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Abstract-We consider a multicast resource allocation problem for the downlink in OFDM-based wireless cellular network systems. In a conventional multicast system, to accommodate users with bad channel conditions, the transmission is based on the worst case user. We show that such a multicast system saturates the capacity when the number of users increases in fading environments. We exploit the multicarrier nature of OFDM and advances in coding techniques such as MDC (multiple description coding), in which arbitrary combinations of layers can be decoded at the receiver. Different MDC layers are carried over different subcarriers and users with good channels receive data from more subcarriers than users with poor channel conditions. We present an optimal subcarrier/bit allocation method requiring full search of possible candidates. To reduce the complexity, we propose a two-step suboptimum algorithm by separating subcarrier allocation and bit loading. Numerical results show that the proposed heuristics significantly outperform the conventional multicast transmission scheme. The difference between optimum and heuristic solutions is less than 5%.

Abstract-This paper compares, through analysis and simulation, a number of multichannel MAC protocols. We first classify these protocols into four categories based on their principles of operation: Dedicated Control Channel, Common Hopping, Split Phase, and Parallel Rendezvous protocols. We then examine the effects of the number of channels and devices, channel switching times, and traffic patterns on the throughput and delay of the protocols. Here are some of the conclusions of our study: 1) Parallel Rendezvous protocols generally perform better than Single Rendezvous protocols, 2) the Dedicated Control Channel protocol can be a good approach with its simplicity when the number of channels is high and the packets are long, and 3) the Split Phase protocol is very sensitive to the durations of the control and data phases. Our study focuses on a single collision domain.

Abstract-Many multiple channel MAC protocols for wireless networks have been proposed to make efficient use of multiple channels where each node has a single radio which allows it to send or receive on one channel at a time. However, most of the proposed protocols are single rendezvous protocols that are subject to the congestion of the control channel. We propose a new parallel rendezvous protocol, McMAC, to avoid control channel congestion so that it can scale to use a large number of channels efficiently. We validate our protocol design using simulation and implementation.