Unlike its competitors using time division multiplexing (TDM), such as GSM, digital cellular technology does not assign a fixed frequency to each caller, but rather allows each channel to use the entire spectrum available. CDMA encodes each group of calls using a quasi random sequence of numbers. Personal digital cellular, operating frequencies of 800MHz and 1500MHz. Encryption technology is the core of achieving secure communication, and authentication and key distribution are important guarantees for achieving secure communication. Intrusion detection is an important security monitoring technology. The Um interface is the air interface of GSM. There are 5 communication protocols on the Um interface, which are physical layer, MAC (MediaAccessControl) layer, LLC (LogicalLinkControl) layer, SNDC (SubnetworkDependantConvergence) layer, and network layer from bottom to top. The physical layer of the Um interface is the RF interface part, while the physical link layer is responsible for providing various logical channels for the air interface. The carrier frequency bandwidth of the GSM air interface is 200kHz, and one carrier frequency is divided into 8 physical channels. If all 8 physical channels are allocated to transmit GPRS data, the raw data rate can reach 200kb/s. Considering the overhead of forward error correction codes, the final data rate can reach around 164kb/s. MAC is the medium access control layer. The main function of MAC is to define and allocate GPRS logical channels for air interfaces, so that these channels can be shared by different mobile terminals. There are three types of logical channels for GPRS, namely public control channels, packet service channels, and GPRS broadcast channels. The common control channel is used to transmit control signaling for data communication, which is specifically divided into
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