System power minimization in non-contiguous spectrum access

Abstract

Wireless transmission using non-contiguous chunks of spectrum is becoming increasingly important due to a variety of scenarios such as secondary users avoiding incumbent users in TV white space, anticipated spectrum sharing between commercial and military systems, and spectrum sharing among uncoordinated interferers in unlicensed bands. multichannel multi-radio (MC-MR) platforms and non-contiguous orthogonal frequency division multiple access (NC-OFDMA) technology are the two commercially viable transmission choices to access these non-contiguous spectrum chunks. Fixed MC-MRs do not scale with increasing number of non-contiguous spectrum chunks due to their fixed set of supporting radio front ends. NC-OFDMA allows nodes to access these noncontiguous spectrum chunks and put null subcarriers in the remaining chunks. However, nulling subcarriers increases the sampling rate (spectrum span) which, in turn, increases the power consumption of radio front ends. Our work characterizes this trade-off from a cross-layer perspective, specifically by showing how the slope of ADC/DAC's power consumption versus sampling rate curve influences scheduling decisions in a multi-hop network. Specifically, we provide a branch and bound algorithm-based mixed integer linear programming solution that performs joint power control, spectrum span selection, scheduling, and routing in order to minimize the system power of multi-hop NC-OFDMA networks. We also provide a low-complexity .O.E 2 M 2 // greedy algorithm where M and E denote the number of channels and links, respectively. Numerical simulations suggest that our approach reduces system power by 30% over classical transmit power minimization based cross-layer algorithms.