JP2006514452A - Uplink SINR estimation - Google Patents

Abstract

This is a configuration for estimating the uplink SINR of the CDMA channel. This configuration includes means (40) for estimating the signal power using the channelization code of the channel. The selector (28) searches for and selects an idle channelization code that is orthogonal to the channelization code of the channel. This idle code is used by yet another means (30) to estimate the power of interference plus noise. These means are then used by means (42) to form SINR estimates.

Description

TECHNICAL FIELD The present invention relates to signal-to-interference plus noise ratio (SINR) estimation for code division multiple access (CDMA) channels.

SINR is an important link performance indicator used in various radio network algorithms such as inner loop power control in CDMA systems. SINR estimation is very important because it indirectly affects power management in both base stations and mobile stations. The estimated SINR actually reflects the radio link quality that is occurring, and needs to be as accurate as possible.
SINR estimation is performed by measuring signal power “S” and interference plus noise power “IN”. Although it is very easy to measure “S”, it is very difficult to understand how to measure “IN”.

A known method for estimating the power of interference plus noise (IN) regenerates the pilot symbols (after restoration) and calculates the deviation of these symbols from the ideal signal point. However, since SINR is measured every time slot, only a few (2-8) pilot symbols are available, which means that the accuracy obtained for IN measurements is very low. Since the same IN estimates are used for SINR estimation for all channels, it can be seen that the accuracy of these estimates is limited.
In another method described in the references [1, 2], one downlink channelization code is reserved as an “interference plus noise measurement code” that is never used for information transmission. In this method, a downlink IN estimated value is generated by restoring a received signal with a reservation code. However, this method has several drawbacks. First, since this method reserves a code for IN measurement, it is necessary to redefine an existing standard. Next, in order to avoid a situation where channelization codes are insufficient, a code having a large spreading factor (SF = 256) is reserved. Increasing the spreading factor means fewer symbols, which limits the accuracy improvement that can be achieved.

SUMMARY OF THE INVENTION It is an object of the present invention to increase the accuracy of uplink SINR estimation, particularly interference plus noise estimation, without requiring changes to existing standards.
This object is achieved by the appended claims.
In summary, the present invention preferably selects an idle (unused) channelization code with the lowest available spreading factor and uses this code to estimate the power of interference plus noise. Since the idle code is selected, there is an advantage that there is no need to change the existing standard. Another advantage of using idle codes (such codes are always available in the uplink) is that there is no code shortage due to SINR measurements. In addition, the method allows the code tree to be searched down to the lowest available spreading factor, thus increasing the number of symbols in the IN measurement, thereby greatly increasing the accuracy of the IN estimation. be able to.

The invention and further objects and advantages of the invention can be best understood from the following detailed description with reference to the accompanying drawings.
In the following description, the same reference symbols are used throughout the drawings to refer to the same or similar components.
Further, it is assumed that only BPSK or QPSK modulation is used, an orthogonal variable spreading factor (OVSF) code is used as a channelization code, and the scrambling code is a complex sequence over a sufficiently long period. Both WCDMA and CDMA2000 meet these assumptions.

上の式において、「Ｅ（ ）」は期待値（統計平均）を指す。位相補償が完全であるとすると、次式が導かれる。

このような理由により、本文書では主として、復調される元のビットのＳＩＮＲについて議論し、「ＳＩＮＲ」という用語は通常、「ＳＩＮＲ_ｂｉｔ」を表わす。 The SINR of the recovered symbol and the demodulated original bit is usually represented by the following equations, respectively.

In the above formula, “E ()” indicates an expected value (statistical average). If the phase compensation is perfect, the following equation is derived:

For this reason, this document mainly discusses the SINR of the original bits to be demodulated, and the term “SINR” usually refers to “SINR _bit ”.

上式中、

であり、Ｎ_{ｐｉｌｏｔｓ}は推定に使用されるパイロットシンボルの数である（ＢＰＳＫの場合は１シンボル＝１ビット、ＱＰＳＫの場合は１シンボル＝２ビット）。関連パイロットに関するこのＳＩＮＲ推定は、上記の一般的なＳＩＮＲ定義に準拠するが、信号電力推定における偏りを取り除いている。 Different vendors have different methods for estimating SINR. As an example, FIG. 1 shows a typical CDMA receiver with functional blocks for estimating SINR by utilizing associated pilots. The associated pilot is a known symbol / bit, which is transmitted simultaneously (in the sense that both the multipath channel and the interference plus noise power both change little) and as data from the same transmitter. Both dedicated and common pilots in WCDMA and CDMA2000 are examples of such related pilots.
FIG. 1 is a conceptual block diagram of a prior art SINR estimation configuration. The received signal samples are transferred to the receiver filter 10. The receiver filter 10 is a multipath channel matched filter or equalizer. The filtered signal is descrambled by the complex conjugate SC ^* of the complex scrambling code. The descrambled signal is multiplied by channelization codes CC _data and CC _pilot , respectively, and integrated in integrators 12 and 14, respectively, to be restored to two parallel signal streams RU _data (n) and RU _pilot (n). The SINR estimation is performed using pilot signal branching, which first obtains the product signal ru _pilot (n) by multiplying ru _pilot (n) by the complex conjugate of the known signal u _pilot (n), This is done by obtaining SINR measurement values based on the product signal ru _pilot (n). The SINR is then estimated in blocks 16, 18 and 20 using the following equation:

In the above formula,

N _pilots is the number of pilot symbols used for estimation (1 symbol = 1 bit for BPSK, 1 symbol = 2 bits for QPSK). This SINR estimate for the associated pilot conforms to the general SINR definition above, but removes the bias in signal power estimation.

上式中の記号は以下のように定義する。
ＭＦ_ｄａｔａ＝データに関する変調率（２＝ＢＰＳＫ，１＝ＱＰＳＫ）
ＭＦ_{ｐｉｌｏｔ}＝関連パイロットに関する変調率（２＝ＢＰＳＫ，１＝ＱＰＳＫ）
ＳＦ_ｄａｔａ＝データに関する拡散率
ＳＦ_{ｐｉｌｏｔ}＝関連パイロットに関する拡散率
Ｐ_ｄａｔａ＝データの送信電力
Ｐ_{ｐｉｌｏｔ}＝関連パイロットの送信電力
ＷＣＤＭＡ及びＣＤＭＡ２０００では、下りリンクにはＱＰＳＫ変調を用い、上りリンクにはＢＰＳＫ変調を用いる。 In general, the SINR of a data channel can be estimated by simply scaling the estimated SINR of the associated pilot.

The symbols in the above formula are defined as follows.
MF _data = modulation rate related to _data (2 = BPSK, 1 = QPSK)
MF _pilot = modulation rate for the associated pilot (2 = BPSK, 1 = QPSK)
SF _data = spreading factor for data SF _pilot = spreading factor for related pilot P _data = transmission power of data P _pilot = transmission power of related pilot In WCDMA and CDMA2000, QPSK modulation is used for the downlink and BPSK modulation is used for the uplink Is used.

すなわち、推定データＳＩＮＲは推定パイロットＳＩＮＲと同じ精度を有する。推定精度は次式により定義される。

「第３世代パートナーシッププロジェクト（３ＧＰＰ）」では、８０ｍｓの平均区間を有する区間−７ｄＢ＜１０・ｌｏｇ_１０（ＳＩＮＲ_{ａｃｔｕａｌ}）＜７ｄＢにおいてＸ_ｄＢ＝３ｄＢである場合の精度が９０％以上であることが必要である。 The disclosed method is typical for uplink dedicated physical data channels that perform SINR estimation using uplink dedicated pilots in WCDMA and CDMA2000. When this estimation method is used, the following equation is obtained.

That is, the estimated data SINR has the same accuracy as the estimated pilot SINR. The estimation accuracy is defined by the following equation.

In the “3rd Generation Partnership Project (3GPP)”, the accuracy when X _dB = 3 dB in an interval having an average interval of 80 ms−7 dB <10 · log ₁₀ (SINR _actual ) <7 dB is 90% or more. is necessary.

In WCDMA, an estimated SINR needs to be generated every time slot (0.667 ms) and input to an inner loop power control algorithm. Assuming that the multipath channel and interference plus noise power hardly change during a time slot, the demodulated original bits are Gaussian and the SINR is fixed over the entire time slot. Depending on the slot format, the dedicated physical control channel has 2 to 8 dedicated pilot symbols (1 symbol = 2 bits) per time slot in the downlink and 3 to 8 dedicated pilot symbols (1 symbol = 1 bit in the uplink). 1 bit). The estimation accuracy depends on the number of related pilots used for estimation. The more the number of pilots, the higher the estimation accuracy.
One solution to improve the estimation accuracy is to measure the effective interference plus noise power for a different measurement object from the measurement of signal power so that more symbols can be utilized. According to the present invention, in the uplink, effective interference plus noise power measurement is performed on the idle code channel. An idle code is an OVSF code that is not occupied as a channelization code or used to generate a channelization code (s). FIG. 2 shows an OVSF code tree. The channelization code is described in a unique form as C _{ch, SF, k} , where SF is the code spreading factor, k is the code number, and 0 ≦ k ≦ SF−1. Each level of the code tree defines a channelization code of length SF corresponding to the spreading factor of SF. The leftmost value of each channelization codeword corresponds to the first transmitted chip on the time axis. An important feature of the OVSF code tree is that the channelization codes of different branches are orthogonal to each other regardless of the spreading factor SF. As will be described later, the present invention uses this feature.

In order to obtain an accurate estimate of the effective interference plus noise power, the spreading factor (SF) of the idle code can be as small as possible so that as many symbols as possible can be used during the same time slot. It is preferable to make it. The minimum SF of the idle code is 2 when all the used codes belong to the same half of the OVSF tree. More specifically, if all channelization codes are derived from the OVSF code (1,1), the OVSF code (1, -1) can be used as an idle code, and vice versa.
In the proposed idle code system, it is not necessary to make any changes to the existing standard, and there is no extra load for notification. Since the base station already knows the user's channelization code and recovers this user's different code channel, the base station can generate the best idle code by looking up the OVSF code tree. More specifically, from the 3GPP specification [3], the following conclusion can be drawn for WCDMA.
1. As shown in FIGS. 3 and 4, the channelization code C _{ch, 2,1} (SF = 2) is always in an idle state when 1 or 2 DPDCHs are transmitted in the uplink (in fact, the lower side All branches contain idle code, but C _{ch, 2,1} is preferred because it has the lowest spreading factor (SF = 2)).
2. As shown in FIG. 5, channelization code C _{ch, 4,2} (SF = 4) (and branch starting from this code) is always idle when 3 or 4 DPDCHs are transmitted in the uplink. .
3. As shown in FIG. 6, the channelization code C _{ch, 8,1} (SF = 8) (and the branch starting from this code) is always idle when 5 or 6 DPDCHs are transmitted on the uplink. .

従って、正しくスケーリングし直すことにより、所望のチャネルの可変推定を代わりにアイドルチャネルに対して実施することができる。 The idle code channel can be regarded as a channel with zero transmission power, and by using the same analysis method as shown in the reference [4], the following equation is derived.

Thus, by re-scaling correctly, variable estimation of the desired channel can be performed on the idle channel instead.

上式中の記号は次式により表わされ、

さらに、
Ｎ_{ｐｉｌｏｔｓ}は推定に使用されるパイロットシンボルの数であり、
Ｎ_ｉｄｌｅは推定に使用されるアイドルシンボルの数である。
ここでは、記号

を使用して平均が信号サンプルのノルム二乗により形成されることを示している。 For example, if the desired code channel has time-multiplexed pilot symbols, corresponding to the case of dedicated physical control channel (DPCCH), the estimated SINR of the desired code channel can be calculated as shown in the configuration of FIG. FIG. 7 shows the parts of the base station that are important for explaining the exemplary embodiment of the present invention. In the present embodiment, the descrambled signals are multiplied by channelization codes CC _DPCCH and CC _idle , respectively, and integrated in integrators 12 and 14, respectively, so that two parallel signal streams RU _DPCCH (n) and ru _idle ( n). The idle channelization code is selected by the idle code selection block 28 based on the OVSF code tree of FIG. 2 and the occupancy code recognized by the base station. The idle channelization code can be used as a simple lookup table, for example. The SINR is then estimated in blocks 16, 30, and 32 using the following equation:

The symbol in the above formula is represented by the following formula:

further,
N _pilots is the number of pilot symbols used for estimation,
N _idle is the number of idle symbols used for estimation.
Here is the symbol

Is used to show that the average is formed by the norm square of the signal sample.

上式中の記号は次式により表わされ、

さらに、
Ｎ_{ＤＰＤＣＨ}は推定に使用される信号シンボルの数であり、
Ｎ_ｉｄｌｅは推定に使用されるアイドルシンボルの数である。
本発明の構成の機能は通常、マイクロプロセッサ又はマイクロ／シグナルプロセッサ結合装置及び対応するソフトウェアとして実行される。 For example, if the desired code channel does not contain any pilot symbols, corresponding to the case of a dedicated physical data channel (DPDCH), the estimated SINR of the desired code channel is calculated non-coherently as shown in the configuration of FIG. FIG. 8 shows the parts of the base station that are important for explaining this exemplary embodiment of the invention. In this embodiment, the descrambled signal is multiplied by the channelization codes CC _DPDCH and CC _idle , respectively, and integrated in the integrators 12 and 14, respectively, whereby two parallel signal streams _{RU DPDCH} (n) and RU _{idle are obtained.} Restored to (n). The idle channelization code is selected by the idle code selection block 28 based on the OVSF code tree of FIG. 2 and the occupancy code recognized by the base station. The idle channelization code can be used as a simple lookup table, for example. The SINR is then estimated in blocks 30, 40 and 42 using the following equation:

The symbol in the above formula is represented by the following formula:

further,
N _DPDCH is the number of signal symbols used for estimation;
N _idle is the number of idle symbols used for estimation.
The functions of the arrangement of the present invention are typically implemented as a microprocessor or micro / signal processor combination device and corresponding software.

For WCDMA uplink, the described prior art method uses only 3-8 dedicated pilot symbols to estimate SINR. In contrast, the method according to the present invention can measure the effective interference plus noise power during one time slot using up to 1280 (2560/2) “idle symbols”. This is a major advantage of using an idle code channel (with a small spreading factor) to assist SINR estimation. The new method can also measure DPCCH power using all 10 DPCCH symbols, and can also measure DPDCH power using all symbols of the DPDCH channel. FIG. 9 illustrates the performance improvement that can be achieved by the present invention. In this figure, the SINR estimate based on the idle code channel (SF = 2) is compared with the SINR estimate based on 8 individual pilot symbols (1 symbol = 1 bit by BPSK modulation). In the present embodiment, the estimation accuracy is improved from 70% to 95% (when X _dB = 3 dB). If there are fewer than 8 individual pilot symbols, the degree of improvement is even greater.
FIG. 10 is a flow chart summarizing an exemplary embodiment of the method according to the present invention. In step S1, the channel channelization code is used to estimate the desired channel power. In step S2, a small SF idle channelization code is retrieved from the OVSF tree using information about the dedicated channelization code and selected. In step S3, the power of interference plus noise is estimated using the obtained idle channelization code. In step S4, an SINR estimate is formed using the determined power estimate. If the channelization code has a different spreading factor, the estimated value obtained in step S3 is rescaled accordingly. Finally, in step S5, the procedure returns to step S1 to estimate the SINR of the next time slot.

  Those skilled in the art will appreciate that various modifications and changes can be made to the present invention without departing from the scope of the invention as defined by the claims.

Reference [1] TSGR1 # 4 (99) 348, “Proposal for downlink information measurement method”. TSG-RAN Working Group 1 meeting # 4, Shin-Yokohama, Japan, April 18-20, 1999.
[2] WO 00/57654.
[3] TS 25.213, “Spreading and modulation (FDD),” version 3.1.0.
[4] Wang Hai, Nilas Wiberg, "Analysis of a CDMA downlink in multi-path fading channels," in Proceeding IEEE Wireless Communication and Network O & M. 17-21, 2002, pp. 517-521.

It is a conceptual block diagram of the SINR estimation structure by a prior art. It is a figure which shows the structure of an OVSF code tree. FIG. 4 is an OVSF code tree diagram showing an idle code when a single DPDCH is used. It is an OVSF code tree figure which shows an idle code in case 2 DPDCH is used. It is an OVSF code tree figure which shows an idle code in case 3-4 DPDCH is used. It is an OVSF code tree figure which shows an idle code in case 5-6 DPDCH is used. FIG. 3 is a conceptual block diagram of an exemplary embodiment of a SINR estimation configuration according to the present invention. FIG. 6 is a conceptual block diagram of another exemplary embodiment of a SINR estimation configuration in accordance with the present invention. It is a figure which shows the performance improvement implement | achieved by this invention. 4 is a flow chart illustrating an exemplary embodiment of a method according to the present invention.

Claims (24)

A method for estimating an uplink SINR of a CDMA channel, comprising:
Determining a first estimate of signal power using the channelization code of the channel;
Searching for and selecting an idle channelization code orthogonal to the channelization code of the channel;
A method comprising: determining a second estimate of interference plus noise power using the idle channelization code; and forming the SINR estimate using the first and second estimates.   The method of claim 1, wherein the forming comprises re-scaling the second estimate when the channel channelization code and the idle channelization code have different spreading factors.   The method of claim 1, comprising selecting an idle channelization code having a minimum available spreading factor. 4. The method according to claim 3, comprising selecting an idle channelization code _{Cch, 2,1} when one or two dedicated physical data channels are used for the uplink. 4. The method according to claim 3, comprising the step of selecting an idle channelization code _{Cch, 4,2} when 3 or 4 dedicated physical data channels are used for the uplink. 4. The method according to claim 3, comprising the step of selecting an idle channelization code _{Cch, 8,1} when 5 or 6 dedicated physical data channels are used for the uplink. A method for estimating uplink interference plus noise power of a CDMA channel, comprising:
A method comprising: searching and selecting an idle channelization code orthogonal to the channelization code of the channel; and determining an estimate of interference plus noise power using the idle channelization code.   8. The method of claim 7, comprising selecting an idle channelization code with a minimum available spreading factor. A configuration for estimating an uplink SINR of a CDMA channel,
Means (16, 40) for determining a first estimate of signal power using the channelization code of the channel;
Means (28) for searching and selecting an idle channelization code orthogonal to the channelization code of the channel;
Means (30) for determining a second estimate of interference plus noise power using the idle channelization code; and means (32) for forming an estimate of the SINR using the first and second estimates. 42)
Configuration including.   10. The arrangement of claim 9, comprising means (32, 42) for rescaling the second estimate when the channel channelization code and the idle channelization code have different spreading factors.   10. The arrangement according to claim 9, comprising means (28) for selecting an idle channelization code having a minimum available spreading factor. 12. Arrangement according to claim 11, comprising means (28) for selecting an idle channelization code _{Cch, 2,1} when one or two dedicated physical data channels are used for the uplink. _{12. Arrangement according} to claim 11, comprising means (28) for selecting an idle channelization code _{Cch, 4,2} when 3 or 4 dedicated physical data channels are used for the uplink. _{12. Arrangement according} to claim 11, comprising means (28) for selecting idle channelization codes _{Cch, 8,1} when 5 or 6 dedicated physical data channels are used for the uplink. A configuration for estimating uplink interference plus noise power of a CDMA channel, comprising:
Means for searching and selecting an idle channelization code orthogonal to the channelization code of said channel; and means for determining an estimate of interference plus noise power using said idle channelization code (30)
Configuration including.   16. The arrangement of claim 15, comprising means (28) for selecting an idle channelization code having a minimum available spreading factor. A base station having a configuration for estimating an uplink SINR of a CDMA channel,
Means (16, 40) for determining a first estimate of signal power using the channelization code of the channel;
Means (28) for searching and selecting an idle channelization code orthogonal to the channelization code of the channel;
Means (30) for determining a second estimate of interference plus noise power using the idle channelization code; and means (32) for forming an estimate of the SINR using the first and second estimates. 42)
Including base stations.   The base station according to claim 17, comprising means (32, 42) for rescaling the second estimate when the channelization code of the channel and the idle channelization code have different spreading factors.   18. A base station according to claim 17, comprising means (28) for selecting an idle channelization code having a minimum available spreading factor. 20. The base station according to claim 19, comprising means (28) for selecting an idle channelization code _{Cch, 2,1} when one or two dedicated physical data channels are used for the uplink. _20. Base station according to claim 19, comprising means (28) for selecting an idle channelization code _{Cch, 4,2} when 3 or 4 dedicated physical data channels are used for the uplink. _20. Base station according to claim 19, comprising means (28) for selecting an idle channelization code _{Cch, 8,1} when 5 or 6 dedicated physical data channels are used for the uplink. A base station configured to estimate uplink interference plus noise power of a CDMA channel, comprising:
Means for searching and selecting an idle channelization code orthogonal to the channelization code of said channel; and means for determining an estimate of interference plus noise power using said idle channelization code (30)
Including base stations.   24. A base station according to claim 23, comprising means (28) for selecting an idle channelization code having a minimum available spreading factor.

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