Abstract-Multiple-input multiple-output (MIMO) spatial multiplexing that needs to separate and detect transmitted signal streams by using processing at the receiver end can increase the data rates of transmissions on independent and identically distributed (i.i.d.) channels. Such channels have been considered to exist in nonline-of-sight (NLOS) environments. However, actual communications may also be conducted in line-of-sight (LOS) environments. While an LOS component can increase the received power level, it may also cause correlated channels that make it difficult to detect the transmitted streams. In this paper, we describe the performance of 4 4 MIMO spatial multiplexing based on LOS and NLOS channel measurements in an indoor environment. For eight configurations of uniform linear arrays (four antenna spacings and two array orientations), we evaluated the cumulative distribution function (CDF) of the channel capacity and bit error rate performance versus transmit power, and we analyzed them in terms of antenna pattern, fading correlation, CDFs of MIMO channel elements, and CDFs of eigenvalues. Results show that, despite higher fading correlations and non i.i.d. channel characteristics, the performance of MIMO spatial multiplexing in the LOS environment is better than that in the NLOS one. However, the performance in the measured LOS environment largely depends on the MIMO configuration.Index Terms-Array element pattern, bit error rate (BER), channel capacity, channel element distribution, eigenvalue distribution, fading correlation, indoor channel measurement, multiple-input multiple-output (MIMO), mutual coupling, spatial multiplexing.
Abstract-Frequency domain equalization (FDE) has been studied for reducing inter-symbol interference (ISI) caused by frequency selective fading in single carrier systems. When a high-mobility terminal exists in the system, the channel state may change within a DFT block. Then, the ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. We propose to divide a received data block into multiple subblocks to decrease the channel transition within the DFT block in fast fading environments. Also, to satisfy periodicity of the received signal in each subblock, we introduce a pseudo cyclic prefix technique. The results of numerical analysis show that the proposed method can effectively decrease the error floor in fast fading environments.Index Terms-Fast fading, single carrier transmission, MMSE-FDE, unique word, subblock processing
Abstract-In this paper, the performance of a multi-user multiple-input multiple-output (MIMO) system in time-varying channels is evaluated using measurement data. We consider the multi-user MIMO system using a block diagonalization (BD) scheme and an eigenbeam-space division multiplexing (E-SDM) technique. In an ideal case, the BD scheme eliminates inter-user interference, and the E-SDM technique suppresses inter-stream interference. In actual radio environments, however, channels change over time. This causes interference in the multi-user MIMO system even though the BD scheme and the E-SDM technique are used. To overcome this problem, the authors have developed a simple channel prediction scheme on the basis of a linear extrapolation and have demonstrated its effectiveness by computer simulations assuming the Jakes' model. To verify the performance of the channel prediction scheme in actual environments, we conducted a measurement campaign in indoor environments and measured a large amount of channel data. Using these data, we examined the channel transition and channel tracking with the prediction method. Then we obtained the biterror rate (BER) performance. The prediction technique was shown to track the channel and improve the BER performance almost to that in the ideal time invariant case.
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