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OFDM-based analog multiband: A scalable design for indoor mm-wave wireless communication

We propose an approach to scaling communication bandwidths over dispersive channels that preserves the advantage of DSP-centric receiver design, while sidestepping the difficulty of scaling analog-to-digital conversion (ADC) to higher and higher bandwidths. This is accomplished by channelizing the available bandwidth into contiguous subbands in the analog domain, with the width of a subband chosen so that digitization is possible at reasonable cost and power using existing ADC technology. We illustrate these ideas for multiGigabit indoor mm-wave communication, with GHz bandwidth divided into subbands of width 250-500 MHz. The channel delay spread even after beamforming can be as large as 20 ns, hence the channel seen within subbands is dispersive. Further, the contiguity of subbands and the sloppy analog channelization implies that adjacent subbands interfere with each other. We show that OFDM within subbands is an attractive approach in these settings: the channel dispersion within subbands can be handled with a moderate cyclic prefix, while the inter-band interference manifests itself only on the edge subcarriers. We clarify the structure of the inter-band interference, and show that it is effectively suppressed by adaptive linear Minimum Mean Squared Error (MMSE) techniques for joint detection across adjacent subbands. Our performance evaluation is carried out using channel models developed for the IEEE 802.1 lad 60 GHz standard.