A method for limiting inter-cell interference and balancing load in a wireless communication system, the method comprising: one larger cell and one or more smaller cells providing overlapping terminal coverage and capacity; the larger cell informing the one or more smaller cells of transmission resources in which the larger cell restricts its own transmission; the one or more smaller cells using the restricted transmission resources for their own transmission; one smaller cell communicating with another cell in the wireless communication system to provide use information about the smaller cell's use of the restricted transmission resources; and the smaller cell and/or the other cell carrying out load balancing in response to the use information.

A method for limiting inter-cell interference and load balancing and a wireless communication system and base station

Full length article: LTE-Advanced and the evolution to Beyond 4G (B4G) systems

The term “ranging” is often used to indicate the operations that make it possible to estimate the distance between two nodes by processing some signals generated and/or received by the nodes. In wireless systems, a very popular ranging method makes use of the radio signal strength (RSS), which is a measure of the received radio signal power. However, RSS-based ranging is considered very inaccurate, particularly in indoor environments, mainly because of the randomness of the received signal power. In this tutorial paper, we provide an in-depth analysis of the main factors that affect the variability of the received signal power and the accuracy of the RSS measurements. Starting from a survey of the most common and widely accepted models for the radio signal propagation and the RSS-based ranging, we then focus our attention on some technological and procedural pitfalls that are often overlooked, but may significantly affect the accuracy of the RSS-based ranging, and we suggest possible techniques to alleviate such problems. The theoretical argumentation is backed up by a set of empirical results in different scenarios. We conclude this paper by providing some best-practice recommendations for proper RSS-based ranging estimation in wireless networks and discussing new approaches and open research challenges.

Best Practice in RSS Measurements and Ranging

To encourage data offloading in heterogeneous networks, range expansion techniques have been introduced in LTE-Advanced system. By adding a positive bias in cell selection process, more users can select picocells as their serving cells even the picocell is not of the strongest signal. Also, to protect offloaded users from severe macrocell interference, a specific subframe called almost blank subframe (ABS) is introduced. Since macrocell is kept silent during ABSs, the offloaded users can be allocated without strong macrocell interference within ABSs. It is noted that the offloaded user's average data rate highly depends on the amount of ABSs rather than the bias value because the scheduling opportunities of offloaded users are limited within ABSs. And from the user's point of view, the cell which is expected to give high data rate should be selected as a serving cell. In this paper, we propose a cell selection scheme based on expected user data rate which is a function of the ABS ratio. Simulation results show that the performance of our proposed cell selection scheme can improve average user rate and increase the number of offloaded users as the ABS ratio increases.

Cell selection for range expansion with almost blank subframe in heterogeneous networks

Enhanced Inter-cell Interference Co-ordination (eICIC) is a time-domain multiplexing technique for improving the performance of legacy co-channel Heterogeneous Networks (HetNets). eICIC offers several benefits, including a more equitable distribution of user traffic across the macro and embedded pico cells (i.e., load balancing), in turn leading to better pico cell utilizations and better edge user throughputs. eICIC uses two mechanisms to achieve load balancing: (i) a cell selection bias to increase the pico coverage area, enabling the pico to attract more users, and (ii) macro muting ("Almost Blank Sub-frame", ABS) to improve SINRs of range extended pico users. Network load in the cellular system varies continuously as a result of user mobility and traffic dynamics (the varying amount of data pending for a user - arising from packet arrivals and eventual departures). Previous work did not consider dynamically changing network conditions in HetNets. Hence, they studied the benefits of eICIC over legacy HetNets arising from static optimization of eICIC parameters. Our approach is dynamic, and further improves performance by keeping the HetNet continuously optimized for improved user experience, by adapting the ABS in response to dynamic variations in network load. We present several analytical formulations, which allow for simple optimizations and an intuitive understanding of the desired system response to load variation. Exhaustive system simulations illustrate the performance gains along different dimensions, such as spectral efficiency, fairness, mean file transfer times, number of file transmissions, number of file drops, and mean queue lengths. Furthermore, we study the impact of different mobility scenarios, traffic mixes, and adaptation rate. We also provide a brief discussion of practical considerations in implementing Dynamic eICIC.

Dynamic eICIC — A Proactive Strategy for Improving Spectral Efficiencies of Heterogeneous LTE Cellular Networks by Leveraging User Mobility and Traffic Dynamics

Heterogeneous networks (HetNets) are expected to be one of the major performance enhancement enablers of LTE-Advanced. Due to significantly challenging interference scenarios, enhanced inter-cell interference coordination (eICIC) based on almost blank subframes (ABS) is the key technology enabler that makes HetNets a reality. The key factor determining the gain of ABS-based eICIC is the configured number of ABS which depends closely on the number of UEs requesting protection from ABS. In this paper, we study the optimal amount of ABS for synchronous ABS configuration by formulating this optimization as a network-wide utility maximization problem. We firstly propose a distributed method to determine victim UEs protected by ABS for any given amount of ABS via dynamic programming, and then find the optimal amount of ABS by evaluating the overall system utility. A remarkable feature of the proposed solution is that only limited information exchange via backhaul is required and the optimal amount of ABS could be individually derived at each eNB. Extensive simulations demonstrate that our solution can not only improve the overall system throughput significantly but also provide better network-wide fairness.

Optimized time-domain resource partitioning for enhanced inter-cell interference coordination in heterogeneous networks

Pico cell has been brought to cellular networks as a new technology to deliver cost-effective coverage and capacity to hard-to-reach places, and also increase capacity by cell splitting in hotspots with very dense phone usage. However, according to existing strongest receiving signal association method, pico cells with the extremely low transmitting power are significantly limited in the presence of macro coverage. Thus, the new introduced pico frequency resource will not be fully exploited in this unbalanced user distributions among macro and pico cells. In this paper, by jointly considering the long term channel condition and load balance in this macro-pico coexisted heterogeneous network, we formulate the cell selection problem into a network-wide proportional fairness optimization. Both optimal solution (by dynamic programming) and cost efficient algorithm (greedy heuristics) are proposed. In 3GPP LTE-A heterogeneous network scenario, the system-level performance evaluation shows that, compared with the conventional strongest signal cell selection scheme, the proposed optimized fairness cell selection methods could achieve significant performance gains especially for the cell edge users.

Optimized Fairness Cell Selection for 3GPP LTE-A Macro-Pico HetNets

Recently, there has been an upsurge of interest in multi-hop relay in both academia and industry. By breaking a long distance low quality link into two or more high quality segments, multi-hop relay is introduced to enable traffic/signaling forwarding between the base station and mobile user. Coverage is effectively extended to heavily shadowed areas in the cell or other distant areas beyond cell range by multi-hop relay. Meanwhile, it also provides throughput enhancement, especially at the cell edge. This paper first reviews the key technical advances with multi-hop relay in cellular networks. Then, novel technical solutions and algorithms for multi-hop relay are introduced and analyzed, including the separation of control and data, effective signal-to-interference-plus-noise ratio (SINR)-based routing algorithms, and cooperative relay schemes. Through extensive system-level and link-level simulations, we present improvements in both capacity and coverage in multi-hop relay networks compared to the legacy cellular network.

Multi-hop relay for next-generation wireless access networks

The present application describes embodiments of methods and apparatuses for controlling communications within a first cell that is overlapped by a second cell. One embodiment of the method includes receiving a signal at the second cell indicating a number of devices selected to communicate with the first cell and identifying a set of subframes during which communications are permitted to take place within the first cell based on the number of devices selected to communicate with the first cell. This embodiment of the method also includes delivering an indication of the set of subframes to the first cell.

Method and apparatus for allocating almost blank subframes

Heterogeneous deployment is a promising solution to enhance both system capacity and coverage, where the planned macro cell is overlaid with pico cells. However, higher transmit power of macro eNB (MeNB) results in small coverage for pico cell, which causes insufficient offloading from macro cell to pico cell and inefficient cell splitting gain exploration. Cell range expansion (CRE) is one of alternative cell associations to enhance offloading, but would bring severe interference on the uplink reception of macro cell. Hence, the use of enhanced inter-cell interference coordination (eICIC) techniques is required to realize the promised performance of macro user equipments (MUEs). In this paper, an adaptive uplink power control scheme is proposed for heterogeneous network (HetNet) with CRE, wherein the uplink power control parameters of pico cells could be dynamically optimized based on admissible interference level of macro cell. In addition, the proposed scheme manages to improve the performance of pico UEs (PUEs) on condition that the Quality of Service (QoS) of MUEs can be well guaranteed. Numerical simulation results verify the validity of the proposed scheme.

Dongyao Wang

Papers

Optimized time-domain resource partitioning for enhanced inter-cell interference coordination in heterogeneous networks

Optimized Fairness Cell Selection for 3GPP LTE-A Macro-Pico HetNets

Multi-hop relay for next-generation wireless access networks

Method and apparatus for allocating almost blank subframes

Uplink power control and interference coordination for heterogeneous network