We introduce two novel joint radio-frequency (RF)-baseband designs for receivers in a MIMO system with N t transmit antennas, N r receive antennas, but only L < N r RF chains at the receiver. The joint design introduces an RF preprocessing matrix that processes the signals from the different antennas, and is followed by selection (if necessary), downconversion, and further processing in the baseband. The schemes are similar to conventional antenna selection in that they use fewer RF chains than antenna elements, but achieve superior performance by exploiting the spatial correlation of the received signals. The first of our proposed designs uses an L × N r RF pre-processing matrix that outputs only L streams followed by baseband signal processing, and, thus, eliminates the need for a selection switch. The second one uses an N r × N r RF preprocessing matrix that outputs N r streams and is followed by a switch that selects L streams for baseband signal processing. Both spatial diversity and spatial multiplexing systems are considered and the optimum pre-processing matrices are derived for all cases. To accommodate practical RF design constraints, which prefer a variable phase-shifter-based implementation, a suboptimal phase approximation is also introduced. Performance better than conventional antenna selection and close to the full complexity receiver is observed in both single cluster and multi-cluster wireless channels. A beam-pattern-based geometric intuition is also developed to illustrate the effectiveness of the optimal solutions.

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Abstract-In a vehicular network, every vehicle broadcasts update messages that contain location and speed information periodically to its one hop neighbors. The broadcast efficiency measures the average rate at which a vehicle receives these packets from any of its neighbors. As the node density increases, heightened interference lowers broadcast efficiency if congestion control mechanism is not used. In this paper, we analyze the broadcast efficiency under Rayleigh fading channel, and provide congestion control and power control strategies that maximize the efficiency. A worst-case guaranteed strategy achieving at least 95% of the optimal is also provided for cases when the network nodes have high mobility. Ns-2 simulations show that our analytical results accurately predict the system dynamic.

The new mobile multi-hop relay-based (MMR) network architecture imposes a demanding performance requirement on relay stations. These relays will functionally serve as an aggregating point on behalf of the BS for traffic collection from and distribution to the multiple MSs associated with them, and thus naturally incorporate a notion of "traffic aggregation". However, the packet construction mechanism in IEEE 802.16/16e standard, which was designed for handling traffic solely on a per-connection basis, cannot apply on the relay link directly, as it may render a potential bottleneck and preponderantly limit the overall network capacity. As a solution, we propose two new efficiency-improvement schemes at the MAC layer, namely MPDU concatenation and MSDU aggregation, both of which incarnate the inherent notion of "aggregation" and alleviate the dismal efficiency degradation on the relay links. As confirmed by the performance evaluation, the proposed concatenation and aggregation schemes can achieve significant overhead reduction, and thus better prepare the 802.16e protocol for its adoption in MMR network. IEEE Mobile WiMAX Symposium 2007This work may not be copied or reproduced in whole or in part for any commercial purpose. Permission to copy in whole or in part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of Mitsubishi Electric Research Laboratories, Inc.; an acknowledgment of the authors and individual contributions to the work; and all applicable portions of the copyright notice. Copying, reproduction, or republishing for any other purpose shall require a license with payment of fee to Mitsubishi Electric Research Laboratories, Inc. All rights reserved. Abstract-The new mobile multi-hop relay-based (MMR) network architecture imposes a demanding performance requirement on relay stations. These relays will functionally serve as an aggregating point on behalf of the BS for traffic collection from and distribution to the multiple MSs associated with them, and thus naturally incorporate a notion of "traffic aggregation". However, the packet construction mechanism in IEEE 802.16/16e standard, which was designed for handling traffic solely on a per-connection basis, cannot apply on the relay link directly, as it may render a potential bottleneck and preponderantly limit the overall network capacity. As a solution, we propose two new efficiency-improvement schemes at the MAC layer, namely MPDU concatenation and MSDU aggregation, both of which incarnate the inherent notion of "aggregation" and alleviate the dismal efficiency degradation on the relay links. As confirmed by the performance evaluation, the proposed concatenation and aggregation schemes can achieve significant overhead reduction, and thus better prepare the 802.16e protocol for its adoption in MMR network.