RS Rate-splitting
Rate-splitting (RS) is a transmission strategy used in wireless communication systems, particularly in multi-user scenarios. It is designed to improve the spectral efficiency and reliability of the system by exploiting the multi-user interference in the network.
In a wireless communication system, multiple users transmit their data simultaneously over the same frequency band. Due to the limited availability of radio resources, these transmissions can interfere with each other, leading to a degradation in the overall system performance. Rate-splitting is a technique that helps mitigate this interference and improve the system capacity.
In conventional communication systems, the data intended for each user is split into multiple streams, each transmitted over a separate channel. However, in rate-splitting, the data is split into multiple substreams, and these substreams are transmitted simultaneously over the same channel.
The key idea behind rate-splitting is to separate the user's data into two parts: a common part that is intended for multiple users and a private part that is specific to each user. The common part is jointly decoded by multiple users, while the private part is decoded separately by each individual user.
Let's consider a scenario with K users in a wireless communication system. The transmitted signal x at the base station is given by:
x = ∑(sqrt(ρc)sc + sqrt(ρp)sp),
where:
- sc represents the common part of the signal intended for all users,
- sp represents the private part of the signal intended for the kth user,
- ρc and ρp are the power allocation coefficients for the common and private parts, respectively.
At the receiver side, the received signal y for the kth user is given by:
y = Hx + n,
where:
- H represents the channel matrix that characterizes the wireless channel between the base station and the kth user,
- n is the additive white Gaussian noise.
To decode the transmitted data, the receiver employs rate-splitting and performs the following steps:
- Common stream decoding: The receiver jointly decodes the common part of the signal intended for all users. This requires treating the interference from the private parts as noise.
- Private stream decoding: After decoding the common stream, the receiver removes the contribution of the common part from the received signal. Then, each user decodes their private part separately, treating the interference from the remaining private parts and the noise as noise.
Rate-splitting allows for better exploitation of the multi-user interference present in the wireless channel. By jointly decoding the common stream, multiple users can effectively cancel out the interference and recover the shared information. Additionally, by decoding the private streams separately, users can extract their individual data without significant interference from other users.
The power allocation coefficients ρc and ρp determine how the power is allocated between the common and private parts. By optimizing these coefficients based on the channel conditions and user requirements, the system can achieve a trade-off between the achievable rates of the common and private streams.
Rate-splitting has been shown to improve the spectral efficiency and overall system capacity in scenarios with multi-user interference. It is particularly beneficial in scenarios with a large number of users or high interference levels. By effectively managing interference, rate-splitting enables higher data rates, improved reliability, and enhanced performance in wireless communication systems.