Develop a Singlecarrier PHY Layer

The given channel bandwidth of 200 kHz is somewhat of an edge-case in terms of frequency selectiveness. Lower channel bandwidths will undergo flat fading, higher bandwidths will undergo frequency selective fading.

For a flat fading scenario, a singlecarrier solution would also be easy to implement and will make it easier to find a PA which amplifies the signal (due to lower PAPR). In case of high frequency selectiveness, the OFDM PHY layer is expected to be more robust but requires a very linear PA.

In order to compare both approaches, we will develop a singlecarrier version of the PHY layer which is compatible to the existing MAC layer.

## Tasks
- [x] definition of the SC PHY layer
- [x] general single carrier modulation functions
- [x] new timing synchronization sequence and correlation algorithm
- [x] include pulse shaping
- [x] include training sequences and a LMS equalizer
- [ ] integrate SC phy to current develop branch

## Open Issues

- [ ] compensate constant phase offsets
- [ ] Initialize Platform for 300kSyms/s instead of the 256kSyms/s
- [ ] Training sequences are currently transmitted regardless whether data is transmitted in a slot. Fix this

## SC PHY Definition

- 300 kSymb/s sampling rate
- RRC filter for pulse shaping, with factor 2 interpolation/decimation -> 150 kSymb/s baseband sampling rate
- LMS Equalizer with 8 (?) taps
- Every data slot will contain 40 training symbols at the beginning of the slot followed by 520 data symbols
- Synchronization sequence is a 119 symbol Zadoff Chu sequence
- Zadoff chu is also used in uplink for initial sync.

Related working branch https://github.com/HAMNET-Access-Protocol/HNAP4PlutoSDR/tree/singlecarrier_phy