A.B. Cooper

Nearly optimal multiuser codes for the binary adder channel

Coding schemes for the T-user binary adder channel are investigated. Recursive constructions are given for two families of mixed-rate, multiuser codes. It is shown that these basic codes can be combined by time-sharing to yield codes approaching most rates in the T-user capacity region. In particular, the best codes constructed herein achieve a sum-rate, R/sub 1/+...+R/sub T/, which is higher than all previously reported codes for almost every T and is within 0.547-bit-per-channel use of the information-theoretic limit. Extensions to a T-user, Q-frequency adder channel are also discussed.

Phase and Polarization Diversity for Minimum MAI in OCDMA Networks

A novel coherent optical code-division multiple-access (OCDMA) network based on spectral phase coding and on phase and polarization diversity balanced reception is proposed. A rigorous model of the network is developed, which shows that spectral efficiencies of 1 bps/Hz and beyond can be achieved by minimizing multiple-access interference (MAI) and by canceling beat noise. While the system achieves full capacity under bit synchronism, it also offers competitive performance at up to 25% of full capacity, even when completely asynchronous. Tree and ring network configurations assure synchronization, making the proposed system robust in the presence of dispersion and phase noise.

ASSIST - Automated System for Surgical Instrument and Sponge Tracking

Every surgical item used during surgery (e.g., sponges) must be accounted for after surgery to ensure that none of these items is left inside the patient. Despite the numerous precautions in place, in approximately 1 in 1500 cases, something gets left behind inside the patients body. This paper presents ASSIST, an automated system for surgical instrument and sponge tracking that increases the safety of surgical procedures. ASSIST utilizes RFID (Radio Frequency Identification) technology to aid in accounting for all items used during surgery. The design takes into account safety, simplicity, ease of deployment, and ease of use. An initial evaluation utilizing RFID-tagged sponges demonstrates that ASSIST can reliably track surgical sponges with minimal impact to current operating room procedures. Sources of error that can impact the reliability of the system are also discussed.

Phase and polarization diversity for OCDMA

A phase sensitive receiver for Optical Code Division Multiplexing (OCDMA) waveforms generated by spectral phase coding (SPC) using phase and polarization diversity offers expanded system capacity due to low values of multiple access interference (MAI).

High spectral efficiency phase diversity coherent optical CDMA with low MAI

Spectrally phase-coded optical code division multiple access (OCDMA), demodulated with phase and polarization diversity devices, exhibits high spectral efficiency and low Multiple Access Interference (MAI). Use in a passive optical network (PON) is discussed.

Optimal Multiuser Codes for the Real Adder Channel

A new family of uniquely decodable binary codes is presented for the T-user real adder channel. The codes consist of T individual codebooks, each containing only two codewords, one of which is the all-zero sequence. These codes achieve a sum rate that is equal, asymptotically in T, to the sum capacity. An iterative decoding algorithm is also presented. Applications are discussed to codes for T active users out of M potential users, and to superimposed codes.

Exponential error bounds for coding through noisy channels with inaccurately known statistics and for generalized decision rules

Generalized decoding decision rules provide added flexibility in a decoding scheme, and some advantages. In a generalized decoding decision rule, the following possibilities are considered: (1) the decoder has the option of not deciding at all, or rejecting all estimates. This is termed an erasure; (2) the decoder has the option of putting out more than one estimate. The resulting output is called a list. Only if the correct codeword is not on the list is there a list error. Taking into account the lack of exact knowledge of the channel statistics and assuming a mismatch between the true channel transition probabilities and the nominal probabilities used in the decoding metric, error bounds are developed for generalized decision rules. Conditions under which the error probabilities converge to zero exponentially with the block length, in spite of the presence of mismatch, are established. >

Coherent Optical CDMA with low MAI

A novel coherent optical code division multiple access (OCDMA) network based on phase and polarization diversity balanced reception of spectrally encoded optical pulses is proposed. Spectral efficiencies of 1 bps/Hz and beyond can be achieved by minimizing multiple access interference (MAI) and by cancelling beat noise. While the system achieves full capacity under bit synchronism, it also offers competitive performance at up to 25% of full capacity, even when completely asynchronous. Tree and ring network configurations can assure synchronization, making the proposed system robust in the presence of dispersion and phase noise.

Mixed-rate multiuser codes for the T-user binary adder channel

Coding schemes for the T-user binary adder channel are investigated. Recursive constructions are given for two families of mixed-rate, multiuser codes. These basic codes can be combined by time-sharing to yield codes approaching most rates in the T-user capacity region. The best codes constructed achieve a rate sum, R/sub 1/+...+R/sub T/, which is higher than all previously reported codes for T/spl ges/4 and is within 0.519 bits/channel use of the information-theoretic limit.