ORALS

Orthogonal frequency division multiplexing (OFDM) with offset quadrature amplitude modulation (OQAM) has been widely discussed in the literature and is considered a popular waveform for 5th generation (5G) wireless telecommunications and beyond. In this work, we show that OFDM-OQAM can be generated using the Hilbert transform and is equivalent to single sideband modulation (SSB), that has roots in analog telecommunications [1]. The symbol density in time-frequency space is greater than unity. OFDM-OQAM is also known as filter bank multicarrier (FBMC). One of the key advantages of OFDM-OQAM/FBMC over OFDM [2, 3, 4] is its immunity against frequency offsets. In other words, it may not be necessary for an OFDM-OQAM/FBMC system to estimate and cancel the frequency offset, unlike OFDM. The other important feature of OFDM-OQAM is the spectral containment of each subcarrier using a transmit filter, which is absent in OFDM. However, OFDM is more attractive than OFDM-OQAM in terms of implementation simplicity.  The transmit filter for OFDM-OQAM is complex valued and is given by    where   is a real-valued pulse shape that satisfies the zero intersymbol interference (ISI) condition, is its Hilbert transform and  .  The real-valued digital data (message) are transmitted through    and frequency division multiplexed on orthogonal subcarriers. The message bandwidth corresponding to each subcarrier is assumed to be narrow enough so that the channel can be considered ideal. Therefore, at the receiver, a matched filter can used to recover the message. Turbo coding is used to achieve bit-error-rate (BER) as low as 10-5 at an average signal-to-noise ratio (SNR) per bit close to 0 db. The system has been simulated in discrete time.

References:
[1] K Vasudevan, Gyanesh Kumar Pathak, Surendra Kota and Lov Kumar, “OFDM-OQAM using the Hilbert Transform”, Invited Talk, WCAM-2023, 8 – 10 May, Tokyo, Japan.
[2] K Vasudevan, “Coherent Detection of Turbo Coded OFDM Signals Transmitted through Frequency Selective Rayleigh Fading Channels”, IEEE International Conference on Signal Processing Computing and Control, 26—28 Sept. 2013, Shimla.
[3] K Vasudevan, “Coherent Detection of Turbo-Coded OFDM Signals Transmitted Through Frequency Selective Rayleigh Fading Channels with Receiver Diversity and Increased Throughput”, Wireless Personal Communications, Springer, vol. 82, no. 3, pp. 1623—1642, June 2015.
[4] K Vasudevan, “Near Capacity Signaling over Fading Channels using Coherent Turbo Coded OFDM and Massive MIMO”, International Journal On Advances in Telecommunications, issn 1942-2601, vol. 10, no. 1 & 2, year 2017, 22:37, http://www.iariajournals.org/telecommunications/.