In this paper, we propose a model of a diversity receiver which uses an antenna whose antenna pattern can periodically change. We also propose a minimum mean square error (MMSE) based interference cancellation method of the receiver which, in principle, can suffer from the interference in neighboring frequency bands. Since the antenna pattern changes according to the sum of sinusoidal waveforms with different frequencies, the received signals are received at the carrier frequency and the frequencies shifted from the carrier frequency by the frequency of the sinusoidal waveforms. The proposed diversity scheme combines the components in the frequency domain to maximize the signal-to-noise power ratio (SNR) and to maximize the diversity gain. We confirm that the bit error rate (BER) of the proposed receiver can be improved by increase in the number of arrival paths resulting in obtaining path diversity gain. We also confirm that the proposed MMSE based interference canceller works well when interference signals exist and achieves better BER performances than the conventional diversity receiver with maximum ratio combining.

This letter presents a computational complexity reduction technique for space diversity based spectrum sensing when the number of receive antennas is greater than three (NR≥3 where NR is the number of receive antenna). The received signals are combined with phase inversion so as to not attenuate the combined signal, and a statistic for signal detection is computed from the combined signal. Because the computation of only one statistic is required regardless of the number of receive antenna, the complexity can be reduced. Numerical examples and simple analysis verify the effectiveness of the presented technique.

This paper presents a weighted diversity combining technique for the cyclostationarity detection based spectrum sensing of orthogonal frequency division multiplexing signals in cognitive radio. In cognitive radio systems, secondary users must detect the desired signal in an extremely low signal-to-noise ratio (SNR) environment. In such an environment, multiple antenna techniques (space diversity) such as maximum ratio combining are not effective because the energy of the target signal is also extremely weak, and it is difficult to synchronize some received signals. The cyclic autocorrelation function (CAF) is used for traditional cyclostationarity detection based spectrum sensing. In the presented technique, the CAFs of the received signals are combined, while the received signals themselves are combined with general space diversity techniques. In this paper, the value of the CAF at peak and non-peak cyclic frequencies are computed, and we attempt to improve the sensing performance by using different weights for each CAF value. The results were compared with those from conventional methods and showed that the presented technique can improve the spectrum sensing performance.

Multiple antenna is introduced into spectrum sensing in cognitive radios recently. However, conventional multiple antenna spectrum sensing schemes exploited only space diversity. In this paper, we propose a new multiple antenna sensing scheme based on space and time diversity (MASS-BSTD). First, the primary user signal to be sensed is over-sampled at each antenna, and signal samples collected at the same time instant from different antennas are stacked into a column vector. Second, each column vector is utilized to estimate space correlation matrix that exploits space diversity, and two consecutive column vectors are utilized to estimate time correlation matrix that exploits time diversity. Third, the estimated space correlation matrix and time correlation matrix are combined and analyzed using eigenvalue decomposition to reduce information redundancy of signals from multiple antennas. Lastly, the derived eigenvalues are utilized to construct the test statistic and sense the presence of the primary user signal. Since the proposed MASS-BSTD exploits both space diversity and time diversity, it achieves performance gain over the counterparts that only exploit space diversity. Furthermore, the proposed MASS-BSTD requires no prior information on the primary user, the channel between primary user transmitter and secondary user receiver, and is robust to noise uncertainty. Theoretical analysis and simulation results show that the proposed MASS-BSTD can sense the presence of primary user signal reliably.

A BICM-ID system with 3-dimensional rotated BPSK constellation and signal space diversity (SSD) is proposed to combat the effect of Rayleigh fading. A new criterion based on mutual information is proposed to find the optimal rotation matrix, and the labeling that fits well with the outer code is presented. Simulation results show that at BER of 10-5 over a Rayleigh fading channel, with the code length of 192,000 bits and the iteration number of 100, the performance of the proposed system is only about 0.8 dB from the Gaussian-input Shannon limit and exceeds the limit constrained by the traditional QPSK input without rotation or SSD, at the spectrum efficiency of 1 bit/s/Hz.

In this letter, a novel method is proposed for carrier-frequency offset (CFO) estimation for multiple users in orthogonal frequency division multiple access (OFDMA) uplink with the generalized carrier assignment scheme (GCAS). The base station (BS) is equipped with multiple antennas, and each user's CFO can be estimated by the ESPRIT-like method that utilizes the rotation invariance of the space-domain snapshot matrix. The method is still effective even in fully loaded system with all subcarriers allocated to users. Simulation results illustrate the high performance of the proposed algorithm.

In multiple input multiple output (MIMO) communication systems, eigenvalues of channel correlation matrices play an essential role for the performance analysis, and particularly the investigation about their behavior under time-variant environment ruled by a certain statistics is an important problem. This paper first gives the theoretical expressions for the marginal distributions of all the ordered eigenvalues of MIMO correlation matrices under i.i.d. (independent and identically distributed) Rayleigh fading environment. Then, an approximation method of those marginal distributions is presented: We show that the theory of SIMO space diversity using maximal ratio combining (MRC) is applicable to the approximation of statistical distributions of all eigenvalues in MIMO systems with the same number of diversity branches. The derived approximation has a monomial form suitable for the calculation of various performance measures utilized in MIMO systems. Through computer simulations, the effectiveness of the proposed method is demonstrated.

In our application targeted here, four on-glass antenna elements are set in an automobile to improve the reception quality of mobile ISDB-T receiver. With regard to the directional characteristics of each antenna, we propose and implement a joint Pre-FFT adaptive array antenna and Post-FFT space diversity combining (AAA-SDC) scheme for mobile ISDB-T receiver. By applying a joint hardware and software approach, a flexible platform is realized in which several system configuration schemes can be supported; the receiver can be reconfigured on the fly. Simulation results show that the AAA-SDC scheme drastically improves the performance of mobile ISDB-T receiver, especially in the region of large Doppler shift. The experimental results from a field test also confirm that the proposed AAA-SDC scheme successfully achieves an outstanding reception rate up to 100% while moving at the speed of 80 km/h.

MIMO leads to dramatic improvement in channel capacity and/or link reliability of wireless systems. However, a MIMO channel has only one degree of freedom in a keyhole environment. As a result, this environment reduces achievable channel capacity and link quality. This paper proposes a MIMO repeater system, which can realize a multi-stream transmission. Although the averaged channel capacity in the MIMO repeater system is discussed in several published papers, the probability density functions of eigenvalues of correlation matrix are not analyzed. MIMO transmission performance can basically be estimated from eigenvalues of the channel correlation matrix. We derive an approximated formula for the probability density function of all eigenvalues linked to the space diversity. It is shown that the calculated values based on the proposed method agrees very well with the simulated values.

In this letter, the system capacity of multiuser diversity combined with spatial multiplexing schemes is analyzed. An analytic expression is derived for the ergodic system capacity with multiuser scheduling and dual multi-input multi-output (MIMO) systems by using a tight lower bound of the link capacity. The proposed analytic approach is verified through comparisons between analytic and simulated results, and is shown to make fairly precise predictions of the ergodic system capacity and the scheduling gains even when the numbers of antennas and users are small.

Software-Defined Radio (SDR) represents a major paradigm shift in the design of radios, allowing a large fraction of the functionality to be implemented through programmable signal processing devices, enabling the radio to change its operating parameters to accommodate new air interface, features and capabilities. However, the actual realization of innovative and software-reconfigurable receiver diversity at mobile handsets in intermediate frequency band to provide wide-ranging benefits, including more effective filtered result, less cost of the mixed channel access, improved capacity, better link reliability, and reduced power consumption, has been slowed down largely due to an absence of effective architecture reducing the complexity of adaptive combining algorithms. This paper proposes a novel reconfigurable architecture for adaptive space diversity at handsets in MC-CDMA (multicode code-division multiple-access) systems. The key to which is the development of a valid and effective alternative to the time-consuming multiplication operation and despreading acquisition. A software definable algorithm can become a multiplier-free architecture if it can restrict the weight factors to power-of-two values and repetitive gradient search procedure to contain shift operations and predicate functions. The results of numerical simulation and experimentation confirm the expectation that the constrained approach should perform comparably to, but not better than the traditional diversity algorithm. That is, the feasibility of SDR depends on its trading some performance for reduced computational complexity, improved area efficiency and less power consumption.

Antennas for Japanese terrestrial microwave relay links have been developed since the1950's and put into commercial use up to now in Japan. In particular, the path-length lens antennas developed in 1953 represents a monumental achievement for terrestrial microwave relay links, and the offset antenna for 256 QAM radio relay links developed in 1989 has the best electrical performance in the world. This paper reviews the antennas for Japanese terrestrial microwave relay links that have historical significance and describes the antenna design technologies developed in Japan.

This paper proposes a symbol-by-symbol-based multilevel transmit power control (MTPC) scheme for orthogonal frequency division multiplexing (OFDM) based adaptive modulation system (AMS) to achieve high quality broadband wireless transmission for high mobility terminals. In the proposed system, delay profile for each OFDM symbol is estimated by linearly extrapolating previously received delay profile information (DPI) sequence to improve tracking ability of OFDM based AMS with MTPC to the fast fading variation. Moreover, 2-branch reception diversity is applied to reduce dynamic range and variation speed of the multipath fading. Computer simulation confirms that the proposed system is effective in supporting higher mobility terminals with keeping high transmission quality.

This paper proposes a novel space diversity reception scheme suitable for packet-based orthogonal frequency division multiplexing (OFDM) wireless access systems that achieves large diversity gain by improving the accuracy of both carrier frequency synchronization and phase tracking. Phase tracking compensates the phase rotation caused by residual carrier frequency error and phase noise and is necessary for high data rate OFDM systems that use coherent detection. In the proposed scheme, the accuracy of carrier frequency synchronization is improved by combining the information of the carrier frequency offset detected on all diversity branches; the accuracy of phase tracking is improved by using pilot signals whose signal to noise ratio (SNR) is raised by maximal ratio combining of the pilot signals extracted from all branches. Computer simulation results show that the proposed scheme effectively improves the diversity gain even in severe environments such as those with low carrier to noise ratios (CNR) and large delay spreads.

We previously proposed a next generation cellular system for IMT-2000 based on the Wideband DS-CDMA with TDD scheme (W-CDMA/TDD) and have evaluated its performance by computer simulation, laboratory and field experiment. With the W-CDMA/TDD, because of its correlation between the downlink and the uplink, transmission and reception space diversity (SD) at a base station and open-loop transmit power control (TPC) can be simply realized. This paper reports performance of laboratory and field experiments using a developed testbed. The results shows it has been confirmed that transmission and reception SD and open-loop TPC have sufficient performance under a field environment as well as laboratory environment.

In this paper, we briefly describe the proposed radio access scheme based on CDMA/FDD for next-generation mobile radio systems, and evaluate its performance through laboratory and field experiments on transmission power control (TPC) and diversity, which are the key technologies to achieve efficient CDMA systems. The design of the practical TPC method is discussed, and a robust method is presented for operation in low signal to interference power ratio (SIR). Laboratory experiments demonstrate that space and path diversity effectively improve the TPC performance in the Doppler frequency range of 40 to 80 Hz, and reduces the required Eb/N0 to achieve the BER of 10-3. The necessary diversity order for multipath fading mitigation in all the Doppler frequency range is also investigated. Through the field experiments in urban area of Tokyo using a developed system at 0. 96 Mcps, a low required Eb/N0 of 2. 8 dB can be obtained because of the effectiveness of the diversity.

We previously proposed a next generation cellular system for IMT-2000 based on wideband DS-CDMA with TDD scheme and have evaluated its performance by computer simulation, laboratory and field experiments. This paper presents the design concept of TDD-mode operation on wideband DS-CDMA systems. These systems employ almost the same techniques with a little difference as FDD-mode. We also present the schemes of the TDD-mode specific techniques such as fast cell search, transmission diversity and transmitter power control and show the evaluation results of them are effective. Performance can be improved by use of enhanced techniques such as interference cancellation and adaptive antenna array diversity.

This paper presents experimental results obtained in indoor broad-band transmission experiments using a QPSK-100 Mbps modem in the 37 GHz band. Transmission performance is measured at many antenna locations in an office. The zone coverage, defined points where as the BER was less than 10-7, was derived in order to evaluate the possibility of high-speed transmission. It was found that adjusting the receiving antenna position a few centimeters greatly improves the zone coverage in utilizing millimeter waves. This result indicates the effectiveness in improving zone coverage of space diversity reception with an antenna spacing of several centimeters. Experimental results obtained show that zone coverage of up to 70% in the measured range is achieved by space diversity reception. Thus, the feasibility of 100 Mbps indoor wireless transmission, conventionally thought to be impossible, is experimentally confirmed.

A new broadband space diversity (B-SD) combining method, which is a key technique in the growth of digital microwave radio system, is proposed. In this B-SD combining method, two received signals, whose bandwidths are 280 MHz, are combined. To develop this combining method, an optimum control algorithm is developed that monitors power levels of all primary carriers and controls the endless phase shifter so that the higher level signal is decreased and the lower level signal is increased. This paper describes the proposed B-SD combining method which effectively operates over a wide bandwidth. Performance evaluations based on simulations and theoretical estimations are given. It is proven that this combining method offers the same performance obtained by the conventional narrowband SD combining method and can be applied to over 50% cases of the propagation paths observed in Japan. The suitability of the proposed combining method and the calculation methods adopted is demonstrated experimentally.

The synergistic effects obtained by adopting both space diversity reception and adaptive equalization play a very important role in circuit outage reduction. This paper quantitatively analyzes these synergistic effects when dispersive and flat fading occur simultaneously. Analytical results show that the synergistic effects are of the same magnitude as the adaptive equalizer improvement factor when only dispersive fading causes outage. The synergistic effects gradually disappear when noise is the predominant cause of outage.