Initial power adjustment and link adaptation from direct-sequence spread-spectrum demodulator statistics

Abstract

Statistics obtained during demodulation are used in a direct-sequence spread-spectrum packet radio network to govern the adjustment of transmitter power within the first few packets of a session. The statistics are also employed by an adaptive transmission protocol to select the modulation parameters and the rate of the error-control code for each packet. The power-adjustment protocol uses the statistics to ensure that the transmitter power level is high enough to satisfy the signal strength requirements at the receiver and low enough to prevent unnecessary interference to nearby radios. We describe a protocol for which modulation and coding parameters are adapted to achieve the most efficient com bination for the given channel conditions. We evaluate the performance of each protocol for several channels. The protocols are not given any information about the type of channel or the channel parameters, yet they are able to use the demodulator statistics to efficiently set the initial power level and adapt transmissions throughout the session.

Cognitive Radio for Tactical Wireless Communication Networks

“…In [BPR08], [BoP09], and [BPR11], we investigated direct-sequence spread-spectrum (DS-SS) modulation formats, which are among the most robust formats for tactical cognitive radio networks. DS-SS modulation with adaptive soft-decision decoding is examined in [BPR08], where we derive a new metric from post-detection signal quality statistics that are developed in the demodulator of the tactical radio.…”

“…For channels with time-varying propagation loss or multiple-access interference, we show in [BPR08] that our adaptive scaling metric, which requires no channel measurements, gives approximately the same performance as the more complex LLR metric and better performance than fixed metrics. DS-SS modulation is also examined in [BoP09] for dynamic spectrum access networks in which initial power adjustments are required at the start of each session and adaptation to time-varying propagation conditions is required throughout the session.…”

“…Our research on direct-sequence spread-spectrum (DS-SS) tactical radio networks [BoP09], [BPR11], [BoP10a] has produced results on initial power adjustment, adaptive coding, and adaptive spreading, and it has integrated the physical-layer adaptation with the media access (MAC) protocol. For adaptive coding and spreading in DS-SS radio transmissions, we rely on a demodulator statistic to provide the necessary information for the adaptation, so our protocol does not need pilot signals, training sequences, channel measurements, or parameter estimates.…”