Hung-Bin Chang

Optimal Downlink and Uplink Fractional Frequency Reuse in Cellular Wireless Networks

Densely deployed cellular wireless networks, which employ small cell technology, are being widely implemented. Mitigating the impact of inter- and intracell signal interferences induced by the operations of these networks is a challenging yet essential task. In this paper, we consider adaptive rate scheduling for a transmitting node, regardless of whether it is a base station (BS) or a mobile user. We aim to maximize the systems throughput through the employment of fractional frequency reuse (FFR) schemes. Each BS employs either an omnidirectional or a directional antenna system. We derive the optimal configuration of the FFR scheme and evaluate the ensuing systems performance behavior under absolute and proportional fairness requirements. To maximize the attained throughput by mobiles, we determine the best method to use to classify cell users into interior and edge mobiles. The bandwidth levels allocated for serving interior and edge mobiles are optimized. We derive approximate closed-form mathematical expressions for calculating the probability distributions of the interference signal levels measured at the destined receivers. We account for the impact of the classification process on intercell interference power levels. Under an absolute fairness requirement, we show that optimally configured FFR schemes lead to much enhanced performance. We show that the optimally configured directional-FFR schemes increase the throughput capacity by a factor of about 60% relative to that obtained by using optimal omnidirectional-FFR schemes. The analyses and simulation results presented in this paper serve to characterize the performance behavior attainable by using such small cell deployed cellular wireless network systems when employing the underlying configurations.

Optimal relay deployment for multihop multicast scheduling in cellular wireless networks

Efficient multicasting of critical messages is of essential importance in public safety and commercial multimedia cellular networks. We study the effectiveness of using relay station nodes to enhance the spectral efficiency of multicast distribution under full coverage in a mobile wireless networks. Coloring oriented adaptive rate scheduling algorithms are considered, including such that temporally employ TDMA schedules with reuse levels of 1, 3, 4 and 7 over a cellular arrangement. These schemes are used to regulate multicast transmissions executed by base station and (when employed) relay station nodes. We examine the utility of using, in each cell, a single layer of placed three and six relay station (RS) nodes. We examine the optimal locations at which such RS nodes should be placed under symmetric deployment in each cell. Base stations coordinate the scheduling of base station (BS) and RS nodal transmissions by employing two-phase reuse schemes. We show that when the inter-site distance (ISD), identifying the range between BSs, is lower than certain threshold levels, it is most effective to employ a reuse-3 scheduling scheme that is based on direct (1-hop) multicast transmissions by base station (BS) nodes to associated mobile station (MS) clients. In turn, under longer ISD ranges (e.g., as employed in less dense cellular layouts), the spectral efficiency of the system can be significantly enhanced by using a joint scheduling and routing scheme that makes use of a relay aided two-hop coverage operation. We also show that it is then more effective to deploy in each cell 3 rather than 6 RS nodes.

Robust multicasting in micro base station aided wireless cellular networks

Efficient multicasting of critical messages is of essential importance in public safety and commercial multimedia cellular networks. We study the effectiveness of using the aid of micro base stations (mBSs) to enhance the spectral efficiency of multicast distribution in a wireless cellular network. Coloring oriented adaptive rate scheduling algorithms are considered, including such that temporally employ TDMA schedules with reuse levels of 1, 3, 4 and 7 over a cellular arrangement. These schemes are used to regulate multicast transmissions executed by macro base stations (MBSs) and to jointly schedule macro and micro base stations (mBSs). We examine the utility of using the aid of mBSs in potentially improving multicasting performance. We also examine a cellular system that has experienced the failure of some MBSs, and identify the adaptive rate coloring-based scheduling mechanism that should be used when a failover operation is pursued. For both pre-failure and post-failure scenarios, we show the schemes with that are aided by mBSs to achieve higher system throughput levels. We also show that when the inter site distance (ISD), identifying the range between MBSs, is lower than a threshold level, reuse-3 scheduling schemes (with or without employing mBSs) yield better performance than reuse-1 schemes. In turn, under longer ISD ranges (e.g., as employed in less dense cellular layouts), the spectral efficiency of the system can be significantly enhanced by using a joint scheduling and routing scheme that makes use of reuse-1 scheme with the aid of mBSs.

Micro Base Station Aided Failover for Multicast Scheduling in Wireless Cellular Networks

We consider scheduling mechanisms for downlink multicasting of critical messages across cellular wireless systems. We study the robustness of such schemes following the failure of a macro base station (MBS) node. We determine whether the additional deployment of micro base station (mBS) nodes can enhance the systems performance. We assume MBS and mBS nodes to coordinate their multicast transmissions by using TDMA or FDMA (rather than an MBSFN-based) adaptive rate and power scheduling algorithms. Neighboring mBS and MBS nodes coordinate their operations to optimally configure their transmission schedules and spectral and/or temporal resources and transmit code rate and power levels. We show that, under low intersite distance (ISD) values, each identifying the distance between neighboring MBS nodes, the use of deployed mBS nodes does not enhance the systems attainable multicast spectral efficiency. Under intermediate ISD levels, the deployment of a backup mBS node that is located near the MBS node limits the post-failure degradation of throughput capacity rate to less than 10%. In turn, under longer ISD range levels, the combined use of a backup mBS and of neighboring mBS nodes, which adjust their code rate levels to reach mobiles located in the failed cell, leads to significant performance improvement.

Optimal fair downlink fractional frequency reuse for cellular wireless networks

We consider adaptive rate scheduling mechanisms used by densely deployed base station (BS) nodes in cellular wireless networks. These BS nodes share downlink channels under the employment of omnidirectional and directional antennas. We study the throughput capacity rates achieved under reuse-k scheduling schemes, for k = 1, 3, with and without the incorporation of fractional frequency reuse (FFR) assignments. We consider an absolute fairness requirement, aiming to maximize the minimum level of the throughput rate realized per mobile. For this purpose, under the inclusion of FFR schemes, we propose an optimal classification for interior and exterior mobiles coupled with optimal bandwidth allocation to each class of mobiles. When omnidirectional antenna beams are employed, we show these schemes to yield a significantly enhanced performance when compared to non-FFR based operations. In turn, when directional antenna beams are used, we show that the FFR scheme does not lead to much performance enhancement.

Multihop relay-aided multicast scheduling for cellular wireless networks

Efficient multicasting of critical messages is of essential importance in public safety and commercial multimedia cellular networks. We study the effectiveness of using relay stations to enhance the spectral efficiency of multicast distribution in a mobile wireless networks. Coloring oriented adaptive rate scheduling algorithms are considered, including such that temporally employ TDMA schedules with reuse levels of 1, 3, 4 and 7 over a cellular arrangement. These schemes are used to regulate multicast transmissions executed by base station and (when employed) relay station nodes. We examine the utility of using in each cell single and double levels of placed relay stations. When the latter are employed, 2-hop and 3-hop relaying paths are considered. We also examine a cellular system that has experienced the failure of base stations, and identify the adaptive rate coloring-based scheduling mechanism that should be used when a failover operation is pursued. For both pre-failure and post-failure scenarios, we show that when the inter site distance (ISD), identifying the range between macro base stations, is lower than certain threshold levels, it is most effective to employ schedules that are based on direct (1-hop) multicast transmissions by base stations (BSs) to associated mobile station (MS) clients. In turn, under longer ISD ranges (e.g., as employed in less dense cellular layouts), the spectral efficiency of the system can be significantly enhanced by using a joint scheduling and routing scheme that makes use of multihop relaying.

Impact of Placement of Small Cells on Downlink Performance for Cellular Wireless Networks

In this paper, we consider a cellular system whose downlink transmissions are managed by the use of a heterogeneous layout of macro and micro base station nodes. Our objective is to determine the impact of the addition of small cells on the throughput capacity of the downlink system in each individual cell. For this purpose, we first determine the locations in each cell at which a mobile would monitor the lowest SINR levels, which is important in evaluating the systems scope level of global coverage. The configuration of modulation/coding sets and related code rate levels are adjusted accordingly. Assuming base station nodes to coordinate their downlink transmissions by using coloring oriented schedules, we prove that mobiles record the lowest SINR levels when they are located at the outer vertices of each cells region. We further prove that in fact, by using properly coordinated scheduling mechanisms, the inclusion of small cells leads to also enhanced throughput rate in each individual cell.

Scalable Video Multicast for Multi-Cell Cellular Wireless Networks

—We consider adaptive-rate multicasting of video streams compressed by using Scalable Video Coding (SVC) over cellular wireless networks. Base station nodes coordinate the scheduling of their downlink transmissions to mitigate intercell interference; as well as, at times, to direct the multicast transmission of the same video streams to a group of clients, as implemented in a Multicast-Broadcast Single-Frequency Network (MBSFN) of LTE system operation. To enhance performance, we study the optimal configuration of a Fractional Frequency Reuse (FFR) scheme. We classify cell users into two groups, based on their experienced SINR (signal-tointerference-plus-noise ratio) levels. Lower-SINR group users will be offered streams at a lower video quality level, while higher-SINR group members will be provided streams at a higher video quality level. For this purpose, through the proper joint setting of the channel encoding rate, video encoding rate and the scheduling schemes, we calculate the minimum bandwidth required per stream. We demonstrate the optimal design of such a system by considering a utility function that includes a metric expressing the users willing-to-pay when the reception is of a sufficient high video-quality. We show that, under high cell coverage requirement, the proposed optimally configured FFR scheduling schemes offer a significantly enhanced performance behavior. We also show that such an MBSFN scheme that involves coordinated cooperation among 3 cells, combined with the optimal FFR scheme, outperforms a system that employs a regular MBSFN operation that involves cooperative transmissions among 7 and 19 cells.

Performance effectiveness of using micro base stations for resilient LTE multicast networking

Efficient downlink multicasting of critical messages aiming at global coverage is of essential importance in public safety and multimedia cellular networks. In this paper, we first determine the extent of throughput rate degradation incurred in a cellular network system under the failure of a macro base station (MBS) node. Our objective is to determine whether the placement of micro BS (mBS) nodes can enhance the performance of such a failed system configuration. We assume base station nodes to coordinate their multicast packet transmission operations by using adaptive rate coloring oriented scheduling algorithms. In particular, TDMA schedules with reuse levels of 1, 3, 4 or 7 are considered. Under the failure of an MBS node, neighboring macro and/or micro base station nodes coordinate their operations to re-regulate multicast transmissions through re-setting of the transmission schedules and code rates. We show that the deployment of mBS nodes to supplement the use of MBS nodes is especially effective for multicast packet distributions when the macro base station layout is sparser.

Joint Adaptive Rate and Scheduling for Unicasting Video Streams in Cellular Wireless Networks

We develop and study adaptive rate scheduling mechanisms over cellular wireless networks, as used for the unicast provision of video streams to client mobiles at variable quality of experience (QoE) levels. Under service type I, mobile users receive video streams at a QoE level that is not lower than a specified value. In addition, mobile users that experience sufficiently high communications channel quality levels may be provided video streams at higher video quality levels. Under service type II, mobile clients receive their video streams at QoE levels that are based on their recorded signal to noise and interference levels. Resource allocations among mobiles are, however, subjected to absolute and proportional fairness objectives. We employ a proxy video manager and resource controller that is located at (or associated with) the base station node. The manager intercepts a channel quality indicator message reported by a mobile client, using it to determine the QoE level at which a requested video stream will be provided. It then selects the proper source and channel encoding schemes to be used for producing and transmitting a compressed version of the stream. To regulate inter-cell signal interference, we examine the joint employment of a number of different spectral-reuse and fractional frequency reuse (FFR) scheduling schemes. To illustrate the use of our models to configure system parameters, we consider a performance metric that incorporates a will-to-pay utility function. We develop analytical techniques for the modeling, analyzing, and designing of such systems. We confirm the precision of these models through the conduct of simulation analyses. Also, we show that, under certain system configurations, FFR-based schemes can lead to substantial enhancement of the systems performance behavior.