Focusing on the problem of encryption and querying of tenant private data on cloud database, a cloud database oriented Attribute Based Encryption (ABE) and query transform service middleware was proposed and realized. Firstly, the tenant symmetric keys were encrypted in the encryption and decryption component of the service middleware through attribute based encryption, and the ciphertext was generated and saved. Secondly, the query statements were translated in the query translation component so that they can be correctly executed on the encrypted database. Finally, the tenant privacy data was stored in the cloud database after symmetric encryption. The experimental results show that compared with the unencrypted database, the write time of the encrypted database is equivalent, while the querying time is increased by 10% to 150% according to the complexity of the query statement. The theoretical analysis shows that the proposed proxy decryption method is secure, and it has superiority over traditional Key Policy Attribute Based Encryption (KP-ABE) algorithm in time complexity.

Concerning the high complexity of the traditional frequency estimation algorithm, a new frequency offset estimation algorithm of Time Domain Synchronous Orthogonal Frequency Division Multiplexing (TDS-OFDM) with low complexity for power line communication was proposed. Firstly, the characteristics of power line network were analyzed, and a frame head was constructed with three equal-length cyclic Pseudo-random Noise (PN) sequences. Secondly, the frame head and body were based on Binary Phase Shift Keying (BPSK) and Quadrature Amplitude Modulation (QAM) modes. Finally, compared with the traditional algorithms based on Cyclic Prefix (CP) or general PN, only the lengths of part of PN were calculated, so the number of autocorrelations was reduced, and better performance could be guaranteed. The simulation results show that, at Bit Error Rate (BER) of 10 ^-4, the improved algorithm has about 5 dB and 1 dB gains while comparing with the algorithms based on CP and general PN, respectively. And compared with algorithm with general PN, when the lengths of inserted sequence and cyclic sequence were 420 and 165, the number of correlations per frame was reduced by 1186. The theoretical analysis and simulation results show that proposed algorithm can effectively reduce the computational complexity and cost of process, meanwhile improves the communication rate.