Mohammad Javad Abdoli

On the Degrees of Freedom of

The K-user single-input single-output (SISO) additive white Gaussian noise (AWGN) interference channel and 2×K SISO AWGN X channel are considered, where the transmitters have delayed channel state information (CSI) through noiseless feedback links. Multiphase transmission schemes are proposed for both channels which possess novel ingredients, namely, multiphase partial interference nulling, distributed interference management via user scheduling, and distributed higher order symbol generation. The achieved degree-of-freedom (DoF) values are greater than the best previously known DoFs for both channels with delayed CSI at the transmitters.

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A novel technique for removing the edge time transitions, a.k.a. tails, as well as the half symbol offset overhead of OFDM/OQAM signal is proposed. The proposed technique, which is called weighted circular convolution, totally removes the signal overheads, while preserving the real-orthogonality of the prototype filter, and as such, does not incur any ISI/ICI on the demodulated OQAM symbols. It is based on extension of the finite-length OQAM sequence to infinite-length such that the resulting signal is periodic. This periodicity together with special structure of OFDM/OQAM enables one to transmit only the desired overhead-removed portion of signal. This is equivalent to a weighted circular convolution instead of linear convolution in the OFDM/OQAM modulator/demodulator. The spectral sidelobe augmentation due to the sharp edge transitions of the overhead-removed signal is resolved by a weighted time-domain windowing. The proposed overhead-removal technique is applicable to an OFDM/OQAM burst of arbitrary length (either even or odd) and, among other benefits, significantly improves the spectral efficiency especially for short-burst signals.

-User SISO Interference and X Channels With Delayed CSIT

The layered interference network is investigated with delayed channel state information (CSI) at all nodes. It is demonstrated how multihopping can be utilized to increase the achievable degrees of freedom (DoF). In particular, a multiphase transmission scheme is proposed for the K-user 2K-hop interference network to systematically exploit the layered structure of the network and delayed CSI to achieve DoF values that scale with K. This result provides the first example of a network with distributed transmitters and delayed CSI whose DoF scales with the number of users.

Weighted circularly convolved filtering in OFDM/OQAM

The multi-hop layered interference network is investigated with delayed knowledge of channel state information (CSI) at all nodes. It is demonstrated how multi-hopping can be utilized to increase the achievable degrees of freedom (DoF). In particular, for the K-user 2K-hop interference network, a multi-phase transmission scheme is proposed which systematically exploits the layered structure of the network and delayed CSI to achieve DoF values which scale with K. As such, this result provides the first example of a network with distributed transmitters and delayed CSI whose DoF scales with the number of users, although sub-linearly.

Layered Interference Networks With Delayed CSI: DoF Scaling With Distributed Transmitters

A K-user downlink transmission is considered, wherein the Nyquist sequences of different users are transmitted with different time offsets so that the entire transmitted signal is deemed a K times faster than Nyquist (FTN) signal. An inter-user interference removal technique is proposed that successively removes the interference using successive trellis update. It is shown by simulations that when the power difference between users is large enough, using only one round of trellis decoding, the system approaches the performance of the successive trellis update.

On degrees of freedom scaling in layered interference networks with delayed CSI

An adjustable pulse bandwidth single carrier waveform for asynchronous low-cost low-power 5G M2M applications is proposed. The solution uses ultra narrow-band pulse to improve coverage, which is a much more efficient coverage enhancement solution than existing repetition solutions. Frequency localized pulse shaping is used, which allows asynchronous transmission and packing more machine-type devices (MTDs) for the same spectrum resources. In addition, bandwidth of each MTD is configurable based on long term channel quality and system load, which supports higher throughput and lower power consumption. Performance comparison with the repetition solution of 3GPP LTE demonstrates significant gain in terms of number of supported connections.

Trellis Decoding for Multi-User Faster-Than-Nyquist Transmission

Faster than Nyquist (FTN) transmission is investigated for a point-to-point AWGN link. The FTN is interpreted as a form of coding at the pulse shape level, and accordingly, the so-called Mazo phenomenon is interpreted as a coding gain. Then, it is shown by simulation that such a gain can disappear in a coded FTN transmission with a powerful FEC code, such as turbo code. This result undermines the FTN transmission as an effective technique in an actual communication system.