Static timing analysis (STA) is essential for timing closure. To address the complicated effects emerging at advanced technology nodes, the Current Source Model (CSM) has been developed to compute timing waveforms for timing propagation. Compared with Non-Linear Delay Model (NLDM), CSM provides superior accuracy but suffers from the efficiency and scalability issue. In this paper, we propose a multi-stage CSM timing propagation framework with three acceleration techniques with the assistance of NLDM. Our acceleration techniques are general and compatible with any CSM-based STA engine. Experimental results demonstrate the effectiveness of our acceleration techniques: Compared with CSM-based analysis, we achieve 4× speedups with only 0.4% accuracy loss.

Gain division multiple access (GDMA), low density spreading code division multiple access (LDS-CDMA) and Sparse code multiple access (SCMA) are non-orthogonal multiple access methods, where SCMA is a method derived from LDS-CDMA with a special design of signal constellation. We compare their performances for transmission over Rayleigh fading channels. Simulation results show that the special constellation design of SCMA does not provide any gain in Rayleigh fading channels. We show that the error performances of a 6-user LDS-CDMA scheme based on 4 resources can be evaluated by applying diversity-2 concept to the 3-user GDMA based on a single resource. However, by using more resources and error-correcting codes, GDMA can also achieve diversity and hence provide error rates similar to LDS-CDMA. In addition, GDMA has the advantage of low complexity.

We construct polar codes for OFDM systems over the frequency selective channel. The channel coefficients are assumed to be available to the transmitter such that the encoder of polar codes can correctly distinguish the input reliabilities and make proper arrangement of frozen bits and message bits. Instead of using the well-known Gaussian approximation method to construct polar codes, we propose a curve fitting method which not only closely approximate the corresponding channel capacity function but also significantly reduce the computational complexity. With the proposed method, the polar coded OFDM systems can achieve good error performances for systems using high- rate polar codes.

We propose a hybrid ARQ (HARQ) scheme for which a rate-1/2 error-correcting code with code length equal to the packet length is used in the HARQ operation, where each packet comprises two subpackets of equal lengths. For the HARQ system with constant packet lengths, the utilization of subpackets enables the flexibility of carrying new message (or data) in the retransmissions. Hence, such a system can gain additional throughput as compared to the system using all-redundancy retransmissions under the conditions of moderate to high signal-to-noise ratios (SNR). In the proposed HARQ scheme, each of the subpackets can be chosen as a data part, or a redundancy part, or a function of two subpackets, where the data part or the redundancy part may belong to different codewords of the rate-1/2 error-correcting code. With a proper design of the function subpacket, we can adaptively control the error-correcting capability used in the HARQ operation. The key idea is that there is possibility of recovering three data subpackets in one retransmission and hence increasing the throughput. The price is that in each retransmission, up to three bits are needed in the feedback channel to indicate which subpacket is successfully recovered.

In this paper, we investigate the soft iterative decoding technique for ternary recoding systems with run-length-limited (RLL) constraints. We employ a simple binary-to-ternary RLL encoder following the LDPC (low density parity check) encoder. In the decoder, the iteratively passing of soft information between the LDPC decoder and a detector is used, where the detector is constructed for a combination of the RLL encoder, PLM (pulse length modulation) precoder and the partial response channel. We provide two different decoding algorithms. For one of the decoding algorithm, we are able to obtain bit-error-rate performance which is inferior to the comparable system without considering the RLL constraint for the high sign-to-noise ratio (SNR) regime and is better for the low-to-moderate SNR regime.

Luby Trasform (LT) codes are regarded as packet-based codes which are useful for multicast communications. High Peak-to-Average Power Ratio (PAPR) is a notorious problem inherently existing in OFDM systems. In this paper, we propose to take the PAPR constraint into account in the encoding of LT codes for OFDM multicast systems. Substantial PAPR reduction can be obtained without sacrificing the decoding performance of LT codes.

OFDM PHY has been selected as North American DSRC standard (IEEE 802.11p). In this paper, we present a robust inner receiver suitable for DSRC communications, whose core is composed by a synchronizer, a one-tap frequency domain equalizer (FDE) and a pilot-based phase estimator. The equalizer uses least-mean-square (LMS) algorithm to track not only the variation of the DSRC channel in 5.9GHz band but also the residual frequency/phase errors that are not yet being corrected by the synchronizer device. In order to keep the LMS equalizer working well, we utilize a pilot-based phase estimator to help estimate the variation and the errors. The simulation results indicate that our proposed inner receiver works fairly well for two DSRC channel models.

We propose a hybrid ARQ scheme which uses QPSK modulation for the first transmission and BPSK modulation for retransmissions. The throughput performance of the proposed ARQ scheme is better that those of ARQ schemes purely using QPSK modulation or purely using BPSK modulation for transmissions. Furthermore, the proposed scheme does not require any operation of error correction as usually required in hybrid ARQ schemes. Therefore, the ARQ scheme proposed in this paper can be easily implemented.>