Algorithms for a Sparse Reconfigurable Adaptive Filter and a Photonic Switch Architecture

Abstract

A nonblocking photonic switch can be used to implement a tapped delay line with a large number of adaptive weights and a wide range of time delays. An advantage of using optical tapped delay lines for adaptive filtering is that the operating frequency can be quite high, in the 10-100 GHz range. We present a sparse reconfigurable adaptive filter (SRAF) based on a photonic switch with an input/output connection architecture that can be represented by a matrix of adaptive weights. This unique parallel structure can be reconfigured in an adaptive manner to implement a sparse filter impulse response for use in many applications. We consider an adaptive algorithm for this filter that chooses the input and output delays using a cross-correlation-based approach and connects these delays by weights that are adapted using a gradient algorithm. An alternative adaptive algorithm is also considered that is based on a system identification formulation where the weights are first adapted, and then the appropriate delay combinations are chosen. A search algorithm for implementing the connection constraint required by the SRAF is also discussed whereby each input is connected to only one output at any moment. Computer simulation examples are presented to illustrate the behavior of the filter for a system identification model. Index Terms-Adaptive filtering, photonic switch, sparse filter impulse response, system identification.

A modified system-based adaptive algorithm for a sparse reconfigurable photonic filter

“…with e j (k) given by (8). 2) Determine the largest element (based on magnitude) of w j subject to the connection constraint in [9].…”

“…The input and desired signals in the system are used to choose the optimal connections, and the weights are updated using the least-mean-square (LMS) algorithm [6]- [7]. The adaptive algorithm [8] used by the SRAF chooses the appropriate time delays and computes the weight values of the optical switch according to the specific application. In previous work [1], we investigated a CCB algorithm for selecting the specific switch connections.…”

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