EESM (Exponential Effective SINR Mapping)
Exponential Effective SINR Mapping (EESM) is a technique used in wireless communication systems to improve the accuracy of signal-to-interference-plus-noise ratio (SINR) estimation. It is commonly used in the design of wireless communication systems that employ Orthogonal Frequency Division Multiple Access (OFDMA) technology, such as Long-Term Evolution (LTE) systems.
In wireless communication systems, SINR is a critical parameter used to measure the quality of communication between a transmitter and receiver. It is the ratio of the desired signal power to the total interference and noise power. Accurately estimating the SINR is important for designing efficient wireless communication systems, as it affects the achievable data rate, reliability, and overall system capacity.
The EESM technique is used to estimate the effective SINR for each subcarrier in an OFDMA system. OFDMA systems divide the available frequency bandwidth into a set of subcarriers, each of which can be used to transmit data to multiple users simultaneously. The effective SINR on each subcarrier is used to calculate the modulation and coding scheme (MCS) that can be used to transmit data on that subcarrier.
The EESM technique improves SINR estimation accuracy by taking into account the nonlinearities introduced by the modulation and demodulation process. In OFDMA systems, the modulation scheme used for each subcarrier can be adjusted based on the SINR on that subcarrier. The modulation scheme used for a given subcarrier is chosen from a predefined set of modulation schemes, each of which has a different data rate and error rate.
In traditional SINR estimation techniques, such as linear interpolation, the SINR is estimated based on the received signal power and the interference and noise power. However, this approach does not take into account the nonlinearities introduced by the modulation and demodulation process. As a result, the estimated SINR may not accurately reflect the true SINR on a given subcarrier.
The EESM technique overcomes this limitation by using an exponential function to map the estimated SINR to the effective SINR. The effective SINR is defined as the SINR that would result in the same error rate as the estimated SINR if the same modulation scheme was used. The exponential mapping function used in EESM is derived from the Shannon capacity formula, which relates the data rate achievable on a given subcarrier to the SINR on that subcarrier.
The EESM technique can be implemented using a lookup table that maps the estimated SINR to the effective SINR for each modulation scheme. The lookup table is generated offline using a channel model that accurately reflects the channel conditions in the wireless communication system. During operation, the estimated SINR is used to select the appropriate modulation scheme from the lookup table, and the effective SINR is used to calculate the data rate and error rate for the selected modulation scheme.
The EESM technique has been shown to significantly improve SINR estimation accuracy in OFDMA systems. This, in turn, improves the overall system capacity and reliability, as the modulation and coding scheme can be optimized for each subcarrier based on the true effective SINR. The EESM technique has been incorporated into several wireless communication standards, including LTE and WiMAX.
In conclusion, EESM is a powerful technique used in wireless communication systems to improve the accuracy of SINR estimation. By taking into account the nonlinearities introduced by the modulation and demodulation process, EESM can provide more accurate estimates of the effective SINR on each subcarrier, which, in turn, can improve the overall performance of the wireless communication system.