Max Robert

On the throughput of Bluetooth data transmissions

Analytical expressions for the throughput (in kbit/s) as a function of channel symbol signal-to-noise ratio (E/sub s//N/sub 0/) are derived for the six Bluetooth ACL packets that use automatic repeat request (ARQ). The analysis is exact under the assumptions that the outer CRC code provides perfect error detection and that the channel remains stationary for the duration of each packet. Using an expression for noncoherent correlated (h<0.5) full response FSK signals, numerical results are provided for AWGN and quasi-static Rayleigh fading channels. These curves are an appropriate benchmark against which practical demodulators and custom error control techniques may be compared.

Custom coding, adaptive rate control, and distributed detection for Bluetooth

Three strategies for improving the performance of point-to-point Bluetooth links are presented. All of the strategies are implemented on the host computer, and therefore no modification of the Bluetooth standard is necessary. The first strategy is custom error control coding, which is achieved by transporting BCH codewords within AUX1 packets. The second concept is adaptive rate control, which involves dynamically selecting the packet type that offers the best throughput for the current channel SNR. Finally, a distributed detection technique is proposed, whereby each packet is broadcast to a group of two or more receivers that are linked over a reliable backbone, and the packet is accepted if it is received correctly at any receiver in the group.

Improving the QoS of Bluetooth through turbo coding

Bluetooth has emerged as a viable COTS alternative for military applications involving low power wireless networks, including wireless sensor networks and personal area networks for the foot soldier. However, the reachability of Bluetooth networks is limited by the weak error control coding used by the predefined packets. We propose a method for improving the performance of Bluetooth by using custom error control coding in general, and turbo codes in particular. An important aspect of the proposed technique is that it is compliant with the Bluetooth standard, and therefore requires no hardware modifications. More specifically, the AUX1 user-defined packet is used to transport rate compatible punctured turbo codes (RCPT). The result, as shown by a combination of analytical/simulation results, is a dramatic increase in throughput and decrease in latency at low signal to noise ratios.

Channel frame error rate for Bluetooth in the presence of microwave ovens

In this paper, radiation from microwave ovens is measured using PRISM, a custom-built device designed to measure transmissions in the ISM band. The measured signals, treated as a rising noise floor, are then applied to a semi-analytic simulation to determine the probability of frame error rate (FER) per channel for six Bluetooth packet types.

Design and implementation of a DSP-based MIMO system prototype for real-time demonstration and indoor channel measurements

The design and implementation of the Virginia Tech Space-Time Advanced Radio (VT-STAR), a multiple antenna element space-time (ST) processing prototype testbed, is presented. The testbed is a research tool for comparing practical and theoretical performance metrics (e.g., throughput, link reliability) in different wireless channel conditions. The prototype builds around software-defined radio (SDR) concepts on a DSP platform and provides the flexibility to implement various forms of ST techniques. Different components of the system are described in detail, including the software implementation, I/O schemes with custom hardware, and data transfer mechanisms between the DSP and the host PC. Two different example realizations are presented, a real-time demonstration and an offline measurement tool. Finally, some representative measurement results obtained in indoor environments are presented. These results show VT-STAR to be a promising tool for performing MIMO experiments and generating channel measurements that can complement simulation studies in this area.

Software Frameworks for SDR

This paper describes the state of the art in software frameworks for executing Software Defined Radio (SDR) components. These frameworks are catalyzing drastic changes in signal processing by enabling software engineers and signal processing engineers to work in tandem on core challenges, such as effectively processing large amounts of data in real-time on limited hardware resources. In addition to a historical perspective of this area, we showcase the REDHAWK framework as an example of a modern SDR framework which provides many facilities for distributed SDR deployment.

Reduced complexity MIMO processing for WLAN (IEEE 802.11b) applications

In this paper, we propose and evaluate a reduced complexity multiple-input-multiple-output (MIMO) system to enhance signal to noise ratio (SNR) and throughput of a WLAN system. The algorithm is based on phase scanning at the transmitter side and maximal ratio combining (MRC) at the receiver side with feedback from the receiver to assist in setting the optimal phase value at the transmitter. This feedback channel is available in the IEEE 802.11b standard, and thus, the proposed algorithm introduces minor modifications to the existing air interface. Simulation results show that the proposed technique increases the throughput sustainability of an 802.11b system.

Software design issues in networks with software-defined-radio nodes

The concept of a software-defined-radio (SDR) has been of considerable academic and industrial interest for several years. SDR allows a radio to be described by its software; thus, a single radio can change its operation to suit the current needs of the system. A parallel trend in wireless technology is the integration of multiple types of nodes into a single network. The challenges associated with a network absorbing multiple types of nodes, each with different quality-of-service (QoS) attributes, are significantly increased when the nodes in the network can be reconfigured in real-time. Issues in object-oriented development are presented, and tradeoffs in design are considered. Radio system designers in the future will need to address not only link-level issues, but, to produce SDR that is easily integrated into a larger infrastructure, will also need to take into consideration the larger network issues.

Statistical back-off method for minimizing interference among distinct network technologies

With the advent of new networking technology operating over license-free bands such as Bluetooth, IEEE 802.11, and HomeRF, network co-existence has become an issue of great concern. This paper presents a method to reduce the interference issue by applying a statistical backoff algorithm to some of the devices in the network. This algorithm modifies the traffic transmitted by devices such that they transmit only when the probability of collision with other systems is lowest. An analytical description of the interference conditions of the channel can then be applied to the device queue to minimize the probability of collision. Simulation results show that, depending on the traffic model selected, this algorithm can provide increases in power efficiency while creating decreases in throughput that are dependent on the selected traffic model.

Role of signal envelope distribution in predicting the performance of a multicarrier communication system

The peak-to-average power ratio of a signal is often used to determine the output power backoff needed to prevent spectral regrowth due the effects of nonlinear power amplifiers. It has been suggested that a better measure of the impact of a nonlinear amplifier on the transmitted signal is the envelope power distribution function. This paper presents simulation results for a multicarrier communication system showing how the peak-to-average power ratio and the envelope power distribution function change as the number of carriers increases, these results show that the envelope power distribution function is a better figure of merit than the peak-to-average power ratio for determining the impact of a nonlinear power amplifier on a communication systems BER.