| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 94 === In order to improve throughput, dynamic link adaptation schemes are designed so that the signal and protocol parameters can be adjusted as the radio link conditions change, according to the quality of a wireless channel. IEEE 802.11 standards, such as 802.11g and 802.11b, support multiple data transfer rate capability in the physical (PHY) layer, which allow medium access control (MAC) management entity to perform dynamic rate switching with the objective of improving the performance. Although the PHY layer supports multi-rate capability, MAC control schemes are required to exploit this capability.
The receiver's signal-to-noise ratio (SNR) and received signal level (RSL) vary with time due to path loss, shadowing effect, multi-path fading and interference. Hence, according to the SNR and RSL of the latest received frame, a link adaptation scheme can quickly respond to the channel variation and suitably adjust parameters for transmissions. This is a cross-layer design because the PHY layer shares the wireless channel information, i.e., SNR and RSL, with the MAC layer. To address the issues of dynamic rate adaptation, improve the data rate and extend the service coverage of an AP, we propose in this thesis a cross-layer link adaptation (CLLA) scheme that is effective and highly executable. The CLLA scheme uses the number of successful transmissions, the number of transmission failures and the channel information from the PHY layer to determine proper transmission parameters for subsequent medium accesses. The CLLA scheme lets frames be transmitted at the highest available data rate using proper medium access methods defined in the scheme, so high throughput can be achieved.
The CLLA scheme is compared with the fixed-rate scheme and other well-known link adaptation schemes, performance comparison is validated against simulations. Simulation results show that the CLLA scheme can achieve higher throughput in stationary or even mobile environment.
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