CDMA Near Far Problem

Multiple users can share the same frequency band with CDMA (Code Division Multiple Access) wireless communication technology because it uses distinct codes to distinguish each user’s signals. However, CDMA can experience the near-far issue, just like other wireless transmission technologies.

CDMA Near-Far Problem

A mobile station that is close to a base station and another mobile station that is far from the base station both attempt to interact with the base station at the same time, which is known as the near-far problem in CDMA. The signal from the mobile station that is near the base station may be significantly stronger than the signal from the mobile station that is far away, which can lead to the loss or significant degradation of the signal from the far mobile station. Reduced network bandwidth and coverage may follow from this.

for example, let’s consider three stations A, B, and C, here terminals A and B send and C receives. The signal strength decreases proportional to the square of the distance, the signal of B, therefore, drowns out A’s Signal, as a result, C cannot able to receive A.

Due to the fact that handsets may be located anywhere within a given cell’s boundaries, the CDMA near-far issue exists. While some handsets will be relatively near to the base station, others will be far away.

In a free space situation or according to the inverse square rule, the signal strength drops by a factor of two with increasing distance.

Signal = k/(d^2)
Where: k = a constant
       d = distance

Effects of the CDMA Near-Far Problem

• Interference can cause users to have poorer call clarity, slower data speeds, and other issues that can make users less satisfied with the service overall.
• Users with stronger signals who are closest to the base station can take more network resources, leaving less for users with signals that are farther away. This might result in an unjust distribution of resources and a poor user experience for people who are farther away.
• When some users’ transmissions are suppressed or compromised due to interference, the network’s overall capacity to serve all users is decreased. This may lead to dropped calls, slow data speeds, and other service issues, that’s how the capacity will be reduced.
• When a user’s signal is blocked or degraded due to interference, the device might need to increase its power output to maintain a connection. As a result, the battery may discharge more rapidly and last for shorter periods of time.

Some Possible Solutions to Near-Far Problem 

Power control is used to address the near-far issue. Each base station in a cellular network controls power, ensuring that all mobile devices within its coverage region send the base station the same amount of signal. This resolves the issue of close subscribers drowning out the base station receiver and distant subscribers’ signals.

In order to solve the near-far problem, interference cancellation is a technique that involves filtering out unwanted signals that interfere with a user’s communication. This can be done using a variety of techniques, such as adaptive filtration and linear prediction.

Sectorization could be done, The base station’s coverage area is split into a number of sectors, each with its own collection of frequencies and codes. This allows the network to accommodate more users while minimizing customer annoyance.

So this was all about the CDMA Near Far problem and its possible solutions, apart from this, there are a lot of different problems also came up while mobile and wireless communication like Exposed terminal problem and Hidden terminal problem. you can also read them.