Multipath Length Research Articles

Experimental full-duplex amplify-and-forward relay scheme for OFDM with power gain control

The fundamental challenges for full-duplex (FD) relay networks are the self-interference cancellation (SIC) and the cooperative transmission design at the relay. This paper presents a practical amplify-and-forward (AF) FD one-way relay scheme for orthogonal frequency division multiplexing (OFDM) transmission with multi-domain SIC. It is found that the residual self-interference (SI) signals at the relay can be regarded as an equivalent multipath model. The effects of the residual SI at the relay are incorporated into the equivalent end-to-end channel model, and the inter-block interference can be removed at the destination by using cyclic prefix (CP) protection. Based on the equivalent multipath model, we present a solution for optimizing the amplification factor on the performance of signal-to-interference-plus-noise ratio (SINR) when the equivalent multipath length is longer than the CP. Furthermore, a practical one way FD relay network with 3 nodes is built and measured. The simulation and measured results verify the superior performance of the proposed scheme.

Ge-on-Si waveguides for sensing in the molecular fingerprint regime.

Low loss, single mode, Ge-on-Si rib waveguides are used to demonstrated optical sensing in the molecular fingerprint region of the mid-infrared spectrum. Sensing is carried out using two spin-coated films, with strong absorption in the mid-infrared. These films are used to calibrate the modal overlap with an analyte, and therefore experimentally demonstrate the potential for Ge-on-Si waveguides for mid-infrared sensing applications. The results are compared to Fourier transform infrared spectroscopy measurements. The advantage of waveguide spectroscopy is demonstrated in terms of the increased optical interaction, and a new multi-path length approach is demonstrated to improve the dynamic range, which is not possible with conventional FTIR or attenuated total reflection (ATR) measurements. These results highlight the potential for Ge-on-Si as an integrated sensing platform for healthcare, pollution monitoring and defence applications.

Simplified Multiaccess Interference Reduction for MC-CDMA With Carrier Frequency Offsets

Multicarrier code-division multiple-access (MC-CDMA) system performance can severely be degraded by multiaccess interference (MAI) due to the carrier frequency offset (CFO). We argue that MAI can more easily be reduced by employing complex carrier interferometry (CI) codes. We consider the scenario with spread gain N, multipath length L, and N users, i.e., a fully loaded system. It is proved that, when CI codes are used, each user only needs to combat 2(L - 1) (rather than N - 1) interferers, even in the presence of CFO. It is shown that this property of MC-CDMA with CI codes in a CFO channel can be exploited to simplify three multiuser detectors, namely, parallel interference cancellation (PIC), maximum-likelihood, and decorrelating multiuser detectors. The bit-error probability (BEP) for MC-CDMA with binary phase-shift keying (BPSK) modulation and single-stage PIC and an upper bound for the minimum error probability are derived. Finally, simulation results are given to corroborate theoretical results.

Joint Transceiver Design for MIMO Channel Shortening

Channel shortening equalizers can be employed to shorten the effective impulse response of a long intersymbol interference (ISI) channel in order, for example, to decrease the computational complexity of a maximum-likelihood sequence estimator (MLSE) or to increase the throughput efficiency of an orthogonal frequency-division multiplexing (OFDM) transmission scheme. In this paper, the issue of joint transmitter-receiver filter design is addressed for shortening multiple-input multiple-output (MIMO) ISI channels. A frequency-domain approach is adopted for the transceiver design which is effectively equivalent to an infinite-length time-domain design. A practical space-frequency waterfilling algorithm is also provided. It is demonstrated that the channel shortening equalizer designed according to the time-domain approach suffers from an error-floor effect. However, the proposed techniques are shown to overcome this problem and outperform the time-domain channel shortening filter design. We also demonstrate that the proposed transceiver design can be considered as a MIMO broadband beamformer with constraints on the time-domain multipath length. Hence, a significant diversity gain could also be achieved by choosing strong eigenmodes of the MIMO channel. It is also found that the proposed frequency-domain methods have considerably low computational complexity as compared with their time-domain counterparts.

Intersymbol decorrelating detector for asynchronous CDMA systems

Estimated channel information, especially multipath length and multipath channel of the desired user, is necessary for most previously reported linear blind multiuser detectors in code division multiple access (CDMA) systems. This paper presents a new blind intersymbol decorrelating detector in asynchronous CDMA systems, which uses the cross correlation matrix of the consecutive symbols. The proposed detector is attractive for its simplicity because no channel estimation is required except the synchronization of the desired user. Compared with other reported multiuser detectors, simulation results show that the proposed detector provides a good performance when the active users have significant intersymbol interference and the multipath length is short.