COWS  Workplan

The objectives of COWS mentioned in the previous section will be achieved by allocating the required activities into a cohesive group of technical workpackages, briefly described below.

WP1. Channel and Link Modeling. The estimation of the channel impulse response, especially in view of the frequency selective nature of the diffuse optical wireless channel is a crucial part of this effort. Although ray‑tracing techniques have been applied in the past in the case of IM/DD systems, the challenge here is to incorporate the phase estimation as well, since the phase information is preserved at the coherent receiver. Besides the channel, the end-to-end link model should also incorporate the transmitter linear and nonlinear response, the non-idealities of the coherent receiver, imperfect phase recovery the influence of the LO phase noise, etc. A full end-to-end simulation tool will be made available at the COWS website under the open source license.   

WP2. Link Design and Specifications. WP2 aims to investigate suitable modulation schemes and channel equalization. The impact of various parameters of system design should be analyzed, including the clipping level, the Peak to Average Power Ratio (PAPR), the modulation level in each subcarrier, the use of adaptive bit loading, etc. It is also interesting to compare the performance of OFDM against other time domain or frequency domain equalization techniques.  WP2 will address several issues pertinent to link design. Since the equipment is to be placed at the customer premises, component choice is mainly driven by cost rather than performance. A key question to address is the transmission wavelength, which must be decided based on cost, safety standards and performance measures. The transmitter and receiver type heavily influences the overall cost and so does the choice of LO technology. WP2 will seek the ultimate compromise between cost and performance in specifying the optical and electronic components of the link.

WP3. Network Architecture and MIMO. WP3 undertakes the task of studying MIMO techniques. This activity aims to identify the best possible propagation regime for COWS. A number of choices including diffuse, quasi-diffuse and wide line of sight should be assessed in terms of the maximum allowable data rate and the coverage. Multiple transmitter and/or multiple receiver architectures will be analyzed as a means of improving coverage and available data rate. Space diversity techniques can be used in order to further enhance the performance of the system. Possible choices include maximum ratio combining (MRC), equal gain combining (EGC) and selection combining (SC).  Alamouti space time block coding (STBC) schemes will be characterized for the diffuse wireless channels in order to ascertain their performance gain in terms of coverage and capacity. Repetition coding schemes will also be evaluated and compared to STBC.

WP4. Measurements and Validation. WP5 aims to provide the necessary experimental validation of the COWS ideas. A variety of measurements will be carried out in the lab in order to complement and extend the system design and measurements. The measurements and validation will target at demonstrating the feasibility of gigabit-per-second transmission. Modulation and coding techniques developed in WP2 will also be applied in either real-time or off-line using an arbitrary waveform generator and a digital signal oscilloscope.

Finally WP5 will handle the dissemination and exploitation activities of the project which include the maintenance of the COWS website. The site will provide full text access to COWS papers in peer reviewed journals and conference proceedings that have been accepted for publication as well as supplementary material WP5 will also coordinate the dissemination of COWS results in social media and related international forums. Video presentations outlining the key project findings will be uploaded in video sharing sites.