2G communication in Japan

Comparison of analog and digital methods

PDC (Personal Digital Cellular) is a digital communication system developed and used in Japan. Unlike the 1G analog system, the PDC digital system has the following advantages:

• Less call noise
• Radio waves that bounce off buildings and other objects can be used to a certain extent.
• Calls are less likely to be eavesdropped on
• Many devices can be used on one frequency

Data Encoding and Decoding

In 1G, analog audio signals were transmitted over radio waves using the FM (frequency modulation) method.

In 2G, we will work on voice signals (sampling). This is appropriate or interval, and in the PDC digital method, it is divided into 8000 times per second, and the volume and frequency are converted into audio data. We process the data so that the size of the audio data can be reduced or repaired even if the data is missing in the middle. This is called data encoding. This allows you to reduce the 64 kbits of digital data per second to 6.7 kbits. When encoding, it is scrambled every time, making it difficult for eavesdroppers to be eavesdropped.

In addition, even if noise is present in the data, it is easier to correct it with digital data, so there is less noise in the call than with analog systems. Decoding involves repairing data or decompressing compressed data, converting digital audio data back into an analog audio signal.

Time Division Multiple Access (TDMA)

The ability to compress data means that one second of voice can be sent to the other party in less than one second. To achieve this, the PDC system uses a method called Time Division Multiple Access (TDMA) to subdivide a certain frequency band and then divide it into fixed time intervals for use by users.

Code Division Multiple Access (CDMA)

Qualcomm developed cdmaOne based on Code Division Multiple Access (CDMA).
In the CDMA system, multiple users share a relatively wide bandwidth wireless channel, and after processing using a unique PN code for each user, the signal is spread over the frequency band to be transmitted. The receiving party restores the voice using the same PN code that was used when transmitting.
Because radio waves can be used widely and large amounts of data can be sent, sound quality improves and high-speed data communication is possible, such as with mobile communications.

Soft Handover

First of all, handover is the process of switching base stations through which mobile phones and other devices exchange data via radio waves.
In the PDC system, when moving from base station A to base station B, adjacent base stations shift their frequencies to avoid interference. Therefore, when switching base stations, a frequency channel change occurs, which causes a momentary interruption in the radio waves, resulting in a momentary interruption in the audio, and if this fails, the line may be cut off.

The cdmaOne system does not shift frequencies because interference does not affect calls. Therefore, it switches channels while simultaneously communicating with multiple base stations using the same frequency band, making it less likely to experience interruptions. This switching method is called soft handover.

Path Diversity

Radio waves are reflected by buildings and obstacles, causing delays in reception. This makes it impossible to restore audio, resulting in silence or noise, and in the worst case scenario, the control signal cannot be interpreted and is cut off.
cdmaOne uses a special receiver called RAKE to reverse the reflected waves and improve call quality. RAKE receives up to three radio waves and combines them to achieve a higher reception level than when receiving a single radio wave.