Jen-Yuan Hsu

Modified layered message passing decoding with dynamic scheduling and early termination for QC-LDPC codes

The convergence speed of layered message-passing decoding (LMPD) is faster than that of standard two phase message passing (TPMP) decoding. We propose to use dynamic scheduling and early termination to reduce computational complexity for a modified LMPD algorithm which was proposed for quasi-cyclic low-density parity-check (QC-LDPC) codes. We dynamically skip or redo the decoding operations for some layers based on appropriate criteria. An early termination strategy which is efficient in hardware implementation is also proposed in this paper. The modified MPD using these two techniques simultaneously can reduce the computational complexity with similar error performance as compared to the case of not using these two techniques.

Baseband design and software-defined-radio implementation for LTE femtocell

In the transmission from the outdoor environment to indoor, the radio wave is severely attenuated due to the complex indoor environment, which insidiously restricts many applications. The concept of femtocell is proposed to overcome the signal attenuation problem for indoor services. In this paper, we show the baseband design and software-defined radio implementation for Long Term Evolution (LTE) femtocell. We design a universal baseband architecture and efficient signal processing procedure, and adopt powerful multicore digital signal processors (DSPs) to execute these signal processing programs. Our implemented LTE femtocell exhibits a real-time communication ability, which is well verified by some testing procedure described in the paper.

Extrinsic data compression method for double-binary turbo codes

This paper presents an extrinsic data compression method for double-binary turbo codes. Frame and extrinsic data memory occupy more area in turbo decoder implementations with the frame size increasing. Besides, non-binary turbo codes have much more extrinsic memory usage than single-binary turbo codes. This proposed compression method utilizes an operation in radix-4 single-binary turbo decoder and also can simplify the integration of single and double-binary turbo decoders in hardware implementations. It can reduce one-third of extrinsic memory size, about 15% of total memory usage. Simulation results show that this method only causes 0.2dB performance loss when bit error rate is equal to 10−5 with slight hardware increment.

Noncoherent coded space-time modulation for a large number of transmit antennas

Recently, a turbo-coded noncoherent space-time modulation scheme, which is aimed at providing both a high data transmission rate and a low receiving complexity, was proposed for noncoherent block fading channels. However, in cases where a large number of transmit antennas exist, the turbo code does not match well with the noncoherent space-time modulation scheme, and results in performance degradation. In this paper, we first investigate a coded noncoherent space-time modulation scheme using an irregular low-density parity-check (LDPC) code. We also design a turbo-coded noncoherent space-time modulation scheme based on the codeword-interleaving strategy. The coded symbols mapped from adjacent codewords are interleaved into the same signal vectors, and the soft information from adjacent codewords are allowed to be exchanged at the receiver. When comparing to the conventional turbo-coded scheme, both proposed schemes achieve a significant improvement in BER performance.

Enhanced HARQ Using Prioritized Bit Selection and Rearrangement for WiMAX Systems

HARQ (hybrid automatic-repeat-request) enhances system throughput by improving SNR and gaining time diversity through retransmissions. To utilizing the coding gain, this paper classifies the priority of FEC coded bits and rearranges the bits for each retransmission at MSB (most significant bit) positions or LSB (less significant bit) positions of modulation symbols according to their priorities. In Addition to time diversity, the proposed HARQ gains frequency and spatial diversities. With themaximum retransmissions of two, numerical simulations showthat the proposed scheme outperforms the conventional ChaseCombining (CC) HARQ and Incremental Redundancy (IR) HARQ for WiMAX systems in terms of BLER (block error rate)and throughput with maximum SNR (signal-to-noise ratio) gainsof 3.5dB and 3dB, respectively.

Bit-Level List Generation for Iterative MIMO Receivers

The list demapper has been widely employed for coded multiple-input multiple-output (coded-MIMO) receivers, where only a list of signal vectors is examined in the calculation of likelihood ratio. In the literature, the search of list is operated in the symbol level in accordance with a search metric defined as a function of signal (symbol) vector. Since a signal vector is mapped from a group of (coded) bits, the search may be operated in the bit level if the search metric is made from the aspect of bit. In this paper, beginning with the study of a posteriori probability of bit, a bit-level list generation is proposed for iterative coded-MIMO receivers. With the information coming out of decoder, promising bit tuples can be searched in a low-complexity way, and then mapped to signal vectors for the calculation of likelihood ratio. By the complexity analysis and performance simulation, the proposed bit-level list generation is shown to have a good performance-complexity tradeoff over other existing methods.

Further results on LDPC decoding scheduling for faster convergence

This paper presents a listed maximum mutual information increase (LM2I2)-based algorithm, which is used to arrange low-density parity-check (LDPC) decoding schedules for faster convergence. The increments in the predicted mutual information for the messages to be updated is used to guide the arrangement of the fixed decoding schedule. Consequently, by looking ahead for several decoding stages, a high-order prediction can be realized. For each decoding stages, the searching branches can be trimmed to fit a predetermined size of list, and the efficiency in the selection of update candidates is thus increased. Comparing to previous algorithms, the proposed LM2I2-based algorithm can be used to arrange the decoding schedules converged in the same speed with lower complexity, or accelerate the convergence with the same computation cost.

A Lattice-Reduction Aided List Demapper for Coded MIMO Receiver

The max-log list demapper has been widely employed in the implementations of a coded multiple-input multiple-output (MIMO) receiver, where only a candidate-list of signal vectors is examined in the likelihood-ratio calculation to reduce complexity. Traditionally, the candidate-list is generated in the original-lattice domain which, unfortunately, results in a severe degradation in the performance of demapper if the channel is in ill-condition. In this paper, a new lattice-reduction aided max-log list demapper is proposed in which the candidate-list is generated after a successive cancellation of multi-layer interference in the lattice-reduced domain. Thanks to the newly designed metrics and search algorithms for the generation of the candidate-list, the proposed demapper provides significant gains over the existing methods, especially for the cases with a small list size and/or under a spatially-correlated channel.

A lower-complexity iterative trellis-based factor search algorithm and blind detector for PTS-based OFDM systems

It is known that partial transmit sequence (PTS) is an effective technique to mitigate the problem of high peak-to-average power ratio (PAPR) in an orthogonal frequency-division multiplexing (OFDM) system. One of the major drawbacks of PTS lies in the high complexity for searching the optimal weighting-factor (phase-rotation) vector. In this paper, a trellis-based iterative algorithm is proposed to choose an appropriate weighting-factor vector. Compared to a previously-proposed non-iterative trellis-based algorithm, the proposed iterative algorithm can achieve a comparable PAPR performance with a lower search complexity. Since explicit side information is not transmitted to the receiver of the OFDM system under investigation, we use a phase-quantization-based receiver, which was originally used in noncoherent receivers, to recover the transmit data. Using such a blind receiver, we can achieve a comparable error performance with a lower complexity compared to previously-proposed blind and semi-blind receivers.