Interference Coordination for 5G New Radio
Summary (2 min read)
OverAll Inter-cell Interference cOOrdInAtIOn desIgn PrIncIPles fOr 5g new rAdIO
- Co-channel inter-cell interference is known to be one of the limiting factors of cellular systems, and it has triggered numerous academic research studies and industrial standardization and implementation efforts in LTE/LTE-A.
- Fifth generation new radio (5G NR) [4, 5] is expected to experience a proliferation in the number of emerging use cases, categorized into three broad service groups [6] .
- Inter-cell pilot sequence coordination techniques are proposed, which improve the link performance because of enhanced channel estimation and coherent demodulation [8] .
- The details of the proposed mechanisms are presented in the next sections.
- For the sake of conciseness, each downlink solution is tailored for a given service, although all UL and DL proposals are applicable to both eMBB and URLLC.
UPlInk Inter-cell PIlOt cOOrdInAtIOn
- In UL, inter-cell pilot interference arises when the assigned uplink pilot sequences across multiple cells, which are non-orthogonal, are scheduled on the same time-frequency resources.
- The received pilots from a target user suffer from pilot interference coming from neighboring cells, resulting in poor channel estimation.
- The available sequences in each cell are constructed by phase rotation of a root sequence identified by a root index, and are mutually orthogonal.
- An alternative implementation is a centralized approach with a central controller sending the indices of all concerned BSs to each BS.
- Going one step further, [8] proposes to optimize the choice of the used sequences such that the channel estimation MSE is further reduced.
dOwnlInk Inter-cell Interference cOOrdInAtIOn
- In the DL, the trend is toward more dynamic ICIC solutions, as already agreed in 3GPP for 5G NR [5] , as well as addressing various network deployments (small cell and macro scenarios), key 5G technologies (dense small cell networks and MU-MIMO), and KPI requirements (spectral efficiency, energy, and reliability).
- DOwnlInk Inter-cell cOOrdInAted smAll cell dtX Cell discontinuous transmission is an energy saving technology that adapts the cell activity to its instantaneous load.
- Second, dormant cells cannot exchange information and implement baseline ICIC solutions or CoMP schemes.
- Additionally, the measurements related to the radio access network capacity can be forwarded to the controller node during the small cell activation.
- In any case, the proposed solution with reinforcement learning manages the small cell activity to limit network energy consumption without reducing the system quality of service (QoS).
dOwnlInk Inter-cell rAnk AdAPtAtIOn
- In a MIMO setting, the downlink serving rank (or number of transmission streams) plays a major role in the interference suppression levels of interference rejection combining (IRC) receivers.
- For 5G NR, an inter-cell rank coordination mechanism can improve the network and the celledge user throughput by coordinating the generated inter-cell interference from the aggressor cell.
- The proposed inter-cell rank coordination aims at limiting the maximum rank of an aggressor, thus providing a guarantee on the experienced interference.
- 2) The serving BS decides what will be the maximum transmission rank for each of the UEs in each group, along with the interference rank it would like to have.
- The granularity provides a tradeoff among performance, overhead and complexity.
dOwnlInk On-demAnd POwer bOOst And cOOrdInAted mUtIng
- The SINR outage is a relevant metric for URLLC in 5G NR, and it can be improved with two well known principles, namely power boost of the desired signal and muting or blanking of the inter-fering signal.
- The power in the rest of the band should accordingly be de-boosted to keep a constant nominal power.
- On the other hand, the same contiguous block of PRBs is muted in the aggressor cell, allowing the neighboring cell to transmit both control channel scheduling information and data channel on those protected resources with enhanced signal and reduced interference.
- In a centralized architecture, a central entity keeps track of available information in terms of received signal and interference to the UEs in the network, and can rapidly take network-wise muting decisions.
- In distributed architectures, the coordination is divided into two phases that work at different time-scales.
PerfOrmAnce evAlUAtIOn Of dOwnlInk Interference cOOrdInAtIOn
- The authors briefly present and discuss the performance of the three proposed downlink enhancements.
- A classical DTX optimized only for energy saving and without interference management serves as the baseline for the small cell DTX scenario.
- There are 30 users requiring near-real time video traffic.
- This issue can be solved by the proposed scheme, which results in a large improvement in terms of PER at the cost of a limited additional complexity and without affecting energy.
Low latency for very fast coordination
- Xn activation of the muting works in a fast basis, and implies the cell sending the protected data to ask the aggressor cell to mute .
- The authors identify and address major interference challenges in the uplink and the downlink.
- They are compatible and they all build toward 5G NR, being highly dynamic, flexible, and multi-service capable.
- Also, on-demand power boosting and coordinated muting is tailored to meet URLLC requirements.
- The performance gains show clear benefits of network coordination with limited complexity and standardization effort.
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Citations
26 citations
Cites background from "Interference Coordination for 5G Ne..."
...On-Demand Power Boost 5G NR will likely introduce more advanced techniques for interference coordination than LTE [14]....
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24 citations
21 citations
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Cites methods from "Interference Coordination for 5G Ne..."
...Furthermore, coordinated multi-point (CoMP) is another technique envisioned to play an important role in 5G systems [9]....
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References
97 citations
34 citations
"Interference Coordination for 5G Ne..." refers background in this paper
...A related work is [14], where the authors propose an assignment of ZC sequences in an Orthogonal Frequency Division Multiplexed (OFDM) system, such that the worst-case channel estimation mean square error (MSE) is minimized....
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...However, a key assumption of [14] is that user pilots occupy all available subcarriers, which is not the case in a practical system, rendering the performed analysis inapplicable....
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13 citations
"Interference Coordination for 5G Ne..." refers background in this paper
...1 The proposed rank coordination mechanism is not bound to any specific rank adaptation algorithm, though interference-aware rank adaptation algorithms such as those presented in [12] are best suited for such applications....
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...Building on the earlier work in [12], novel solutions for coordination of the maximum transmission rank between neighboring cells is also presented....
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11 citations
"Interference Coordination for 5G Ne..." refers background in this paper
...The proposed on-demand power boost and coordinated muting [13] works as follows....
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...Another proposal is to support the challenging reliability and delay requirements of URLLC through highly agile and fast coordination techniques, offering benefits for both control and the data channel performance [13]....
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8 citations
"Interference Coordination for 5G Ne..." refers methods in this paper
...In the downlink (DL), we propose a scheme for joint interference control and energy efficiency in dense small cell scenarios [9] by means of enhanced methods for discontinuous transmissions at the cell level (cell discontinuous transmission DTX) based on fuzzy Q-learning [10]....
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...We design a fuzzy Q-learning based cell DTX controller that uses its decisions in the previous time slot to estimate the interference level experienced by the active small cells....
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