Medium Access Control Protocol for HFC and LMDS Headends and Terminals
Ying-Dar Lin
Mentor Data Inc.
Local Multi-point Distribution Systems, Digital Video
Broadcasting, time slots, upstream channel, bandwidth scheduling, collision
resolution, Quality of Services
Local multi-point distribution systems (LMDS) has large bandwidth, say
1GHz, and its system establishment cost is low. Therefore, LMDS is likely to
be the promising delivery system of the broadband internet. Digital video
broadcasting (DVB), thus, initiated a working group for specifying the
physical (PHY) layer and media access control (MAC) layer of the air interface
of such fixed point-to-multipoint access systems. In MAC layer, both
upstream channels and downstream channels are framed and further slotted
within a frame. In this slotted-framed architecture, each active RF modem must
synchronize with the base station, so that the transmitted packet could arrive
the base station at the right time with an acceptable power level. Three major
access modes, contention-based access, fixed rate access, and reservation
access, are provided in this system. In addition, the base station
centrally controls the bandwidth allocation. Notably, in the contention access
area, the transmission is subject to collision; thus, a collision resolution
mechanism is necessary.
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For above mechanisms, which cause no harm on interoperability, the
standard left the design issues open. Actually, how the mechanisms are
designed highly effects the performance of LMDS system. In this work, the
issues are further studied as follows: (1) propose an efficient collision
resolution mechanism to optimize the packet throughput as well as decrease the
packet access delay, (2) give recommendations for allocating right number
of collision resolution engines under different packet arrival rates, and (3)
design a bandwidth scheduling algorithm, so that the QoS of integrated
services could be achieved. Afterwards, we are expected to control and
facilitate the wireless broadband network.