Implications of Electronics Constraints for Solid-State Quantum Error Correction and Quantum Circuit Failure Probability

In this paper we present the impact of classical electronics constraints on a solid-state quantum dot logical qubit architecture. Constraints due to routing density, bandwidth allocation, signal timing, and thermally aware placement of classical supporting electronics significantly affect the quantum error correction circuit's error rate. We analyze one level of a quantum error correction circuit using nine data qubits in a Bacon-Shor code configured as a quantum memory. A hypothetical silicon double quantum dot quantum bit (qubit) is used as the fundamental element. A pessimistic estimate of the error probability of the quantum circuit is calculated using the total number of gates and idle time using a provably optimal schedule for the circuit operations obtained with an integer program methodology. The micro-architecture analysis provides insight about the different ways the electronics impact the circuit performance (e.g., extra idle time in the schedule), which can significantly limit the ultimate performance of any quantum circuit and therefore is a critical foundation for any future larger scale architecture analysis.Comment: 10 pages, 7 figures, 3 table

Transmission scheduling for wireless and satellite systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 135-137).We study queuing systems with time-varying service rates, as a natural model of satellite and wireless communication systems. Packets arrive at a satellite to be transmitted to one of the sub-regions (channels) in a service area. The packets are stored in an on-board buffer and in a separate queue for each channel. The satellite has a limited power available for scheduling transmissions, and a fixed number of transmitters. The power allocated to a particular channel, in conjunction with the channel state, determines the transmission rate of the channel, i.e., the service rate for the queue corresponding to that channel. The assignment of transmitters to the queues as well as the power allocated to each transmitter are modeled as control variables. The goal is to design a power allocation policy so that the expected queue size, in steady-state, is minimized. We model the system as a slotted system with N queues, and i.i.d. Bernoulli arrivals at each queue during each slot. Each queue is associated with a channel that changes between "on" and "off" states according to i.i.d. Bernoulli processes. We assume that the system has K identical transmitters ("servers").(cont.) Each server, during each slot, can transmit up to Co packets from a queue associated with an "on" channel. We show that when K and Co are arbitrary and a total of up to KCo packets can be served from all the N queues in a time slot, a policy that assigns the K servers to the "on" channels associated with the K longest queues is optimal. We also consider a "fluid" service model under which fractional packets can be served, for the case K = N, and subject to a constraint that at most C packets can be served in total over all of the N queues. We show that there is an optimal policy which serves the queues so that the resulting vector of queue lengths is "Most Balanced." We also describe techniques to upper bound the expected queue size in steady-state under an optimal policy.by Anand Ganti.Ph.D

Mismatch capacity per unit cost

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (p. 48).The mismatch channel capacity per unit cost represents the maximum number of bits per unit cost that can be transmitted reliably across a channel under receiver mismatch conditions. It's reciprocal is the minimal cost of transmitting a bit reliably under these conditions. We derive lower bounds for the mismatch channel capacity per unit cost and discuss some of its properties.by Anand Ganti.S.M

Power Control for an Asynchronous Multi-rate

The varied Quality of Service (QoS) or bit error rate (BER) requirements of multimedia traffic require the use of power control for CDMA wireless systems employing multiuser detection. Using a decorrelator in an asynchronous multi-rate DS/CDMA system, it may be necessary for different users to combat the noise enhancement and the propagation losses to varying degrees depending on individual requirements. In this context, we propose a power control algorithm for a multi-rate decorrelator that is suitable for a class of BER based link quality objectives. If the uplink channel gain of the desired user is known, then it is simple for each user to choose the transmitter power needed to meet its target BER objective. In practice, however, the uplink channel gain is often difficult to measure. To avoid this measurement, we employ stochastic approximation methods to develop a simple, distributed, iterative power control algorithm. In this algorithm, each mobile will use the output of its own decorrelator to update its transmitted power in order to achieve its QoS objective. We will show that when a user’s bits have nonzero asymptotic efficiencies, then the power control algorithm converges quickly in the mean square sense to an optimal power at which the desired user achieves its QoS objective.

Transmission Scheduling for Multi-Channel Satellite and Wireless Networks

We consider a slotted system with N queues, and i.i.d. Bernoulli arrivals at each queue during each slot. Each queue is associated with a beam and a channel that changes between "on" and "o# " states according to i.i.d. Bernoulli processes

Power Control for an Asynchronous Multi-rate Decorrelator

The varied Quality of Service (QoS) or bit error rate (BER) requirements of multimedia traffic require the use of power control for CDMA wireless systems employing multiuser detection. Using a decorrelator in an asynchronous multi-rate DS/CDMA system, it may be necessary for different users to combat the noise enhancement and the propagation losses to varying degrees depending on individual requirements. In this context, we propose a power control algorithm for a multi-rate decorrelator that is suitable for a class of BER based link quality objectives. If the uplink channel gain of the desired user is known, then it is straightforward for each user to choose the transmitter power needed to meet its target BER objective. In practice, however, the uplink channel gain is often difficult to measure. To avoid this measurement, we employ stochastic approximation methods to develop a simple iterative power control algorithm. In this algorithm, each mobile will use the output of its own decorrelator to update its transmitted power in order to achieve its QoS objective. We will show that when a user's bits have nonzero asymptotic efficiencies, then the power control algorithm converges quickly in the mean square sense to the minimum power at which a user achieves its QoS objective