SCIENTIA SINICA Informationis, Volume 47 , Issue 6 : 789-799(2017) https://doi.org/10.1360/N112017-00038

An SCMA control channel accessing scheme based on codebook-hopping under hyper-cellular network architecture

• AcceptedMar 27, 2017
• PublishedJun 13, 2017
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Abstract

To satisfy the growing demand on data traffic in hyper-cellular networks while at the same time ensuring high-energy efficiency, soft coverage can be effectively utilized in networks, by separating the control and data channels. In this view, with no data to be transmitted the system is in the sleep mode, and with a certain demand on data transmission the system will wake up and will send control signals in a grant-free manner. As one of the most promising random access schemes, Sparse Code Multiple Access (SCMA) allows users to adopt dedicated codebooks to send their data, with superposed code words. However, owing to the lack of scheduling in random access, different users may accidentally use the same codebook, which is called codebook collision and would result in performance degradation. To alleviate this degradation, we propose a codebook-hopping scheme by adopting time-variant codebooks with different patterns for different users. Simulation results show that the proposed scheme improves the performance in terms of the block error rate. In addition, with selective elimination of SCMA sub-blocks in the case of severe codebook collision, the complexity and latency of decoding can be significantly reduced. By doing so, the system can achieve high reliability and low latency for controlling signals in hyper-cellular networks.

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• Figure 1

(Color online) SCMA factor graph when all users adopt different codebook. $L=4$, $N=2$, $K=6$, $U=6$

• Figure 2

(Color online) SCMA factor graph when codebook collision occurs on codebook 3

• Figure 3

(Color online) Codebook collision pattern under codebook-hopping SCMA scheme

• Figure 4

(Color online) Codebook collision pattern under original SCMA scheme

• Figure 5

(Color online) BLER of different schemes

• Figure 6

(Color online) Complexity of different schemes

• Table 1   Codebook collision situations with their corresponding probability
 $\alpha$ b Probability 1 [6] 0.002% 3[0]*2 [5,1] 0.39% [4,2] 3.86% [3,3] 0.64% 2[0]*3 [4,1,1] 0.97% [3,2,1] 15.43% 2[0]*4 [3,1,1,1] 15.43% [2,2,1,1] 34.73% 5 [2,1,1,1,1] 23.15% 6 [1,1,1,1,1,1] 1.54%
• Table 2   Simulation parameter
 Meaning Simulation parameter Average accessing users $U$ 6 Resources per SCMA sub-block $L$ 4 Resources taken up per user per SCMA sub-block $N$ 2 SCMA codebook numbers $J$ 6 SCMA mother constellation size $M$ 16 SCMA sub-block size 4 bits Information block size 200 bits Coding efficiency of turbo code 2/3 Channel model Block fading, Gaussian channel

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