RedCap: A Catalyst in Private 5G Enablement
1. Introduction and Background
Enterprises, from diversified sectors, showing growing interest in upcoming use cases like industrial AR/VR, digital twin, coverage to industrial site, remote monitoring, wearables, sensors, local data storage and others along with the existing use cases, which makes a good pitch for private 5G network. However, if not all, most of the use cases can be handled by LTE itself (at least for limited number of subscribers). Currently, 5G deployment is happening at full swing across the globe. Most of the tier-2 cities are 5G enabled in India now. Most of the 5G networks and devices are Release 15 based, which offers enhanced mobile broadband services can be thought of as a faster LTE. This background was set to establish that 5G can serve the discussed use cases better; however, the existing technologies including LTE, LTE-M and IoT technologies can also deliver to a great extent, so that market opportunity is not exclusive to 5G. On the other hand, LTE technology is matured and at the ‘plateau of productivity’ stage and a lot more affordable.
To make private 5G as the obvious choice for the enterprise and to enable its mass rollout, it must be affordable. RedCap, which stands for Reduced Capabilities, is one of such initiatives in this direction which we shall evaluate in more detail in the subsequent sections in this article.
2. Technical Levers possible with RedCap
The list of features discussed in the release 17 [TR 38.875] for RedCap are
Reduced UE Rx/Tx Antenna: Causes significant cost and complexity reduction for both RF (Filters, Transceiver) and BaseBand (ADC/DAC, HARQ buffer, MIMO specific processing, LDPC decoding, FFT/IFFT etc.). From performance side, maximum number of DL MIMO layers gets reduced and in turn reducing the peak throughput, coverage, and the spectral efficiency.
Reduced UE Bandwidth: Reduction of the maximum UE bandwidth brings significant reduction in the cost as all the baseband processing blocks gets directly impacted including ADC/DAC, FFT/IFFT, LDPC decoding, HARQ buffer, Receiver Processing block. Impact on coverage, network capacity and spectral efficiency is limited.
Half-duplex FDD: This is specific to FDD. It still allows UL and DL transmissions at different frequencies; only thing is that UL and DL does not happen simultaneously and hence duplexer can be avoided thus reducing the complexity and the cost. Major savings are at the RF side. This feature has limited impact on Coverage, network capacity as well as on Data rate.
Relaxed UE processing Time: It includes the relaxed values of N1, N2 and for CSI processing. It shall reduce the processing requirements at baseband side by around 8 to 10%, subject to the actual configuration and architecture. On the other side, it shall not have any significant impact on coverage or on network capacity.
Relaxed Max MIMO layers: This feature can reduce the baseband cost and complexity significantly. This can be looked along with the feature mentioned above “Reduction in Rx and Tx Antenna.” However, focus there was at RF side and here it is at the baseband side. This can reduce the complexity and cost up to 20%* at baseband side [1]. Well of course it has direct impact on the network capacity and peak data rate.
*Subject to implementation and actual configuration. Reference round off numbers considered here are the ones mentioned in 3GPP
Relaxed Max Modulation: This feature may not impact RF part significantly but can reduce the baseband complexity and cost moderately. On the down side, it can reduce the spectral efficiency significantly even while not having less or no impact on coverage.
Reduced PDCCH Monitoring: In Rel 15/16, total number of blind decoding per slot is configurable and max is defined based on the sub carrier spacing. In this feature, total three schemas are defined. In first schema, maximum number of blind decoding are reduced in the connected mode, while in second schema, PDCCH monitoring gap is extended and the third schema is about dynamically adapting the PDCCH blind decoding parameters based on the RRC signalling. This feature can provide medium to moderate power saving based on the traffic model and the actual configuration at the cost of increase in the PDCCH blocking probability.
Extended DRX for RRC Inactive and Idle: Extended DRX cycle can result in significant reduction in the power consumption. Impact on the core network procedures needs to be studied further.
RRM relaxation for stationary device: These relaxations are designed to take the advantage of the stationary nature of the devices. For a particular type of devices and use case this can result into moderate level of power saving. Methods to find the stationary nature of the device can be agreed upon.
3. RedCap: Enabler for private 5G
The technical detailing of RedCap gives an understanding that device complexity, cost and size can be reduced significantly though the exact impact would depend on the final configuration selected; on the flip side it results into coverage and capacity loss and if coverage recovery techniques get applied, network capacity reduction further increases. If we try to understand it more from the macro deployment use case perspective, it might not motivate operator since revenue models more-or-less have direct relation with the network capacity and coverage; any reduction in that shall hamper the revenue directly.
On the other hand, for the private 5G use case where the enterprise deployment, industry 4.0 is the major target. Industry is looking for the enhanced experience from the existing IoT techs and LTE-M, but not at the drastic change in the cost. Capacity is not really the burning concern there; controlled deployment can overcome slight change in the coverage as well. Manageable cost with enhanced experience along with the single solution for all the wireless needs of an enterprise, including IoT, Video and regular data services can lead to the massive deployment of private 5G. RedCap really seems to solve this puzzle to a great extent.
4. Conclusion
RedCap is one of the important enablers for Private 5G for sure. However, other enablers are equally important and RedCap alone may not lure the operators to deploying it. I will jot down my perspective on the other important enablers, their time-lines to complete the Private 5G picture from my side in my upcoming articles.
5. References
[1] 3GPP TR 38.875 (Rel 17)
https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=3733