Existing mobile devices have the capability to use multiple network technologies simultaneously to help increase performance; but they rarely, if at all, effectively use these technologies in parallel. We first present empirical data to help understand the mobile environment when three heterogeneous networks are available to the mobile device (i.e., a WiFi network, WiMax network, and an Iridium satellite network). We then propose a reliable, multi-path protocol called Multi-Path TCP with Network Coding (MPTCP/NC) that utilizes each of these networks in parallel. An analytical model is developed and a mean-field approximation is derived that gives an estimate of the protocol's achievable throughput. Finally, a comparison between MPTCP and MPTCP/NC is presented using both the empirical data and mean-field approximation. Our results show that network coding can provide users in mobile environments a higher quality of service by enabling the use of multiple network technologies and the capability to overcome packet losses due to lossy, wireless network connections.

We design a cross-layer approach to aid in developing a cooperative solution using multi-packet reception (MPR), network coding (NC), and medium access (MAC). We construct a model for the behavior of the IEEE 802.11 MAC protocol and apply it to key small canonical topology components and their larger counterparts. The results obtained from this model match the available experimental results with fidelity. Using this model, we show that fairness allocation by the 802.11 MAC can significantly impede performance; hence, we devise a new MAC that not only substantially improves throughput, but provides fairness to flows of information rather than to nodes. We show that cooperation between NC, MPR, and our new MAC achieves super-additive gains of up to 6.3 times that of routing with the standard 802.11 MAC. Furthermore, we extend the model to analyze our MAC's asymptotic and throughput behaviors as the number of nodes increases or the MPR capability is limited to only a single node. Finally, we show that although network performance is reduced under substantial asymmetry or limited implementation of MPR to a central node, there are some important practical cases, even under these conditions, where MPR, NC, and their combination provide significant gains.

We introduce a novel feedback protocol, called SMART, for wireless broadcast networks that use linear network coding. We consider transmission of packets from a single source to many receivers over a single-hop broadcast erasure channel with heterogeneous links. We propose a predictive model to minimize feedback as well as extraneous data transmissions by the source. In addition, we use the method of types to provide a lower bound for the expected total transmission time, and use simulations to show that our protocol operates close to this lower bound. We show that with SMART, counter to conventional wisdom, the average user's QoE improves slightly as the number of users increases. We demonstrate that SMART's algorithmic simplicity enables multicast transmissions that on average take fewer than 2 feedback rounds to complete. We show the favorable scalability of our technique with the number of users, which enables reliable quality of experience. We also show the robustness of this scheme to uncertainty in the number of receiving nodes, and packet erasure probability, as well as to partial loss of the feedback. Furthermore, we show that SMART performs nearly as well as an omniscient transmitter that requires no feedback.

We present a novel feedback protocol for wireless broadcast networks that utilize linear network coding. We consider transmission of packets from one source to many receivers over a single-hop broadcast erasure channel. Our method utilizes a predictive model to request feedback only when the probability that all receivers have completed decoding is significant. In addition, our proposed NACK-based feedback mechanism enables all receivers to request, within a single time slot, the number of retransmissions needed for successful decoding. We present simulation results as well as analytical results that show the favorable scalability of our technique as the number of receivers, file size, and packet erasure probability increase. We also show the robustness of this scheme to uncertainty in the predictive model, including uncertainty in the number of receiving nodes and the packet erasure probability, as well as to losses of the feedback itself. Our scheme, SMART, is shown to perform nearly as well as an omniscient transmitter that requires no feedback. Furthermore, SMART, is shown to outperform current state of the art methods at any given erasure probability, file size, and numbers of receivers.

We present analytical results characterizing the effects of multipath interference on an FM subcarrier data channel. A closed form expression for the FM discriminator output (or the instantaneous received frequency) is obtained when there are M reflected path signals in addition to the primary path signal. We derive the power spectral density when the multipath interference is weak, and determine the conditions under which multipath interference causes nonlinearities in the instantaneous frequency of the received signal. In order to verify our analytical results, we have built an SPW simulator of HSDS (the high speed data service) system, and we have observed close agreement between our analysis and simulations. The analytical techniques presented could potentially be applied to other FM subcarrier systems, as well as to digital wireless systems that adopt FSK or its variants. Hence, our results could be useful in understanding noncoherent reception of the GSM digital cellular system, for example.

We demonstrate how to calculate the packet traffic density as a function of distance from a central receiver in an ALOHA network with capture parameter /spl alpha/>1. Given a general function for the desired throughput density inside a circle of radius /spl rho/ and boundary conditions, the packet traffic density is derived at all radii less than /spl rho/. The packet traffic density is first obtained in an annulus between radii /spl rho/ and /spl rho///spl alpha/, and then is found in each of a number of successive inner annuli in terms of the solution in the adjacent outer annulus. Applications of this method are illustrated for a few throughput densities, boundary conditions, and capture parameters. Restriction of a class of throughput densities to a region of radius /spl rho/ is shown to be necessary in order to obtain a finite packet traffic density, and an upper bound on /spl rho/ is found in this case.