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To support realtime multimedia communication, future mobile communications will require a high-bit-rate transmission system with high utilization of the frequency spectrum in very rich multipath channels [1]. Systems capable of fulfilling this requirement, with features such as orthogonal frequency division multiplexing (OFDM) [2], [3] and multiple-input multiple-output (MIMO) [4]–[7], have been studied extensively. Furthermore, the use of Mary quadrature amplitude modulation (M-ary QAM) with coherent detection helps to meet the transmission requirements. Such systems overcome frequency selective fading by using a narrowband multiple-carrier signal called a sub-channel. Those systems use sophisticated and refined techniques and several of those techniques are usually combined in one system. To make full use of the techniques in the system design and achieve high-quality transmission, we must design a system taking into consideration wide and detailed multipath properties in a domain with time and frequency axes. OFDM works best with a lot of narrow bands for the sub-channel. MIMO also requires multipath properties between the antennas composing the MIMO antenna, and it requires a low correlation coefficient. Mary QAM detection also requires the device to compensate accurately for both the in-phase and quadrature (I and Q) components of the sub-channel for the ever-changing multipath channel associated with terminal movement, and this is achieved by putting a pilot signal in the information data [8]. Figure 1 shows an example of the sub-channel state of the I and Q components and phase ψ (tan-1(Q/I)) as movement in a multipath channel, and Fig. 2 shows the signal state diagram at the moment. With movement, the I, Q, and the phase ψ change irregularly as shown by solid lines in Fig.1, so we cannot use the sub-channel as a transmission line. Therefore, the subchannel needs to be a stable state with compensation by a pilot signal. The states of the subchannel compensated every 10Tsy (Tsy: symbol length) in information data, which

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Correlation Coefficients of Received Signal I and Q Components in a Domain with Time and Frequency Axes under Multipath Mobile Channel with LOS and NLOS