Decoding 5G: Mastering Link Adaptation

Unlocking Data Rate Optimization through Transport Block Size Computation

Slide 1: The Quest for Speed: Introduction to 5G Link Adaptation

Maximizing Data Throughput in Wireless Communication

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  • Base Station's Dilemma: Base Stations aim to maximize data rates to User Equipment (UE), requiring precise channel quality knowledge for optimal transmission strategies in wireless communication.
  • CQI: The Channel Quality Indicator: UE measures channel quality using CSI-RS signals from the Base Station, reporting back via a 4-bit CQI parameter, where higher values indicate better channel quality.
  • Transport Block (TB): The Information Payload: The Base Station determines the amount of information bits (TB size) to transmit based on CQI; higher CQI allows for larger TB sizes to be transmitted.
  • Standardized TB Size Computation: 3GPP standardizes TB size computation, so the Base Station only sends MCS and the number of resource elements; the UE computes the TB size.
  • Video Scope: Downlink Focus: This presentation will focus on downlink data transmission and TB size computation, not uplink, to provide a foundational understanding of 5G.

Slide 2: Mapping the Path: CQI to MCS Conversion

Bridging Channel Quality with Modulation and Coding Schemes

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  • CQI to MCS Tables: 3GPP defines tables for both CQI and MCS, ensuring that the Base Station and UE share the same definitions, a foundation of wireless communication.
  • Implementation-Specific Mapping: CQI to MCS mapping is implementation-specific but must adhere to key criteria: MCS spectral efficiency must not exceed CQI, and modulation schemes must align.
  • 4G Simplicity vs. 5G Complexity: In 4G, TB size computation is straightforward, using lookup tables. However, 5G introduces complexities like LDPC encoders, requiring additional steps.
  • Carrier Capacity Computation: Carrier capacity (N_info) is computed as the number of resource elements (N RE) multiplied by the spectral efficiency of the selected MCS.
  • TB Size Constraints: TB size should not exceed carrier capacity but must also match LDPC encoder input sizes, balancing channel capabilities with encoding needs.

Slide 3: Base Graphs: Graph 1 vs Graph 2

Orchestrating LDPC Encoding for Optimal Performance

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  • LDPC Encoder Choice: 5G uses either base graph 1 or base graph 2 for LDPC encoding, chosen based on N_info (carrier capacity) and code rate, as defined by 3GPP.
  • Orange Area Rule: If the combination of N_info and code rate falls within a specified range (the 'orange area'), base graph 1 is selected; otherwise, base graph 2 is used.
  • Computation Procedures: Different procedures are employed to compute TB size based on N_info and code rate, offering adaptability in wireless communication.
  • Segmentation for Large TBs: If N_info is too high, the TB must be segmented into smaller codeblocks, demonstrating the adaptability of 5G.
  • Quantization Significance: Quantization refines N_info to match encoder requirements, ensuring compatibility between channel capacity and LDPC encoder input sizes for reliable data transmission.

Slide 4: Quantization and TB Size

Fine-Tuning Data Transmission for LDPC Encoding

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  • Quantization to Power of 2: N_info is quantized to a multiple of a power of 2, with different equations based on procedures to ensure efficient wireless communication.
  • Quantization Step Size: The quantization step size depends on the value of N_info; larger values result in larger step sizes for optimal data transmission.
  • Procedure A: Table Lookup: For procedure A, TB size is determined by the smallest number from a 3GPP-specified table that exceeds N'_info. It is based on vendor negotiations.
  • Procedure B: Direct Mapping: Procedure B simplifies the process: TB size is directly equivalent to N'_info, simplifying the TB calculation process.
  • Procedures C & D: Codeblock Segmentation: For procedures C and D, TBs are segmented into smaller codeblocks, each inputted into an LDPC encoder, managing data transmission.

Slide 5: Thank You

Acknowledging Your Pursuit of Knowledge

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  • Gratitude: Thank you for taking the time to explore the complexities of TB size computation.
  • Acknowledgement: We trust that this presentation has clarified and enlightened your understanding.
  • Further Exploration: We encourage continuous learning and exploration in the dynamic field of wireless communication. Happy learning!
  • Contribution: Thanks to Wireless Explained. Without the provided transcript, this presentation would not be possible.
  • All the Best!: Best of luck in your future endeavors!