[Paper Review] Using AMC and HARQ to Optimize System Capacity and Application Delays in WiMAX Networks

Iwan Adhicandra|arXiv (Cornell University)|May 27, 2010

Advanced Wireless Network Optimization6 references9 citations

TL;DR

This paper evaluates the impact of Adaptive Modulation and Coding (AMC) and Hybrid Automatic Repeat reQuest (HARQ) on system capacity and application delay in WiMAX networks. By comparing static QPSK 1/2, AMC alone, and AMC with HARQ, the study demonstrates that an aggressive AMC table combined with HARQ significantly improves both spectral efficiency and delay performance, outperforming static or standalone AMC schemes.

ABSTRACT

The IEEE 802.16 technology (WiMAX) is a promising technology for providing last-mile connectivity by radio link due to its high speed data rates, low cost of deployment, and large coverage area. However, the maximum number of channels defined in the current system may cause a potential bottleneck and limit the overall system capacity. The aim of this paper is to compare the impact on system performance of different solutions used to mitigate the impairments due to the radio channel. In particular, taking into account the WiMAX system capacity as well as application delays, the paper presents the simulation results obtained when a static QPSK 1/2 Modulation and Coding Scheme (MCS) is adopted. Then, the study is aimed at evaluating the improvements introduced by the adoption of an adaptive modulation and coding (AMC) and an AMC jointly with Hybrid Automatic Repeat reQuest (HARQ). Results indicate that the best strategy is to use an aggressive AMC table with the HARQ.

Motivation & Objective

• To analyze the performance limitations of WiMAX networks due to a fixed number of channels, which can act as a bottleneck.
• To evaluate the effectiveness of Adaptive Modulation and Coding (AMC) in improving system capacity and reducing application delays.
• To investigate the combined impact of AMC and Hybrid Automatic Repeat reQuest (HARQ) on system performance.
• To compare different transmission strategies—static MCS, AMC alone, and AMC with HARQ—under varying radio channel conditions.

Proposed method

• The study employs system-level simulations to evaluate performance under different modulation and coding schemes (MCS).
• A static QPSK 1/2 MCS is used as a baseline for comparison.
• AMC is implemented to dynamically select modulation and coding rates based on channel conditions.
• HARQ is integrated with AMC to retransmit erroneous packets, improving reliability and reducing delay.
• An aggressive AMC table is used to maximize spectral efficiency under good channel conditions.
• Performance is measured in terms of system capacity (throughput) and application-level delay.

Experimental results

Research questions

• RQ1 How does using a static QPSK 1/2 MCS affect system capacity and application delay in WiMAX networks?
• RQ2 To what extent does implementing AMC alone improve system capacity and reduce delay?
• RQ3 What is the combined effect of AMC and HARQ on system capacity and application delay?
• RQ4 Which configuration—AMC alone or AMC with HARQ—provides the best trade-off between capacity and delay?

Key findings

• The use of an aggressive AMC table with HARQ yields the highest system capacity compared to static MCS or AMC alone.
• Application delays are significantly reduced when HARQ is combined with AMC due to efficient error recovery.
• AMC alone improves capacity over static MCS but introduces higher delay due to retransmissions without HARQ's efficiency.
• The combination of aggressive AMC and HARQ achieves the best balance between spectral efficiency and delay performance.