Multihop Cellular Networks Research Articles

Cluster-Based Design for Two-hop Cellular Networks

Optimal resource allocation with an objective of maximizing the system capacity is an NP-hard problem in multihop cellular networks. Hence, different heuristic algorithms have been developed over the years that would improve the network system capacity. In this paper, a novel cluster-based architecture is proposed for a two-hop cellular network whereby the transmission distance between any communicating pair is restricted to half the cell radius. In this design, a given radio resource is used by two simultaneously communicating pairs in every hexagonal cell, but for only half the time slot period. The characteristic feature of this cluster-based design is that it enables a frequency reuse ratio of one. The proposed hierarchical system is analyzed and tested under realistic propagation conditions including lognormal shadowing. It has been observed that the system capacity of a cluster-based design is 2.5 times that obtained from the single-hop cellular system with no relaying. In addition, the cluster-based design achieves higher capacity compared to state-of-the-art two-hop algorithms. This is an important finding since the hierarchical cluster-based approach has fewer degrees of freedom in the selection of the routing path for the end-to-end connection. Practical routing algorithms should be able to benefit from this.

Asymmetric FCA for Downlink and Uplink Transmission in Clustered Multihop Cellular Network

A clustered multihop cellular network (CMCN) with virtual cells has been proposed to achieve the characteristics of macrocell/microcell hierarchically overlaid architecture by applying clustering techniques. As a complement to the traditional cellular networks, CMCN is able to incorporate the flexibility of ad hoc networks by allowing multihop transmission. In this paper, we first propose to use dedicated information ports (DIPs) as clusterheads for CMCN; then we analyze the performance of fixed channel assignment (FCA) for downlink transmission in CMCN. Two multi-dimensional Markov chain models are developed to study the call blocking probability. Due to the nature of multihop transmission in CMCN, channel assignment for uplink and downlink transmission is different and unbalanced. We then propose an asymmetric FCA (AFCA) for uplink and downlink transmission in CMCN. By making use of the proposed AFCA for uplink and downlink transmission, we can reduce the call blocking probability significantly as compared with the FCA for traditional single-hop cellular networks. The salient contribution is that the proposed CMCN with AFCA scheme can increase the spectrum efficiency and the system capacity by introducing the structure of CMCN with DIPs for virtual microcells.

Application of IEEE 802.16 Mesh Networks as the Backhaul of Multihop Cellular Networks

Cellular networks have been widely used to support many new audio-and video-based multimedia applications. The demand for higher data rate and diverse services has driven the research on multihop cellular networks (MCNs). With its ad hoc network features, an MCN can offer many additional advantages, such as increased network throughput, scalability and coverage. However, providing ad hoc capability to MCNs is challenging as it may require proper wireless interfaces. In this article, the architecture of IEEE 802.16 network interface to provide ad hoc capability for MCNs is investigated, with its focus on the IEEE 802.16 mesh networking and scheduling. Several distributed routing algorithms based on network entry mechanism are studied and compared with a centralized routing algorithm. It is observed from the simulation results that 802.16 mesh networks have limitations on providing sufficient bandwidth for the traffic from the cellular base stations when a cellular network size is relatively large.

Multihop Cellular Networks: Potential Gains, Research Challenges, and a Resource Allocation Framework

Recently, there has been increasing interest in integrating multihop relaying functionalities into cellular wireless networks. Multihop cellular networks can potentially enhance coverage, data rates, QoS performance in terms of call blocking probability, bit error rate, as well as QoS fairness for different users. However, in-depth investigations and careful system designs are required to exploit these potential advantages. Specifically, routing and resource allocation algorithms should be designed such that the maximum performance gain can be achieved. A number of different architectures, protocols, and analytical models for MCNs have been proposed in the literature where different system aspects were investigated. This article aims to present an overview of existing work in this area, pointing out key research issues and their possible solutions. Also, we present a resource allocation framework for out-of- band relaying. The throughput enhancement due to the proposed framework is demonstrated through numerical results.

Nested Network Mobility on the Multihop Cellular Network

The multihop cellular network architecture has been actively studied due to its capability to significantly increase cellular system capacity and coverage, and at the same time greatly reduce the transmission range of mobile nodes. The majority of the literature on MCN, however, is based on discussions from the physical or link layer point of view. In this article we look at the logical MCN architecture from the IP layer aspect. We believe that this aspect is critical to general deployment of Internet applications on the MCN because IP is the dominant supporting protocol for such applications. We introduce a new architecture based on the integration of nested network mobility (nested NEMO), which is a pure IP layer architecture, and MCN. We name the resulting architecture nested NEMO on MCN. We illustrate how nested NEMO on MCN operates and how it realizes the advantages provided by MCN on the IP layer. We also unveil a potential problem specific to the nested NEMO on MCN architecture: recursive IP fragmentation. A simple technique to overcome this problem is proposed.

Implementation Issues for OFDM-Based Multihop Cellular Networks

In this article we present various issues that need careful design for the successful implementation of OFDMA-based multihop cellular networks which need incorporation of relay terminals. The first issue we present is synchronization. We show that it is not a problematic issue for infrastructure-based relaying, where the relay is deployed by a system operator at strategic points in the cell. Second, we focus on the advantage of adaptive relaying and provide a frame structure to enable adaptive relaying in a cellular network operating according to the IEEE 802.16e standard. The third issue we present is related to hardware implementation aspects. Hardware performance and resource usage analysis will show that cooperative diversity schemes increase hardware resource usage and power/energy consumption at mobile terminals. The last issue we present is within the context of link layer ARQ, where we propose a novel retransmission method, named local retransmission-ARQ (LR-ARQ), which is designed to take advantage of the multihop nature of the cellular network. Practically, we show that LR-ARQ improves performance with respect to its single-hop counterpart in terms of cell latency, goodput, and throughput.

A dynamic channel assignment scheme for clustered multihop cellular networks

AbstractWhereas cellular systems have traditionally adopted single‐hop transmissions between the mobile station (MS) and the base station (BS), researchers expect multihop transmission to be utilised in the future. Cellular systems present several challenges, such as channel assignment, which are exacerbated by multimedia service traffic and an increasing number of subscribers. Recently, a clustered multihop cellular network (cMCN) architecture that complements traditional cellular systems has been proposed and studied using fixed channel assignment (FCA). However, the performance of FCA is limited when the traffic pattern varies in a service area. This paper proposes the use of dedicated information ports (DIPs) as clusterheads in cMCN, followed by a multihop dynamic channel assignment (mDCA) scheme. The mDCA works by assigning channels based on information about interference in surrounding cells. Two different channel searching strategies are developed and evaluated. Through computer simulation, we show that the proposed mDCA is able to achieve a significantly improved capacity which is maintained when the number of system channels is increased. Finally, issues regarding the implementation of the mDCA and future work on this topic are discussed. Copyright © 2007 John Wiley & Sons, Ltd.

A Relay-Assisted Handover Technique with Network Coding over Multihop Cellular Networks

A relay-assisted handover technique exploiting network coding for multihop cellular networks is described. In the scheme, each MS (mobile station) in the outer region receives data related to the home cell from the home BS (base station) as well as a coded version of data related to a neighboring BS from a relay node located in the cell boundary via the use of network coding. Thus, MSs can achieve more reliable macro diversity with the assistance of the relay-based handover technique. In a simulation, it is demonstrated that this technique is very effective in maintaining QoS (quality of service) in terms of outage probability over a multi-cell environment

Coverage Extension of WiMax Using Multihop in a Low User Density Environment

The usage of multihop transmission en- ables a cost efficient extension of the coverage of a base station (BS) especially in low user density environment. In this paper, a network consisting of BSs and fixed subscriber stations (SSs) is consid- ered in which the SSs are capable to act as relay stations (RSs). SSs connected to a BS forward the traffic to SSs at the cell border not having a direct link to a BS. The IEEE 802.16 (WiMax) standard defines a mesh mode enabling multihop transmission and communication between SSs. In this paper, the connectivity of a cellular multihop network based on IEEE 802.16 is analysed. The maximum number of hops of a connection is limited to two. Even with a low density of SSs, the cell size can be increased. Increasing cell radius leads to a higher fraction of multihop connections and a higher usage of robust modulation and coding schemes (MCS) which causes a decreasing cell throughput.

Integrated Radio Resource Allocation for Multihop Cellular Networks With Fixed Relay Stations

Recently, the notion that a logical next step towards future mobile radio networks is to introduce multihop relaying into cellular networks, has gained wide acceptance. Nevertheless, due to the inherent drawbacks of multihop relaying, e.g., the requirement for extra radio resources for relaying hops, and the sensitivity to the quality of relaying routes, multihop cellular networks (MCNs) require a well-designed radio resource allocation strategy in order to secure performance gains. In this paper, the optimal radio resource allocation problem in MCNs, with the objective of throughput maximization, is formulated mathematically and proven to be NP-hard. Considering the prohibitive complexity of finding the optimal solution for such an NP-hard problem, we propose an efficient heuristic algorithm, named integrated radio resource allocation (IRRA), to find suboptimal solutions. The IRRA is featured as a low-complexity algorithm that involves not only base station (BS) resource scheduling, but also routing and relay station (RS) load balancing. Specifically, a load-based scheme is developed for routing. A mode-aware BS resource-scheduling scheme is proposed for handling links in different transmission modes, i.e., direct or multihop. Moreover, a priority-based RS load balancing approach is presented for the prevention of the overloading of RSs. Within the framework of the IRRA, the above three functions operate periodically with coordinated interactions. To prove the effectiveness of the proposed IRRA algorithm, a case study was carried out based on enhanced uplink UMTS terrestrial radio access/frequency-division duplex with fixed RSs. The IRRA is evaluated through system level simulations, and compared with two other cases: 1) nonrelaying and 2) relaying with a benchmark approach. The results show that the proposed algorithm can ensure significant gains in terms of cell throughput

MuPAC: A new multi-power architecture for capacity enhancement in cellular networks

We have considered the problem of providing greater throughput in cellular networks. We propose a novel packet data cellular architecture, the Multi-Power Architecture for Cellular networks (MuPAC), based on multi-hop relaying with multiple channels. MuPAC has the unique capability of providing a coarse grained frequency reuse factor that contributes to its enhanced throughput. MuPAC utilizes multi-hop wireless relaying in the presence of the infrastructure nodes such as base station (BS) in order to provide a very high network capacity. Multiple data channels each of which is designated to operate at a different transmission power are used in order to provide a coarse grained frequency reuse factor. MuPAC also includes solutions to problems faced in multi-hop networks: performance degradation at high mobility, partitions, etc. MuPAC provides increased throughput compared to existing schemes such as the current day cellular systems which can be classified as single-hop cellular network (SCN), and the recently proposed multi-hop cellular network (MCN). We provide an analytical treatment of MuPAC to support its superiority over SCN and MCN. We also show using extensive simulations, that MuPAC performs well over a range of node densities, under high mobility, varying traffic generation characteristics and also improves fairness across a cell.

QoS and energy trade off in distributed energy-limited mesh/relay networks: a queuing analysis

In a distributed multihop mesh/relay network (e.g., wireless ad hoc/sensor network, cellular multihop network), each node acts as a relay node to forward data packets from other nodes. These nodes are often energy-limited and also have limited buffer space. Therefore, efficient power saving mechanisms (e.g., sleeping mechanisms) are required so that the lifetime of these nodes can be extended while at the same time the quality of service (QoS) requirements (e.g., packet delay and packet loss rate) for the relayed packets can be satisfied. In this paper, we present a novel queueing analytical framework to study the tradeoff between the energy saving and the QoS at a relay node. Specifically, by modeling the bursty traffic arrival process as a MAP (Markovian arrival process) and the packet service process as having a phase-type (PH) distribution, we model each node as a MAP/PH/1 nonpreemptive priority queue. The relayed packets and the node's own packets form two priority classes and the medium access control (MAC)/physical (PHY) layer protocol in the transmission protocol stack acts as the server process. Moreover, we use a phase-type vacation model for the energy-saving mechanism in a node when the MAC/PHY protocol refrains from transmitting in order to save battery power. Two different power saving mechanisms due to the standard exhaustive and the number-limited exhaustive vacation models (both in multiple vacation cases) are analyzed to study the tradeoff between the QoS performance of the relayed packets and the energy saving at a relay node. Also, an optimization formulation is presented to design an optimal wakeup strategy for the server process under QoS constraints. We use matrix-geometric method to obtain the stationary probability distribution for the system states from which the performance metrics are derived. Using phase-type distribution for both the service and the vacation processes and combining the priority queueing model with the vacation queueing model make the analysis very general and comprehensive

Location-based incentive pricing for tree-based relaying in multi-hop cellular networks

Multi-hop cellular networks that integrate the characteristics of both cellular and mobile ad hoc networks have received increasing attention. Providing incentives to foster cooperation among nodes is an important prerequisite for the success of the multi-hop cellular networks. In this paper, we present a location-based incentive pricing scheme to enhance service availability for tree-based relaying topology. The proposed scheme adjusts the price of feedback incentives based on the degree of the mobile nodes contributing to successful hop-by-hop connections. Simulation results indicate that the location-based incentive pricing scheme results in higher service availability than the fixed-rate pricing scheme under different relationships between price of feedback and willingness of forwarding packets. Moreover, the proposed pricing scheme shifts incentives from the nodes of low importance to the nodes of high importance in the routing topology so that it increases service availability without additional costs.

Analysis and modeling of upstream throughput in multihop packet CDMA cellular networks

We consider the problem of throughput modeling of wireless multihop packet CDMA networks with cellular overlay using simple forwarding strategies in the upstream. Considering the effect of shadowing and distance-dependent path loss, we approximate the probability density of interference at each base station (BS) and compare numerical and simulation results for different path-loss parameters. We derive the probability density of the received power at each BS due to transmission of one packet from a random node, as well as the probability distribution of the number of packets received at each node per time slot. Subsequently, we use the above results to approximate the probability density of the total received power at each BS based on calculations of moments. We observe that the probability density of intercell interference due to transmissions from terminals and routers may be approximated by normal and log-normal densities, respectively. We quantify the network performance based on throughput, total consumed power, and outage probability for different system parameters. For homogeneous link efficiencies, introducing routers into the network while reducing the transmission power increases the mean and variance of interference to the desired signal, hence higher outage probability. However, there are ample opportunities inherent to multihop structure, applicable to any of the physical, data link, and network layers, which help increase the overall achievable network throughput.

Comparison of motivation-based cooperation mechanisms for hybrid wireless networks

Today’s public Wireless LANs are restricted to hotspots. With the current technology, providers can only target a small audience and in turn charge high prices for their service to generate revenue. Also, providers cannot react appropriately to dynamic changes in the demand. With multi-hop cellular networks the coverage area can be increased and the installation costs as well as investment risks for the provider can be reduced. However, the individual customers play an important role in such networks and their participation must be ensured. Therefore, we propose a cooperation and accounting scheme which introduces monetary rewards. We compare our scheme called CASHnet with the Nuglet scheme using simulations under the criteria of network liveliness, goodput, overhead, and packet drop reasons as well as cash flow.

Capacity enhancement of uplink channel through spatial reuse in multihop cellular networks

Some multihop cellular networks use spatial resource reuses for concurrent data transmission in a cell. However, there are no fundamental resource reuse policies am ong multiple hops to analyze the capacity of multihop iellulae networks. So, in this letter, we propose a basic resource reuse scheme by applying a general resource reuse scheme that is used for cellular networks to multihop cellular networks. Then, we examine the capacity gains of the proposed resource reuse scheme through mathematical analysis based on Shannon capacity.

Capacity enhancement of uplink channel through spatial reuse in multihop cellular networks

Capacity enhancement of uplink channel through spatial reuse in multihop cellular networks

On the Use of Multiple Hops in Next Generation Wireless Systems

Traditional cellular networks provide a centralized wireless networking paradigm within the wireless domain with the help of fixed infrastructure nodes such as Base Stations (BSs). On the other hand, Ad hoc wireless networks provide a fully distributed wireless networking scheme with no dependency on fixed infrastructure nodes. Recent studies show that the use of multihop wireless relaying in the presence of infrastructure based nodes improves system capacity of wireless networks. In this paper, we consider three recent wireless network architectures that combine the multihop relaying with infrastructure support - namely Integrated Cellular and Ad hoc Relaying (iCAR) system, Hybrid Wireless Network (HWN) architecture, and Multihop Cellular Networks (MCNs), for a detailed qualitative and quantitative performance evaluation. MCNs use multihop relaying by the Mobile Stations (MSs) controlled by the BS. iCAR uses fixed Ad hoc Relay Stations (ARSs) placed at the boundaries to relay excess traffic from a hot cell to cooler neighbor cells. HWN dynamically switches its mode of operation between a centralized Cellular mode and a distributed Ad hoc mode based on the throughput achieved. An interesting observation derived from these studies is that, none of these architectures is superior to the rest, rather each one performs better in certain conditions. MCN is found to be performing better than the other two architectures in terms of throughput, under normal traffic conditions. At very high node densities, the variable power control employed in HWN architecture is found to be having a superior impact on the throughput. The mobility of relay stations significantly influences the call dropping probability and control overhead of the system and hence at high mobility iCAR which uses fixed ARSs is found to be performing better.

Multi-hop cellular networks: Architecture and protocols for best-effort and real-time communication

Until recently, research on cellular networks concentrated only in single-hop cellular networks. The demand for high throughput has driven to architectures that use multiple hops in the presence of infrastructure. We propose an architecture for multihop cellular networks (MCNs). MCNs combine the benefits of having a fixed infrastructure of base stations and the flexibility of Ad hoc networks. They are capable of achieving much higher throughput than current cellular systems, which can be classified as single-hop cellular networks (SCNs). In this work, we propose an extended architecture for MCN using the IEEE 802.11 standard for wireless LANs for connection-less service and a TDMA-based solution for real-time support. We provide a general overview of the architecture and the issues involved in the design of MCNs, in particular the challenges to be met in the design of a routing protocol, a channel assignment scheme, and a mobility management scheme. We also propose a routing protocol called Base-Assisted Ad hoc Routing (BAAR) protocol for use in such networks and a model for the performance analysis of MCNs and SCNs. We also conduct extensive experimental studies on the performance of MCNs and SCNs under various load (TCP, UDP, and real-time sessions) and mobility conditions. These studies clearly indicate that MCNs with the proposed architecture and routing protocol are viable alternatives for SCNs, in fact they provide much higher throughput. MCNs are very attractive for best-effort packet radio where they can achieve an increase in throughput up to four when compared to similar SCNs. But for real-time traffic, even though they do outperform SCNs, they also suffer from a few disadvantages such as frequent hand-offs and throughput degradation at high mobility. We also present results from a detailed comparison study of our architecture for MCN with the Hybrid Wireless Network (HWN) architecture and Integrated Cellular Ad hoc Relaying (iCAR) Architecture.

A Minimum Hop Routing Algorithm for Multihop Cellular Networks

This paper presents a nurumum hop routing algorithm for the multihop cellular CDMA network. A mechanism to update routing paths in case of network topology change is also developed. Mobile terminals will be separated into two groups and each group will only transmit on one of two timeslots so that terminals do not have to transmit and receive simultaneously on the same frequency band. The routing algorithm in this paper is designed in order to optimize criteria including SNIR, delay, power consumption, and network lifetime. Simulation is used to evaluate these criteria for the multihop cellular network and its performance is compared with the traditional cellular network. Simulations show that the total power consumption in the multihop cellular network is much lower than a traditional cellular network with a capacity that is nearly as high. Simulations also show that the network lifetime of the multihop cellular network is much higher than that of a traditional cellular network.