Uplink OFDM detection with random multiple access.

Orthogonal Frequency-Division Multiplexing with Random multiple access (OFDRMA) is discussed for uplink communications, whereby several active users send information towards a single base-station (BS), while all other users are dormant. Originally, uplink communication methods included sharing the frequency resources among the active users in an orthogonal fashion, i.e., a central unit is required to dynamically allocate the resources. More recently, non-orthogonal methods have arisen, meaning that several active users share the same frequency bins, but they still do require a central unit to dynamically allocate the resources in a uniform (as possible) manner over the available bandwidth. The task and overhead required for managing the frequency allocations among the users can be quite cumbersome. In OFDRMA, the frequency allocations for any user are independent of the frequency allocations for the other users, and independent of which of the other users are currently active. Rather, OFDRMA relies on random, yet predetermined, allocation of frequency bins for each user, known only to that user and the BS. A multi-user detection approach is presented based on a graphical representation of the system. It is shown to provide robustness against the forced randomness of the scheme. Capacity of OFDRMA and its optimization are analyzed and provided in detail. Simulation results are provided for demonstrating the performance attainable with OFDRMA and the proposed detection scheme. Both the capacity and the simulations are compared with modern multi-user multiple-input multiple-output (MU-MIMO) schemes.

Backward Data Transfer From Deeply Implanted Device Employing Ultrasonic Load Amplitude-Phase Shift Keying.

Ultrasonic transcutaneous energy transfer (UTET) is used to wirelessly energize low-power miniature implanted devices. Whenever backward data transfer from the implant is of interest, load modulation may be utilized. With load modulation, data is sent backward by imposing ultrasonic reflections from the implant-tissue contact surface. This may be achieved by imposing unmatched electrical load over the implanted transducer electrical terminals. In order to sustain sufficient ultrasonic average power harvesting also during backward data transfer, only a small portion of the impinging ultrasonic energy is allowed to reflect backward. Previous work focused primarily on load modulation via ON- OFF keying (OOK). Herein, it is further shown that phase shift keying can be realized by exploiting the phase characteristics of a matched transducer around its vibration resonance. Load amplitude shift keying (ASK) properly combined with load phase shift keying (LPSK) may be applied, for introducing energy-efficient, high-order signaling schemes, thus improving utilization of the ultrasonic channel. LPSK is realized by momentary imposing reactive loads across the implanted transducer electrical terminals, according to the bit stream of the data to be sent. In this work, LPSK with various constellations and coding are demonstrated, exploiting the acoustic impedance dependency of the implanted piezoelectric resonator on its electrical loading. To support the theoretical notion, a backward data transfer using two-state phase modulation at a bit rate of 20 kbit/s over an ultrasonic carrier frequency of 250 kHz is demonstrated, using finite-element simulation. In the simulation, an implanted transducer was constructed of a 4-mm-diameter hard lead-zirconate-titanate (PZT) disk (PZT8, unloaded mechanical quality property Qm of 1000). The PZT resonator was acoustically matched to the tissue impedance, using a layer of 2.72-mm epoxy filled glue and a 2-mm-thick layer of polyethylene.

Linearized electro-optic racetrack modulator based on double injection method in silicon.

Racetrack-based modulator of increased linearity for optical links is presented and analyzed. The modulator is referred to as FLAME - Finer Linearity Amplitude Modulation Element. Linearity is improved via the introduction of a Double Injection approach. Large spurious-free-dynamic-range (SFDR) of 132dB·Hz(4/5) can thus be theoretically obtained. The FLAME is studied for silicon platform and requires small footprint size (100 × 50µm2) and low operation voltage, 2.5V. This makes the FLAME an appealing candidate for large scale integration in RF photonics.

Approaching coherent performance in differential detection via diversity.

Digital self-coherent detection (DSCD) can be employed to approach coherent performance in optical receivers by digitally reconstructing the samples of the electrical field without employing a local oscillator. One major deficiency of this scheme is the abrupt loss of field reconstruction, and consequently phase tracking, immediately following the occurrence of a low intensity sample. A cross-polarization DSCD scheme is introduced to mitigate this problem via diversity. The proposed scheme, termed X-DSCD, provides significantly improved signal reconstruction capabilities while doubling the achievable communication rate as compared to the original single-polarization DSCD scheme: two different and independent symbol streams are transmitted via two linear polarizations. X-DSCD performance is analyzed for the case of two cross-polarized, Gaussian signals. The analysis is supported by simulation results. Introducing coding into the system, the error performance attained by X-DSCD is shown to potentially approach that of a coherent receiver.

Integrated photonic threshold comparator based on square-wave synthesis.

A photonic threshold comparator is presented. A step-like electrical-to-optical (E/O) response is obtained by employing Fourier series synthesis in which a set of sine-wave responses of different amplitudes and phases are superimposed according to the Fourier series representation of a square-wave. The proposed comparator does not rely on optical material non-linearity; rather it consists of multimode interference (MMI) couplers and phase shifters.

Generating arbitrary optical signal constellations using microring resonators.

It is shown that two mutually uncoupled microresonators in series can adequately cover the entire I-Q space and render the realization of QAM signals possible. This approach is based on the independent optimization of each microresonator for amplitude and phase modulation respectively. Generation of 16 quadrature amplitude modulation is demonstrated by means of simulation.