Near-End Far-End Interference in Mobile Communication Systems

Key Takeaways

• System-generated cellular interference can be classified into co-channel interference and non-co-channel interference.

• The signals adjacent to the frequency of the desired signals interfere with mobile communication and are called adjacent channel interference.

• The type of interference that only exists in mobile or cellular communication systems is called near-end far-end interference. 

Near-end far-end interference only occurs in mobile communication systems

Today's world is a highly noisy environment and mobile or cellular communication is increasing at a rapid pace. Anything that interferes, disrupts, or damages mobile communication signals is labeled interference.

In cellular communication systems, interference can be classified as co-channel interference or non-cochannel interference. Near-end far-end interference is one type of non-cochannel interference that occurs in mobile communication systems. We will explore interference in communication systems as well as take a closer look at this particular type of interference in this article.  

Interference in Mobile Communication 

Interference is any distortion polluting the desired signal in mobile communication. In cellular communication, interference limits performance as well as the capacity of the system. The effects of interference on voice channels include crosstalk and noisy call backgrounds. There may also often be dropped calls due to interference on control channels.

The interference in cellular radio communication can be caused by:

• Another mobile in the same cell.
• Other base stations operating at the same frequency.
• A call in progress in a neighboring cell.
• Any non-cellular system leaking energy into the cellular frequency band. 

The severity of interference in mobile communication is high in urban areas. A high radio frequency noise floor is one of the major reasons that urban areas are prone to interference. There are more mobile stations and base stations in big cities compared to rural and suburban areas, and this increases the influence of interference on mobile communication in urban areas. 

Types of Interference

System-generated cellular interference can be classified into:

• Co-channel interference (CCI) - Co-channel interference is due to frequency reuse. Frequency reuse increases the efficiency of the frequency spectrum usage at the cost of co-channel interference. The cells in cellular communication use the same frequency set under the frequency reuse method and are called co-channels. Repeated use of the same frequency channels in different co-channel cells produces co-channel interference.

• Non-co-channel interference (NCCI) - Non-co-channel interference is due to signals that are adjacent in the frequency to the desired signal. The causes of non-co-channel interference can be imperfect or inadequate filtering (such as receiver filters allowing the adjacent frequencies to leak in), poor frequency control in the reference channel, the interfering channel, or both, or improper tuning. The effect of non-co-channel interference is high when the interfering agent is close to the subscriber's receiver. There are different types of non-co-channel interference, including:

1. Adjacent-channel interference (ACI)
2. Near-end far-end interference
3. Interference between systems
4. Long-distance interference
5. UHF TV Interference

We will briefly discuss the first two types of non-co-channel interference in the upcoming sections.

Adjacent Channel Interference 

The signals adjacent to the frequency of the desired signals interfere with mobile communication and are called adjacent channel interference. Adjacent channel interference includes two types of interference:

1. Next-channel interference - Next-channel interference is the interference concerning the channel next to the operating channel. In the case of a poorly designed cellular communication system, next-channel interference interferes with the mobile unit from other cell sites. In certain cases, a mobile unit with a call in progress in the control channel in a cell can interfere with the next control channel at another cell site. Next-channel interference can be mitigated using filters with a sharp falloff slope. 
2. Neighboring channel interference - Neighboring channel interference is the interference concerning more than one channel away from the operating channel. In cellular communication, there are a fixed set of channels assigned for each cell site. If all the channels are simultaneously transmitting at one cell site antenna with insufficient frequency band isolation, it will result in neighboring channel interference caused by unwanted intermodulation products. 

Near-End Far-End Interference 

Near-end far-end interference only exists in mobile or cellular communication systems. The occurrence of near-end far-end interference is in relation to the distance between the mobile unit and the base station, which is compared with the distance to another mobile transmitter. 

When Does Near-End Far-End Interference Occur?

Consider a mobile unit at a relatively far distance of d₁ from the desired base station transmitter. The mobile unit is at a distance of d₂ from the undesired adjacent mobile transmitter. Let the distances be such that d₁> d₂. When the two transmitters happen to transmit signals simultaneously, then the signals received by the mobile unit from the desired source are masked by the signals received from the undesired source.

Another scenario that leads to near-end far-end interference is when a base station receives signals simultaneously from the mobile units that are located at unequal distances from the base station. In this particular case, the power difference due to path loss between the base station and the two mobile units is defined by a term called near-end-to-far-end ratio interference. The near-end-to-far-end ratio-interference is expressed as the ratio of path loss at distance d₁ to path loss at distance d₂.

The near-end far-end interference is a unique phenomenon that only occurs in mobile communication systems. It can occur within one cell or within cells of two mobile radio systems. Cadence offers software tools for designing near-end far-end interference mitigation techniques for mobile communication systems. Subscribe to our newsletter for the latest updates. If you’re looking to learn more about how Cadence has the solution for you, talk to our team of experts.