Antenna architectures for network MIMO

Inter-Cell Interference Coordination (ICIC) using frequency reuse schemes in Orthogonal Frequency Division Multiple Access (OFDMA) cellular networks is one of the most promising approaches to reduce the effect of interference and to improve the system performance. Fractional Frequency Reuse (FFR) schemes are efficient interference mitigation techniques that have been used to improve system performance in multirelay multi-cell OFDMA cellular networks, especially for the cell edge users. The purpose of FFR design is to deploy frequency patterns (sets) in such a way that a Mobile Station (MS) user can reduce interference from adjacent cells. The Frequency Reuse Factor (FRF) of 7/3 with frequency reuse pattern (7, 3, 1) is used to improve the system performance of FRF=1 and FRF=3. This paper proposes a new frequency pattern and deploys frequency sets with Amplify and Forward (AF) fixed relays to improve the performance of the system. Simulation results show that the proposed pattern achieves significant Inter-Cell Interference (ICI) reduction when compared to other cooperative and noncooperative schemes.

In next generation broadband wireless networks, the orthogonal frequency division multiple access (OFDMA) technique provides a flexible physical interface for mobile users (MS) to share the radio resources. Since OFDMA allows MSs in different cells to reuse the same frequency subchannels to increase network spectrum utilization, MSs at the edge of a cell suffer from severe inter-cell interference from co-channel MSs in the neighboring cells. In WiMAX and LTE networks, fractional frequency reuse (FFR) is employed to mitigate the interference for edge users, but may incur a cost in terms of a lower overall spectrum utilization. In this paper, we propose a novel frequency planning scheme to improve the signal-to-interference (SIR) ratio of edge MSs in a multi-cell OFDMA system. A cell is partitioned in a way that minimizes the interference to the edge areas while sustaining a full frequency reuse factor (FRF) for each cell. Simulation results show that our scheme substantially outperforms FFR methods in terms of SIR under the condition of full frequency reuse and high traffic load.

Multiuser Orthogonal Frequency Division Multiple Access (OFDMA) networks, such as Long Term Evolution networks, use the frequency reuse-1 model to face the tremendous increase of mobile traffic demands, and to increase network capacity. However, inter-cell interference problems are generated, and they have a negative impact on cell-edge users performance. Resource and power allocation should be managed in a manner that alleviates the negative impact of inter-cell interference on system performance. In this paper, we formulate a novel centralized multi-cell resource and power allocation problem for multiuser OFDMA networks. The objective is to maximize system throughput while guaranteeing a proportional fair rate for all the users. We decompose the joint problem into two independent problems: a resource allocation problem and a power allocation problem. We prove that each of these problems is a convex optimization problem, and that their optimal solution is also an optimal solution to the original joint problem. Lagrange duality theory and subgradient projection method are used to solve the centralized power allocation problem. We study the convergence of our centralized approach, and we find out that it reduces inter-cell interference, and increases system throughput and spectral efficiency in comparison with the frequency reuse-1 model, reuse-3 model, fractional frequency reuse, and soft frequency reuse techniques.

We propose a distributed transmission power control method based on soft fractional frequency reuse (SFR) for cellular downlink orthogonal frequency division multiple access (OFDMA). The proposed method adaptively controls the transmission power density in the protected and non-protected bands of SFR depending on the user distribution within a cell in order to maximize the geometric mean of the user throughput (in other words, log sum of user throughput). Thus, it is based on the proportional fair (PF) criteria. The proposed method assumes a decentralized approach, in which complicated inter-base station (BS) cooperation is not required. Since the optimal power allocation to the protected and non-protected bands is dependent on the resource allocation of the protected and non-protected bands to the respective users, the proposed method jointly optimizes the power allocation and resource allocation by using an iterative algorithm. Computer simulation results show the effectiveness of the proposed method compared to conventional universal frequency reuse (UFR) and non-adaptive SFR.

This paper presents a performance analysis of reuse partitioning (RUP)-based subchannelized orthogonal frequency-division multiple-access (OFDMA) uplink systems in multicell environments. The cochannel interference (CCI) statistic is calculated for OFDMA uplink systems. The derived statistic is then used to analyze the performance of subchannelized OFDMA systems based on RUP. Analysis and simulation results show that the performance of a subchannelized OFDMA system in multicell environments is noticeably dependent on the CCI, and the effect of CCI can be reduced by the RUP scheme. Finally, the results of the analysis yield the optimum RUP area for achieving the maximum system throughput.

This paper presents efficient interference-mitigation techniques, such as fractional frequency reuse (FFR) and soft frequency reuse (SFR) schemes, in multicell orthogonal frequency division multiple access networks under the composite multipath fading environment, where Rayleigh fading is superimposed over log-normal shadowing. We begin by outlining the obtained explicit expressions of area spectral efficiency in down-link transmission for both FFR and SFR schemes. The theoretical result are shown to be very accurate with their simulated counterparts using Monte Carlo simulations.

In CDMA system, co-channel interference (CCI) includes intracell multiple-access interference and intercell interference. In TD-SCDMA mobile systems, intracell MAI can be eliminated by joint detection. In this paper, one approach combined joint detector and spatial filter which can eliminate both intercell and intracell interference is proposed. Moreover, this approach can be implemented with low computational complexity. Link simulation shows that the performance of TD-SCDMA systems with this approach is better than joint detection with antenna diversity.

We propose a coordinated inter-cell resource allocation (CICRA) approach that can reuse efficiently the radio spectrum through inter-cell interference (ICI) management over a cluster of adjoining cells in some coordinated manner. In this, the entire radio spectrum is assigned to all the cells within the cell cluster. We use a set of coordinated cell-specific resource allocation sequences in order to manage ICI. The set of sequences should be designed and assigned in a coordinated manner over all cells within the cell cluster, so that ICI from nearer interfering cells could be preferentially avoided and the average ICI level according to the loading factor (LF) could be monotonic and minimally incremented. By the virtue of such ICI-managing mechanism, the CICRA approach can govern efficiently the average ICI level only through individual resource allocation without intervention among cells. In this paper, we would apply the CICRA approach to orthogonal frequency division multiple access (OFDMA) cellular systems. A system-level simulator for an OFDMA cellular system covering surrounding cells up to 3rdtier has been implemented. Simulation results show that the proposed CICRA approach can improve noticeably the system performance in terms of both the outage probability and spectral efficiency as compared with the classical UFR scheme and the soft frequency reuse (SFR) scheme over the entire LF range.

In this paper, the parameters estimation for the interference rejection combining (IRC) technique with the inter-cell interference (ICI) and narrowband interference (NBI) in single-carrier frequency-division multiple access (SC-FDMA) systems is considered. Due to the characteristics of the interferences in uplink SC-FDMA systems is quite different from that in downlink orthogonal frequency-division multiple access (OFDMA) systems, the traditional autocorrelation matrix estimation and channel estimation schemes, which refine the estimation in both the time and frequency domain, can not be employed in SC-FDMA systems directly. Therefore, a simple but effective autocorrelation matrix estimation scheme is suggested in this paper, besides, an EVD-based channel estimation which can filter out the energy of the interference plus noise with low complexity is proposed. Simulation results display the effectiveness of the autocorrelation matrix estimation and the advantage of the EVD-based channel estimation with the ICI and NBI in SC-FDMA systems.

Orthogonal Frequency-Division Multiple Access (OFDMA) systems have attracted considerable attention through technologies such as 3GPP Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX). OFDMA is a flexible multiple-access technique that can accommodate many users with widely varying applications, data rates, and Quality of Service (QoS) requirements. OFDMA has the advantages of handling lower data rates and bursty traffic at a reduced power compared to single-user OFDM or its Time Division Multiple Access (TDMA) or Carrier Sense Multiple Access (CSMA) counterparts. In our work, we propose a Particle Swarm Optimization based resource allocation and scheduling scheme (PSORAS) with improved quality of service for OFDMA Systems. Simulation results indicate a clear reduction in delay compared to the Frequency Division Multiple Access (FDMA) scheme for resource allocation, at almost the same throughput and fairness. This makes our scheme absolutely suitable for handling real time traffic such real time video-on demand.

Intercell interference (ICI) is one of the major factors that limit the performance of wireless cellular network systems. Soft frequency reuse (SFR) as well as its modified algorithms such as Soft fractional frequency reuse (Soft FFR) and Distributed fractional frequency reuse (Distributed FFR) have been introduced as an effective way to optimize spectrum and control the ICI. However, the comparison between these algorithms has not fully been presented by the researchers proposing the models. This paper presents a comparison of the performance of well-known frequency reuse algorithms in term of system throughput, average packet loss ratio and average packet delay. The simulation results indicate that the simplest scheme, i.e. Soft FR, archives the highest system performance comparing to Soft FFR and Distributed FFR. Hence, it is noticed that one of the effective methods which optimize frequency reuse is to reduce the algorithm complexity.

The severe interference in full-duplex (FD) cellular network largely degrade the system performance, especially for cell edge users. In this paper, hybrid full/half duplex cellular network which is composed of a mixture of FD and half duplex (HD) base-stations (BSs) is focused. In order to relieve the received inter-cell interference, frequency reuse (FR) is applied. The adopted FR schemes include traditional full FR and two kinds of fractional FR (FFR) named Strict FFR (StFFR) and Soft FFR (SoFFR). Stochastic geometry is adopted to evaluate the system performance. Tractable results of the ergodic rate and coverage probability for different FR schemes are obtained. Through the numerical results, we can observe that full FR and StFFR schemes can improve the user coverage probability at the expense of system spectrum efficiency (SE). SoFFR can improve both the coverage probability and the system SE. The numerical results also show that if the residual Self-interference is not very strong, operating all the BSs in FD mode can achieve the best performance, otherwise, it is better to operate all the BSs in HD mode.

This paper investigates an adaptive frequency and transmission power partitioning method between cell-interior and cell-edge users in the downlink orthogonal frequency division multiple access (OFDMA) with fractional frequency reuse (FFR). In the conventional FFR method, the frequency and transmission power partitioning between cell-interior and cell-edge users is fixed and this results in limited system-level performance in terms of the average and cell-edge user throughput. This paper presents enhancements to a previously proposed partitioning algorithm to improve the system-level performance. The computer simulation results show that the enhanced method increases both the average and cell-edge user throughput compared to the conventional FFR and the previous method.

For the upcoming 4G systems, network multiple-input multiple-output (MIMO) and inter-cell interference coordination (ICIC) are two of key techniques adopted in 4G systems to mitigate the serious inter-cell interference (ICI) and improve coverage and cell-edge throughput. Network MIMO is referred to as coordinated multi-point (CoMP) in LTE-A. In this paper, we propose a simulation platform to analyze the handover issue for downlink CoMP transmissions in LTE-A cellular systems. Among the variety of ICIC strategies, we apply the widely adopted soft frequency reuse (SFR) and the fractional frequency reuse (FFR) schemes. Both schemes are based on the idea of applying a frequency reuse factor of one in cell-center areas, and a higher reuse factor in cell-edge areas. Therefore, the ICI is reduced at the expense of the available frequency resources for each cell.

The project to define Long Term Evolution (LTE) of UMTS cellular technology started in year 2004 is well established to the world. The subsequent evolve of LTE-Advanced however targets for enhancement in average spectrum efficiency and cell-edge user throughput. The limiting factor of the system performance at cell-edge is inter-cell interference (ICI). The challenge that is discussed in this paper focuses on ensuring the overall satisfaction mainly cell-edge system performance through the analysis on Fractional Frequency Reuse (FFR) and hybrid Macro system which involves small cell technology — Femtocell technology. This paper discussed the three frequency allocation schemes. The schemes include without the application of Femtocell, with randomly application of Femtocell and with preplanned Femtocell scheme. The FFR mechanism divides the cell into two regions (inner and outer). The inner radius and inner region resource is determined base on overall average throughput and overall user satisfaction.