Elsevier

Computer Communications

Volume 33, Issue 18, 15 December 2010, Pages 2224-2245
Computer Communications

Fuzzy logic based layers 2 and 3 handovers in IEEE 802.16e network

https://doi.org/10.1016/j.comcom.2010.08.002Get rights and content

Abstract

In outdoor wireless communication networks such as mobile WiMAX (802.16e), mobile stations move all the time, thus they need to be handed off to different base stations based on certain criteria. In this paper, a fuzzy logic based scheme for fast selection of best base station and of handover technique at the handover time is presented in order to minimize the delay during handover for sensitive multimedia traffic. The scheme considers several parameters such as receiver power levels, handover type, traffic type, base station load and mobile station speed for making the handover decision by the mobile station. Through simulations, we compare our proposed handover scheme based on fuzzy logic modeling with classical handover decision. And finally, we present results based on Quality of Service (QoS) criteria to confirm the validity of the proposed approach.

Introduction

The core of the mobile WiMAX [1] network in rural or urban area is formed of several cells covered by base stations with different sizes. Each base station belongs to a network element called ASN-GW (Access Service Network Gateway), and this element can manage one or more base stations [2], [3], [4]. In such network, a major issue that needs efficient real-time solutions is the problem of handing off mobile stations between base stations. It is required that the supporting system choose a target base station and perform handover as fast as possible to provide reasonable QoS levels to the end users.

In mobile WiMAX networks, if the mobile station performs a handover between two cells covered by two base stations belonging to the same ASN-GW, the handover is of layer two (L2) type [2], [3], [4]. On the contrary, if the mobile station performs a handover between two cells covered by two base stations belonging to different ASN-GW, the handover is of layer three (L3) type [2], [3], [4].

The main idea of the modeling suggested in this paper is to measure some criteria such as the receiver signal strength, the base station load and the mobile station speed, based on some attributes such as handover type (L2 or L3) and traffic type (VoIP or video or data). After the measurement and the determination of criteria values, a decision of handover based on some handover protocols and techniques will be taken by the mobile station.

To prove the efficiency of our proposition, we will run some simulations focused on QoS parameters by applying our decisional handover scheme and the classical handover scheme on a proposed mobility model composed of several cells managed by base stations, and some ASN-GW managing each some base stations. The architecture of mobility model is formed by a highway between two cities. The mobility in the two cities is low or medium, and in the highway the mobility is high (see Section 7).

In this paper, we will present first the IEEE 802.16e architecture, second L2 and L3 handover protocols, third the fuzzy logic modeling method, then we will describe our handover algorithm based on fuzzy logic for the decision, after that the simulation model and the mobility scenarios, and finally the simulations results and the conclusion.

Section snippets

IEEE 802.16e network (mobile WiMAX)

Mobile WiMAX (IEEE 802.16e) [1] is the mobile extension of the IEEE 802.16e [5] standard, that defines the specifications for radio metropolitan networks offering broadband to achieve a high flow rate and using techniques to cover large areas.

The architecture of mobile WiMAX is composed of mobile stations (MS), that communicate freely (radio link) with base stations (BS), which act as relays with the terrestrial infrastructure of IP network. The base stations themselves are connected to the

Layer 2 handover protocols in mobile WiMAX

In the IEEE 802.16e, there are three types of L2 handover [1], [6], [7]: the Hard Handover that is applied in the case of a low speed, it uses the mechanism break-before-make (interruption of connection with the old BS before the connection with the new BS), and in this case the mobile communicates with a single BS only.

The handover scheme describing the steps of operation with the Hard HO is presented in the figure.

The Soft Handover – MDHO (Macro Diversity Handover) [1], [6], [7] is applied in

CMIP and PMIP protocols

IEEE 802.16e defines two types of layer 3 handover [2], [3], [4]: mobile IPv4 (MIP) or Client-MIPv4 (CMIP) and Proxy-MIPv4 (PMIP).

CMIP [8] provides a set of extensions to the Internet protocol standards defined by the IETF. It allows users to register on foreign networks and connect back to their home network via a combination of FA (Foreign Agent) and HA (Home Agent).

In CMIP mechanism, the MIP standard exists in the MS, therefore there is a lot of complexity in MS. Also, CMIP is incompatible

Fuzzy logic

In this section, we will present the modeling method used in our algorithm to decide the handover in IEEE 802.16e network.

Fuzzy logic can be viewed as a theory for dealing with uncertainty about complex systems, and as an approximation theory. This perspective shows that fuzzy logic has two objectives: (a) to develop computational methods that can perform reasoning and problem solving tasks that require human intelligence, and (b) to explore an effective trade-off between precision and the cost

Fuzzy logic handover decision algorithm

A handover algorithm must be capable of making a final decision based on input parameters. We design an adaptive multi-criteria multi-attribute handover decision algorithm that incorporates fuzzy logic because of the inherent strength of fuzzy logic in solving problems exhibiting imprecision and the fact that many of the terms used for describing radio signals are fuzzy in nature [19], [20]. The algorithm gives users the option to influence the handoff result by specifying user preferences such

Simulation model

The mobility model proposed for the simulations is very close to the reality. Its infrastructure is composed of two cities composed each by six cells. The two cities are bound by a highway containing four cells. The highway is localized in the rural area, so the four cells of the highway are covered by base stations with 10 km of coverage.

The six cells localized in each city classed urban area, are of variable radius varying between 1 and 3 km and covered by base stations.

In this model, we

Simulations parameters

To make these simulations, we have added the NIST modules in NS2 [25] for the WiMAX network and for the mobility [26], [27].

The simulations parameters adopted in NS2 simulator are illustrated in those two tables (Table 4, Table 5):

Performance criteria

The performance criteria adopted in our simulations are: end-to-end delay, throughput (rate) and packets loss ratio. The end-to-end delay is the time taken for a packet to be transmitted across a network from source to destination. The throughput is the information

Conclusion

In this paper, we aim to improve the QoS during the handover for the multimedia traffic in IEEE 802.16e network. The algorithm based on fuzzy logic modeling proposes several input parameters which will apply on rules table to help the mobile to make an accurate and rapid decision about the handover by choosing the good technique type during the handover.

The major novelties of the proposed algorithm are:

  • (1)

    The add to new input parameters before the handover to allow to the MS to make a good

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