Band, Carrier Component (CC), Bandwidth Part (BWP)

In ns-3, to configure scenarios, we should define operational bands, CCs, and BWPs (🔗). While studying the example “cttc-nr-demo,” I have a question about the criteria for configuring bands, CCs, and BWPs. Thus, in this post, I’m going to organize the concepts of Band, CC, and BWP.

Band

Predefined physical bandwidth

• This is a physical frequency range defined by regulatory bodies or standardization organizations.

Considerations

• Frequency Range: When selecting a frequency range, you must follow national or regional regulations.
• Bandwidth: The bandwidth to be used within the chosen frequency range must be determined. This directly impacts network performance.

Carrier Component (CC)

User-defined physical bandwidth

• CCs are physical frequency ranges defined by users or network operators within a given band.
• One or more Carrier Components (CCs) can be assigned within a single frequency band.
• Introduced for flexible management of frequency resources.
• They are physical bandwidths, so overlapping CCs can cause interference between CCs.
• Using carrier aggregation (CA), a UE can be configured to use multiple CCs as well as a single CC.
  • When multiple CCs are configured, gNB (base station) and UE (user equipment) can use a single CC by default, but multiple CCs can be aggregated to provide higher bandwidth and performance as needed.

Carrier Aggregation (CA)

Carrier Aggregation is a technology that combines multiple frequency bands to provide higher data rates and capacity.

• Multiple carrier components can be combined to provide higher bandwidth.
• When using CA, the frequency and bandwidth of each carrier component must be adjusted.
• CA is managed dynamically and can be activated or deactivated based on network conditions or user requirements.
  • When network load increases or higher data rates are needed, the gNB activates additional CCs for communication with the UE. This allows for higher data transmission through wider bandwidth.

CA can be classified into three modes:

• Intra-band contiguous: Combining CCs within the same frequency band continuously.
• Intra-band non-contiguous: Combining CCs within the same frequency band non-continuously.
• Inter-band: Combining CCs from different frequency bands.

Considerations

• Traffic Load: CCs can be dynamically allocated based on the traffic demands of each UE. UEs requiring high traffic can use multiple aggregated CCs, while UEs with lower traffic demands can use a single CC.
• Frequency Interference: When allocating frequencies for each carrier component, they must be chosen carefully to minimize interference and maximize performance.
• Network Conditions: The bandwidth of each CC and the allocated BWP impact network performance. CC allocation should be dynamically adjusted based on current network conditions and resource availability.
• QoS Requirements: CC configuration and BWP settings should be adjusted according to user demand and service quality (QoS) requirements.

Bandwidth Part (BWP)

User-defined logical bandwidth

• BWPs are logical subdivisions of a CC. Multiple BWPs can be configured within a single CC.
• In 5G NR, the concept of BWP was introduced to use frequency resources more efficiently and meet various service requirements.
  • Different numerologies can be used within the same CC. BWP represents a specific part of the frequency range, and each BWP can have its unique numerology.
  • Each BWP can be configured for specific users or services to meet different service requirements.
• While it is ideal for BWPs not to overlap, there is no strict requirement that BWPs must not overlap. However, overlapping BWPs can cause interference and should be managed carefully.

Considerations

• Flexible Frequency Resource Management: Using BWPs allows efficient use of frequency bandwidth. For example, the frequency range can be divided into multiple BWPs, with each BWP optimized for specific UEs or service types.
• QoS Requirements: BWPs can be configured with different transmission parameters (bandwidth, subcarrier spacing, etc.) to meet various QoS requirements.
• Dynamic Allocation: BWPs can be dynamically allocated and reconfigured based on network conditions.

Configuring All

When defining bands, CCs, and BWPs in a cellular system, resources should be managed flexibly considering the scenario to meet the traffic demands present in the scenario.

Considerations

1. Traffic Pattern Analysis: CCs and BWPs can be dynamically allocated based on the traffic demands of each UE. Configuration should be optimized according to expected traffic patterns and user demands.
2. QoS Requirements: UEs with specific QoS requirements can be allocated multiple CCs to provide broader bandwidth.
3. Frequency Interference: Different CCs and BWPs should be allocated to minimize interference between them.
4. Network Conditions (Capacity and Coverage): Configuration should consider network capacity and coverage requirements. This is especially important in densely populated urban areas. Additionally, CC and BWP allocation can be dynamically adjusted based on current network conditions and resource availability.

Example Scenario

For example, given the 3.5GHz band (3400MHz - 3600MHz), it can be divided into multiple CCs. Each CC is tailored to specific services or requirements, and within each CC, multiple BWPs are defined to flexibly manage resources based on user or service demands. Additionally, UEs can be allocated to different BWPs within these CCs based on their requirements.

Band: 3.5GHz (3400MHz - 3600MHz)
  - CC1: 3400MHz - 3500MHz (100MHz bandwidth)
    - BWP1: 3400MHz - 3420MHz (20MHz bandwidth, numerology 0)
        - UE1: General internet browsing, lower power consumption
    - BWP2: 3420MHz - 3440MHz (20MHz bandwidth, numerology 1)
        - UE2: High-definition video streaming
    - BWP3: 3440MHz - 3460MHz (20MHz bandwidth, numerology 2)
        - UE3: Real-time gaming, requires low latency
  - CC2: 3500MHz - 3600MHz (100MHz bandwidth)
    - BWP1: 3500MHz - 3520MHz (20MHz bandwidth, numerology 0)
        - UE4: IoT devices, periodic low data rate communication
    - BWP2: 3520MHz - 3540MHz (20MHz bandwidth, numerology 1)
        - UE5: Augmented reality applications
    - BWP3: 3540MHz - 3560MHz (20MHz bandwidth, numerology 2)
        - UE6: Large file transfers, requires high throughput

Conclusion

As I studied, all three (Band, CC, and BWP) can be represented by central frequency and bandwidth. However, their definitions and ways of usage are different, and they have a dependency relationship. Band contains CCs, and CC contains BWPs. This can be visualized as:

• Band (Predefined physical bandwidth)
  • CC (User-defined physical bandwidth)
    • BWP (User-defined logical bandwidth)

This structure allows flexible and efficient management of frequency resources in a 5G network. Network operators can define multiple CCs within a given Band and further subdivide each CC into various BWPs to meet different service requirements.