Adaptive Modulation and Coding for IEEE802.11n
The link adaptation is critical to achieve high throughput and sustain reliable communications for MIMO-OFDM based IEEE802.11n WLAN. We developed an intelligent link adaptation technique for IEEE802.11n MIMO-OFDM WLAN with convolutional coding. Our technique dynamically selects the best modulation and coding scheme based on channel condition and MAC layer performance (coded BER or PER) requested by applications. We have shown that the coded performance at decoder output can be modeled as a function of decoder-input uncoded BER and the code rate. For MIMO-OFDM systems with different modulation types for different spatial streams at each subcarrier, we developed a simple and closed form solution to compute the BER and PER for each spatial stream mixed from different subcarrier.
Background & Objective: IEEE802.11n standard employs multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) transmission technology to enable high throughput communication for up to 600 Mbps in a 40 MHz channel bandwidth. Since the wireless fading channel varies with time, link adaptation must be employed to sustain reliable communications and maximize throughput. To fully exploit MIMO channel variations and transmit beacomforming on a MIMO link, IEEE802.11n standard defines a large set of modulation and coding schemes (MCS) to facilitate this goal. Therefore, the efficient and practical link adaptation techniques are needed to be developed for IEEE802.11n WLAN. Our objective is to develop a simple and intelligent link adaptation technique to dynamically select the best link for IEEE802.11n WLAN.
Technical Discussion: There are extensive techniques proposed on adaptive modulation and coding. However, these techniques do not benefit IEEE802.11n WLAN well since they are either too complicated for implementation or do not fully exploit characteristics of MIMO fading channel. We have developed a dynamic link adaptation technique that maximizes the throughput while satisfying the application performance requirement: code bit-error rate (BER) or MAC packet-error rate (PER). We have demonstrated that our dynamic link adaptation technique is a simple and practical solution for IEEE802.11n MIMO-OFDM WLAN with or without beamforming.
Future Direction: The proposed link adaptation technique needs to be incorporated into IEEE802.11n WLAN to achieve a better performance.
Contacts:
Jianlin Guo
Jinyun Zhang
Technology Area: Digital Communications
Modification Date: September 12, 2007
