Abstract: Small AUVs are constrained by platform size, power, and computational capability, making it difficult for existing underwater acoustic communication schemes to balance algorithmic complexity and performance. To address this issue, this paper proposes an orthogonal hyperbolic frequency modulated carrier low-rate combinatory spread spectrum (OHFM-LCSS) scheme, which integrates the Doppler tolerance and quasi-orthogonality of HFM signals with parallel combinatory spread spectrum. A low-complexity sub-block Doppler estimation method is designed to estimate frequency offset via the peak position difference of periodic symbols, avoiding high-complexity time-frequency transformations, and a time-domain relocation carrier frequency offset compensation method is further proposed without resampling or high-order filters. Experimental results from a small AUV platform in a pool demonstrate that under mobile conditions with a speed of approximately 2 knots and significant multipath, the raw BER after compensation is reduced to 0–0.0186, and zero BER is achieved with Polar coding.