• Low latency parallel turbo decoding implementation for future terrestrial broadcasting systems

      Zhang, Xun; Luo, Hua; Zhang, Yue; Li, Wei; Huang, Li-Ke; Cosmas, John; Li, Dayou; Maple, Carsten; Institute Supérieur d’Electronique de Paris; University of Warwick; et al. (Institute of Electrical and Electronics Engineers Inc., 2017-06-21)
      As a class of high-performance forward error correction codes, turbo codes, which can approach the channel capacity, could become a candidate of the coding methods in future terrestrial broadcasting (TB) systems. Among all the demands of future TB system, high throughput and low latency are two basic requirements that need to be met. Parallel turbo decoding is a very effective method to reduce the latency and improve the throughput in the decoding stage. In this paper, a parallel turbo decoder is designed and implemented in field-programmable gate array (FPGA). A reverse address generator is proposed to reduce the complexity of interleaver and also the iteration time. A practical method of modulo operation is realized in FPGA which can save computing resources compared with using division operation. The latency of parallel turbo decoder after implementation can be as low as 23.2 us at a clock rate of 250 MHz and the throughput can reach up to 6.92 Gbps.
    • Self-IQ-demodulation based compensation scheme of frequency-dependent IQ imbalance for wideband direct-conversion transmitters

      Li, Wei; Zhang, Yue; Huang, Li-Ke; Cosmas, John; Maple, Carsten; Xiong, Jian; Cobham Wireless; University of Bedfordshire; Brunel University; University of Warwick; et al. (Institute of Electrical and Electronics Engineers Inc., 2015-09-25)
      A low cost frequency-dependent (FD) I/Q imbalance self-compensation scheme is investigated in this paper. The direct conversion transmitters are widely used in wireless systems. However, the unwanted image-frequencies and distortions are inevitably introduced into the direct conversion system. This problem is even severer in wideband systems. Therefore, the accurate estimation and compensation of I/Q imbalance is crucial. The current compensation method is based on external instruments or internal feedback path which introduces additional impairments and is expensive. This paper proposes a low cost FD I/Q imbalance self-IQ-demodulation based compensation scheme without using external calibration instruments. First, the impairments of baseband and RF components are investigated. Further, I/Q imbalance model is developed. Then, the proposed two-step self-IQ-demodulation based compensation scheme is investigated. In the first step of the scheme, the local oscillator (LO) related I/Q impairments parameters are estimated. Then in the second step, the overall FD I/Q imbalance parameters are estimated by utilizing the transmitter LO. To realize this self-IQ-demodulation algorithm, this paper introduces minor modifications to the current power detector circuit. Afterwards, the estimated parameters are applied to the baseband equivalent compensator. This sophisticated algorithm guarantees low computation complexity and low cost. The compensation performance is evaluated in laboratory measurement.