The number of Internet of Things is growing exponentially, among which the ZigBee devices are being widely deployed, incurring severe collision problem in ZigBee networks. Instead of collision avoidance or packet retransmissions which introduce extra time/energy overhead, existing methods try to decompose multi-packet collision directly. For example, state-of-the-art mZig exploits collision-free chips to decompose the collided chips iteratively, however, suffers from the high bit error rate and low frame reception rate which limit the practical applications. Toward this end, we observe three major issues of existing solutions: 1) all existing solutions adopt the priori-chip-dependent decomposition pattern, leading to the error propagation; 2) the available samples for chip decoding can be scarce, resulting in severe scarce-sample errors; 3) existing solutions assume the consistent frequency offset for consecutive packets, leading to inaccurate frequency offset estimation. To solve these issues in collision decomposition, we propose FORWARD, a novel physical layer design to enable accurate collision decoding in ZigBee. The key idea is to generate all possible overlapping combinations as reference waveforms. The decomposition is determined by comparing the collided signal with the reference waveforms. Such a priori-chip-independent design has the advantages to eliminate the error propagation. To ensure sufficient samples for decoding, FORWARD always choose the longest segment as reference. Furthermore, the real-time channel estimation and frequency offset calibration ensure the accurate collision decoding. We implement FORWARD on USRP platform and evaluate its performance. Experimental results demonstrate that FORWARD reduces bit error rate by order of magnitude and increases frame reception rate by 10% ~ 50% compared with the state-of-the-art.

中文翻译：

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ZigBee通信中的参考波形正向并发传输

物联网的数量呈指数增长，其中ZigBee设备得到了广泛部署，在ZigBee网络中引起了严重的冲突问题。现有的方法不是避免避免冲突或进行包重发而引入额外的时间/能量开销，而是尝试直接分解多包冲突。例如，最新的mZig利用无碰撞芯片来迭代地分解被碰撞的芯片，但是，其遭受高误码率和低帧接收率的困扰，这限制了实际应用。为此，我们观察到现有解决方案的三个主要问题：1）所有现有解决方案均采用与先验芯片相关的分解模式，从而导致误差传播；2）用于码片解码的可用样本可能很稀少，导致严重的稀缺样本错误；3）现有解决方案假定连续数据包的频率偏移一致，从而导致频率偏移估计不准确。为了解决冲突分解中的这些问题，我们提出了FORWARD，这是一种新颖的物理层设计，可以在ZigBee中实现精确的冲突解码。关键思想是生成所有可能的重叠组合作为参考波形。通过将碰撞信号与参考波形进行比较来确定分解。这种与先验芯片无关的设计具有消除误差传播的优点。为了确保有足够的样本进行解码，FORWARD始终选择最长的片段作为参考。此外，实时信道估计和频率偏移校准可确保准确的冲突解码。我们在USRP平台上实施FORWARD并评估其性能。