| Abstract | This thesis contributes to the concept of wireless broadband access networking infrastructures by the design, implementation and evaluation of a novel network configuration that utilises a cellular architecture and provides symmetric interactivity over broadband downlink and uplink transmission channels.
The design of the network configuration converges current wireless broadband access technologies, integrates all the appropriate hardware and software tools, and finally proposes a prototype wireless network, which is capable of providing access via the same platform to: i) high quality interactive multimedia services such as audio/video on demand (featuring bitrates higher than IMbps) over the TCP/IP stack, ii) fast Internet services (>lMbps), and iii) digital TV broadcasts (MPEG-2 format) based on the digital video broadcasting (DVB) standard. According to the proposed design, the network uses an innovative cellular architecture that utilises macro-cell configuration in the downlink and micro-cell configuration in the uplink. In this way, both digital TV broadcasts and the data for the interactive multimedia services (along with the Internet traffic) are multiplexed and transmitted to the user's neighbourhood (cell) wirelessly in the frequency band of 42GHz, by utilising the broadcasting delivery method and local multipoint distribution service (LMDS) technology. End-users of each cell may access the Internet or multimedia services via an intermediate communication node, the cell main node (CMN). The bi-directional communication between each user and the corresponding CMN is via 2.4GHz multichannel multipoint distribution service (MMDS) based links. These links provide for multiple user access under the IEEE 802.11 communication protocol, while enabling for user-to-user communication at rates of about 3Mbps (within a cell). For symmetric communication, each user returns to the service provider over the 42GHz frequency band via the intermediate CMN. The use of the 42GHz LMDS technology in both the uplink and downlink transmission paths enables symmetric interactivity, providing end-to-end data rates higher than IMbps.
The network performance was evaluated using simulation tests (concerning the network throughput during multimedia services provision over the TCP/IP), the results of which indicated that the proposed architecture provides equal sharing of the system's resources during multiple users access.
Based on the proposed design, this research involves the implementation of a prototype testbed that utilises a single-cell wireless network, incorporating a service provider about 5km away from the CMN, and a number of wireless users, geographically neighbouring the CMN.
The implementation of the prototype system has been deployed in the frame of the E.U. funded project entitled CRABS (Cellular Radio Access for Broadband Services ACTS96/AC215). The service provider broadcasts a bouquet of live digital TV programmes (at a rate of 27.5Msymbols/s) multiplexed with interactive data information via the 42GHz link. All users within the cell receive the digital TV programmes over the 42GHz downlink. Users' requests for the provision of interactive services (i.e. fast Internet access, video/audio on demand) are carried from each user's premises to the CMN in the 2.4GHz band (IEEE 802.11 with frequency hopping) and subsequently to the service provider via a 42GHz uplink, at rates higher than IMbps.
The implemented test-bed makes use of the TCP/IP stack, over which all interactive services are provided. In this respect, the research also involved performance evaluation tests on the test-bed regarding its network throughput. The work also examines the feasibility of the implemented test-bed to distribute non-live MPEG-2 encoded video streams (i.e. video on demand - VoD, audio on demand - AoD) over the TCP/IP stack and elaborates on the tradeoff between encoding rate, picture quality and network throughput. Towards this, a prototype objective picture quality evaluation method was developed, and experimental measurements verified this approach.
The account of the research presented in this thesis is structured as follows: After a brief review and evaluation of relevant and currently available wireless access technologies, the thesis describes the design and the architecture of a prototype wireless broadband interactive access network capable of providing MPEG-2 multimedia services, distribute digital TV broadcasts and enable fast Internet access by converging MMDS and LMDS technologies.
The research then evaluated the proposed design by conducting simulation tests, that concern the sharing of network resources during multimedia services' provision to single and multiple users, and a formula was derived, which provides an accurate estimation of the network throughput (in terms of available bit-rate) that an end-user accommodates, versus the number of concurrent end-users. Subsequently, the research discusses the implementation and evaluation of a prototype network, built according to the design specifications. In this respect, the work elaborated on the network performance during the provision of multimedia services (over the IP stack) for stationary and portable/mobile access by conducting a series of real condition tests (indoor and/or outdoor experiments) that were performed on the prototype network. Comparison of the real condition test-results with those of the simulation tests, confirmed the validity of the proposed design and network architecture and verified the capability of the prototype to distribute efficiently wireless broadband interactive audio-visual services and to share, equally, the network resources among all simultaneous users. The research then investigated the capability of the prototype network to deliver wirelessly (with the unicast method) MPEG-2 encoded video streams over the TCP/IP with satisfactory picture quality. An assessment was then made on the trade-off between picture quality and MPEG-2 video encoding rate, elaborating on the minimum rate that provides for acceptable picture quality. There is an examination of the trade-off between network resources and picture quality, and an evaluation of the minimum network throughput for satisfactory picture quality. Finally the research proposes an objective picture quality evaluation method and defines a threshold below which the picture quality (received by the end-user wirelessly over the TCP/IP stack in a VoD application) is acceptable. Based on this approach, real condition tests were undertaken that confirmed the capability of the proposed network to distribute wirelessly MPEG-2 video on demand streams over the TCP/IP with satisfactory picture quality. The thesis concludes by proposing further opportunities and directions for future exploitation and new configurations, including related topics for future research. |
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