Multihop Cellular Networks Research Articles

Capacity Enhancement in Hybrid Wireless Relay Network with Network Coding

Network coding technique increases wireless network communication efficiency. Wireless multihop relay network has been shown to achieve capacity gain over conventional single-hop wireless networks. Hybrid wireless relay networks integrate multihop ad hoc relay and infrastructure base stations to achieve better wireless network performance. Applying the promising network coding technique to hybrid wireless relay networks could increase wireless network capacity. Capacity of multihop cellular network with network coding is derived. To enhance network throughput, data forwarding strategy is proposed to determine if a packet should be transmitted through intra-cell ad hoc relay, inter-cell ad hoc relay, or infrastructure-assisted inter-cell transmission.

Traffic adaptive relaying topology control

The optimization of the relaying topology in multihop cellular network should provide the answer to the question who is transmitting to whom, and when, in such a way to insure the best system performance. In the case of temporally and spatially varying traffic distribution the optimal topology will also vary in time and an efficient way for topology control is needed in order to maximize the system performance. In this paper we present an algorithm for efficient relaying topology control, which is aware of the intercell interference, requiring coordinated action between the cells and resulting in multicell jointly optimal relaying topology. Numerical results demonstrate that an adaptive relaying topology control provides the network utility improvements and presents the framework for quantifying these improvements for spatially and temporally varying traffic.

Optimal transmission methodology for QoS provision of multi-hop cellular network

In this paper, we present a framework of link capacity analysis for optimal transmission over uplink MCN (Multi-hop Cellular Network) environments. An overlaid architecture is employed as the network topology, i.e., single-hop transmission over the inner region and multi-hop transmission over the outer region. In particular, we analyzed the gain that accrued from grafting a relay method onto a conventional, SCN (Single-hop Cellular Network) and investigated the conditions for optimal performance through the numerical results. At high-user density, a MCN exhibits a much more reliable transmission than the SCN. For maximal link capacity, optimal region partitioning is approximately accomplished at the normalized cell radius of 0.6 in most of cases for region division. Finally, the link capacity can be improved 1.2---1.8 times better than the SCN when the number of relay hops is 1.6 and the half-duplex mechanism is used. In addition, the proposed MCN scheme demonstrates an effective reduction in transmission power relative to the SCN.

Multihop cellular networks toward LTE-advanced

This article presents the architecture of MCN toward 3G LTE-Advanced with TDD. On the assumption that L2 RN and L3 RN can provide their own RRM functions, several important RRM functions including routing, link adaptation, and scheduling in MAC layers at RNs can help the eNB to handle the radio resources efficiently. In general, the RN with higher implementation complexity has the ability to provide more flexible RRM with more overhead. Our dynamic system-level simulations show that the MCN outperform the networks without relaying in terms of SINR and throughput.

Identifying the capacity gains of multihop cellular networks

Claims for the advantages of applying multihop relay in CDMA cellular networks have been widely accepted in the literature. However, such claims have yet to be closely examined. In this paper, capacity increase in CDMA cellular networks through multihop relay is quantified. As CDMA networks are interference-limited, interference has to be analyzed to estimate the system capacity. Toward this end, we derive formulas to calculate interference experienced in multihop CDMA cellular networks by both base stations and mobile terminals. The formulas are generic and applicable whether or not power control is exercised between mobile terminals. The capacity of multihop CDMA cellular network is compared to that of single hop CDMA cellular network to verify the claimed advantage. We demonstrate that a 23% capacity increase is achieved when relaying with power control. We also extend the work to illustrate the effect of call distribution on the capacity of the cell and its neighbors - both in the single and multiple hop cases. Furthermore, we ascertain that call distribution inside a cell hardly affects the capacity of adjacent cells when using multihop relay. This specific advantage overcomes the inherent capacity degradation caused by near border calls, which is the biggest burden on the capacity of single hop CDMA cellular networks. To the best of our knowledge, this effort is the first of its kind in this area.

Relay Architectures for 3GPP LTE-Advanced

The Third Generation Partnership Project's Long Term Evolution-Advanced is considering relaying for cost-effective throughput enhancement and coverage extension. While analog repeaters have been used to enhance coverage in commercial cellular networks, the use of more sophisticated fixed relays is relatively new. The main challenge faced by relay deployments in cellular systems is overcoming the extra interference added by the presence of relays. Most prior work on relaying does not consider interference, however. This paper analyzes the performance of several emerging half-duplex relay strategies in interference-limited cellular systems: one-way, two-way, and shared relays. The performance of each strategy as a function of location, sectoring, and frequency reuse are compared with localized base station coordination. One-way relaying is shown to provide modest gains over single-hop cellular networks in some regimes. Shared relaying is shown to approach the gains of local base station coordination at reduced complexity, while two-way relaying further reduces complexity but only works well when the relay is close to the handset. Frequency reuse of one, where each sector uses the same spectrum, is shown to have the highest network throughput. Simulations with realistic channel models provide performance comparisons that reveal the importance of interference mitigation in multihop cellular networks.

A Cross Layer Routing Protocol for Multihop Cellular Networks

We propose a cross-layer routing protocol for a Code Division Multiple Access (CDMA) Multihop Cellular Network (MCN). In designing the routing protocol for MCN, multiple constraints are imposed on intermediate relay node selection and end-to-end path selection. The constraints on relay nodes include willingness for cooperation, sufficient neighbourhood connectivity and the level of interference offered on the path. Path constraints include end-to-end throughput and end-to-end delay. A facile incentive mechanism is presented to motivate the cooperation between nodes in call forwarding. In addition, we present a route resilience scheme in the event of dynamic call dropping. In particular, a fast neighbour detection scheme for route resilience is proposed. Instead of using periodic HELLO messages as in traditional ad-hoc routing, the proposed neighbour detection scheme adopts an explicit handshake mechanism to reduce neighbour detection latency. We conclude the paper by demonstrating the superior performance of the proposed routing protocol compared with the other well known routing algorithms.

Handover in multihop cellular networks

This article introduces various handover scenarios in multihop cellular networks. In addition, this article presents handover schemes where relay stations are located either inside a cell or on the boundary between two adjacent cells and investigates the effects of the deployment position of relay stations to handover performance. The simulation results show that multihop cellular networks for both deployment scenarios can achieve 90 percent throughput increase over single-hop cellular networks. The results also show that the overall throughput of the multihop cellular networks with relay stations inside a cell is higher than for those with relay stations on the boundary between two adjacent cells, whereas the opposite is observed for the throughput of cell-boundary users. The intercell handover latency in multihop cellular networks is increased by 20 ~ 56 percent compared with that in single-hop cellular networks because of the increased number of handovers and signaling overhead. However, by deploying relay stations on the boundary between two adjacent cells, the service-interruption time caused by inter-cell handover is reduced by 80 percent compared with that of single-hop cellular networks.

Downlink Resource Allocation for Autonomous Infrastructure-based Multihop Cellular Networks

Considering a multihop cellular system with one relay per sector, an effective modeling for the joint base-station/relay assignment, rate allocation, and routing scheme is proposed and formulated under a single problem for the downlink. This problem is then formulated as a multidimensional multichoice knapsack problem (MMKP) to maximize the total achieved throughput in the network. The well-known MMKP algorithm based on Lagrange multipliers is modified, which results in a near-optimal solution with a linear complexity. The notion of the infeasibility factor is also introduced to adjust the transmit power of base stations and relays adaptively. To reduce the complexity, and in order to analyze the underlying key factors in the system, the framework is restricted to a two-base-station two-relay system. In fact, the output of the proposed algorithm is the joint optimization of the routing path, and base-station selection to achieve the maximum total throughput in the system, which in conjunction with the proposed adaptive scheme leads to the implementation of the cell breathing via allocating the proper transmit power to the base-stations and relays.

Optimum number of gateways for cluster-based two-hop cellular networks

An ever increasing number of mobile users combined with an increase in the demand for data rates has led researchers to explore the feasibility of multihop cellular networks. However, due to the NP-hard complexity in resource allocation and scheduling techniques in a multihop cellular network, the focus of multihop cellular design is mostly restricted to two-hop. In this work, we analyze the capacity of a cluster-based hierarchical two-hop multi-cellular network, with a frequency reuse of one. We prove mathematically that when there are six cells surrounding the center cell, and the number of simultaneous communicating pairs in all the six cells are same, there are six distinct locations in any cell where the link capacity reaches its maximum and six distinct locations where the link capacity reaches its minimum. Significantly, all these twelve points are equidistant. Similarly, we observe that if a cell is surrounded by four cells such that all the base stations (BSs) of the adjacent cells are equidistant from the BS of the center cell, then the number of locations where the capacity is maximum or minimum is found to be exactly four each. This provides an insight on the exact number and the location where the gateways should be placed in a hierarchical cellular architecture in order to maximize the system capacity in a multi-cellular environment. In addition, for a hexagonal geometry, when the number of simultaneously communicating pairs are different in different adjacent cells, the optimum number of gateways per cell that maximizes the system capacity for all the cases is not a fixed number, but varies between a minimum value of one and a maximum value of six, depending on the number of cells which has two simultaneously communication pairs.

Media handling for multimedia conferencing in multihop cellular networks

This article addresses the media-handling aspects of multimedia conferencing in multihop cellular networks. Participation in multimedia conferences in MCNs may be confined to either the conventional cellular network or the MANET. Participation also can span both networks. However, neither the media-handling architectures currently in use in conventional cellular networks, nor the ones in use in MANETs are appropriate. When they are used, either the participants in the conventional cellular network, or the ones in the MANETs, might experience long and potentially unacceptable end-to-end stream delays. Furthermore, these architectures are the antipodes of each other. Reconciling them is not an easy task. We evaluate the architectures currently in use in cellular networks and MANETs, show that none is suitable, and propose a new architecture that bridges the two worlds. The new architecture uses the MANET media-handling architectures as a starting point. It is based on media mediators. A media mediator is composed of two functional entities: the media gateway controller mediator and the media gateway mediator. A proof-of-concept prototype was implemented, and extensive simulations were conducted to evaluate performance.

Optimal Positions of Relay Stations for Cluster-Based Two-Hop Cellular Network

Multihop cellular networks is an exciting and a fledgling area of wireless communication which offers huge potential in terms of coverage enhancement, data-rates, power reduction, and various other quality of service improvements. However, resource allocation in MCN is an NP-hard problem. Hence, significant research needs to be done in this field in order to efficiently design the radio network. In this paper, optimal position of relay stations in a hierarchical cluster-based two-hop cellular network is investigated. Vector algebra has been used to derive general equation for carrier-to-interference ratio (C/I) of a mobile station. It has been observed that when the transmit power of base station (BS) and the gateway (GTW)/relay station (RS) are same, the RSs should be located close to mid-point of BS and the edge of the cell. However, significantly, when the transmit power of the BS is greater than that of the GTW, then the RSs should be placed closer to the edge of the cell, in order to maximize the minimum C/I at any point in the cell. This in turn results in higher modulation technique at the physical layer, and hence, a higher data-rate to all the users in the system.

Performance analysis of multihop cellular network with fixed channel assignment

Multihop cellular network (MCN) has been proposed to incorporate the flexibility of ad hoc networks into traditional single-hop cellular networks (SCNs). The performance analysis of MCN through analytical models is not trivial because the classic Erlang B formula no longer applies to MCN where multihop transmission is allowed. In this paper, we first propose a clustered MCN (cMCN) architecture with the use of dedicated information ports (DIPs), which are deployed wireless ports functioning as central controllers for multihop users. The proposed cMCN can be considered as a complement of the existing cellular network. Then, we study the feasibility of modeling time division multiple access (TDMA)-based cMCN with fixed channel assignment (FCA) scheme for uplink transmission. An exact multi-dimensional Markov chain model to analyze the performance of cMCN with FCA is developed. Furthermore, an approximated model which results in reduced complexity is also presented. The analytical results from both models are matched with the simulation results closely. The results show that cMCN with the proposed FCA scheme can reduce the call blocking probability significantly as compared to SCNs with either the conventional FCA or a dynamic channel assignment (DCA) scheme.

QoS-guaranteed transmission mode selection for efficient resource utilization in multi-hop cellular networks

This paper considers the problem of efficient usage of subcarriers in downlink orthogonal frequency-division multiple access (OFDMA) multi-hop cellular networks. Multi-hop transmission can either save or waste subcarriers depending on quality of service (QoS) requirements, interference from other cells, and the location of a given mobile station (MS). Preventing unnecessary usage of multi-hop transmission requires the use of a transmission mode selection (TMS) scheme, and we propose two types of TMS in this paper. The first of these is distance-based TMS (TMS-D), which determines the transmission mode based on the MSiquests location, and the second is subcarrier-based TMS (TMS-S), which selects whichever transmission mode uses fewer subcarriers. Numerical results on blocking probability demonstrate that TMS improves overall subcarrier usage efficiency, meaning that more MSs can be supported with low blocking probability within a cell. Furthermore, the performance of TMSS, even given its higher complexity, is shown to be superior to that of TMS-D.

A cross-layer architecture for signaling in multihop cellular networks

Multihop cellular networks (MCNs) combine traditional single-hop cellular networks with ad hoc networks. They have emerged recently as an active research topic due to their throughput advantages and low cost. Most of the research on MCNs has been focused on lower-layer issues such as routing. Application layer issues in MCNs are seldom addressed. In this article we tackle one of these issues: signaling for conferencing. Conferencing enables a range of "killer" applications such as videoconferencing, gaming, and distance learning. Signaling is a critical component that handles session initiation, modification, and termination. We have proposed a general signaling architecture for integrated 3G/ MANETs that is applicable to the specific case of MCNs. This architecture is based on application- layer clusters and faces several performance drawbacks. This article focuses on optimizing the architecture performance for the specific environment of an MCN. We first present this MCN environment and discuss conferencing scenarios. We propose an optimization architecture based on cross-layer design, which is then compared to the existing proposals, followed by a set of optimization schemes. The article also discusses initial evaluation results.

A Route Establishment Scheme for Multi-route Coding in Multihop Cellular Networks

Since the network topology in multihop cellular networks is flexible, multiple routes from a user station to a base station can be established. To reduce packet reception errors of wireless links, a multi-route coding scheme was proposed. An important issue of the multi-route coding is to develop an efficient route establishment scheme. In this paper, we propose a route establishment scheme for multiroute coding in multihop cellular networks. Our proposed scheme consists of a route selection method based on the bit error rate of each wireless link and a hybrid-type multipletree routing protocol. We evaluate the performance of our proposed scheme by a computer simulation and show the resulting improvement in the packet error.

A Dynamic Channel Assignment Scheme for TDMA-based Multihop Cellular Networks

In this paper, we propose a multihop dynamic channel assignment (MDCA) scheme for time division multiple access (TDMA)-based multihop cellular networks. The proposed MDCA assigns channels to calls based on interference information in surrounding cells, provided by the interference information table (IIT) in the network. Two different channel searching strategies, Sequential channel searching (SCS) and packing-based channel searching (PCS), for use in MDCA are proposed and studied. A channel reassignment procedure to further enhance the performance is also investigated. Simulation results show that MDCA significantly improves the system capacity. Furthermore, the MDCA can efficiently alleviate the call blocking in hot-spot cells.

Dynamic Channel Assignment for Multihop Cellular Networks with Any Reuse Factor

A clustered multihop cellular network (cMCN) architecture is recently proposed and studied using fixed channel assignment (FCA) with a reuse factor, Nr=7. In this Letter, we propose and develop a multihop dynamic channel assignment (mDCA) scheme applicable with any reuse factor. The mDCA assigns channels with the knowledge of the information about interference in surrounding cells. Simulations show that the capacity improvements at call blocking probability of 1% for mDCA over the conventional FCA are 96% and 210% for Nr=4 and Nr=7, respectively.

Multihop cellular networks: Technology and economics

Recently, multihop cellular networks (MCNs) were proposed to preserve the advantages of traditional single-hop cellular networks with multihop ad hoc relaying networks, while minimizing the drawbacks that they involved. In this way, MCNs enhance the performance of both the existing cellular networks and ad hoc networks. Consequently, MCN-type system is considered as a promising candidate of fourth generation (4G) wireless network for future mobile communications. This paper surveys a number of MCN-type architectures in literature through a comprehensive comparison and discussion among the proposed architectures. The discussion is divided into two phases. In the first phase, we review the concept of MCN and compare the selected MCN-type architectures from a technology perspective. In the second phase, we further compare and discuss the economic perspective on the deployment of MCNs. Specifically, we focus on the economic considerations for deploying relays in MCN-type systems.

On the performance of time division multiple access-based multihop fixed cellular networks with respect to available frequency carriers

In multihop cellular networks (MCN), the user nodes can act as relays and forward other nodes' traffic to/from base stations. There are several advantages of MCN such as the improved signal quality and higher coverage. However, it is known that multihop relaying networks require extra radio resources. Therefore the performance of MCN depends to a great extent on the availability of adequate radio resources. The performance of a time division multiple access (TDMA)-based multihop fixed cellular network is analysed with highlighting the dependence of the system performance on the amount of available radio resources, namely, the number of frequency carriers. Results show that in a fixed cellular network, the multihop architecture significantly outperforms the traditional single-hop architecture in terms of the outage probability and throughput if an adequate amount of frequency carriers is available in the network. Otherwise, the multihop fixed cellular networks architecture loses its superiority and might even lead to performance degradation, particularly at high loading levels.