Noriaki Miyazaki

MIMO-OFDM Throughput Performances on MIMO Antenna Configurations Using LTE-Based Testbed with 100 MHz Bandwidth

This paper presents throughput performance of 22 multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) using a testbed in line with the Long Term Evolution (LTE) numerology. Then, this paper clarifies the relation among the throughput, modulation schemes and antenna polarization. The field experiments clearly demonstrate that a measured throughput exceeding 200 Mbps can be obtained in a coverage area more than 50% and a throughput of 456.0 Mbps is achieved for a limited number of users even when a maximum Doppler frequency is higher than 125 Hz. In addition, it is found that the single polarization antenna configuration is suitable for 16QAM while the dual polarization antenna configuration is suitable for 64QAM. It is concluded from analysis of the eigenvalue ratio and signal to noise power ratio that the aforementioned trade-off is caused by sensitivity to the eigenvalue ratio depending on the modulation scheme and distribution of the eigenvalue ratio depending on the MIMO antenna configuration.

Experimental evaluation of open-loop precoding MIMO using the testbed targeted at IMT-Advanced system

This paper presents an experimental evaluation of open-loop precoding MIMO (multiple input multiple output) using a testbed targeted at IMT-Advanced systems. Open-loop MIMO is realized by applying rotational OFDM (R-OFDM), that is previously proposed by authors, to MIMO transmission. MIMO R-OFDM is more robust with respect to correlated channels than conventional open-loop MIMO-OFDM, because it optimizes the distances between the constellation points using simple phase rotation. The angle of phase rotation depends on the modulation orders and coding rate, hence the receiver does not need to feed the CSI (channel state information) back to the transmitter. In this paper, MIMO R-OFDM is implemented in a testbed targeted at IMT-Advanced systems, it is then evaluated experimentally and by computer simulations. The results of the evaluation reveal that MIMO R-OFDM is effective in correlated channels, and the gain in terms of the CIR (carrier to interference ratio) with respect to conventional MIMO OFDM to achieve PER (packet error rate) = 0.01 is about 1.5 dB when MIMO R-OFDM is used in correlated channels.

Shared Remote Radio Head architecture to realize semi-dynamic clustering in CoMP cellular networks

In conventional cellular systems, transmission rate degrades at cell-edge because of inter-cell interference and pathloss. This problem is called “cell-edge problem”. To solve this problem, Coordinated Multi-Point (CoMP) technique has been proposed recently. CoMP can convert inter-cell interference signals from neighbor base stations (BSs) to desired signals. However, CoMP requires accurate synchronization among cooperative BSs as well as Channel State Information (CSI) between target user and all cooperative BSs. For practical realization of CoMP, new BS architecture in which a BS unit is connected to multiple Remote Radio Heads (RRHs) located apart through optical fiber has been proposed. Even using this architecture, however, CoMP can only be realized within the predefined connected RRHs (CoMP cluster). Therefore, cluster-edge users cannot experience throughput improvement by means of CoMP. This paper proposes a novel BS architecture called shared RRH network, in which each RRH is additionally connected to multiple BS units. As flexible clustering is made possible by this architecture, semi-dynamic clustering using geometrically overlapped cluster patterns allocated with orthogonal resources can be achieved which alleviates the cluster-edge problem. Simulation with parameters based on the 3GPP is setup for performance evaluation of the proposed system. Numerical results show that semi-dynamic CoMP using shared RRHs can significantly improve the system performance both at cell-inner and cell-edge compared with the conventional RRH systems, which confirms the effectiveness of the proposed network.

Field Experiments on Open-Loop Precoding MIMO Using Testbed Targeted at IMT-Advanced System

This paper presents field experiments on open-loop precoding Multiple Input Multiple Output (MIMO) using a testbed targeting International Mobile Telecommunication - Advanced (IMT-Advanced) systems. Open-loop MIMO is realized by applying Rotational OFDM (R-OFDM) to MIMO transmission. MIMO R-OFDM is more robust with respect to correlated channels than conventional open-loop MIMO-OFDM as was shown by the authors in a previous study. MIMO R-OFDM is implemented in a testbed targeting IMT-Advanced systems and is evaluated in a mobile environment. The antenna spacings are changed, i.e. the correlation coefficients between two antennas are changed, then the validity of MIMO R-OFDM is evaluated. The results of the field experiment reveal that MIMO R-OFDM is effective when the transmitter antenna spacings are decreased. The maximum cumulative distribution function (CDF) gain of MIMO R-OFDM with respect to conventional MIMO-OFDM is 6% when the antenna spacing of the transmitter is same as the wave length of the carrier. In addition, it was also found that the rotational angle should be determined based not only on modulation order and coding rate, but also on the correlation coefficients between transmitter and receiver antennas.

A Study on Rotational OFDM Transmission with Multi-Dimensional Demodulator and Twin Turbo Decoder

This paper proposes rotational orthogonal frequency division multiplexing (R-OFDM) transmission with multi-dimensional demodulator (MDD) and twin turbo decoder (T2D). R-OFDM uses rotational multi-carrier modulation (R-MCM), which provides suitable frequency diversity gain in any coding rates although coded OFDM cannot obtain it in high coding rates. In addition, by applying MDD to its receiver, R-OFDM does not cause inter symbol interference degrading multi-carrier code division multiplexing (MC-CDM) with Walsh code multiplexing (WCM). Then, aiming at high spectrum efficiency, T2D is also proposed. T2D is based on a turbo decoder and has the proposed likelihood estimation taking into account the mutual information between multiplexed bits in the identical received symbol. Computer simulations verify that the proposed scheme improves the packet error rate (PER) performance of not only MC-CDM with WCM, but also OFDM, and the required Es/N0 of the OFDM obtaining a PER of 1% is improved by about 1.5 dB at the maximum.

Optimization of picocell locations and its parameters in heterogeneous networks with hotspots

This work analyzes the optimal pico base station (BS) deployment in heterogeneous cellular networks (HetNet) with hotspots. Most of conventional works for HetNet focused on interference coordination and effective cell association methods, however, the problem of pico BS deployment (cell planning) for HetNet with hotspots has not been analyzed so much. In this paper, we extend the previously proposed optimization problem in terms of network parameters (spectrum splitting ratio and SINR bias value) to the optimal pico BS locations to maximize the system rate. Furthermore, the average user and outage user rates are evaluated numerically to show the effectiveness of the proposed optimization method. Numerical results show that the optimized pico BS locations can improve both the average and outage user rates in HetNet with hotspots.

MIMO capacity estimation based on single and dual-polarization MIMO channel measurements

Multiple-Input Multiple-Output (MIMO) wireless system is one of the most promising technologies for providing a large transmission capacity without expanding the frequency band in cellular mobile systems. This paper focuses on 2×2 MIMO capacity estimation through propagation measurements at 2GHz band. The authors conducted the measurement campaign in two regions in Fujimino (Saitama prefecture) and Yokohama (Kanagawa prefecture) Japan. The former is a typical residential area and the latter is an urban area. The paper compares MIMO spatial multiplexing efficiency in terms of the eigenvalue ratio between the single and orthogonal dual-polarization antenna configurations. The eigenvalue ratio is characterized by two parameters. One is cross-polarization discrimination (XPD) and the other is the normalized received signal strength indicator (RSSI), which represents the difference from the RSSI when free space propagation is assumed. It is verified that the MIMO capacity of the dual-polarization can be estimated from just the SNR because the dependency of the eigenvalue ratio on the propagation environment is small. In contrast, that of the single-polarization needs to consider both the eigenvalue ratio and the SNR because the eigenvalue ratios change significantly due to the propagation environment.

A Study on Likelihood Estimation Method Taking Account of Mutual Information in Multi-Level Symbol ~ A Proposal of Twin Turbo Decoder ~

Aiming at high spectrum efficiency, this paper proposes the twin turbo decoder. The received symbol carried by multi-level modulation or MIMO (multi-input multi-output) transmission consists of two or more bits, and these bits share mutual information. However, the conventional likelihood estimation neglects this mutual information and deteriorates the estimation accuracy. This paper presents an alternative estimation method taking into account the above mutual information and applies our proposal to an iterative MAP (maximum a posteriori probability) decoder in order to improve its error correction capability. Computer simulations verify that the proposed scheme improves the PER (packet error rate) performance with the conventional method, and the required E SN0 obtaining a PER of 1 % is improved by about 1.0 dB at maximum. Note that our proposed method is called the twin iterative decoder (twin turbo decoder) because it has double feedback loops

A Study on Forward Link Capacity in MC-CDMA Cellular System with MMSEC Receiver

This paper focuses on the MC-CDMA (Multi Carrier-Code Division Multiple Access) with the MMSEC (Minimum Mean Square Error Combining) receiver, which is a good candidate of a transmission scheme for beyond 3G systems. This paper evaluates the forward link capacity using the MMSEC receiver in the MC-CDMA cellular system, which employs TDM (Time Division Multiplex) transmission for multiple users. In this paper, the PDF (Probability Distribution Function) of the SINR (Symbol to Interference plus Noise energy Ratio) after MMSEC under multi-cell environment are calculated with the various number of the code division multiplexes. Based on the PDF, the numerical relation can be derived between the peak rate of the adaptive transmission and the average transmission rate per sector.

Implementation and Experimental Results of Rotational OFDM Transmission: Rotational OFDM Performance with Turbo Decoder

This paper presents the experimental results of rotational orthogonal frequency division multiplexing (R-OFDM) performance with a turbo decoder implemented in an IMT-Advanced testbed. Taking into account recent advances in research and development toward realization of the IMT-Advanced system era, the authors are developing the testbed. The R-OFDM is multi-carrier transmission scheme and previously proposed by the authors. Its feature is to use rotational code division multiplexing that enables OFDM to obtain suitable frequency diversity gain. However, the previous work is only predicated on computer simulation. In this paper, the R-OFDM is implemented on the testbed and experimentally evaluated by distorting the R-OFDM signal on radio wave with a fading simulator. When packet error rate is measured, it is verified that measurement results are in good agreement with simulation results. The measured deterioration of required carrier-to-interference power ratio (CIR) is suppressed by about 0.5 dB compared with the simulation. The experimental results also demonstrate that the R-OFDM can reduce the required CIR of OFDM even without T2 decoder by about 1.1 dB.