1. Physical Layer Synchronisation Techniques for UWB Communication Systems
1.) Acquisition Phase
Task:
Synchronisation of the Transmitters and Receivers Time Base by detecting an ongoing Transmission at a Receiver
Problems:
White Noise and other Interference may affect Detection Performance at the Receiver.
2.) Tracking Phase
Task:
Maintenance of Synchronisation during an Ongoing Transmission
Problems:
Clock Inaccuracies degrade Performance

2. Acquisition Phase (1/13):
2 different Synchronisation Sequences are introduced:
Synchronisation Sequence A:
consisting of M equidistantly arranged monocycles
followed by a start symbol

3. Acquisition Phase (2/13):
2 different Synchronisation Sequences are introduced:
Synchronisation Sequence B:
Autocorrelation
Amplitude in Volts
consisting of M monocycles with increasing time intervals between the pulses
creates clear time information at the receiver

4. Acquisition Phase (3/13):
The incoming signal x(t) is influenced by the channel impulse response and superposed by noise and interference. A detector has to decide whether there is a synchronisation sequence present in the signal y(t) or not.
-Hard Decision Detection is used when transmitting the Synchronisation Sequence A
-Soft Decision Detection is used when transmitting the Synchronisation Sequence B

5. Acquisition Phase (4/13):
Receiver Structure:
Input
Filter
Amplifier
Sampler
Adjustable
Threshold
Clock/
Counter
Trigger
Delay …
Logic
TimeSample
Tracking/ Sampling Unit
Antenna

6. Acquisition Phase (5/13):
Hard Detection Decision:
When a first threshold Tr1 becomes exceeded a detection logic is initiated, which samples the filter output at the estimated times of the following monocycles belonging to the sequence.
By taking into account a second threshold Tr2 for each sample a decision in favour or against a pulse is made. A final decision is taken after taken M-1 single decisions.
At least N out of M pulses have to be detected.
By doing so the probability to detect the synchronisation sequence A in thermal noise can be calculated as:
with:

7. Acquisition Phase (6/13):
Hard Detection Decision:
The figures display the detection and false alarm probabilities in thermal noise with a SNR of 0dB for each pulse of the training sequence at the detector in dependency of M,N and Tr2 :

8. Acquisition Phase (7/13):
Soft Detection Decision:
When considering Soft Detection a correlation filter matched to the whole synchronisation sequence is used. If the output exceeds a threshold T the Sequence has been detected an data detection may follow.
correlation filter for synchronisation sequence B
Detection Probability in AGWN for Synchronisation Sequence B:

9. Acquisition Phase (8/13):
Channel Model:
Additional to an AWGN channel model 4 more channel models provided by U.C.A.N are implemented to get more realistic results:
Line of Sight Channel Model “LOS”
Hard Non Line of Sight Channel Model “Hard NLOS”
Soft Non Line of Sight Channel Model “Soft NLOS”
Corridor Channel Model “Corridor”

10. Acquisition Phase (9/13):
detection probability when using different channel models

11. Acquisition Phase (10/13):
Multiuser Interference:
Interference from Multiuser network access is heavily influenced by the pulse repetition rate and the radio channel.

12. Acquisition Phase (11/13):
Narrowband Radio Interference:
In order to simulate Interference from narrowband Radio Systems two different modulations are introduced:
Quadrature Amplitude Modulation (QAM)
Frequency Shift Keying (FSK)
A power relation is defined as:
with:

13. Acquisition Phase (12/13):
In a worst case scenario, a UWB receiver is located next to an high power narrowband transmitter. For this case a notch filter can be enabled which is able to suppress disturbing frequency band.

14. Acquisition Phase (13/13):
Detection probability in presence of a narrowband Interference Source when using SynchronisationSequence B:

15. Tracking (1/3): with: nominal frequency frequency offset
The Oscillators belonging to different UWB network participants supply independent timing signals.
In order to investigate impacts on UWB performances a clock model is used to describe clock inaccuracies.
with:
nominal frequency
frequency offset
Random phase offset with Gaussian probability density function and zero mean
When considering deviations between two different clocks with same nominal frequency, only the frequency offset and the random phase offset are taken into account. A drift factor d expresses frequency offset and the value j(t) the random phase offset, jitter respectively.

16. Tracking (2/3):
In order to compensate time deviations between a transmitters and a receivers clock a sampler bank takes several samples before and after the estimated time of the next monocycle.
Measured deviations are feed in a tracking loop, capable to compensate drifts, frequency offsets between two clocks.
The tracking loop is realised as a integral loop.

17. Tracking (3/3):
Input sequence E(z) when using PAM modulation.

18. Conclusions:
The synchronisation sequence B combined with soft decision detection is a feasible method to get two network participants synchronised
Even in presence of different interference sources a good detection probability can be reached
This soft detection approach requires an input correlation filter matched to the whole synchronisation sequence
Reliable tracking performance can be achieved by using an digital integral control loop
An adjustment of the different clocks is not necessary.