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Mobile Communications SystemsMobile Communications Systems
5th Generation Non-Orthogonal Waveforms for Asynchronous Signalling
0
5GNOW: Sparse Message Delivery in PRACH
References
Pulse Shaped PRACH
Signalling in Physical Uplink Shared Channel (PUSCH) and the
Physical Random Access Channel (PRACH)
Orthogonal design principle to minimize the interference between the
channels, several subcarriers on both edges of PRACH are left zeros as
a guard band
Preamble generation: The
preamble is constructed by
Zadoff Chu sequence
[1] P. Jung and G. Wunder, “The WSSUS Pulse Design Problem in Multicarrier
Communications”, IEEE Transactions on Communications, vol. 55, no. 10, pp.
1918-1928
[2] P. Jung and G. Wunder, “On Time-Variant Distortions in Multicarrier
Transmission with Application to Frequency Offsets and Phase Noise”, IEEE
Transactions on Communications, September 2005, vol. 53, no. 9, pp. 1561-
1570
LTE/LTE-A PRACH and PUSCH
Sporadic Traffic
5GNOW adresses sporadic traffic as an enabler of the
‚Internet of Things‘.
Sources for sporadic traffic
Smartphone short message delivery
Machine-type communications (MTC)
Approach:
Waveform design, sparse signal processing
Goal:
Reduce the uplink overhead to 5%, improve the energy-efficiency of
MTC uplink data transmission by a factor of 20
Conclusion
Proof-of-concept: we have shown that short messages can be
signalled over PRACH
Goal in current setting only achievable with advanced signal
processing and tailored waveforms.
Some properties of optimal signalling derived
Simulation Results
5GNOW PRACH: asynchronous non-orthogonal multi-user
access under sparsity constraints.
Trinity of (1) link aquistion, (2) channel estimation, and (3)
demodulation must be achieved at the same time with good
performance
Approach
Biorthogonal Frequency Division Multiplexing (BFDM) scheme for
transmitting the preamble in PRACH
Set of shifted pulses on time-frequency lattice points, transmit/receive
pulses form biorthogonal Riesz bases
Joint acquisition, channel estimation, and demodulation by iterative
multi-user sparse detection
Waveform Design
Based upon 𝑳𝟏-norm optimality property
Time and frequency localization based on grid matching rule
Verification by simulation whether
utilizing the PRACH guard bands
with messages is really feasible
Parameters according to LTE
specification as given in Table I
Initial Waveform Results
Classical localization property is the uncertainty
principle: Gaussian signalling is optimal
In our approach waveform is designed to
minimize 𝑔 1 s.t. 𝑔 2 = 1, for a waveform
𝑔 ∈ 𝒫𝒲𝜋1 (Paley-Wiener space of integrable
bandlimited signals with normalized bandwidth
𝜋) which depends on bandwidth extension
factor 𝐿 ≥ 1
However: Gaussian
signalling is not
necessarily optimal
in a specific setting.
L 1 1.2 1.4 1.6
𝒈 𝟏 ∞ 2.15 1.75 1.6
Waveform design properties: