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.

翻译：由于传统的正方位实验数量有限,试点碰撞将严重降低基于争议的无赠款传输的性能。为了减轻试点碰撞,并尽可能利用空间自由度,提议了一个极为稀少的正方位实验计划,用于上行无赠款传输。拟议的零位试验用于积极检测用户和估计空间通道。随后,用户间干扰通过空间利用估计空间通道将收到的数据符号进行空间整合进行抑制。此后,利用综合数据符号的几何特征对无线频道和时间/频率抵消进行估计和补偿。试点任务已大大减轻,因此,极稀疏的正方位试验可以占用最小的资源,而圆形试验的数量可以大幅增加,从而大大降低了试点碰撞的可能性。数字结果显示,拟议的极稀疏或分层试验计划大大改进了高超载无赠款情景的性能。