Huan Yao

Lattice-reduction-aided detectors for MIMO communication systems

Lattice-reduction (LR) techniques are developed for enhancing the performance of multiple-input multiple-output (MIMO) digital communication systems. When used in conjunction with traditional linear and nonlinear detectors, LR techniques substantially close the gap to fundamental performance limits with little additional system complexity. Results for individual channels and ensembles are developed, and illustrated in detail for the case of small (2 /spl times/ 2), uncoded, coherent systems. For example, we show that, relative to the maximum likelihood bound, LR techniques get us within 3dB for any Gaussian channel, and allow us to achieve the same diversity on the Rayleigh fading channel, when sufficiently large constellations are used.

Structured space-time block codes with optimal diversity-multiplexing tradeoff and minimum delay

It is well-known that using multiple antennas can substantially increase the data rate and robustness of communication systems in a fading environment. It was recently established that there is a tradeoff between these two types of gains, termed diversity-multiplexing tradeoff. We develop a family of short structured space-time block codes that achieves the optimal tradeoff for the two-transmit two-receive antenna system with the minimum delay of two necessary for optimality. It uses the idea of rotation of cross-diagonal entries of an uncoded system to achieve spreading of information across space and time to obtain the maximum diversity while preserving multiplexing gain. Rotation angles that are optimal in terms of a determinant criterion and universal for all rates are identified. Performance analysis and simulation results are presented to demonstrate the achieved tradeoff.

Dynamic Resource Allocation DAMA Alternatives Study for satellite communications systems

We consider the design of Demand Assigned Multiple Access (DAMA) algorithms that efficiently utilize limited RF uplink resources for packet switched military satellite communication networks. In previous work, we designed DAMA algorithms that optimized link layer efficiency and throughput while controlling delay and jitter. In this work we assess the ability of our DAMA algorithm to meet Service Level Agreements (SLA) between the Network Management System and the terminals. We evaluate the ability of four DAMA algorithms to provide terminals Committed Information Rates (CIR) under various system loading conditions. The designs have increasing levels of confidence in the accuracy of the predicted demand. Results show that although traffic demand cannot be predicted precisely, current demand provides insight into future demands and that this information can be used to more efficiently provide CIR guarantees to terminals.

QoS considerations for future packet switched satellite communication systems with dynamic resource allocation

To efficiently utilize limited RF resources, future packet-switched satellite networks are being designed to dynamically allocate resources on the uplink and downlink. These dynamic-resource allocation algorithms may result in uplinks and downlinks with time varying data rates. Providing QoS over these time varying channels is a difficult task. Several issues are examined including the required interaction between the network layer and link layer, the impact of links with time varying data rates on QoS schedulers, and downlink queuing strategies for achieving downlink QoS

Link-layer dynamic resource allocation for TCP over satellite networks

Future packet switched satellite communication networks are being designed with dynamic resource allocation on the up and down links in order to efficiently utilize the limited RF resources. The resource allocation algorithms must be designed to maximize system efficiency and user performance rather than simply optimizing link layer efficiency. An OPNET simulation environment is used to model and evaluate system performance for a satellite network with dynamically provisioned up and down links under dynamic traffic and channel variations. Link-layer resource allocation algorithms are developed and tested to ensure network layer objectives can be satisfied while maximizing system throughput.

On delay in real-time streaming communication systems

We focus on the problem of real-time streaming over a blockage channel with long feedback delay, as arises in real-time satellite communication from a comm-on-the-move (COTM) terminal. For this problem, we introduce a definition of delay that captures the real-time nature of the problem, which we show grows at least as fast as O(log(k)) for memoryless channels, where k corresponds to the number of packets in the transmission. Moreover, we show that a tradeoff exists between this delay and a natural notion of throughput that captures the bandwidth requirements of the communication. We develop and analyze an efficient “multi-burst” transmission protocol for achieving good delay-throughput tradeoffs within this framework, which we show can be augmented with coding for additional performance gains. Simulations validate the new protocols on channels with and without memory.

Link level ARQ for satellite-mobile communications over blockage channels with memory

We consider communication from a geosynchronous satellite to a mobile ground terminal that suffers from an intermittent channel due to blockages by objects in its environment. Since the blockage has memory and the duration is potentially long, a selective-repeat ARQ scheme is employed to mitigate packet losses. The paper studies the amount of memory required to store packets for retransmission and the amount of delay induced. The blockage channel with memory is modeled by a two-state Markov model. We also assume error-free acknowledgments with a certain delay and Bernoulli arrivals at the satellite of packets intended for a single mobile ground terminal. We derive closed-form expressions for the distributions and averages of both the queue length and the delay. Interpretations are given in terms of how they are affected by channel statistics and design parameters. Numerical examples are given to provide additional intuitions.

Jitter-aware time-frequency Resource Allocation and packing algorithm

One of the main components of the next generation protected military satellite communication systems is Dynamic Bandwidth Resource Allocation (DBRA). A centralized DBRA algorithm on the satellite dynamically grants terminals time and frequency resources as their traffic demands and channel conditions change, leading to significant increase in the overall system throughput.

Network layer performance of a satellite network with dynamic link-layer resource allocation†

Future packet switched military satellite communication networks are being designed with dynamic resource allocation on the up- and down-links in order to efficiently utilize the limited Radio Frequency (RF) resources. The resource allocation algorithms must be designed to achieve good system efficiency and user performance in addition to optimizing link-layer efficiency. An OPNET simulation environment is used to model and evaluate system performance for a satellite network with dynamically provisioned up- and down-links under dynamic traffic and channel variations. Link-layer resource allocation algorithms are developed and performance is evaluated in terms of application layer throughput, loss, delay, and jitter as well as system resource utilization. Copyright

Dynamic Resource Allocation for SATCOM Mobile Terminals in Blockage Environments

To maximize link layer efficiency, future protected military satellite communication networks will be provisioned dynamically as traffic demands and channel conditions vary. As a significant number of terminals supported by the system will be Comm-on-the-Move terminals, which suffer from channel blockage in addition to weather events, dynamic resource allocation requires careful coordination between terminals and the payload. Via an OPNET simulation, protocols that are robust to control message losses yet allow the system to be dynamic and responsive to changes are studied. A transmit-until-acknowledged approach is used for less frequent messages while a periodic-transmit approach is used for more frequent messages. The performance of both constant-rate and TCP-based application traffic in blockage environments over this dynamically allocated network is also evaluated