  We propose Multi-Antenna (MA) Towards Inband Shift Keying (TISK): a new
multi-carrier radio concept to cope with critical link budgets. In contrast to
common proposals that rely on analog beamforming at both transmitter and
receiver, MA-TISK does not require beam alignment. The transmitted signals have
all constant envelope in continuous time, which allows for efficient, low-cost
power amplification and up-conversion. The concept is compatible with any
linear PSK-modulation as well as pulse position modulation. Each sub-carrier is
sent over a separate antenna that is equipped with a voltage-controlled
oscillator. The phases of these oscillators are controlled by digital baseband.
Temporal signal combining makes up for the lack of beamforming gain at the
transmitter. A common message may be broadcast to many receivers,
simultaneously. Demodulation can be efficiently implemented by means of fast
Fourier transform.
  MA-TISK does not suffer from spectral re-growth issues plaguing other
constant envelope modulations like GMSK. Almost rectangular signal spectra
similar to those for linear modulation with root-raised-cosine pulse shaping
are possible.
  For the 100 MHz-wide spectral mask of 5G downlink, QPSK-modulation allows for
160 MBit/s with 5.74 MHz subcarrier spacing when using 16 transmit antennas.
The wide carrier spacing makes the signals insensitive to Doppler effects.
There is no loss in link budget gain compared to spatial beamforming at the
transmitter.
