On Interface Rate Allocation for a Fiber Aided Wireless Network Architecture

The concept of a fiber aided wireless network architecture (FAWNA) is introduced in [Ray et al., Allerton 2005], which allows high-speed mobile connectivity by leveraging the speed of optical networks. Reference [Ray et al., ISIT 2006] considers a single-input, multiple-output (SIMO) FAWNA: A SIMO wireless channel interfaced with an optical fiber through wireless-optical interfaces. Though the architecture is similar to that of the classical CEO problem, the problem is different from it. In this paper, we address the question of how rate should be allocated among the interfaces in a SIMO-FAWNA, i.e., how fiber capacity should be divided between the interfaces. The interface has noise from two sources, receiver front end and quantizer. We show that an optimal rate allocation is one which ensures that each interface gets enough rate so that its noise is dominated by front end noise rather than by quantizer distortion. This implies higher rates for interfaces seeing higher channel gains. After this rate requirement is met, SIMO-FAWNA capacity is almost invariant to allocation of left over fiber capacity. Hence, large capacity of the optical fiber ensures robustness of SIMO-FAWNA capacity to interface rate allocation. We also show that rather than dynamically changing rate allocation based on channel state, a fixed rate allocation scheme can be adopted with very small loss in capacity. This translates into considerable reduction in FAWNA complexity.