Due to the limited number of traditional orthogonal pilots, pilot collision will severely degrade the performance of contention-based grant-free transmission. To alleviate the pilot collision and exploit the spatial degree of freedom as much as possible, an extremely sparse orthogonal pilot scheme is proposed for uplink grant-free transmission. The proposed sparse pilot is used to perform active user detection and estimate the spatial channel. Then, inter-user interference suppression is performed by spatially combining the received data symbols using the estimated spatial channel. After that, the estimation and compensation of wireless channel and time/frequency offset are performed utilizing the geometric characteristics of combined data symbols. The task of pilot is much lightened, so that the extremely sparse orthogonal pilot can occupy minimized resources, and the number of orthogonal pilots can be increased significantly, which greatly reduces the probability of pilot collision. The numerical results show that the proposed extremely sparse orthogonal pilot scheme significantly improves the performance in high-overloading grant-free scenario.

中文翻译：

---

具有极稀疏正交试验方案的基于竞争的无授权传输

由于传统正交导频数量有限，导频冲突会严重降低基于竞争的无授权传输的性能。为了减少导频冲突并尽可能地利用空间自由度，提出了一种极稀疏正交导频方案用于上行链路无授权传输。提出的稀疏导频用于执行主动用户检测和估计空间信道。然后，通过使用估计的空间信道对接收的数据符号进行空间组合来执行用户间干扰抑制。之后，利用组合数据符号的几何特征进行无线信道和时频偏移的估计和补偿。飞行员的任务减轻了很多，使得极稀疏的正交导频占用最少的资源，并显着增加正交导频的数量，大大降低了导频冲突的概率。数值结果表明，所提出的极稀疏正交导频方案显着提高了高过载免授权场景的性能。