James A. Norris

An investigation of phase pulse shape diversity to generate parallel branches, increase data rate, and reduce the complexity of CPM modulation

Continuous phase modulation is a well understood modulation scheme which utilizes a constant envelope signal with inherent memory to create a bandwidth efficient waveform. The pulse shapes defined for CPM modulation influence the bandwidth, demodulation complexity, and power efficiency and can be spread across multiple symbols. This paper investigates a novel modulation scheme that is comprised of a family of pulse shapes which add parallel branches to the existing CPM trellis. The resulting modulation scheme maintains the power efficiency of the underlying modulation while increasing the data rate of the waveform. The spectral efficiency is not affected by the increase in data rate while the receiver complexity is reduced. The first part of the paper outlines the standard CPM modulation and a pair of complementary (non-orthogonal) phase pulse shapes is presented. The corresponding effect on bandwidth, power efficiency, and receiver complexity is analyzed and the advantages of this modulation technique are discussed. Then, a novel methodology for generating a family of optimal pulse shapes is discussed and various generation methods are compared. The spectral and power efficiencies of the resulting M-ary waveform are then compared to an equivalent, standard CPFSK modulation.

Evaluation of a novel Constant Envelope Spread-Spectrum Modulation technique

Constant envelope, spread spectrum modulation is highly desirable for low-power, battery-operated systems - but only if the cost of any increase in receiver complexity or reduction in bit error rate performance is offset by a realizable reduction in either the transmit power or DC power requirements for the system. This paper defines and analyzes a novel approach to a constant envelope spread spectrum modulation type and provides an analysis of the complexity and performance of the modulation scheme. The hybrid continuous phase modulation (CPM) waveform is a constant-envelope modulation that provides an inherent phase and frequency diversity which has similar properties to the standard spread-spectrum m-PSK DSSS modulation. The performance in AWGN, multipath, and a severe interference environment is provided and compared to a simple example of random PN spread-spectrum BPSK modulation and a gold-code spread MSK modulation - both modulation schemes with a similar receiver complexity as the hybrid CPM modulation scheme.

Performance of MIL-STD-188-181C CPM SATCOM with Reduced State Demodulation

The continuous phase modulation (CPM) waveform defined in the MIL-STD-188-181C satellite communications standard has a thirty-two state trellis structure. The complexity of the maximum-likelihood sequence estimator used to demodulate this signal is further increased because the CPM signal has two modulation indices (h-values) that require that the decoder store two sets of path metrics-one for each of the h-values. This paper describes a set of approaches which can be taken to reduce the complexity of the trellis structure of the CPM signal without significantly reducing the demodulation performance for the range of signal to noise ratio values required by the UHF Satellite Communications standard. The first state reduction method uses Ungerboeck-style set partitioning. The resulting decoder structure is described and the performance of the reduced state decoder is provided. Another approach utilizes a completely different 4-state trellis structure with branch transitions defined that take advantage of the differential properties of the CPM modulation

Methods of Detection of Bandlimited Signals on UHF MILSATCOM Downlinks

Providing satellite terminals with an indication of whether or not traffic is present on the downlink of an ultra high frequency (UHF) military satellite communications (MILSATCOM) channel requires consideration not needed for terrestrial radio systems. The UHF satellite transponder contains a bandpass filter and a hard-limiting amplifier that results in a constant downlink power level regardless of the uplink signal level. Therefore, its not possible to rely on a simple metric such as the receive signal strength (RSS) to tell whether or not traffic is present on the channel. Additionally, symbol rate, timing and frequency characteristic metrics may fail to detect signals of unknown modulation or bandwidth. This paper will explore three different carrier detection schemes useful for collision avoidance on a UHF MILSATCOM channel. These methods are directly applicable to a satellite communication system where transmission is uncoordinated and multiple modulation types may be present (for example, MIL-STD-188-181C single-access mode). The modulation agnostic characteristic of these methods also lends them to applications to other fields such as cognitive radio.

Endoscopic laser range scanner for minimally invasive, image guided kidney surgery

Image guided surgery (IGS) has led to significant advances in surgical procedures and outcomes. Endoscopic IGS is hindered, however, by the lack of suitable intraoperative scanning technology for registration with preoperative tomographic image data. This paper describes implementation of an endoscopic laser range scanner (eLRS) system for accurate, intraoperative mapping of the kidney surface, registration of the measured kidney surface with preoperative tomographic images, and interactive image-based surgical guidance for subsurface lesion targeting. The eLRS comprises a standard stereo endoscope coupled to a steerable laser, which scans a laser fan beam across the kidney surface, and a high-speed color camera, which records the laser-illuminated pixel locations on the kidney. Through calibrated triangulation, a dense set of 3-D surface coordinates are determined. At maximum resolution, the eLRS acquires over 300,000 surface points in less than 15 seconds. Lower resolution scans of 27,500 points are acquired in one second. Measurement accuracy of the eLRS, determined through scanning of reference planar and spherical phantoms, is estimated to be 0.38 ± 0.27 mm at a range of 2 to 6 cm. Registration of the scanned kidney surface with preoperative image data is achieved using a modified iterative closest point algorithm. Surgical guidance is provided through graphical overlay of the boundaries of subsurface lesions, vasculature, ducts, and other renal structures labeled in the CT or MR images, onto the eLRS camera image. Depth to these subsurface targets is also displayed. Proof of clinical feasibility has been established in an explanted perfused porcine kidney experiment.

Quasi-coherent performance of convolutionally-coded continuous phase modulation

Continuous Phase Modulation (CPM) schemes are advantageous for low-power radios. The constant envelope transmit signal is more efficient for both linear and non-linear amplifier architectures. A standard, coherent CPM receiver can take advantage of modulation memory and is more complex than a coherent Phase Shift Keyed receiver. But the CPM signal can be demodulated non-coherently and still take advantage of the trellis structure inherent in the modulation. With this complexity reduction, the CPM receiver is comparable in performance to a Phase Shift Keyed radio with the power utilization of a Frequency Shift-Keyed design. In this paper, we discuss two methods for increasing the modulation memory of the CPM signal. In the first method, the distribution of the transmitted symbol across multiple phase pulses is investigated and the bit error rate analyzed. In the next method we address the addition of convolutioncodes. In both cases the effects of the CPM memory to quasi-coherent demodulation is analyzed and discussed. The differences in complexity will be analyzed and the overall performance enhancements of several different modulation schemes will be illustrated. 1

Anatomically correct deformable colon phantom

We describe a technique to build a soft-walled colon phantom that provides realistic lumen anatomy in computed tomography (CT) images. The technique begins with the geometry of a human colon measured during CT colonography (CTC). The three-dimensional air-filled colonic lumen is segmented and then replicated using stereolithography (SLA). The rigid SLA model includes large-scale features (e.g., haustral folds and tenia coli bands) down to small-scale features (e.g., a small pedunculated polyp). Since the rigid model represents the internal air-filled volume, a highly-pliable silicone polymer is painted onto the rigid model. This thin layer of silicone, when removed, becomes the colon wall. Small 3 mm diameter glass beads are affixed to the outer wall. These glass beads show up with high intensity in CT scans and provide a ground truth for evaluating performance of algorithms designed to register prone and supine CTC data sets. After curing, the silicone colon wall is peeled off the rigid model. The resulting colon phantom is filled with air and submerged in a water bath. CT images and intraluminal fly-through reconstructions from CTC scans of the colon phantom are compared against patient data to demonstrate the ability of the phantom to simulate a human colon.

Application and analysis of rake receiver to hybrid CPM modulation

Constant Envelope, Spread Spectrum Modulation is highly desirable for low-power, battery-operated systems. It has been demonstrated that Hybrid CPM is a constant envelope modulation with similar frequency diversity properties to the standard spread-spectrum m-PSK DSSS and spread-MSK modulation schemes while retaining a superior emissions profile. This paper continues the analysis of the novel constant envelope spread spectrum modulation technique with an analysis of the commonly utilized rake receiver signal processing. Initially, a simple channel model is developed to illustrate and compare the convergence of the channel estimate over a fixed, non-time-varying channel. A more complex, wireless channel model is then developed and a new corresponding method for channel estimation created. A Monte- Carlo simulated bit error rate performance of Hybrid CPM is then generated to evaluate the overall performance of the Hybrid CPM modulation scheme.

On the use of orthogonal signals to generate parallel branches and improve the spectral efficiency of CPM and TCM modulation

Continuous phase modulation (CPM) and trellis-coded modulation are well-understood schemes that layer trellis codes with multilevel modulation to produce efficient bandwidth waveforms. This paper describes a novel modulation scheme which takes advantage of existing trellis codes and adds parallel branches to create a new modulation with greater spectral efficiency and reduced receiver complexity. The first part of the paper discusses the trade-off between Euclidean distance and modulation bandwidth for the standard 1-REC CPM waveform. A set of orthogonal signals can be added to the CPM constellation which provides a series of parallel branches in the natural trellis structure of the CPM modulation. The corresponding bandwidth expansion and throughput improvement is analyzed and the advantages of this modulation technique are discussed. This new, non-constant envelope CPM waveform is compared to the multi-level, multi-amplitude CPM waveform (described in Proakis). In similar fashion, a trellis-coded, shaped PSK modulation is expanded to include orthogonal signal shaping and the power and spectral efficiencies are discussed.

A new UHF narrowband satellite communications PHY layer for HPW

The High Performance Waveform (HPW) was developed before parallel concatenated codes (PCCC) and serial concatenated codes (SCCC) were in wide use and so it makes sense to take advantage of the advancements in communication theory and processor computation speed that have taken place since its inception. In its current form, HPW transmits a Raised-Cosine Continuous Phase Modulation (1RC CPM) modulation with a trellis code that is designed to provide, with the use of a Cyclic Redundancy Check Code error detection (CRC), error free transmission over a single, narrowband UHF satellite communications channel. In this paper we present an additional set of coding and modulation schemes which take advantage of serial concatenated code (SCCC) technology to simultaneously improve throughput at the lower end of the signal-to-noise ratio (SNR) range while increasing the highest throughput at the highest SNR available on UHF satellites. The overall bit error rate and throughput of each individual modulation type is analyzed and the framework for the adaptive modulation protocol is provided. To provide for a gradual release of a newer revision of HPW, a framework for a PHY layer is provided which will allow a heterogeneous network of legacy and updated radio terminals.