WO2008014631A1 - A demodulation method for downlink received signal in cdma - Google Patents
A demodulation method for downlink received signal in cdma Download PDFInfo
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- WO2008014631A1 WO2008014631A1 PCT/CN2006/001493 CN2006001493W WO2008014631A1 WO 2008014631 A1 WO2008014631 A1 WO 2008014631A1 CN 2006001493 W CN2006001493 W CN 2006001493W WO 2008014631 A1 WO2008014631 A1 WO 2008014631A1
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- 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
Definitions
- the present invention relates to a mobile station receiving technique in a CDMA wireless communication system, and more particularly to a Rake receiving method of a CDMA downlink Rake receiver. Background technique
- the receiver In CDMA mobile communication systems, the receiver usually uses the Rake scheme. In this receiving method, the receiver uses the estimated multipath information to perform channel estimation for each path, and then performs channel correction for each path, and finally corrects the deviation of the respective paths for maximum ratio combining.
- L is the effective multipath number of multipath search. . Is the target symbol to be detected, A is the product of channel distortion and the transmitted power of the symbol, and y is a column vector, 3 ⁇ 4 is thermal noise and inter-cell interference (modeled as white noise) descrambling the target symbol The total interference and noise of the despread output is the column vector;
- / is the channel estimation result of each path, which is a column vector
- This reception method is optimal in the case where the interference of each path (i.e., u) is independent.
- different users spread the spectrum with different channelization codes, and in the case of synchronous transmission, they are orthogonal to each other. Since multipath breaks this orthogonality, inter-path interference is introduced. This inter-path interference can be colored as long as some improvements are made to the multipath distribution.
- Literature [1] proposed a method for whitening colored interference, called generalized
- Rake (g-Rake, or generalized Rake) achieves better performance than conventional Rake receivers.
- g-Rake needs to calculate the interference correlation matrix and its inverse, requiring additional processing.
- the inverse of the matrix can cause anomalies, and the matrix is not reversible under any circumstances.
- the technical problem to be solved by the present invention is to provide a demodulation method for a CDMA downlink received signal.
- the path-to-noise ratio of the path number is 2 and the path difference is large, and the interference in the small area is dominant, the operation is simple and does not need to be performed.
- the matrix inverse is obtained, and better performance than Rake can be obtained.
- the present invention provides a method for demodulating a CDMA downlink received signal, which includes the following steps:
- CDMA downlink receivers usually use conventional Rake reception or chip-level Balanced.
- the invention provides an improved Rake receiving method, which adopts a simple method of interference cancellation, further enhances the combined signal to noise ratio based on the original maximum ratio combining, and has a small number of paths (preferably 2).
- the multipath SNR is large, a better performance than the original Rake reception can be obtained.
- the structure is simple and the amount of calculation is not large.
- the present invention is more suitable for downlink reception of a CDMA system, that is, applied to a user terminal (UE:).
- UE user terminal
- Figure 1 is a schematic illustration of the virtual path set forth in the present invention.
- the virtual path refers to the symmetrical position of one effective multipath relative to the other effective multipath
- the assignable virtual path refers to the virtual path and any other effective multipath or assigned virtual path.
- the distance must be greater than or equal to one chip.
- L is the number of effective multipaths searched by the multipath searcher.
- ⁇ is called the virtual path of the diameter ⁇ relative to the diameter ⁇ ; where ⁇ and ⁇ are the effective multipaths searched by the multipath searcher.
- FIG 1 there are two effective multipaths P1 and P2.
- the horizontal direction represents the time delay of the diameter; the vertical direction represents the signal-to-noise ratio (strength) of the diameter.
- the path P2 delay is larger than P1, but the signal-to-noise ratio is weaker than P1.
- the diameter P2—1 is indicated by a dotted line, indicating that it is a virtual path and is the virtual path of the diameter P2 relative to P1.
- P2-1 and P2 are symmetric about the center of P1.
- threshold is a simulation parameter and is a variable to be optimized. If the above formula is satisfied, it is considered that the difference in signal-to-noise ratio between the two paths is large enough.
- the virtual path of the weak path ⁇ 2 with respect to the strong path ⁇ is preferentially assigned.
- the allocation process is as follows:
- y 3 is the despreading result of the increased virtual path f; therefore, its despreading result does not contain signal components, all of which are interference and noise, and the channel estimation value corresponding to f can be regarded as zero (ignoring reception) The effect of the shaping filter).
- A is a channel estimation vector, hn o], corresponding to channel estimation values of the first path, the second path, and the third path (virtual path), respectively.
- A means a channel estimation value in the first path ([eta]) descrambling and despreading process, a second path interference ( ⁇ ) is formed by dividing a second diameter; [alpha] Similarly, the first means 2 In the two-path (r 2 ) descrambling and despreading process, the interference formed by the first path ( ⁇ ) is divided by the channel estimation value of the first path; and the diameter of the three paths (ie, the demagnetization result of the virtual path, p' Is the correlation result of the signal of the second path and the spreading code of the target symbol (ie, the multiplication of the channelization code and the scrambling code) divided by the channel estimation value of the second path; / 3 ⁇ 4 , « 2 , « 3 are the first The correlation between the thermal noise (including inter-cell interference) of the second, third, and third paths and the spreading code of the target symbol.
- the interference of the first path contains the same component/3 ⁇ 4 as the despreading result of the third path (virtual path), and only one coefficient is difference; then one of the first paths can be subtracted by a simple elimination method.
- the interference term A 23 ⁇ 4 whose formula is expressed as follows: y; a H ⁇ p' + ⁇ n3 ) +f (1.7) Therefore, the interference term is removed / but the interference term + ⁇ is added. As long as this newly added interference term The power of the first path is increased by less than /3 ⁇ 4 Al .
- the signal-to-noise ratio of the first path is much larger than the signal-to-noise ratio of the second path, which is equivalent to i/zj / 2 , and since the intra-cell interference dominates, the thermal noise (including inter-cell interference) Power is negligible. Then you can infer: The last equal sign in the above equation can be considered to be average.
- the demodulation process of the received baseband digital IQ signal in the CDMA downlink receiver of this embodiment is as shown in FIG. 2, and includes the following steps:
- Step 10 After receiving the baseband digital IQ signal, the CDMA downlink receiver first performs multipath search, searches for L effective multipaths, and performs channel estimation on the L effective multipaths to obtain a channel estimation value column vector A;
- the invention can be applied to a CDMA downlink receiver, and further enhances the combined signal-to-noise ratio on the basis of the original maximum ratio combining, when the number of paths is small (preferably 2) and the multipath SNR is large, Can get better performance than the original Rake reception, and the structure is simple, the amount of calculation is not large.
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Description
一种 CDMA下行接收信号的解调方法
技术领域
本发明涉及 CDMA 无线通信系统中移动台接收技术， 尤其涉及一种 CDMA下行 Rake接收机的 Rake接收方法。 背景技术
在 CDMA移动通信系统中， 通常接收机都采用 Rake方案。 在这种接收 方法中， 接收机利用估计的多径信息， 进行各径的信道估计， 然后进行各径 信道纠偏， 最后各径的纠偏结果进行最大比合并。
其原理用公式可表达为， 各径的解扰解扩输出：
y = hS0 + u (1)
上式中，
, L是多径搜索出来的有效多径数。 。是待检 测的目标符号， A是信道畸变及该符号发射功率的乘积， 同 y—样是列向量， ¾是热噪声及小区间干扰 (建模为白噪声)对该目标符号各径解扰解扩输出的 总干扰和噪声， 是列向量；
最大比合并为：
z = hHy (2)
上式中， /;是各径的信道估计结果， 为列向量；
z就是符号 S0的一个估计。
这种接收方法在各径的干扰 (即 u)是独立的情况下是最优的。 然而， 在 CDMA 下行链路中， 不同的用户以不同的信道化码进行扩频， 在同步发送 的情况下， 是彼此正交的。 由于多径破坏了这种正交性， 引入了径间干扰。 而这种径间干扰可以是有色的， 只要对多径分配进行一些改进。
文献 [1]提出了一种对有色干扰进行白化的方法， 称为 generalized
Rake(g-Rake, 或广义 Rake), 获得了比常规 Rake接收机更好的性能。
文献 [1]: G.E. Bottomley, T. Ottosson, Y.-P.E. Wang, "A generalized Rake
receiver for interference suppression", IEEE Journal on Selected Areas in Communication, Volume 18, Number 8, August/2000.
但是， g-Rake需要计算干扰相关矩阵及它的逆， 需要额外的处理。 矩阵 的逆的求取可能会引起异常， 并不是任何情况下矩阵都是可逆的。
发明内容
本发明要解决的技术问题是提出一种一种 CDMA下行接收信号的解调 方法， 在径数为 2且径的信噪比相差较大， 小区内干扰占主导地位时， 运算 简单， 不必进行矩阵逆的求取， 可获得比 Rake更好的性能。
为了解决上述技术问题， 本发明提供了一种 CDMA下行接收信号的解 调方法， 包括以下步骤:
( a )对接收到的基带数字信号进行多径搜索， 对搜索出的 L个有效多 径进行信道估计， 得到信道估计值列向量/
( b )若 L=2且有效径中强径^和弱径 2的信噪比之比大于设定的门限， 则分配三个径： 强径 弱径 r2 , 及弱径 2相对于强径 η的虚径 3 ;
( c )对分配得到的径进行多径的解扰解扩 , 得到对于目标符号的解扩 列向量 ；^ ^^，；^ ^^分别指强径^、 弱径 r2和虚径 r3的解扩结果；
( d ) 将强径 η的一个干扰项用虚径 r3的解扩结果 乘以一个系数来替 换， 得到更新后的强径 η的解扩结果 ；
( e ) 用更新后的强径的解扩结果 代替原解扩结果; i进行最大比合 并， 得到解调的目标符号 z。
进一步地， 上述解调方法还可具有以下特点： 所述更新后的强径 η的 解扩结果 3; = ;^ - 3 * ，其中 ¾为强径 η的信道估计结果， 为弱径的信道估 计结果。
进一步地， 上述解调方法还可具有以下特点： 所述解调的目标符号 z = + h2y2。 可以看出， CDMA下行接收机通常采用常规的 Rake接收或者码片级的
均衡。本发明提出一种改进的 Rake接收方法， 采用了干扰对消的简单方法， 在原来最大比合并的基础上进一步增强了合并后的信噪比， 在径数较少 (最 好是 2)且多径信噪比相差较大时， 可以得到比原 Rake接收更好的性能。 且 结构简单， 运算量不大。 本发明比较适用于 CDMA系统的下行接收， 即应 用于用户终端 (UE：)。 附图概述
图 1 是本发明中所阐述的虚径的示意图。
图 2是本发明实施例的流程图。 本发明的较佳实施方式
下面先结合附图介绍一下多径分配的基本原理。
首先介绍虚径及可分配的虚径：虚径是指一个有效多径相对另一个有效 多径的对称位置；可分配的虚径指此虚径与其它任何有效多径或已分配虛径 的距离都必须大于或等于一个码片。 公式表达就是：
+ z' l,2,〜£ j = \,2,...L, i≠ j (0.1) 上式中， L是多径搜索器搜索出来的有效多径个数。那么 ϊ就被称为径 τ 相对于径 η的虚径； 其中， ^和 ^都是多径搜索器搜索出来的有效多径。 例 如， 如果多径搜索器搜索出来两个有效多径 η =0( /φ), 2=10( ρ), 那么 72相 对^的虚径就应当为 2*η -T2 =-I0(chip) , 即有一个虛径 f的位置在 -lOchip处； 同理， η相对 72的虚径就应当为 2*τ2-
, 另一个虚径 f的位置在 20chip处； 径延时的单位可随取样速率调整。
图 1中， 存在两个有效多径 P1和 P2。 横向表示径的时延； 纵向表示径 的信噪比 (强度)。 图中， 径 P2时延比 P1大， 但信噪比比 P1要弱。 径 P2—1 以虚线表示， 表明它是一个虚径， 是径 P2相对于 P1的虚径。 P2—1与 P2关 于 P1中心对称。
进一步， 如果 f还满足
\ τ - τι \≥ oversampleRate
I 对于所有的 (0.2) - rm \≥ oversampleRate 则称 f为径 r,.相对于径 r,.可 ^的虚径。 上式中， Ζ是已分配的虚径个 数； oversampleRate是每 chip的过采样点数。 此时径延时的单位也应当为过 采样后的点数目。 当不是每 chip采样一次， 而是每 chi 采样 oversampleRate 次时，相当于径的时间分辩精度增加了；此时一个 chip相当于 oversampleRate 个样点。 由于多径搜索中， 一般都是过采样的， 即一个 chip可采出多于一 个的样点，径的位置精度就提高到样点，所以这里换算成了样点精度。所以， 我们把？和 T等都换算成样点。 以上内容可参照文献 [1]。
在本实施例所应用的场景中， 搜索出来的有效径数 L=2, 且两个有效径 的信噪比相差较大。
对这两个有效多径按信噪比由大到小排列如下：
{ ,τ2} satisfy {SNR{TX) » SNR{T2)} (1.3)
其中 η (i=l , 2)存放的是径的位置。 两个有效径的信噪比的差别是否足 够大可用一个门限来判决：
SNR{ x ) I SNR(T2 ) > threshold (1.4)
上式中， threshold是仿真参数， 是个待优化变量。 满足上式， 则认为两 径的信噪比差别足够大了。
在只有两个有效径的情况下， 为了加强干扰的对消效果，优先分配弱径 τ·2相对于强径 ^的虛径。 在本实施例中， 只分配一个虚径， 其分配过程如下:
= 2 - τ2 (1.5)
改进的 Rake接收机原理
如上所述， 增加了一个虚径？， 那么共三个径， 进行目标符号 <S。的解扰 解扩， 该步骤可用现行方法， 结果为：
^ = ^0 + u (1.6)
上式中， y3是增加的虚径 f的解扩结果； 因此它的解扩 结果中不含有信号分量， 全是干扰和噪声， 对应于 f的信道估计值可认为是 零 (忽略掉接收成型滤波器的影响)。 A是信道估计向量， hn o], 分别 对应于第一径， 第二径， 第三径 (虚径)的信道估计值。 且有：
上式中， A 指在对第一径 （η)解扰解扩过程中， 第二径 (^)所形成的 干扰除以第二径的信道估计值； 同理 Α,2指在对第二径 (r2)解扰解扩过程中， 第一径 (η)所形成的千扰除以第一径的信道估计值； 而径三径 (即虛径 的解 扩结果中， p'是第二径的信号与目标符号 的扩频码 (即信道化码与扰码的 复乘)的相关结果除以第二径的信道估计值； /¾,«2,«3分别是第一径， 第二径， 第三径的热噪声 (含小区间干扰)与目标符号的扩频码的相关结果。
可以看到， 第一径的干扰中含有与第三径 (虚径)的解扩结果相同的成分 /¾, 只相差一个系数； 那么可以通过简单的消去法来减掉第一径中的一个 干扰项 A2¾, 其公式表述如下： y;a H ^p'+^~n3)+f (1.7) 因此， 去掉了干扰项/ 但增加了干扰项 +^^ .只要这个新增 加的干扰项的功率小于 /¾ Al， 那么第一径的信噪比就会得到增加。
由于 '可以认为它们的均值是一样的， 统计特性是一样的。 由前 面的预设条件， 第一径的信噪比远大于第二径的信噪比， 相当于 i/zj / 2, 而且由于小区内干扰占主导， 那么热噪声 (含小区间干扰)的功率可忽略。 则 可推知：
上式中的最后一个等号可认为是平均意义上如此。
因此， 第一径的信噪比确实提高了。
最后对径 2解扩结果, y2和更新后的径 1解扩结果 ， 进行最大比合并：
按上述方法，本实施例 CDMA下行接收机对接收到的基带数字 IQ信号 的解调过程如图 2所示， 包括以下步骤： '
步骤 10, CDMA下行接收机接收到基带数字 IQ信号后， 首先进行多径 搜索， 搜索出 L个有效多径， 并对这 L个有效多径进行信道估计， 得到信 道估计值列向量 A；
步骤 20,若 L=2且有效径中强径 η和弱径 r2的信噪比之比大于设定的门 限 threshold, 则分配三个径： 强径 η、 τ2及弱径 r2相对于强径 的虚径； 步骤 30, 对分配得到的径进行多径的解扰解扩， 得到对于目标符号的 解扩列向量 ， y = [yi,y2,y3]T , , ， 分别指强径 η、 弱径 r2和虚径 r3的解扩 结果； 步骤 40, 按照公式 (1.7), 更新最强径的解扩结果， 即： = 1—；3 * _ , 因为是实际使用， 因此采用强径 ^的信道估计结果¾和弱径的信道估计结果 进行运算；
步骤 50,按照公式 (1.9)对解扩结果进行最大比合并，得到解调的目标符 号， 即 z = ^y; + ¾j 2。
工业实用性
本发明可应用于 CDMA下行接收机， 在原来最大比合并的基础上进一 步增强了合并后的信噪比，在径数较少 (最好是 2)且多径信噪比相差较大时， 可以得到比原 Rake接收更好的性能， 且结构简单， 运算量不大。
Claims
1、 一种 CDMA下行接收信号的解调方法， 包括以下步骤：
( a )对接收到的基带数字信号进行多径搜索， 对搜索出的 L个有效多 径进行信道估计， 得到信道估计值列向量 A；
( b )若 L=2且有效径中强径 η和弱径 r2的信噪比之比大于设定的门限， 则分配三个径： 强径 弱径 r2 , 及弱径 r2相对于强径 η的虚径 r3;
(C)对分配得到的径进行多径的解扰解扩， 得到对于目标符号的解扩 列向量 ;， y = [yi,y2,y3f , ^ 分别指强径 、弱径 2和虚径 r3的解扩结果；
(d) 将强径 η的一个干扰项用虚径 r3的解扩结果 乘以一个系数来替 换， 得到更新后的强径 η的解扩结果；;；
( e) 用更新后的强径的解扩结果 代替原解扩结果 Λ进行最大比合 并， 得到解调的目标符号 ζ。
2、 如权利要求 2所述的解调方法，其特征在于，所述更新后的强径 η的 解扩结果 ;;= - 其中 为强径 η的信道估计结果， 为弱径的信道估
Κ
计结果。
3、 如权利要求 3所述的解调方法， 其特征在于， 所述解调的目标符号
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| US20030202568A1 (en) * | 2002-04-26 | 2003-10-30 | In-Kyeong Choi | Interference canceling device and method in mobile communication system |
| CN1471252A (zh) * | 2002-07-26 | 2004-01-28 | 华为技术有限公司 | 基站接收信号的频率偏差纠正方法以及瑞克接收机 |
| US20060072651A1 (en) * | 2004-10-06 | 2006-04-06 | Mark Kent | Method and system for single antenna receiver system for WCDMA |
-
2006
- 2006-06-29 WO PCT/CN2006/001493 patent/WO2008014631A1/zh not_active Ceased
- 2006-06-29 CN CN200680053572XA patent/CN101390319B/zh active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1411191A (zh) * | 2001-09-21 | 2003-04-16 | 华为技术有限公司 | 一种信道估计方法及装置 |
| US20030202568A1 (en) * | 2002-04-26 | 2003-10-30 | In-Kyeong Choi | Interference canceling device and method in mobile communication system |
| CN1471252A (zh) * | 2002-07-26 | 2004-01-28 | 华为技术有限公司 | 基站接收信号的频率偏差纠正方法以及瑞克接收机 |
| US20060072651A1 (en) * | 2004-10-06 | 2006-04-06 | Mark Kent | Method and system for single antenna receiver system for WCDMA |
Also Published As
| Publication number | Publication date |
|---|---|
| CN101390319A (zh) | 2009-03-18 |
| CN101390319B (zh) | 2011-11-23 |
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