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Multi-user Detection

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Introduction

Single User Detection

Detection

•Single User Detection (SUD)

–Equal Gain Combining (EGC)

–Maximum Ratio Combining (MRC)

–Orthogonal Restoring Combing (ORC)

–Minimum Mean Square Error Combining (MMSE)

•Multi User Detection (MUD)

–Successive Interference Cancellation (SIC)

–Parallel Interference Cancellation (PIC)

SUD

•Equal Gain Combining (EGC)

•Maximum Ratio Combining (MRC)

Orthogonal Restoring Combing (ORC)

Minimum Mean Square Error Combining (MMSE)

MAI

MAI (multi-access interference)

•Multiple Access Interference (MAI) is a factor which limits the capacity and performance of DS-CDMA systems. MAI refers to the interference between direct sequence users. This interference is the result of random time offsets between signals, which makes it impossible to design the code waveforms to be completely orthogonal. While the MAI caused by any one user is generally small, as the number of interferers or their power increases, MAI becomes substantial.

Multi User Detection

MUD

•Multi-user Detection (MUD)

–Successive Interference Cancellation (SIC)

–Parallel Interference Cancellation (PIC)

Successive Interference Cancellation (SIC)

The Successive Interference Cancellation (SIC) detector takes a serial approach to interference cancellation. Each stage of this detector decisions, regenrates and cancels out one direct sequence user from the received signal, so that the remaining users see less MAI in the next stage. The result is that the strongest user will not benefit from any MAI reduction; the weakest user will however see a huge reduction in its MAI.

Assume the SNR is：user2 > user1 > user3

Parallel Interference Cancellation (PIC)

Simulation Result

System parameter

•Modulation ：BPSK

•User number：8

•Subcarrier number：16 (half load)

•Channel：independent complex Gaussian distributed