Seamless Dynamic Runtime Reconfiguration in a Software-Defined Radio

We discuss implementation aspects of a software-defined radio system that allows for dynamic waveform reconfiguration during runtime without interrupting data-flow processing. Traditional software-defined radio systems execute a waveform statically, exactly as it is programmed. Reconfiguration is provided by executing a different waveform, which requires the system to stop processing data while reconfiguration occurs, and also may incur an unacceptable delay for some applications. Recent research has demonstrated basic reconfiguration by programming multiple branches into a waveform and dynamically switching between branches. This technique requires redundant resources and in general cannot be expanded to encompass all possible waveforms of interest, but, if implemented carefully, could be made to seamlessly process data. We propose a system that allows for dynamic insertion and removal of entire waveforms, individual constituent blocks, and block algorithm implementations tailored to specific processors. Our system performs this reconfiguration while maintaining processing state, seamlessly without interrupting data-processing, and with only the resources necessary for the given waveform and processors. In order to leverage this new level of reconfigurability, we created a new system component: a supervisor. This system supervisor monitors the state of each processor and waveform execution, and moves computations among available processors as their loads, capabilities, and block algorithm implementations allow. An example using a simple supervisor is provided to demonstrate the effectiveness of our system.     

Wideband distributed spectrum sharing with multichannel immediate multiple access

This paper describes a radio architecture for distributed spectrum sharing of multiple channels among secondary users (SUs) in a wide band of frequencies and a localized area. A novel multichannel immediate multiple access (MIMA) physical layer is developed such that each SU can monitor all the channels simultaneously for incoming signals and achieve fast rendezvous within the multiple channels. The spectrum utilized by an SU pair can be changed dynamically based upon spectrum sensing at the transmitter and tracking synchronization and control messages at the receiver. Although information about the number of active SUs can be used to improve the spectrum sharing efficiency, the improvement is small relative to the cost of obtaining such information. Therefore, the architecture adopts multichannel carrier sense multiple access for medium access control regardless of the number of active SUs. A prototype implementation of the architecture has been developed using an advanced software defined radio platform. System tests demonstrate that the spectrum sharing efficiency of the prototype is close to an upper bound if the signal-to-noise ratio is sufficiently high. Among other practical issues, imaged interference caused by hardware IQ imbalance limits system performance. In the prototype, the MIMA is based on an LTE waveform. Therefore, the spectrum sharing radio can be potentially applied to the 3.5 GHz radar band for citizens broadband radio service (CBRS).     

Asymmetric hydrogenations of diketopiperazines

The dehydrodiketopiperazines 6 undergo face selective hydrogenation with a 5% palladium on carbon catalyst to give the diketopiperazines 7 in high yield with excellent diastereoisomeric ratios (>97%). This revised version was published online in June 2006 with corrections to the Cover Date.     

Cognitive Legacy Networks via Cooperative Diversity

In this letter, we deal with the cognitive radio (CR) concept for legacy primary links optimized for non-interference surroundings. In this type of network, primary destinations are not able to deal with possible interference and a missed cognitive detection significantly reduces the system performance. The enhancement of the primary network with cooperative diversity in addition to the well-known diversity gain for the primary link improves the sensing ability of the system and protects the primary user from possible interference. The proposed solution provides CR benefits without complicated network modifications and seems to be an attractive solution for future legacy networks.     

Distributed space-time-coded protocols for exploiting cooperative diversity in wireless networks

We develop and analyze space-time coded cooperative diversity protocols for combating multipath fading across multiple protocol layers in a wireless network. The protocols exploit spatial diversity available among a collection of distributed terminals that relay messages for one another in such a manner that the destination terminal can average the fading, even though it is unknown a priori which terminals will be involved. In particular, a source initiates transmission to its destination, and many relays potentially receive the transmission. Those terminals that can fully decode the transmission utilize a space-time code to cooperatively relay to the destination. We demonstrate that these protocols achieve full spatial diversity in the number of cooperating terminals, not just the number of decoding relays, and can be used effectively for higher spectral efficiencies than repetition-based schemes. We discuss issues related to space-time code design for these protocols, emphasizing codes that readily allow for appealing distributed versions.     

Benefits of Spatial Correlation for Multi-Antenna Non-Coherent Communication over Fading Channels at Low SNR

For fading channels without channel state information (CSI) at the transmitter or the receiver, fundamental challenges arise for realizing efficient communication, especially under stringent constraints on average and peak input powers. To mitigate these challenges, in this paper we investigate the benefits of spatial correlation among multiple transmit and receive antennas. Based upon asymptotic analyses, we first show that spatially correlated antennas lead to both multiplicative rate gain as well as peak power reduction, at no cost of additional transmit power. Then we turn to a simple communication scheme employing on-off signaling with hard-decision demodulation. For this low-complexity scheme, we demonstrate that most of the benefits promised by the asymptotic analyses are realizable     

Improving control performance across AWGN channels using a relay node†

Consider an unstable linear time-invariant system in which the sensor transmits information to a controller across an additive white Gaussian noise channel. The designer can optionally utilise a relay node to assist the controller; however, the total transmission power consumed by the sensor and the relay node is constant. We consider two topologies: (1) a Gaussian relay channel and (2) a cascade of two Gaussian point-to-point channels. We propose coding schemes and present sufficient conditions for the stabilisability of the plant through such schemes. The analysis suggests that it is useful to utilise a relay node, even if the total transmission power remains the same.