Vol.28 No.9 刘向东等：DMA中干扰消除多用户检测器的研究 ·885· 一般情况下4心会匠则方差表达式可简化 比较，M V-PIC的软判决量方差减小，均值增大， 其误码率必小于传统PIC. 为专的二次函数： va=++ 3结论 干扰消除检测器不依赖于信号的周期稳定 [1-+K-2+ 性，比较适用于长码方案.相对于传统检测器，部 分干扰消除(PPIC)检测器在消除均值偏差、抑 8(K-2K-3)-2K-2月合. 制由于地址长码正交性变差引起的干扰方面有所 改进.基于最小均方误差的PPIC检测器(MV- 采用统一的部分干扰消除系数ξ不可能消 除全部的MAI干扰，但如果选择一个恰当的可 PIC)进一步减小了PPIC的运算量，选用使输出 以改善均值和方差.观察上式由于2的系数为 软判决量方差最小的部分干扰消除系数m,使 正，故该二次函数图形是凹的，方差具有最小值. MV-PIC的输出均值增大、方差减小，误码性能 令dV出-0可得： 优于传统PIC检测器. ds 参考文献 [+k-+k-2k-+ [1]Patel P.Holtzman J.Analysis of a simple successive interfer ence cancellation scheme in DS-CDMA system.IEEE J Sel 水k-=[+k-列合2 Areas Commun.1995(5):796 [2 Patel P,Holtzman J.Performance comparison of a DS-CDMA 从而可得： system using a successive interference cancellation (IC)scheme Sov= and a paralel IC scheme under fading channels//Pmc of ICC' 4N2+2NMK-2) 94.New0rens,1994:510 [3 Divsalr D.Simon M.Improved CDMA Perfomance using 4W2+6N(K-2)+(K-2)(K-3)+ 2N(K -1)NO Paralel Interference Cancelation:Technical Report,JPL Publicat ion 95-21.Pasedena Je Pmopulsion Laboratory.Cah =2 ifornia Instituteof Technology.1995 若不计噪声项有： [4韦辉，路鸣，赵春明.移动卫星通信系统中干扰抵消技术 4W2+2NK-2) 5m=4W2+6NK-2)+(K-2)(K-3 的研究.通信学报，1998,19(9)：27 [习卢光跃，邵朝.DS/CDMA通信系统中干扰消除法.西安邮 显然，v一定小于1，与传统PIC检测器(=1) 电学院学报，2001,6(3)：30 Research of an interference cancellation multi-user detector for CDMA LIU Xiangdong,GU Xuemai Hadbin Institute of Technology.Hadbin 150001,China ABSTRACT Based on the method of statistics,this paper derived the output mean value and variance of conventional parallel interference cancellation(PIC),partial parallel interference cancellation(P-PIC)and minimum mean-squared error(MV-PIC)detectors for CDMA.The results indicated that the deviations of mean value and variance of the linear decision parameters were reduced by P-PIC compared with PIC.The output mean value was increased and the variance was decreased by choosing suitable partial interference cancellation coefficient for M V-PIC,and its perfo mance of code error is superior to PIC. KEY WORDS mobile communication system;parallel interference cancellation;linear decision;minimum mean-squared error一般情况下 A 2 1 ∑ K k =2 A 2 k , 则方差表达式可简化 为 ξ的二次函数 : Var[ y ( 2) 1 i ] = N0 2 T b 1 + K -1 2 N ξ2 + 1 2N ( 1 -ξ) 2 + 3 4 N 2 (K -2) ξ 2 + 1 8 N 3 (K -2)( K -3) ξ2 - 1 2N 2 ( K -2) ξ ∑ K k =2 A 2 k . 采用统一的部分干扰消除系数 ξ不可能消 除全部的 MAI 干扰, 但如果选择一个恰当的 ξ可 以改善均值和方差.观察上式, 由于 ξ2 的系数为 正, 故该二次函数图形是凹的, 方差具有最小值. 令 dVar[ y (2) 1i ] d ξ =0 可得 : 1 N + 3 2N 2 ( K -2) + 1 4 N 3 ( K -2) ( K -3) ∑ K k =2 A 2 k + N 0 2N Tb ( K -1) ξ= 1 N + 1 2 N 2 (K -2) ∑ K k =2 A 2 k . 从而可得 : ξmv = 4 N 2 +2N( K -2) 4N 2 +6 N( K -2) +( K -2) ( K -3) + 2N 2 ( K -1) N0 T b ∑ K k =2 A 2 k . 若不计噪声项, 有: ξmv = 4N 2 +2N ( K -2) 4N 2 +6N ( K -2) +( K -2)( K -3) . 显然, ξmv一定小于 1, 与传统 PIC 检测器( ξ=1) 比较, M V-PIC 的软判决量方差减小, 均值增大, 其误码率必小于传统 PIC. 3 结论 干扰消除检测器不依赖于信号的周期稳定 性, 比较适用于长码方案.相对于传统检测器, 部 分干扰消除( P -PIC) 检测器在消除均值偏差、抑 制由于地址长码正交性变差引起的干扰方面有所 改进.基于最小均方误差的 P-PIC 检测器(M V￾PIC) 进一步减小了 P-PIC 的运算量, 选用使输出 软判决量方差最小的部分干扰消除系数 ξmv, 使 MV-PIC 的输出均值增大 、方差减小, 误码性能 优于传统 PIC 检测器. 参 考 文 献 [ 1] Pat el P, Holtzman J.Analysis of a simple successive interfer￾ence cancellation scheme in DS-CDMA syst em .IEEE J Sel Areas Commun, 1995( 5) :796 [ 2] Pat el P, Holtzman J.Performance comparison of a DS-CDMA syst em using a successive interference cancellation ( IC) scheme and a parallel IC scheme under f ading channels∥Proc of ICC' 94.New Orleans, 1994:510 [ 3] Divsalar D, Simon M .Improved CDMA Performance using Parallel Interference Cancellation:Technical Report, JPL Publication 95-21.Pasedena:J et Propulsion Laborat ory, Cal￾if ornia Institut e of T echnology, 1995 [ 4] 韦辉, 路鸣, 赵春明.移动卫星通信系统中干扰抵消技术 的研究.通信学报, 1998, 19( 9) :27 [ 5] 卢光跃, 邵朝.DS/ CDMA 通信系统中干扰消除法.西安邮 电学院学报, 2001, 6( 3) :30 Research of an interference cancellation multi-user detector for CDMA LIU Xiangdong, GU X uemai Harbin Institute of Technology, Harbin 150001, China ABSTRACT Based on the method of statistics, this paper derived the output mean value and variance of conventional parallel interference cancellation ( PIC) , partial parallel interference cancellation ( P-PIC) and minimum mean-squared error ( MV-PIC) detectors for CDMA .The results indicated that the deviations of mean value and variance of the linear decision parameters w ere reduced by P-PIC compared with PIC .The output mean value w as increased and the variance w as decreased by choosing suitable partial interference cancellation coefficient for M V-PIC, and its perfo rmance of code error is superior to PIC . KEY WORDS mobile communication system ;parallel interference cancellation ;linear decision ;minimum mean-squared error Vol.28 No.9 刘向东等:CDMA 中干扰消除多用户检测器的研究 · 885 ·