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transmission signal is generated. As was shown in Fig. 2, in the structure of the radio frame under this radio access method, guard time is set in order to avoid interference from the following time slots. rough a combination of the coding rate and modulation scheme, transmittable in-formation bit numbers (message size) in the unit data signal section can be changed to between 17–54 bytes. Because a 20 byte message size is assumed in the usage scenario for mMTC [2], the design is made in accordance with this scenario.2.2Interference suppression/cancellation technologyHere we discuss technology that suppresses or cancels interference in data signals. In transmission without grant, because a UE-specic cyclic shi number is given in or-thogonal sequence for reference signals, signal separation is possible. However, because data signals are not in or-thogonal sequence there needs to be suppression or cancel-lation of interference between UE terminals. All UEs sharing the same frequency at the same time are assumed as using the same coding rate and modulation scheme, and, using the channel impulse response estimated from the reference signal, interference among UE data signals is suppressed or cancelled. Regarding the method, we evalu-ate the two shown in Fig. 5 ( successive interference cancel-lation (SIC) and parallel interference cancellation (PIC)).With SIC, demodulation and decoding is carried out in order of the highest strength incoming signal, and when it is determined from the result of the CRC decision there is no bit error, a signal replica is created and interference is removed by subtracting this from the received signal wave form. However, in order for the demodulation and decod-ing to succeed, as a condition, some signal-to-interference ratio (SIR) must be required. On the other hand, because the computational cost will increase in a linear fashion in accordance with an increase in the number of connected UEs, processing can be completed with less latency com-pared with the PIC method, which is discussed below.With PIC, from the received wave form and the esti-mated channel impulse response of each UE, the likelihoods are calculated for all possible combinations of transmission signals from each UE terminal, and from that result, log likelihood ratio (LLR) of the codeword bit sent from the UE is calculated. Aer that, decoding is carried out in a turbo decoder, and the obtained external information is fed back and used to update the LLR and the transmitted data from each UE is estimated. Although there are no restric-tions on the SIR condition among UE signals in the PIC method, because all combinations of transmission signals need to be taken into account, the computational cost in-FiF4　Data signal generation block diagramCyclic Redundancy Check (CRC)Turbo EncoderScramblerModulationCP insertionFiF6Performance evaluation results for interference suppression/cancellation technologiesParallel Interference CancellationHistogram（# of trials=10000）# of UEs successfully received by BSSuccessive Interference Cancellation# of UEs successfully received by BSHistogram（# of trials=10000）FiF5Outline of interference suppression/cancellation techniquesMultiuser detectorTurbo decoderLLRTurbo decoderＵＥ１ＵＥＫ．．．LLRReceived signal(a) Successive Interference Cancellation (SIC) [3][5]–[8]Equalization/demodulationTurbo decoderReplica generationReceived signal‐ＵＥｋｋ＝１～ＫLLRLLR: log likelihood ratio(b) Parallel Interference Cancellation (PIC) [6][9][10]152-2 Radio Access Technologies for Massive Machine-Type Communications