Abstract:We propose a parameterized modeling technique for wireless relay networks based on IEEE 802.16j standard operating in nontransparent mode. Our modeling is able to represent the downlink throughput in a concise closed form and thus very useful for predicting the downlink system throughput with a few estimated parameters. The key parameters include α which represents how much portion of the whole data from MR-BS to be transmitted over access link without going through relays (0 ≤ α ≤ 1). Another key parameter is r, which determines how much portion of DL (down link) zone is used for access (0 ≤ r ≤ 1). We also add a parameter θ i , which determines how much portion of the data to be relayed via RSi (0 ≤ θ i ≤ 1). Our contribution lies in that our formula can be used to estimate the expected downlink system throughput without going through extensive simulation in the early design stage for IEEE 802.16j relay systems. Optimization can be easily performed using our formula.

SummaryWe propose a robust end-to-end loss differentiation scheme to identify the packet losses due to congestion for TCP connections over wired/wireless networks. We use the measured RTT values in determining whether the cause of packet loss is due to congestion over wired path or regular bit errors over wireless paths. The classification should be as accurate as possible to achieve high throughput and maximum fairness for the TCP connections sharing the wired/wireless paths. The accuracies of previous schemes in the literature depends on varying network parameters such as RTT, buffer size, amount of cross traffic, wireless loss rate and congestion loss rate. The proposed scheme is robust in that the accuracy remains rather stable under varying network parameters. The basic idea behind our scheme is to set the threshold for the classification to be a function of the minimum RTT and the current sample RTT, so that it may automatically adapt itself to current congestion level. When the congestion level of the path is estimated to be low, the threshold for a packet loss to be classified as a congestion loss is increased. This avoids unnecessary halving of the congestion window on packet loss due to regular bit errors over wireless path and hence improves the TCP throughput. When the congestion level of the path is estimated to be high, the threshold for a packet loss to be classified as a congestion loss not to miss any congestion loss is decreased and hence improves the TCP fairness. In our ns 2 simulations, the proposed scheme correctly classifies the congestion losses under varying network parameters while previous schemes show some dependency on subsets of parameters.

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