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As the demand of down link high speed data packet service such as wireless Internet increases, the standardization for high speed downlink packet access (HSDPA) in wideband code division multiple access (WCDMA) system is in progress. HSDPA adopts adaptive modulation and coding (AMC) scheme, which changes the modulation level (for example, M-PSK, where M=4, 16, etc.) and channel coding rate adaptively to wireless channel conditions to maximize throughput. To adopt AMC, the receiver should measure the signal energy to interference power spectral density ratio (SIR) as the channel quality for feedback to the transmitter. The SIR estimation method, which has been used for the conventional voice services, was un-biased and had no problem in case of low power, low data rate, and low cell loading (i.e., single code transmission). However, the bias error of the conventional method increases as the transmitter has higher power, higher data rate, and more full loading (i.e., multi-code transmission), which are typical of the HSDPA service environment. To solve this problem, this paper proposes and verifies the validity of a SIR estimation method using the symbol patterns which are conventionally used to separate the pilot signals of transmit antennas. This paper also shows the method is always un-biased even with the HSDPA service environments.