We present an attractive approach for OFDM transmission using an adaptive pre-FFT equalizer, which can select ICI reduction mode according to channel condition, and a degenerated-inverse-matrix-based channel estimator (DIME), which uses a cyclic sinc-function matrix uniquely determined by transmitted subcarriers. In addition to simulation results, the proposed system with an adaptive pre-FFT equalizer and DIME has been laboratory tested by using a software defined radio (SDR)-based test bed. The simulation and experimental results demonstrated that the system at a rate of more than 100 Mbps can provide a bit error rate of less than 10-3 for a fast multi-path fading channel that has a moving velocity of more than 200 km/h with a delay spread of 1.9 µs (a maximum delay path of 7.3 µs) in the 5-GHz band.

In this paper, we study low complexity transceiver for double space time transmit diversity (DSTTD) and orthogonal frequency division multiplexing (OFDM) system with antenna shuffling. Firstly, we propose a novel antenna shuffling method based on the criterion of minimizing the condition number of channel correlation matrix. The condition number is an indicator about the quality of the channel. By selecting the minimum of condition number which has better channel quality, consequently, a linear detector with respect to this new channel may achieve better performance results. A low complexity variant of the condition number calculation is also proposed, and it is shown that this criterion can be reduced to the minimum mean square error (MMSE) based criterion. Furthermore, the weighted soft decision Viterbi decoding is applied to mitigate noise enhancement inherent to zero forcing (ZF) and MMSE linear receivers and improve error rate performance. Next, we propose an algorithm to reduce the amount of feedback by exploiting the fact that the channel frequency responses across OFDM subcarriers are correlated. In the proposed algorithm, subcarriers are clustered in blocks, which are allocated the same shuffling pattern with the largest number of the shuffling patterns in the cluster. This way, the signaling overhead can be reduced in comparison with each subcarrier based feedback. Extensive simulations show that the proposed techniques for DSTTD-OFDM system outperform other existing techniques under both uncorrelated and highly spatial correlated frequency selective MIMO fading channels.

We propose a scalable parallel interface that provides an ideal aggregated bandwidth link for an application. The scalable parallel interface uses time information to align packets and allows dynamic lane and/or path change, a large difference in transmission delays among lanes, and so on. The basic performance of the scalable parallel interface in 10 Gb/s 2 lanes is verified using an estimation board that is newly developed to evaluate the basic functions used in a Terabit LAN. The evaluation shows that the scalable parallel interface achieves a very low delay variation that is almost the same as that under back-to-back conditions. The difference in the delay variation between the scalable parallel interface and the back-to-back condition is approximately 10 ns when the transmission delay time varies from 10 µs to 1 s.

This paper describes an evolution and standardization trends of the wireless channel modeling activities towards IMT-Advanced. After a background survey on various channel modeling approaches is introduced, two well-known multiple-input-multiple-output (MIMO) channel models for cellular systems, namely, the 3GPP/3GPP2 Spatial Channel Model (SCM) and the IMT-Advanced MIMO Channel Model (IMT-Adv MCM) are compared, and their main similarities are pointed out. The performance of MIMO systems is greatly influenced by the spatial-temporal correlation properties of the underlying MIMO channels. Here, we investigate the spatial-temporal correlation characteristics of the 3GPP/3GPP2 SCM and the IMT-Adv MCM in term of their spatial multiplexing and spatial diversity gains. The main goals of this paper are to summarize the current state of the art, as well as to point out the gaps in the wireless channel modeling works, and thus hopefully to stimulate research in these areas.

In this paper, the performance of multiuser MIMO E-SDM systems in downlink transmission is evaluated in both uncorrelated and correlated time-varying fading environments. In the ideal case, using the block diagonalization scheme, inter-user interference can be completely eliminated at each user; and using the E-SDM technique for each user, optimal resource allocation can be achieved, and spatially orthogonal substreams can be obtained. Therefore, a combination of the block diagonalization scheme and the E-SDM technique applied to multiuser MIMO systems gives very good results. In realistic environments, however, due to the dynamic nature of the channel and processing delay at both the transmitter and the receiver, the channel change during the delay may cause inter-user interference even if the BD scheme is used. In addition, the change may also result in large inter-substream interference and prevent optimal resource allocation from being achieved. As a result, system performance may be degraded seriously. To overcome the problem, we propose a method of channel extrapolation to compensate for the channel change. Applying our proposed method, simulation results show that much better system performance can be obtained than the conventional case. Moreover, it also shows that the system performance in the correlated fading environments is much dependent on the antenna configuration and the angle spread from the base station to scatterers.

In direct-conversion orthogonal frequency division multiplexing (OFDM) receivers, the impact of frequency-dependent I/Q mismatch (IQ-M) with carrier frequency offset (CFO) must be considered. A preamble-assisted estimation is developed to circumvent the frequency-dependent IQ-M with CFO. The results of a simulation and an experiment show that the proposed method could provide good estimation efficiency and enhance the system performance. Moreover, the proposed scheme is compatible with current wireless local area network standards.

Kalman filters are effective channel estimators but they have the drawback of having heavy calculations when filtering needs to be done in each sample for a large number of subcarriers. In our paper we obtain the steady-state Kalman gain to estimate the channel state by utilizing the characteristics of pilot subcarriers in OFDM, and thus a larger portion of the calculation burden can be eliminated. Steady-state value is calculated by transforming the vector Kalman filtering in to scalar domain by exploiting the filter charactertics when pilot subcarriers are used for channel estimation. Kalman filters operate optimally in the steady-state condition. Therefore by avoiding the convergence period of the Kalman gain, the proposed scheme is able to perform better than the conventional method. Also, driving noise variance of the channel is difficult to obtain practical situations and accurate knowledge is important for the proper operation of the Kalman filter. Therefore, we extend our scheme to operate in the absence of the knowledge of driving noise variance by utilizing received Signal-to-Noise Ratio (SNR). Simulation results show considerable estimator performance gain can be obtained compared to the conventional Kalman filter.

Threshold-based ordered successive interference cancellation (OSIC) detection algorithm is proposed for per-antenna-coded (PAC) two-input multiple-output (TIMO) orthogonal frequency division multiplexing (OFDM) systems. Successive interference cancellation (SIC) is performed selectively according to channel conditions. Compared with the conventional OSIC algorithm, the proposed algorithm reduces the complexity significantly with only a slight performance degradation.

One major drawback of orthogonal frequency-division multiplexing is the high peak-to-average power ratio (PAPR) of the output signal. The selected mapping (SLM) and partial transmit sequences (PTS) methods are two promising techniques for PAPR reduction. However, to generate a set of candidate signals, these techniques need a bank of inverse fast Fourier transforms (IFFT's) and thus require high computational complexity. In this paper, we propose two low-complexity multiplication-free conversion processes to replace the IFFT's in the SLM method, where each conversion process for an N-point IFFT involves only 3N complex additions. Using these proposed conversions, we develop several new SLM schemes and a combined SLM & PTS method, in which at least half of the IFFT blocks are reduced. Computer simulation results show that, compared to the conventional methods, these new schemes have approximately the same PAPR reduction performance under the same number of candidate signals for transmission selection.

Vector Coding (VC) is a novel vector modulation scheme that partitions a SISO (Single-Input Single-Output) channel into orthogonal subchannels by singular value decomposition (SVD). Because the orthogonal transmissions enabled by VC cannot cope with inter block interference (IBI) that is inevitable in delay spread channels, this paper proposes an IBI cancelling demodulator which can remove IBI by an iterative technique. We also show that code elimination in which insignificant eigencodes with lowermost eigenvalues are intentionally removed from transmission vectors greatly reduces BER (Bit Error Rate). The VC which utilizes the IBI cancelling demodulator and code elimination to reduce BER is compared with the original VC in not only delay spread SISO channels but also delay spread MIMO (Multi-Input Multi-Output) channels while emphasis is placed on the MIMO cases. Simulation results show that, under a predetermined BER, the enhanced MIMO-VC can improve effective transmission rate than the natural extension of VC to delay spread MIMO channels.

This paper proposes efficient single-carrier (SC) based multiplexing schemes for Layer 1 (L1)/Layer 2 (L2) control signals in SC-FDMA radio access using DFT-Spread OFDM in the Evolved UTRA uplink. L1/L2 control signals are necessary for key packet access techniques such as downlink scheduling, link adaptation, hybrid automatic repeat request (ARQ) with soft combining, and for uplink feedback control signals. We first propose a SC-based multiplexing scheme for L1/L2 control signals within a shared data channel for a set of user equipment (UE) that transmits both an uplink shared data channel and L1/L2 control signals within the same subframe. We also propose a multiplexing scheme for L1/L2 control signals without uplink data transmission that takes advantage of intra-subframe frequency hopping (FH) using multiple exclusively-assigned time-frequency resource blocks (RBs) to obtain a frequency diversity gain. Furthermore, we propose an orthogonal CDMA-based multiplexing scheme using cyclic shifts of a constant amplitude zero auto-correlation (CAZAC) sequence for L1/L2 control signals from different UEs within the same narrowband time-frequency RB. Computer simulation results show that the proposed SC-based multiplexing scheme for the L1/L2 control signals within the shared data channel achieves a higher user throughput than a multicarrier-based multiplexing scheme. The results also show that the proposed multiplexing scheme for the L1/L2 control signals that takes advantage of the intra-subframe FH for the UE without uplink data transmission achieves high quality reception through large frequency diversity gain. Furthermore, we show that the proposed cyclic-shift based orthogonal CDMA multiplexing is effective in the multiplexing of multiple L1/L2 control signals from different UEs within the same RB.

Arrayed waveguide grating (AWG) is a promising technology for constructing high-speed large-capacity WDM switches, because it can switch fast, is scalable to large size and consumes little power. To take the full advantage of high-speed AWG, the routing control of a massive AWG-based switch should be as simple as possible. In this paper, we focus on the self-routing design of AWG-based switches with O(1) constant routing complexity and propose a novel construction of self-routing AWG switches that can guarantee the attractive nonblocking property for both the wavelength-to-wavelength and wavelength-to-fiber request models. We also fully analyze the proposed design in terms of its blocking property, hardware cost and crosstalk performance and compare it against traditional designs. It is expected that the proposed construction will be useful for the design and all-optical implementation of future ultra high-speed optical packet/burst switches.

This paper proposes an adaptive selection algorithm for the surviving symbol replica candidates (ASESS) based on the maximum reliability in maximum likelihood detection with QR decomposition and the M-algorithm (QRM-MLD) for Orthogonal Frequency Division Multiplexing (OFDM) multiple-input multiple-output (MIMO) multiplexing. In the proposed algorithm, symbol replica candidates newly-added at each stage are ranked for each surviving symbol replica from the previous stage using multiple quadrant detection. Then, branch metrics are calculated only for the minimum number of symbol replica candidates with a high level of reliability using an iterative loop based on symbol ranking results. Computer simulation results show that the computational complexity of the QRM-MLD employing the proposed ASESS algorithm is reduced to approximately 1/4 and 1/1200 compared to that of the original QRM-MLD and that of the conventional MLD with squared Euclidian distance calculations for all symbol replica candidates, respectively, assuming the identical achievable average packet error rate (PER) performance in 4-by-4 MIMO multiplexing with 16QAM data modulation. The results also show that 1-Gbps throughput is achieved at the average received signal energy per bit-to-noise power spectrum density ratio (Eb/N0) per receiver antenna of approximately 9 dB using the ASESS algorithm in QRM-MLD associated with 16QAM modulation and Turbo coding with the coding rate of 8/9 assuming a 100-MHz bandwidth for a 12-path Rayleigh fading channel (root mean square (r.m.s.) delay spread of 0.26 µs and maximum Doppler frequency of 20 Hz).

In this letter, we propose a multi-cell cooperation method for broadcast packet transmission in the OFDM-based cellular system with multiple transmit antennas. In the proposed method, to transmit two streams of spatially demultiplexed or transmit diversity coded symbols, we divide a coded packet into subparts to each of which different cell group and antenna pairs are assigned. It is shown that the proposed method reduces the outage probability with only negligible increase in channel estimation.

Recently, there has been growing interest in the design of wireless cooperative protocol to achieve higher diversity-multiplexing tradeoff among single antenna devices. We propose an automatic request for cooperation (ARC) scheme for wireless networks which can achieve higher order diversity by selecting the best relay. In this scheme, a source transmits a data packet towards a destination and a group of relays. The destination tries to decode the information from the source and if the detection is correct the process will stop. Otherwise, the destination transmits an ARC towards the relays. We utilize this ARC signal for selecting the best relay from the set of relays that have successfully decoded the source packet. The selected relay generates and transmits redundant information for the source packet. The destination combines the two packets received from the source and the best relay to improve the reliability of the packet. We analyze the packet error rate, spectral efficiency and diversity-multiplexing tradeoff of our proposal and compare them with some existing protocols. Analysis shows that our proposal can achieve higher diversity multiplexing tradeoff than conventional cooperative protocols.

We demonstrated all-optical demultiplexing of 160-Gb/s signal to 40- and 80-Gb/s by a Mach-Zehnder Interferometric all-optical switch, where the picosecond cross-phase modulation (XPM) induced by intersubband excitation in InGaAs/AlAsSb coupled double quantum wells is utilized. A bi-directional pump configuration, i.e., two control pulses are injected from both sides of a waveguide chip simultaneously, increases a nonlinear phase shift twice in comparison with injection of single pump beam with forward- and backward direction. The bi-directional pump configuration is the effective way to avoid damaging waveguide facets in the case where high optical power of control pulse is necessary to be injected for optical gating at repetition rate of 40/80 GHz. Bit error rate (BER) measurements on 40-Gb/s demultiplexed signal show that the power penalty is decreased slightly for the bi-directional pump case in the BER range less than 10-6. The power penalty is 1.3 dB at BER of 10 - 9 for the bi-directional pump case, while it increases by 0.3-0.6 dB for single pump cases. A power penalty is influenced mainly by signal attenuation at "off" state due to the insufficient nonlinear phase shift, upper limit of which is constrained by the current low XPM efficiency of 0.1 rad/pJ and the damage threshold power of 100 mW in a waveguide facet.

The wireless systems that establish multiple input multiple output (MIMO) channels through multiple antennas at both ends of the communication link, have been proved to have tremendous potential to linearly lift the capacity of conventional scalar channel. In this paper, we present two efficient decision feedback equalization algorithms that achieve optimal and suboptimal detection order in MIMO spatial multiplexing systems. The new algorithms combine the recursive matrix inversion and ordered QR decomposition approaches, which are developed for nulling cancellation interaface Bell Labs layered space time (BLAST) and back substitution interface BLAST. As a result, new algorithms achieve total reduced complexities in frame based transmission with various payload lengths compared with the earlier methods. In addition, they enable shorter detection delay by carrying out a fast hybrid preprocessing. Moreover, the operation precision insensitivity of order optimization greatly relaxes the word length of matrix inversion, which is the most computational intensive part within the MIMO detection task.

Eigen-beamforming (EB) transmission for multiple-input multiple-output (MIMO) systems is an effective means to maximize the receiver signal-to-noise ratio (SNR) in a noise-limited environment, but suffers a performance degradation when strong interference signals exist. In this letter, we propose an interference cancellation method for EB signals by constructing a new receive beamforming vector which jointly utilizes the EB matrix and minimum mean-square error (MMSE) spatial demultiplexing. The proposed method is shown to outperform the conventional EB receiver in the entire cell range, with a significant increase in the effective signal-to-interference plus noise ratio (SINR) near the cell boundary.

We present a novel frequency partitioning technique of fractional frequency reuse (FFR) that reduces the effect of co-channel interference and increases the capacity of OFDM systems. The usable sub-channel sets are classified into the common sub-channel sets for all cells and the dedicated sub-channel sets for specific cell types in FFR. The proposed fractional frequency reuse with ordering scheme (FFRO) can decrease the amount of interference in the common sub-channel sets by specially designing the sub-channel sets and the order of sub-channel assignment for specific cell types. Simulation results show that the proposed FFRO yields enhanced performance for both uniform and non-uniform distributions of traffic load.

In multiple antenna systems that use spatial multiplexing to raise transmission rates, it is preferable to use maximum likelihood (ML) detection to exploit the full receive diversity and minimize the error probability. In this paper, we present two tree based approximate ML detectors that use new two ordering criteria in conjunction with efficient search strategies. Unlike conventional tree detectors, the new detectors closely approximate the error performance of the exact ML detector while achieving a dramatic reduction in complexity. Moreover, they ensure a fixed detection delay and high level of parallelization in the tree search.