This is mainly due to the following points:
I. Qualcomm patent fee
The patents of telecom CDMA technology are in the hands of "baseband madman" Qualcomm, including 2G CDMA 1x and 3G CDMA EVDO. Although telecom 4G is not CDMA, if you want to make a phone call or send a text message, you still need to use CDMA network.
Besides producing SoC chips, another main source of profit for Qualcomm is baseband expenses. Every time a mobile phone manufacturer sells a telecom mobile phone, it has to pay a patent fee to Qualcomm. Because this fee is calculated according to the baseband, if it is a dual telecom baseband, it will give Qualcomm twice the patent fee, which greatly increases the production cost of mobile phones.
Second, there is little demand for dual telecommunications.
The cost of dual telecom cards is high, but there are not many users of telecom mobile phone cards, and even fewer people need dual telecom cards. If mobile phone manufacturers produce dual telecom card mobile phones specifically for this small number of users, the final sales volume may be only tens of thousands, which is obviously not cost-effective from the profit point of view.
Extended data
In CDMA communication system, the signals used by different users to transmit information are not distinguished by different frequencies or time slots, but by different coding sequences or different signal waveforms. If viewed from frequency domain or time domain, multiple CDMA signals overlap each other.
A correlator for a receiver can select a signal using a predetermined code pattern among a plurality of CDMA signals. Other signals using different code types cannot be demodulated because they are different from the code types generated locally by the receiver. Their existence is similar to introducing noise and interference into the channel, which is usually called multiple access interference.
In CDMA cellular communication system, the information transmission between users is forwarded and controlled by the base station. In order to realize duplex communication, forward transmission and reverse transmission each use a frequency, commonly known as frequency division duplex.
Regardless of forward transmission or reverse transmission, in addition to transmitting business information, corresponding control information must also be transmitted. In order to transmit different information, corresponding channels need to be set. However, CDMA communication system does not divide channels or time slots, and no matter what information channels are transmitted, different code types are used to distinguish them.
Similar channels belong to logical channels, which overlap each other in frequency domain and time domain, or occupy the same frequency band and time.
References:
Code Division Multiple Access (CDMA)- Baidu Encyclopedia
Self-service Function-China Telecom Online Business Hall