How to Calculate the Chip Rate


Digital communications use electronic pulses of amplitude +1 and -1 to form a binary code. These pulses are then modulated to obtain a clear signal by using a variety of techniques. One of these modulation techniques is direct sequence spread spectrum (DSSS). DSSS is used in satellite navigation systems such as GPS, and by radio communication technologies such as code division multiple access, the channel access method that Verizon Wireless uses.

Each pulse modulated by DSSS is called a chip. The chip rate of a device is the number of chips or pulses it receives every second. It is measured in megachips, or millions of chips per second. For example, the chip rate of a GPS L1 clear acquisition code, the system that civilian devices uses, is 1.024 Mhz, or 1.024 megachips per second. The chip rate of a communications device contains the information signal, the useful data being sent and the noise signal used to codify the information in a unique way. Therefore, the chip rate is usually several times the data transfer rate, because it contains the entire spreading signal used in the transmission.

  • Find out the data rate of the device. You may find this information in a device's user manual or written on its specifications label. Alternatively, if you can connect the device to a personal computer with a Microsoft Windows operating system, then you can read the data rate of the device in the Network and Sharing Center.

  • Find out the spreading factor: the ratio of chips to information signal of the modulation technique you are using to transmit. Wideband CDMA, for example, has a spreading factor of 256.

  • Multiply the spreading factor by the data rate. This is the chip rate of the device. For example, if a device has a 125K data rate and a spreading factor of 256, then it will have a chip rate of 32 megachips per second.

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