WO2012072108A1

WO2012072108A1 - Device and method for adaptive power control

Info

Publication number: WO2012072108A1
Application number: PCT/EP2010/068487
Authority: WO
Inventors: Per-Olof Gerhard Gustavsson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2010-11-30
Filing date: 2010-11-30
Publication date: 2012-06-07

Abstract

A radio unit (105) arranged to transmit electromagnetic signals to another radio unit (110), also being arranged to receive measurement reports from the other radio unit (110). The radio unit (105) is arranged to receive measurements in the measurement reports of the other radio unit's (110) Signal to Noise and Interference Ratio, the S/(N+I), as well as measurements of the other radio unit's (110) received Signal power, S, and to compare the other radio unit's S/(N+I) with a threshold value S/(N+I)thr, and to increase or decrease the output power of its transmissions according to said comparison, but to also use an upper limit SMAX for S which S is not allowed to exceed.

Description

DEVICE AND METHOD FOR ADAPTIVE POWER CONTROL TECHNICAL FIELD

The present invention discloses a radio unit with adaptive power control for its transmissions.

BACKGROUND

When using radio units such as radio links for communication, variations in propagation conditions have an impact on the attenuation between a transmitting radio link and a receiving radio link, due to which the highest output power used by the transmitting radio link is only needed during a small part of the operational time in order to guarantee transmission performance. The transmission performance is measured as, for example, a low bit error rate in the case of digital transmissions. It is thus possible to use radio links with transmitters which have a variable output power level, and still obtain good transmission performance.

Another reason for varying the output power level in a transmitting radio link is in order to limit the interference level in neighbouring radio connections, a technique usually known as Automatic Transmit Power Control, abbreviated as ATPC, which is sometimes also referred to as Adaptive Transmit Power Control. An additional benefit of using ATPC is that reducing the output power level of a radio link's transmission also reduces the power consumption of the radio link.

One implementation of ATPC is to measure the received power level, S, in a radio unit, and to compare S with a threshold, S^_r. If the received power level exceeds the threshold, i.e. if S> S_th_r, this is communicated to the transmitting radio unit and a control loop in the transmitting radio seeks to decrease the output power level down to a minimum transmit power level. Vice versa, if the received power level falls below the threshold, i.e. S<S_Bnri the control loop seeks to increase the output power level up to a maximum transmit power level.

The effect of ATPC on spectrum efficiency can be optimized by, for instance, limiting the range of the output power levels, i.e. the range within which the output power levels can be varied by the ATPC. SUMMARY

It is a purpose of the present invention to improve upon ATPC techniques used in a radio unit. This purpose is met by the present invention in that it discloses a radio unit which is arranged to transmit electromagnetic signals with a certain output power to another radio unit and is also arranged to receive measurement reports from the other radio unit.

The radio unit is arranged to receive measurements in the measurement reports of the other radio unit's Signal to Noise and Interference Ratio, the S/(N+I), as well as measurements of the other radio unit's received Signal power, S, and to compare the other radio unit's S/(N+I) with a threshold value S/(N+I)t r, and to increase or decrease the output power of its transmissions according to said comparison, whilst also using an upper limit SMAX for S which S is not allowed to exceed. In this manner, the output power of the radio unit can be adapted to take into account the fact that not only the received power level but also the interference level varies with propagation conditions.

In some embodiments, the radio unit is arranged to determine SMAX as

where IMAX is a maximum value for the interference. In some embodiments, the radio unit is arranged to determine I_MAX as x*N, where x is a system dependent factor. In some embodiments, the radio unit is arranged to use an x which is in the range of 0.25 to 2. in other embodiments, the radio unit is arranged to make its transmissions to the other radio unit with one of a number of modulation levels, and to choose modulation level according to its transmission capacity need, and to increase or decrease the modulation level with increases and decreases in the transmission capacity need. In some embodiments, the radio unit is arranged to determine its transmission capacity need by means of measuring the insertion rate of idle cells and/or by measuring one or more queues or buffers in the radio unit.

In some embodiments, the radio unit is arranged to let SMAX vary depending on the modulation level. The invention also discloses a method for use in operating a radio unit, comprising transmitting electromagnetic signals with a certain output power to another radio unit and receiving measurement reports from the other radio unit. The method also comprises receiving measurements in the measurement reports of the other radio unit's Signal to Noise and Interference Ratio, the S/(N+I), as well as measurements of the other radio unit's received Signal power, S, and comparing the other radio unit's S/(N+I) with a threshold value S/(N+I)thn The output power of the transmissions to the other radio unit are increased or decreased according to the comparison, whilst also using an upper limit SMAX which S is not allowed to exceed.

In some embodiments, the method comprises determining SMAX as SMAX=S/(N-HMAX), where l_MAx is a maximum value for the interference.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following, with reference to the appended drawings, in which

Fig 1 shows an overview of a system in which an embodiment of a radio unit of the invention is used, and

Fig 2 shows a schematic block diagram of an embodiment of a radio unit of the invention, and

Fig 3 shows a schematic flow chart of an embodiment of a method of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Like numbers in the drawings refer to like elements throughout.

The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the invention.

Fig 1 shows an overview of a system 100 in which a radio unit 105 of the invention is used. As shown, the radio unit 105 is arranged to be in communication with another radio unit 110, i.e. it is arranged to make transmissions to and receive transmissions from the radio unit 1 10. Although the radio unit 105 is shown in fig 1 as being a "point to point" radio unit, i.e. a radio unit which is only in communication with one other radio unit 110, this is by way of example only; the principles disclosed herein may equally well be applied to a "point to multipoint" radio unit.

The radio unit 105 makes its transmissions with a certain output power level POUT, and the receiving radio unit 1 10 receives the transmissions with a certain received power level, PIN, which can also be expressed as a signal level S. Given a certain POUT from the radio unit 105, the signal level S at the radio unit 1 10 will vary with, among other factors, the propagation conditions between the radio units 105 and 1 10. In addition, the interference level I will also vary with the propagation conditions, so that at the receiving radio unit 1 10, the transmission performance will be determined by the Signal to noise and Interference ratio, S/(N+I), in the receiving radio unit 1 10. Based on this expression alone, the radio unit 105 could be equipped with a function for ATPC, i.e. Automatic/Adaptive Transmit Power Control, which used the expression S/(N+I) in the receiving radio unit 110 to vary POUT- However, such an ATPC function could lead to interference in adjacent radio units, so that adjacent radio units would force each other to increase their output power levels.

In order to take S/(N+I) at the receiving radio unit into account while also keeping interference with adjacent radio units in mind, the radio unit 105 is arranged to vary its output power level POUT as follows:

The transmitting radio unit 105 is arranged to receive measurement reports from the receiving radio unit 1 10, where these measurement reports comprise measurements of the receiving radio unit's 1 10 Signal to Noise and Interference Ratio, the S/(N+I), as well as measurements of the receiving radio unit's 1 10 received Signal power, S .

Using the measurement of the radio unit's 1 10 S and S/(N+I), the radio unit 105 is arranged to compare S/(N+I) with a threshold value S/(N+I)th_r for S/(N+I), and to vary, i.e. to increase or decrease POUT depending on said comparison, i.e. if S/(N+I) is above the threshold, Ρ₀υτ is decreased, and conversely, if S/(N+I) is below the threshold, Ρ₀υτ is increased. However, as an additional condition, the radio unit 105 is also arranged to use an upper limit SMAX in the variations of POUT, SO that S does not exceed SMAX-

In this manner, an ATPC function is obtained which takes into account both the S/(N+I) at the receiving radio and interference with adjacent radio units. Suitably, the radio unit 105 is arranged to determine SMAX as

where I MAX is a maximum interference rate which equals x*N and x is a system dependent factor. Suitably but not necessarily, x is in the range of 0.25 to 2. SMAX and consequently IMAX are suitably determined as follows: for a certain desired transmission quality, here defined as a certain Bit Error Rate, BER, a certain S/(N+I)_th_r is needed. If a certain maximum interference rate IMAX is allocated to this desired BER, SMA can then be determined as SMAX=[S/(N+

I MAX)]*[S/(N+I) _thr].

Regarding the measurement reports which the radio unit 105 is arranged to receive from the other radio unit 1 0 , these can either, as assumed above, comprise measurements of S and S/(N+I) as such from the other radio unit 1 0 , but they can also, as an alternative, comprise "difference values", i.e. a value which indicates the difference between, for example, the other radio unit's S/(N+I) and the S/(N+I)thr, or the difference between S and SMAX at the other radio unit 110.

In further embodiments, the radio unit 105 is also arranged to use different modulation levels in its ATPC function, as explained in the following: in order to meet increased demands for higher transmission capacity, the radio unit 105 is arranged to use so called Adaptive Modulation, AM, i.e. to use different modulation schemes, such as for instance 4QAM, 8QAM, 16 QAM, up to, for example, 1024 QAM, together with the ATPC function.

Adaptive Modulation, AM, means that the radio unit 105 is arranged to make its transmissions to the other radio unit 1 10 with one of a number of modulation levels, where the radio unit 105 is arranged to choose modulation level according to its transmission capacity need, and to increase or decrease the modulation level with increases and decreases in the transmission capacity need.

In some embodiments, the radio unit 105 is arranged to determine its transmission capacity need by means of measuring the insertion rate of idle cells and/or by measuring one or more queues or buffers in the radio unit, e.g. measuring the "fill level" of the one or more queues or buffers.

In the case where the transmission capacity is determined by means of the idle cell rate, the modulation level is suitably selected to provide an idle cell rate between an upper and a lower threshold. If the upper threshold is exceeded, the modulation level is decreased, and the idle cell rate falls below the lower threshold, the modulation level is increased.

Suitably, the thresholds are made modulation level dependent, and are selected to provide a predefined overlap in transmission capacity. In the case where the transmission capacity is determined by means of measuring one or more queues or buffers in the radio unit, in one embodiment a filtered version of a queue such as a lowest priority queue is used to increase the modulation level if exceeding a threshold. In one such an embodiment, in order to decrease the modulation level, a combination of priority queue buffer levels which fall below a threshold can be used as a "trigger" to decrease the modulation level. In this case as well, the thresholds are suitably made modulation level dependent.

In some embodiments, the radio unit 105 uses a modulation level control based on a combination of measuring the insertion rate of idle cells and of measuring one or more queues or buffers in the radio unit, e.g. measuring the "fill level" of the one or more queues or buffers. In this case as well, the thresholds are suitably made modulation level dependent.

In some embodiments, the radio unit 105 is arranged to use the ATPC function of any of the embodiments described herein in combination with any of the embodiments of the Adaptive Modulation, AM, described herein. Such combinations of ATPC and AM serve to secure a transmission performance which is adaptive both to the transmission needs and to the propagation conditions.

Fig 2 shows a schematic block diagram of a radio unit 105 as disclosed herein: the radio unit comprises an antenna interface 1 17 for interfacing with an antenna unit which may or may not be internal to the radio unit 105. In addition, the radio unit 105 also comprises a transmitter unit Tx 1 11 , and a receiver unit Rx 1 12, both of which interface with the antenna interface 1 17. As is also shown in fig 2, the radio unit 105 comprises a control unit Ctrl 1 13, which controls the function of the radio unit 1 05, and which is suitably the unit which performs the comparisons described herein, such as for example comparing the S/N+l of the other radio unit with a threshold S/(N+I)_thr, and which is suitably also the unit which serves to increase or decrease the output power of the radio unit's 105 transmissions according to this comparison, while also observing an upper limit S_MAX for S which S is not allowed to exceed. In addition, the radio unit 105 also comprises a memory unit 1 1 5, for access by the control unit 1 1 3.

Fig 3 shows a schematic flow chart of a method 300 of the invention. The method 300 comprises, as indicated in step 305, transmitting electromagnetic signals with a certain output power POUT to another radio unit, and receiving, as indicated in step 310, measurement reports from the other radio unit. The method 300 also comprises, as indicated in step 31 5, receiving measurements in said measurement reports of the other radio unit's Signal to Noise and Interference Ratio, the S/(N+I), as well as measurements of the other radio unit's received Signal power, S. As indicated in step 320, the method comprises comparing the other radio unit's S/{N+I) with a threshold value S/(N+I)_thr, and, as indicated in step 325, increasing or decreasing the output power of the transmissions to the other radio unit according to said comparison, whilst also using an upper limit S_MAX which S is not allowed to exceed.

In some embodiments, as shown in step 330, the method comprises determining S_MAx as SMAX=S/(N+IMAX), where IMAX is a maximum value for the interference. In some embodiments, the method 300 comprises determining I AX as x^*N, where x is a system dependent factor. in some embodiments of the method 300, x is in the range of 0.25 to 2.

In some embodiments, the method 300 comprises making the transmissions to the other radio unit with one of a number of modulation levels, and choosing modulation level according to the current transmission capacity need, and to increase or decrease the modulation level with increases and decreases in the transmission capacity need.

In some embodiments, the method 300 comprises determining the current transmission capacity need by measuring the insertion rate of idle cells and/or by measuring one or more queues or buffers in the radio unit.

In some embodiments, the method 300 comprises varying SMAX depending on the modulation level.

Embodiments of the invention are described with reference to the drawings, such as block diagrams and/or flowcharts. It is understood that several blocks of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by computer program instructions. Such computer program instructions may be provided to a processor of a general purpose computer, a special purpose computer and/or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer and/or other programmable data processing apparatus, create means for implementing the functions/acts specified in the block diagrams and/or flowchart block or blocks. These computer program instructions may also be stored in a computer- readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function/act specified in the block diagrams and/or flowchart block or blocks.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the function s/acts specified in the block diagrams and/or flowchart block or blocks. . in some implementations, the functions or steps noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

In the drawings and specification, there have been disclosed exemplary embodiments of the invention. However, many variations and modifications can be made to these embodiments without substantially departing from the principles of the present invention. Accordingly, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation. The invention is not limited to the examples of embodiments described above and shown in the drawings, but may be freely varied within the scope of the appended claims.

Claims

1. A radio unit (105) arranged to transmit electromagnetic signals with a certain output power to another radio unit (110), the radio unit (105) also being arranged to receive measurement reports from said other radio unit (1 0), the radio unit (105) being characterized in that it is arranged to receive measurements in said measurement reports of the other radio unit's ( 0) Signal to Noise and Interference Ratio, the S/(N+I), as well as measurements of the other radio unit's (110) received Signal power, S, and to compare the other radio unit's S/(N+I) with a threshold value S/(N+I)_thr, and to increase or decrease the output power of its transmissions to said other radio unit according to said comparison, whilst also using an upper limit SMAX which S is not allowed to exceed.

2. The radio unit (105) of claim 1 , being arranged to determine SMAX as S AX=S/(N+IMAX), where IMAX is a maximum value for the interference.

3. The radio unit (105) of claim 1 , being arranged to determine IMAX as x^*N, where x is a system dependent factor.

4. The radio unit (105) of claim 3, in which x is in the range of 0.25 to 2.

5. The radio unit (105) of any of claims 1 -4, being arranged to make its transmissions to the other radio unit (1 10) with one of a number of modulation levels, the radio unit (105) being arranged to choose modulation level according to its transmission capacity need, and to increase or decrease the modulation level with increases and decreases in the transmission capacity need.

6. The radio unit (105) of claim 5, being arranged to determine its transmission capacity need by means of measuring the insertion rate of idle cells and/or by measuring one or more queues or buffers in the radio unit.

7. The radio unit (105) of any of claims 2-6, being arranged to let S_MAX vary depending on the modulation level.

8. A method (300) for use in operating a radio unit (105), comprising (305) transmitting electromagnetic signals with a certain output power to another radio unit (1 10) and receiving (310) measurement reports from said other radio unit (1 10) the method (300) being characterized in that it comprises receiving (31 5) measurements in said measurement reports of the other radio unit's (1 10) Signal to Noise and Interference Ratio, the S/(N+I), as well as measurements of the other radio unit's (1 1 0) received Signal power, S, and comparing (320) the other radio unit's S/(N+I) with a threshold value S/(N+I)t r, and (325) increasing or decreasing the output power of the transmissions to the other radio unit according to said comparison, whilst also using an upper limit SMAX which S is not allowed to exceed.

9. The method (300) of claim 10, comprising (330) determining SMAX as

where !_MAX is a maximum value for the interference.

10. The method (300) of claim 9, comprising determining I AX as x*N, where x is a system dependent factor.

1 1 . The method (300) of any of claims 8-10, according to which x is in the range of 0.25 to 2.

12. The method (300) of claims 8-1 1 , comprising making said transmissions to the other radio unit (1 10) with one of a number of modulation levels, and choosing modulation level according to the current transmission capacity need, and to increase or decrease the modulation level with increases and decreases in the transmission capacity need.

13. The method (300) of claim 12, comprising determining the current transmission capacity need by measuring the insertion rate of idle cells and/or by measuring one or more queues or buffers in the radio unit.

14. The method (300) of any of claims 9-13, comprising varying S_MAx depending on the modulation level.