  Head-mounted holographic displays (HMHD) are projected to be the first
commercial realization of holographic video display systems. HMHDs use liquid
crystal on silicon (LCoS) spatial light modulators (SLM), which are best suited
to display phase-only holograms (POH). The performance/watt requirement of a
monochrome, 60 fps Full HD, 2-eye, POH HMHD system is about 10 TFLOPS/W, which
is orders of magnitude higher than that is achievable by commercially available
mobile processors. To mitigate this compute power constraint, display-ready
POHs shall be generated on a nearby server and sent to the HMHD in compressed
form over a wireless link. This paper discusses design of a feasible HMHD-based
augmented reality system, focusing on compression requirements and per-pixel
rate-distortion trade-off for transmission of display-ready POH from the server
to HMHD. Since the decoder in the HMHD needs to operate on low power, only
coding methods that have low-power decoder implementation are considered.
Effects of 2D phase unwrapping and flat quantization on compression performance
are also reported. We next propose a versatile PCM-POH codec with progressive
quantization that can adapt to SLM-dynamic-range and available bitrate, and
features per-pixel rate-distortion control to achieve acceptable POH quality at
target rates of 60-200 Mbit/s that can be reliably achieved by current wireless
technologies. Our results demonstrate feasibility of realizing a low-power,
quality-ensured, multi-user, interactive HMHD augmented reality system with
commercially available components using the proposed adaptive compression of
display-ready POH with light-weight decoding.
