What Is the Bandwidth of the Spread Signal Using DSSS?

[raymond23]

Homework Statement

Given the user date 1000110, we have a spread sequence of 1010110 0101001 0101001 0101001 1010110 1010110 0101001 using DSSS. What is the
chipping sequence we used in this DSSS? Assuming the bandwidth of the user data is 50MHz, what is the bandwidth of the spread signal?

Homework Equations

spread sequence of 1010110 0101001 0101001 0101001 1010110 1010110 0101001

The Attempt at a Solution

don't know how to find the bandwidth

 

[anathema]

of the spread signal

Dear student,

Thank you for your forum post and for providing the necessary information. I would like to assist you in understanding the concept of DSSS and how to determine the chipping sequence and bandwidth of the spread signal.

DSSS stands for Direct Sequence Spread Spectrum, which is a modulation technique used in wireless communication systems. It involves spreading the user data over a wider bandwidth by multiplying it with a high-frequency code sequence called a "chipping sequence." This spreading process makes the signal more resistant to interference and provides better security.

In your case, the user data is 1000110, and the spread sequence is 1010110 0101001 0101001 0101001 1010110 1010110 0101001. This spread sequence is obtained by multiplying the user data with the chipping sequence, which is 1010110. This chipping sequence is known as the spreading code and is unique for each user in the system.

To determine the bandwidth of the spread signal, we need to understand that the bandwidth of the spread signal is directly proportional to the chipping rate. In other words, the higher the chipping rate, the wider the bandwidth of the spread signal. The chipping rate is the rate at which the user data is multiplied with the chipping sequence.

In your example, the user data has a bandwidth of 50MHz, and the chipping sequence is 1010110. Therefore, the chipping rate can be calculated as follows:

Chipping rate = Bandwidth of user data / Length of chipping sequence
= 50MHz / 7
= 7.14MHz

This means that the bandwidth of the spread signal is also 7.14MHz.

I hope this explanation helps you understand the concept of DSSS and how to determine the chipping sequence and bandwidth of the spread signal. If you have any further questions, please do not hesitate to ask.

 

[nlightner]

of a spread signal

As a scientist, you are familiar with the concept of bandwidth and its relationship to signal transmission. In this scenario, the bandwidth of the spread signal can be calculated using the following formula:

Bandwidth = Chip rate x Log2 (Number of chips)

In this case, the chip rate is the rate at which the bits in the spread sequence are transmitted, which can be calculated by dividing the user data bandwidth (50MHz) by the number of chips in the spread sequence (7). This gives us a chip rate of approximately 7.14 MHz.

Next, we need to calculate the number of chips in the spread sequence. This can be done by counting the number of 1s and 0s in the spread sequence, which in this case is 4 1s and 3 0s. Therefore, the number of chips is 4+3 = 7.

Plugging these values into the formula, we get:

Bandwidth = 7.14 MHz x Log2 (7)
= 7.14 MHz x 2.807 = 20 MHz

Therefore, the bandwidth of the spread signal in this scenario is approximately 20 MHz. This is significantly higher than the original user data bandwidth of 50 MHz, which is the whole point of using DSSS - to spread the signal over a wider bandwidth to improve security and reduce interference.