On the capacity and energy efficiency of training-based transmissions over fading channels
IEEE Transactions on Information Theory
Bursty wideband relay networks
WCNC'09 Proceedings of the 2009 IEEE conference on Wireless Communications & Networking Conference
Bursty relay networks in low-SNR regimes
IEEE Transactions on Communications
MIMO wireless communications under statistical queueing constraints
Allerton'09 Proceedings of the 47th annual Allerton conference on Communication, control, and computing
Noncoherent capacity of underspread fading channels
IEEE Transactions on Information Theory
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Channel uncertainty limits the achievable data rates of certain ultra-wideband systems due to the need to estimate the channel. The use of bursty duty-cycled transmission reduces the channel uncertainty because the receiver has to estimate the channel only when transmission takes place, but the maximum amount of burstiness and hence the possible reduction of channel uncertainty both depend on the spectral efficiency of the modulation scheme used. This general principle is demonstrated by comparing the channel conditions that allow duty-cycled direct-sequence spread spectrum (DSSS) and pulse position modulation (PPM) to achieve the additive white Gaussian noise (AWGN) channel capacity in the wideband limit. We show that duty-cycled DSSS systems achieve the wideband capacity as long as the number of independently faded resolvable paths increases sublinearly with the bandwidth, while duty-cycled PPM systems can achieve the wideband capacity only if the number of paths increases sublogarithmically. The difference is due to the fact that DSSS is spectrally more efficient than PPM and hence allows more bursty transmission