Ming Jia

Filtered OFDM: A new waveform for future wireless systems

A spectrally-localized waveform is proposed based on filtered orthogonal frequency division multiplexing (f-OFDM). By allowing the filter length to exceed the cyclic prefix (CP) length of OFDM and designing the filter appropriately, the proposed f-OFDM waveform can achieve a desirable frequency localization for bandwidths as narrow as a few tens of subcarriers, while keeping the inter-symbol interference/inter-carrier interference (ISI/ICI) within an acceptable limit. Enabled by the proposed f-OFDM, an asynchronous filtered orthogonal frequency division multiple access (f-OFDMA)/filtered discrete-Fourier transform-spread OFDMA (f-DFT-S-OFDMA) scheme is introduced, which uses the spectrum shaping filter at each transmitter for side lobe leakage elimination and a bank of filters at the receiver for inter-user interference rejection. Per-user downsampling and short fast Fourier transform (FFT) are used at the receiver to ensure a reasonable complexity of implementation. The proposed scheme removes the inter-user time-synchronization overhead required in the synchronous OFDMA/DFT-S-OFDMA. The performance of the asynchronous f-OFDMA is evaluated and compared with that of the universal-filtered OFDM (UF-OFDM), proposed in [1], [2].

Weighted circularly convolved filtering in OFDM/OQAM

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.

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

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.

Adjustable ultra narrow-band pulse for asynchronous 5G M2M communications

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.

Turbo-coded single-carrier 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.

Universal Receiver for Weighted Circularly Convolved OFDM/OQAM

The weighted circularly convolved OFDM/OQAM (WCC-OFDM/OQAM), a variant of OFDM/OQAM without time-domain tail overhead, is investigated in a doubly dispersive fading environment. A new receiver is proposed that resolves the self-interference present at a regular WCC-OFDM/OQAM receiver when the channel variations are too fast compared to the signal burst duration. This is achieved by exploiting the channel state information (CSI) available at the receiver to compensate for the channel discontinuity that appears in the receivers circular operations. The proposed receiver is universal in two regards: first, it performs equally well for a wide range of speeds and modulation and coding schemes (MCSs), and second, it does not require any change to the WCC-OFDM/OQAM signal structure, and thus, is transparent to the transmitter.