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WSLM Weighted Selective Mapping Technique

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Weighted Selective Mapping (WSLM) is a powerful error correction technique used in Orthogonal Frequency Division Multiplexing (OFDM) systems, particularly in the context of wireless communication and digital broadcasting. OFDM is a popular modulation scheme that divides the available spectrum into multiple subcarriers, allowing for efficient data transmission. However, the performance of OFDM can be degraded in the presence of non-linear effects, such as distortion caused by high-power amplifiers.

Selective Mapping (SLM) is a well-known error correction technique used in OFDM systems to combat nonlinear distortion. It involves transmitting multiple versions of the same data signal, each with a different phase sequence, to create diversity in the transmitted signals. At the receiver, the multiple received versions of the signal are combined to mitigate the impact of distortion and improve the overall bit error rate (BER) performance.

Weighted Selective Mapping (WSLM) is an enhancement of the original SLM technique that introduces weighted selection probabilities for different phase sequences. These weights are based on the channel conditions and are used to optimize the diversity gain achieved by SLM. The main objective of WSLM is to increase the probability of selecting phase sequences that are more likely to lead to better performance under the given channel conditions.

The key steps involved in WSLM are as follows:

  1. Data Generation: In the first step, the original data to be transmitted is divided into multiple sub-blocks. Each sub-block is associated with a specific phase sequence.
  2. Phase Sequence Generation: WSLM generates multiple phase sequences, which are orthogonal to each other, to create diversity in the transmitted signals. These phase sequences are known to both the transmitter and receiver.
  3. Phase Rotation: Each sub-block of data is multiplied by the corresponding phase sequence. This phase rotation process introduces diversity among the transmitted signals.
  4. Peak-to-Average Power Ratio (PAPR) Calculation: After phase rotation, the PAPR of each transmitted signal is calculated. PAPR is a metric that quantifies the ratio of the peak power to the average power of an OFDM signal. High PAPR values can cause non-linear distortion in high-power amplifiers.
  5. Selection of Optimal Sequence: The phase sequence with the lowest PAPR is selected for transmission. This sequence is chosen to minimize the peak power of the transmitted signal and reduce the likelihood of non-linear distortion.
  6. Weight Assignment: Weighted probabilities are assigned to the phase sequences based on their PAPR values. Sequences with lower PAPR values are assigned higher weights, making them more likely to be selected for transmission.
  7. Transmission and Reception: The selected phase sequence is transmitted over the wireless channel. At the receiver, multiple versions of the signal are received due to channel fading and multipath effects.
  8. Combining Received Signals: The received signals, corresponding to different phase sequences, are combined at the receiver. The weights assigned during the transmission stage are used to optimize the combining process. This combining operation enhances the overall signal quality and reduces the impact of nonlinear distortion.

WSLM offers several advantages over traditional SLM:

  1. Performance Improvement: By intelligently selecting phase sequences based on channel conditions, WSLM can achieve better diversity gain and provide improved BER performance compared to conventional SLM.
  2. Reduced Complexity: WSLM introduces minimal additional complexity compared to SLM, making it an attractive option for practical implementation in OFDM systems.
  3. Adaptability: WSLM's ability to adapt to varying channel conditions makes it robust in different wireless environments, ensuring reliable communication even in challenging scenarios.

WSLM has been extensively studied and has demonstrated its effectiveness in improving the performance of OFDM systems, especially in the presence of non-linear distortion. As wireless communication technologies continue to evolve, error correction techniques like WSLM will play an increasingly important role in ensuring reliable and efficient data transmission in various wireless communication systems.