a new concept of power control. The concept is applicable to real systems, since it uses the available measurements for estimating parameters necessary for the power control. It also supports the use of an adequate quality measure together with a quality specification supplied by the operator. We will use frequency hopping GSM as an example and the resulting control algorithm is ready for implementation in the software in the base stations where the output powers are computed. No modifications are needed in the GSM standard, the mobile terminals, the radio interfaces or in the base station transmitters. Finally we provide simulation results confirming the benefits of using the new concept for power control.

Stability is a fundamental property desirable for any controlled system. We briefly review the root locus and describing function techniques, which are tools for stability analysis, and show how they can be applied to power control algorithms in cellular radio networks. The root locus method is used to find stability limits on controller parameters, and describing functions for predicting the presence of oscillations in the system. Thus these methods can be used to support the design phase, when deciding upon the appropriate controller parameters. These tools are demonstrated for various control algorithms and when different smoothing filters are applied. The analysis reveals that the distributed power control (DPC) algorithm, which works fine under ideal circumstances, yields an unstable system when subject to a small time delay. Furthermore, it is concluded that the performance with respect to stability is better when the measurements are averaged by an exponential forgetting filter than by the moving average filter.

Due to the rapid expansion of the cellular radio systems market, and the need for wireless multimedia services, the available resources have to be utilized efficently. A common strategy is to control the transmitter powers of the mobiles and base stations. However, when applying power control to real systems, a number of challenges are prevalent. The performance is limited by time delays, nonlinearities and the availability of measurements and adequate quality measures. In this paper we present a Power Regulator concept, which comprises an Unknown Input Observer, a Quality Mapper and a Power Control Algorithm. The applicability of the concept is exemplified using frequency hopping GSM, and simulations indicate benefits of employing the proposed concept.

Transmission power control is essential in WCDMA in order to optimize the bandwidth utilization which is critical when variable data ratesare used. One remaining problem is oscillations in the output powers due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete-time describing functions, which are introduced and applied. More importantly, Time Delay Compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm operates more stable, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved and thus less fading margin is needed. The latest news from standardization is to try to operate without additional delay when close to a base station. Nevertheless, there will still be more distant mobile stations for which TDC will be beneficial.

Time delays reduces the performance of any controlled system. If neglected in the design phase, the system may even become unstable when using the designed controller. Several power control strategies have been proposed in order to improve the capacity of cellular radio systems, but time delays are usually neglected. Here, it is shown that the problems can be handled by considering the time delays in the design phase in order to choose the appropriate parameter values. Most popular algorithms can be seen as special cases of an integrating controller. This structure is extended first to a proportional integrating (PI)-controller and then further on to a general linear controller of higher orders. Corresponding design procedures are outlined based on techniques, such as pole placement, from the field of automatic control. The PI-controller is a very appealing choice of structure, with better performance compared to an I-controller and less complex than a higher order controller. The benefits are further illuminated by network simulations.

The problem to track time-varying parameters in cellular radio systems is studied, and the focus is on estimation based only on the signals that are readily available. Previous work have demonstrated very good performance, but were relying on analog measurement that are not available. Most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). For that matter a maximum likelihood estimator have been designed and exemplified in the case of GSM. Simulations indicate good performance both when most parameters are varying slowly, and when subject to fast variations as in realistic cases. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

The problem to track time-varying parameters in cellular radio systems is studied. The focus is on estimation based only on the signals that are readily available. Previous work has demonstrated very good performance relying on analog measurement. In a real system most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). Therefore a different approach is required and for that matter a maximum likelihood estimator has been designed and exemplified in the case of GSM. The needed probability functions of the measurements cannot be described analytically. Instead point-mass approximations can be obtained from Monte-Carlo simulations for each point in a grid covering the interesting parameter space. The proposed algorithm can be tuned to track both slowly and fast varying parameters individually. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

When employing power control algorithms in real systems there are anumber of problems that have to be considered, of which some are addressed in this work. It is probably impossible to solve the problems using a linear controller, and as an extension, various nonlinear components and their applicability are discussed. Problems due to hardware and external constraints have been identified in previous work, and here anti-reset windup techniques are reviewed and employed. Previous proposals can be seen as special cases. Sometimes it is desirable to employ several algorithms in parallel, and then use a device to state priorities, i.e., to switch between the algorithms. The applicability of switches and selectors are described and exemplified as proposed solutions to the low interference problem, where a C/I balancing algorithm causes a user to use a too low a power. The benefits of using the proposed nonlinear components are further illustrated by network simulations.

Time delays reduces the performance of any controlled system. If neglected in the design phase, the system may even become unstable when using the designed controller. Several power control strategies have been proposed in order to improve the capacity of cellular radio systems, but time delays are usually neglected. Here, it is shown that the problems can be handled by considering the time delays in the design phase in order to choose the appropriate parameter values. Most popular algorithms can be seen as special cases of an integrating controller. This structure is extended first to a proportional integrating (PI)-controller and then further on to a general linear controller of higher orders. Corresponding design procedures are outlined based on techniques, such as pole placement, from the field of automatic control. The PI-controller is a very appealing choice of structure, with better performance compared to an I-controller and less complex than a higher order controller. The benefits are further illuminated by network simulations.

When employing power control algorithms in real systems there are anumber of problems that have to be considered, of which some are addressed in this work. It is probably impossible to solve the problems using a linear controller, and as an extension, various nonlinear components and their applicability are discussed. Problems due to hardware and external constraints have been identified in previous work, and here anti-reset windup techniques are reviewed and employed. Previous proposals can be seen as special cases. Sometimes it is desirable to employ several algorithms in parallel, and then use a device to state priorities, i.e., to switch between the algorithms. The applicability of switches and selectors are described and exemplified as proposed solutions to the low interference problem, where a C/I balancing algorithm causes a user to use a too low a power. The benefits of using the proposed nonlinear components are further illustrated by network simulations.

When employing power control algorithms in real systems there are anumber of problems that have to be considered, of which some are addressed in this work. It is probably impossible to solve the problems using a linear controller, and as an extension, various nonlinear components and their applicability are discussed. Problems due to hardware and external constraints have been identified in previous work, and here anti-reset windup techniques are reviewed and employed. Previous proposals can be seen as special cases. Sometimes it is desirable to employ several algorithms in parallel, and then use a device to state priorities, i.e., to switch between the algorithms. The applicability of switches and selectors are described and exemplified as proposed solutions to the low interference problem, where a C/I balancing algorithm causes a user to use a too low a power. The benefits of using the proposed nonlinear components are further illustrated by network simulations.

The problem to track time-varying parameters in cellular radio systems is studied, and the focus is on estimation based only on the signals that are readily available. Previous work have demonstrated very good performance, but were relying on analog measurement that are not available. Most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). For that matter a maximum likelihood estimator have been designed and exemplified in the case of GSM. Simulations indicate good performance both when most parameters are varying slowly, and when subject to fast variations as in realistic cases. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

The problem to track time-varying parameters in cellular radio systems is studied. The focus is on estimation based only on the signals that are readily available. Previous work has demonstrated very good performance relying on analog measurement. In a real system most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). Therefore a different approach is required and for that matter a maximum likelihood estimator has been designed and exemplified in the case of GSM. The needed probability functions of the measurements cannot be described analytically. Instead point-mass approximations can be obtained from Monte-Carlo simulations for each point in a grid covering the interesting parameter space. The proposed algorithm can be tuned to track both slowly and fast varying parameters individually. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

When the systems evolved from analog to digital, the performance was improved by the use of power control on the one hand and different modulations and coding schemes on the other. Condensing the available information we are able to propose a new concept of power control. The concept is applicable to real systems, since it uses the available measurements for estimating parameters necessary for the power control. It also supports the use of an adequate quality measure together with a quality specification supplied by the operator. We will use frequency hopping GSM as an example and the resulting control algorithm is ready for implementation in the software in the base stations where the output powers are computed. No modifications are needed in the GSM standard, the mobile terminals, the radio interfaces or in the base station transmitters. Finally we provide simulation results confirming the benefits of using the new concept for power control.

Stability is a fundamental property desirable for any controlled system. We briefly review the root locus and describing function techniques, which are tools for stability analysis, and show how they can be applied to power control algorithms in cellular radio networks. The root locus method is used to find stability limits on controller parameters, and describing functions for predicting the presence of oscillations in the system. Thus these methods can be used to support the design phase, when deciding upon the appropriate controller parameters. These tools are demonstrated for various control algorithms and when different smoothing filters are applied. The analysis reveals that the distributed power control (DPC) algorithm, which works fine under ideal circumstances, yields an unstable system when subject to a small time delay. Furthermore, it is concluded that the performance with respect to stability is better when the measurements are averaged by an exponential forgetting filter than by the moving average filter.

Time delays reduces the performance of any controlled system. If neglected in the design phase, the system may even become unstable when using the designed controller. Several power control strategies have been proposed in order to improve the capacity of cellular radio systems, but time delays are usually neglected. Here, it is shown that the problems can be handled by considering the time delays in the design phase in order to choose the appropriate parameter values. Most popular algorithms can be seen as special cases of an integrating controller. This structure is extended first to a proportional integrating (PI)-controller and then further on to a general linear controller of higher orders. Corresponding design procedures are outlined based on techniques, such as pole placement, from the field of automatic control. The PI-controller is a very appealing choice of structure, with better performance compared to an I-controller and less complex than a higher order controller. The benefits are further illuminated by network simulations.

Due to the rapid expansion of the cellular radio systems market, and the need for wireless multimedia services, the available resources have to be utilized efficently. A common strategy is to control the transmitter powers of the mobiles and base stations. However, when applying power control to real systems, a number of challenges are prevalent. The performance is limited by time delays, nonlinearities and the availability of measurements and adequate quality measures. In this paper we present a Power Regulator concept, which comprises an Unknown Input Observer, a Quality Mapper and a Power Control Algorithm. The applicability of the concept is exemplified using frequency hopping GSM, and simulations indicate benefits of employing the proposed concept.

Transmission power control is essential in WCDMA in order to optimize the bandwidth utilization which is critical when variable data ratesare used. One remaining problem is oscillations in the output powers due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete-time describing functions, which are introduced and applied. More importantly, Time Delay Compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm operates more stable, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved and thus less fading margin is needed. The latest news from standardization is to try to operate without additional delay when close to a base station. Nevertheless, there will still be more distant mobile stations for which TDC will be beneficial.

The problem to track time-varying parameters in cellular radio systems is studied. The focus is on estimation based only on the signals that are readily available. Previous work has demonstrated very good performance relying on analog measurement. In a real system most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). Therefore a different approach is required and for that matter a maximum likelihood estimator has been designed and exemplified in the case of GSM. The needed probability functions of the measurements cannot be described analytically. Instead point-mass approximations can be obtained from Monte-Carlo simulations for each point in a grid covering the interesting parameter space. The proposed algorithm can be tuned to track both slowly and fast varying parameters individually. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

When employing power control algorithms in real systems there are anumber of problems that have to be considered, of which some are addressed in this work. It is probably impossible to solve the problems using a linear controller, and as an extension, various nonlinear components and their applicability are discussed. Problems due to hardware and external constraints have been identified in previous work, and here anti-reset windup techniques are reviewed and employed. Previous proposals can be seen as special cases. Sometimes it is desirable to employ several algorithms in parallel, and then use a device to state priorities, i.e., to switch between the algorithms. The applicability of switches and selectors are described and exemplified as proposed solutions to the low interference problem, where a C/I balancing algorithm causes a user to use a too low a power. The benefits of using the proposed nonlinear components are further illustrated by network simulations.

The problem to track time-varying parameters in cellular radio systems is studied, and the focus is on estimation based only on the signals that are readily available. Previous work have demonstrated very good performance, but were relying on analog measurement that are not available. Most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). For that matter a maximum likelihood estimator have been designed and exemplified in the case of GSM. Simulations indicate good performance both when most parameters are varying slowly, and when subject to fast variations as in realistic cases. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

When the systems evolved from analog to digital, the performance was improved by the use of power control on the one hand and different modulations and coding schemes on the other. Condensing the available information we are able to propose a new concept of power control. The concept is applicable to real systems, since it uses the available measurements for estimating parameters necessary for the power control. It also supports the use of an adequate quality measure together with a quality specification supplied by the operator. We will use frequency hopping GSM as an example and the resulting control algorithm is ready for implementation in the software in the base stations where the output powers are computed. No modifications are needed in the GSM standard, the mobile terminals, the radio interfaces or in the base station transmitters. Finally we provide simulation results confirming the benefits of using the new concept for power control.

Due to the rapid expansion of the cellular radio systems market, and the need for wireless multimedia services, the available resources have to be utilized efficently. A common strategy is to control the transmitter powers of the mobiles and base stations. However, when applying power control to real systems, a number of challenges are prevalent. The performance is limited by time delays, nonlinearities and the availability of measurements and adequate quality measures. In this paper we present a Power Regulator concept, which comprises an Unknown Input Observer, a Quality Mapper and a Power Control Algorithm. The applicability of the concept is exemplified using frequency hopping GSM, and simulations indicate benefits of employing the proposed concept.

Transmission power control is essential in WCDMA in order to optimize the bandwidth utilization which is critical when variable data ratesare used. One remaining problem is oscillations in the output powers due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete-time describing functions, which are introduced and applied. More importantly, Time Delay Compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm operates more stable, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved and thus less fading margin is needed. The latest news from standardization is to try to operate without additional delay when close to a base station. Nevertheless, there will still be more distant mobile stations for which TDC will be beneficial.

Stability is a fundamental property desirable for any controlled system. We briefly review the root locus and describing function techniques, which are tools for stability analysis, and show how they can be applied to power control algorithms in cellular radio networks. The root locus method is used to find stability limits on controller parameters, and describing functions for predicting the presence of oscillations in the system. Thus these methods can be used to support the design phase, when deciding upon the appropriate controller parameters. These tools are demonstrated for various control algorithms and when different smoothing filters are applied. The analysis reveals that the distributed power control (DPC) algorithm, which works fine under ideal circumstances, yields an unstable system when subject to a small time delay. Furthermore, it is concluded that the performance with respect to stability is better when the measurements are averaged by an exponential forgetting filter than by the moving average filter.

Time delays reduces the performance of any controlled system. If neglected in the design phase, the system may even become unstable when using the designed controller. Several power control strategies have been proposed in order to improve the capacity of cellular radio systems, but time delays are usually neglected. Here, it is shown that the problems can be handled by considering the time delays in the design phase in order to choose the appropriate parameter values. Most popular algorithms can be seen as special cases of an integrating controller. This structure is extended first to a proportional integrating (PI)-controller and then further on to a general linear controller of higher orders. Corresponding design procedures are outlined based on techniques, such as pole placement, from the field of automatic control. The PI-controller is a very appealing choice of structure, with better performance compared to an I-controller and less complex than a higher order controller. The benefits are further illuminated by network simulations.

The problem to track time-varying parameters in cellular radio systems is studied. The focus is on estimation based only on the signals that are readily available. Previous work has demonstrated very good performance relying on analog measurement. In a real system most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). Therefore a different approach is required and for that matter a maximum likelihood estimator has been designed and exemplified in the case of GSM. The needed probability functions of the measurements cannot be described analytically. Instead point-mass approximations can be obtained from Monte-Carlo simulations for each point in a grid covering the interesting parameter space. The proposed algorithm can be tuned to track both slowly and fast varying parameters individually. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

The problem to track time-varying parameters in cellular radio systems is studied, and the focus is on estimation based only on the signals that are readily available. Previous work have demonstrated very good performance, but were relying on analog measurement that are not available. Most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). For that matter a maximum likelihood estimator have been designed and exemplified in the case of GSM. Simulations indicate good performance both when most parameters are varying slowly, and when subject to fast variations as in realistic cases. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

When employing power control algorithms in real systems there are anumber of problems that have to be considered, of which some are addressed in this work. It is probably impossible to solve the problems using a linear controller, and as an extension, various nonlinear components and their applicability are discussed. Problems due to hardware and external constraints have been identified in previous work, and here anti-reset windup techniques are reviewed and employed. Previous proposals can be seen as special cases. Sometimes it is desirable to employ several algorithms in parallel, and then use a device to state priorities, i.e., to switch between the algorithms. The applicability of switches and selectors are described and exemplified as proposed solutions to the low interference problem, where a C/I balancing algorithm causes a user to use a too low a power. The benefits of using the proposed nonlinear components are further illustrated by network simulations.

Time delays reduces the performance of any controlled system. If neglected in the design phase, the system may even become unstable when using the designed controller. Several power control strategies have been proposed in order to improve the capacity of cellular radio systems, but time delays are usually neglected. Here, it is shown that the problems can be handled by considering the time delays in the design phase in order to choose the appropriate parameter values. Most popular algorithms can be seen as special cases of an integrating controller. This structure is extended first to a proportional integrating (PI)-controller and then further on to a general linear controller of higher orders. Corresponding design procedures are outlined based on techniques, such as pole placement, from the field of automatic control. The PI-controller is a very appealing choice of structure, with better performance compared to an I-controller and less complex than a higher order controller. The benefits are further illuminated by network simulations.

When employing power control algorithms in real systems there are anumber of problems that have to be considered, of which some are addressed in this work. It is probably impossible to solve the problems using a linear controller, and as an extension, various nonlinear components and their applicability are discussed. Problems due to hardware and external constraints have been identified in previous work, and here anti-reset windup techniques are reviewed and employed. Previous proposals can be seen as special cases. Sometimes it is desirable to employ several algorithms in parallel, and then use a device to state priorities, i.e., to switch between the algorithms. The applicability of switches and selectors are described and exemplified as proposed solutions to the low interference problem, where a C/I balancing algorithm causes a user to use a too low a power. The benefits of using the proposed nonlinear components are further illustrated by network simulations.

When the systems evolved from analog to digital, the performance was improved by the use of power control on the one hand and different modulations and coding schemes on the other. Condensing the available information we are able to propose a new concept of power control. The concept is applicable to real systems, since it uses the available measurements for estimating parameters necessary for the power control. It also supports the use of an adequate quality measure together with a quality specification supplied by the operator. We will use frequency hopping GSM as an example and the resulting control algorithm is ready for implementation in the software in the base stations where the output powers are computed. No modifications are needed in the GSM standard, the mobile terminals, the radio interfaces or in the base station transmitters. Finally we provide simulation results confirming the benefits of using the new concept for power control.

Stability is a fundamental property desirable for any controlled system. We briefly review the root locus and describing function techniques, which are tools for stability analysis, and show how they can be applied to power control algorithms in cellular radio networks. The root locus method is used to find stability limits on controller parameters, and describing functions for predicting the presence of oscillations in the system. Thus these methods can be used to support the design phase, when deciding upon the appropriate controller parameters. These tools are demonstrated for various control algorithms and when different smoothing filters are applied. The analysis reveals that the distributed power control (DPC) algorithm, which works fine under ideal circumstances, yields an unstable system when subject to a small time delay. Furthermore, it is concluded that the performance with respect to stability is better when the measurements are averaged by an exponential forgetting filter than by the moving average filter.

Transmission power control is essential in WCDMA in order to optimize the bandwidth utilization which is critical when variable data ratesare used. One remaining problem is oscillations in the output powers due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete-time describing functions, which are introduced and applied. More importantly, Time Delay Compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm operates more stable, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved and thus less fading margin is needed. The latest news from standardization is to try to operate without additional delay when close to a base station. Nevertheless, there will still be more distant mobile stations for which TDC will be beneficial.

Due to the rapid expansion of the cellular radio systems market, and the need for wireless multimedia services, the available resources have to be utilized efficently. A common strategy is to control the transmitter powers of the mobiles and base stations. However, when applying power control to real systems, a number of challenges are prevalent. The performance is limited by time delays, nonlinearities and the availability of measurements and adequate quality measures. In this paper we present a Power Regulator concept, which comprises an Unknown Input Observer, a Quality Mapper and a Power Control Algorithm. The applicability of the concept is exemplified using frequency hopping GSM, and simulations indicate benefits of employing the proposed concept.

The problem to track time-varying parameters in cellular radio systems is studied. The focus is on estimation based only on the signals that are readily available. Previous work has demonstrated very good performance relying on analog measurement. In a real system most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). Therefore a different approach is required and for that matter a maximum likelihood estimator has been designed and exemplified in the case of GSM. The needed probability functions of the measurements cannot be described analytically. Instead point-mass approximations can be obtained from Monte-Carlo simulations for each point in a grid covering the interesting parameter space. The proposed algorithm can be tuned to track both slowly and fast varying parameters individually. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

The problem to track time-varying parameters in cellular radio systems is studied, and the focus is on estimation based only on the signals that are readily available. Previous work have demonstrated very good performance, but were relying on analog measurement that are not available. Most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). For that matter a maximum likelihood estimator have been designed and exemplified in the case of GSM. Simulations indicate good performance both when most parameters are varying slowly, and when subject to fast variations as in realistic cases. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.

When the systems evolved from analog to digital, the performance was improved by the use of power control on the one hand and different modulations and coding schemes on the other. Condensing the available information we are able to propose a new concept of power control. The concept is applicable to real systems, since it uses the available measurements for estimating parameters necessary for the power control. It also supports the use of an adequate quality measure together with a quality specification supplied by the operator. We will use frequency hopping GSM as an example and the resulting control algorithm is ready for implementation in the software in the base stations where the output powers are computed. No modifications are needed in the GSM standard, the mobile terminals, the radio interfaces or in the base station transmitters. Finally we provide simulation results confirming the benefits of using the new concept for power control.