Driven primarily by cloud service and data-center applications, short-reach optical communication has become a key market segment and growing research area in recent years. Short-reach systems are characterized by direct detection-based receiver configurations and other low-cost and small form factor components that induce transmission impairments unforeseen in their coherent counterparts. Innovative signaling and digital signal processing (DSP) play a pivotal role in enabling these components to realize their ultimate potentials and meet data rate requirements in cost-effective manners. This paper presents an overview of recent DSP developments for short-reach communications systems and discusses future trends.

BACKGROUND.: Podoplanin is a mucin‐like glycoprotein that is important in lymphangiogenesis but not blood vessel formation. Recent studies suggested a potential role of podoplanin in certain tumor cells. The purpose of the current study was to determine the role of podoplanin in head and neck squamous cell carcinoma (HNSCC).METHODS.: Podoplanin expression was analyzed in 35 patients with HNSCC including 16 oral tumors and 19 hypopharyngeal tumors by immunohistochemical analysis and the association between the podoplanin expression status and patients' clinical and pathologic characteristics was evaluated. An independent set of 60 patients with oral tongue cancer was then analyzed for associations between the podoplanin expression status and patients' clinical and pathologic characteristics, including survivals.RESULTS.: Podoplanin was not expressed in normal oral epithelial cells but was detected in some hyperplastic and dysplastic lesions. High podoplanin expression was found in 20 (57%) of the 35 tumors and was more frequent in tumors with lymph node metastasis, particularly for tumors in the oral cavity. In the second set of 60 oral tongue cancers, 36 (60%) expressed high levels of podoplanin. Patients whose tumors expressed high levels of podoplanin had a statistically significantly higher rate of lymph node metastasis (P < .0001). Patients with lymph node metastasis and high‐level podoplanin showed the shortest disease‐specific survival (P = .0004) than other patients.CONCLUSIONS.: Podoplanin is involved in oral tumorigenesis and may serve as a predictor for lymph node metastasis and poor clinical outcome. Cancer 2006. © 2006 American Cancer Society.

Modulation format independence is one of the key challenges in digital signal processing (DSP) techniques for future elastic optical transmissions. We proposed a modulation-format-independent blind phase search (MFI-BPS) algorithm for square M-ary quadrature amplitude modulation (M-QAM) systems, in which modulation format recognition (MFR) and carrier phase estimation (CPE), are included and implemented both in a feed-forward manner. Comprehensive simulation and the experimental studies on 224 Gbit/s polarization multiplexing 16-QAM (PM-16QAM) systems demonstrate the feasibility and the effectiveness of the proposed MFI-BPS algorithm.

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The transmission performance of 112 Gbit/s PAM-4 signal with commercial 25 G-class EML and APD is experimentally studied by using advanced digital signal processing (DSP) algorithms, i.e. pre-equalization (Pre-EQ), error-table based pre-correction (ETC), least-mean square (LMS) based equalization, direct detection faster than Nyquist (DD-FTN) algorithm. Among them, Pre-EQ and ETC are implemented at the transmitter, and ETC is a symbol-pattern-dependent pre-compensation algorithm based on the look-up-table approach. In order to obtain these pre-compensated parameters readily, a joint equalization and error table generation (JEEG) module is proposed. Employing the combination of ETC, LMS, and DD-FTN, a single line 112 Gbit/s PAM-4 40 km amplifier-less transmission with a record receiver sensitivity of −16.6 dBm (at 7% HD-FEC threshold) is experimentally demonstrated. In addition, the computational complexities of different DSP schemes are analyzed and discussed in detail. The receiver computational complexity can be effectively reduced by employing appropriate ETC and Pre-EQ in the transmitter.