Heterogeneous wireless networks based on varieties of radio access technologies (RATs) and standards will coexist in the future. In order to exploit this potential multiaccess gain, it is required that different RATs are managed in a cooperative fashion. This paper proposes two advanced functional architecture supporting the functionalities of interworking between WiMAX and 3GPP networks as a specific case: Radio Control Server- (RCS-) and Access Point- (AP-) based centralized architectures. The key technologies supporting the interworking are then investigated, including proposing the Generic Link Layer (GLL) and researching the multiradio resource management (MRRM) mechanisms. This paper elaborates on these topics, and the corresponding solutions are proposed with preliminary results.

Zhuo Sun

Wenbo Wang

Investigation of Cooperation Technologies in Heterogeneous Wireless Networks

IEEE 802.16j is an emerging wireless broadband
networking standard that integrates infrastructure base stations
with multihop relay technology. Based on the idle mode operation
in IEEE 802.16j, we propose a novel location management and
paging scheme. It integrates the paging area-based and the
timer-based location update mechanism. In paging area-based
scheme, an idle mode mobile station updates when it moves to
a new paging area. In timer-based scheme, an idle mode MS
updates when the location update timer expires. In this work, we
formulate the mathematical model to evaluate the performance of
the proposed paging scheme. A new random walk mobility model
that is suitable for modeling in multihop relay network is created.
Optimization of location update timer is also investigated.

Kuan-Po Lin

Hung-Yu Wei

Paging and Location Management in IEEE 802.16j Multihop Relay Network

Handoff in a distributed IEEE 802.11 Wireless LAN network is a source of significant amount of problems on the video transmission environment. The visual quality of video streaming applications is lowered when stations are in handoff status. In this paper, we introduce an architecture of a session proxy (SP), which tries to preserve the quality of the streaming video upon each handoff between access points. We have evaluated thresholds of RSSI and Loss Frame Rate (LFR) for deciding the moment when the handoff process shall begin. Our solution performance was evaluated in a testbed implementation for MPEG-4 video on demand with one video server (VLS) and two FreeBSD-based access points supporting  Mobile IP, DHCP Server and IAPP approach.

Claudio de Castro Monteiro

Paulo Roberto de Lira Gondim

Vin&#237;cius de Miranda Rios

Seamless Video Session Handoff between WLANs

Carrier frequency offset (CFO) synchronization is a crucial issue in the implementation of orthogonal frequency division multiplexing (OFDM) systems. Since current technology tends to implement different standards in the same wireless device, a common frequency synchronization structure is desirable. Knowledge of the physical frame and performance and cost system requirements are needed to choose the most suitable scheme. This paper analyzes the performance and FPGA resource requirements of several data-aided (DA) and decision-directed (DD) schemes for four wireless standards: 802.11n, 802.16d, LTE, and DVB-T/H. Performance results of the different methods are shown as BER plots and their resource requirements are evaluated in terms of the number of computations and operators that are needed for each scheme. As a result, a common architecture for the four standards is proposed. It improves the overall performance of the best of the schemes when the four standards are considered while reducing the required resources by 50&#37;.

Javier Gonz&#225;lez-Bay&#243;n

Carlos Carreras

Ove Edfors

A Multistandard Frequency Offset Synchronization Scheme for 802.11n, 802.16d, LTE, and DVB-T/H Systems

This paper introduces an effective joint scheme of channel estimation and tracking for downlink partial usage of subchannel (DL-PUSC) mode of mobile WiMAX system. Based on the pilot pattern of this particular system, some channel estimation methods including conventional interpolations and a more favorable least-squares line fitting (LSLF) technique are comparatively studied. Besides, channel estimation performance can be remarkably improved by taking advantage of channel tracking derived from the preamble symbol. System performances in terms of packet error rate (PER) and user link throughput are investigated in various channels adopted from the well-known ITU models for mobile environments. Simulation results show a significant performance enhancement when the proposed joint scheme is utilized, at least 5&#x2009;dB, compared to only commonly used channel estimation approaches.

Phuong Thi Thu Pham

Tomohisa Wada

Effective Scheme of Channel Tracking and Estimation for Mobile WiMAX DL-PUSC System

We present a simple analytical method for capacity evaluation of IEEE 802.16e Mobile WiMAX networks. Various overheads that impact the capacity are explained and methods to reduce these overheads are also presented. The advantage of a simple model is that the effect of each decision and sensitivity to various parameters can be seen easily. We illustrate the model by estimating the capacity for three sample applications—Mobile TV, VoIP, and data. The analysis process helps explain various features of IEEE 802.16e Mobile WiMAX. It is shown that proper use of overhead reducing mechanisms and proper scheduling can make an order of magnitude difference in performance. This capacity evaluation method can also be used for validation of simulation models.

Chakchai So-In

Raj Jain

Abdel-Karim Tamimi

Capacity Evaluation for IEEE 802.16e Mobile WiMAX

We discuss query optimization in a secure distributed database system, called the Secret Sharing Distributed DataBase System (SSDDBS). We have to consider not only subquery allocations to distributed servers and data transfer on the network but also decoding distributed shared data. At first, we formulated the subquery allocation problem as a constraints satisfaction problem. Since the subquery allocation problem is NP-complete in general, it is not easy to obtain the optimal solution in practical time. Secondly, we proposed a heuristic evaluation function for the best-first search. We constructed an optimization model on an available optimization software, and evaluated the proposed method. The results showed that feasible solutions could be obtained by using the proposed method in practical time, and that quality of the obtained solutions was good.

Toshiyuki Miyamoto

Takeshi Ikemura

Subquery Allocation Problem and Heuristics for Secret Sharing Distributed Database System

This paper presents a flexible interleaver architecture supporting multiple standards like WLAN, WiMAX, HSPA+, 3GPP-LTE, and DVB. Algorithmic level optimizations like 2D transformation and realization of recursive computation are applied, which appear to be the key to reach to an efficient hardware multiplexing among different interleaver implementations. The presented hardware enables the mapping of vital types of interleavers including multiple block interleavers and convolutional interleaver onto a single architecture. By exploiting the hardware reuse methodology the silicon cost is reduced, and it consumes 0.126&#x02009;<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mtext>mm</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math> area in total in 65&#x02009;nm CMOS process for a fully reconfigurable architecture. It can operate at a frequency of 166&#x02009;MHz, providing a maximum throughput up to 664&#x02009;Mbps for a multistream system and 166&#x02009;Mbps for single stream communication systems, respectively. One of the vital requirements for multimode operation is the fast switching between different standards, which is supported by this hardware with minimal cycle cost overheads. Maximum flexibility and fast switchability among multiple standards during run time makes the proposed architecture a right choice for the radio baseband processing platform.

Rizwan Asghar

Dake Liu

Multimode Flex-Interleaver Core for Baseband Processor Platform

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Journal of Computer Networks and Communications publishes original research and review articles that investigate both the theoretical and practical aspects of computer networks and communications.

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Journal of Computer Networks and Communications