Quentin Spencer - Academia.edu (original) (raw)

Papers by Quentin Spencer

IEEE Globecom 2006, 2006

This paper proposes a method for correcting errors in messages encoded using cyclic redundancy ch... more This paper proposes a method for correcting errors in messages encoded using cyclic redundancy checks (CRCs), which are typically only used for error detection. This is accomplished for messages of a known length by deriving a parity-check matrix representation of the CRC. The parity-check matrix can then be used to correct errors using the message-passing decoder (MPD) commonly used to decode LDPC codes. The CRC parity-check matrix is not sparse, which inhibits performance of the MPD, but this effect can be reduced by modifying the matrix using recently proposed sparsification techniques to eliminate short cycles. The technique is practical mainly for codes with short block sizes, and can also be applied to coding schemes that concatenate a CRC with an outer error correcting code. Simulation results demonstrate some performance gains, although less than what can be gained using custom-designed LDPC codes for the same rate and message length.

International Symposium on Power Line Communications and Its Applications, Apr 2, 2008

Abstract The current trend in the electric utility industry is toward time-varying pricing models... more Abstract The current trend in the electric utility industry is toward time-varying pricing models where the price varies with demand. This requires automated meter reading (AMR) systems that can obtain accurate data about the consumption of electricity over relatively short intervals, which requires that AMR systems have increasingly higher bandwidth and make more efficient use of available bandwidth. Efficiency of existing AMR technologies can be improved by the use of data compression. Based on data from a large number of electric ...

International Symposium on Power Line Communications and Its Applications, 2005., 2005

Abstract The TWACS power-line communication system is used by electric utilities for communicatin... more Abstract The TWACS power-line communication system is used by electric utilities for communicating over long distances with power meters and other devices. Data packets tend to be short, and increasing demand for bandwidth requires that error detection and correction add minimal overhead. We have investigated low-density parity-check (LDPC) codes as a replacement for the existing error control coding scheme. In this paper we investigate the error detection capabilities of LDPC codes with high rate and short block ...

2003 IEEE 58th Vehicular Technology Conference. VTC 2003-Fall (IEEE Cat. No.03CH37484), 2003

In this paper, we consider a multiuser communication network where all the nodes in the network a... more In this paper, we consider a multiuser communication network where all the nodes in the network are equipped with multiple antennas and different users are identified through their spatial signatures. We present some results on the capacity of such networks. We consider two cases of interest: (i) when the transmitter (the base) has full knowledge of the channel state information (CSI) between itself and the receiving nodes (users); and (ii) when the base does not have CSI, but it does know which users currently have the best channel (e.g., measured in terms of a condition number). In the first case, we establish coordinated beamforming between the base and a number of users to whom data is to be transmitted. In the second case, partial knowledge of the quality of the users' channels will be used to transmit data to the users with better channel condition, without performing any beamforming at the base. In both cases, the base transmits independent data streams to multiple users. This will guarantee a higher minimum quality of service for all the users compared to the case where the user with best channel is selected and all the available capacity is devoted to it. In addition, as we will show, this approach may increase the overall capacity/throughput of the network.

International Conference on Acoustics, Speech, and Signal Processing, 2003

In the downlink of a multi-user MIMO (multiple input multiple output) communication system where ... more In the downlink of a multi-user MIMO (multiple input multiple output) communication system where each user has an arbitrary QoS requirement, intelligent algorithms are needed to choose transmit vectors. Here we present a new method of choosing transmit vectors that minimizes total transmitted power. The approach is based on previous iterative interference balancing algorithms, but it is initialized by applying

2001 IEEE International Conference on Acoustics, Speech, and Signal Processing. Proceedings (Cat. No.01CH37221)

A statistical space-time model for indoor wireless propagation based on empirical measurements is... more A statistical space-time model for indoor wireless propagation based on empirical measurements is compared with results from the deterministic ray-tracing simulation tool WiSE for the same environment. Excellent agreement is found in terms of the distributions of arrival times and angular spread for both modeling approaches. The WiSE package is also use to synthesize MIMO channel matrices and determine the theoretical capacity available in the tested environments. It is found that, for narrowband channels, the spatial clustering of the multipaths limits the capacity gains associated with increased array size.

IEEE Antennas and Propagation Society International Symposium, 1999

The use of space-division multiple access (SDMA) in the downlink of a multi-user MIMO wireless co... more The use of space-division multiple access (SDMA) in the downlink of a multi-user MIMO wireless communicationsnetwork can provide a substantial gain in system throughput. The challenge in such multi-user systems is designingtransmit vectors while considering the co-channel interference of other users. Typical optimization problems of interestinclude the capacity problem: maximizing the sum information rate subject to a power constraint, or the power controlproblem: minimize transmitted power such that a certain quality-of-service ...

Improvements in the detection of TWACS outbound message signals. A first improvement involves mat... more Improvements in the detection of TWACS outbound message signals. A first improvement involves matching some (or all) of the intermediate points in an outbound preamble occurring between bits of the preamble currently being detected. This reduces the possibility of a false synchronization and therefore decreases the probability of missing outbound message signals. A second improvement is to require some or all of the known preamble bits to exceed a predetermined threshold where both the thresh-old and which bits are ...

Complete Patent Searching Database and Patent Data Analytics Services.

A method for producing a set of inbound pulse patterns and detection vectors for lengths longer t... more A method for producing a set of inbound pulse patterns and detection vectors for lengths longer than 4 cycles in an AC waveform. These are used for generating inbound messages in a two-way automatic communication system (TWACS). The method uses Hadamard matrices adapted to generate a set of detection vectors by permuting rows of a matrix and removing certain columns of the matrix to meet system design requirements. The method can be extended to any length and modified to accommodate multiple pulses per half- ...

A method of data compression for use in a data communication's system for an electrical util... more A method of data compression for use in a data communication's system for an electrical utility or the like to affect the most efficient transfer of data. The data is first formed into a forming a block (B). A parameter (M) is selected from among a group of parameters. Each data value in the block is divided by the selected parameter to produce, for each data value, a quotient (q=└ n/M┘) and a remainder (r= n− qM). The quotient of each data value is encoded using unary coding in which the value for the quotient is encoded by transmitting ...

Abstract: A method of detecting a signal transmitted over one phase of a multi-phase power distri... more Abstract: A method of detecting a signal transmitted over one phase of a multi-phase power distribution system, components of the signal concurrently appearing on all phases of the system. The method includes detecting the components of each signal appearing on each phase, including neutral, of the system. Detected signals are provided to a signal processor which processes them to produce a detected signal which is a composite of all the components. The signals are combined by a weighted summation scheme that takes into ...

A “super-fast” polling method for electrical meters for outage detection. In response to a query,... more A “super-fast” polling method for electrical meters for outage detection. In response to a query, a large group of electric meters (M) all simultaneously transmit reply signals over an electrical distribution network using TWACS®. The signals are separated by an inbound detector (IB) at a receiving end of the network. This allows a very large number of meters to be polled in a very short period of time to determine whether or not an outage has occurred at the location of each meter. Each meter transmits a bit pattern, and bit patterns are ...

A method of correcting errors in a message transmitted over a digital communication channel, wher... more A method of correcting errors in a message transmitted over a digital communication channel, where the message was encoded using a CRC for purposes of error detection. A parity-check matrix representation of the CRC is computed for any fixed-length message, and that parity-check matrix is combined with the parity-check matrix for any error correcting code that used in conjunction with the CRC. The combined parity-check matrix is extended using sparsification algorithms to allow it to work well under a message passing decoder ( ...

BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the disserta... more BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the dissertation of Quentin H. Spencer in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university and department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the graduate committee and is ready for submission to the university library. Date A. Lee Swindlehurst Chair, Graduate Committee

A set of irregular LDPC (Low Density Parity Check) codes having a pseudo-random structure and low... more A set of irregular LDPC (Low Density Parity Check) codes having a pseudo-random structure and low encoding complexity. A block-cyclic LDPC code has an irregular row or an irregular column weight and includes a parity check matrix and an encoding matrix each of which has a pseudo-random structure. This allows the code to have the irregular row weight or irregular column weight together with an overall randomness to the code structure. Blocks within the code can be shortened, adjacent blocks of code can be overlapped, and ...

In this paper, we consider a multiuser communicationnetwork where all the nodes in the network ar... more In this paper, we consider a multiuser communicationnetwork where all the nodes in the network are equippedwith multiple antennas and different users are identified throughtheir spatial signatures. We present some results on the capacityof such networks. We consider two cases of interest:(i) when thetransmitter (the base) has full knowledge of the channel stateinformation (CSI) between itself and the receiving nodes (users); and (ii) when the base does not have CSI, but it does know whichusers currently have the best channel (eg, ...

Vehicular Technology Conference Fall 2000. IEEE VTS Fall VTC2000. 52nd Vehicular Technology Conference (Cat. No.00CH37152)

Recent research has demonstrated that the capacity of a multipath-rich channel (such as indoors) ... more Recent research has demonstrated that the capacity of a multipath-rich channel (such as indoors) is dramatically increased when antenna arrays are used at both transmitter and receiver. This is achieved by using the multipath to create parallel sub-channels. This ability to achieve parallelism in the channel is influenced by how much information about the channel is known at the transmitter, the structure of the channel, and the structure of the arrays. This paper discusses the influence of the transmitter's knowledge of the channel on capacity, presents closed-form solutions for capacity when there are two paths in the channel, and then presents numerical results based on simulations. For the two-path case, the simulation data compare capacity based on differing assumptions about the transmitter, and compare different array structures. Simulation results are also presented for random channels generated using a statistical model for indoor multipath propagation.