Backpressure-based adaptive routing algorithms where each packet is routed along a possibly different path have been extensively studied in the literature. However, such algorithms typically result in poor delay performance and involve high implementation complexity. In this paper, we develop a new adaptive routing algorithm built upon the widely-studied back-pressure algorithm. We decouple the routing and scheduling components of the algorithm by designing a probabilistic routing table which is used to route packets to per-destination queues. The scheduling decisions in the case of wireless networks are made using counters called shadow queues. The results are also extended to the case of networks which employ simple forms of network coding. In that case, our algorithm provides a low-complexity solution to optimally exploit the routing-coding tradeoff.

Multi-user MIMO downlink scenario has been paid considerable attentions in recent years for its potential large capacity. However, when there are not enough antennas at the transmitter, making all the users available may not be a good solution. The situation can be improved by selecting the right users among all users at the receiver and meanwhile a maximum capacity can be achieved. In this paper, we use the correlation of channel matrices of users and develop an algorithm to select the right users with low complexity to achieve the total capacity of the whole system. Moreover, we design a strategy to adaptively select receive antennas of users at the receiver which can further increase the capacity of the MIMO system.

We consider small generalized switches with less than or equal to four links, and study scheduling policies designed to minimize the total number of packets in the system. By focusing on very small switches, we are able to derive optimal or heavy-traffic optimal policies whose performance can then be compared to previously conjectured optimal policies. In particular, it has been conjectured that the max-weight policy with weight q α is optimal in heavy-traffic when α → 0. Our results show that this conjecture is not true.

No abstract