I. What is a baseband chip?
The baseband chip is used to synthesize the baseband signal to be transmitted or to decode the received baseband signal. Specifically, during transmission, it compiles the audio signal into baseband code for transmission; during reception, it decodes the received baseband code back into an audio signal. It is also responsible for compiling address information (phone numbers, website addresses), text information (SMS text, website text), and image information.
The baseband chip can be divided into five sub-blocks: CPU processor, channel encoder, digital signal processor, modem, and interface module.
The CPU processor controls and manages the entire mobile station, including timing control, digital system control, radio frequency control, power-saving control, and human-machine interface control. If frequency hopping is used, it should also include frequency hopping control. Simultaneously, the CPU processor completes all software functions of the GSM terminal, namely the GSM communication protocol's layer 1 (physical layer), layer 2 (data link layer), layer 3 (network layer), MMI (human-machine interface), and application layer software.
Channel encoder: It mainly performs channel coding and encryption of service information and control information. Channel coding includes convolutional coding, FIRE code, parity check code, interleaving, and burst pulse formatting.
Digital Signal Processor: Primarily responsible for channel equalization using the Viterbi algorithm and speech encoding/decoding based on Regular Impulse Excitation-Long-Term Prediction (RPE-LPC) technology.
Modem: Primarily performs Gaussian Minimum Frequency Shift Keying (GMSK) modulation/demodulation as required by the GSM system.
Interface module: includes three sub-blocks: analog interface, digital interface, and human-machine interface;
II. What is a radio frequency chip?
Radio frequency (RF) is an abbreviation for Radio Frequency, referring to electromagnetic frequencies that can be radiated into space, ranging from 300 kHz to 300 GHz. RF is essentially radio frequency current, abbreviated as RF, which is a type of high-frequency alternating electromagnetic wave. Alternating current that changes less than 1000 times per second is called low-frequency current, while that that changes more than 10,000 times per second is called high-frequency current; RF is such a high-frequency current. RF (300 kHz - 300 GHz) is a higher frequency band within the high-frequency band (greater than 10 kHz), and the microwave band (300 MHz - 300 GHz) is an even higher frequency band within RF.
Radio frequency (RF) chips are electronic components that convert radio signals into specific radio signal waveforms and transmit them via antenna resonance. The RF chip architecture consists of two main parts: a receive channel and a transmit channel. For existing GSM and TD-SCDMA modes, adding a frequency band to a terminal's support requires an additional receive channel to the RF chip. However, whether an additional transmit channel is needed depends on the spacing between the new and existing frequency bands. For mobile communication systems with receive diversity, the number of RF receive channels is twice the number of RF transmit channels. This means that the more LTE frequency bands a terminal supports, the more significant the increase in the number of receive channels on its RF chip will be. For example, if M new GSM or TD-SCDMA frequency bands are added, the number of receive channels on the RF chip will increase by M; if M new TD-LTE or FDD LTE frequency bands are added, the number of receive channels will increase by 2M. LTE spectrum is more fragmented compared to 2G/3G. To achieve international roaming via FDD LTE, terminals need to support more frequency bands, which will lead to increased cost and size challenges for RF chips.
To reduce chip area and cost, multiple adjacent frequency bands and modes can be supported in a single receiver channel of an RF chip. When a terminal needs to support multiple frequency bands contained in this single receiver channel, switching devices need to be added to the RF front-end to adapt to the corresponding SAW filters or duplexers for multiple frequency bands. This will increase the size and cost of the RF front-end, and the introduction of switches will also reduce the RF performance of the receiver channel. Therefore, how to balance the trade-offs between the size and cost of the RF chip and the RF front-end will affect the overall size and cost of the terminal.
III. The Relationship Between the Two
A baseband chip can be considered to include, but is not limited to, a modem; it also includes channel encoding/decoding, source encoding/decoding, and some signaling processing. An RF chip, on the other hand, can be viewed as simply performing up-conversion and down-conversion of baseband modulated signals.
Modulation is the process of modulating the signal to be transmitted onto a carrier wave according to certain rules and then transmitting it through a wireless transceiver (RF transceiver). Demodulation is the reverse process.
