This paper presents field experimental results on a vertical antenna element grouping for Smart Vertical (SV)-Multiple-Input Multiple-Output (MIMO) in the Long Term Evolution-Advanced downlink. Experimental results clarify that SV-MIMO achieves a higher fading correlation compared to a horizontally-arranged antenna configuration when the same antenna spacing is used. Then, when the combination of SV-MIMO and multi-user (MU)-MIMO is employed, we confirm that a gain is obtained by adaptively selecting the spacing among antenna element groups (group spacing) based on the different periods of the antenna grating lobes for each transmission mode. Finally, in measurement courses in urban and suburban areas, field experimental results show that the total throughput of greater than 1 Gbps is achieved for Rank 4 MU-MIMO by utilizing SV-MIMO with the group spacing of 3.1λ to 9.4λ.

This paper presents field experimental results on a base station (BS) antenna configuration associated with the fading correlation when using 4-by-2 multi-user (MU) multiple-input multiple-output (MIMO) in the Long Term Evolution (LTE)-Advanced downlink. In field experiments conducted in urban and suburban areas, we consider four antenna configurations, i.e., combinations of cross-/co-polarized antennas with an antenna array/space diversity antennas. The field experimental results show that the cross-polarized antenna configuration with low and high correlated antenna pairs is very effective in achieving throughput of greater than 800 Mbps when 4-by-2 Rank-4 MU-MIMO is applied in a suburban area under line-of-sight (LOS) conditions. In an urban area, where the majority of the measurement course is under non-LOS (NLOS) conditions, the experimental results show limited improvement in throughput for Rank-4 MU-MIMO. In this environment, we also show that Rank-2 MU-MIMO employing a space diversity antenna configuration achieves relatively high throughput irrespective of the angular difference between spatially multiplexed mobile stations.

This paper presents field experimental results on real-time 1-Gbps data transmission using 4-by-2 multi-user (MU) multiple-input multiple-output (MIMO) when a cross-polarized linear antenna array is employed as the base station (BS) transmitter antennas in the Long Term Evolution (LTE)-Advanced downlink. In the evaluations, we clarify the influence of the difference between directions of departure (DoDs) for two spatially multiplexed mobile stations (MSs) on the achievable throughput using experimental equipment, where eigenvalue decomposition (EVD)-based channel state information (CSI) feedback for each subband is implemented for MU-MIMO operation. Field experiments are conducted in urban and suburban areas where one MS travels at the average speed of 10 km/h and the other MS is static. Field experimental results show that the total throughput of greater than 1 Gbps can be achieved for Rank-4 MU-MIMO by utilizing a cross-polarized linear antenna array with low and high correlated antenna pairs when the difference between the DoDs for the spatially multiplexed MSs is within the range of approximately 40 to 70 and 50 to 55 degrees in suburban and urban areas, respectively. Furthermore, we show that the achievable throughput for Rank-2 MU-MIMO is relatively robust against the difference in the DoD and line-of-sight (LOS) or non-LOS (NLOS) conditions.

This paper presents indoor experimental results on the achievable throughput for 4-by-2 multi-user (MU)-MIMO using 2 mobile stations (MSs) and carrier aggregation with 5 component carriers (90-MHz bandwidth) considering various transmitter antenna arrangements in the LTE-Advanced downlink. Under two centralized and two distributed antenna arrangement (CAAs and DAAs) conditions, the throughput performance is evaluated using the implemented LTE-Advanced transceiver, where extended channel state information (CSI) feedback based on eigenvalue decomposition (EVD) is implemented for MU-MIMO operation. The experimental results show that the peak throughput of greater than 1 Gbps is achieved for the CAAs in an indoor environment. The results also showed that although the MS moving speed strongly influences the throughput for Rank-4 MU-MIMO, MU-MIMO is robust against the antenna separation, i.e., fading correlation. Furthermore, we confirm that, in the DAAs, although the peak throughput of 1 Gbps is not observed, the throughput of approximately 700 to 950 Mbps is achieved.

This paper presents laboratory experimental results on 4-by-2 multi-user (MU)-MIMO that achieves up to 1 Gbps throughput using carrier aggregation with a 100-MHz bandwidth in the LTE-Advanced downlink. The achievable throughput performance employing adaptive modulation and coding (AMC) with outer-loop threshold control based on acknowledgement (ACK) / negative ACK (NACK) feedback signaling in order to compensate for the fluctuation in the measured signal-to-interference plus noise ratio (SINR) value due to MU-MIMO multiplexing is evaluated using the implemented LTE-Advanced transceivers. Additionally, we evaluate the influence of the angle between spatially multiplexed users and the user combination in MU-MIMO operation with different received signal-to-noise ratio (SNR) conditions. Laboratory experimental results show that by performing AMC with outer-loop threshold control, the throughput of approximately 1 Gbps is achieved at the average received SNR of 30 dB. Furthermore, based on the experimental results, we confirm that angles narrower or wider than approximately 60 degrees between spatially multiplexed mobile stations (MSs) yield a lower ability to decrease the mutual interference using minimum mean square error (MMSE)-based precoding in 4-by-2 MU-MIMO. We also show that especially when the angle between spatially multiplexed MSs is narrower or wider than approximately 60 degrees, selecting the user pairs with a large difference in the average received SNR is effective in improving the total throughput.

This paper presents experimental results to clarify the throughput performance and effective location probability for closed-loop single-user (SU)-MIMO transmission considering the effect of antenna configurations in the LTE-Advanced uplink. The achievable throughput performance with adaptive modulation and coding (AMC) and hybrid automatic repeat request (HARQ) is evaluated using the implemented LTE-Advanced transceivers, where the total transmission power and bandwidth per component carrier of a mobile station (MS) are set to 23 dBm and 17.28 MHz, respectively. The experimental results show that when 2-by-2 Rank-2 SU-MIMO, i.e., spatial multiplexing, is applied, a cross-polarized antenna configuration exhibits better throughput performance compared to that using co-polarized antennas and the location probability for achieving throughput greater than 200 Mbps is clearly increased. Furthermore, we confirm that the throughput performance using cross-polarized antennas is very robust against the variation in MS antenna angles irrespective of the rank values for SU-MIMO transmission. The experimental results also show that 2-by-2 Rank-2 SU-MIMO using the cross- polarized antennas improves the throughput performance compared to 1-by-2 SIMO at the location probability of greater than 60% even when the MS antenna gain imbalance level of 12 dB is considered.

A three-stage coherent multistage interference canceller (COMSIC) employing pilot symbol-assisted (PSA) channel estimation for replica generation of multiple access interference (MAI) is implemented and its performance in the presence of frequency selective multipath fading is experimentally evaluated by a multipath fading simulator. A fast transmission power control (TPC) method suitable for COMSIC is also proposed, in which the signal-to-interference plus background noise power ratio (SIR) at the matched filter (MF) based RAKE receiver is measured to achieve a short TPC delay and the target signal-to-interference ratio value is compensated by an outer loop so that the measured block error rate (BLER) is equal to the prescribed target value. The experimental results show that as expected the COMSIC satisfactorily reduces the MAI even when the number of active users is equal to the spreading factor in a multipath fading environment, and thus, improves the bit error rate (BER) performance in a multiuser environment. The results also show that the proposed fast TPC method with a two-slot delay associated with COMSIC works satisfactorily and the combination of COMSIC and fast TPC significantly decreases the transmission power of a mobile station (required transmission power of a mobile station with COMSIC at the average BER of 10/sup -3/ is decreased by approximately 2.0 (3.0) dB compared with the MF-based RAKE receiver with (without) antenna diversity reception). This extends the cell coverage, battery life, and increases the system capacity in the reverse link.

The combined effect of coherent RAKE combining using the weighted multislot averaging (WMSA) channel estimation filter and closed-loop fast transmit power control (TPC) in the 4.096 Mchip/s direct sequence code division multiple access (DS-CDMA) mobile radio reverse link is experimentally evaluated. The WMSA channel estimation filter utilizes periodically transmitted pilot symbols (four pilot symbols are time-multiplexed in each 40-symbol time slot). Its observation period is extended to 2-K slots in order to improve the accuracy of the channel estimation. The fast TPC is based on the measurement of signal-to-interference plus background noise ratio (SIR) using pilot symbols. Laboratory experiments show that the use of the K=2 WMSA channel estimation filter reduces the required E/sub b//I/sub 0/ at the average BER of 10/sup -3/ by approximately 0.5 dB compared to use of the linear interpolation filter, and that the required E/sub b//I/sub 0/ is minimized when the SIR measurement interval is M=10 symbols (one slot TPC delay). It was also clarified that SIR-based TPC works satisfactorily when two users with different information data rates, i.e., SF, independently employ fast TPC. Field experimental results obtained in an area nearby Tokyo showed that the average BER of 10/sup -3/ is achieved at the target E/sub b//I/sub 0/ per antenna of approximately 2.5 dB by using four-finger branch RAKE and two-branch antenna diversity. Although the target E/sub b//I/sub 0/ to achieve same BER, when there is one interfering user with a fourfold greater transmit power than that of the desired user that independently employs fast TPC, is almost the same as that in the single-user case, the mobile transmit power is increased by 1.0-2.0 dB due to the increased MAI. These results indicate that the combination of coherent RAKE combining and fast TPC works well in practical multipath fading channels.

A 3-stage coherent multistage interference canceller for DS-CDMA mobile radio was implemented and its performance in a frequency selective multipath fading channel is experimentally evaluated by using a multipath fading simulator. The implemented interference canceller applied pilot symbol-assisted channel estimation for data decision and replica generation of multiple access interference (MAI). The laboratory experiment demonstrated that, as is expected, the coherent multistage interference canceller can reduce the MAI to satisfactory levels in a multipath fading environment and thus, improving the bit error rate (BER) performance under multiuser environment.

Coherent DS-CDMA forward and reverse links periodically transmitting pilot symbols every data slot to estimate the fading channels are considered; Np-pilot systems are placed at the beginning of each data slot. A pilot symbol-assisted channel estimation scheme that uses weighted multi-slot averaging (WMSA) is presented for coherent RAKE combining. The BER performance achievable by WMSA coherent RAKE combining is evaluated by computer simulations under multipath Rayleigh fading environments and compared with those of other channel estimation methods. For the DS-CDMA reverse link, fast transmit power control (TPC) based on measured signal-to-interference plus noise ratio (SINR) is employed so the simulation also considers fast closed loop TPC. It is demonstrated by computer simulations that the required signal energy per bit-to-background noise power spectrum density ratio (E/sub b//N/sub 0/) can be reduced by about 0.8 dB compared to RAKE combining using simple linear interpolation and that the E/sub b//N/sub 0/ loss from the ideal channel estimation is as small as 0.5 dB both with and without antenna diversity. The BER performance achievable by the time multiplexed pilot is also compared with that of the parallel pilot channel.

Channel segregation was previously proposed as a self-organized dynamic channel assignment. Its performance was examined by applying it to frequency-division multiple access systems. Its applications to the TDMA/FDMA (time-division multiple access/frequency-division multiple access) or multicarrier TDMA system is discussed. The spectrum efficiency of the TDMA/FDMA cellular system deteriorates due to the problem of unaccessible channel: a call can be blocked in a cell even when there are idle channels because of the restriction on simultaneous use of different carrier frequencies in the cell. It is shown that channel segregation can resolve this problem with a small modification of its algorithm. The performance of the TDMA/FDMA system with channel segregation on the call blocking probability versus traffic density is analyzed with computer simulation experiments. The effect of losing the TDMA frame synchronization between cells on the performance is also discussed.>