Search Results (3)

The demand for a local oscillator (LO) signal of high quality and integrity in local area network (WLAN) communication is growing with the increasing date rate. The LO signals for high data rate WLAN applications are desired to not only have proper shape waveforms and adequate voltage amplitude but also to achieve relatively stable and clean outputs with low phase noise and low spur. Fractional-N frequency planning is critical for a quadrature LO-generator, which is achieved by a single-sideband (SSB) mixer and multiple dividers since it can avoid the frequency pulling and alleviate the self-mixing and DC offset issues, while spur levels are easily increased due to harmonic mixing, imbalance, and leakage of the SSB mixer. This article proposes a simple and innovative quadrature LO-generator, which adopts a current-mode-logic (CML) inductive peaking (IP) circuit to improve phase noise and suppress spurious tones. Four types of LO delivery methods using IP circuits are proposed and compared. Among four methods, the CML-IP circuit presents the optimum performance for driving long wires of multi-mm length. Instead of previous digital spur cancellation, the CML-IP circuit achieves higher spur suppression, lower jitter, and a greater figure of merit (FoM). The quadrature LO-generator can be configured to either VCO mode or bypass mode supporting external VCO input. Implemented in 55 nm CMOS technology, the proposed quadrature LO-generator achieves −52.6 dBc spur suppression, −142 dBc/Hz phase noise at 1 MHz offset at the 4.8 GHz frequency, and −271 FoM. Furthermore, the quadrature LO-generator occupies an active area of 0.178 mm² and consumes 23.86 mW. Full article

Single-sideband (SSB) modulation through Hilbert transformation has successfully transmitted data using only half the bandwidth of the traditional scheme for the same amount of contained information. Toward this end, the four single-sideband (4-SSB) approach for high order modulation is a promising approach for the next-generation communications by applying soft-input soft-output (SISO) equalizer algorithms over orthogonal frequency division multiplexing (OFDM). However, OFDM is challenging for realizing the feasible 5G communications, compared to the emerging techniques, e.g., non-orthogonal multiple access (NOMA), orthogonal multiple access (OMA) or multiple-input multiple-output (MIMO). Since the 4-SSB is an orthogonal modulation which was successfully applied over the traditional OFDM, in this article, we propose a novel 4-SSB modulation scheme over OFDM Guard Interval (GI) and massive MIMO. Besides the carrier signal, from the receiver side, we also apply the shadow equalizer algorithm in the uncoded and coded environment using turbo codes to achieve the 4-SSB with high efficiency from low complexity and energy consumption for 5G. The evaluation results validate that our system consumes lower energy due to low complexity gained from same number of iterations without the heavy decoding as of the 4-SSB SISO based on the turbo equalizer. In addition, the 4-SSB over the OFDM GI achieves the best performance among the relevant approaches conducted in 4-SSB. The proposal then acts as a practical communication system designed to solve the inter-symbol interference (ISI) induced by additional Hilbert transform in the wireless environment toward fifth generation (5G), given that turbo code is considered as a potential channel coding scheme for 5G radio specification. Full article

As the demand for high data volumes keeps increasing in optical access networks, transmission capacities and distance are becoming bottlenecks for passive optical networks (PONs). To solve this problem, a novel scheme based on multi-twin single sideband (SSB) modulation with direct detection is proposed and investigated in this paper. At the central office, two SSB signals are generated simultaneously with the same digital-to-analog converters (DACs). The twin-SSB signal is not only robust against frequency selected power fading introduced by chromatic dispersion (CD), but also improves the spectral efficiency (SE). By combining a twin-SSB technique with multi-band carrier-less amplitude/phase modulation (multi-CAP), different optical network units (ONUs) can be supported by flexible multi-band allocation based on software-reconfigurable optical transceivers. The Kramers–Kronig (KK) scheme is adopted on the ONU side to effectively mitigate the signal–signal beat interference (SSBI) induced by the square-law detection. The proposed system is extensively studied and validated with four sub-bands using 50 Gbps 16 quadrature amplitude modulation (QAM) modulation for each sub-band using numerical simulations. Digital pre-equalization is introduced at the transmitter-side to balance the performance of different ONUs. After system optimization, a bit error rate (BER) threshold for hard decision forward error correction (HD-FEC) code with 7% redundancy ratio (BER = 3.8 × 10⁻³) can be reached for all ONUs over 50-km standard single-mode fiber. Full article