With the advent of the coherent age the implementation of massive digital signal processors (DSP) co-integrated with high speed AD and DA converters became feasible allowing for the realization of huge flexibility of transponders. Today the implementation of variable transponders is mainly based on variable programming of DSP to support different modulation formats and symbol rates. Modulation formats with high flexibility are required such as pragmatic QAM formats and hybrid modulation formats. Furthermore, we report on an implementable probabilistically shaping technique allowing for adjusting the bitrate. We introduce fundamental characteristics of all modes and describe basic operation principles. The modifications of the operational modes are enabled simply by switching between different formats and symbol rates in the DSP to adjust the transponders spectral efficiency, the bitrate and the maximum transmission distance. A fine granularity in bitrate and in maximum transmission distance can be implemented especially by hybrid formats and by probabilistically shaped formats. Furthermore, latter allow for ~+25% increase of the maximum transmission distance due their operation close to the Shannon limit as a consequence of their 2D Gaussian like signal nature. If the flexibility and programmability of transponders is implemented, it can be utilized to support different strategies for the application. The variability in symbol rate is mainly translated into variability in bitrate and in bandwidth consumption. Contrary the variable spectral efficiency translates into a variation of the maximum transmission reach and of the bitrate. A co-adjustment of both options will lead to a superior flexibility of optical transponders to address all requirements from application, transponder and fiber infrastructure perspective.
For efficient and accurate diagnosis of ultrasound images, the appropriate time gain compensation (TGC) and dynamic range (DR) control of ultrasound echo signals are important. TGC is used for compensating the attenuation of ultrasound echo signals along the depth, and DR is for controlling the image contrast. In recent ultrasound systems, those two factors are automatically set by a system and/or manually adjusted by an operator to obtain the desired image quality on the screen. In this paper, we propose an algorithm to find the optimized parameter values for TGC and DR automatically. In TGC optimization, we determine the degree of attenuation compensation along the depth by reliably estimating the attenuation characteristic of ultrasound signals. For DR optimization, we define a novel cost function by properly using the characteristics of ultrasound images. Experimental results are obtained by applying the proposed algorithm to a real ultrasound (US) imaging system. The results prove that the proposed algorithm automatically sets values of TGC and DR in real-time so that the subjective quality of the enhanced ultrasound images may become good enough for efficient and accurate diagnosis.