CoMP and interference coordination in heterogeneous network for LTE-Advanced

In 3GPP LTE-Advanced Release 11, coordinated multi-point transmission and reception (CoMP) which applies interference coordination between base stations (or eNBs) was introduced to improve cell-edge performance of the network and specified under the assumption that ideal backhaul is deployed. However, in practice, network operators may have non-ideal backhaul, especially between macro eNB and small eNB, which may result in limited CoMP gain. Hence, in this paper, a centralized coordination scheme based on two-step processing which can reduce backhaul delay impact on CoMP is introduced. In the first step of the centralized coordination scheme, the central coordinator decides and forwards resource allocation of the cells in coordination area. In the second step, each eNB conducts user scheduling on the resources allocated to each of its cells and applies link adaptation to meet the link performance requirement for the interference condition according to the resource allocation result. Simulation results show that the coordination based on two-step processing outperforms other coordinated scheduling schemes and maintains CoMP gain even in non-ideal backhaul.

본 논문에서는 원격송신국을 활용하는 이종 네트워크 시스템 (HetNet, heterogeneous network)에서 다수의 전송 노드가 협력적으로 신호를 전송하여 셀 경계에 위치한 사용자의 성능 개선을 위한 방법을 제안한다. 이를 위해 셀 경계지역의 특정 위치에 원격송신국을 배치하며, 기지국과 셀 경계 원격송신국 간의 동작 빈도를 조정함으로써 효율적인 동작 방식을 제안한다. 특히 제안방식에서는 LTE-Advanced (Long Term Evolution - Advanced) 표준 회의에서 논의되고 있는 CoMP (coordinated multi-point transmission and reception) 시나리오에서의 시스템 모델 파라미터를 사용한 컴퓨터 시뮬레이션을 활용하여 실험 결과의 신뢰성을 높였다. 또한 기존의 방식과의 비교를 통해 셀 경계지역에 원격송신국을 위치시킴으로 특히 평균 전송률 측면의 하위 사용자 성능을 향상시키는 효과가 있음을 보임으로써 사용자 간의 공평성 문제를 개선할 수 있는 방식임을 입증한다. In this paper, we propose a method to improve cell edge users' performance in HetNet (heterogeneous network) systems by cooperatively transmitting signals using remote radio heads (RRHs) located near coverage boundaries, referred to as edge RRHs. The proposed method locates the edge RRHs in specific locations of the cell boundary and provides an efficient operational strategy by adjusting the duty cycle of the edge RRHs and base stations. The effectiveness of the method is demonstrated by experimental performance based on the system model parameters of the CoMP (coordinated multi-point transmission and reception) scenario, which is discussed in LTE-Advanced (Long Term Evolution - Advanced) standard contributions. When compared with conventional methods, utilization of edge RRHs is especially advantageous for the performance improvement of lower percentile users in terms of average throughput and effectively improves the fairness among users.

In this work, we propose two high-rate quasi-orthogonal space-time coding (STC) schemes which are designed in conjunction with the successive interference cancellation (SIC) based receiver. The symbols of the proposed STC are of judiciously designed diversity order which can be effectively exploited by the SIC based receiver to cancel interference as well as to obtain diversity gain. The proposed STC scheme's amicable quasi-orthogonal structure lends itself to efficient low-complexity linear decoding. Simulation results show that the proposed STC scheme achieves better multiplexing-diversity tradeoffs than the existing conventional schemes in noise-limited single-cell scenarios. In the interference-limited multi-cell scenario, the application of proposed SIC-amiable STC to the coordinated multi-point transmission and reception (CoMP) also achieves higher throughput than the conventional schemes.

With picocells deployed in the coverage of a macrocell in heterogeneous networks (HetNets), the macrocell evolved NodeB (MeNB) may receive interference signals from the picocell users, which results in more severe co-channel interference (CCI) problem in the uplink. In this paper, the spatial uplink interference coordination is investigated in multiple antenna systems, according to which the receiver coding matrix is generated by MeNB to mitigate the CCI from picocell users. Two interference coordination (IC) schemes are proposed based on whether the receiver coding matrix is full rank or not, named as full coding (IC-FC) and part coding (IC-PC), respectively. The application of the proposed schemes is discussed in single picocell and multiple picocell scenarios. The CCI can be totally canceled in single picocell scenario, and an algorithm is developed in multiple picocell networks to mitigate the most severely interfering picocell. Link level and system level simulations are applied, and it is shown that significant performance gain is achieved by our proposed schemes over traditional IC receivers.

Heterogeneous Networks (HetNet), particularly Femto cells, were introduced to meet the exigent need for higher network capacity. Although Femto cells increased the network capacity, they increased the interference to the Macro Indoor users.In order to avoid the high decrease in cell edge throughput different interference mitigation techniques were introduced like Inter-Cell Interference Coordination and Power Control techniques. In this paper, Non- Unanimous Power Inter-cell Interference Coordination (NUP-ICIC), and Non Unanimous Power Control with Constraint (NUP-C) algorithms are proposed . The schemes can achieve high spectral efficiency with an increase the cell-edge and with high power efficiency.

Deployment of relay nodes (RNs) in cellular orthogonal frequency division multiple access (OFDMA) systems provides an effective solution to increase high data rate coverage and improve cell throughput. However, a challenging issue is that additional interferences caused by RNs may substantially compromise the performance gain if no measure is taken. In this study, the authors address the problem of interference coordination in relay-aided cellular OFDMA systems, aiming at exploiting the benefits of RNs while minimising the negative effects of interferences introduced. The authors first analyse the possible interference scenarios in multi-cell systems. Based on the insights into their analysis, the authors propose resource allocation with interference coordination (RAIC) scheme for cellular OFDMA systems. RAIC selectively perform one of three resource allocation algorithms according to the offered traffic load in the system, to mitigate interferences and thus enhance system throughput. The authors conduct intensive simulation experiments based on the model with realistic broadband channel propagation conditions. Numerical results demonstrate that their proposed RAIC can effectively improve system throughput compared with the resource allocation schemes without appropriate interference coordination.

Relay is a key technique in the 3G long term evolution (LTE), it uses wireless backhaul to communicate with the donor eNodeB. Relay can be deployed to improve the cell-edge coverage and throughput. However, when relay is introduced into the network, it will also cause additional inter-cell interference for both uplink (UL) and downlink (DL). A field test is done to understand the inter-cell interference impacts of TD-LTE in-band relay. The results show that without coordination, relay may increase both UL and DL inter-cell interference to the neighbor cells, and this may impair the cell-edge user throughput of the neighbor cells. Therefore a coordination mechanism tailor made for relay is proposed, and the analyses show that it can help to reduce the inter-cell interference due to the introduction of relay.

In this paper, a joint control method for the user association and almost blank sub-frame (ABSF) based interference coordination (IC) technique in heterogeneous cellular networks is proposed. The optimization objective is simultaneously improving system throughput and guaranteeing proportionally fairness. Usually, user and base station (UE-BS) association is performed before ABSF rate determination, which is suboptimal with respect to UE- BS association. We formulate the joint optimization of UE-BS association and ABSF rate as a combinatorial optimization problem. To deal with it, we proposed an iterative method to discover the ABSF rate, the optimal association and the optimal resource blocks(RBs) allocation that can maximum long-term average throughput. Besides, as we cannot know the interference before user-association and resource allocation, we proposed a graph-based BS clustering method to estimate the interference before user-association and resource allocation. Simulation results show the efficiency of our proposed scheme.

Joint Transmission (JT) as an example of downlink coordinated multi-point (CoMP) transmission can improve the overall system performance, particularly cell average and cell-edge throughput. Many studies are related to JT in homogeneous network and based on full buffer traffic which is not a practical scenario. We propose a JT method for LTE-Advanced systems with non-full buffer traffic in both homogeneous and heterogeneous networks. System-level simulations demonstrate that the proposed JT techniques clearly outperform single cell transmission scheme in terms of cell average and cell-edge performance.

Co-channel interference is considered as one of the most important issues limiting the performance of cellular systems. In LTE-A systems, the Coordinated Multi-Point (CoMP) transmission technology was introduced to effectively manage data traffic at the transmission nodes for reducing co-channel interference. CoMP transmission is realized by exchanging coordination information via backhaul links, typically available between the transmission nodes. However, in practical networks the backhaul links may have capacity constraints hindering the use of CoMP techniques with high-rate information exchange. In scenarios where ideal backhaul link is not available, coordinated scheduling and coordinated beamforming (CS/CB) CoMP schemes can be used. However, the conventional CS/CB CoMP scheme only assumes interference coordination between the transmission nodes which significantly limits the expected performance benefits that can be additionally achieved by using traffic management techniques. In this paper, we propose a CS/CB CoMP scheme with semi-static traffic offloading. Traffic management in the proposed scheme is achieved by using the cell range expansion concept that takes into consideration a limited set of the transmission points that can be simultaneously coordinated to reduce interference. For comparison, the LTE-A time-domain enhanced inter-cell interference coordination (eICIC) scheme with conventional cell range expansion is considered.

Range expansion and inter-cell interference coordination can improve the capacity and fairness of heterogeneous networks by off-loading macrocell users to low-power nodes like picocells. In contrast to previous studies, which rely mostly on simulations, we here consider analytical models for base station and user (UE) locations in a macro network with pico-cell overlay and derive closed-form expressions for the distribution of the signal to interference plus noise ratio (SINR) and spectral efficiencies (SEs) of UEs associated with macro- and pico-cells. These results illuminate the effects on SE of (i) duration of the macro almost blank subframes (ABSs), (ii) the SINR threshold for a UE to be served by a picocell during ABSs, and (iii) the range expansion bias. They also help determine the optimum settings of these parameters.

Scheduling restriction is attracting much attention in LTE-Advanced as a technique to reduce power consumption and network overhead in interference coordinated heterogeneous networks (HetNets). Such a network with inter-cell interference coordination (ICIC) provides two radio resources with different channel quality statistics. One of the resources is protected (unprotected) from inter-cell interference (hence, called protected (non-protected) resource) and has higher (lower) average channel quality. Without scheduling restriction, the channel quality feedbacks would be doubled to reflect such quality difference of the two resources. We present a simple scheduling restriction scheme that addresses the problem without significant performance degradation. Users with relatively larger (smaller) average channel quality difference between the two resources are scheduled in the protected (non-protected) resource only, and a boundary user, determined by a proportional fair resource allocation (PFRA) under simplified static channels, is scheduled on either of the two resources or both depending on PFRA. Having most users scheduled in only one of the resources, power consumption and network overheads that would otherwise be required for the channel quality feedbacks on the other resource can be avoided. System level simulation of LTE-Advanced downlink shows that the performance degradation due to our scheduling restriction scheme is less than 2%, with the average feedback reduction of 40%.

Intercell Interference is the main issue limiting the capacity of modern OFDMA-based cellular networks. Recently, extensive research work has been focused on intercell interference coordination since it has been recognized as a key concept to achieve seamless levels of quality of service. Nevertheless, very often this problematic is addressed as a standalone issue. In this work, a novel channel state information feedback scheme is proposed aiming at improving the overall system performance when both channel state information and static interference coordination are jointly considered. By means of the proposed scheme, gains in terms of users throughput, cell edge performance and energy efficiency are achieved with respect to existing aperiodic LTE-based mechanisms without additional complexity.

The exponential growth in mobile data traffic, coupled with finite radio frequency resources, has intensified the challenges associated with efficient radio access network (RAN) planning and optimization in spectrum-constrained environments. As operators strive to meet increasing demands for high-speed connectivity and low-latency services, there is an urgent need for innovative strategies that can maximize spectral efficiency while ensuring quality of service (QoS) and user experience. This paper proposes a conceptual model for radio access planning and optimization specifically tailored to spectrum-limited settings, with a focus on dynamic resource allocation, interference management, and adaptive network configurations. The proposed model integrates multi-layered radio planning techniques, including spectrum reuse, frequency refarming, and heterogeneous network deployment, supported by real-time data analytics and artificial intelligence. The model introduces a feedback-driven architecture that continuously monitors network performance metrics—such as signal-to-interference-plus-noise ratio (SINR), throughput, and user mobility patterns—to guide adaptive reconfiguration of RAN parameters. Furthermore, it incorporates a spectrum-aware decision engine that enables efficient traffic offloading and load balancing across macro, micro, and small cells. To ensure robustness, the model accounts for regulatory constraints, spectrum licensing scenarios (licensed, unlicensed, and shared bands), and co-existence with legacy technologies. Emphasis is placed on the strategic placement of base stations, beamforming techniques, and interference coordination schemes such as enhanced Inter-Cell Interference Coordination (eICIC) and Coordinated Multipoint (CoMP). The framework also facilitates spectrum aggregation, dynamic carrier selection, and energy-efficient operations to enhance capacity without additional spectrum acquisition. This conceptual model serves as a valuable tool for mobile network operators, planners, and policymakers aiming to optimize network coverage and capacity under spectrum scarcity. It provides a scalable and technology-neutral blueprint applicable to 4G LTE, 5G NR, and emerging radio access technologies. Future work will focus on validating the model through simulations and real-world testbeds to refine its components and quantify its performance gains in diverse deployment scenarios.

In this paper, we analyze the behavior of several radio resource scheduling strategies under different power and subcarrier allocation (PSA) and inter-cell interference (ICI) coordination schemes in mobile OFDMA networks. The aim is to test the capability of these scheduling strategies to deal with quality of service (QoS) requirements both in a single-service scenario or when a mixture of services takes place. This work shows that radio resource allocation schemes managing ICI have strong impact on the scheduling policy behavior, and that traffic delay is a key parameter to track in order to provide QoS when services with different delay constraints simultaneously occur.