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Digital Coherent Optical Technologies
Published in Zhensheng Jia, Luis Alberto Campos, Coherent Optics for Access Networks, 2019
For the next-gen pluggable module, there are two major form factors being implemented for 400G transceivers from the largest to smallest: QSFP Double Density (QSFP-DD) and Octal Small Formfactor Pluggable (OSFP). QSFP-DD is a new module similar to current QSFP, but with an additional row of contacts providing an eight-lane electrical interface. The term “Double Density” refers to the doubling of the number of high-speed electrical interfaces compared to the regular QSFP28 module. Therefore, QSFP-DD expands on the QSFP pluggable form factor, a widely adopted four-lane electrical interface. One of the major benefits of QSFP-DD is backward compatibility with QSFP+ (40G), QSFP28 (100G), and QSFP56 (200G). Backward compatibility is critically important to the industry. Since ASICs are designed to support multiple interface rates, it is critically important that the system can take advantage of this. However, OSFP allows more power (12–15 W) than the QSFP-DD (7–12 W) because of larger size and direct integration of thermal management. For the 100G-only next-gen pluggable module in access application, QSFP28-DCO is one favorable option, which is compatible with most current 100G client interfaces. The target power dissipation is less than 5 W for I-temp application.
Three-Dimensional Video Coding
Published in Ling Guan, Yifeng He, Sun-Yuan Kung, Multimedia Image and Video Processing, 2012
ISO/IEC 23002-3 (also referred to as MPEG-C Part 3) specifies the representation of auxiliary video and supplemental information. In particular, it enables signaling for depth map streams to support 3DV applications. Specifically, the well-known 2D plus depth format as illustrated in Figure 9.7 is specified by this standard. It is noted that this standard does not specify the means by which the depth information is coded, nor does it specify the means by which the 2D video is coded. In this way, backward compatibility to legacy devices can be provided.
AM Considerations
Published in David P. Maxson, The IBOC Handbook, 2007
In the reception of such an AM broadcast signal, a simple legacy receiver “detects” the carrier envelope using a diode that only responds to one excursion of the RF carrier, either positive or negative. By low-pass-filtering the resulting RF pulse train, a good copy of the original audio waveform can be recovered. The simplicity of this concept allows schoolchildren to build receivers using rocks out of the back yard and coils of wire wrapped around cardboard toilet-tissue rolls. Easy access to these crystal radio sets helped fuel the dawn of the broadcast industry. Advances in receiver technology have produced newer methods of demodulating an analog AM carrier, but the hybrid IBOC signal was designed to not render obsolete any legacy analog receiver topologies, including these early crystal radio receivers. This characteristic of a new technology protecting the continued performance of an old technology is “backward compatibility.”
Applications of federated learning in smart cities: recent advances, taxonomy, and open challenges
Published in Connection Science, 2022
Zhaohua Zheng, Yize Zhou, Yilong Sun, Zhang Wang, Boyi Liu, Keqiu Li
Previous work relieved the communication bottleneck by compressing the gradient before transmission. Two commonly used methods are (A) quantisation and (B) sparse gradient quantisation. It follows the lossy compression idea of using a small number of bits to describe the gradient. These low-precision gradients are transmitted back to the parameter server. However, these independent compression techniques have not been adjusted to the underlying communication channel exchanged between users and the parameter server, and channel resources may not be fully utilised. Another study of FL through wireless channels includes a more general multiple-access channel. The stacked nature of wireless channel allows gradients to be clustered in the air and enables more effective training. These methods can be roughly classified as digital or analogue solutions depending on the transmission of gradient through the channel. In the simulation scheme, the local gradient is scaled and transmitted directly through the wireless channel. In the digital scheme, slave users are decoded separately, but transmission still occurs on multiple access channels. In terms of bandwidth, the analogue solution is better than the digital solution (Amiri & Gündüz, 2020b). Digital solutions have the following advantages: Backward compatibility, i.e. they can be easily implemented on existing digital systems.It is difficult to slow down users.They are more reliable because various error control codes can be used.Digital solutions do not require the tight synchronisation required for analogue transmission.