Aiming at the shortcoming of large access delay in industrial Internet of Things （IoT）， a sink location algorithm of Power Domain NonOrthogonal Multiple Access （PD-NOMA） for real-time industrial IoT was proposed. In this algorithm， based on the PD-NOMA technology， the location of the sink was used as an optimization method to minimize access delay by realizing power division multiplexing among users as much as possible. Firstly， for any two users， an assertion that the decodable area of the qualified sink must be a circle if parallel transmissions are successful was proven， and therefore， the decodable area set of the sink was able to be obtained by combining all of the combinations of two users， and every minimal intersection of the area set must be a convex region. So， the optimal location of the sink must be included in these minimal intersection areas. Secondly， for each minimal intersection area where the sink was deployed， the minimum number of chain partition of the network generation graph in the area was computed and used as the metric for evaluating the access delay. Finally， the optimal location of the sink was determined by comparing these minimum number of chain partitioning. Experimental results show that when the decoding threshold is 2 and the number of users is 30， the average access delay of the proposed algorithm is about 36.7% of that of the classic time division multiple access， and besides， it can be decreased almost linearly with the decrease of the decoding threshold and the increase of the channel decay factor. The proposed algorithm can provide reference from the access layer perspective for massive ultra-reliable low-latency communications.

To solve the problem of discontinuity when blending two surfaces with coplanar perpendicular axis, this paper discussed how to improve the equations about the blending surface so as to obtain the smooth and continuous blending surface. At first, this paper analyzed the reason of the uncontinuousness in the blending surface and pointed out that the items in one variable were removed when other variables equaled to some specified values. In this case, the blending equation was independent to this variable in these values and this indicated that the belending surface was disconnected. Then, a method which guarantees the blending surface countinuous was presented on the basis of above discussion. Besides this, this paper discussed how to smoothen it once the continuous blending surface was computed out. As for the G0 blending surface, regarding the polynomial of auxiliary surface as a factor, this factor was mulitiplied to a function f′ with degree one and the result was added to the primary surface fi. The smoothness of blending surface can be implemented by changing the coefficients in f. For the Gn blending surface, a compensated polynomial with degree at most 2 was added to the proposed primary blending equation directly when computing blending surface. This method smoothens the blending surface but does not increase the degree of G0 blending surface.