Real-time communications (RTC) is a core technology for emerging applications in 6G, such as cloud gaming, teleoperation, and extended reality (XR), which require consistently low latency and high bitrates. Existing RTC solutions fundamentally struggle to maintain low latency while supporting high bitrates due to their reliance on trial-and-error-based mechanisms. These mechanisms fail to probe the available bandwidth (ABW) promptly and accurately, leading to a trade-off between latency reliability and bandwidth utilization. The tension becomes extremely more critical as the cellular bandwidth and application's demand fluctuate with a larger range in cellular networks nowadays. To address this trade-off, we propose OCC, a novel approach that utilizes physical-layer information to explicitly obtain the ABW in real time, enabling rapid adaptation to dynamic wireless network conditions. However, the unique characteristics of RTC, including traffic bursts, application (APP) limits, and encoder lag, make the physical-layer informed control non-trivial. OCC effectively addresses these issues through three innovative strategies: frame-aware bandwidth measurement, APP-limit-aware bandwidth estimation, and encoder-friendly rate control. Extensive over-the-air experiments on an open-source cellular testbed demonstrate that OCC significantly enhances the performance of mobile RTC, reducing tail network latency by $13\%$ to $68\%$ and improving video frame bitrate by $1.2\times$ to $3.5\times$.

翻译：实时通信（RTC）是6G新兴应用（如云游戏、远程操作和扩展现实XR）的核心技术，此类应用对持续低延迟和高比特率有严格要求。现有RTC解决方案因依赖试错机制，在支持高比特率的同时难以维持低延迟，无法及时准确地探测可用带宽（ABW），导致延迟可靠性与带宽利用率之间产生权衡。随着当今蜂窝网络中带宽与应用需求波动范围扩大，这一矛盾变得尤为尖锐。为解决此问题，我们提出OCC——一种利用物理层信息实时显式获取ABW的新方法，能够快速适应动态无线网络条件。然而，RTC的独特特性（包括流量突发、应用APP限制和编码器延迟）使得基于物理层信息的控制变得困难。OCC通过三项创新策略有效应对这些挑战：帧感知带宽测量、APP限制感知带宽估计以及编码器友好的速率控制。在开源蜂窝测试平台上进行的广泛无线实验表明，OCC显著提升了移动RTC性能，将尾部网络延迟降低13%至68%，并将视频帧比特率提升1.2倍至3.5倍。