Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
  • H04W52/247—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters where the output power of a terminal is based on a path parameter sent by another terminal
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/06—TPC algorithms
  • H04W52/14—Separate analysis of uplink or downlink
  • H04W52/146—Uplink power control
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
  • H04W52/241—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account channel quality metrics, e.g. SIR, SNR, CIR, Eb/lo
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/69—Spread spectrum techniques
  • H04B1/707—Spread spectrum techniques using direct sequence modulation
  • H04B1/7097—Interference-related aspects
  • H04B1/711—Interference-related aspects the interference being multi-path interference
  • H04B1/7115—Constructive combining of multi-path signals, i.e. RAKE receivers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/30—Monitoring; Testing of propagation channels
  • H04B17/309—Measuring or estimating channel quality parameters
  • H04B17/336—Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/06—TPC algorithms
  • H04W52/16—Deriving transmission power values from another channel

Definitions

• the present invention relates to the field of radio communication systems, and particularly to an improved method for estimating the signal-to-interference ratio (SIR) giving an unbiased SIR estimate.
• SIR signal-to-interference ratio
• the unbiased SIR estimate can for example be used in an uplink power control method in a W-CDMA system.
• CDMA Code Division Multiple Access
• TPC Transmission power control
• the SIR- value can be estimated accurately. Particularly, it is important that the SIR measurement is linear, so that the power commands sent from the base stations accurately reflect proper adjustments for the true input signal strength. In case of a non-linear estimation, the base stations may provide power level adjustments that bear little relation to the true input signal levels.
• inter-path interference or self-interference
• RAKE-receiver after RAKE combining
• None of the SIR algorithms described in the above mentioned documents take the inter-path interference into account, and these algorithms are not linear in the case when multi-path fading consists of more than one path.
• the non- linearity is caused, among other things, by inter-path interference and must be removed or corrected for in order to get a linear SIR estimate.
• a measured SIR-value is corrected for nonlinearity to obtain a corrected SIR-value.
• a correction function may be calculated in real time based on currently received SIR-values or the correction function may be used to generate a look-up table stored in memory for a desired range of measured SIR-values.
• a method for providing an unbiased signal-to-interference ratio estimation in a receiver of a radio communication system comprises the steps of : receiving a transmitted signal, estimating the signal energy and an interference value of the received signal, calculating a first SIR estimate based on the estimated signal energy and the interference value, correcting the first estimated SIR-value for nonlinearity by means of a correction function and thereby obtaining a corrected SIR—value, while taking inter-path interference into account, repeatedly calculating the corrected SIR-value on the basis of received signal samples, whereby the same accuracy being achieved regardless of the number of paths occurring in the receiver.
• the modified algorithm for SIR estimates in accordance with the present invention accounts for non-linear contributions to a SIR-value arising from multi-path interference in a receiver, and said improved algorithm gives the same accuracy regardless of how many paths that are used in the receiver, thus overcoming the disadvantages with the prior art where nonlinearities are compensated for in the same manner irrespective of the number of paths, i.e. irrespective of the number of fingers used in a RAKE-receiver .
• said corrected SIR-value is obtained by calculating the product between a first SIR estimate and a multiplicative factor, D, given by
• G is a gain factor for power control, G 2 is obtained by
• ⁇ s is the number of pilot bits used in the estimation
• N r is the number of rake fingers used in a RAKE-receiver
• E b is the received signal energy per data bit
• S c is the spreading factor for the control channel
• ⁇ c and ⁇ a are the gain factors that sets the power ratio between a dedicated physical control channel (DPCCH) and a dedicated physical data channel (DPDCH) (for details see 3 rd Generation Partnership Project (3GPP, TS 25,213).
• DPCCH dedicated physical control channel
• DPDCH dedicated physical data channel
• This embodiment thus accounts for the number of paths used in the receiver, and thus gives an accurate SIR estimate taking the multi-path interference into account.
• said method provides a linear corrected SIR-value even for SIR- values above 12 dB .
• an unbiased SIR estimation can be provided even for rather high SIR-values, not underestimating nor overestimating the actual SIR-value.
• the last known pair of ⁇ c and ⁇ d is used for the first frame in a time transmission interval (TTI) , and the correct values of ⁇ c and ⁇ d are used for the other frames.
• TTI time transmission interval
• the invention also relates to a power control method, using the improved method for estimating SIR-values.
• the power control method comprises the step of : controlling the transmitted power in a transmitter on the basis of the corrected SIR-value calculated .
• the invention further relates to a receiver comprising means for performing the improved method for estimating SIR-values.
• the invention further relates to a radio communication system comprising at least one of said receivers.
• a receiver for use within a communication system comprising a means for receiving a transmitted signal, a means for estimating the signal energy and an interference value of the received signal, a means for calculating a first SIR estimate based on the estimated signal energy and the interference value, the receiver being characterized in further comprising a means for correcting the first estimated SIR-value for nonlinearity by means of a correction function and thereby obtaining a corrected SIR-value, wherein the means for obtaining a corrected SIR-value is arranged to repeatedly calculate the corrected SIR-value on the basis of received signal samples, while taking inter-path interference into account and to give the same accuracy regardless of the number of paths occurring in the receiver.
• the radio communication system for communication of signals between at least two receivers, comprising at least one receiver as described above. Further, the radio communication system comprises at least one base station being provided with said at least one receiver and at least one transmitter for transmitting power command signals to mobile communication units located within an associated range of the base station.
• a mobile communication unit for use in a radio communication system as described above comprises a receiver for receiving power command signals and a transmitter for transmitting communication signals at a power level being controlled by the power commands signals being based on unbiased SIR-estimates .
• Fig. 1 shows the basics of an uplink power control loop.
• Fig. 2 shows the uplink spreading scheme in UTRA/FDD.
• Fig. 3 shows a TTI as function of time, where the first frame in the new TTI is shadowed.
• Fig. 4 shows the error between the true SIR and the estimated SIRs.
• Fig. 5 shows SIR estimates without power control.
• Radio Network Controller sets a target SIR, or a reference SIR, and informs the base stations (Node B) about this target SIR.
• the base stations use the target SIR and lower or raise the power used by the mobile stations accordingly.
• adjustments of the set target SIR are made if necessary based on a desired block error rate.
• an inner loop see fig. 1 , between the base stations and the mobile stations, where the power is increased or decreased based on received power levels in the respective receivers.
• the uplink inner power control loop in UTRA/FDD has as a task to mitigate the effects of a fast fading radio channel.
• the uplink transmit power control (TPC) commands are sent to the user equipment (UE) from a Node B of a W-CDMA system.
• the TPC commands are based on the estimated Signal -to-Interference Ratio (SIR) at the Node B, as shown in fig. 1.
• SIR is defined as the ratio of the energy per data bit (E ) to the average received interference power (I) .
• E energy per data bit
• I average received interference power
• SIR is the signal -to- interference ratio at the input of the receiver. It means that in the case of a multipath channel the powers of all received signal components should be added to calculate the received signal bit energy. At the same time only the input (i.e. external) interference should be measured.
• each subsequent access attempt is transmitted at a power level that is a specified amount higher (1 dB for example) than the previous one.
• the mobile waits a specified period to receive an acknowledgment from the base station.
• the access attempt ends, and the mobile keeps the same power level for subsequent transmission on the traffic channel. Therefore, when the base station begins to receive the traffic channel signal transmitted by the mobile, the transmitted mobile power can be very high and quite possibly saturate the SIR measurement at the base station. This may continue to be a problem as long as the transmitted mobile power is not reduced by a traffic channel power control loop, such as the inner power loop described above. However, the power control loop requires more time and may even fail to reduce the mobile power if the measured SIR-values are not correct. It is thus most important to be able to provide an SIR-estimate that is as accurate as possible .
• the uplink spreading scheme in UTRAN/FDD is shown in fig. 2.
• the received signal y (m) can be represented as
• a () ja(k) ⁇ c GS c + ⁇ ⁇ a(n)(j ⁇ e + A / (m))Gc(/ « - ⁇ admir )c * ( - r, ) + W k (/).
• ⁇ l n ⁇ k
• de-spread symbols Pk(i) can thus be expressed as
• subindex k stands for path k
• ⁇ k is the delay for path k
• a (k) is the channel coefficient for path k
• C d (m) is the channelization code for DPDCH
• C c is the channelization code for DPCCH, it equals 1 for all index, and is thus not shown in (1) ,
• c* is the complex conjugate of the scrambling code
• N r is the number of active rake fingers used in the RAKE- receiver
• G is a gain factor for power control
• ⁇ c and ⁇ d are gain factors that determine the power ratio between the dedicated physical control channel (DPCCH) and the dedicated physical data channel (DPDCH) . That is, ⁇ c is the gain factor for the control part of the signal, and ⁇ d is the gain factor for the data part of the signal, and the factors ⁇ c and ⁇ d may vary for each TFC (Transport Format Combination, see 3 rd Generation Partnership Project (3GPP) , TS 25.212), and may vary on a radio frame basis.
• the total power of the channel coefficients equals to 1,
• N s is the number of pilot bits used in the estimation
• N r is the number of paths
• Pk d is the i : th de- spread symbol
• P p (i ) is the i : th transmitted pilot bit
• a is the filter coefficient for the interference estimate
• the bit energy is estimated by using the pilot bits to estimate the signal power in each path, and then after summing the energy from all paths, by multiplying the estimated power with the spreading factor, as it is shown in (3) , (4a) and (4b) .
• the pilot symbols are more reliable to estimate the power of the pilot symbols than the power of the voice (or data) symbols since the pilot symbols are usually transmitted at higher power levels.
• estimating the power of other symbols than the pilot symbol is considered to be within the scope of the present invention.
• the interference power is obtained by estimating the variance of the difference between estimated signal amplitude and the received signal samples, as shown in equations (5a) to (5c) .
• the UE (user equipment) will probably end up with maximum allowed transmission power.
• Two examples of cases when nonlinear SIR measurement causes problems with the power control loops are underestimation and overestimation respectively of the SIR-measurement .
• the case of underestimating the SIR will lead to unnecessary power up commands which means that the outer power control loop will be faster than in the case of a linear SIR-measure.
• the UE will transmit with a higher power than needed, and thus cause more interference than necessary in the system, and also unnecessarily shorten the battery life of the UE .
• the second case, in which the SIR is overestimated more power down commands will be issued to the UE and the outer power control loop will be slower than in the case of linear SIR estimation.
• the SIR measurement is linear, the power commands from the base station will accurately reflect proper adjustments for the true input signal strength. But, when there is a non-linear estimation the base station may provide power level adjustments that bear little relation to the true input signal levels, as was explained earlier
• the signal energy per data bit, E b is estimated as the summation of the squares of the average value of the despreaded pilot symbols, p k (i ) .
• the instantaneous interference,/ is estimated as the summation of the squares of difference between pilot symbols and the average value of the pilot symbols.
• the average received interference power, I, used when forming the SIR estimate is a filtering of the instantaneous interference and the previous interference I .
• SIR' An first SIR estimate, SIR' , is then calculated as the ratio between E b and I.
• N r is the number of paths and N s is the number of pilot symbols used.
• a modified algorithm is used, taking multi -path interference into account and giving the same accuracy irrespective of the number of active paths used.
• this corrected SIR estimate will be the same as (2), i.e. it will be unbiased.
• the amount of degradation for the proposed algorithm in the first frame of each TTI depends mostly on the difference between the last known values of ⁇ c and ⁇ d and the new set of ⁇ c and ⁇ d .
• the ratio between ⁇ c and ⁇ d is in the range of 1/15-1, but a range used in practice is in the range of 4/15, 5/15,..., 10/15 for the different spreading factors on the dedicated physical data channel (DPDCH) .
• DPDCH dedicated physical data channel
• Fig. 4 shows the errors e new and e a id between the true SIR and the estimated SIRs that will be introduced in the first frame in a new TTI when the ratio between ⁇ c and /? d is changed.
• the error between the true SIR and the SIR estimates is shown along the Y-axis in dB.
• the worst-case scenario for both methods occurs when e new and e 0 ⁇ d are positive and have the maximum absolute values. In that case the SIR will be underestimated and unnecessary power up commands will be generated. The larger absolute values of such positive errors, the larger number of power up commands will be issued.
• This worst case happens when the ratio between ⁇ c and ⁇ d changes from 10/15 to 4/15.
• the error e new for the unbiased algorithm is smaller than the error e oid for the biased algorithm.
• the error e new in the first frame in the TTI is d.new around 1.7 dB for the present unbiased algorithm and e ol ⁇ is around 2.3dB for the current biased algorithm.
• the TTI is usually greater than one frame period, which means that for the rest of the frames in the TTI the error for the proposed method will be zero while the error for the current method will remain the same for all frames in a TTI .
• the present invention thus modifies the current algorithm, which modification gives an unbiased SIR estimation even in cases when the SIR is above 12dB.
• the currently used SIR estimation algorithm does not take the inter-path interference (IPI) into account. This may lead to unnecessary power-up commands being sent to the mobile station, which will introduce more interference and limit the number of users in the system.
• IPI inter-path interference
• the transmit power control method in a radio communication system comprises the step of : controlling the transmitted power in a transmitter on the basis of a corrected SIR-value calculated, calculating the corrected SIR-value in a base station of the radio communication system, transmitting a power command signal based on the corrected SIR- value to a mobile communication unit located within an associated range of the base station and comprising a transmitter whose transmitting power is controlled by the power command signal .
• the receiver comprises a means for receiving a transmitted signal, a means for estimating the signal energy and an interference value of the received signal, a means for calculating a first SIR estimate based on the estimated signal energy and the interference value, a means for correcting the first estimated SIR-value for nonlinearity by means of a correction function and thereby obtaining a corrected SIR-value, wherein the means for obtaining the corrected SIR-value is arranged to repeatedly calculate a corrected SIR-value on the basis of received signal samples, while taking inter-path interference into account and to give the same accuracy regardless of the number of paths occurring in the receiver.
• the means for obtaining the corrected SIR- value can be arranged to calculating the product between the first estimated SIR-value, provided by the means for correcting the first estimated SIR-value, and a multiplicative factor, D, given by the formula (7) .
• the first estimated SIR-value is given by formula (6) .
• the receiver further comprises a means for providing a linear corrected SIR-value even for SIR-values above 12 dB .
• the receiver further comprises a means for using the last known pair of ⁇ c and ⁇ d for the first frame in a time transmission interval (TTI), and a means for using the correct values of ⁇ c and ⁇ d for the other 5 frames in W-CDMA system.
• TTI time transmission interval
• the radio communication system for communication of signals between at least two receivers, comprises at least one receiver as above described, at least one base station being provided with said at least one receiver and at least one transmitter 10 for transmitting power command signals to mobile communication units located within an associated range of the base station.
• the mobile communication units comprises a receiver for receiving power command signals and a transmitter for transmitting communication signals at a power level being L5 controlled by the power commands signals being based on unbiased SIR-estimates .
• C d (m) is the channelization code for DPDCH
• c is the scrambling code
• c * is the complex conjugate of the scrambling c
• N r is the number of active rake fingers used in the RAKE receiver
• G is a gain factor for power control. !0 ⁇ c and ⁇ d are the gain factors that sets the power ratio between the dedicated physical control channel (DPCCH) and the dedicated physical data channel (DPDCH) .
• DPCCH dedicated physical control channel
• DPDCH dedicated physical data channel
• Each symbol consists of three independent parts, the desired signal, inter-path interference (IPI) and additive white noise.
• IPI inter-path interference
• the expectation value and variance of the first part is given by
• the expectation value and variance of v(m) and v'( ⁇ n) are calculated as:
• the expectation value and variance for the de-spread symbols P k (i) can be calculated by using (A.l), (A.3) and (A.4)

Landscapes

• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Quality & Reliability (AREA)
• Mobile Radio Communication Systems (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

Family

ID=32400061

Family Applications (1)

Country Status (4)

Cited By (7)

Families Citing this family (2)

Citations (4)

• 2002
  • 2002-12-02 WO PCT/CN2002/000860 patent/WO2004051902A1/en not_active Application Discontinuation
  • 2002-12-02 CN CN02829965.5A patent/CN100481756C/zh not_active Expired - Lifetime
  • 2002-12-02 AU AU2002368404A patent/AU2002368404A1/en not_active Abandoned
• 2006
  • 2006-04-20 HK HK06104734.7A patent/HK1084523A1/xx not_active IP Right Cessation

Patent Citations (4)

Also Published As

Similar Documents

Legal Events