How could raised cosine concept meet the requirements of the recently standardized reduced capability (Redcap) device by 3GPP?
It can affect the desired data rate, spectral efficiency, delay, complexity, and reliability by combating noise levels and channel characteristics.
let's break down the concepts related to the raised cosine filter and how they impact the spectral efficiency and bandwidth of the recently standardized reduced capability device (Redcap) by 3GPP.
The Telecom market is experiencing a rapid increase in the demand for 5G devices with limited functionalities. The implementation of the 3GPP RedCap NR feature is aimed at simplifying user equipment (UE) by minimizing the number of RX/TX antennas, reducing UE bandwidth usage, lowering power consumption, relaxing data rates, and easing UE processing time and capability. These enhancements facilitate the realization of various promising use cases, particularly in the domains of industrial wireless sensors, video surveillance, and wearable technology.
In 3GPP Rel-17 the RedCap ecosystem and framework was defined, including principles of network awareness of device capabilities. However, not all aspects were completed and therefore some functionality was moved into Rel-18 for as enhancement.
The features now being introduced in 3GPP Rel-18 for enhanced support of RedCap NR devices include those for emerging 5G use cases, including Smart city and eHealth coverage. The following figure summarize what is covered by 3GPP Rel-17 and 3GPP Rel-18.
Now, let’s move on to discuss the most important points when it comes to designing a raised cosine filter that can meet some of the Redcap device requirements.
Raised Cosine Filter (RC Filter):
The raised cosine filter is a commonly used filter in digital signal processing and telecommunications. It is used for pulse shaping in digital modulation schemes to control the spectral characteristics of the transmitted signal and to minimize the interference between adjacent channels. The filter's impulse response is a truncated cosine function raised to a power.
Impact of Roll-Off Factor (α):
The roll-off factor, denoted as α, determines the excess bandwidth of the filter. It controls the trade-off between the main lobe width and the level of side lobes. A smaller value of α leads to a wider main lobe, resulting in better spectral containment but a higher level of inter-symbol interference. A larger value of α leads to a narrower main lobe, causing more spectral leakage but less inter-symbol interference.
Filter Span in Symbols:
The filter span in symbols determines the duration over which the filter operates. A longer filter span allows for better pulse shaping and thus improved spectral containment, but it also introduces more delay in the system, which can be a concern for real-time applications.
Interpolation:
Interpolation refers to the process of estimating unknown data points within the range of known data points. In the context of the raised cosine filter, interpolation can be used to upsample the signal, allowing for a smoother transition between data points and enabling a more accurate representation of the original signal.
Gain:
The gain of the filter is used to control the amplitude of the filter's output. Adjusting the gain can impact the signal-to-noise ratio and the overall power of the transmitted signal.
To achieve high spectral efficiency and optimal bandwidth utilization, you should consider the following tuning strategies for the raised cosine filter:
Choose an Optimal Roll-Off Factor (α): Select a roll-off factor that balances the trade-off between spectral containment and inter-symbol interference based on the specific requirements of your application. Lower values of α generally provide better spectral containment at the cost of increased inter-symbol interference.
Optimize Filter Span: Choose a filter span that allows for effective pulse shaping while minimizing unnecessary delay. Longer filter spans may provide better spectral containment, but they can introduce higher latency, which might not be suitable for real-time applications.
Utilize Interpolation Techniques: Employ appropriate interpolation techniques to improve the accuracy of signal representation and reduce distortion during the filtering process.
Adjust Gain for Signal-to-Noise Ratio (SNR): Adjust the gain of the filter to optimize the signal-to-noise ratio, ensuring that the transmitted signal has sufficient power while minimizing interference and noise.
It's crucial to conduct thorough simulations and analyses to fine-tune these parameters based on the specific requirements and constraints of your Redcap communication device, considering factors such as the desired data rate, spectral efficiency, delay, complexity, noise levels, and channel characteristics.